The effects of captivity on the endangered Comal Springs riffle beetle, Heterelmis comalensis




Mays, Zachary

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Combining culture-dependent with culture-independent studies can offer insight into the ecological patterns between microbiomes and their environments. H. comalensis, commonly known as the Comal Springs riffle beetle (CSRB), is an aquatic, endangered species that feeds on biofilm from terrestrial detritus near the outflow of the Comal and San Marcos Springs. In this study, I characterize members of the CSRB microbiome by genetic and phenotypic methods. By combining these two methods, I can explain the ecological dynamics between the CSRB microbiome and its habitat in captivity versus the wild. Over 300 bacteria were isolated from beetles, water, and biofilm from beetle environments. After extracting the genome, I sequenced the 16S rRNA gene of 142 isolates to identify them to the genus-level. I found 30 genera belonging to 4 different phyla with culture methods and 22 genera within 10 phyla using high-throughput sequencing of the beetles. I found higher amounts of Acidobacteria and other phyla in the captive CSRBs from both culture and sequencing studies and confirmed the microbiomes were statistically different. A statistical analysis revealed 24 amplicon sequence variants (ASVs) that were significantly different between wild and captive beetles. Estimating the core microbiome also demonstrated that the beetle microbiomes are different in size and composition. This work has provided a skeleton for more detailed research into the mechanistic details of the CSRB microbiome.



Heterelmis, Comalensis, Microbiome, Acidobacteria, Nitrospira, Riffle, Conservation


Mays, Z. (2020). <i>The effects of captivity on the endangered Comal Springs riffle beetle, Heterelmis comalensis</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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