Variation in the mitochondrial DNA of theSylvilaguscomplex occupying the northeastern United States

Abstract

We compared the variation in mitochondrial DNA among species of cottontail rabbits in the northeastern United States to (i) assess the effects of historic transplants of eastern cottontails (Sylvilagus floridanus) on subspecific status, (ii) examine the extent of hybridization between invading eastern cottontails and declining populations of endemic New England cottontails (S. transitionalis), and (iii) evaluate the recent reclassification of S. transitionalis into two sister-species, New England cottontail and Appalachian cottontail (S. obscurus). Sequence variation in the tRNAProand the first 310 base pairs of the control region supported a separation of the two species S. floridanus and S. transitionalis/S. obscurus. However, geographic structuring of haplotypes was not detected for either group. Genetic similarity among populations of S. floridanus indicated that subspecific designations are not warranted for this species in the northeastern United States. Comparisons of sequence information from populations of S. transitionalis/S. obscurus that were never sympatric (Maine), recently sympatric (New Hampshire), or sympatric with eastern cottontails since the last glaciation of eastern North America (Virginia, West Virginia, Maryland, North Carolina) indicated that hybridization is not occurring between eastern cottontails and New England or Appalachian cottontails. Limited variation in mitochondrial DNA does not support the recent reclassification of S. transitionalis into sister-species. However, karyotypic and morphological differences between northern and southern populations should be considered during any efforts to restore declining populations of this species.