Figure 1. Map depicting the supposed evolutionary history of terrestrial leeches in North America. Shaded area represents the Appalachian Range. (●) Haemopis ottorum, ( ) Haemopis terrestris, ( ) Haemopis septagon (Wirchansky and Shain, 2010).

There are geographic barriers, such as water bodies and

mountain ranges, that keep organisms from either side of the

barrier from exchanging genetic information. In allopatric

speciation, the geographic isolation causes the separated groups

to become too genetically distinct to be considered members of

the same species. While gene flow between certain species is

restricted, the geographic barriers might not have such a large

effect on other species, allowing them to be able to cross the

barriers and mate with different populations.

The Appalachian Mountains can be considered a geographic

dispersal barrier for many organisms, resulting in high levels of

biodiversity and endemic species. Morphological features alone

are often not sufficient in the distinction of different species in this

region and genetic analyses are used to recognize obscure

lineages. This was observed in a study comparing different

populations of Brownback Salamanders in the southern

Appalachian region (Timpe et al. 2009). The series of alternating

ridgelines and valleys of the Appalachian Mountain Range creates

numerous barriers that many organisms are unable to cross.

Helobdella stagnalis is an aquatic leech that lives in lakes,

ponds, and rivers in parts of North America and Europe. This leech

species demonstrates a passive dispersal mechanism in which they

latch onto rocks, fish, plants, humans, birds, and other substrates

(biotic and abiotic), which can then be used to transport the leech

to new habitats. By using passive dispersal to move from one

habitat to another instead of active dispersal, in which an

organism uses its own energy to physically move itself to a new

habitat, Helobdella stagnalis is able to cross many geographic

barriers and exchange genetic information with species on the

other side.

(Wirchansky and Shain, 2010)• With the Appalachian Mountains acting as a

geographical barrier to East-West dispersal, Haemopis terrestris had to actively disperse south along the mountain range and circle around the southern end, where it eventually speciated to form Haemopis septagon (Figure 1).

• The lineage continued northward, with Haemopis ottorum representing the leading edge of the northern expansion.

• This pattern suggests an active dispersal mechanism since passive dispersal should have permitted colonization of all three Haemopis species on either side of the Appalachian Range.

The Effects of the Appalachian Mountain Range on Gene Flow for the Aquatic Leech Helobdella stagnalis

Katherine Willever

Department of Biological Sciences, York College of Pennsylvania

(Timpe et al. 2009)• Due to similar body type and overlapping habitats,

Eurycea aquatica (Brownback Salamander) was considered a local ecomorph of E. cirrigera, but genetic analyses recognized E. aquatica as a distinct species.

• Lineages of E. aquatica from three geographically different locations showed low genetic divergence and diversity, suggesting recent regional spread or high levels of gene flow among populations.

(Sipe and Browne, 2004)• Due to the mountainous nature of the

Appalachian Mountain Range, there should be an increasing number of potential barriers to dispersal as geographic distance increases.

• Because dispersal barriers cause a reduction in the free movement of individuals, there should be a marked reduction in gene flow between separated populations of species that are unable to overcome the barriers.

• Populations that have the greatest geographic distance between them tend to exhibit the greatest genetic dissimilarity.

• The Appalachian Mountain Range does not act as a barrier to gene flow for Helobdella stagnalis because this species has a passive dispersal mechanism.

• DNA is able to be exchanged from either side of the mountains by the use of other organisms, such as plants, birds, fish, and humans, and other substrates.

• Because of this enabled exchange, collected samples on either side are not substantially different from each other (Figure 2).

Observe if the Appalachian Mountain Range acts as a barrier to gene flow for Helobdella stagnalis by analyzing DNA sequences of collected samples from various locations on either side of the mountain range.

Elayna, D. 2008. Helobdella stagnalis. Virtual Zoo. Retrieved 4 March 2012 from <http://pioneerunion.ca.schoolwebpages.com/education/components/scrapbook/default.php?sectiondetailid=2803&linkid=nav-menu-container-4-13697>.

Siddall, M.E. and Borda, E. 2003. Phylogeny and revision of the leech genus Helobdella (Glossiphoniidae) based on mitochondrial gene sequences and morphological data and a special consideration of the triserialis complex. Zoologica Scripta 32: 23-33.

Sipe, T.W. and Browne, R.A. 2004. Phylogeography of Masked (Sorex cinereus) and Smoky shrews (Sorex fumeus) in the Southern Appalachians. Journal of Mammalogy 85(5):875-885.

Timpe, E.K., Graham, S.P., and Bonett, R.M. 2009. Phylogeography of the Brownback

Salamander reveals patterns of local endemism in Southern Appalachian springs. Molecular Phylogenetics and Evolution 52:368-376.

Wirchansky, B.A. and Shain, D.H. 2010. A new species of Haemopis (Annelida: Hirudinea): Evolution of North American terrestrial leeches. Molecular Phylogenetics and Evolution 54: 226-234.

Collect samples of H. stagnalis from either side of and within the Appalachian Mountain Range

Run PCR amplifications and gel electrophoresis to amplify nuclear 18S and 28S rDNA and mitochondrial 16S rRNA,

cytochrome c oxidase subunit 1 (COI), and NADH dehydrogenase subunit 1 (ND-I) fragments

Extract tissue from caudal sucker and solubilize with Proteinase K enzyme

Sequence DNA

Use PAUP computer program to perform maximum parsimony and

maximum likelihood analyses

Use MrBayes v.3.1 computer program to perform Bayesian

Inference

Choose the best rooted phylogenetic tree based upon results of sequence

analysis and interpret results

Haementeria gracilis

H.stagnalis West sample 4H.stagnalis East sample 17H.stagnalis West sample 1H.stagnalis West sample 8H.stagnalis East sample 9 H.stagnalis East sample 14H.stagnalis West sample 5H.stagnalis West sample 7H.stagnalis East sample 11H.stagnalis East sample 16H.stagnalis West sample 3H.stagnalis East sample 10H.stagnalis East sample 13H.stagnalis East sample 15H.stagnalis West sample 2H.stagnalis East sample 12H.stagnalis West sample 6

Figure 2. Phylogenetic tree showing expected results from 17 H. stagnalis samples collected from either side of Appalachian Mountain Range. Bayesian posterior probability indicated above internode branch, and bootstrap values indicated below branch.

1.00100

Image of the key identification characteristic for H. stagnalis, the scute, located on somite VIII (Siddall and Borda, 2003).

Helobdella stagnalis (Elayna 2008)

Some examples of substrates H. stagnalis can use to disperse into new habitats

AcknowledgmentsI would like to thank Dr. Kleiner and Dr. Hagerty for their continuous support and help in the development of my research project.

Introduction

Review of Literature

Review of Literature (continued) Objective

Research Design

Expected Results

Literature Cited

Perform bootstrap analysis on phylogenetic trees

Record morphological features of collected specimens