Variation in scale numbers is consistent with ecologically based natural selection acting within and between lizard species

Recent studies have demonstrated that changes in scale number are correlated with ecological variables such as precipitation, and this suggests that scale number may be under selection to maintain water balance in reptiles. Here, we present new evidence that variation in scale numbers within and among species of Anolis lizards is under ecologically based natural selection. We measured scalation of the brown anole, Anolis sagrei, in two habitat types on each of five islands in the Bahamas. We also measured scalation for 12 species of anole representing six different ecomorphs from the Greater Antilles. Within populations of A. sagrei, scale numbers increased with increasing precipitation and with decreasing temperature in open arid habitats. Variation measured among species of Anolis from the Greater Antilles showed similar patterns with temperature, precipitation, and elevation. Independent contrasts using scale count data indicated that variation in scale number was congruent within and between species, even after accounting for the influence of phylogeny. We measured natural selection (survival to maturity) on scale number in A. sagrei over two different habitat types in the Bahamas. Patterns of natural selection were congruent with the correlational results described. Finally, results from a breeding experiment in the laboratory provide preliminary evidence that variation in scale number is heritable, and suggests a mechanism for generating these correlations. Our results provide new evidence that the diversification of anoles has been shaped by natural selection and that ecologically based selection pressures help explain diversification at both the population and species levels. Co-ordinating editor: M. Klaassen     

Facultative sex allocation in snow skink lizards (Niveoscincus microlepidotus)

Mathematical models suggest that reproducing females may benefit by facultatively adjusting their relative investment into sons vs. daughters, in response to population‐wide shifts in operational sex ratio (OSR). Our field studies on viviparous alpine skinks (Niveoscincus microlepidotus) document such a case, whereby among‐ and within‐year shifts in OSR were followed by shifts in sex allocation. When adult males were relatively scarce, females produced male‐biased litters and larger sons than daughters. The reverse was true when adult males were relatively more common. That is, females that were courted and mated by few males produced mainly sons (and these were larger than daughters), whereas females that were courted and mated by many males produced mainly daughters (and these were larger than sons). Maternal body size and condition also covaried with sex allocation, and the shifting pattern of sexual size dimorphism at birth may reflect these correlated effects rather than a discrete component of an evolved sex‐allocation strategy.     

Comparative analysis of fiber-type composition in the iliofibularis muscle of phrynosomatid lizards (Squamata).

The lizard family Phrynosomatidae comprises three subclades: the closely related sand and horned lizards, and their relatives the Sceloporus group. This family exhibits great variation in ecology, behavior, and general body plan. Previous studies also show that this family exhibits great diversity in locomotor performance abilities; as measured on a high-speed treadmill, sand lizards are exceptionally fast sprinters, members of the Sceloporus group are intermediate, and horned lizards are slowest. These differences are paralleled by differences in relative hindlimb span. To determine if muscle fiber-type composition also varies among the three subclades, we examined the iliofibularis (IF), a hindlimb muscle used in lizard locomotion, in 11 species of phrynosomatid lizards. Using histochemical assays for myosin ATPase, an indicator of fast-twitch capacity, and succinic dehydrogenase, denoting oxidative capacity, we classified fiber types into three categories based on existing nomenclature: fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG), and slow-twitch oxidative (SO). Sand lizards have a high proportion of FG fibers (64-70%) and a low proportion of FOG fibers (25-33%), horned lizards are the converse (FG fibers 25-31%, FOG fibers 56-66%), and members of the Sceloporus group are intermediate for both FG (41-48%) and FOG (42-45%) content. Hence, across all 11 species %FOG and %FG are strongly negatively correlated. Analysis with phylogenetically independent contrasts indicate that this negative relationship is entirely attributable to the divergence between sand and horned lizards. The %SO also varies among the three subclades. Results from conventional nested ANCOVA (with log body mass as a covariate) indicate that the log mean cross-sectional area of individual muscle fibers differs among species and is positively correlated with body mass across species, but does not differ significantly among subclades. The log cross-sectional area of the IF varies among species, but does not vary among subclades. Conversely, the total thigh muscle cross-sectional area does not vary among species, but does vary among subclades; horned lizards have slimmer thighs. Muscle fiber-type composition appears to form part of a coadapted suite of traits, along with relative limb and muscle sizes, that affect the locomotor abilities of phrynosomatid lizards.     

Ultrastructural evidence for secretion from the epithelium of ampulla ductus deferentis of the fan-throated lizard Sitana ponticeriana Cuvier

Among reptiles, an ampulla ductus deferentis has been reported only in Squamata. Fairly detailed studies are available only for two species, the lizard Calotes versicolor (Fam: Agamidae) and the snake Seminatrix pygaea (Fam: Colubridae). The light microscopic study on C. versicolor revealed the ampulla to be a prominent organ, whereas the light and transmission electron microscopic study in S. pygaea revealed it to be discernable only in histological preparations. Further, the epithelium of the ductal portion of vas deferens as well as the ampulla of C. versicolor appears to contribute to the seminal plasma and can also phagocytose dead sperm, whereas in S. pygaea neither of these roles has been established. Thus, we hypothesize that there may be variations in the anatomy, histology, and the role of the vas deferens in general, and the ampulla in particular, of the squamate reptiles. In this study, the ductus deferens of the small fan-throated lizard Sitana ponticeriana (Fam: Agamidae) was subjected to light and transmission electron microscopic analysis. In this lizard the ampulla is more prominent than in C. versicolor. The epithelium of the ductal portion of vas deferens consists of principal cells (with features reflecting roles in endocytosis and phagocytosis of dead sperm), dark cells (which are absent in the epithelium of the ductal portion of vas deferens of snakes), and basal cells. The ampulla of S. ponticeriana is differentiated into storage and glandular portions. The epithelium of the storage portion is like that in the ductal portion of the vas deferens, whereas that of the glandular portion, consisting of dark and light principal cells and foamy cells, is tall and forms into smooth villous folds. All three cell types show evidence for a role in secretion, in all likelihood different from each other, for release into the lumen to contribute to seminal plasma. These cells do not provide evidence of a role in phagocytosis of dead sperm. It appears that within the Squamata, the ductal ampulla differs in structure as well as function. We suggest that the ductal ampulla of agamid lizards is a composite gland of the ampulla ductus deferentis and seminal vesicles of mammals.     

Distribution and characterization of proteins associated with cornification in the epidermis of gecko lizard

The distribution and molecular weight of epidermal proteins of gecko lizards have been studied by ultrastructural, autoradiographic, and immunological methods. Setae of the climbing digital pads are cross-reactive to antibodies directed against a chick scutate scale beta-keratin but not against feather beta-keratin. Cross-reactivity for mammalian loricrin, sciellin, filaggrin, and transglutaminase are present in alpha-keratogenic layers of gecko epidermis. Alpha-keratins have a molecular weight in the range 40-58 kDa. Loricrin cross-reactive bands have molecular weights of 42, 50, and 58 kDa. Bands for filaggrin-like protein are found at 35 and 42 kDa, bands for sciellin are found at 40-45 and 50-55 kDa, and bands for transglutaminase are seen at 48-50 and 60 kDa. The specific role of these proteins remains to be elucidated. After injection of tritiated histidine, the tracer is incorporated into keratin and in setae. Tritiated proline labels the developing setae of the oberhautchen and beta layers, and proline-labeled proteins (beta-keratins) of 10-14, 16-18, 22-24 and 32-35 kDa are extracted from the epidermis. In whole epidermal extract (that includes the epidermis with corneous layer and the setae of digital pads), beta-keratins of low-molecular weight (10, 14-16, and 18-19 kDa) are prevalent over those at higher molecular weight (34 and 38 kDa). In contrast, in shed epidermis of body scales (made of corneous layer only while setae were not collected), higher molecular weight beta-keratins are present (25-27 and 30-34 kDa). This suggests that a proportion of the small beta-keratins present in the epidermis of geckos derive from the differentiating beta layer of scales and from the setae of digital pads. Neither small nor large beta-keratins of gecko epidermis cross-react with an antibody specifically directed against the feather beta-keratin of 10-12 kDa. This result shows that the 10 and 14-16 kDa beta-keratins of gecko (lepidosaurian) have a different composition than the 10-12 kDa beta-keratin of feather (archosaurian). It is suggested that the smaller beta-keratins in both lineages of sauropsids were selected during evolution in order to build elongated bundles of keratin filaments to make elongated cells. Larger beta-keratins in reptilian scales produce keratin aggregations with no orientation, used for mechanical protection.     

不同经度地区北草蜥的喜好体温和热耐受性

在外温动物热生理特征的进化理论中,“静态”和“易变”是两个持续争论的对立观点。热生理学特征的种内变异是检验此类假设的最有力证据。本研究比较了不同经度地区北草蜥的热环境和热生理特征,以检验“静态”和“易变”假设。东部沿海地区(宁德)的环境温度高于内陆地区(贵阳),与之相适应,沿海地区北草蜥的喜好体温也高于内陆地区。然而,两地区蜥蜴的上临界温度和下临界温度无显著差异。尽管这些热生理学特征的种群间变异趋势并不一致,但是喜好温度随环境温度变化而改变的结果符合“易变”假设的预测。此外,本研究表明蜥蜴的喜好体温存在沿经度方向的地理变异。     

Ornament evolution in dragon lizards: multiple gains and widespread losses reveal a complex history of evolutionary change

The expression in females of ornaments thought to be the target of sexual selection in males is a long-standing puzzle. Two main hypotheses are proposed to account for the existence of conspicuous ornaments in both sexes (mutual ornamentation): genetic correlation between the sexes and sexual selection on females as well as males. We examined the pattern of ornament gains and losses in 240 species of dragon lizards (Agamidae) in order to elucidate the relative contribution of these two factors in the evolution of mutual ornamentation. In addition, we tested whether the type of shelter used by lizards to avoid predators predicts the evolutionary loss or constraint of ornament expression. We found evidence that the origin of female ornaments is broadly consistent with the predictions of the genetic correlation hypothesis. Ornaments appear congruently in both sexes with some lineages subsequently evolving male biased sexual dimorphism, apparently through the process of natural selection for reduced ornamentation in females. Nevertheless, ornaments have also frequently evolved in both sexes independently. This suggests that genetic correlations are potentially weak for several lineages and sexual selection on females is responsible for at least some evolutionary change in this group. Unexpectedly, we found that the evolutionary loss of some ornaments is concentrated more in males than females and this trend cannot be fully explained by our measures of natural selection.     

Shoaling preference and evidence for maintenance of sibling groups by juvenile black perch Embiotoca jacksoni

Group sizes in free‐living juvenile black perch Embiotoca jacksoni were quantified and predictions of the hypothesis that such groups comprise sibling brood‐mates were tested. Group sizes in the field were within the range of female brood sizes and often occurred close to each other but did not merge. In captivity, juveniles formed groups immediately after birth. In laboratory experiments, they also associated significantly more with chambers containing familiar members of their own brood than empty chambers but did not associate more with chambers containing similar‐sized juveniles from a different brood. Juvenile E. jacksoni also associated significantly more with chambers containing familiar brood‐mates than with chambers containing unfamiliar members of a different brood. The strength of this preference increased with the number of days fish had been together since birth. When two broods were placed in a large outdoor tank, all individuals from both broods directed significantly more aggressive acts towards members of the other brood than towards members of their own brood. While the relative effects of familiarity and relatedness cannot be completely separated in this viviparous species, associating with familiar individuals would facilitate the maintenance of sibling groups in the field.     

The use of nuclear DNA molecular markers for studying speciation and systematics as exemplified by the “Lacerta agilis complex” (Sauria: Lacertidae)

Four types of nuclear DNA markers identified by the taxonprint, RAPD, and IMP (Inter-MIR-PCR) methods, and the nucleotide sequences of satellite DNA monomers have been used to analyze the molecular genetic similarity between some populations, subspecies, and species of lizards combined into the group Lacerta s. str., as well as representatives of some other genera. The notions on the systematics and phylogeny of this group based on morphological and zoogeographic criteria have been compared to the conclusions based on molecular genetic data. The genus and species subdivisions of populations based on nuclear molecular markers and morphological characters generally agree with each other, the degree of genetic differences being correlated with the taxonomy suggested by zoomorphologists. The degree of differences between the subspecies of one of the species studied, Lacerta agilis, varies depending on the molecular markers used: according to the results of RAPD analysis, all subspecies substantially differ from one another, the variation within populations being small; with respect to other markers, the differences are smaller and not equivalent. The existence of the so-called eastern and western clades of this species earlier assumed by other researchers on the basis of mtDNA and morphological data has been confirmed. There are no distinct gradations exceeding individual variation in 14 populations of L. agilis exigua (the eastern clade) with respect to IMP markers, although these populations inhabit a vast area from the Ural Mountains to the Kabardino-Balkar Republic (the Caucasus). These data suggest that the subspecies has been rapidly spreading northwards since the Pleistocene glaciation (about 15,000 years ago).     

A tiny lizard (Lepidosauria,Squamata) from the Lower Cretaceous of Spain

Abstract: The smallest living amniotes are all lizards, but the fossil history of this size trait in Squamata is difficult to follow because small skeletons have low preservation potential and are often hard to detect in the field. A new squamate taxon, Jucaraseps grandipes gen. et sp. nov., is here described on the basis of an articulated skeleton from the Early Cretaceous Spanish lagerstätten of Las Hoyas. It differs from other known Mesozoic lizards in combining very small body size with a short rostrum, low maxillary tooth count, a relatively slender and elongated body, and short limbs with large hind feet. Phylogenetic analysis using TNT places it on the stem of a clade encompassing scincomorphs, gekkotans, snakes, amphisbaenians and anguimorphs. Comparison with modern lizards suggests it was probably a cryptic surface or subsurface ground dweller but not a burrower.