Provided by: Kerstin L. Edberg
I. Title of Document
Genetic Isolation as a Result of Dam Construction: A Look at the Effects on Five Species of
Fish
I.
Purpose of the Study
When a dam is built, the physical impoundment put into place causes a once lotic (freeflowing) environment to turn into a lentic (slow or static flow) environment. This type of
disruption to river flow has been shown to change the type of habitat that is available,
consequently changing the makeup of the fish assemblage that inhabits the impounded
area. In West Point Lake (Shelton and Davies, 1981), 26 of 53 native fish species were lost
within five years following dam construction. In addition to affecting the fish community in
the impounded area, dams also affect fish communities upstream and downstream of the
dam. The western sand darter, Ammocrypta clara, was once an abundant species in the
upper Mississippi River. Their decline has been attributed to the siltation that has built up
in their former habitat as a result of the dams constructed on the Mississippi River
(Pflieger, 1997). The construction of dams has been shown to genetically isolate
populations of bull trout and many other species from other populations downstream of
the dam (Neraas and Spruell, 2001).
The building of a dam brings obvious change to the channel onto which it was built.
What may not be as apparent are the changes that occur in the free-flowing tributaries
upstream of the reservoir (Lienesch et al., 2001; Matthews and Marsh-Matthews, 2007).
The reservoir may act as a habitat barrier that impedes the movement of species between
populations in tributaries adjacent to one another (Lienesch et al., 2001; Matthews and
Marsh-Matthews, 2007). Habitat that was once passable or accessible to one species of
riverine fish may not be accessible anymore. In 2006, a study was performed in Northeast
Kansas to examine the effects of a reservoir on stream fish communities. This study found
that streams connected directly into a reservoir are able to maintain their fish community
without interference from reservoir species, with only a few species occurring at a lower
abundance or lost (Falke and Gido, 2006). Although all fishes may not be affected by the
impoundment downstream, certain species are more sensitive to the changes in their
environment, and may therefore be adversely affected. The purpose of this study will be
to see whether Barren River Lake acts as a genetic barrier to five species of fish: Semotilus
atromaculatus, Pimephales notatus, Lepomis cyanellus, Campostoma oligolepis, and
Etheostoma caeruluem.
I propose to use genetic analysis to test whether dams isolate fish living in tributaries
that are directly connected to a reservoir. One way to test whether genetic isolation
occurs between populations is to examine allele frequencies within their microsatellite
DNA. Microsatellites are sections of an organism’s DNA that consists of repeated short
segments of nucleotides. Microsatellite DNA is found widely throughout the genome,
occurring every 10,000 base pairs (O’Connell and Wright, 1997). Microsatellites are small,
non-coding regions of the DNA. This means they do not produce proteins, allowing them
to evolve very quickly (Stallings, 1995). Microsatellite DNA has been used in the past for
many things (Anderson et al., 2000; Hendry et al., 2000; Paetkau, 1995). Previous research
has shown that microsatellite DNA examination can detect reproductive isolation in as little
as 13 generations (Hendry et. al, 2000). In Hendry’s study of salmon reproduction
isolation, microsatellite DNA was examined from a population from Lake Washington and
population from Cedar River (the Cedar River Population was once a part of the Lake
Washington). The researchers found that 13 generations were enough to see physical
differences between the populations, as well as detect differences at microsatellite loci
(Hendry et al., 2000). Microsatellite DNA has also been used to examine 4 populations of
Canadian Polar Bear, Ursus maritimus. They found 60 percent heterozygosity within each
of the 4 populations, but found that the variation between those populations was high.
They suggest that the gene flow is restricted between these 4 populations, despite the
seasonal migrations of Ursus maritimus (Paetkau, 1995).
I will use microsatellite DNA to examine the reproductive isolation of five fish living in
streams directly connected to Barren River Lake as well as Barren River (upstream of the
reservoir). I will examine the allelic diversity of populations in streams directly connected
to the reservoir and compare them with the allelic diversity of populations upstream in the
drainage. If the reservoir is acting as a genetic barrier to any of the 5 species of fish, we
would expect to see a lower heterozygosity (less diversity) in the streams connected to the
reservoir. Heterozygosity refers to having two different alleles at a given loci on the
genome (Lincoln et al., 2003, p.139). It is measured as the proportion of individuals in the
populations that are heterozygous at the selected gene (Raven et al., 2008, p.397).
Isolated streams are expected to show a lower heterozygosity because there would not be
individuals from outside the population bringing in new alleles. The streams connected to
the river would show a higher heterozygosity (higher diversity) because of the ability of
individuals to pass through the river to get to other reproductive populations.
II. Design of the Study
I plan on collecting fish specimens at 6 total sites (3 streams directly connected to
Barren Lake, 3 streams directly connected to Barren River upstream of the reservoir). At
each of these sites, 15 individuals of each fish species will be collected in order to
determine the allele frequency within the population. DNA will be removed from the
muscle tissue of the collected specimens using QIAGEN DNeasyTM DNA extraction kits. The
extracted DNA will then be run through a polymerase chain reaction (PCR) with the
appropriate fluorescently-labeled DNA primers in order to amplify segments of
microsatellite DNA. DNA primers are made to attach to a section of the genome, one at
the beginning of a segment, one at the end of a segment. During PCR, the primers bind to
their matching base pairs and replicate the segment between them. This results in large
amounts of the replicated segments of DNA. The samples will then be run through a DNA
sequencing machine which can accurately measure the size of each segment, in order to
determine the alleles present for each individual. From this, the allele frequency of each
microsatellite loci for each species at each site will be determined. Allele frequencies of
each species will be compared at each of the six sites.
III. Intended Use of Results
The results from this study will be used as the basis for my master’s thesis. This thesis
will be submitted for publication to a national scientific journal, and be presented at a
national scientific meeting. The information acquired from this study will be of great
interest to conservation biologists trying to preserve native and endangered species that
inhabit systems fragmented by dams.
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