Variation in body size and sexual size dimorphism in the most widely ranging lizard: testing the effects of reproductive mode and climate

Is Fluctuating Asymmetry a Sufficient Indicator of Stress Level in Two Lizard Species (Zootoca vivipara and Lacerta agilis) from Alpine Habitats?

Alpine habitats are exposed to increasing anthropogenic pressure and climate change. The negative impacts can lead to chronic stress that can affect the survival and reproductive success of individuals and even lead to population extinction. In this study, we analyse different morphological and ecological traits and indices of abiotic and biotic stressors (such as head size and shape, fluctuating asymmetry, body condition index, tail autotomy, and population abundance) in alpine and subalpine populations of two lacertid species (Zootoca vivipara and Lacerta agilis) from Serbia and North Macedonia. These lizards live under different conditions: allotopy/syntopy, different anthropogenic pressure, and different levels of habitat protection. We found differences between syntopic and allotopic populations in pileus size, body condition index (in both species), pileus shape, fluctuating asymmetry (in L. agilis), and abundance (in Z. vivipara). Differences between populations under anthropogenic pressure and populations without it were observed in pileus shape, body condition index (in both species), pileus size, fluctuating asymmetry, tail autotomy and abundance (in L. agilis). On the basis of our results, it is necessary to include other stress indicators in addition to fluctuating asymmetry to quickly observe and quantify the negative effects of threat factors and apply protective measures.

Climate aridity and habitat drive geographical variation in morphology and thermo-hydroregulation strategies of a widespread lizard species

Thermo-hydroregulation strategies involve concurrent changes in functional traits related to energy, water balance and thermoregulation and play a key role in determining life-history traits and population demography of terrestrial ectotherms. Local thermal and hydric conditions should be important drivers of the geographical variation of thermo-hydroregulation strategies, but we lack studies that examine these changes across climatic gradients in different habitat types. Here, we investigated intraspecific variation of morphology and thermo-hydroregulation traits in the widespread European common lizard (Zootoca vivipara louislantzi) across a multidimensional environmental gradient involving independent variation in air temperature and rainfall and differences in habitat features (access to free-standing water and forest cover). We sampled adult males for morphology, resting metabolic rate, total and cutaneous evaporative water loss and thermal preferences in 15 populations from the rear to the leading edge of the distribution across an elevational gradient ranging from sea level to 1750 m. Besides a decrease in adult body size with increasing environmental temperatures, we found little effect of thermal conditions on thermo-hydroregulation strategies. In particular, relict lowland populations from the warm rear edge showed no specific ecophysiological adaptations. Instead, body mass, body condition and resting metabolic rate were positively associated with a rainfall gradient, while forest cover and water access in the habitat throughout the season also influenced cutaneous evaporative water loss. Our study emphasizes the importance of rainfall and habitat features rather than thermal conditions for geographical variation in lizard morphology and physiology.

Body Size Structure and Sex Ratio in a Population of the Common Lizard Zootoca vivipara (Lichtenstein, 1823) from SW Poland

We present data on the population structure, body size variations and allometric growth patterns for a common lizard (Zootoca vivipara) population from Southwestern Poland. We measured 339 lizards (89 males, 75 females, 63 subadults and 111 juveniles). The sex ratio did not differ from 1:1; however, we recorded intra-seasonal variations. There was significant sexual size dimorphism (males were smaller in body length), as well as tail length (males had longer tails) and body mass dimorphism (females were heavier). We also found sexual differences in the allometric pattern of tail growth, i.e. there was an isometry for males but a negative allometry for females.

Radial porosity profiles: a new bone histological method for comparative developmental analysis of diametric limb bone growth

In fossil tetrapods, limb bone histology is considered the most reliable tool not only for inferring skeletal maturity-a crucial assessment in palaeobiological and evolutionary studies-but also for evaluating the growth dynamics within the ontogenetic window represented by the primary bone cortex. Due to its complex relationship with bone growth and functional maturation, primary cortical vascularity is an indispensable osteohistological character for reconstructing growth dynamics, especially in the context of various developmental strategies along the precocial-altricial spectrum. Using this concept as our working hypothesis, we developed a new quantitative osteohistological parameter, radial porosity profile (RPP), that captures relative cortical porosity changes in limb bones as trajectories. We built a proof-of-concept RPP dataset on extant birds, then added fossil paravian dinosaurs and performed a set of trajectory-grouping analyses to identify potential RPP categories and evaluate them in the context of our ontogeny-developmental strategy working hypothesis. We found that RPPs, indeed, reflect important developmental features within and across elements, specimens and taxa, supporting their analytical power. Our RPPs also revealed unexpected potential osteohistological correlates of growth and functional development of limb bones. The diverse potential applications of RPPs open up new research directions in the evolution of locomotor ontogeny.

Effects of Early Thermal Environment on Growth, Age at Maturity, and Sexual Size Dimorphism in Arctic Charr

The effects of early thermal environment on growth, age at maturity, and sexual size dimorphism in Arctic charr (Salvelinus alpinus) are investigated. This study is a 654-day long rearing trial split into two sequential experimental phases termed EP1 and EP2 and lasting 315 and 339 days, respectively. EP1 started at the end of the yolk sac stage when the experimental fish were divided into three groups and reared at different target temperatures (7, 10 and 12 °C). During EP2, all groups were reared at the same temperature (7–8 °C) until harvest (~1300 g). Growth rates increased with temperature from 7 to 12 °C, and at the end of EP1 the 12C group had 49.0% and 19.2% higher mean weight than groups 7C and 10C, respectively. Elevated early rearing temperatures were, however, found to cause precocious sexual maturation and reduce the long-term growth performance. At the end of EP2, the 7C group had 3.6% and 14.1% higher mean weight than 10C and 12C, respectively. Elevated early rearing temperatures had a much stronger effect on the maturity incidence of females, and while male-biased sexual size dimorphism (SSD) was found in all groups, the magnitude of SSD was positively associated with temperature.

Sexual size and shape dimorphism in Turkish common toads (Bufo bufo Linnaeus 1758)

Differences in male and female traits (sexual dimorphism [SD]) are widespread in animals. Dimorphism in morphological characters evolves under the effect of environmental and genetic factors and is shaped by natural and sexual selection. In this study, intersexual differences in size and shape in common toad, Bufo bufo, populations in Turkey were investigated. For this, linear measurements of 27 body-related morphometric characters in a sample of 140 individuals (70 males and 70 females) were compiled. The data were analyzed using univariate and multivariate statistical methods. The results show SD in body size with females having larger body size, a trait related with fecundity and thus probably under sexual selection. Body shape differences, which are associated with head width and dorsal head, are likely to prey size. Male-biased differences observed in nasal characters and tympanum may also be associated with sexual selection (male-male competition). Our findings are consistent with previous studies of major of Anura and support a role for selection pressures acting differentially upon individuals from both sexes, resulting in the evolution of sexually dimorphic traits.

Sexual size dimorphism in lizards: Rensch's rule, reproductive mode, clutch size, and line fitting method effects

Rensch's rule relates to a pattern whereby sexual size dimorphism is more female-biased in small-sized species and more male-biased in large-sized ones. We collected literature and museum data on the body size of males and females belonging to 4032 lizard species, as well as data on their reproductive modes and clutch sizes. We used phylogenetic comparative analyses, and general linear mixed models, to test Rensch's rule and examined how reproductive mode and clutch size affect sexual size dimorphism. Sexual size dimorphism was independent of clutch size in lizard species with variable clutch sizes and in oviparous lizards. Large litters were associated with female-biased sexual dimorphism in viviparous and in scincomorph lizards. Inference regarding Rensch's rule depended on the analytical method used to identify it. The widely used, but less conservative, reduced major axis regression usually support Rensch's rule while ordinary least squares regressions mostly show isometric relationships. The rule tended to apply more to oviparous than to viviparous lizards. We infer that Rensch's rule is, at best, a weak pattern in lizards. This is especially true in viviparous lineages where females reproduce infrequently and therefore evolve large sizes to maximise fecundity, resulting in female-biased dimorphism.