Histochemical and ultrastructural analyses of adhesive setae of lizards indicate that they contain lipids in addition to keratins.

We studied the distribution of lipid material and organelles in the epidermal layers of toe pads from two species of lizards representing the two main lizard families in which adhesive scansors are found (gekkonids and polychrotids), the dull day gecko, Phelsuma dubia and the green anole, Anolis carolinensis. Although lipids are a conspicuous component of the mesos layer of squamate reptiles and function in reducing cutaneous water loss, their distribution has not been specifically studied in the highly elaborated epidermal surface of adhesive toe pads. We found that, in addition to the typical cutaneous water loss-resistant mesos and alpha-layer lipids, the Oberhutchen (including the setae) on the most exterior layers of the epidermis in P. dubia and A. carolinensis also contain lipid material. We also present detailed histochemical and ultrastructural analyses of the toe pads of P. dubia, which indicate that lipid material is closely associated spatially with maturing setae as they branch during the renewal phase of epidermal regeneration. This lipid material appears associated with the packing of keratin within setae, possibly affecting permeability to water loss in the pad lamella, where the surface area is from 4­60-fold greater compared with normal scales.

Population structure of spotted salamanders (Ambystoma maculatum) in a fragmented landscape.

Understanding the impacts of landscape-level processes on the population biology of amphibians is critical, especially for species inhabiting anthropogenically modified landscapes. Many pond-breeding amphibians are presumed to exist as metapopulations, but few studies demonstrate the extent and consequences of this metapopulation structure. Gene flow measures may facilitate the construction of more realistic models of population structure than direct measures of migration. This is especially true for species that are cryptic, such as many amphibians. We used eight polymorphic microsatellite loci to determine the genetic population structure of spotted salamanders (Ambystoma maculatum) breeding at 17 ponds in northeastern Ohio, a landscape fragmented by roads, agriculture, urban areas and the Cuyahoga River. Using a variety of analyses (Bayesian clustering, F-statistics, AMOVA) we generated a model of salamander population genetic structure. Our data revealed patterns of genetic connectivity that were not predicted by geographical distances between ponds (no isolation by distance). We also tested for a relationship between population structure and several indices of landscape resistance, but found no effect of potential barriers to dispersal on genetic connectivity. Strong overall connectivity among ponds, despite the hostile habitat matrix, may be facilitated by a network of riparian corridors associated with the Cuyahoga River; however, high gene flow in this system may indicate a general ability to disperse and colonize beyond particular corridors.

Energy budgets, growth rates, and thermal constraints: toward an integrative approach to the study of life-history variation.

Variation in thermal constraints on activity has been hypothesized to be an important ecological source of geographic variation in growth rates of juvenile eastern fence lizards Sceloporus undulatus. However, most of the evidence to support this hypothesis is either inferential or indirect. In this study, I quantitatively compared thermal constraints on activity and their relationship to growth rates of free-ranging juvenile fence lizards from two extremes of the range of variation in growth rate (Nebraska and New Jersey) used in a reciprocal transplant experiment. I also examined energy allocation made to growth and storage by yearling lizards. Reduced growth rates in New Jersey of normally fast-growing hatchlings from Nebraska were associated with a more stringent thermal constraint on activity corresponding to a 2-3-h shorter predicted daily activity period in New Jersey compared to Nebraska. The thermal constraint on activity was particularly strong (24% less time available in New Jersey compared to Nebraska) during the period when hatchling lizards emerge (August-October). An 8% reduction in total activity time available over the course of a single year was associated with a 7% reduction in the total amount of energy accumulated by lizards in New Jersey. Differences in the total amount of energy available for allocation were also accompanied by differences in how energy was allocated. Lizards from New Jersey had an allocatable energy pool of approximately 40.34 kJ (88% to growth, 12% to storage, and 0% to reproduction). Lizards from Nebraska had an allocatable pool of 43.44 kJ (22% to growth, 18% to storage, and 60% to reproduction). This study joins others in advocating and illustrating an integrative approach to determining the causes and consequences of life-history variation by combining experimental, comparative, and phylogenetic methods in a single system.

Phenotypic effects of leptin in an ectotherm: a new tool to study the evolution of life histories and endothermy?

Leptin is a hormone that regulates energy expenditure and body mass in mammals, and it has attracted considerable attention because of its potential in treating human obesity. Comprehensive data from both pathological and non-pathological systems strongly support a role for leptin in regulating energy metabolism, in thermoregulation and in regulating the onset of puberty. We report here that daily injections of recombinant murine leptin in fence lizards (Sceloporus undulatus) produce phenotypic effects similar to those observed when leptin injections are given to mice. Lizards injected with leptin had body temperatures 0.6 degrees C higher, ate 30 % less food and showed a 14 % reduction in activity rates, and females showed a 2. 5-fold increase in resting metabolic rates, compared with lizards injected with vehicle only (phosphate-buffered saline). We also detected native lizard leptin using an immunoassay. Our results indicate that leptin is expressed in ectotherms and may be conserved both functionally and structurally. In the wake of unprecedented research activity on the role of leptin as a cause of, and potential treatment for, human obesity, we believe that other applications of leptin research have been ignored. For example, the response of lizards to leptin injection in our study has important implications for two broad areas of research in evolutionary biology: the evolution of age at first reproduction and of endothermy. We argue that research in these areas, previously limited to comparative approaches, may now benefit from experimental manipulations using leptin.