A fundamental goal of evolutionary biology is to understand how diversity arises within and among species. Among sexually reproducing species, many traits have evolved astonishing diversity, although the processes that drive this pattern remain poorly understood. The baculum fits this classic pattern of rapid divergence over time. In some cases, baculum shape correlates with reproductive success, implying that this change over time is shaped by selective, rather than random, processes. Unfortunately, rigorous testing of evolutionary hypotheses has been hampered by the lack of appropriate methods to quantify complex morphology, and the absence of integrated methods to evaluate different evolutionary hypotheses. Thus, many basic questions about how morphological diversity arises remain unanswered. Is morphological divergence accelerated by some form of selection? Do different parts of the baculum experience different strengths of selection? Do different species accumulate baculum divergence differently, and might this be related to the evolution of their mating systems? Does the baculum respond to environmental conditions such as mating history? These questions span multiple time scales, from understanding evolutionary processes acting across species and populations within a species, to the development of the bone over an individual?s lifetime. This project will support the training of a postdoctoral researcher, a citizen science initiative, and participation in a large science outreach festival to engage the broader community.
To answer these questions, the researchers have proposed three specific aims that combine modern morphometrics with comparative phylogenetic methodology, as well as laboratory manipulation. First, relying on museum collections, they will quantify baculum size and shape variation across species from three large mammal groups (primates, carnivores, and Peromyscus rodents) using state-of-the-art methods to test if and how selection shapes morphological divergence over time, and how that divergence correlates with variation in mating systems. In the second aim, they extend their approach to well-defined populations and subspecies of raccoons, while generating low coverage sequence data from these same specimens to rigorously test how morphological divergence scales with genetic divergence. Lastly, in a series of laboratory manipulations, they test how baculum morphology varies across mice with different mating histories or diet. Ultimately, this work will lead to a better understanding of the forces that generate diversity.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
