Comparison of Genetic Diversity and Differentiation of the Lizard Sceloporus occidentalis at High and Low Elevations Over Time on a Mojave Desert Sky Island

Undergraduate #76
Discipline: Ecology Environmental and Earth Sciences
Subcategory: Genetics

Justin Jacobs - California State University, Long Beach
Co-Author(s): The Oso Sand Member is the highly fossiliferous, nearshore facies of the Capistrano Formation, that spans the southeastern rim of the Los Angeles Basin in Orange County, California. Over 20 vertebrate taxa have been identified from this unit, including well-preserved fossils such as a nearly complete skull of a blue marlin and the most complete fossil walrus found to date. In addition to other marine species, terrestrial mammals are also known from the Oso Sand, including gomphotheriids, rhinocerotids, and antelocaprids. Despite the abundance of material produced from Oso Sand Member sites however, just three papers have reported on this unit: one paper focused on the skull of the blue marlin mentioned above, the other two mentioned the assemblage only in passing. Due to lack of study, the age of the Oso Sand remains unclear. Based on stratigraphic correlation, the Capistrano Formation is reported as Upper Miocene to Lower Pliocene, and previous workers have referred to undescribed specimens to place the Oso Sand Member in the Hemphillian North American Land Mammal Age (10.3 - 4.9 Ma). This study provides an overview of all known vertebrate fossils from Oso Sand Member, and uses biostratigraphic analysis to establish a more refined age for the Oso Sand Member.

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Desertification of the American southwest since the end of the Pleistocene has isolated mesic adapted species, such as the western fence lizard (Sceloporus occidentalis), and restricted their range to high elevation sky islands (Thompson, 2000). Historical climatic fluctuations in this region have included extended periods of drought during which time population sizes of these lizards are likely to have fluctuated drastically. Results from a parallel demography study have demonstrated that populations at higher elevations fluctuate, but remain at substantially higher densities (50/h) than at lower elevations (18/h) (Louwsma 2011). The populations are predicted to diverge over time from historically large populations (HLPs) in adjacent mountain ranges as well as from each other. We sampled lizards from one high elevation and one low elevation site from 2011 to 2014. Variability at six microsatellite loci were analyzed to determine if the sites have diverged from each other over time and to compare them to HLPs. The results show that they are well differentiated from HLPs, cannot be distinguished from one another statistically, but appear to be becoming more differentiated. Future efforts will be made to include data from 2015 and upcoming years.

Funder Acknowledgement(s): This research was supported in part by the National Science Foundation- Grant #HRD-1302873 and the California State University Chancellor's Office.

Faculty Advisor: James Archie,