High incidence of limb skeletal variants in a peripheral population of the red-backed salamander, Plethodon cinereus (Amphibia: Plethodontidae), from Nova Scotia

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Abstract
A single population of P. cinereus from northwestern Nova Scotia shows a high incidence of limb skeletal variants, which is exceptional for this morphologically conservative species. Included are 9 carpal patterns and 5 tarsal patterns, which result from the variable occurrence of 11 different combinations of fused adjacent mesopodial elements, and frequent absence of 1 or more ossified phalanges; 1 instance of increased phalanageal number also is noted. Primitive plethodontid carpal and tarsal patterns, which characterize P. cinereus from other parts of its range, occur in 69 and 71% of the carpi and tarsi examined, respectively. Modal phalangeal formulae also are those typical of P. cinereus generally. Several mesopodial variants resemble those seen in other plethodontid genera; they may have appeared independently in P. cinereus. Others are unique to this population. Both the genetic basis and geographical extent of this variation are unknown.