Adult Male Lizards Research Articles

Analysis of subcellular energy metabolism in five Lacertidae lizards across varied environmental conditions

Aerobic respiration is the main energy source for most eukaryotes, and efficient mitochondrial energy transfer greatly influences organismal fitness. To survive environmental changes, cells have evolved to adjust their biochemistry. Thus, measuring energy metabolism at the subcellular level can enhance our understanding of individual performance, population dynamics, and species distribution ranges. We investigated three important metabolic traits at the subcellular level in five lacertid lizard species sampled from different elevations, from sea level up to 2000 m. We examined hemoglobin concentration, two markers of oxidative stress (catalase activity and carbonyl concentration) and maximum rate of metabolic respiration at the subcellular level (potential metabolic activity at the electron transport system). The traits were analysed in laboratory acclimated adult male lizards to investigate the adaptive metabolic responses to the variable environmental conditions at the local sampling sites. Potential metabolic activity at the cellular level was measured at four temperatures – 28 °C, 30 °C, 32 °C and 34 °C – covering the range of preferred body temperatures of the species studied. Hemoglobin content, carbonyl concentration and potential metabolic activity did not differ significantly among species. Interspecific differences were found in the catalase activity, Potential metabolic activity increased with temperature in parallel in all five species. The highest response of the metabolic rate with temperature (Q10) and Arrhenius activation energy (Ea) was recorded in the high-mountain species Iberolacerta monticola.

Stable isotopes reveal sex- and context-dependent amino acid routing in green anole lizards (Anolis carolinensis).

Allocation of acquired resources to phenotypic traits is affected by resource availability and current selective context. While differential investment in traits is well documented, the mechanisms driving investment at lower levels of biological organization, which are not directly related to fitness, remain poorly understood. We supplemented adult male and female Anolis carolinensis lizards with an isotopically labelled essential amino acid (13C-leucine) to track routing in four tissues (muscle, liver, gonads, and spleen) under different combinations of resource availability (high and low-calorie diets) and exercise training (sprint training and endurance capacity). We predicted sprint training should drive routing to muscle, and endurance training to liver and spleen, and that investment in gonads should be of lower priority in each of the cases of energetic stress. We found complex interactions between training regime, diet, and tissue type in females, and between tissue type and training and tissue type and diet in males, suggesting that males and females adjust their 13C-leucine routing strategies differently in response to similar environmental challenges. Importantly, our data show evidence of increased 13C-leucine routing in training contexts not to muscle as we expected, but to the spleen, which turns over blood cells, and to the liver, which supports metabolism under differing energetic scenarios. Our results reveal the context-specific nature of long-term tradeoffs associated with increased chronic activity. They also illustrate the importance of considering the costs of locomotion in studies of life history strategies.

Testosterone is closely related to Leydig cell activity, environmental factors, and androgen receptor distribution in adult male lizards of Liolaemus cuyanus (Reptilia: Liolaemidae) during the reproductive cycle.

Testosterone, the primary sex hormone in male lizards, is closely linked to Leydig cell activity (the cells where steroidogenesis occurs) throughout the reproductive cycle, but testosterone action is related to androgen receptors (ARs) distribution in the seminiferous epithelium. In temperate zones, environmental factors detected through the hypothalamic-pituitary-gonadal axis, downregulate plasma testosterone, resulting in a seasonal reproductive cycle. The aim of this work is to study plasma testosterone in adult male lizards of Liolaemus cuyanus, an oviparous species, throughout its reproductive cycle and its relationship with Leydig cell histology, TotalLeydigCell/ActiveLeydigCell (TLC/ALC) ratio, environmental factors (temperature, relative humidity and solar irradiation) and ARs distribution in seminiferous epithelium. Specimens (N = 27) were captured (October to March) in a semi-arid zone (Valle de Matagusanos, San Juan, Argentina) and grouped into three relevant reproductive periods: pre-reproductive (PrR), reproductive (R), and post-reproductive (PsR). Significant differences in plasma testosterone were found among these periods, highest during R than in PsR. A significant positive correlation between plasma testosterone and TLC/ALC ratio was also observed. Plasma testosterone has a significant positive correlation only with solar irradiation, but not with the other variables. In PrR and R, ARs distribution was cytoplasmic and nuclear, shifting to only cytoplasmic in PsR. These results highlight the close correspondence between plasma testosterone, Leydig cell histology and activity, environmental factors, and ARs distribution, resulting in a synchronization that allows males of L. cuyanus to coordinate their reproductive cycle with the most favorable environmental conditions, probably for mating and birth of offspring.

Tick-tock, racing the clock: parasitism is associated with decreased sprint performance in the Eastern fence lizard

Abstract Host–parasite relationships are important components of ecological systems that influence the evolution of both hosts and parasites. High levels of ectoparasitic infections can disrupt host homeostasis, causing adverse effects on health and performance. However, the effects of natural ectoparasite levels on host physiology are less understood, with most research designs implementing experimental or hormonal manipulations of hosts. In this study, we examined the interplay between tick parasitism and host characteristics on body condition and locomotor performance in Eastern fence lizards in natural settings. We found a higher frequency of tick infections in male lizards relative to females, with larger males being more likely to experience tick infection. Infected lizards had reduced locomotor performance, max sprint speed and 2-m run speed. Together this suggests an energetic trade-off between increased immune function and reduced locomotor performance, which is consistent with the immunocompetence–handicap hypothesis. Higher numbers of ticks on adult male lizards may be explained by age as well as the immunosuppressive effects of testosterone. Tick infection did not appear to reduce overall body condition of lizard hosts. Our findings shed light on the interplay between ectoparasitic infection, host characteristics, and locomotor performance under natural conditions. Such insights are crucial for understanding host–parasite dynamics and determining the trade-offs for hosts within ecological contexts.

Changes in clinicomorphometrical findings, lipid profiles, hepatorenal indices and oxidant/antioxidant status as thermoregulatory adaptive mechanisms in poikilothermic Dabb lizard (Uromastyx aegyptia)

Wildlife has exposed to various environmental stressors. Reptiles (ectothermic) are highly susceptible to climatic changes due to their behaviour, physiology, and life history that were so heavily reliant on the ambient environmental temperature. The present work aims to monitor different biochemical and haematological indices of Dabb lizards (Uromastyx aegyptia) at various thermal gradients as well as their adaptation to oxidative stress. This has been reflected through assessment of their impact on some adaptive physiological traits i.e. thermoregulation, and muscle metabolic biomarkers, blood pictures and oxidant/antioxidant status. This experiment is carried out on non-hibernating adult male Dabb lizards (U. aegyptia; n = 24) of age of 18–24 months. These Dabb lizards are divided into four equal groups (n = 6 for each one) where they are exposed to different thermal treatments for one week as following; control group [Exposed to terrarium temperature 38–39 °C], low temperature exposed group [Exposed to 12–14 °C], Gp. C; moderate temperature exposed group [Exposed to 41–43 °C] and high temperature exposed group [Exposed to 43–45 °C]. Each independent group (n = 6) are kept at separated glass terraria. The investigated lizards are monitored for body temperature, morphometric measurements i.e. body weight (g) and total body length (cm; TBL), muscle biochemical analysis, haematological pictures indices and serum biochemical assays including mainly oxidant/antioxidants biomarkers throughout the current experiment. The results state that the thermoregulatory behaviour of Dabb varies with the increase of concentration of muscular metabolic enzymes. In low temperature exposed group, the increase in red blood corpuscles (RBCs), haemoglobin concentrations (Hb), white blood cell (WBC), serum antioxidant biomarkers and anaerobic Lactate dehydrogenase (LDH) enzyme are associated with a marked reduction in serum levels of total cholesterol (TC), triglycerides (TGs), total proteins (TPs), albumin, glucose and electrolytes. In moderate temperature exposed group, a significant elevation in serum values of TC, TGs, TPs, glucose, urea and uric acids levels are mentioned. In high temperature exposed Dabb group, a remarkable increase in blood values of RBCs, Hb, haematocrit value (HCT), WBC, T. chol., TGs, TPs, glucose, urea, uric acids, triiodothyronine (T3) and thyroxine (T4) levels are also observed. Moreover, significant increases in muscular anaerobic/aerobic metabolic enzymes as well as stimulation of antioxidant defence system have been reported. Different significant correlations have been stated between variably estimated laboratory indices in the investigated Dabb lizards under different thermal treatments. The study concludes that the Dabb lizards have a strong antioxidant defence system and undergo physiological thermoregulatory adaptive mechanisms, that involve biochemical and metabolic acclimatization as a response to environmental temperature changes that act as a protective mechanism against oxidative stress as well as maintained homeostatic responses and normal physiological functions.

Histological features of the spleen and pancreas of the Egyptian Nile monitor lizard (Varanus niloticus)

The present study investigated the histological features of the spleen and pancreas of the Egyptian Nile monitor lizard (Varanus niloticus). After gross observations the representative samples were collected from three adult male monitor lizards and were processed for histological examination. Grossly, the spleen was brownish in color and embedded in the mesentery near the stomach and pancreas. The pancreas was yellowish in color and consisted of a ventrally placed principal lobe which was pyramidal and extended in the mesentery, whereas the dorsally located splenic lobe was small and was attached to the spleen. a single duct was emerged from the pancreas. Histologically, the spleen was nodular and was encapsulated by the connective tissue capsule covered by mesothelium. it was composed of white and red pulps. Many ellipsoids, melano-macrophage centers, periarterial and periellipsoidal lymphatic sheaths (PALS and PELS; respectively) were observed. The pancreas demonstrated a thicker capsule covered by mesothelium and the exocrine portion was formed of tubule-acinar cells. Main pancreatic duct passed across the length of the pancreas and was lined by stratified cuboidal epithelium. The Islets were found in the ventral lobe where it was in various sizes. This is the first report about the histological structure of the spleen and pancreas of the Egyptian Nile monitor lizard, where the spleen showed a unique structure while the pancreas was similar to what was described in other varanus species. The information in this study will be a baseline knowledge for future studies regarding endocrine or immune organs in this species.

Energy expenditure across immune challenge severities in a lizard: consequences for innate immunity, locomotor performance and oxidative status

Reptiles, like other vertebrates, rely on immunity to defend themselves from infection. The energetic cost of an immune response is liable to scale with infection severity, prompting constraints on other self-maintenance traits if immune prioritization exceeds energy budget. In this study, adult male side-blotched lizards (Uta stansburiana) were injected with saline (control) or high (20 µgg-1 body mass) or low (10 µgg-1 body mass) concentrations of lipopolysaccharide (LPS) to simulate bacterial infections of discrete severities. The costs and consequences of the immune response were assessed through comparisons of change in resting metabolic rate (RMR), energy metabolites (glucose, glycerol, triglycerides), innate immunity (bactericidal ability), sprint speed and oxidative status (antioxidant capacity, reactive oxygen metabolites). High-LPS lizards had the lowest glucose levels and greatest sprint reductions, while their RMR and bactericidal ability were similar to those of control lizards. Low-LPS lizards had elevated RMR and bactericidal ability, but glucose levels and sprint speed changes between those of high-LPS and control lizards. Levels of glycerol, triglycerides, reactive oxygen metabolites and antioxidant capacity did not differ by treatment. Taken together, energy expenditure for the immune response varies in a non-linear fashion with challenge severity, posing consequences for performance and self-maintenance processes in a reptile.

Functional remodeling of adrenal steroidogenic tissue by food deprivation in the lizard, Sceloporus undulatus

The present study examined how food availability interacts with age to modulate lizard adrenal steroidogenic function at the cellular level. Adult male and juvenile male and female Eastern Fence Lizards (Sceloporus undulatus) underwent a period of food deprivation with or without a shorter re-feeding period. Lizards maintained on a full feeding regimen served as the controls. Across the feeding regimens, plasma corticosterone of adult lizards was unchanged whereas that of food-deprived juvenile lizards was increased nearly 7 times and this increase was normalized by a short re-feeding period. Freshly dispersed adrenocortical cells derived from these lizards were incubated with ACTH and the production of selected steroids was measured by highly specific radioimmunoassay. Net maximal steroid rates of juvenile cells were 161% greater than those of adult cells. Adult and juvenile progesterone rates were consistently suppressed by food deprivation (by nearly 48%) and were normalized by a re-feeding period, whereas divergent effects were seen with corticosterone and aldosterone rates. Food deprivation suppressed corticosterone rates of adult cells by 43% but not those of juvenile cells. In a reciprocal manner, food deprivation had no significant effect on aldosterone rates of adult cells, but it suppressed those of juvenile cells by 52%. A short re-feeding period normalized most rates in both adult and juvenile cells and further augmented the adult aldosterone rate by 54%. The effect of the feeding regimens on ACTH sensitivity varied with life stage and with steroid. The overall sensitivity of adult cells to ACTH was nearly three times that of juvenile cells. Collectively, the data presented here and data from previous work indicate that food restriction/deprivation in Sceloporus lizard species causes a functional remodeling of the adrenocortical tissue. Furthermore, life stage adds more complexity to this remodeling.

OctylPhenol (OP) Alone and in Combination with NonylPhenol (NP) Alters the Structure and the Function of Thyroid Gland of the Lizard Podarcis siculus

Different environmental contaminants disturb the thyroid system at many levels. AlkylPhenols (APs), by-products of microbial degradation of AlkylPhenol Polyethoxylates (APEOs), constitute an important class of Endocrine Disrupting Chemicals (EDCs), the two most often used environmental APs being 4-nonylphenol (4-NP) and 4-tert-octylphenol (4-t-OP). The purpose of the present study was to investigate the effects on the thyroid gland of the bioindicator Podarcis siculus of OP alone and in combination with NP. We used radioimmunoassay to determine their effects on plasma 3,3′,5-triiodo-L-thyronine (T3), 3,3′,5,5′-L-thyroxine (T4), thyroid-stimulating hormone (TSH), and thyrotropin-releasing hormone (TRH) levels in adult male lizards. We also investigated the impacts of AP treatments on hepatic 5′ORD (type II) deiodinase and hepatic content of T3 and T4. After OP and OP + NP administration, TRH levels increased, whereas TSH, T3, and T4 levels decreased. Lizards treated with OP and OP + NP had a higher concentration of T3 in the liver and 5′ORD (type II) activity, whereas T4 concentrations were lower than that observed in the control group. Moreover, histological examination showed that the volume of the thyroid follicles became smaller in treated lizards suggesting that that thyroid follicular epithelial cells were not functionally active following treatment. This data collectively suggest a severe interference with hypothalamus–pituitary–thyroid axis and a systemic imbalance of thyroid hormones.Graphic

Do males pay more? A male-biased predation of common lizard (Zootoca vivipara) by great grey shrike (Lanius excubitor)

Predation is one of the most important factors affecting biology, ecology and behaviour of the prey. We have studied predation of the common lizard (Zootoca vivipara) by the great grey shrike (Lanius excubitor) in farmland habitats in western Poland. Shrike caches were used as a source of information about preyed lizards. Shrikes hunt significantly more adult males than females, juveniles and sub-adults; the pattern was similar over all three study years. Male lizard had longer activity time than female; therefore, they seem to be under predation pressure for a longer time during breeding season. Capture and count transect data of common lizard populations living within and outside shrike territories showed significant seasonal differences: within shrike territories, there was lower proportion of males than females; moreover, in some territories, the number of males in the lizard population was negatively correlated with the number of males impaled by shrikes. Our findings suggest that in this particular predator-prey system, shrikes may be a strong selective force for lizards’ population dynamics. Male-biased predation could be caused by differences in the behaviour of adult male and female lizards, namely longer activity of males and differences in space and refuge use.

Conflict, compensation, and plasticity: Sex-specific, individual-level trade-offs in green anole (Anolis carolinensis) performance.

Trade-offs in performance expression occur because animals must perform multiple whole-organism performance tasks that place conflicting demands on shared underlying morphology. Although not always detectable within populations, such trade-offs may be apparent when analyzed at the level of the individual, particularly when all of the available data are taken into account as opposed to only maximum values. Detection of performance trade-offs is further complicated in species where sexual dimorphism drives performance differences between males and females, leading potentially to differing patterns of trade-offs within each sex. We tested for within- and between-individual trade-offs among three whole-organism performance traits (sprint speed, endurance, and bite force) in adult male and female Anolis carolinensis lizards using all of the measured performance data. Sprinting and endurance did not trade-off among individuals in either sex, but we found a significant negative among-individual relationship between sprint speed and bite force in females only, likely driven by the mechanical burden of larger than optimal heads imposed on females through intralocus sexual conflict. We also found evidence for marked within-individual plasticity in male bite force, but no within-individual trade-offs between any traits in either sex. These data offer new insight into the sex-specific nature of performance trade-offs and plasticity and, ultimately, into the constraints on multivariate performance evolution.

Evidence for a double mutualistic interaction between a lizard and a Mediterranean gymnosperm,Ephedra fragilis

An increasing number of double mutualisms (i.e. two interacting species benefiting each other in two different functions, e.g. pollination and seed dispersal) have been reported, mainly from island ecosystems, although we still lack much information on how effective such species are in both processes. Here, we assessed the pollination effectiveness of a double mutualism between an ancient Mediterranean gymnosperm, Ephedra fragilis, and a lizard, Podarcis lilfordi. On the one hand, we assessed the lizard contribution to different fitness measures (seed set and germination success), relative to that of insects and the wind effect; on the other, we determined the lizards’ seed removal rate (i.e. the quantity component of seed dispersal effectiveness). In both processes, we further tested for differences in their contributions among male, female and juvenile lizards. Ephedra fragilis showed to be mostly anemophilous, lizards and insects playing only a minor role on seed set. However, lizards qualitatively contributed to pollination success, as seeds coming from lizard-pollinated cones germinated at higher rates than those pollinated by wind or insects, although this was detected only for small seeds (<8 mg). The plant produced a low seed set (c. 23 %), which was compensated by a high seed germinability (c. 70 %). Adult male lizards were those most implicated in pollination, quantitatively more important than insects, and in seed dispersal. This work, thus, reports the importance of a lizard species in one of the few double mutualisms found in the World involving a gymnosperm, and it represents the first documentation of a double mutualism in the Mediterranean region. Our findings further contribute to highlight the role of both inter- and intraspecific differences in the effectiveness of mutualistic interactions.

Effects of energy and thermoregulation time on physiological state and sexual signal in a lizard.

Theory of sexual selection states that males often develop showy signals, which reduce their survival but increase their reproductive success. During mate choice, these conspicuous signals can be honest indicators of individual quality conveying information about the signaler's physiological state. Sexually selected signals are influenced by many environmental factors; however, whether signals and physiological state are affected together is rarely studied. The ultraviolet-blue throat color of male Lacerta viridis is an intra- and intersexually selected signal connected to blood parasite infection and influenced by environmental factors. The aim of this study was to experimentally investigate how ecologically relevant environmental factors affect color signal intensity and key physiological traits parallel. During the mating season, we exposed 40 adult male lizards infected with blood parasites to food and basking time treatments in a full factorial design. We measured color, amount of reactive oxygen metabolites (ROMs), hematocrit, immunocompetence, and blood parasite intensity before and after treatments. High basking time resulted in elevated immunocompetence coupled with increased ROMs. The high food treatment increased nuptial color brightness, but also increased ROMs and decreased immunocompetence. In summary, our study provides experimental evidence about environmentally induced parallel changes in an honest sexual signal and several quality-indicator physiological traits. We showed that available energy and time for high metabolism have independent and sometimes opposite effects on individual state.

Hot-blooded lizard illuminates endothermy origins

Understanding the evolution of endothermy in birds and mammals is a central question in evolutionary physiology, because thermal biology intertwines with numerous ecologically important life-history traits, such as body size and shape, foraging ranges, growth rates and the production of offspring. Theories about the selective drivers for the evolution of endothermy have been debated for decades, and include: the prevention of overheating during locomotion; expanded ability to sustain exercise; the generation of heat during digestion; and parental control of the reproductive environment. The discovery that a lizard (Salvator merianae) develops endothermy when arousing from hibernation and preparing to reproduce by growing gonads, mating and depositing yolk in their eggs, recently reported by Glenn Tattersall and colleagues in Science Advances, informs this debate in a number of ways.The authors measured the environmental temperature and the body temperatures of adult male and female lizards weighing approximately 2 kg throughout the year. During the fall and winter, the lizards hibernate in underground burrows for 5–6 months. However, the researchers discovered that between days 160 and 180 of the hibernation fast, the night-time body temperature of both the males and females was raised markedly above the ambient temperature. At the end of the hibernation, the lizards resumed activity, basking during the day to supplement their own heat production and returning to the burrows at night. The team noticed that the lizards’ body temperatures remained elevated throughout the night, by up to 10°C above the burrow temperature, during the period when they were preparing to reproduce, whereas at other times of the year the nocturnal body temperatures equilibrated with the burrow. And when the authors placed fasting adults that were prepared to reproduce in a thermostatically controlled chamber for 8 days, they learned that the lizards maintained a body temperature that was higher than that of their surroundings without the benefit of heat generated by digestion or the insulation of their burrows. However, when the lizards were disturbed, their body temperature fell, perhaps because of heat loss caused by increased blood flow to the limbs, skin, tail, head or other peripheral tissues. So heat production and the ability to regulate body temperature were not associated with either feeding or activity in this lizard.The discovery that these lizards are able to maintain a body temperature that is greater than their surroundings is important in several ways. It refutes conventional wisdom, which holds that small animals that lack body insulation cannot raise body temperatures significantly, and complements previous work showing that, during reproduction, some species of python raise their body temperature up to 13°C above the surroundings when brooding eggs in insulated nests. It also shows that the ability to maintain a raised body temperature is not an oddity of one family of snake, but fits within a pattern of greater thermal stability during the reproductive period observed even in fully endothermic species, such as birds and mammals. Also, embryos are generally less tolerant of thermal fluctuations than adults, so it is not surprising to find strong selection for characteristics that confer thermal stability during development. Convergent evolution is one of the strongest lines of evidence for the significance of a characteristic; therefore, the discovery by Tattersall and colleagues of the convergent evolution of reproductive endothermy in this lizard supports the hypothesis that the same selective pressure drove the evolution of endothermy in birds and mammals.

Immune responses of a wall lizard to whole-body exposure to radiofrequency electromagnetic radiation

Purpose During the last three decades, the number of devices that emit non-ionizing electromagnetic radiation (EMR) at the wireless communication spectrum has rapidly increased and possible effects on living organisms have become a major concern. The purpose of this study was to investigate the effects of radiofrequency EMR emitted by a widely used wireless communication device, namely the Digital Enhanced Communication Telephony (DECT) base, on the immune responses of the Aegean wall lizard (Podarcis erhardii).Materials and methods Adult male lizards were exposed 24 h/day for 8 weeks to 1880–1900 MHz DECT base radiation at average electric field intensity of 3.2 V/m. Immune reactivity was assessed using the phytohemagglutinin (PHA) skin swelling and mixed lymphocyte reaction (MLR) tests.Results Our results revealed a noticeable suppression (approximately 45%) of inflammatory responses in EMR-exposed lizards compared to sham-exposed animals. T cell-mediated responses were marginally affected.Conclusion Daily radiofrequency EMR exposure seems to affect, at least partially, the immunocompetence of the Aegean wall lizard.

Estrogenic contamination by manure fertilizer in organic farming: a case study with the lizard Podarcis sicula.

In the last years, worldwide organic farming has grown exponentially; as a consequence, the use of animal manure as a soil fertility source has become the principal agricultural choice. However, the use of manure as fertilizer can increase the amount of steroid hormone metabolites in the soil. In southern Italy, lacertidae lizards are the most abundant vertebrate group in agroecosystems and have been identified as potential model species for ecotoxicological studies. The aim of this study was to understand if the manure applied in organic farming has estrogen-like effects in the lizard Podarcis sicula. Adult male lizards were captured in two organic agricultural fields (manure-treated sites) and in an uncultivated field (control site). Lizards from the two organic farms displayed hepatic biosynthetic alterations typical of an estrogenic contamination; hepatocytes contained both vitellogenin and estrogen receptor alpha transcripts and proteins, detected by in situ hybridization and immunocytochemistry. The same cells did not show cadmium, lead and metallothionein accumulation, indicative of the lack of inorganic contamination. These findings suggest that exogenous estrogens, arising from the use of manure, could affect the welfare of wild animals and animal breeding, leading to bioaccumulation of estrogens in food chain, with possible risk for human consumers. For this reason, organic farming should implement the use of sustainable practices such as crop rotation to preserve the soil biological activity, rather than organic manure as fertilizer.

A place in the sun: interspecific interference affects thermoregulation in coexisting lizards

Solar radiation is in theory an unlimited resource on Earth, but can be locally limited. Heliothermic organisms use solar radiation to elevate their body temperatures, leading them to compete for sun-exposed areas, where interference for limited resource can occur. In coexisting lizard species, interference for basking sites could promote and direct interspecific interactions, which can be related to broader geographic species distribution patterns. We compared two competing lizard species (Podarcis muralis and Iberolacerta horvathi) that occupy sun-exposed gaps in a forested landscape in the Northern Dinaric Mountains (southern Europe). Both species exhibit an altitudinal segregation pattern with a high zone of overlap at middle altitudes. Using experimental thermal gradients, we tested for existence of interference competition. We used adult male lizards in three social contexts, alone as a measure of preferred body temperature (T p) and in conspecific or heterospecific pairs as a measure of realized body temperature (T r). I. horvathi achieved lower T r compared to its T p (alone), while T r of P. muralis did not vary between social contexts. The evidence for interference found in I. horvathi could not be explained by a change in their general movement pattern in a thermal gradient. Our results suggest that interference was a result of direct agonistic interactions, assessed by the frequency of approaches and touches. I. horvathi showed higher interference-susceptibility than P. muralis indicating an asymmetric interaction between the two species. Sunlight (as a resource) is an important factor influencing distribution patterns in assemblages of heliothermic ectotherms where sun-exposed basking sites are limited.

Sex, Age, and Population Density Affect Aggressive Behaviors in Island Lizards Promoting Cannibalism

AbstractIsland populations may evolve distinct behavioral repertoires as a response to the conditions of insular life. Strong intraspecific competition is typical in insular lizards and may include cannibalism. In this study, we investigated sexual and age patterns of aggression in two populations of the Skyros wall lizard (Podarcis gaigeae), one from the main island of Skyros (Aegean Sea, Greece) and another from the satellite islet Diavates. The latter is terrestrial predator‐free biotope, hosting a dense population of large‐bodied lizards that have been reported to exert cannibalism. In staged encounters, we examined the aggressive propensities of adult male and female lizards against their age‐peers and juveniles. Males from both populations were much more aggressive than females toward juveniles and other adults. Males from Diavates were more frequently aggressive to juveniles and other male lizards than males from Skyros. Diavates cannibals also captured their targets at shorter latency. We ascribe this distinct behavioral pattern to the high population density. Infanticide and intramale aggressiveness confer two great advantages to cannibals: food and elimination of future rivals.

A new simplex approach to highlight multi-scale feeding behaviors in forager species from stomach contents: Application to insectivore lizard population

Stomach contents represent complex mixture systems which depend on feeding mode and level of forager species (carnivores, herbivores) as well as on natural availability/distribution of food resources (preys, plants). Such mixture systems can be considered as small black boxes condensing wide ecological information on (i) feeding behaviors of predator (or herbivore) and (ii) local diversity of preys (or host plants). Feeding behaviors of a hunter species toward different prey taxa show a complex variability whose investigation requires multivariate statistical tools. This paper presents a new computational approach which statistically analyzes stomach contents' variability in a predator population to graphically highlight different feeding behaviors. It is a simulation approach iteratively combining the variability of different diet patterns by using a simplex mixture design. Average combinatorial results are graphically visualized to highlight scale-dependent relationships between consumption rates of different food types found in the stomachs. The simplex approach was applied on different subpopulations of Phrynosoma douglassi brevirostre, an insectivore lizard species. These subpopulations were initially defined by different criteria including statistical clusters, gender and sampling periods. Results highlighted successive trade-offs over months of captured potential preys switching from small and less mobile preys to large and flying ones. In these dietary transitions, P. douglassi manifested a systematic memorization of previous preys and a gradual foraging learning of the next ones. These results highlighted lightness on dietary flexibility helping this specialist predator to switch between diets based on different potential preys. Adult male and adult female lizards showed different feeding behaviors due to some predation lag-time between them and different dietary ratios toward the same considered preys.

Influence of gaze and directness of approach on the escape responses of the Indian rock lizard, Psammophilus dorsalis (Gray, 1831)

Animals often evaluate the degree of risk posed by a predator and respond accordingly. Since many predators orient their eyes towards prey while attacking, predator gaze and directness of approach could serve as conspicuous indicators of risk to prey. The ability to perceive these cues and discriminate between high and low predation risk should benefit prey species through both higher survival and decreased energy expenditure. We experimentally examined whether Indian rock lizards (Psammophilus dorsalis) can perceive these two indicators of predation risk by measuring the variation in their fleeing behaviour in response to type of gaze and approach by a human predator. Overall, we found that the gaze and approach of the predator influenced flight initiation distance, which also varied with attributes of the prey (i.e. size/sex and tail-raise behaviour). Flight initiation distance (FID) was 43 percent longer during direct approaches with direct gaze compared with tangential approaches with averted gaze. In further, exploratory, analyses, we found that FID was 23 percent shorter for adult male lizards than for female or young male (FYM) lizards. In addition, FYM lizards that showed a tail-raise display during approach had a 71 percent longer FID than those that did not. Our results suggest that multiple factors influence the decision to flee in animals. Further studies are needed to test the generality of these factors and to investigate the proximate mechanisms underlying flight decisions.