Abstract
BackgroundMorphological characters of birds reflect their adaptive evolution and ecological requirements and are also relevant to phylogenetic relationships within a group of related species. The tits (Paridae) are known to be outwardly homogeneous in shape, with one aberrant member, the Ground Tit (Pseudopodoces humilis), which is quite different from its relatives in both body morphology and beak shape. We combined traditional measurements and geometric morphometrics to quantify the variation in body morphology and beak shape of 14 Paridae species distributed in China. Based on these results, we sought to assess the contribution of phylogeny, altitude and species interactions to the evolution of morphological traits.ResultsThe basic features for discriminating among the 14 species studied here were overall body size, the ratio of body and tail length to culmen and tarsus length, and beak shape (long/slender/pointy vs. short/robust/blunt). These dimensions clearly separate Ps. humilis and Melanochlora sultanea from the other species in shape space. Body length and PC3 of beak shape (round outline vs. straight outline) show significant phylogenetic signals. Across 14 species, altitude is related to tarsus, culmen length and PC1 of beak shape. Within Parus major, altitude is related to body weight, body length, culmen length and PC1 of body morphology. Morphological distances and geographic distances among species are positively correlated.ConclusionsThe body morphology of Paridae species shows extensive evolutionary changes, while their beak has mainly evolved along the long/slender/pointy vs. short/robust/blunt dimension. Only body length and beak curvature show a phylogenetic signal. Altitude correlates with multiple traits both across and within species, suggesting that altitude is an important factor in promoting morphological divergence. The deviant appearance of Ps. humilis corresponds to its foraging and feeding adaptations to high-altitude steppe habitats. Our results also show a higher level of morphological divergence with greater difference in distribution ranges among the Paridae species involved in this study.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0162-0) contains supplementary material, which is available to authorized users.
Highlights
Morphological characters of birds reflect their adaptive evolution and ecological requirements and are relevant to phylogenetic relationships within a group of related species
We looked for morphological variation along the altitudinal gradient both among Paridae species and within P. major, which occurs from 400 m to as high as 4400 m above sea level
The results of both tests indicate a differentiation in body morphology among the Paridae species
Summary
Morphological characters of birds reflect their adaptive evolution and ecological requirements and are relevant to phylogenetic relationships within a group of related species. We combined traditional measurements and geometric morphometrics to quantify the variation in body morphology and beak shape of 14 Paridae species distributed in China. Pseudopodoces humilis is endemic to the QTP and dwells exclusively on the treeless steppes, which has been identified as an extreme example in the evolution of Paridae species [16, 20] It had long been misclassified as a small species of ground jay due to its strikingly aberrant appearance, while recent studies have revealed that this species is closely related to Parus major and P. monticolus, with a divergent time of approximately 7.7 - 9.9 million years [21,22,23]. Few studies have quantified morphological variation across the main clades and investigated potential factors that could shape the patterns of diversity in this family
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