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Jumping Spiders Reveal A Web of Connectedness Between Desert Oases
By Susana Rinderle
As part of the Mojave drainage basin, Anza-Borrego Desert State Park has undergone multiple dramatic ecological shifts over the eons. By turns, it's been inland sea, desert, riparian habitat, and desert again. It's therefore a natural lab for studying evolutionary dynamics in animals due to the natural isolation that occurs when a group of organisms is isolated by its ecosystem – into desert oases.
Brendan Rajah-Boyer, MS, MEd and his colleagues at the Hedin Lab at San Diego State University, saw an opportunity to explore these dynamics through a common, yet important group of jumping spiders known as the Habronattus tarsalis species complex. These spiders have been subject to separation and isolation over space and time by the appearance and disappearance of bodies of water in the desert. This can offer insight not only into the ecological history of Anza-Borrego Desert State Park, but the broader processes of how organisms change and evolve in relation to geography, and when periodically separated into oases by the ebb and flow of water.
Brendan and his colleagues posed two questions: (1) What patterns of diversification can be observed among desert populations of Habronattus tarsalis through genetic, morphological, and geographic data? (2) What genetic lineages exist within the Habronattus tarsalis species complex, and how do these lineages compare to those established in previous literature?
Using genetic and morphological data, the researchers analyzed geographic patterns and estimated the relationships between different populations and the timing for when they separated. Evolutionary relationships among the specimens were estimated by running phylogenomic analyses, which groups more similar populations together into genetic clusters. Additionally, Brendan and colleagues studied the physical morphology of 73 male H. tarsalis specimens, and identified 24 discrete morphological characters, which were used to group populations by physical characteristics.
The findings show a rapid evolution in both the morphology and genetics of H. tarsalis jumping spiders. While many of the populations in this species complex were initially thought to be the same species, the adult males show characteristics unique to specific populations that likely evolved due to female preference (sexual selection). The research illustrates the changes that have occurred geographically in southwestern deserts, highlighting the shifting nature of land and oases over deep geologic time. Due to this, some current populations are genetically unique, which is vital in preserving genetic diversity across living organisms and understanding how life has changed over time. The results also show that many of these populations experienced rapid evolutionary divergence that coincides with the desertification of their habitats during the last 600,000 years.
Brendan's study was published in Molecular Phylogenetics and Evolution in March 2020, and he also presented at the "Anza-Borrego: In Focus" lecture series last February. "This research highlights the intermittent connectivity of aquatic habitats in western North American deserts, including during the late Pliocene and Pleistocene epochs," says Brendan, "It suggests a deeper connectedness beyond modern isolation and that population kinship and connectivity can be inferred from paleoclimatic and geologic data.”
Brendan believes researchers should focus on recognizing the ongoing processes of active and rapid evolution occurring presently. He sees opportunities to expand the study's sampling to additional geographies and drainage basins. This expansion may result in a deeper understanding of how species change in relation to geography and even the discovery of new spider species.
Brendan earned a Master's in Evolutionary Biology from San Diego State University in 2019, where he developed a passion for teaching. Last year, he obtained a Master's in Education and a math teaching credential. He currently teaches math and science at High Tech Middle North County, where he enjoys teaching his students about how science and math can relate to the real world
"This research highlights the intermittent connectivity of aquatic habitats in western North American deserts, including during the late Pliocene and Pleistocene epochs," says Brendan
If you would like to reach Brendan, Please email him at boyermisc@gmail.com
