Sergio Naretto

Sexual selection and dynamics of jaw muscle in Tupinambis lizards

Sexual dimorphism patterns provide an opportunity to increase our understanding of trait evolution. Because selective forces may vary throughout the reproductive period, measuring dimorphism seasonally may be an interesting approach. An increased male head size may be important in intersexual and intrasexual interactions. In Tupinambis lizards, a big head is attributed in part to a large adductor muscle mass. Competition for mating can differ in species with different sex ratio and different degrees of sexual size dimorphism. We examined sexual differences in mass of the pterygoideus muscle, its temporal variation throughout the reproductive period and the relationship between muscle and reproductive condition in Tupinambis merianae and T. rufescens. We characterized sexual size dimorphism and sex ratio in both species. Mature males had larger jaw muscles than mature females in both species, mainly during the reproductive season. The dimorphism in jaw muscle was due to an increase in muscle mass in sexually active males. Seasonal increases in muscle mass and variation between immature and mature individuals suggest that the jaw muscle might be a secondary sexual character. We propose that the pterygoideus muscle may act as a signal of reproductive condition of males because it is associated with testis size and sperm presence. The patterns of sexual dimorphism in jaw muscle in both species were similar; however, the comparison shows how sexual characters remain dimorphic in different competition contexts and in species with different degrees of body size dimorphism. Our results suggest that jaw muscle as sexual character could be influenced by inter- and intrasexual selective pressures.

Understanding the ecological niche to elucidate spatial strategies of the southernmost Tupinambis lizards

Understanding factors that shape ranges of species is central in evolutionary biology. Species distribution models have become important tools to test biogeographical, ecological and evolutionary hypotheses. Moreover, from an ecological and evolutionary perspective, these models help to elucidate the spatial strategies of species at a regional scale. We modelled species distributions of two phylogenetically, geographically and ecologically close Tupinambis species (Teiidae) that occupy the southernmost area of the genus distribution in South America. We hypothesized that similarities between these species might have induced spatial strategies at the species level, such as niche differentiation and divergence of distribution patterns at a regional scale. Using logistic regression and MaxEnt we obtained species distribution models that revealed interspecific differences in habitat requirements, such as environmental temperature, precipitation and altitude. Moreover, the models obtained suggest that although the ecological niches of Tupinambis merianae and T. rufescens are different, these species might co-occur in a large contact zone. We propose that niche plasticity could be the mechanism enabling their co-occurrence. Therefore, the approach used here allowed us to understand the spatial strategies of two Tupinambis lizards at a regional scale.

The Role of Landscape in Contact Zones of Sister Species of Lizards

Elucidating the factors regulating the spatial distribution of ecologically similar species is a key pursuit (Dammhahn and Kappeler, 2008; Peres-Neto, 2006). Many biotic and abiotic variables might influence species distribution and determine allopatry or simpatry (Di Cola & Chiaraviglio, 2010). Moreover, species patterns are strongly associated with habitat variables at different spatial scales (Hatten & Paradzick, 2003). However, the role of landscapes in contact zones is not completely understood.

Importance of reproductive biology of a harvest lizard, Tupinambis merianae, for the management of commercial harvesting

Abstract Context. Management of the exploitation of resources requires biological information on exploited species. The skins of large reptiles have a commercial value as luxury leather items and Tupinambis lizards from southern South America have historically been exploited for this purpose. Argentina implemented management plans for Tupinambis lizards since 1988 that established a minimum capture size based on the width of dried skins, but this prescription has not been linked to local reproductive attributes of species. Aim. In this study, we aim to determine the reproductive parameters of Tupinambis merianae and evaluate which class sizes of individuals are susceptible to commercial trade in central Argentina to generate local and species-specific information to improve available management tools. Methods. We determined the relationship between the width of dried skins and live body sizes. We identified size at sexual maturity in males and females. Moreover, we determined status of reproductive individuals by body size and characterised gonadal development and seasonal reproductive events in central Argentina. We evaluated the relationship between female body size and clutch size. Key results. Reproduction of T. merianae in central Argentina is markedly seasonal, with both sexes concentrating their reproductive activities between October and December. Size at sexual maturity was smaller for males than females, and the percentage of reproductive females was lower than males. In both sexes, the frequency of reproductive individuals was low in smaller lizards, and bigger females had bigger clutch size. The width of dried skins was positively related to body size. Conclusions. Size at sexual maturity, and reproductive period, should be taken into account when management plans are designed to minimise any negative impacts of harvesting. Implications. In central Argentina, the breeding season coincides with hunting periods set by national legislation. The results of our study have prompted local authorities to impose hunting closures for part of December and to raise the minimum catch size. Further, we offer an equation that can be used as a monitoring tool for estimating snout to vent length of live animals from skins. Studies like ours should be replicated in different areas and extrapolated to other models.

Phenotypic Diversity in Female Body Shape is Related to Reproductive Potential in Tupinambis merianae Lizards

A major goal in evolutionary biology is to determine the mechanisms responsible for maintaining phenotypic variation. Species that have evolved intersexual differences provide an opportunity to increase our understanding of trait evolution. We hypothesize that phenotypic diversity is related to reproductive strategies of female lizards and therefore, to their reproductive potential. Consequently, we evaluated sexual dimorphism in several morphological traits and assessed phenotypic variability and selection on body traits of female lizards in a model species (Tupinambis merianae). The results support our hypothesis that certain phenotypic traits of body shape are sexually dimorphic and that females present large continuous variation in these traits. Moreover, some morphological traits in females favor the increment of energetic reserves and reproductive output. These results contribute to the identification of characters upon which selection may have acted and suggest that phenotypic variation in female lizards are related to a diversity of reproductive strategies. Therefore, we fill part of the knowledge gap on the proximate mechanisms that link maternal morphology and reproductive potential in female lizards.

Pre- and Postcopulatory Traits of Salvator Male Lizards in Allopatry and Sympatry

The reproductive traits of males are under influence of sexual pressures before and after copulation. The strength of sexual selection varies across populations because they undergo varying competition for mating opportunities. Besides intraspecific pressures, individuals seem to be subjected to pressures driven by interspecific interactions in sympatry. Lizards may vary their reproductive strategies through varying sexual characters, body size, gonadal investment, and sperm traits. We evaluated the reproductive traits, involved in pre- and postcopulatory competition, in allopatric and sympatric populations of Salvator lizards. We observed a spatial gradient of male competition among populations, with the following order: allopatric zone of S. rufescens; sympatric zone; and allopatric zone of S. merianae. Accordingly, variation in secondary sexual character, the relative testis mass, and the length of sperm component was observed between allopatry and sympatry in each species, suggesting differences in the investment of reproductive traits. However, we found that these two Salvator species did not differ in secondary sexual characters in sympatry. Interestingly, the trade-off between testes and muscle varied differently from allopatry to sympatry between these Salvator species, suggesting that the influence of social context on reproductive traits investment would affect lizard species differently.

Do sex, body size and reproductive condition influence the thermal preferences of a large lizard? A study in Tupinambis merianae

Body temperature is a key factor in physiological processes, influencing lizard performances; and life history traits are expected to generate variability of thermal preferences in different individuals. Gender, body size and reproductive condition may impose specific requirements on preferred body temperatures. If these three factors have different physiological functions and thermal requirements, then the preferred temperature may represent a compromise that optimizes these physiological functions. Therefore, the body temperatures that lizards select in a controlled environment may reflect a temperature that maximizes their physiological needs. The tegu lizard Tupinambis merianae is one of the largest lizards in South America and has wide ontogenetic variation in body size and sexual dimorphism. In the present study we evaluate intraspecific variability of thermal preferences of T. merianae. We determined the selected body temperature and the rate at which males and females attain their selected temperature, in relation to body size and reproductive condition. We also compared the behavior in the thermal gradient between males and females and between reproductive condition of individuals. Our study show that T. merianae selected body temperature within a narrow range of temperatures variation in the laboratory thermal gradient, with 36.24±1.49°C being the preferred temperature. We observed no significant differences between sex, body size and reproductive condition in thermal preferences. Accordingly, we suggest that the evaluated categories of T. merianae have similar thermal requirements. Males showed higher rates to obtain heat than females and reproductive females, higher rates than non-reproductive ones females. Moreover, males and reproductive females showed a more dynamic behavior in the thermal gradient. Therefore, even though they achieve the same selected temperature, they do it differentially.

Influence of Life History Traits on Trophic Niche Segregation between Two Similar Sympatric Tupinambis Lizards

Abstract. Segregation of habitat resources is an important mechanism that allows the coexistence of species. The diet is an important and dynamic component that can generate interactions among co-existing species. Differences in food resource use between related sympatric species have been associated frequently with divergence in multiple phenotypic traits; hence, it is interesting to explore how phenotypic differences allow sympatric species to minimize niche overlap. We aimed to evaluate trophic niche segregation between Tupinambis merianae and T. rufescens in relation to life history traits in a sympatric zone. We compared the volume of the stomach food items between species considering sexual dimorphism, body size classes, sexual maturity and reproductive activity. The obtained Morisitas index indicated trophic niche overlap between T. merianae and T. rufescens; however, considering particular food items, we observed differences in diet composition. Moreover, our results indicate that body size, sexual maturity and reproductive activity are relevant factors influencing the diet of these species. Life history traits of these two species of Tupinambis are important because they shape diet composition, contributing to interspecific segregation of the trophic niche and, therefore, allowing species coexistence.

Modeling the distributions of tegu lizards in native and potential invasive ranges

Invasive reptilian predators can have substantial impacts on native species and ecosystems. Tegu lizards are widely distributed in South America east of the Andes, and are popular in the international live animal trade. Two species are established in Florida (U.S.A.) - Salvator merianae (Argentine black and white tegu) and Tupinambis teguixin sensu lato (gold tegu) – and a third has been recorded there— S. rufescens (red tegu). We built species distribution models (SDMs) using 5 approaches (logistic regression, multivariate adaptive regression splines, boosted regression trees, random forest, and maximum entropy) based on data from the native ranges. We then projected these models to North America to develop hypotheses for potential tegu distributions. Our results suggest that much of the southern United States and northern México probably contains suitable habitat for one or more of these tegu species. Salvator rufescens had higher habitat suitability in semi-arid areas, whereas S. merianae and T. teguixin had higher habitat suitability in more mesic areas. We propose that Florida is not the only state where these taxa could become established, and that early detection and rapid response programs targeting tegu lizards in potentially suitable habitat elsewhere in North America could help prevent establishment and abate negative impacts on native ecosystems.