Successful crossbreeding between Oreochromis niloticus and Sarotherodon melanotheron to produce a commercial hybrid has been difficult.The karyotypes and isoenzyme of these two species and their reciprocal hybrids（O....Successful crossbreeding between Oreochromis niloticus and Sarotherodon melanotheron to produce a commercial hybrid has been difficult.The karyotypes and isoenzyme of these two species and their reciprocal hybrids（O.niloticus ♀ × S.melanotheron ♂,S.melanotheron ♀ × O.niloticus ♂,the last not included in the isoenzyme study） were investigated via metaphase chromosomes obtained from head kidney cells and electropherogram of lactate dehydrogenase（LDH） isoenzymes from the liver,kidney,white muscle,heart,and eye balls.The diploid chromosome number（2n=44） and the fundamental number（NF=50） of the four tilapia genotypes were the same.However,the karyotype of O.niloticus had three pairs of sub-metacentric（sm）,twelve pairs of sub-telocentric（st）,and seven pairs of telocentric（t） chromosomes,while S.melanotheron had one pair of metacentric（m）,two pairs of sm,12 pairs of st,and seven pairs of t chromosomes.The reciprocal hybrids both showed a mixed karyotype range between their parents：0.5 pair of m,2.5 pairs of sm,12 pairs of st,and seven pairs of t chromosomes.In view of the electropherogram of isozymes,only the LDH of the kidney showed significant clear bands,with five bands in O.niloticus,three bands in S.melanotheron,and duplicated six bands in the hybrids.The bands varied depending on their activities and mobilities.We considered that the differences in karyotype and isoenzyme were related to the genetic mechanism for post-mating isolation,and provided some additional basic genetic background of their taxonomy.展开更多
According to the fitness of heterozygote was lower than homozygote among panmictic population,the process of generational accumulate of mutant gene r was considered.Branch point of r＇s frequency by generational evolu...According to the fitness of heterozygote was lower than homozygote among panmictic population,the process of generational accumulate of mutant gene r was considered.Branch point of r＇s frequency by generational evolution which revealed the hereditary incompatibility between R and r,was worked out,and it was found that genetic drift can make r have higher frequency to surpass the branch point to form reproductive isolation.It was not enough to have the three conditions of mutation,genetic drift and natural selection to be the drive of biological evolution;hybrid weakness,the repelling interaction between the genetic background of original population and the new mutation,were also needed.展开更多
Sexual selection via female mate choice is thought to have played a key role in the speciation ofhaplochromine cichlids, but a dominant role for visual signals in such processes has lately been called into question. I...Sexual selection via female mate choice is thought to have played a key role in the speciation ofhaplochromine cichlids, but a dominant role for visual signals in such processes has lately been called into question. In addition, the possible role of male mating preferences in haplochromine speciation has been little studied. We studied patterns of both female and male mate choice, based exclusively on visual signals, in order to evaluate potential reproductive isolation between two populations of the Lake Malawi haplochromine Labeotropheus fuelleborni. In the first experiment, females were allowed to choose between two males, one from the same population and the other allopatric with respect to the female. Females in this experiment responded more frequently to males from their own population. Similarly, the males in these trials displayed more frequently when presented with females of their own population. In the second experiment, a female was allowed to choose between two males, either both from her own population or both allopatric. In these trials, both males and females from the Katale population interacted significantly more frequently in settings in which all three individuals were from the same population （＂same-population trios＂）, and those from the Chipoka population showed a similar trend. Thus, patterns in both male and female courtship behavior suggest that visual signals contribute to at least incipient reproductive isolation between populations of L. fuelleborni [Current Zoology 56 （ 1 ）： 65-72 2010].展开更多
Drosophila lacertosa is widely distributed from northern India to Far East of Russia throughout China.We have studied geographical distributions of three kinds of chromosomal karyotypes,type D(2n=10,4 pairs of V-shape...Drosophila lacertosa is widely distributed from northern India to Far East of Russia throughout China.We have studied geographical distributions of three kinds of chromosomal karyotypes,type D(2n=10,4 pairs of V-shaped metacentric chromosomes and a pair of micro-chromosomes),type L(2n= 10,5V with a pair of large-sized heterochromatic autosomes)and type M(2n=10,5V with middle-sized ones).Type D was found exclusively in local populations of D.lacertosa distributed in Yun-Gui Plateau,southwestern China.Both type L and M have a wide range of distribution,and the former occurred in subtropical regions of China including Taiwan Island,whereas the latter in cool temperate regions of East Asia covering Far East of Russia,Korea and the Japan Islands.A strong premating isolation was detected between flies with type D and those with type L or M.These data demonstrate that genetic differentiation leading to cryptic speciation might have occurred in natural populations of Drosophila lacertosa.展开更多
Heterosis,also known as hybrid vigor,is commonly observed in rice crosses.The hybridization of rice species or subspecies exhibits robust hybrid vigor,however,the direct harnessing of this vigor is hindered by reprodu...Heterosis,also known as hybrid vigor,is commonly observed in rice crosses.The hybridization of rice species or subspecies exhibits robust hybrid vigor,however,the direct harnessing of this vigor is hindered by reproductive isolation.Here,we review recent advances in the understanding of the molecular mechanisms governing reproductive isolation in inter-subspecific and inter-specific hybrids.This review encompasses the genetic model of reproductive isolation within and among Oryza sativa species,emphasizing the essential role of mitochondria in this process.Additionally,we delve into the molecular intricacies governing the interaction between mitochondria and autophagosomes,elucidating their significant contribution to reproductive isolation.Furthermore,our exploration extends to comprehending the evolutionary dynamics of reproductive isolation and speciation in rice.Building on these advances,we offer a forward-looking perspective on how to overcome the challenges of reproductive isolation and facilitate the utilization of heterosis in future hybrid rice breeding endeavors.展开更多
Reproductive isolation is defined as processes that prevent individuals of different populations from mating, survival or producing fertile offspring. Reproductive isolation is critical for driving speciation and main...Reproductive isolation is defined as processes that prevent individuals of different populations from mating, survival or producing fertile offspring. Reproductive isolation is critical for driving speciation and maintaining species identity, which has been a fundamental concern in evolutionary biology. In plants,reproductive isolation can be divided into prezygotic and postzygotic reproductive barriers, according to its occurrence at different developmental stages. Postzygotic reproductive isolation caused by reduced fitness in hybrids is frequently observed in plants, which hinders gene flow between divergent populations and has substantial effects on genetic differentiation and speciation, and thus is a major obstacle for utilization of heterosis in hybrid crops. During the past decade, China has made tremendous progress in molecular and evolutionary basis of prezygotic and postzygotic reproductive barriers in plants. Present understandings in reproductive isolation especially with new data in the last several years well support three evolutionary genetic models, which represent a general mechanism underlying genomic differentiation and speciation. The updated understanding will offer new approaches for the development of wide-compatibility or neutral varieties, which facilitate breeding of hybrid rice as well as other hybrid crops.展开更多
It is of critical importance for our understanding of speciation process to determine the forms of reproductive isolation and their relative importance in species divergence. Oryza nivara and O. rufipogon are direct a...It is of critical importance for our understanding of speciation process to determine the forms of reproductive isolation and their relative importance in species divergence. Oryza nivara and O. rufipogon are direct ancestors of Asian cultivated rice and a progenitor-daughter species pair. Investigating the reproductive isolation between them provides insights into plant speciation and helps understanding of the rice domestication. Here, we quantitatively measured the major components of reproductive isolation between the two species based on common garden and crossing experiments for three pairs of sympatric populations in Nepal, Cambodia and Laos.We revealed significant differences in the flowering times between species pairs, with O. nivara flowering much earlier than O. rufipogon. A very weak reduction in seed set but no reduction in F1 viability and fertility were detected for the crosses between species relative to those within species. Moreover, we detected asymmetrical compatibility between species and found that emasculation significantly decreased pollination success in O. nivara but not in O. rufipogon.Our study demonstrates that the divergence between O. nivara and O. rufipogon is maintained almost entirely by the difference in flowering times and suggests that differential flowering times contribute to both habitat preferences and reproductive isolation between species.展开更多
Reproductive isolation defines the biological species concept and plays a key role in the formation and maintenance of species. The relative contributions of different isolating stages has been suggested to be closely...Reproductive isolation defines the biological species concept and plays a key role in the formation and maintenance of species. The relative contributions of different isolating stages has been suggested to be closely associated with phylogenetic relatedness. Few studies have focused on the relative contributions of pre- versus post-zygotic mechanisms, and even fewer have been conducted under strict phylogenetic frameworks. Pre-and post-zygotic reproductive isolation stages have been investigated in the sister species Mussaenda kwangtungensis and M. pubescens var. alba. The two species have partly overlapping distribu-tion ranges and flowering times, while the principal pollinators differed strikingly for them, demonstrating strong pre-zygotic isolations. Natural hybrids were detected by simple sequence repeat markers and their maternal parents were identified based on chloroplast gene sequen-ces. Five out of 81 individuals were suggested to be hybrids that fall into the categories F2, BC1, and BC2 by the NewHybrids analysis. Interspecific crossings resulted in significantly reduced fruit set and seed germination rates. Phylogenetic analysis revealed short Kimura-2-parameter distance between M. kwangtungensis and M. pubescens var. alba. These findings strongly supported the hypothesis that for species with a closer phylogenetic relationship, pre-zygotic isolation plays an important part in limiting gene exchange in sympatric areas.展开更多
Research on sexual selection and hybridization has focused on female mate choice and male-male competition. While the evolutionary outcomes of interspecific female preference have been well explored, we are now gainin...Research on sexual selection and hybridization has focused on female mate choice and male-male competition. While the evolutionary outcomes of interspecific female preference have been well explored, we are now gaining a better understanding of the processes by which male-male compe- tition between species in secondary contact promotes reproductive isolation versus hybridization. What is relatively unexplored is the interaction between female choice and male competition, as they can oppose one another or align with similar outcomes for reproductive isolation. The role of female-female competition in hybridization is also not well understood, but could operate similarly to male-male competition in polyandrous and other systems where costs to heterospecific mating are low for females. Reproductive competition between either sex of sympatric species can cause the divergence and/or convergence of sexual signals and recognition, which in turn influences the likelihood for interspecific mating. Future work on species interactions in secondary contact should test the relative influences of both mate choice and competition for mates on hybridization outcomes, and should not ignore the possibilities that females can compete over mating resources, and males can exercise mate choice.展开更多
Natural hybridization frequently occurs in plants and can facilitate gene flow between species, possibly resulting in species refusion. However, various reproductive barriers block the formation of hybrids and maintai...Natural hybridization frequently occurs in plants and can facilitate gene flow between species, possibly resulting in species refusion. However, various reproductive barriers block the formation of hybrids and maintain species integrity. Here, we conducted a field survey to examine natural hybridization and reproductive isolation （RI） between sympatric populations of Primula secundiflora and P. poissonii using ten nuclear simple sequence repeat （SSR） loci. Although introgressive hybridization occurred, species boundaries between P. secundiflora and P. poissonii were maintained through nearly complete reproductive isolation. These interfertite species provide an excellent model for studying the RI mechanisms and evolutionary forces that maintain species boundaries.展开更多
Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis; however, few studies have examined variation of nectary structure and/or nectar secretion in the genus, particu...Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis; however, few studies have examined variation of nectary structure and/or nectar secretion in the genus, particularly among closely related species. Here we investigated nectary morphology, nectar quality, and nectar production dynamics in flowers of Pedicularis section Cyathophora. We found a conical floral nectary at the base of the ovary in species of the rex-thamnophila clade. Stomata were found on the sudace of the nectary, and copious starch grains were detected in the nectary tissues. In contrast, a semi-annular nectary was found in flowers of the species of the superba clade. Only a few starch grains were observed in tissues of the semi-annular nectary, and the nectar sugar concentration in these flowers was much lower than that in the flowers of the rexthamnophila clade. Our results indicate that the floral nectary has experienced considerable morphological, structural, and functional differentiation among closely related species of Pedicularis. This could have affected nectar production, leading to a shift of the pollination mode. Our results also imply that variation of the nectary morphology and nectar production may have played an important role in the speciation of sect. Cyathophora.展开更多
The term ＇assortative mating＇ has been applied to describe two very different phenomena： （1） the tendency for indi- viduals to choose phenotypically similar mates from among conspecifics; or （2） the tendency to...The term ＇assortative mating＇ has been applied to describe two very different phenomena： （1） the tendency for indi- viduals to choose phenotypically similar mates from among conspecifics; or （2） the tendency to prefer conspecific over hete- rospecific mates （behavioral reproductive isolation）. Both forms of assortative mating are widespread in nature, but the relation- ship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics in cidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin＇s Finches （Geospiza spp）. We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating [Current Zoology 58 （3）： 484-492, 2012].展开更多
To elucidate reproductive isolating mechanisms in the Bangladesh coastal bullfrog Hoplobatrachus litoralis and its congeneric species, we performed crossing experiments using three species： H. litoralis, H. tigerinus...To elucidate reproductive isolating mechanisms in the Bangladesh coastal bullfrog Hoplobatrachus litoralis and its congeneric species, we performed crossing experiments using three species： H. litoralis, H. tigerinus and H. rugulosus. In addition, we conducted histological observations on spermatogenesis of the hybrids. The reciprocal hybrids between H. litoralis and H. tigerinus developed normally with somewhat lower viability at the metamorphosis stage compared with the controls. Most of the metamorphosed frogs became mature. On the other hand, almost all hybrids between female H. rugulosus and male H. litoralis or H. tigerinus died of underdevelopment at the tadpole stage, and only a few hybrids metamorphosed normally and survived to maturity. The inner structures of the testes of the control H. litoralis and H. tigerinus were completely normal, with seminiferous tubules filled with compact bundles of normal spermatozoa. Those of the reciprocal hybrids between H. litoralis and H. tigerinus were almost normal or slightly abnormal, with seminiferous tubules that contained pycnotic nuclei in addition to normal bundles of normal spermatozoa, which demonstrates slight abnormalities in spermatogenesis. In contrast, the hybrids between female H. rugulosus and male H. litoralis or H. tigerinus had no bundles of spermatozoa nor spermatids in the seminiferous tubules, which indicates entirely abnormal spermatogenesis. Meiotic chromosome figures in the reciprocal hybrids between H. litoralis and H. tigerinus showed slight abnormalities, with the occurrence of univalents and increase of rod-shaped bivalents. These results indicate that H. litoralis and H. tigerinus are not isolated from each other by hybrid inviability nor by hybrid sterility, although the hybrids showed somewhat abnormal spermatogenesis in hybrids and that H. rugulosus is isolated from both H. litoralis and H. tigerinus by incomplete hybrid inviability and complete hybrid sterility.展开更多
Anthropogenic introduction of species has resulted in a breakdown of geographical barriers and hybridization in previously allopatric species.Thus,examining hybridization proneness of exotic species contributes to rev...Anthropogenic introduction of species has resulted in a breakdown of geographical barriers and hybridization in previously allopatric species.Thus,examining hybridization proneness of exotic species contributes to revealing its potential threat.Moreover,reproductive barriers may be strengthened or weakened due to long-term geographical isolation for these newly sympatric species.However,few studies have evaluated multiple barriers between alien and native species.In this study,we quantified the importance of four pre-pollination barriers(phenological,floral traits,pollen production,and floral constancy)and four post-pollination barriers(pollen-pistil incompatibility,seed set,seed viability,and seedling survival)between two introduced and five native Sagittaria species.Results showed that introduced S.platyphylla was cross-compatible with two native species,whereas introduced S.montevidensis was incapable of hybridizing with any native species.Different barriers were asymmetric within species pairs and multiple barriers acted in concert to maintain species boundaries.Postpollination barriers contributed more to total reproductive isolation in native species,whereas prepollination barriers played a stronger role in total reproductive isolation for two introduced species.Seed set was the only barrier that was positively correlated with genetic distance.Our results provide a perspective to better understand reproductive barriers for secondary contact species.We highlight the importance of monitoring hybridization events before human introduction and the possible conservation strategies to remove invasive species with hybridization proneness.展开更多
The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups ha...The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups have been a subject of debate.Recent phylogenetic analyses indicate that B.tabaci is a complex composed of 28 morphologically indistinguishable species.In this article,we first review the debate and difficulties associated with B.tabaci＇s taxonomy and systematics,and argue for the need to apply the biological species concept in order to elucidate B.tabaci＇s systematics.We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B.tabaci.Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs,and observations on mating behaviour have been conducted for seven species pairs.Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species.We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility.Finally,we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B.tabaci groups and propose future research directions on the systematics of this complex.展开更多
The Asian cultivated rice(Oryza sativa L.) grown worldwide is divided into two subspecies, indica and japonica. It is well known that the heterosis of inter-subspecies is usually stronger than that of intra-subspecies...The Asian cultivated rice(Oryza sativa L.) grown worldwide is divided into two subspecies, indica and japonica. It is well known that the heterosis of inter-subspecies is usually stronger than that of intra-subspecies. Since the 1970 s, indica hybrid rice, an intra-subspecific hybrid rice, has being widely used in China and even in the world. However, the inter-subspecific hybrid rice between indica and japonica is still unavailable. The major obstacle is the hybrid sterility of the inter-subspecies. In recent decades, the genetic and molecular basis of indica-japonica hybrid sterility was understood more and more clearly. Some breeding approaches for overcoming inter-subspecific hybrid sterility were proposed and used to develop the indicajaponica hybrid rice. The updated understanding will offer new approaches for development of breeding lines for overcoming indica-japonica hybrid sterility, which facilitates developing of inter-subspecific hybrid rice.展开更多
Background:Understanding how species diversify is a long-standing question in biology.The allopatric speciation model is a classic hypothesis to explain the speciation process.This model supposes that there is no gene...Background:Understanding how species diversify is a long-standing question in biology.The allopatric speciation model is a classic hypothesis to explain the speciation process.This model supposes that there is no gene flow during the divergence process of geographically isolated populations.On the contrary,the speciation with gene flow model supposes that gene flow does occur during the speciation process.Whether allopatric species have gene flow during the speciation process is still an open question.Methods:We used the genetic information from 31 loci of 24 Chinese Bamboo Partridges(Bambusicola thoracicus)and 23 Taiwan Bamboo Partridges(B.sonorivox)to infer the gene flow model of the two species,using the approxi-mate Bayesian computation(ABC)model.The ecological niche model was used to infer the paleo-distribution during the glacial period.We also tested whether the two species had a conserved ecological niche by means of a back-ground similarity test.Results:The genetic data suggested that the post-divergence gene flow between the two species was terminated before the mid-Pleistocene.Furthermore,our ecological niche modeling suggested that their ecological niches were highly conserved,and that they shared an overlapping potential distribution range in the last glacial maximum.Conclusions:The allopatric speciation model cannot explain the speciation process of the two Bamboo Partridges.The results of this study supported a scenario in which speciation with gene flow occurring between the allopatric species and have contributed to our understanding of the speciation process.展开更多
Delimiting species requires multiple sources of evidence.Here,we delimited two varieties of Halenia elliptica(Gentianaceae)using several lines of evidence,including morphological traits and mating system in a sympatri...Delimiting species requires multiple sources of evidence.Here,we delimited two varieties of Halenia elliptica(Gentianaceae)using several lines of evidence,including morphological traits and mating system in a sympatric population,phylogenetic relationships based on nrITS and cpDNA(rpl16)data,and complete chloroplast genome sequences.Comparative analysis of 21 morphological traits clearly separates the two varieties of H.elliptica.Examination of the flowering process and pollination treatments indicate that H.elliptica var.grandiflora produces seeds via outcrossing,whereas H.elliptica var.elliptica produces seeds via mixed mating.Furthermore,hand-pollinated hybridization of the two varieties produced no seeds.Observations of pollinators showed that when bees began a pollination bout on H.elliptica var.grandiflora they preferred to continue pollinating this variety;however,when they began a pollination bout on H.elliptica var.elliptica,they showed no preference for either variety.Phylogenetic analysis confirmed the monophyly of H.elliptica,which was further divided into two monophyletic clades corresponding to the two varieties.A large number of variants from the chloroplast genomes reflected remarkable genetic dissimilarities between the two varieties of H.elliptica.We recommend that the two varieties of H.elliptica should be revised as two species(H.elliptica and H.grandiflora).Our findings indicate that H.elliptica varieties may have split into two separate species due to a shift in mating system,changes in flowering phenology and/or post-pollination reproductive isolation.展开更多
The sweetpotato whitefly Bemisia tabaci（Homoptera：Aleyrodidae）is a destructive pest of agriculture and horticulture worldwide.Recent phylogenetic analysis using mitochondrial cytochrome oxidase 1 sequences indicate...The sweetpotato whitefly Bemisia tabaci（Homoptera：Aleyrodidae）is a destructive pest of agriculture and horticulture worldwide.Recent phylogenetic analysis using mitochondrial cytochrome oxidase 1 sequences indicates that this whitefly is a species complex including at least 24 morphologically indistinguishable but genetically distinct cryptic species.In this study,the inter-species crosses of Middle East-Asia Minor 1（MEAM1）,Mediterranean（MED）and Asia II 7 cryptic species,which were referred to as B,Q and Cv biotypes before,were conducted in two different devices,leaf cages（7 cm3）and cylinder cages（280 cm3）,and at three temperatures of 22,30 and 38°C.Results indicated that no female progeny were produced in the reciprocal cross between MEAM1×Asia II 7,between MED×Asia II 7 cryptic species neither in leaf cage nor in cylinder cages,while 0.81 and 1.37% of females in the offspring were recorded in the reciprocal cross between MEAM1×MED in leaf cage experiments.Approximately 0.95-0.98% female progeny were recorded in the reciprocal cross between MEAM1×MED at 30°C,0.77% female progeny were recorded in the single cross direction between MEAM1 × MED at 22°C,and no female progeny were found in their reciprocal cross at 38°C in leaf cage.Our findings indicated that neither space dimension nor temperature have a significant effect on the hybridization of different B.tabaci cryptic species.展开更多
To detect the intergeneric hybridization between the oyster Crassostrea angulata and Saccostrea cucullata coexisting along the southern coast of China, reciprocal crosses were conducted between the two species. Barrie...To detect the intergeneric hybridization between the oyster Crassostrea angulata and Saccostrea cucullata coexisting along the southern coast of China, reciprocal crosses were conducted between the two species. Barriers for sperm recognizing, binding, penetrating the egg, and forming the pronucleus were detected by fluorescence staining. From the results, although fertilization success was observed in hybrid crosses, the overall fertilization rate was lower than that of intraspecific crosses. A large number of hybrid larvae died at 6–8 d after hatching, and those survived could not complete metamorphosis. C. angulata ♀× S. cucullata ♂ larvae had a growth rate similar to that of the maternal species, whereas S. cucullata ♀× C. angulata ♂ larvae grew the slowest among all crosses. Molecular genetics analysis revealed that hybrid progeny were amphimixis hybrids. This study demonstrated that hybrid embryos generated by crossing C. angulata and S. cucullata could develop normally to the larval state, but could not complete metamorphosis and then develop to the spat stage. Thus, there is a post-reproductive isolation between C. angulata and S. cucullata.展开更多
文摘Successful crossbreeding between Oreochromis niloticus and Sarotherodon melanotheron to produce a commercial hybrid has been difficult.The karyotypes and isoenzyme of these two species and their reciprocal hybrids（O.niloticus ♀ × S.melanotheron ♂,S.melanotheron ♀ × O.niloticus ♂,the last not included in the isoenzyme study） were investigated via metaphase chromosomes obtained from head kidney cells and electropherogram of lactate dehydrogenase（LDH） isoenzymes from the liver,kidney,white muscle,heart,and eye balls.The diploid chromosome number（2n=44） and the fundamental number（NF=50） of the four tilapia genotypes were the same.However,the karyotype of O.niloticus had three pairs of sub-metacentric（sm）,twelve pairs of sub-telocentric（st）,and seven pairs of telocentric（t） chromosomes,while S.melanotheron had one pair of metacentric（m）,two pairs of sm,12 pairs of st,and seven pairs of t chromosomes.The reciprocal hybrids both showed a mixed karyotype range between their parents：0.5 pair of m,2.5 pairs of sm,12 pairs of st,and seven pairs of t chromosomes.In view of the electropherogram of isozymes,only the LDH of the kidney showed significant clear bands,with five bands in O.niloticus,three bands in S.melanotheron,and duplicated six bands in the hybrids.The bands varied depending on their activities and mobilities.We considered that the differences in karyotype and isoenzyme were related to the genetic mechanism for post-mating isolation,and provided some additional basic genetic background of their taxonomy.
基金Supported by Research Projects from Education Department of Guangxi(200807MS065)Mathematical Modeling in Population Genetics from Talents Scheme of Universities in Guangxi~~
文摘According to the fitness of heterozygote was lower than homozygote among panmictic population,the process of generational accumulate of mutant gene r was considered.Branch point of r＇s frequency by generational evolution which revealed the hereditary incompatibility between R and r,was worked out,and it was found that genetic drift can make r have higher frequency to surpass the branch point to form reproductive isolation.It was not enough to have the three conditions of mutation,genetic drift and natural selection to be the drive of biological evolution;hybrid weakness,the repelling interaction between the genetic background of original population and the new mutation,were also needed.
基金supported by the Milwaukee County Zoological Societythe American Cichlid Association Guy D. Jordan Endowment+1 种基金Clifford Mortimer Awardsupported in part by NSF RUI and REU grants
文摘Sexual selection via female mate choice is thought to have played a key role in the speciation ofhaplochromine cichlids, but a dominant role for visual signals in such processes has lately been called into question. In addition, the possible role of male mating preferences in haplochromine speciation has been little studied. We studied patterns of both female and male mate choice, based exclusively on visual signals, in order to evaluate potential reproductive isolation between two populations of the Lake Malawi haplochromine Labeotropheus fuelleborni. In the first experiment, females were allowed to choose between two males, one from the same population and the other allopatric with respect to the female. Females in this experiment responded more frequently to males from their own population. Similarly, the males in these trials displayed more frequently when presented with females of their own population. In the second experiment, a female was allowed to choose between two males, either both from her own population or both allopatric. In these trials, both males and females from the Katale population interacted significantly more frequently in settings in which all three individuals were from the same population （＂same-population trios＂）, and those from the Chipoka population showed a similar trend. Thus, patterns in both male and female courtship behavior suggest that visual signals contribute to at least incipient reproductive isolation between populations of L. fuelleborni [Current Zoology 56 （ 1 ）： 65-72 2010].
基金supported by National Natural Science Foudation of China,(No.39930100,30024004)Chinese Academy of Science(No.KSCX2-1-05)Japan Society for the Promotion of Science(No.12375002)
文摘Drosophila lacertosa is widely distributed from northern India to Far East of Russia throughout China.We have studied geographical distributions of three kinds of chromosomal karyotypes,type D(2n=10,4 pairs of V-shaped metacentric chromosomes and a pair of micro-chromosomes),type L(2n= 10,5V with a pair of large-sized heterochromatic autosomes)and type M(2n=10,5V with middle-sized ones).Type D was found exclusively in local populations of D.lacertosa distributed in Yun-Gui Plateau,southwestern China.Both type L and M have a wide range of distribution,and the former occurred in subtropical regions of China including Taiwan Island,whereas the latter in cool temperate regions of East Asia covering Far East of Russia,Korea and the Japan Islands.A strong premating isolation was detected between flies with type D and those with type L or M.These data demonstrate that genetic differentiation leading to cryptic speciation might have occurred in natural populations of Drosophila lacertosa.
基金supported by National Key R&D Program of China(2022YFD1200801)National Natural Science Foundation of China(31991224 and U2002202)+3 种基金Jiangsu Research and Development Program(BE2021360)the Natural Science Foundation of Jiangsu Province,China(BK20200023)the Fundamental Research Funds for the Central Universities(ZJ22195020)the Jiangsu Collaborative Innovation Center for Modern Crop Production.
文摘Heterosis,also known as hybrid vigor,is commonly observed in rice crosses.The hybridization of rice species or subspecies exhibits robust hybrid vigor,however,the direct harnessing of this vigor is hindered by reproductive isolation.Here,we review recent advances in the understanding of the molecular mechanisms governing reproductive isolation in inter-subspecific and inter-specific hybrids.This review encompasses the genetic model of reproductive isolation within and among Oryza sativa species,emphasizing the essential role of mitochondria in this process.Additionally,we delve into the molecular intricacies governing the interaction between mitochondria and autophagosomes,elucidating their significant contribution to reproductive isolation.Furthermore,our exploration extends to comprehending the evolutionary dynamics of reproductive isolation and speciation in rice.Building on these advances,we offer a forward-looking perspective on how to overcome the challenges of reproductive isolation and facilitate the utilization of heterosis in future hybrid rice breeding endeavors.
基金supported by grants from the National Key Research and Development Program of China (2016YFD0100801)the National Natural Science Foundation of China (No.31771873)the National Program for Support of Top-notch Young Professionals
文摘Reproductive isolation is defined as processes that prevent individuals of different populations from mating, survival or producing fertile offspring. Reproductive isolation is critical for driving speciation and maintaining species identity, which has been a fundamental concern in evolutionary biology. In plants,reproductive isolation can be divided into prezygotic and postzygotic reproductive barriers, according to its occurrence at different developmental stages. Postzygotic reproductive isolation caused by reduced fitness in hybrids is frequently observed in plants, which hinders gene flow between divergent populations and has substantial effects on genetic differentiation and speciation, and thus is a major obstacle for utilization of heterosis in hybrid crops. During the past decade, China has made tremendous progress in molecular and evolutionary basis of prezygotic and postzygotic reproductive barriers in plants. Present understandings in reproductive isolation especially with new data in the last several years well support three evolutionary genetic models, which represent a general mechanism underlying genomic differentiation and speciation. The updated understanding will offer new approaches for the development of wide-compatibility or neutral varieties, which facilitate breeding of hybrid rice as well as other hybrid crops.
基金supported by the National Natural Science Foundation of China (91731301)the grants from the Chinese Academy of Sciences (XDB31000000, XDA08020103)CAS/SAFEA International Partnership Program for Creative Research Teams。
文摘It is of critical importance for our understanding of speciation process to determine the forms of reproductive isolation and their relative importance in species divergence. Oryza nivara and O. rufipogon are direct ancestors of Asian cultivated rice and a progenitor-daughter species pair. Investigating the reproductive isolation between them provides insights into plant speciation and helps understanding of the rice domestication. Here, we quantitatively measured the major components of reproductive isolation between the two species based on common garden and crossing experiments for three pairs of sympatric populations in Nepal, Cambodia and Laos.We revealed significant differences in the flowering times between species pairs, with O. nivara flowering much earlier than O. rufipogon. A very weak reduction in seed set but no reduction in F1 viability and fertility were detected for the crosses between species relative to those within species. Moreover, we detected asymmetrical compatibility between species and found that emasculation significantly decreased pollination success in O. nivara but not in O. rufipogon.Our study demonstrates that the divergence between O. nivara and O. rufipogon is maintained almost entirely by the difference in flowering times and suggests that differential flowering times contribute to both habitat preferences and reproductive isolation between species.
基金supported by the National Natural Science Foundation of China (31170184, U1202261, 31000109, 31370269)the International Foundation for Science (AD/22476)
文摘Reproductive isolation defines the biological species concept and plays a key role in the formation and maintenance of species. The relative contributions of different isolating stages has been suggested to be closely associated with phylogenetic relatedness. Few studies have focused on the relative contributions of pre- versus post-zygotic mechanisms, and even fewer have been conducted under strict phylogenetic frameworks. Pre-and post-zygotic reproductive isolation stages have been investigated in the sister species Mussaenda kwangtungensis and M. pubescens var. alba. The two species have partly overlapping distribu-tion ranges and flowering times, while the principal pollinators differed strikingly for them, demonstrating strong pre-zygotic isolations. Natural hybrids were detected by simple sequence repeat markers and their maternal parents were identified based on chloroplast gene sequen-ces. Five out of 81 individuals were suggested to be hybrids that fall into the categories F2, BC1, and BC2 by the NewHybrids analysis. Interspecific crossings resulted in significantly reduced fruit set and seed germination rates. Phylogenetic analysis revealed short Kimura-2-parameter distance between M. kwangtungensis and M. pubescens var. alba. These findings strongly supported the hypothesis that for species with a closer phylogenetic relationship, pre-zygotic isolation plays an important part in limiting gene exchange in sympatric areas.
基金S.E.L. was supported by a National Science Foundation （NSF） Graduate Research Opportunities Worldwide （GROW） Fellowship in Switzerland and NSF Graduate Research Fellowship under Grant No. 1154145. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the NSF.
文摘Research on sexual selection and hybridization has focused on female mate choice and male-male competition. While the evolutionary outcomes of interspecific female preference have been well explored, we are now gaining a better understanding of the processes by which male-male compe- tition between species in secondary contact promotes reproductive isolation versus hybridization. What is relatively unexplored is the interaction between female choice and male competition, as they can oppose one another or align with similar outcomes for reproductive isolation. The role of female-female competition in hybridization is also not well understood, but could operate similarly to male-male competition in polyandrous and other systems where costs to heterospecific mating are low for females. Reproductive competition between either sex of sympatric species can cause the divergence and/or convergence of sexual signals and recognition, which in turn influences the likelihood for interspecific mating. Future work on species interactions in secondary contact should test the relative influences of both mate choice and competition for mates on hybridization outcomes, and should not ignore the possibilities that females can compete over mating resources, and males can exercise mate choice.
基金supported by the National Natural Science Foundation of China(31500194 and U1202261)
文摘Natural hybridization frequently occurs in plants and can facilitate gene flow between species, possibly resulting in species refusion. However, various reproductive barriers block the formation of hybrids and maintain species integrity. Here, we conducted a field survey to examine natural hybridization and reproductive isolation （RI） between sympatric populations of Primula secundiflora and P. poissonii using ten nuclear simple sequence repeat （SSR） loci. Although introgressive hybridization occurred, species boundaries between P. secundiflora and P. poissonii were maintained through nearly complete reproductive isolation. These interfertite species provide an excellent model for studying the RI mechanisms and evolutionary forces that maintain species boundaries.
基金supported by the National Natural Science Foundation of China(31330008 and 31160047)the Key Research Program of the Chinese Academy of Sciences (KJZD-EW-L07)Science and Technology Basic Work (2013FY112100)
文摘Floral nectar is thought to be one of the most important rewards that attract pollinators in Pedicularis; however, few studies have examined variation of nectary structure and/or nectar secretion in the genus, particularly among closely related species. Here we investigated nectary morphology, nectar quality, and nectar production dynamics in flowers of Pedicularis section Cyathophora. We found a conical floral nectary at the base of the ovary in species of the rex-thamnophila clade. Stomata were found on the sudace of the nectary, and copious starch grains were detected in the nectary tissues. In contrast, a semi-annular nectary was found in flowers of the species of the superba clade. Only a few starch grains were observed in tissues of the semi-annular nectary, and the nectar sugar concentration in these flowers was much lower than that in the flowers of the rexthamnophila clade. Our results indicate that the floral nectary has experienced considerable morphological, structural, and functional differentiation among closely related species of Pedicularis. This could have affected nectar production, leading to a shift of the pollination mode. Our results also imply that variation of the nectary morphology and nectar production may have played an important role in the speciation of sect. Cyathophora.
文摘The term ＇assortative mating＇ has been applied to describe two very different phenomena： （1） the tendency for indi- viduals to choose phenotypically similar mates from among conspecifics; or （2） the tendency to prefer conspecific over hete- rospecific mates （behavioral reproductive isolation）. Both forms of assortative mating are widespread in nature, but the relation- ship between these behaviors remains unclear. Namely, it is plausible that a preference for phenotypically similar conspecifics in cidentally reduces the probability of mating with phenotypically divergent heterospecifics. We present a model to calculate how the level of reproductive isolation depends on intraspecific assortative mating and the phenotypic divergence between species. For empirically reasonable levels of intraspecific assortment on a single trait axis, we show that strong reproductive isolation requires very substantial phenotypic divergence. We illustrate this point by applying our model to empirical data from threespine stickleback Gasterosteus aculeatus and Darwin＇s Finches （Geospiza spp）. We conclude that typical levels of intraspecific assortment cannot generally be extrapolated to explain levels of interspecific reproductive isolation. Instead, reproductive isolation between species likely arises from different mate choice behaviors, or multivariate assortative mating [Current Zoology 58 （3）： 484-492, 2012].
基金supported by Grantsin-Aid for Scientific Research(C and B)(Nos.20510216 and 24310173)to M.Sumida from the Ministry of Education,Culture,Sports,Science and Technology,Japan
文摘To elucidate reproductive isolating mechanisms in the Bangladesh coastal bullfrog Hoplobatrachus litoralis and its congeneric species, we performed crossing experiments using three species： H. litoralis, H. tigerinus and H. rugulosus. In addition, we conducted histological observations on spermatogenesis of the hybrids. The reciprocal hybrids between H. litoralis and H. tigerinus developed normally with somewhat lower viability at the metamorphosis stage compared with the controls. Most of the metamorphosed frogs became mature. On the other hand, almost all hybrids between female H. rugulosus and male H. litoralis or H. tigerinus died of underdevelopment at the tadpole stage, and only a few hybrids metamorphosed normally and survived to maturity. The inner structures of the testes of the control H. litoralis and H. tigerinus were completely normal, with seminiferous tubules filled with compact bundles of normal spermatozoa. Those of the reciprocal hybrids between H. litoralis and H. tigerinus were almost normal or slightly abnormal, with seminiferous tubules that contained pycnotic nuclei in addition to normal bundles of normal spermatozoa, which demonstrates slight abnormalities in spermatogenesis. In contrast, the hybrids between female H. rugulosus and male H. litoralis or H. tigerinus had no bundles of spermatozoa nor spermatids in the seminiferous tubules, which indicates entirely abnormal spermatogenesis. Meiotic chromosome figures in the reciprocal hybrids between H. litoralis and H. tigerinus showed slight abnormalities, with the occurrence of univalents and increase of rod-shaped bivalents. These results indicate that H. litoralis and H. tigerinus are not isolated from each other by hybrid inviability nor by hybrid sterility, although the hybrids showed somewhat abnormal spermatogenesis in hybrids and that H. rugulosus is isolated from both H. litoralis and H. tigerinus by incomplete hybrid inviability and complete hybrid sterility.
基金This study was supported by the National Science Foundation of China(31970250).
文摘Anthropogenic introduction of species has resulted in a breakdown of geographical barriers and hybridization in previously allopatric species.Thus,examining hybridization proneness of exotic species contributes to revealing its potential threat.Moreover,reproductive barriers may be strengthened or weakened due to long-term geographical isolation for these newly sympatric species.However,few studies have evaluated multiple barriers between alien and native species.In this study,we quantified the importance of four pre-pollination barriers(phenological,floral traits,pollen production,and floral constancy)and four post-pollination barriers(pollen-pistil incompatibility,seed set,seed viability,and seedling survival)between two introduced and five native Sagittaria species.Results showed that introduced S.platyphylla was cross-compatible with two native species,whereas introduced S.montevidensis was incapable of hybridizing with any native species.Different barriers were asymmetric within species pairs and multiple barriers acted in concert to maintain species boundaries.Postpollination barriers contributed more to total reproductive isolation in native species,whereas prepollination barriers played a stronger role in total reproductive isolation for two introduced species.Seed set was the only barrier that was positively correlated with genetic distance.Our results provide a perspective to better understand reproductive barriers for secondary contact species.We highlight the importance of monitoring hybridization events before human introduction and the possible conservation strategies to remove invasive species with hybridization proneness.
基金funded by the National Basic Research Program of China(2009CB119203)the National NaturalScience Foundation of China(30730061)the ChinaAgriculture Research System(CARS-25-B-08)
文摘The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups have been a subject of debate.Recent phylogenetic analyses indicate that B.tabaci is a complex composed of 28 morphologically indistinguishable species.In this article,we first review the debate and difficulties associated with B.tabaci＇s taxonomy and systematics,and argue for the need to apply the biological species concept in order to elucidate B.tabaci＇s systematics.We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B.tabaci.Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs,and observations on mating behaviour have been conducted for seven species pairs.Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species.We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility.Finally,we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B.tabaci groups and propose future research directions on the systematics of this complex.
基金supported by the National Natural Science Foundation of China (91435207 and 91735304)the Project of Science and Technology of Guangzhou, China (201607020040)
文摘The Asian cultivated rice(Oryza sativa L.) grown worldwide is divided into two subspecies, indica and japonica. It is well known that the heterosis of inter-subspecies is usually stronger than that of intra-subspecies. Since the 1970 s, indica hybrid rice, an intra-subspecific hybrid rice, has being widely used in China and even in the world. However, the inter-subspecific hybrid rice between indica and japonica is still unavailable. The major obstacle is the hybrid sterility of the inter-subspecies. In recent decades, the genetic and molecular basis of indica-japonica hybrid sterility was understood more and more clearly. Some breeding approaches for overcoming inter-subspecific hybrid sterility were proposed and used to develop the indicajaponica hybrid rice. The updated understanding will offer new approaches for development of breeding lines for overcoming indica-japonica hybrid sterility, which facilitates developing of inter-subspecific hybrid rice.
基金This work was supported by the China Postdoctoral Science Foundation(2019M660044)National Natural Science Foundation of China(31872244)Biodiversity Survey,Monitoring and Assessment Project of Ministry of Ecology and Environment,China(2019HB2096001006 to Z.W.Z).
文摘Background:Understanding how species diversify is a long-standing question in biology.The allopatric speciation model is a classic hypothesis to explain the speciation process.This model supposes that there is no gene flow during the divergence process of geographically isolated populations.On the contrary,the speciation with gene flow model supposes that gene flow does occur during the speciation process.Whether allopatric species have gene flow during the speciation process is still an open question.Methods:We used the genetic information from 31 loci of 24 Chinese Bamboo Partridges(Bambusicola thoracicus)and 23 Taiwan Bamboo Partridges(B.sonorivox)to infer the gene flow model of the two species,using the approxi-mate Bayesian computation(ABC)model.The ecological niche model was used to infer the paleo-distribution during the glacial period.We also tested whether the two species had a conserved ecological niche by means of a back-ground similarity test.Results:The genetic data suggested that the post-divergence gene flow between the two species was terminated before the mid-Pleistocene.Furthermore,our ecological niche modeling suggested that their ecological niches were highly conserved,and that they shared an overlapping potential distribution range in the last glacial maximum.Conclusions:The allopatric speciation model cannot explain the speciation process of the two Bamboo Partridges.The results of this study supported a scenario in which speciation with gene flow occurring between the allopatric species and have contributed to our understanding of the speciation process.
基金the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK0502)National Key R&D Program of China(2017YFC0505200)+1 种基金National Natural Science Foundation of China(31460096 and 31590823)State Key Laboratory of Phytochemistry and Plant Resources in West China(P2020-KF04).
文摘Delimiting species requires multiple sources of evidence.Here,we delimited two varieties of Halenia elliptica(Gentianaceae)using several lines of evidence,including morphological traits and mating system in a sympatric population,phylogenetic relationships based on nrITS and cpDNA(rpl16)data,and complete chloroplast genome sequences.Comparative analysis of 21 morphological traits clearly separates the two varieties of H.elliptica.Examination of the flowering process and pollination treatments indicate that H.elliptica var.grandiflora produces seeds via outcrossing,whereas H.elliptica var.elliptica produces seeds via mixed mating.Furthermore,hand-pollinated hybridization of the two varieties produced no seeds.Observations of pollinators showed that when bees began a pollination bout on H.elliptica var.grandiflora they preferred to continue pollinating this variety;however,when they began a pollination bout on H.elliptica var.elliptica,they showed no preference for either variety.Phylogenetic analysis confirmed the monophyly of H.elliptica,which was further divided into two monophyletic clades corresponding to the two varieties.A large number of variants from the chloroplast genomes reflected remarkable genetic dissimilarities between the two varieties of H.elliptica.We recommend that the two varieties of H.elliptica should be revised as two species(H.elliptica and H.grandiflora).Our findings indicate that H.elliptica varieties may have split into two separate species due to a shift in mating system,changes in flowering phenology and/or post-pollination reproductive isolation.
基金funded by the National Basic Research Program of China(2009CB119203)the National NaturalScience Foundation of China(31071732)the Foundation of Lingnan Fruit Innovation Team of GuangdongProvince,China(2009-14)
文摘The sweetpotato whitefly Bemisia tabaci（Homoptera：Aleyrodidae）is a destructive pest of agriculture and horticulture worldwide.Recent phylogenetic analysis using mitochondrial cytochrome oxidase 1 sequences indicates that this whitefly is a species complex including at least 24 morphologically indistinguishable but genetically distinct cryptic species.In this study,the inter-species crosses of Middle East-Asia Minor 1（MEAM1）,Mediterranean（MED）and Asia II 7 cryptic species,which were referred to as B,Q and Cv biotypes before,were conducted in two different devices,leaf cages（7 cm3）and cylinder cages（280 cm3）,and at three temperatures of 22,30 and 38°C.Results indicated that no female progeny were produced in the reciprocal cross between MEAM1×Asia II 7,between MED×Asia II 7 cryptic species neither in leaf cage nor in cylinder cages,while 0.81 and 1.37% of females in the offspring were recorded in the reciprocal cross between MEAM1×MED in leaf cage experiments.Approximately 0.95-0.98% female progeny were recorded in the reciprocal cross between MEAM1×MED at 30°C,0.77% female progeny were recorded in the single cross direction between MEAM1 × MED at 22°C,and no female progeny were found in their reciprocal cross at 38°C in leaf cage.Our findings indicated that neither space dimension nor temperature have a significant effect on the hybridization of different B.tabaci cryptic species.
文摘To detect the intergeneric hybridization between the oyster Crassostrea angulata and Saccostrea cucullata coexisting along the southern coast of China, reciprocal crosses were conducted between the two species. Barriers for sperm recognizing, binding, penetrating the egg, and forming the pronucleus were detected by fluorescence staining. From the results, although fertilization success was observed in hybrid crosses, the overall fertilization rate was lower than that of intraspecific crosses. A large number of hybrid larvae died at 6–8 d after hatching, and those survived could not complete metamorphosis. C. angulata ♀× S. cucullata ♂ larvae had a growth rate similar to that of the maternal species, whereas S. cucullata ♀× C. angulata ♂ larvae grew the slowest among all crosses. Molecular genetics analysis revealed that hybrid progeny were amphimixis hybrids. This study demonstrated that hybrid embryos generated by crossing C. angulata and S. cucullata could develop normally to the larval state, but could not complete metamorphosis and then develop to the spat stage. Thus, there is a post-reproductive isolation between C. angulata and S. cucullata.
