Nuria Polo-Cavia

Competitive interactions during basking between native and invasive freshwater turtle species.

The red-eared slider (Trachemys scripta elegans) is currently introduced in many Mediterranean countries, where it behaves as an invasive species that competes and displaces native populations of the endangered Spanish terrapin (Mauremys leprosa). However, the nature of competitive interactions is relatively unknown. During basking activity, factors like greater body size or pre-existing behavioral adaptations to an original habitat with higher levels of interspecific competition might confer competitive advantages to introduced T. scripta with respect to native terrapins. We hypothesized that competition for basking places with the introduced T. scripta might negatively affect the efficiency of basking and thermoregulation of the native Spanish terrapin. We experimentally analyzed the basking activity of T. scripta and M. leprosa under occasional and long-term situations of intra- and inter-specific competition. Native M. leprosa subjected to interspecific competition reduced their basking activity, basked for shorter periods than T. scripta, and avoided basking stacked with the exotic turtles. These results suggested the displacement from the basking sites of the native terrapin by the introduced T. scripta. The decreased basking activity of native M. leprosa when competing directly for basking places with introduced sliders may lead native terrapins to a loss in the efficiency of physiological functions related to ineffective thermoregulation, such as digestion or locomotor performance, thus favoring the expansion of the invasive species.

Aggressive interactions during feeding between native and invasive freshwater turtles

The red-eared slider (Trachemys scripta elegans) is a worldwide highly invasive species, currently introduced in most freshwater habitats as a consequence of massive pet trade. In the Iberian Peninsula, this species is competing with and displacing the endangered native Spanish terrapin (Mauremys leprosa). Sliders are considered environmentally-aggressive turtles, capable of threatening or biting other individuals during competitive activities such as feeding. We hypothesized that agonistic behavior of introduced sliders against native terrapins might negatively affect the feeding efficiency of M. leprosa. We compared food ingestion of turtles and aggressive interactions during feeding, under situations of conspecific and heterospecific competition. The amount of food ingested by native and introduced turtles was similar under conspecific competition, but T. scripta ingested a greater percentage of food supplied under heterospecific competition. Also, introduced sliders initiated most of the aggressions observed during feeding activity, and aggression was more frequently directed to heterospecifics. Our results suggest a more aggressive and competitive behavior of introduced T. scripta in vying for food resources, which might contribute to explain the observed displacement of native populations of M. leprosa.

Social aggregation behaviour in the North African amphisbaenian Trogonophis wiegmanni

Abstract The ecology and behaviour of Amphisbaenians is poorly known due to their fossorial habits. However, amphisbaenians are often found under rocks where they thermoregulate, and probably engage in social interactions. We describe aggregations under rocks in a North African population of the little studied amphisbaenian Trogonophis wiegmanni. These observations could be used to make initial inferences about the social behaviour of this amphisbaenian. Results showed that amphisbaenians were sometimes found in pairs under the same rock. However, these aggregations were not random. Adult males were only found together with adult females, but we did not find pairs of adult males or adult females. This might suggest that there is intra-sexual intolerance, and that adult individuals of the same sex do not occupy the same rock space. Pairs of adults were more frequently found in spring than in autumn, coinciding with the mating season. Also, juvenile individuals were often found together with an adult, but juveniles tended to be more often with an adult female than with an adult male. This might indicate that juveniles are allowed to remain with their parents until they are older, which might enhance offspring fitness by providing access to high-quality habitats.

Head coloration reflects health state in the red-eared slider Trachemys scripta elegans

Sexual signals can be evolutionarily stable if they are honest and condition-dependent or costly to the signaler. One possible cost is the existence of a trade-off between maintaining physiological health and elaboration of ornaments, such that only healthier individuals may afford to produce more elaborate sexual displays. We analyzed the relationship between head coloration and health state of Trachemys scripta elegans turtles. Results showed that turtles with a higher immune response and with a higher body condition had postorbital red patches with brighter coloration with higher values of long-wavelength reflectance (i.e., more reddish). Similarly, turtles with a higher immune response and with a lower heterophil/lymphocyte (H/L) ratio had chin yellow stripes with darker coloration with higher values of medium wavelengths (i.e., more yellowish). These relationships suggest that the health state of T. scripta elegans turtles is reflected by the colorful skin patches and stripes of the head. Characteristics of coloration did not differ between sexes, suggesting that this visual signal may be used by both sexes in intrasexual and intersexual communication. Because many other turtle species have similar colorful patches, it is likely that coloration may have a still unexplored significant role in sexual selection in many turtles.

Sexual Dimorphism in the North African Amphisbaenian Trogonophis wiegmanni

Abstract Sexual dimorphism in size or shape is common in many reptile species. Amphisbaenians are morphologically specialized for a fossorial life, which might constrain the evolution of sexual dimorphism. This might explain why some amphisbaenian species, but not others, show some type of sexual dimorphism. To understand the differential occurrence of sexual dimorphism in amphisbaenians, studies on a wide number of species belonging to different families and inhabiting different ecological conditions are needed. We measured several morphological variables in a population of the amphisbaenian Trogonophis wiegmanni, a representative of the little-studied family Trogonophidae from North Africa. Results show that males and females have similar body size; but for individuals of similar size, males are heavier, have longer tails, and have larger heads than do females. These differences might be explained by sexual selection, if males with larger heads had advantages in intrasexual contests, or by sexual diet differences. However, most ecological and behavioral aspects of this and other amphisbaenian species remain poorly known, thereby leaving unresolved which selective pressures are responsible for the sexual dimorphism that was evident in this species.

STRUCTURE OF A POPULATION OF THE AMPHISBAENIAN TROGONOPHIS WIEGMANNI IN NORTH AFRICA

Abstract Amphisbaenians are a group of reptiles specialized for a fossorial life, which makes the study of their peculiar biological and ecological adaptations difficult. The population biology of amphisbaenians is almost unknown. We described the seasonal variation in the size, age, and sex structure of a population of the amphisbaenian Trogonophis wiegmanni from the Chafarinas Islands, in North Africa. We specifically described body size (length and weight), frequency distribution of newborn and older juvenile individuals and adults, sex ratio of adults (which did not differ from a 1∶1 ratio), and proportion of juveniles and newborn individuals in the population. The results indicated that T. wiegmanni is a viviparous species that delays reproduction until at least 2.5 yr, that almost half of adult females do not reproduce every year, and that females have a very small brood size (i.e., reproductive females give birth to a single juvenile at the beginning of autumn). We also used our data to infer growth and survival of juveniles, suggesting that mortality of newborn individuals is low. There are many aspects of the population biology of amphisbaenians that remain unknown and further studies are clearly needed.

Low levels of chemical anthropogenic pollution may threaten amphibians by impairing predator recognition.

Recent studies suggest that direct mortality and physiological effects caused by pollutants are major contributing factors to global amphibian decline. However, even sublethal concentrations of pollutants could be harmful if they combined with other factors to cause high mortality in amphibians. Here we show that sublethal concentrations of pollutants can disrupt the ability of amphibian larvae to recognize predators, hence increasing their risk of predation. This effect is indeed much more important since very low amounts of pollutants are ubiquitous, and environmental efforts are mostly directed towards preventing lethal spills. We analyzed the effects of two common contaminants (humic acid and ammonium nitrate) on the ability of tadpoles of the western spadefoot toad (Pelobates cultripes) to recognize chemical cues from a common predator, nymphs of the dragonfly Anax imperator. We compared the swimming activity of tadpoles in the presence and absence of water-borne chemical cues from dragonflies at different concentrations of humic acid and ammonium nitrate. Tadpoles reduced swimming activity in response to predator cues in the absence of pollutants, whereas they remained unresponsive to these cues when either humic acid or ammonium nitrate was added to the water, even at low concentrations. Moreover, changes in tadpole activity associated with the pollutants themselves were non-significant, indicating no toxic effect. Alteration of the natural chemical environment of aquatic systems by pollutants may be an important contributing cause for declines in amphibian populations, even at sublethal concentrations.

Pigmentation plasticity enhances crypsis in larval newts: associated metabolic cost and background choice behaviour

In heterogeneous environments, the capacity for colour change can be a valuable adaptation enhancing crypsis against predators. Alternatively, organisms might achieve concealment by evolving preferences for backgrounds that match their visual traits, thus avoiding the costs of plasticity. Here we examined the degree of plasticity in pigmentation of newt larvae (Lissotriton boscai) in relation to predation risk. Furthermore, we tested for associated metabolic costs and pigmentation-dependent background choice behaviour. Newt larvae expressed substantial changes in pigmentation so that light, high-reflecting environment induced depigmentation whereas dark, low-reflecting environment induced pigmentation in just three days of exposure. Induced pigmentation was completely reversible upon switching microhabitats. Predator cues, however, did not enhance cryptic phenotypes, suggesting that environmental albedo induces changes in pigmentation improving concealment regardless of the perceived predation risk. Metabolic rate was higher in heavily pigmented individuals from dark environments, indicating a high energetic requirement of pigmentation that could impose a constraint to larval camouflage in dim habitats. Finally, we found partial evidence for larvae selecting backgrounds matching their induced phenotypes. However, in the presence of predator cues, larvae increased the time spent in light environments, which may reflect a escape response towards shallow waters rather than an attempt at increasing crypsis.