Enbody, E. D. | Search bioRxiv

bioRxiv2021

Transspecies beak color polymorphism in the Darwin's finch radiation

Carotenoid-based polymorphisms are widespread in populations of birds, fish, and reptiles1, but little is known of how they affect fitness and are maintained as species multiply2. We report a combined field and molecular-genetic investigation of a nestling beak color polymorphism in Darwins finches. Beaks are pink or yellow, and yellow is recessive3. Here we show that the polymorphism arose in the Galapagos approximately half a million years ago through a regulatory mutation in the BCO2 gene, and is shared by 14 descendant species. The frequency of the yellow genotype is associated with cactus flower abundance in cactus finches, and is altered by introgressive hybridization. The polymorphism is most likely a balanced polymorphism, maintained by ecological selection pressures associated with diet, and augmented by occasional interspecific introgression. Polymorphisms that are hidden as adults, as here, may contribute to evolutionary diversification in underappreciated ways in other systems.

evolutionary biology↗

bioRxiv2020

Testosterone induces a female ornament followed by enhanced territoriality in a tropical songbird

We know little of the proximate mechanisms underlying expression of signaling traits in female vertebrates. Across males the expression of sexual and competitive traits, including ornamentation and aggressive behavior, is often mediated by testosterone. In the White-shouldered Fairywren (Malurus alboscapulatus) of New Guinea, females of different subspecies differ in presence or absence of white shoulder patches and melanic plumage, while males are uniformly ornamented. Previous work has shown that ornamented females circulate more testosterone and exhibit more territorial aggression than do unornamented females. We investigated the degree to which testosterone regulates expression of ornamental plumage and territorial behavior by implanting free-living unornamented females with testosterone. Every testosterone-treated female produced a male-like cloacal protuberance, and 15 of 20 replaced plucked brown feathers with white shoulder patch feathers, but did not produce melanic plumage characteristic of ornamented females. Testosterone treatment did not elevate territorial behavior prior to production of the plumage ornament and exhaustion of the implant. However, females with experimentally induced ornamentation, but exhausted implants, increased the vocal components of territory defense relative to fully unornamented control and also to testosterone-implanted females. Our results suggest that testosterone induces partial acquisition of the ornamental plumage phenotype, and that ornament expression, rather than testosterone alone, results in elevated territorial behavior. Lay SummaryTestosterone regulates expression of a suite of competitive traits in male organisms and could have similar function in females. Empirical tests are needed to determine the extent to which testosterone promotes production of ornamentation and competitive behaviors in female animals. We supplemented testosterone in unornamented females of a species where naturally occurring ornamented females circulate higher testosterone and are more territorially aggressive. Implanted females produced partial ornamentation, which was followed by increased territoriality that was apparently unrelated to testosterone circulation itself.

animal behavior and cognition↗