Comparison of head size and bite force in two sister species of parrotbills

Background: Brain size is associated with morphological evolution and behavioral flexibility because animals with large brain size tend to utilize new resources and colonize novel environments more successfully.Therefore, animals with larger brain size should possess larger distribution ranges.Brain size is strongly positively correlated with head size in birds, but also with prey size and vocalizations, because individuals with large heads eat large food items and produce high frequency calls.Methods: To test if there exists an association between head morphology and bite performance, we compared head size and bite force in two sympatric sister species of parrotbills, Ashy-throated Parrotbill(Paradoxornis alphonsianus) and Vinous-throated Parrotbill(P.webbianus), which both originated from the Himalayan area, but differ significantly in their distribution ranges.Results: In Guizhou, southwestern China, the Ashy-throated Parrotbill with a restricted distribution range had smaller heads whilst the Vinous-throated Parrotbill with a large distribution range had larger heads.However, there were no differences in head size between Ashy-throated Parrotbills and allopatric populations of Vinous-throated Parrotbills(Jiangxi and Hebei).Furthermore, the tendency of variation in bite force was opposite to that in head size with populations with larger head size having weaker bite force.Conclusions: We showed that there are no differences in head size between the Ashy-throated Parrotbill and allopatric populations of Vinous-throated Parrotbill, which provides evidence for the hypothesis that differences in head size in the Guizhou populations of two sister species are probably the result of local adaptation rather than species-specific.Our study has implications for avian dispersal and adaption related to head size such as diet ecology and vocalizations.

Egg color polymorphism and morph-ratio variation in Korean populations of the Vinous-throated Parrotbill

Understanding the occurrence of multiple distinct phenotypes in a population of a species,i.e.,polymorphism,is one of the challenges encountered in evolutionary biology.Egg color polymorphism in birds is one example of morphological polymorphism and disruptive selection has been proposed as a hypothetical mechanism to explain its occurrence.We studied how polymorphic egg colors(immaculate blue and white) occur in Korean populations of the Vinous-throated Parrotbill(Paradoxornis webbianus).Egg color ratios(the proportion of nests with blue eggs in a population) were monitored over a large spatial scale and egg colors were quanti ed using a spectrophotometer.We found egg color ratios to vary spatially among populations.Interestingly,there was a latitudinal morph-ratio cline in egg color ratios.e proportion of nests with blue eggs increased considerably with the latitude declined towards the southern part of the Korean peninsula.ere were some quantitative variations in egg colors among populations.However,the pattern of variations was not consistent with those of the population egg color ratios.Based on these results,we discuss a potential scenario for the evolution of egg color polymorphism in the Vinous-throated Parrotbill.