Lake Erie watersnake COSEWIC assessment and status report: chapter 9

Special Significance of the Species

Lake Erie Watersnakes are discussed in the scientific literature (Camin and Ehrlich 1958; Ehrlich and Camin 1960).  The colour pattern polymorphism found in Lake Erie Watersnakes is a classic example of microevolutionary change in which effects of selection, gene flow, inheritance, and population history are well understood (King 1987b, 1992, 1993b; King and Lawson 1995, 1997; Hendry et al. 2001).

Selection favours the reduced patterning of Lake Erie Watersnakes on the Lake Erie islands because the unbanded variants are more cryptic against the limestone and dolomite shorelines, and therefore visual predators such as gulls, herons, and raptors are less successful in detecting these watersnakes as prey (King 1987a, 1993a; King and Lawson 1995, 1997; Hendry et al. 2001; USFWS 2003).  Regularly banded, mainland Northern Watersnakes are cryptic in their more heavily vegetated habitat (King and Lawson 1995, 1997; USFWS 2003). 

King and Lawson (1995, 1997) found significant genetic variation in colour patterns in Lake Erie Watersnakes and patterns are heritable.  Positive genetic correlations indicate that one major locus is responsible for influencing colour pattern because of the variation in morphs within watersnake families.

King (1987b) predicts that, as Lake Erie Watersnake populations decline, the effect of selection for unbanded snakes will be overwhelmed by increased gene flow due to immigration from mainland (banded N. s. sipedon) snakes and future island populations will possess mainly banded morphs.  Therefore, population size is an important factor in maintaining the unbanded Lake Erie Watersnake subspecies.

Although microevolutionary changes of colour patterns in watersnakes are well understood, data on the processes influencing differentiation are still incomplete because expected differences between island and mainland watersnakes exceed those observed (King and Lawson 1997).  Lake Erie Watersnakes provide insight on multiple evolutionary processes that influence patterns of variation in many other organisms.

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