Discovery of Populations of the Eastern Red-Backed Salamander (Plethodon cinereus) with High Frequencies of the Lead-Backed Morph Beyond the Species’ Northern Range Limit

The Eastern Red-Backed Salamander (Plethodon cinereus) is one of the most abundant vertebrate species in the forests of eastern North America and is considered an important species for ecological processes. Two phenotypes most commonly coexist in most populations, but in different proportions: the red-backed (striped) and lead-backed (unstriped) morphs. Recent large-scale studies suggested that both color morphs of P. cinereus occur in and beyond the species’ current northern range. The presence of lead-backed morphs in this area would contradict some previous studies that link the lead-backed morph with warmer conditions. To test this hypothesis, we conducted inventories in the boreal forest of northwestern Quebec (Canada), outside or at the edge of the species’ known northern range, where temperatures are among the coldest encountered by this species. We documented 11 sites with the lead-backed morph, including five sites in the Parent area that fill a large gap in the species’ known distribution. Among the latter, we found three distinct populations in which the lead-backed morph reached frequencies of 43–96%. These occurrences of P. cinereus are noteworthy given the harsh climatic conditions that prevail throughout the year and the recurrence of large-scale disturbances in these far-north forests. Although a previous study observed relatively high frequencies of the lead-backed morph in the northern part of the species’ range, this is the first report of such high frequency findings so far north, outside of the known species’ range. Our findings agree with the mounting evidence that variation in color morph frequency is not related only to temperature or shifts in climate.