WHY ARE CLUTCH SIZES MORE VARIABLE IN SOME SPECIES THAN IN OTHERS?

Animal species differ in the variability of their clutch sizes, as well as in mean clutch sizes. This phenomenon is particularly obvious in lizards, where virtually invariant clutch sizes have evolved independently in at least 23 lineages in seven families. Reduced variance in clutch size may arise either as an adaptation (because females with less variable clutch sizes have higher fitness) or as an indirect by-product of selection on other life-history characteristics. Comparative data on Australian scincid lizards indicate that variance in clutch sizes is lowest among species with low mean clutch sizes, small body sizes and a low variance in body sizes of adult females. Phylogenetic analysis shows that evolutionary decreases in the variance of clutch size have accompanied decreases in mean clutch sizes and decreases in the variance of adult female body sizes. Tropical lizards may also exhibit lower variance in clutch size. Most of these characteristics are correlated in occurrence, and may be allometrically tied to small body size. Hence, low variance in clutch size may be a consequence of allometric effects on a correlated suite of life-history characteristics. Exceptions to the general patterns noted above-especially, lizard species with invariant clutch sizes but large body sizes-may be due to loss of genetic variance for clutch sizes in lineages that have passed through a "bottleneck" of small body sizes and hence, low variance in clutch sizes.

Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution

Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.

Evolution of body elongation in gymnophthalmid lizards: relationships with climate

The evolution of elongated body shapes in vertebrates has intrigued biologists for decades and is particularly recurrent among squamates. Several aspects might explain how the environment influences the evolution of body elongation, but climate needs to be incorporated in this scenario to evaluate how it contributes to morphological evolution. Climatic parameters include temperature and precipitation, two variables that likely influence environmental characteristics, including soil texture and substrate coverage, which may define the selective pressures acting during the evolution of morphology. Due to development of geographic information system (GIS) techniques, these variables can now be included in evolutionary biology studies and were used in the present study to test for associations between variation in body shape and climate in the tropical lizard family Gymnophthalmidae. We first investigated how the morphological traits that define body shape are correlated in these lizards and then tested for associations between a descriptor of body elongation and climate. Our analyses revealed that the evolution of body elongation in Gymnophthalmidae involved concomitant changes in different morphological traits: trunk elongation was coupled with limb shortening and a reduction in body diameter, and the gradual variation along this axis was illustrated by less-elongated morphologies exhibiting shorter trunks and longer limbs. The variation identified in Gymnophthalmidae body shape was associated with climate, with the species from more arid environments usually being more elongated. Aridity is associated with high temperatures and low precipitation, which affect additional environmental features, including the habitat structure. This feature may influence the evolution of body shape because contrasting environments likely impose distinct demands for organismal performance in several activities, such as locomotion and thermoregulation. The present study establishes a connection between morphology and a broader natural component, climate, and introduces new questions about the spatial distribution of morphological variation among squamates.

Rainfall and reproduction in females of the tropical lizard Mabuya striata striata

The reproduction of females of the lizard Mabuya striata striata was studied at two sites in Central Africa in an area with distinct rainy and dry seasons. The two sites differed in the amount of rain received. At the wetter site, a high proportion of M. s. striata were reproductive at all seasons. At the drier site, a high proportion of females were reproductive during the rainy season, but fewer were reproductive during the dry season. In addition, clutch size was lower at the drier site in the dry season. At both sites, low rainfall during the dry season appeared to constrain reproduction, but this constraint was greater at the drier site. At both sites, abdominal fat bodies were large during the rainy season and the early dry season and much smaller in the late dry season. In the early dry season abdominal fat bodies were larger at the drier than the wetter site. Females at the drier site apparently channel energy differentially into adult survival rather than present reproduction.

Female reproductive cycles in two subspecies of the tropical lizard Mabuya striata

Female reproductive cycles were examined in two subspecies of the live-bearing lizard Mabuya striata from Central Africa, an area with distinct rainy and dry seasons. The low altitude M. s. striata was reproductive throughout the year apart from a brief period at the start of the rainy season, and probably produced three clutches a year. Most females of the high altitude M. s. punctatissima were non-reproductive in the rainy season, came into reproductive condition in the early dry season, and gave birth in the late dry season. For some females, there was a second reproductive cycle starting in the late dry season with birth in the rainy season. For the low altitude M. s. striata it appears that availability of moisture may affect reproduction. For the high altitude M. s. punctatissima it appears that the low temperatures and short hours of sunshine of the early dry season constrain reproduction, and that reproductive cycles are timed to avoid birth occurring in the early dry season.