Pablo Iraeta

Effects of gravidity on the locomotor performance and escape behaviour of two lizard populations: the importance of habitat structure

In lizards, locomotor costs of gravidity may depend on habitat structure and refuge availability. We compared the locomotor performance and escape tactics in the laboratory, before and after oviposition, of two populations of Psammodromus algirus separated by 700 m altitude. When gravid, females escaped using a larger number of slower and shorter runs, and had lower temperatures at the time of trial, than after oviposition. Some of these effects differed between populations: when gravid, but not after oviposition, low-elevation females ran shorter distances at a slower average speed than high-elevation ones. Low-elevation females laid their clutches earlier than high-elevation ones, which conditioned their lower speed when gravid in simultaneous running trials. However, their escape distances were still shorter after controlling for the effects of temperature and laying date. In the field, refuge availability was lower at the low-elevation site, where females spent more time inside refuges and perching above ground. The shorter escape distance of low-elevation females may, thus, represent a behavioural response to minimize detectability, especially if predator avoidance depends primarily on whether or not the lizard is seen by the predator. Such behavioural adjustments might inhibit selection for evolutionary shifts in the performance of gravid females.

A reciprocal transplant study of activity, body size, and winter survivorship in juvenile lizards from two sites at different altitude

Abstract We examined activity rates prior to hibernation, age-adjusted body size, growth rates, and probability of recapture after spring emergence of juveniles from 2 populations of the lizard Psammodromus algirus separated by 600–700 m altitude. We captured gravid females, incubated the eggs, and released the juveniles into the wild. We used a reciprocal transplant design in a year of severe drought to distinguish between environmental and population-specific sources of variation. The levels of autumn activity differed between release sites (activity was higher at the more productive, high-elevation site) and between maternal sites of origin (at the low-elevation site, juveniles of low-elevation origin were less active than those of high-elevation origin). Although clutch mass was similar at both sites, eggs from low-elevation females were larger but fewer than those from high-elevation ones. Larger juveniles and those from high-elevation clutches had higher survival rates. The juveniles recaptured in autumn at the low-elevation site were smaller as neonates than those that were not recaptured until next spring. Our results suggest that the scarcity of prey at the low-elevation site is a selective pressure resulting in limitation of activity, given the increased energy expenditure and risk of predation incurred by active lizards. Thus, at the low-elevation site inactivity would be advantageous for most juveniles, and only the smaller ones would have to remain active frequently enough to accumulate sufficient reserves prior to hibernation. This is consistent with the selective advantage of large eggs (and small clutches) at the low-elevation site.

Life-history traits of two Mediterranean lizard populations: a possible example of countergradient covariation

The trade-off between clutch and offspring size, which is a central topic in life-history research, is shaped by natural selection to maximize the number of surviving offspring, but it also depends on the resources available for reproduction. Conspecific populations living in different environments may differ in adult body size, clutch mass, clutch size, offspring size, and/or post-natal growth rates, due either to phenotypic plasticity or to local adaptation. Here, we compare these traits and their relationships between two populations of the lizard Psammodromus algirus separated by a 600-m altitudinal gradient. We used a common garden design to control incubation temperature and food availability, with two different feeding treatments. Females were larger at the high-elevation site. Although SVL-adjusted clutch mass did not differ between populations, high-elevation females laid more but smaller eggs than low-elevation ones. Hatchlings were larger at lower elevation. Our common garden experiment revealed that low-elevation hatchlings grew faster than high-elevation hatchlings under both feeding treatments. However, higher food availability at higher altitude allows high-elevation lizards to grow faster and attain larger adult sizes, especially in the case of females. The two key adaptations of low-elevation lizards, large eggs and hatchlings and the ability to grow rapidly after hatching, are likely to enhance survival in low-productivity Mediterranean lowlands. Our data support the hypothesis that the reproductive strategies of these populations provide an example of countergradient variation, because the genotypes that encode for fast growth and large body size occurred in low food availability habitats where juveniles grew slowly and attained small adult sizes.

Nest-site Selection by Psammodromus Algirus in a Laboratory Thermal Gradient

Abstract Oviposition site choice, which is one of the most important forms of parental care in oviparous reptiles, has major effects on incubation duration, reproductive success, and offspring phenotype. We determined the thermal characteristics of nest-sites selected by females of the lacertid lizard Psammodromus algirus in laboratory thermal gradients, and we linked results with information on the effects of temperature on incubation times and hatchling phenotypes. Temperatures at oviposition sites (mean ± SD = 26.0 ± 1.9°C) were on average lower and had a lower variance than those at available sites (32.0 ± 6.2°C). The duration of incubation decreased dramatically as temperature increased. In fact, the hatching dates predicted by the temperatures selected in the thermogradients were delayed with respect to the mean emergence dates observed in the field. Such disparity might occur because (1) natural incubation temperatures are variable rather than constant, (2) they are expected to rise later in the season, and (3) temperatures that are too high can severely compromise embryonic survival. In addition, females might select relatively low nest-site temperatures because hatching too early can force juveniles to face limited growth opportunities caused by food shortage in the Mediterranean environments in which they live.

Differences in males’ chemical signals between genetic lineages of the lizard Psammodromus algirus promote male intrasexual recognition and aggression but not female mate preferences

Interpopulational variation in sexual signals may lead to premating reproductive isolation and eventually may result in speciation. We explored the role of chemical cues secreted by the femoral glands of male lizards Psammdoromus algirus in chemosensory recognition between two distinct genetic lineages from Central Spain. We hypothesized that if there were differences in chemical sexual signals between lineages, these may result in differential recognition and mate preferences. This might lead to reproductive isolation, which would allow the observed morphological and genetic differences between lineages. Our results showed that males of each lineage secreted a singular mixture of compounds in their femoral secretions. However, females were apparently not able to discriminate the lineage of males by chemosensory cues or, alternatively, this discrimination may not be important for females. Moreover, females did not select or reject areas scent marked by males of their own vs. the other lineage. However, previous studies suggest that females might prefer scent of males with particular chemical characteristics that show interindividual variability but do not vary between lineages. Similarly, males did not discriminate between the scents of females of the two lineages, although they had greater chemosensory responses to scents of larger females. In contrast, males clearly discriminated the lineage of other males based on their scents alone, showing chemosensory and aggressive responses that were higher to scents of males of the other lineage. If males of the opposite lineage were more prone to be detected and excluded from a male territory due to their differences in chemical signals, this may probably impede the access of males of one lineage to females of the opposite lineage. This might result in reproductive isolation between lineages. We suggest that the current genetic divergence observed between lineages of P. algirus lizards may be mediated by intrasexual relationships among males, but not by female mate preferences. Significance statement Sexual signals often vary geographically to maximize their efficiency in communication under local conditions. Such variation may, however, affect recognition between individuals of different populations, resulting in reproductive isolation and speciation. We studied two populations (lineages) of a lizard with genetic and morphological differences. We found clear inter-lineage variation in chemical profiles of sexual signals of males. However, females did not recognize these differences by chemosensory cues and did not prefer or reject areas scent-marked by males of the two lineages. In contrast, males recognized and responded more aggressively toward scent of males of the opposite lineage. This might impede access of males of one lineage to females of the other. We suggest that the observed differences between lineages may result from partial reproductive isolation, which can be mediated by agonistic interactions between males rather than by female mate preferences.

Effects of Caudal Autotomy on Postnatal Growth Rates of Hatchling Psammodromus algirus

Abstract Tail autotomy has clear advantages regarding predator escape, but it also has several associated costs (i.e., impaired locomotion, loss of social status, and reduced growth and reproductive output). We examined the costs of severe autotomy on growth rates of hatchlings of the lacertid lizard Psammodromus algirus during the first weeks of postnatal development. Hatchlings from two populations in central Spain were autotomized on the fifth day after hatching and kept in common garden conditions for 35 days when they were measured again. Hatchlings from both populations, independently of the autotomy treatment, did not differ in the mass gained during the experiment. However, there were differences in body growth between tailless and tailed hatchlings; tailless hatchlings grew at a slower rate than tailed ones, after controlling for the effects of body condition at the onset of the experiment and the resources assimilated. Moreover, independently of their population of origin, hatchlings that invested more in body growth also invested more in regenerating their tails, and no trade-offs were apparent. Because hatchlings were housed in common garden conditions, this result could be attributable to differences in individual capacity to obtain and assimilate resources.