Nontechnical Abstract Understanding the factors that control the origin and extinction of biodiversity is a central goal of evolutionary biology and is directly relevant to the conservation and management of biodiversity on the Earth today. Recent research suggests that speciation (i.e., the evolution of new species) and extinction can be affected by sexual selection, a process that occurs when individuals compete with each other for access to mates. To date, tests of this hypothesis have not examined actual speciation and extinction events, relying instead on proxies, such as the conservation status of modern species. Here the researchers test the effects of sexual selection on speciation and extinction using the rich fossil record of tiny crustaceans called ostracodes. These animals are unusual because their sex can be determined from their shells, even as fossils, and the researchers can use the extent to which males and females differ in shell shape and size as a measure of the intensity of sexual selection. In this research, the researchers will relate the strength of sexual selection in ostracode species to patterns of speciation and extinction in samples that span a time interval from 85 to 60 million years ago along a swath of the southeastern United States from Texas to Georgia that was under the sea during this time period.
In addition to the scientific goals of this research, the researchers will mentor a post-doctoral scientist as both a teacher and scholar, and involve multiple undergraduate students in the project. The researchers will also develop several public education activities for the Smithsonian Museum of Natural History.
Understanding the mechanisms that underlie species extinction and origination is central to macroevolutionary theory and helps to explain the diversity and history of life. Recent empirical evidence and theoretical models suggest that sexual selection, a form of natural selection that acts upon variation in mating success, can drive both speciation and extinction. To date, tests of the association of sexual selection with either extinction or speciation have relied heavily on neontological data and use weak proxies of actual macroevolutionary events, such as conservation status (for extinction) or clade richness (for speciation). Here the project capitalize on the rich fossil record of ostracodes and propose to perform the first examination of whether sexual dimorphism, an indicator of the strength of sexual selection, is associated with differential rates of actual extinction and speciation.
The research provides the first test of the macroevolutionary hypothesis that sexual selection is positively association with both speciation and extinction, focusing on the well-preserved and well-sampled record of Late Cretaceous through Paleocene ostracodes on the US Gulf Coastal Plain (GCP). Specifically, the project will: (1) measure the magnitude of sexual dimorphism?a proxy for sexual selection?using outline-based morphometrics; (2) document the stratigraphic ranges of taxonomically vetted ostracode species from the Late Cretaceous and early Paleocene; (3) test, using likelihood-based model fitting, the influence of sexual dimorphism on the propensity of species to originate or go extinct.
