Phylogeographic and population genetic studies have shown that species with broad geographic ranges are often composed of multiple, unique genetic lineages. The Southern Leopard Frog (Rana sphenocephala) is widely distributed in the U. S., from New Jersey to Florida to Texas. Two subspecies of R. sphenocephala are currently recognized by some authorities: R. s. sphenocephala, found in Florida, and R. s. utricularia, found throughout the remainder of the species’ geographic range. Rana sphenocephala has a long, complicated taxonomic history fraught with disagreements over whether or not R. sphenocephala actually consists of multiple cryptic species, and if so, what each should be named. The goals of this research are to 1) reconstruct the phylogenetic history of R. sphenocephala, and 2) resolve controversy concerning the taxonomic status of the subspecies R. s. sphenocephala inhabiting peninsular Florida, and any other unique lineage. To determine geographic boundaries for genetic variation, we are analyzing the ND1 gene in the mitochondrial genome in multiple individuals collected from various locations throughout the species’ geographic range. In addition to molecular data, we are using ecological niche modeling to infer the role of environment—climate, in particular—in lineage divergence and speciation.

Results/Conclusions

Preliminary data show little genetic differentiation between R. s. sphenocephala in Florida and R. s. utricularia in other areas of the Southeast.  However, the maximum likelihood tree generated from the sequence data shows clear structure correlated with geography. Two strongly supported clades appear: an eastern clade (including Florida, Georgia, South Carolina, North Carolina, and Virginia) and a western clade (including the remaining states in the range). Statistical analyses of genetic and geographic distances also show strong evidence of isolation by distance, corroborating the phylogenetic analyses. Furthermore, statistical analyses of climate variables indicate climate variation between the two clades; however, genetic distance is not significantly correlated with climate. Although this suggests that environment does not play a significant role in lineage divergence within this species, it is possible that small-scale factors in divergence are being masked by other, non-significant variables. Further analyses in genetics, niche modeling, and statistics are currently being conducted to reconstruct the evolutionary history of this widespread species.