Do high-latitude environments constrain life histories of ectotherms? One expectation is that shorter and cooler active seasons at high latitudes limit opportunities for maintenance of optimum body temperature and restrict time for foraging and therefore for growth and reproduction. Thus, under this hypothesis, individuals in high-latitude populations of wide-ranging species would be predicted to grow more slowly, have lower reproductive output, and perhaps reproduce less frequently than lower-latitude conspecifics. However, at Miquelon Lake in central Alberta, the Plains Garter Snake (Thamnophis radix) grows as fast annually as more southerly conspecifics and reaches sexual maturity at the same age. Here, we make a comparable test of latitudinal variation in reproductive traits. Both litter size and offspring size were larger in the Miquelon Lake population than at lower latitudes. Moreover, female snakes could reproduce annually, although the frequency of annual reproduction remains unknown. Litter size was positively related to female size, but also varied annually, apparently in relation to the previous year's weather (higher litter size with lower rainfall and higher temperature the previous year); the most parsimonious interpretation of this observation is that warm, sunny weather facilitates the acquisition of capital resources for the subsequent year's reproduction. Overall, the Miquelon Lake snakes appear to have a ‘fast’ life history, presumably as a result of a productive environment that provides an abundance of anurans, which constitute the primary prey of T. radix at this site, but this hypothesis is untested.
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Vol. 2014 • No. 1