Using a Habitat Suitability Model and Molecular Analyses to Aid in the Conservation Management of the Texas tortoise, Gopherus berlandieri




Parandhaman, Anjana

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The Texas tortoise, Gopherus berlandieri (Agassiz 1857), is a threatened species in the state of Texas and strict conservation action is required to ensure that continuing population decline does not occur. The historical range of the Texas tortoise includes a much larger area than recent observations support. Assessing the habitat suitability of the eastern portion of the historical range of the species and determining whether this region still supports the species will aid in its conservation. Firstly, road surveys were conducted from March to October of 2014 and seven tortoises were found during this period. None of these tortoises were from the eastern portion of the range that was the focus of the surveys. GPS coordinates of tortoises from these surveys along with coordinates obtained from online databases were used with environmental predictors to model habitat suitability for the species using ArcGIS (v10.2) and Maxent (v3.3.k). I found that there are some patches of habitat in the eastern portion that could potentially support the species. In addition, I found areas of suitability in far south Texas, as well as in the northern and western regions of their historical range. Secondly, 22 molecular markers in the form of microsatellite loci that were previously found to amplify in G. polyphemus, were re-tested for cross-amplification in G. berlandieri. Nineteen out of the 22 loci cross-amplified successfully. Seven additional untested markers were further focused on and I found that four of the seven were polymorphic, and had variable levels of allelic richness. I then performed a population genetics analysis using STRUCTURE v2.3.4 to determine whether tortoises found out of their range fell into a known subpopulation to allow for repatriation and this indicated that G. berlandieri has no segregation into multiple populations or clusters. This might be due to low sample size and less markers used or an artifact of most samples being from the same area. These studies attempt to explain the poorly understood factors of habitat suitability, and aid genetic diversity research for the Texas tortoise. This in turn will allow for better management and conservation of the species throughout its range.



Texas tortoise, Gopherus berlandieri, Habitat suitability, ArcGIS, Population genetics, Eastern portion of range, Microsatellite loci


Parandhaman, A. (2015). <i>Using a habitat suitability model and molecular analyses to aid in the conservation management of the Texas tortoise, Gopherus berlandieri</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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