Population structure can be defined as a difference in the frequencies of alleles among populations, and it is often caused by barriers to dispersal. I used mitochondrial DNA sequences to examine the population structure of two large, aquatic salamanders, Amphiuma means (the Two-Toed Amphiuma) and Siren lacertina (the Greater Siren), at two spatial scales in peninsular Florida. Both species appear to have similar life histories, including poor dry land dispersal capabilities, and I hypothesized that they would exhibit significant population structure at both broad and fine scales. Wetland loss and landscape fragmentation are certain to have caused decreases in abundance and even extirpation of local populations of both species. Understanding current levels of genetic diversity is important in conservation efforts, particularly if individuals must be translocated in the future. A portion of the cytochrome b gene was analyzed for 34 Amphiuma means and 21 Siren lacertina sequences. A neighbor-joining tree and haplotype network showed that A. means exhibited statistically significant population structure at the broad, but not the fine scale. The lack of structure at the fine scale was attributed to periodic flooding among drainage basins in the low-lying study area. The same analyses showed that S. lacertina did not exhibit statistically significant population structure at the broad scale (analyses were not conducted at the fine scale because of low sample size). The difference in broad-scale population structure between the two species is the result of a difference in gene flow, which in turn, can be the result of a difference in effective population size (Ne), female dispersal capability and/or behavior, chance of bait-bucket transfer, or biogeographic history. The best of these possible explanations seems to be a difference in biogeographic history. For the two sites from which both species were sampled, estimated population divergence date was 3.3-6.4 million years ago (mya) for A. means and 0.04-0.5 mya for S. lacertina. The large difference in estimated divergence dates suggests that S. lacertina colonized peninsular Florida from somewhere else following a glacial sea level rise or an interglacial sea level fall, at a time when A. means was already present in refugia within peninsular Florida. This is the first study to explicitly examine the population genetics of A. means and S. lacertina, and future studies should examine their population genetics range wide, to elucidate how gene flow and/or historical biogeography may have contributed to population structure elsewhere.

The salamander family Sirenidae is composed of two extant genera, Siren and Pseudobranchus, each with two known species. Several questions regarding Sirenidae life history persist, and much of the available life history data for Pseudobranchus are attributed to studies of P. axanthus in northern Florida. Information on the reproductive biology of P. axanthus is limited, and historical references often suggest contradictory results. This study was undertaken to clarify information and expand on the limited data regarding P. axanthus reproductive biology, specifically for southern Florida populations. The study population was most likely the P. a. belli subspecies. P. axanthus in southern Florida exhibited year round, continuous reproduction with oviposition documented in nine months. Potential clutch size was positively correlated to female size. The largest observed potential clutch was a female with 58 pre-ovulatory oocytes. The largest observed bout was a female with 15 oviductal eggs. Female P. axanthus in southern Florida oviposited eggs singly and at total densities of 3-4 eggs/m2. Developmental time to egg hatching lasted about 30 days, larvae hatched at 16mm TL, and minimum size at female sexual maturity was 115mm TL and 72mm SVL. The reproductive biology of P. axanthus was distinctly contrasting to other members of the family Sirenidae, S. intermedia and S. lacertina, that occupy the same habitat at the same study location.