The macroevolutionary drivers of avian sexual traits
File(s)
Author(s)
Barber, Robert
Type
Thesis
Abstract
It is no surprise that sexual traits have long fascinated evolutionary biologists. They include some of the most extraordinary examples of evolution, but on the surface have little survival benefit. This fascination has spawned countless hypotheses for their origin and maintenance, often with similar studies producing conflicting evidence. One reason for this conflict is that studies investigating sexual traits are often limited in taxonomic and geographic scope, and therefore only reveal a partial picture of selection. To determine if a consensus exists to explain interspecific variation in sexual traits, I collated a wide range of data on avian life history traits with established links to sexual traits. Birds are an ideal study system for macroevolutionary studies of sexual selection and represent some of the most elaborate traits known in the animal kingdom. I first demonstrate that sexual selection, estimated using avian mating systems, shows a strong latitudinal gradient in intensity, peaking at temperate latitudes. Phylogenetic analyses suggest this sexual selection intensity is predominantly correlated with spatial and temporal heterogeneity in food resources. Then, using morphological data, I show that sexual size dimorphism (SSD) is driven by a suite of selection pressures, including, but not limited, to sexual selection. Moreover, these selection pressures primarily correlate with specific aspects of avian morphology linked to their ecological function, such as a significant relationship between diet and trophic SSD. Focusing on suboscine birds, the largest clade of neotropical passerines, I show that sexual selection is the predominant driver of sexual dichromatism. However, by quantifying elaboration independently in each sex, I show evidence that natural and social selection have equally strong effects on both male and female plumage. Together, these results suggest that although sexual selection is consistently linked to sexual traits, its effect on avian species is mediated through a variety of ecological contexts.
Version
Open Access
Date Issued
2024-02-02
Date Awarded
2024-05-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Tobias, Joseph
Pigot, Alex
Sponsor
Natural Environmental Research Council
Grant Number
NE/P012345/1
Publisher Department
Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)