Local adaptation versus historical isolation as sources of melanin‐based coloration in the white‐throated thrushTurdus assimilis

Abstract

Local adaptation seems to be one of the causes of variation in melanin‐based colors in bird plumages, related mainly to the heterogeneity of the environmental conditions along the distribution of a species. Based on comparisons of genetic (mtDNA sequences), ecological (niche models), and quantitative colorimetric data, we explored variation in plumage coloration of the white‐throated thrush Turdus assimilis, a Mesoamerican species whose dorsal color varies from brown (northern and central Mexico) to dark gray (southern Mexico and Central America). Our results suggest the existence of two major patterns of coloration in this bird, which are congruent with the genetic structure, and comparisons of ecological niche models showed that population's niches were more similar than expected by chance, suggesting that color variation in plumage of T. assimilis is not consequence of local adaptation to different environmental conditions. Our results also showed that a greater geographic distance between populations is correlated with greater colorimetric differences, suggesting that color variation in T. assimilis may be consequence of historical isolation.

Drivers of phenotypic divergence in a Mesoamerican highland bird

“…The lack of relationship between color variation and geographical distance indicates that the mechanism underlying this variation is not isolation by distance. This is in contrast to the findings of Núñez Zapata et al (2018) and by Ramírez-Barrera et al (2019) , who used a similar approach and found that for Turdus assimilis and Habia rubica respectively, Isolation by Distance is the model that best explains color variation. This, coupled with the lack of genetic structure that correlates to geography suggests that there may be more gene flow than previously thought and/or that carotenoid-based coloration in this species is fairly plastic.…”

Lack of conspecific visual discrimination between second-year males and females in the Saffron Finch

“…Chromatic and achromatic contrasts are expressed in just noticeable differences (JNDs) and indicate how different are two spectra perceived given the visual space of the receiver; values > 1 are considered discernible by birds [56,65] only under extremely controlled conditions [66,67]. Therefore, we used a conservative value of > 2 JNDs as the threshold above which visual discrimination could take place [68,69].…”

Morphological variations in a widely distributed Eastern Asian passerine cannot be consistently explained by ecogeographic rules

“…A large body of empirical data supports various ecogeographic rules (e.g., Meiri, 2011;Salewski & Watt, 2017 for Bergmann's rule; Betti et al, 2015;Laiolo & Rolando, 2001;VanderWerf, 2012;Yom-Tov & Yom-Tov, 2005 for Allen's rule; and Delhey, 2019 for Gloger's rule) although it is not uncommon to document exceptions to these rules (e.g., Núñez-Zapata et al, 2018;Riemer et al, 2018;Tattersall et al, 2017). Moreover, most of these studies focused on European and North American species (Betti et al, 2015;Delhey, 2019;Laiolo & Rolando, 2001;Meiri, 2011;Salewski & Watt, 2017;VanderWerf, 2012;Yom-Tov & Yom-Tov, 2005), and the rules remain to be tested against evolutionary lineages endemic to other geographic regions.…”