From Hormones to Genomes: Investigating Testosterone, Social Behavior, and Evolution In Manakins

Abstract

Researchers can gain novel insights into complex biological questions by focusing on species with uncommon evolutionary trajectories, rather than solely relying on traditional model organisms. Furthermore, integrating multiple research perspectives is essential for building a comprehensive understanding of how organisms interact with each other and their environment. This dissertation investigated the behavioral biology of manakins (Aves: Pipridae), neotropical birds notable for their unique polygynous breeding system. In Chapter I, I introduced the relationship between hormones, fitness, and behavior exploring the Cort-Fitness Hypothesis and the Challenge Hypothesis. Chapter II, I reviewed available studies on manakins, synthesizing findings on acrobatics and display behaviors, physiological adaptations for performance, the influence of androgen hormones on social behavior, phylogenetic relationships, genomic mechanisms of evolution, and environmental drivers of behavior. Chapter III, I broadened this perspective by examining the influence of androgen and glucocorticoid hormones on survival estimates across multiple bird species to understand their role in species annua survival estimates. I found that the proportional corticosterone response (a glucocorticoid) was the only hormonal measurement that predicted estimated annual survival in birds. Chapter IV, I tested the Challenge Hypothesis to investigate the role of androgen hormones in the aggressive and reproductive behavior of the red-capped manakin (Ceratopipra mentalis), which exhibits traditional lekking. I found that testosterone increased with simulated male-female interactions but not with simulated male-male interactions. Chapter V, I examined the genetic and genomic mechanisms underlying cooperative courtship displays. This intriguing behavior involves males performing coordinated displays to attract females, where only the dominant male reproduces while a subordinate forfeits his own reproduction, gaining future reproductive opportunities by achieving dominant status later in life. In this chapter, we focused on the independent evolution of this behavior in two non-closely related clades, the Pipra clade and the Chiroxiphia clade, and determined if convergent genetic mechanisms can explain convergence in complex behaviors. I did not find convergence in genes previously linked to social behavior, but we found convergence of 14 genes that had never been linked to social behavior. I highlight the importance of widely exploring the genome for animal behavior studies. Finally in Chapter VI, I summarized the findings from these studies, highlighting the importance of considering understudied species like manakins to address behavioral, physiological, and evolutionary questions from unique perspectives.