Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses am...Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites.According to the latitudinal gradient in diversity,species richness and abundance of parasites peak near the equator.The uropygial gland is an im portant defensive exocrine gland against pathogens in birds.Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts.Therefore,we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes.However,this hypothesis has not yet been explored.Here,we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical(Peru)and 3 temperate areas(Spain).Relative uropygial gland volum e was 12.52%larger in bird species from the tropics than from temperate areas.This finding is consistent w ith the relative size of this defensive organ being driven by selective pressures imposed by parasites.We also explored the potential role of this gland as a means of avoiding haemosporidian infection,showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection,regardless o f their geographical origin.This result provides additional support for the assum ption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.展开更多
The vertical transport of mass at the top of the boundary layer is considered as a link between the boundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layer is studied un...The vertical transport of mass at the top of the boundary layer is considered as a link between the boundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layer is studied under the consideration of the interaction between the boundary layer and free atmosphere.The vertical motion at the top of the boundary layer is evaluated.The results show that the distinguished differ- ences of the present results from classical Ekman layer do exist and they are discussed in the paper.展开更多
基金This work was supported by the Spanish Ministry of Economy and Competitiveness research projects[grant CGL2015-64650P]Junta de Extremadura[grant IB16121]S.M.and A.M.were supported by a Ph.D.grant from the Ministry of Economy and Competition of Spain and a mobility grant of Junta de Extremadura(129/2015),respectively.L.G.-L.was supported by the Junta de Extremadura[PO17024,Post-Doc grant].
文摘Parasites are globally widespread pathogenic organisms,which impose im portant selective forces upon their hosts.Thus,in accordance with the A djustm ent to parasite pressure hypothesis,it is expected that defenses among hosts vary relative to the selective pressure imposed by parasites.According to the latitudinal gradient in diversity,species richness and abundance of parasites peak near the equator.The uropygial gland is an im portant defensive exocrine gland against pathogens in birds.Size of the uropygial gland has been proposed to vary among species of birds because of divergent selection by pathogens on their hosts.Therefore,we should expect that bird species from the tropics should have relatively larger uropygial glands for their body size than species from higher latitudes.However,this hypothesis has not yet been explored.Here,we analyze the size of the uropygial gland of 1719 individual birds belonging to 36 bird species from 3 Neotropical(Peru)and 3 temperate areas(Spain).Relative uropygial gland volum e was 12.52%larger in bird species from the tropics than from temperate areas.This finding is consistent w ith the relative size of this defensive organ being driven by selective pressures imposed by parasites.We also explored the potential role of this gland as a means of avoiding haemosporidian infection,showing that species with large uropygial glands for their body size tend to have lower mean prevalence of haemosporidian infection,regardless o f their geographical origin.This result provides additional support for the assum ption that secretions from the uropygial gland reduce the likelihood of becoming infected with haemosporidians.
文摘The vertical transport of mass at the top of the boundary layer is considered as a link between the boundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layer is studied under the consideration of the interaction between the boundary layer and free atmosphere.The vertical motion at the top of the boundary layer is evaluated.The results show that the distinguished differ- ences of the present results from classical Ekman layer do exist and they are discussed in the paper.
