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Ectothermic vertebrates such as reptiles were assumed to be indeterminate growers, which means that there is no terminal point in time or size for growth in their lifetime. In recent years, evidence for the determinate nature of growth in lizards has accumulated, necessitating a re‐examination of models of their ontogeny and evolution of sexual size dimorphism (SSD). In the female‐larger gecko Paroedura vazimba, we monitored post‐embryonic growth over a period of 15 months. After hatching, females grew faster than males but also reached their final body size, that is, closed growth of their vertebrae, earlier than males. The closure of bone growth in females correlates with the onset of reproductive maturation. We compared this pattern with the previously minutely studied, male‐larger species Paroedura picta, where we documented determinate growth as well. We propose a model to explain the evolutionary switches in the direction of SSD in lizards based on bipotential effects of ovarian hormones on growth. In this model, male growth is assumed to require no male‐specific growth modifier, such as sex‐limited hormonal regulators, while growth is feminized by ovarian hormones in females. Low levels of ovarian hormones can promote bone growth, but high levels associated with maturation of the reproductive organs promote senescence of bone growth plates and thus cessation of bone growth. We suggest that models on growth, life‐history and evolution of body size in many lizards should acknowledge their determinate nature of growth. Research highlights: Ontogeny of sexual size dimorphism (SSD) is complex in a gecko Paroedura vazimba with determinate growth: females grow faster, but close vertebral growth plates earlier than males. Development of SSD in male‐larger and female‐larger geckos is compared. [ABSTRACT FROM AUTHOR]

The prevalence of environmental sex determination (ESD) in squamate reptiles is often overestimated in the literature. This is surprising because we have reliable data demonstrating ESD in only a few species. The documentation of ESD in three species of geckos presented here has significantly increased our knowledge, given that satisfactory evidence for ESD existed in only eight other gecko species. For the first time, we document the occurrence of ESD in the family Sphaerodactylidae. Our finding of unexpected variability in the shapes of reaction norms among geckos highlights that traditional descriptions using parameters such as pivotal temperature, that is, temperature producing a 50:50 sex ratio, are unsatisfactory. For example, the gecko Pachydactylus tigrinus lacks any pivotal temperature and its sex ratios are strongly female‐biased across the entire range of viable temperatures. We argue for the effective capture of the relationship between temperature and sex ratio using specific nonlinear models rather than using classical simplistic descriptions and classifications of reaction norms. Research highlights: Variability in norms of reaction of environmental sex determination (ESD) among three species of geckos is documented. In Pachydactylus tigrinus, highly female‐biased sex ratios were found across all temperatures. [ABSTRACT FROM AUTHOR]

Squamate reptiles have been considered to be indeterminate growers for a long time. However, recent studies demonstrate that bone prolongation is stopped in many lizards by the closure of bone growth plates. This shift in the paradigm of lizard growth has important consequences for questions concerning the proximate causes of sexual size dimorphism. The traditional model of highly plastic and indeterminate growth would correspond more to a long-term action of a sex-specific growth regulator. On the other hand, determinate growth would be more consistent with a regulator acting in a sex-specific manner on the activity of bone growth plates operating during the phase when a dimorphism in size develops. We followed the growth of males and females of the male-larger Madagascar ground gecko (Paroedura picta) and monitored the activity of bone growth plates, gonad size, levels of steroids, expression of their receptors (AR, ESR1), and expression of genes from the insulin-like growth factor network (IGF1, IGF2, IGF1R, and IGF2R) in livers. Specifically, we measured gene expression before the onset of dimorphic growth, at the time when males have more active bone growth plates and sexual size dimorphism was clearly visible, and after a period of pronounced growth in both sexes. We found a significant spike in the expression of IGF1 in males around the time when dimorphism develops. This overexpression in males comes long after an increase in circulating testosterone levels and sexual maturation in males, and it might be suppressed by ovarian hormones in females. The results suggest that sexual size dimorphism in male-larger lizards can be caused by a positive effect of high levels of IGF1 on bone growth. The peak in IGF1 resembles the situation during the pubertal growth spurt in humans, but in lizards, it seems to be sex-specific and disconnected from sexual maturation. [ABSTRACT FROM AUTHOR]

Facultative parthenogenesis in vertebrates is believed to be exceptional, and wherever documented, it always led to single‐sex progeny with genome‐wide homozygosity. We report the first challenge to this paradigm: frequent facultative parthenogenesis in the previously assumed sexually reproducing tropical night lizard Lepidophyma smithii results in offspring of both sexes and preserves heterozygosity in many loci polymorphic in their mothers. Moreover, we documented a mixture of sexually and parthenogenetically produced progeny in a single clutch, which documents how cryptic a facultative parthenogenesis can be. Next, we show that in the studied species, 1) parthenogenetically produced females can further reproduce parthenogenetically, 2) a sexually produced female can reproduce parthenogenetically, 3) a parthenogenetically produced female can reproduce sexually, and 4) a parthenogenetically produced male is fully fertile. We suggest that facultative parthenogenesis should be considered even in vertebrates with frequent males and genetically variable, heterozygous offspring. [ABSTRACT FROM AUTHOR]

Elevated levels of gonadal androgens are often required for the expression of male-specific behavioral and morphological traits in all classes of vertebrates, including reptiles. Here, we tested the role of male gonadal androgens in the control of male sexual behavior, aggressive behavior, and size of the hemipenes in the gecko Paroedura picta . We performed hormonal manipulations involving castration with and without testosterone (T) replacement in males and application of exogenous T and ovariectomy in females. Castration suppressed sexual behavior and hemipenes size in males, and these effects were fully rescued by exogenous T. Sexual behavior and growth of the hemipenes were masculinized by male-typical levels of T in females, while ovariectomized females retained female-typical expression of these traits. These results indicate that the development of male sexual behavior in adult females does not require early or pubertal organization. Elevated T increased the likelihood of aggressive behavior directed toward a male intruder, but aggression occurred only rarely. Elevated T is necessary and sufficient for enlargement of the hemipenes and the expression of male sexual behavior in both males and females of Paroedura picta . In contrast to sexual behavior, the expression of aggressive behavior is apparently more dependent on other factors in addition to T itself. [ABSTRACT FROM AUTHOR]

Variable clutch size is unambiguously an ancestral state in reptiles. Only several lizard lineages have evolved so-called invariant clutch size, where all females lay just one or two eggs per clutch. This mode of reproduction is characteristic for geckos. In some gecko lineages, decreased fecundity in a single clutch is compensated by conspicuous shortening of interclutch intervals. The proximate mechanism of high clutch frequency in these geckos is not known. Here, we document that three subsequently laid clutches develop simultaneously in females of the Madagascar ground gecko (Paroedura picta). The extremely short interclutch intervals in this species--even as short as a week--thus could be attributed to the overlap of female reproductive cycles. Such overlap should be associated with altered female hormonal cycles. Based on measurements of hormonal levels, we suggest that cycles of estradiol and progesterone during reproductive cycles of females in P. picta are largely independent. Thus, in contrast to the presumable ancestral reptile state, higher levels of progesterone do not seem to interfere with vitellogenesis in this species. We discuss potential consequences of this derived mode of reproduction, such as possible simultaneous maternal transfer of nutrients and other yolk components to several subsequent clutches. [ABSTRACT FROM AUTHOR]

1. Large clutch size is unambiguously an ancestral state in reptiles. However, females of several lizard lineages lay just one or two eggs per clutch, called invariant clutch size. Selective forces leading to a dramatic drop in fecundity during a single reproductive bout are poorly understood. 2. We compared interspecific egg and clutch mass allometries in four lizard lineages with contrasting ways of reproduction. Lacertids and sceloporines have ancestral variable clutch size, while anoles and eublepharid geckos independently evolved invariant clutch size. To reconstruct the anoles’ ancestral situation more precisely, we included data from a member of the closely related genus Polychrus, which is also arboreal but possesses variable clutch size. 3. We found the relative mass of the eublepharid double-egg clutch is comparable with the relative mass of the whole clutch in lizards with variable clutch size. Clutch mass in eublepharids and lizards with variable clutch size increases proportionally to female size. However, single-egg anole clutches show similar negative allometry as the sole egg of lizards with variable clutch size. 4. It appears that invariant clutch size evolved under (and is maintained by) selection on offspring enlargement in geckos, but selection on reducing female reproductive burden in anoles, i.e. the phenomenon of invariant clutch size apparently evolved in these individual groups for different reasons. 5. Besides understanding lizard life history, our study illustrates how singular events in life-history evolution can be reconstructed by comparing the ancestral and evolved reproductive allometries. [ABSTRACT FROM AUTHOR]

Sex steroid hormones of presumably maternal origin have been found in yolk of many oviparous vertebrates. Their effects on behavioural or physiological traits are well documented in birds, but until now are largely unknown in reptiles. The investigations of yolk steroids in reptiles have been focused mainly on species with temperature-dependent sex determination, where steroid levels are suggested to determine the sex of progeny. Here we report initial oestradiol (E2) and testosterone (T) levels in the yolk of the Madagascar ground gecko, Paroedura picta (Peters, 1854), a species with genetic sex determination. The yolk concentration was 0.39 ± 0.02 ng/g (mean ± SE) in E2, whereas the concentration of T was much higher (1.48 ± 0.06 ng/g, mean ± SE). Geckos usually lay two exceptionally large eggs per clutch; vitellogenesis and ovulation of both eggs proceed in phase. Individual two-egg clutches differed considerably in E2 and T levels. A clutch mean of E2 levels varied from 0.22 to 0.53 ng/g, whereas T levels varied from a clutch mean of 1.02 to 1.99 ng/g. Both eggs in a clutch possessed very similar levels of E2 and T. Initial yolk steroid levels thus presumably reflect maternal conditions during egg formation rather than differential allocation of hormones according to offspring sex. [ABSTRACT FROM AUTHOR]