Effects of natural habitat fragmentation on an endemic scrub lizard (Sceloporus woodi): an historical perspective based on a mitochondrial DNA gene genealogy

The Florida scrub lizard, Sceloporus woodi, is endemic to scrub habitat pat ches along the central portion of the Florida peninsula and xeric coastal r egions. Scrub ecosystems are the patchily distributed remnants of previousl y widespread habitats formed during the Pleiocene and early Pleistocene. Sc rub lizards appear to have limited dispersal capabilities due to high habit at specificity and low mobility. To assess the population structure and phy logeography of S. woodi, 135 samples were collected from 16 patches on five major ridges in Florida, USA. Analysis of 273 bp of mitochondrial DNA (mtD NA) cytochrome b reveals a very strong geographic distribution of genetic d iversity. Haplotype frequencies are significantly different in 63 of 66 com parisons between patches. With one exception, samples from the five major r idges are characterized by fixed differences in haplotype distribution and deep evolutionary separations (3-10%). Fixed genetic differences were also observed between northern and southern segments of several ridges. Analysis of molecular variance (AMOVA) shows an estimated 10.4% total genetic varia tion within patches, 17.5% among patches (within ridges), and 72.1% among r idges. This strong population structure among patches within ridges indicat es that the distribution of S. woodi is tightly linked to sandy scrub habit at and that the discontinuous distribution of scrub habitats significantly inhibits dispersal and gene now. Phylogeographic analyses indicate a patter n of dispersal down the Florida peninsula during the late Pliocene-early Pl eistocene, followed by habitat fragmentation and vicariant isolation events . Therefore, the deep genetic structuring among scrub lizard populations on separate ridges is attributed to ancient isolation events induced by a shi ft from dry (xeric) to wet (mesic) conditions on the Florida peninsula. The se findings indicate that some scrub lizard populations have persisted in i solation for time frames in excess of 1 Myr, providing a case history on th e genetic consequences of habitat fragmentation.