Reproductive ecology of red-chinned lizards (Sceloporus undulatus erythrocheilus) in Southcentral Colorado: comparisons with other populations of a wide-ranging species

Geographic variation in nesting behavior and reproductive biology of an insular iguana (Cyclura cychlura)

Intraspecific comparisons among geographically separated populations of wide-ranging species are particularly useful in elucidating variation in behavioral and reproductive life histories resulting from proximate and ultimate causes. From 2001 to 2004, we investigated geographic variation in nesting behavior and reproductive biology of a large-bodied Bahamian iguana ( Cyclura cychlura Cuvier, 1829) inhabiting two distinct island systems varying in area, topography, and rainfall. Studies of C. cychlura cychlura were conducted on Andros Island (approx. 6000 km2; annual rainfall 1100 to 1300 mm) and the results were compared with those for C. cychlura inornata Barbour and Noble, 1916 inhabiting two cays (each <4 ha; annual rainfall <600 mm) in the northern Exuma Island chain (approx. 140 km distant). Female iguanas from Andros Island initiated oviposition 5 to 6 weeks earlier than females from the Exumas. The Andros Island population deposited eggs primarily in termitaria, whereas the lizards in the Exumas deposited eggs in subterranean sand chambers. Female iguanas from Andros deposited significantly more eggs per clutch, heavier total clutches, and wider eggs than conspecifics from the Exumas. Despite egg size differences, hatchling snout–vent length and body mass per clutch did not differ significantly between the Andros and Exuma populations. Our results support the hypothesis that proximate environmental factors play an important role in determining geographic variation associated with not only reproductive output but also reproductive behavior.

Direct and Indirect Effects of Environmental Temperature on the Evolution of Reproductive Strategies: An Information‐Theoretic Approach

For ectotherms, environmental temperature affects the optimal size and number of offspring via multiple mechanisms. First, temperature influences the performance of offspring, which directly affects the optimal size of offspring. Second, temperature influences maternal body size, which indirectly affects the optimal size and/or number of offspring when larger females acquire more energetic resources or provide better parental care. Although traditional statistical approaches might distinguish the relative importance of these effects, an information-theoretic approach enables one to estimate effects more accurately by identifying the best evolutionary model in a set of candidate models. Here, we use the Akaike Information Criterion to calculate the likelihoods of seven path models, each derived from one or more optimality models of reproduction. Variation in reproductive traits among populations of lizards (Sceloporus undulatus) was used to quantify support for the models. Our results overwhelmingly supported a model based on an indirect effect of temperature that is mediated by maternal size. Path coefficients of this model were consistent with the hypotheses that, first, larger females can acquire more energy for reproduction and, second, the survival of offspring depends on both their size and their density. Our analyses exemplify how information theory can identify evolutionary hypotheses that merit experimental testing.

Seasonal effects on circulating leptin in the lizard Sceloporus undulatus from two populations

Characterizing leptin's structure and function in mammals has been the subject of thousands of studies since 1994. Recently, the study of leptin has expanded to include its distribution in non-mammalian taxa, and the role that leptin plays in the reproductive axis. We demonstrated in a previous study that Sceloporus undulatus, fence lizards (ectotherms), express a leptin-like protein. In the current study we quantified seasonal variation in this putative leptin among free-ranging fence lizards from two populations characterized by early and late reproductive maturation (after one or two years, respectively). Immunoblots were performed on whole blood samples to detect leptin and estimate its titer. Leptin titers were higher in the reproductive population of S. undulatus (early maturing: 2.5+/-0.2 microg/mL; late-maturing 2.2+/-0.3 microg/mL; mean+/-2 S.E.), but both populations showed the same seasonal pattern. Leptin titers were lowest in fall when fat stores are expected to be highest (spring: 2.6+/-0.3 microg/mL; summer: 2.6+/-0.3; microg/mL; fall: 1.8+/-0.3 microg/mL), consistent with findings of seasonal variation in free-ranging mammals. Our data support previous work asserting that lizards express leptin and that it has a similar physiological function in endotherms and ectotherms. Our long-term goal is to use leptin to manipulate age at maturity and to test fundamental questions in the evolution of life-history strategies.