DixonZigler2009CSI - DSpace Home

Groves Dixon
University of the South Sewanee, TN
June 1st – August 1st
Survey of Obligate Cave Fauna of the Sewanee Domain
The University of the South boasts an impressive availability of resources for
study in the natural sciences. In particular, its domain incorporates 13,000 acres within
one of the major karst regions of the United States (Culver et al. 2000). This makes
Sewanee the home not only of numerous caves, but the many species that live within
them. Caves are highly particular microhabitats in which unique biological interactions,
selective pressures, and subsequent evolution, result in a fascinating array of adapted
species. The isolated nature of the development of these species makes them, and the
caves they live in, excellent sources for studies of natural selection and patterns of
morphological and genetic variation (Culver et al. 2000).With two months supported by
the Yeatman Scholarship, I looked to take advantage of our unique campus, explore its
caves, and investigate the life they support. The ongoing goal of my study is to establish a
comprehensive list of the toglobites, obligate terrestrial cave fauna, found within
Sewanee’s domain, as well as establish a DNA barcode for each. My work was made up
of three divisions, field work, sorting and identifications, and genetic work.
Field work entailed actually going into caves to collect the samples for the study.
I made over 20 visits to the 7 caves selected for my study. Visits lasted from 45 minutes
to 2 hours depending on the cave, as well as time spent hiking to and from their
entrances. My methods for sampling included hand collecting, pitfall traps, and litter
samples. Hand collecting is the straightforward method of spying individuals and
snatching them up with a pair of tweezers. Pitfall traps make use of strong smelling
cheese speared around the edge of a plastic cup which remains, dug into a hole, for
Groves Dixon
University of the South Sewanee, TN
June 1st – August 1st
several days in the cave with a dollop of alcohol in the bottom. Lured through the
darkness by the cheese’s effluvium, unsuspecting arthropods fall down the smooth edge
of the cup to be collected on a return visit. Litter samples are bagged up piles of leaves
and other natural debris. With samples safely stowed away in tubes of alcohol, and bags
of litter I would make my way back to Spencer to identify and store them.
When not in the field, I was in the lab sorting, identifying, and doing DNA work.
From each cave visit I placed sets of individuals of the same genus or species into tubes
with a number associating it to a spreadsheet where the genus, species, cave, sampling
method, and date of sampling were recorded. In this way I built an encompassing list of
information on each individual collected. Once they were logged into the spreadsheet, I
could use individuals for DNA extraction. This process involves separating the DNA
from cells of the individual. Following this process I would run a PCR (polymerase chain
reaction) to amplify the specific stand of the DNA I wished to sequence for the barcode. I
then sent the successful amplifications to Yale for sequencing. The final product is an
email, with a list of series of As Cs Gs and Ts each representing the same segment of
each troglobite’s mitochondrial DNA.
This internship was an exceptional experience for me. I learned a large amount
about cave life, I spent a substantial portion of my work hours out of doors, I generated
sequences of DNA for animals unrecorded in our government run genetic data bases, and
during it all made as much money as I would likely make doing ordinary work. I can
think of no better way to have spent two months of my summer, and only wish I had
originally planned to include more time. Additionally, the exposure to research bolstered
Groves Dixon
University of the South Sewanee, TN
June 1st – August 1st
in me what was previously a pendulous interest in graduate school. I realized how
enjoyable such work can be when the lab is not preset by a textbook, and the results are
data that is new and exciting. I would recommend such an opportunity to all other
biology students.
Literature Cited:
Culver. D. C., L. L. Master, M. C. Christman, H. H. Hobbs. 2000. Obligate Cave Fauna
of the 48 Contiguous United States. Conservation Biology. Vol. 14. No. 2.