Abstract

The primary aim of this study was to assess the conservation status of the East Texas population of the Kistachie Painted Crayfish, Orconectes maletae. Orconectes maletae has been given a Global Heritage Ranking of G2, or imperiled, because of population declines in the Kisatchie Bayou drainage in Louisiana; however, similar data for Texas is lacking. For the current study, surveys of 25 historical sites in Texas were conducted in the Cypress Creek and Caddo Lake drainage from June to August 2014 and revealed that O. maletae was either absent or in low enough abundance to evade detection at close to 60% of these sites.

Because of the lack of natural history data available for O. maletae, very little is known about the optimal habitat requirements and the population biology of this organism. The current distribution of the species in Texas and Louisiana is disjunct. As such, the current study used molecular genetic techniques and ecological niche modeling to determine if the geographically isolated subpopulations of O. maletae in East Texas and Louisiana are differentiated genetically or ecologically.

Molecular analyses were conducted using the mitochondrial gene segments COI and 16S as well as the nuclear gene segment GADPH. Results of the AMOVAs for COI and 16S suggests that significant divergence (possibly even speciation) may have occurred between the two subpopulations. The results of the percent sequence divergence, pairwise sequence divergence, and fixation indices all supported this conclusion. The nuclear gene AMOVA did not yield significant results. A haplotype network was generated to compare the unique haplotypes from both subpopulations and showed separation of the Texas and Louisiana haplotypes intounconnected networks because they could not be linked with 95% certainty or greater.

The ecological niche modeling data obtained for this study further supported the idea that divergence may have occurred, as the models proved to be more fit when run as separate species than when they were run together as a single species. Specifically, the Texas Kisatchie Painted Crayfish differ in habitat associations from their counterpart in Louisiana indicating that they likely occupy separate niches in their respective states.

The molecular and ecological data together support the notion that the subpopulations have undergone divergence resulting in the emergence of a cryptic species that, superficially, looks morphologically identical to its counterpart. Because of the evidence supporting divergence, and the decline in optimal habitat leading to the absence of O. maletae in both East Texas and Louisiana, it might be appropriate to consider federal conservation for these organisms. Action must be taken to preserve the remaining habitat in both states to conserve these organisms and prevent one or both from becoming extinct. However, before this claim can be made, further analysis of these organisms should be conducted.

In future studies, more samples should be collected from both states for further phylogenetic analysis, where a phylogeny is constructed to enhance the understanding of the lineage of O. maletae in both Texas and Louisiana. It would also be appropriate to ground truth the Maxent models generated for this analysis. This would both verify if the areas predicted to be suitable for O. maletae support populations, and possibly allow for range expansion if the organism is found to exist outside of its known range.

Date of publication

Spring 4-7-2017

Document Type

Thesis

Language

english

Persistent identifier

http://hdl.handle.net/10950/576

Committee members

John S. Placyk, Jr., Lance R. Williams, Joshua A. Banta

Degree

Masters in Biology

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