Search

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana.Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated males assiduously mate guard females on their territory. Yellow-throated males do not defend a territory, but patrol a large home range. They obtain secretive copulations from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, activity, and home range size and concomitantly gained greater control over female home ranges than blue- or yellow-throated males. Experimentally elevating plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels that were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is not without costs. Orange-throated males had low survival compared to the other morphs. Finally, some yellow-throated males transformed to a partial blue morphology late in the season and the endurance of these transforming yellow-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly higher plasma T late in the season compared to the plasma T earlier in the season. T appears to play an important role in the physiological changes that all three color morphs undergo during the process of maturation. In some yellow males, T plays an additional role in plastic changes in behavior and physiology late in the reproductive season. We discuss natural and sexual selection on physiological and behavioral traits that leads to the evolution of steroid regulation in the context of alternative male strategies.

Previous studies of locomotor performance from a variety of perspectives often assumed that speed and limb length were strongly correlated. Despite support of this assumption from biomechanical models, few empirical studies have demonstrated a significant relationship between measures of locomotor capacity, such as maximum velocity, and length of the hindlimb at either the inter- or intra-specific level. We examined whether one measure of locomotor performance, maximum velocity, correlates with body size and elements of the hindlimb in hatchling marine iguanas (Amblyrhynchus cristatus). Larger hatchlings ran faster. Removing the effects of body size revealed that relative lengths of the tibia and hindfoot correlated with size-adjusted maximum velocity. Individuals with relatively long tibia and short pes were relatively faster than individuals with short tibia and long pes. Functional morphological analyses predict that femur length should correlate with maximum velocity. However, our analyses failed to support this prediction. Because hatchling marine iguanas exploit relatively open habitats, the relationship between maximum velocity and limb morphology may be interpreted as an adaptation enhancing escape from predators.

Life-history traits involved in trade-offs are known to vary with environmental conditions. Here, we evaluate the response of the trade-off between ‘offspring number’ versus ‘energy invested per offspring’ to ambient temperature in 11 natural populations of the common lizard, Zootoca vivipara. We provide evidence at both the intra- and interpopulation levels that the trade-off is reduced with an increase in air temperature. If this effect enhances current individual fitness, it may lead to an accelerated pace of life in warmer environments and could ultimately increase adult mortality. In the context of global warming, our results advocate the need for more studies in natural populations to explore interactions between life-history traits' trade-offs and environmental conditions.

While global variation in taxonomic diversity is strongly linked to latitude, the extent to which morphological disparity follows geographical gradients is less well known. We estimated patterns of lineage diversification, morphological disparity and rates of phenotypic evolution in the Old World lizard family Lacertidae, which displays a nearly inverse latitudinal diversity gradient with decreasing species richness towards the tropics. We found that lacertids exhibit relatively constant rates of lineage accumulation over time, although the majority of morphological variation appears to have originated during recent divergence events, resulting in increased partitioning of disparity within subclades. Among subclades, tropical arboreal taxa exhibited the fastest rates of shape change while temperate European taxa were the slowest, resulting in an inverse relationship between latitudinal diversity and rates of phenotypic evolution. This pattern demonstrates a compelling counterexample to the ecological opportunity theory of diversification, suggesting an uncoupling of the processes generating species diversity and morphological differentiation across spatial scales.

SYNOPSIS. Models of global climate change predict an increase in the mean surface temperature between 1.5° and 4.5°C by the middle of the next century. Even a moderate increase of 3°C is likely to result in a shift in the distribution of North American habitat types and vegetational associations, either in latitude or elevation or both. The challenge to Conservation Biology is to predict the responses of terrestrial organisms to the expected alteration in habitats and ecosystems. Recent biophysical models have been expanded to demonstrate the intimate associations between the thermal environment, organismal physiology and ecology. Thus, the expected turnover in habitats may have a profound influence on the distribution of organisms. I describe one possible approach that couples temporal and spatial variation in an ecologically relevant physiological trait, locomotory performance, in a widespread species of lizard, Urosaurus ornatus, to predict the expected response of species to global change. Estimates of maximum velocity and endurance capacity were obtained from 16 populations throughout the range of U. ornatus. Information on spatial variation was supplemented with data on temporal variation spanning an eight year period from a single reference population. I used thesedata to address two questions: 1) is there an association between locomotory performance and the expected habitat changes predicted from global climate models and 2) is there sufficient variation within a population to respond to habitat modification. Populations of U. ornatus varied significantly in sprint speed and stamina. Several environmental factors expected to correlate with global climatechange were evaluated using the patterns of variation in locomotor performance. Results from this study suggest that high elevation populations found in ponderosa pine forests should be most susceptible to changes in climate. Within-population variation was found to span the range of variation seen among populations and was sensitive to temporal variation in climatic conditions. Given the expected and rapid change in environments, small, ectothermic, terrestrial species may not have the ability to modify their geographic distribution. However, the results presented here suggest that only certain populations are at risk; yet the evolutionary response of the population may be long relative to the rate of environment change.