Hibernation and emergence pattern ofTupinambis merianae(Squamata: Teiidae) in the Taim Ecological Station, southern Brazil

Skin lipids alone enable conspecific tracking in an invasive reptile, the Argentine black and white tegu lizard (Salvator merianae)

Locating potential mates in non-native habitats is one of the most important challenges faced by invasive vertebrate species. The Argentine black and white tegu lizard (Salvator merianae) is a major invasive reptile species in the contiguous United States and is rapidly expanding its range across Florida and the Southeast, in part due to inadequate management strategies and tools. Because a wide array of reptiles, especially squamates (snakes and lizards), have been well-studied for their reliance on chemical cues to locate conspecifics, our project aimed to isolate chemical cues from tegus and assess the ability of adult males and females to use only these cues to make navigation decisions within a Y-maze. Previously, we found that both males and females can follow conspecific scent trails, but the nature of the specific cues used by the tegus was unknown. In this study, we extracted skin lipids from male and female shed skins acquired during the breeding season then tested the extracts for bioactivity at different dilutions prior to Y-maze trials. Both sexes showed positive reactions (e.g., tongue-flicking, nose taps, scratching) to 2:1 skin lipid:hexane dilutions. In the Y-maze, males (n = 7) and females (n = 7) were run in three types of trailing scenarios with these skin lipid extracts: Male-only (pooled lipid extracts from male shed skins), Female-only (extracts from female shed skins), and Male vs. female. Regardless of the tegu lipid type present, tegus preferred to follow the conspecific lipid trail when paired with a neutral control (peanut oil; 2:1 dilution). They also preferred opposite-sex skin lipid trails when paired with same-sex skin lipid trails. We analyzed our results further by comparing them to those of Richard, Bukovich, et al. (2020). We found a synchronization effect of the skin lipids: sex differences in behavior detectable in the scent trail trials were absent when only conspecific skin lipids were present in the environment. Our results indicate that skin lipids alone are sufficient to facilitate mate tracking in S. merianae, these chemical cues induce reliable behavior, and extracted skin lipids have potential for modifying movement patterns of an invasive reptile in their non-native range. If leveraged in concert with current tegu management strategies (i.e., trapping), extracted skin lipids have the potential to bolster management efficacy but field trials are a requisite next step.

Seasonal changes in steroid and thyroid hormone content in shed skins of the tegu lizard Salvator merianae

Sampling blood for endocrine analysis from some species may not be practical or ethical. Quantification of hormones extracted from nontypical sample types, such as keratinized tissues, offers a less invasive alternative to the traditional collection and analysis of blood. Here, we aimed to validate assays by using parallelism and accuracy tests for quantification of testosterone, corticosterone, progesterone, and triiodothyronine (T₃) in shed skins of tegu lizards. We assessed whether hormone content of sheds varied across one year similar to what was previously detected in plasma samples. In addition, we aimed to identify the phase relationship between hormone levels of shed skin and plasma levels obtained from the same animals. High frequency of shedding occurred during the active season for tegus (spring/summer), while shedding ceased during hibernation (winter). All hormones measured in shed skins exhibited seasonal changes in concentration. Levels of testosterone in shed skins of male tegus correlated positively with plasma testosterone levels, while corticosterone in both males and females exhibited an inverse relationship between sample types for the same month of collection. An inverse relationship was found when accounting for a lag time of 3 and 4 months between sheds and plasma testosterone. These results indicate that endocrine content of sheds may be confounded by factors (i.e., seasons, environmental temperature, thermoregulatory behavior, among others) that affect frequency of molting, skin blood perfusion, and therefore hormone transfer from the bloodstream and deposition in sheds of squamates.

Argentine Black and White Tegu (Salvator merianae) can survive the winter under semi-natural conditions well beyond their current invasive range

The Argentine Black and White Tegu (Salvator merianae, formerly Tupinambis merianae) is a large lizard from South America. Now established and invasive in southern Florida, and it poses threats to populations of many native species. Models suggest much of the southern United States may contain suitable temperature regimes for this species, yet there is considerable uncertainty regarding either the potential for range expansion northward out of tropical and subtropical zones or the potential for the species establishing elsewhere following additional independent introductions. We evaluated survival, body temperature, duration and timing of winter dormancy, and health of wild-caught tegus from southern Florida held in semi-natural enclosures for over a year in Auburn, Alabama (> 900 km northwest of capture location). Nine of twelve lizards emerged from winter dormancy and seven survived the greater-than-one-year duration of the study. Average length of dormancy (176 d) was greater than that reported in the native range or for invasive populations in southern Florida and females remained dormant longer than males. Tegus grew rapidly throughout the study and the presence of sperm in the testes of males and previtellogenic or early vitellogenic follicles in female ovaries at the end of our study suggest the animals would have been capable of reproduction the following spring. The survival and overall health of the majority of adult tegus in our study suggests weather and climate patterns are unlikely to prevent survival following introduction in many areas of the United States far from their current invasive range.

Conspecific chemical cues facilitate mate trailing by invasive Argentine black and white tegus

Squamate reptiles (snakes and lizards) rely on chemical cues from conspecifics to search the environment for potential mates. How such cues are used by invasive species to facilitate reproduction, especially seasonally, is a key question that can inform management practices. The Argentine black and white tegu (Salvator merianae) is an invasive reptile species in south Florida threatening native fauna in biodiverse regions such as Everglades National Park. While some information exists on the reproductive ecology of this species in its native range in South America, the chemical ecology of S. merianae is unclear especially in its invasive range. By testing both male (n = 7) and female (n = 7) tegus in a Y-maze apparatus, we assessed if either sex follows chemical trails left by conspecifics and if behaviors were sex- or season-specific. We conducted three types of trials where conspecifics created odor trails: Male-only (male scent only in base and one arm of Y), Female-only, and Male vs. female. Males did not preferentially follow scent trails from either sex, but they did differentially investigate conspecific scent from both sexes. Seasonally, males showed increased rates of chemosensory sampling (rates of tongue-flicking) during the spring (breeding season; March-May) compared to fall (non-breeding season; September-November). Males also had reduced turning and pausing behavior while trailing in the spring. Female tegus exhibited stronger conspecific trailing abilities than males, following both male and female scent trails, and they explored the maze less before making an arm choice. Females also investigated the scent trails intensely compared to males (more passes in scented arms, more time with scent trails). Our results demonstrate for the first time that females of an invasive reptile species can follow conspecific scent trails. Given the strong female responses to odor, sex-specific targeting of tegus via application of a conspecific chemical cue in traps could enhance removal rates of females during the breeding season.

Hormonal correlates of the annual cycle of activity and body temperature in the South-American tegu lizard (Salvator merianae)

Life history transitions and hormones are known to interact and influence many aspects of animal physiology and behavior. The South-American tegu lizard (Salvator merianae) exhibits a profound seasonal shift in metabolism and body temperature, characterized by high daily activity during warmer months, including reproductive endothermy in spring, and metabolic suppression during hibernation in winter. This makes S. merianae an interesting subject for studies of interrelationships between endocrinology and seasonal changes in physiology/behavior. We investigated how plasma concentrations of hormones involved in regulation of energy metabolism (thyroid hormones T₄ and T₃; corticosterone) and reproduction (testosterone in males and estrogen/progesterone in females) correlate with activity and body temperature (Tb) across the annual cycle of captive held S. merianae in semi-natural conditions. In our initial model, thyroid hormones and corticosterone showed a positive relationship with activity and Tb with independent of sex: T₃ positively correlated with activity and Tb, while T₄ and corticosterone correlated positively with changes in Tb only. This suggests that thyroid hormones and glucocorticoids may be involved in metabolic transitions of annual cycle events. When accounting for sex-steroid hormones, our sex separated models showed a positive relationship between testosterone and Tb in males and progesterone and activity in females. Coupling seasonal endocrine measures with activity and Tb may expand our understanding of the relationship between animal's physiology and its environment. Manipulative experiments are required in order to unveil the directionality of influences existing among abiotic factors and the hormonal signaling of annual cyclicity in physiology/behavior.

Insights into the introduction history and population genetic dynamics of the Argentine black-and-white tegu (Salvator merianae) in Florida

Invasive species are a major threat to global biodiversity. The US state of Florida is especially susceptible to the spread of exotic reptiles due to its subtropical climate, disturbed habitats, and robust pet trade. The Argentine black-and-white tegu (Salvator merianae) is a large, omnivorous lizard currently established in two different regions of Southern Florida. These two populations pose potential threats to sensitive ground nesting species such as gopher tortoises, American crocodiles, and migratory birds. At present, the introduction histories of these populations and the degree to which they are connected by gene flow are largely unknown. To address these issues, we genotyped S. merianae from Hillsborough and Miami-Dade Counties at ten microsatellite loci to assess intrapopulation genetic diversity, the degree of gene flow between populations, and compare the plausibilities of several potential introduction scenarios. Our results indicate that both populations have low genetic diversity [mean number of effective alleles across loci in both populations = 2.09 and are highly differentiated from each other (G_ST = 0.170; G″_ST = 0.545)]. In addition, our results suggest that these populations underwent a bottleneck event prior to their divergence. We discuss what our results suggest about the histories of Florida's invasive tegu populations, as well as how they inform ongoing management strategies.

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.

Seasonal reproductive endothermy in tegu lizards

With some notable exceptions, small ectothermic vertebrates are incapable of endogenously sustaining a body temperature substantially above ambient temperature. This view was challenged by our observations of nighttime body temperatures sustained well above ambient (up to 10°C) during the reproductive season in tegu lizards (~2 kg). This led us to hypothesize that tegus have an enhanced capacity to augment heat production and heat conservation. Increased metabolic rates and decreased thermal conductance are the same mechanisms involved in body temperature regulation in those vertebrates traditionally acknowledged as "true endotherms": the birds and mammals. The appreciation that a modern ectotherm the size of the earliest mammals can sustain an elevated body temperature through metabolic rates approaching that of endotherms enlightens the debate over endothermy origins, providing support for the parental care model of endothermy, but not for the assimilation capacity model of endothermy. It also indicates that, contrary to prevailing notions, ectotherms can engage in facultative endothermy, providing a physiological analog in the evolutionary transition to true endothermy.

Daily and annual cycles in thermoregulatory behaviour and cardio-respiratory physiology of black and white tegu lizards

This study was designed to determine the manner in which metabolism is suppressed during dormancy in black and white tegu lizards (Tupinambis merianae). To this end, heart rate (fH), respiration rate (fR), and deep body temperature (Tb) were continuously monitored in outdoor enclosures by radio-telemetry for nine months. There was a continuous decline in nighttime breathing and heart rate, at constant Tb, throughout the late summer and fall suggestive of an active metabolic suppression that developed progressively at night preceding the entrance into dormancy. During the day, however, the tegus still emerged to bask. In May, when the tegus made a behavioural commitment to dormancy, Tb (day and night) fell to match burrow temperature, accompanied by a further reduction in fH and fR. Tegus, under the conditions of this study, did arouse periodically during dormancy. There was a complex interplay between changes in fH and Tb associated with the direct effects of temperature and the indirect effects of thermoregulation, activity, and changes in metabolism. This interplay gave rise to a daily hysteresis in the fH/Tb relationship reflective of the physiological changes associated with warming and cooling as preferred Tb alternated between daytime and nighttime levels. The shape of the hysteresis curve varied with season along with changes in metabolic state and daytime and nighttime body temperature preferences.

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.

Pampean lizard assemblage from subtropical Brazil: a temporal analysis

The increasing human occupation of natural environments is one of the greatest threats to biodiversity. To mitigate the negative anthropogenic effects, it is necessary to understand the characteristics of natural populations and the natural history of species. A study was conducted with an assemblage of lizards from a disturbed area of the Pampa biome, from February 2001 to January 2004. The assemblage showed a unimodal seasonal pattern, with the recruitment period occurring during the warmer months. The captures were seasonal for two of the three monitored years, and concentrated within warmer months. The minimum temperature explained the number of catches for the assemblage as a whole. However, when the species were analyzed individually, the temperature only explained the seasonal occurrence of Teius oculatus. The abundance of species was significantly different in the third year of study for Cercosaura schreibersii and Ophiodes striatus. This latter species was no longer registered in the study area from May 2003 until the end of the study. Therefore, O. striatus may be more sensitive to environmental changes, considering the events of change in vegetation during the study. With frequent and increasing environmental disturbances, it is necessary to take conservation measures and encourage the increase of knowledge on Pampean lizards.