Turbek, S. P. | Search bioRxiv

bioRxiv2025

A multiscale physicochemical characterization of melanin-based feather coloration in the rapid Capuchino Seedeater radiation

Melanin-based plumage coloration in birds is shaped by pigment composition as well as melanosome morphology and distribution, however, the ways in which these factors together modulate observable color remain poorly understood. We investigate this relationship in the Capuchino Seedeaters (genus Sporophila), whose recent, rapid radiation driven by sexual selection resulted in 12 species with diverse coloration patterns. Using scanning electron microscopy (SEM) and micro-computed tomography ({micro}CT), combined with a novel application of Fontana-Masson stain to image melanosomes at high resolution, we characterize melanosome distribution and morphology in several variably colored plumage patches across Capuchino species. Melanosome morphologies followed patch-specific patterns that did not directly correlate with coloration: crown feather melanosomes were larger, more elongated, and had greater percent eumelanin content than those in belly, throat, or dorsum/rump patches. We also observed that dorsal patches had more total melanin than ventral ones, with pigment and coloration patterns suggesting possible signaling and photoprotective roles. More generally, we show how the patch-specific coloration of male Capuchinos is accompanied by differences in melanosome morphology and melanin composition and abundance. Our work highlights the challenges that remain in understanding how the nanoscale mechanisms of melanin-based pigmentation translate into macroscale plumage coloration.

evolutionary biology↗

bioRxiv2022

An Experimental Analysis of the Fine-Scale Effects of Nest Ectoparasites on Incubation Behavior

Avian incubation is a highly complex, adjustable behavior essential to embryo development and survival. When incubating, parents face a tradeoff between investing in incubation to maintain optimal temperatures for egg development or in self-maintenance behaviors to ensure their own survival and future reproduction. Because nest ectoparasites are costly and can reduce nestling quality and survival, infections could shift parental investment in current vs. future offspring. However, it is not well understood whether birds change investment in incubation in response to nest ectoparasitism, particularly in the context of other factors that are known to influence incubation behavior, such as ambient temperature, clutch size, and embryo development. We hypothesized that parents could respond to nest parasites by 1) investing more in incubation to promote the development of high-quality offspring to help offset the cost of parasites, 2) investing less in incubation or even abandoning their nest during incubation to save resources for future reproduction, or 3) being unresponsive to parasite infections, as incubation is more constrained by other factors. We tested these hypotheses by experimentally removing and adding mites in barn swallow nests at the start of incubation and deploying thermocouple eggs to measure egg temperatures at one-minute intervals until hatching. We found that while ambient temperature, clutch initiation date, embryo age, and clutch size were the main factors driving variation in egg conditions and parental incubation behavior, parasitized nests had higher mean egg temperatures, which could aid in nestling immune development. However, despite more optimal developmental temperatures, eggs in parasitized nests also had lower hatching success. Our results indicate that incubation is a dynamic behavior that is largely driven by the constraints of maintaining appropriate egg temperatures for development. Although quite costly upon hatching, ectoparasites appear to play a relatively minor role in driving variation in parental incubation investment. LAY SUMMARYO_LIIncubation is a complex behavior shaped by both internal and external factors. C_LIO_LIEctoparasites often decrease quality and survival of nestlings and could influence investment in incubation because of tradeoffs in how parents spend energy. C_LIO_LIWe manipulated parasites in barn swallow nests and used fake eggs with temperature sensors to collect data on egg temperatures and parental behavior throughout incubation. C_LIO_LIWe found that other factors were the main drivers of variation in incubation behavior, but that eggs in parasite nests were warmer on average, which could help nestlings better cope with parasites upon hatching. C_LIO_LIDespite more optimal developmental temperatures, eggs in parasitized nests had lower hatching success. C_LIO_LIAlthough quite costly to nestlings, ectoparasites played a minor role in shaping parental incubation behavior. C_LI

animal behavior and cognition↗

bioRxiv2019

Migratory divides coincide with species barriers across replicated avian hybrid zones above the Tibetan Plateau

Migratory divides are proposed to be catalysts for speciation across a diversity of taxa. However, the relative contribution of migratory behavior to reproductive isolation is difficult to test. Comparing reproductive isolation in hybrid zones with and without migratory divides offers a rare opportunity to directly examine the contribution of divergent migratory behavior to reproductive barriers. We show that across replicate sampling transects of two pairs of barn swallow (Hirundo rustica) subspecies, strong reproductive isolation coincided with an apparent migratory divide spanning 20 degrees of latitude. A third subspecies pair exhibited no evidence for a migratory divide and hybridized extensively. Within migratory divides, migratory phenotype was associated with assortative mating, implicating a central contribution of divergent migratory behavior to reproductive barriers. The remarkable geographic coincidence between migratory divides and genetic breaks supports a longstanding hypothesis that the Tibetan Plateau is a substantial barrier contributing to the diversity of Siberian avifauna.

evolutionary biology↗