The phylo-geographical histories of Lake Erie Water Snakes



These three neonates show the full range of variation of the Northern Water Snake (Nerodia sipedon) across Lake Erie. The strongly banded morph is typical of N. sipedon throughout most of its range in North America. The slate-grey morph is more typical of the populations found on the islands of the Lake Erie Archipelago, described as Nerodia sipedon insularum by Roger Conant and Richard Clay in 1937. The snakes show continuous variation among sub-populations, as illustrated by the intermediate morph. These snakes are unique to Lake Erie, and are not found on mainland Ohio, Michigan, or Ontario. There have been isolate instances of this morph occurring in the mountains of Missouri and Pennsylvania, but no evidence exists to say that these are anything more than historical coincidence.

Incidentally, these snakes are somewhat threatened. Populations have been decimated by habitat loss and are oftentimes mistakenly killed by people who think they are poisonous. The good news? Recent population estimates by Richard King show the species is making a come-back.





*Photo courtesy of Richard King.


Description of Project:

Unique to the islands of the Lake Erie Archipelago is a subspecies of northern water snake, [Nerodia] sipedon insularum (Conant and Clay, 1937), the history of which is unknown. Nerodia s. insularum is distinguished from the more typical Nerodia s. sipedon by a wide range of variation of dorsal banding pattern, with complete absence of bands typifying N. s. insularum. The lack of discreet characters on which to study the genealogy and population dynamics of N. s. insularum inspired Richard King and Robin Lawson to investigate allozyme variation.1 Although informative, the results of the allozyme study have left much to be resolved. More complete evidence of the histories of these populations can be acquired from DNA sequences.
Mitochondrial DNA is useful for inferring recent phylogenetic history, as well as population structure. Its use for intraspecific study of snake populations has not been taken advantage of. Of great interest is the presence of a duplicate control region within the snake mitochondrial genome. The control region of the mitochondrion accumulates mutations at a very fast rate, enabling nucleotide differences between subpopulations to diagnose shared recent history.
Richard King, of Northern Illinois State University, has made N. s. insularum one of the focuses of his research. He generously donated blood samples from various populations of N. s. insularum, of which a number of samples have yielded DNA for preliminary study. It is my intention to sequence 25 samples from five locations (two mainland and three island) for both mitochondrial control regions. When complete, this project will be the first to apply mitochondrial DNA sequence evidence to hypotheses of intraspecific biogeography and phylogeny of snakes. Also, it will expand on previous knowledge of the duplicate mitochondrial control region.
Professor Arnold Kluge is serving as my principle faculty advisor. Dr. D. Andrew Merriwether and Dr. Mark Siddall have graciously allowed me use of their laboratories for DNA extraction, amplification and sequencing, as well as providing technical support.

1R.B. King and Robin Lawson. 1995. Color-pattern variation in Lake Erie water snakes: the role of gene flow. Evolution 49(5):885-896.

Research Methodology:

Extraction: Extraction of whole genomic DNA from blood samples is performed by both the IsoQuick extraction kit, as well as the QIAAmp extraction kit. Both kits contain chemicals for lysing cells, extracting and precipitating DNA.

Amplification: Amplification of the mitochondrial control regions is accomplished by the polymerase chain reaction (PCR). Sequence-specific primers for the mitochondrial control regions of snakes already have been designed. Each control region is roughly 1,700 bp long. Once amplifications are complete, samples are electrophoresed on an agarose gel and stained with ethidium bromide to determine amplification success.

Sequencing: Amplified sequences are purified and complementary strands are assessed separately in sequencing reactions using the original primers and dye-labled nucleotides. The products of the sequencing reactions (both light and heavy strands) are then loaded into an ABI 377 automated sequencer. The sequencer is only capable of sequencing 700 bp per sample; to sequence through both control regions should require eight separate runs per complementary strand, or 16 sequencing lanes per sample.

Analysis: Sequences will be aligned and cropped to equal lengths. A parsimony analysis will be done using PAUP*.

Itemized Budget:




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