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Effects of Limb Length, Body Mass, Gender, Gravidity, and Elevation on Escape Speed in the Lizard Psammodromus algirus

Most animals rely on their escape speed to flee from predators. Here, we test several hypotheses on the evolution of escape speed in the lizard Psammodromus algirus. We test that: (1) Longer limbs should improve speed sprint. (2) Heavier lizards should be impaired regarding their sprint speed ability, suggesting a trade-off between fat storage and escape capability. (3) Males should achieve faster speeds due to their higher exposure to predators. (4) Gravid females, with increased body mass, should perform lower speed than non-gravid females. And (5) there are inter-population differences in sprint speed across an elevational gradient. We measured lizards sprint speed in a lineal raceway in the laboratory, filming races in standardized conditions and then calculating their maximal speed. We found that hind limb length greatly determined maximal sprint speed, lizards with longer limbs being faster. In parallel, higher body masses reduced maximal speed, which points to a trade-off between fat storage and escaping capability. Sexual differences also arose, as males were faster than females, as a consequence of males having longer limbs. Regarding females, gravidity did not impair maximal sprint speed, suggesting adaptations which compensate for the increased body mass. Finally, we found no elevational trend in both limbs length and sprint speed. In any case, this study suggests that selection on escape capacity may cast morphological evolution, and affect other life-history traits, such as fat storage and reproduction.

Elevational variation in body-temperature response to immune challenge in a lizard.

Immunocompetence benefits animal fitness by combating pathogens, but also entails some costs. One of its main components is fever, which in ectotherms involves two main types of costs: energy expenditure and predation risk. Whenever those costs of fever outweigh its benefits, ectotherms are expected not to develop fever, or even to show hypothermia, reducing costs of thermoregulation and diverting the energy saved to other components of the immune system. Environmental thermal quality, and therefore the thermoregulation cost/benefit balance, varies geographically. Hence, we hypothesize that, in alpine habitats, immune-challenged ectotherms should show no thermal response, given that (1) hypothermia would be very costly, as the temporal window for reproduction is extremely small, and (2) fever would have a prohibitive cost, as heat acquisition is limited in such habitat. However, in temperate habitats, immune-challenged ectotherms might show a febrile response, due to lower cost/benefit balance as a consequence of a more suitable thermal environment. We tested this hypothesis in Psammodromus algirus lizards from Sierra Nevada (SE Spain), by testing body temperature preferred by alpine and non-alpine lizards, before and after activating their immune system with a typical innocuous pyrogen. Surprisingly, non-alpine lizards responded to immune challenge by decreasing preferential body-temperature, presumably allowing them to save energy and reduce exposure to predators. On the contrary, as predicted, immune-challenged alpine lizards maintained their body-temperature preferences. These results match with increased costs of no thermoregulation with elevation, due to the reduced window of time for reproduction in alpine environment.

Opposed elevational variation in prevalence and intensity of endoparasites and their vectors in a lizard

Abstract Studying the causes of parasite geographic distribution is relevant to understand ecological and evolutionary processes that affect host populations as well as for species conservation. Temperature is one of the most important environmental variables affecting parasite distribution, as raising temperatures positively affect development, reproduction, and rate of transmission of both endo- and ectoparasites. In this context, it is generally accepted that, in mountains, parasite abundance decreases with elevation. However, empirical evidence on this topic is limited. In the present study, we analyzed the elevational variation of hemoparasites and ectoparasites of a lizard, Psammodromus algirus, along a 2,200-m elevational gradient in Sierra Nevada (SE Spain). As predicted, ectoparasite (mites, ticks, mosquitoes, and sandflies) abundance decreased with elevation. However, hemoparasite prevalence and intensity in the lizard augmented with altitude, showing a pattern contrary to their vectors (mites). We suggest that tolerance to hemoparasites may increase with elevation as a consequence of lizards at high altitudes taking advantage of increased body condition and food availability, and reduced oxidative stress. Moreover, lizards could have been selected for higher resistance against hemoparasites at lowlands (where higher rates of replication are expected), thus reducing hemoparasite prevalence and load. Our findings imply that, in a scenario of climate warming, populations of lizards at high elevation may face increased abundance of ectoparasites, accompanied with strong negative effects.

Ultraviolet radiation does not increase oxidative stress in the lizard Psammodromus algirus along an elevational gradient

Lizards, as ectotherms, spend much time basking for thermoregulating exposed to solar radiation. Consequently, they are subjected to ultraviolet radiation (UVR), which is the most harmful component of solar radiation spectrum. UVR can provoke damages, from the molecular to tissue level, even cause death. Photooxidation triggered by UVR produces reactive oxidative species (ROS). When antioxidant machinery cannot combat the ROS concentration, oxidative stress occurs in the organisms. Given that UVR increases with elevation, we hypothesised that lizards from high elevations should be better adapted against UVR than lizards from lower elevations. In this work, we test this hypothesis in Psammodromus algirus along an elevation gradient (three elevational belts, from 300 to 2500 m above sea level). We ran an experiment in which lizards from each elevation belt were exposed to 5-hour doses of UVR (UV-light bulb, experimental group) or photosynthetically active radiation (white-light bulb, control group) and, 24 h after the exposure, we took tissue samples from the tail. We measured oxidative damage (lipid and protein peroxidation) and antioxidant capacity as oxidative-stress biomarkers. We found no differences in oxidative stress between treatments. However, consistent with a previous work, less oxidative damage appeared in lizards from the highlands. We conclude that UVR is not a stressor agent for P. algirus; however, our findings suggest that the lowland environment is more oxidative for lizards. Therefore, P. algirus is well adapted to inhabit a large elevation range, and this would favour the lizard in case it ascends in response to global climate change.

Raman Spectroscopy Reveals the Presence of Both Eumelanin and Pheomelanin in the Skin of Lacertids

Abstract Melanic pigments play a key role in the coloration of animals, but the type of melanin pigment in black, brown, and blue colored scales of Squamata has not been studied. Based on research on birds and mammals, we may expect that pheomelanin is the majority pigment in brownish colorations and eumelanin is the majority pigment in black and blue colorations of Squamata. To characterize the pigments that underlie the melanin-based colorations of lizards, we analyzed the skin of nine genera of lacertids using dispersive Raman spectroscopy. Our results suggest that no prediction can be made on the type of pigmentary melanin present in the skin of the lacertids based alone on the hue of the sample. Indeed, brownish patterns in the skin of Psammodromus, Gallotia, Acanthodactylus, and Algyroides lizards presented both chemical forms of melanin: eumelanin and pheomelanin. Therefore, pheomelanogenesis might be an ancient characteristic within Lacertidae, because it was detected in genera in the Lacertini, Eremini, and Gallotini. Raman spectra of melanic-based patterns of genus Zootoca and ultraviolet (UV)-blue patches of Podarcis, Iberolacerta, Lacerta, and Timon lizards suggested that eumelanin is the majority pigment in these patches. Raman spectroscopy is a suitable nondestructive technique useful to identify melanin forms in the skin of lizards, and it demonstrated that pheomelanin is synthesized by Squamata. Resumen Los pigmentos melánicos juegan un papel clave en la coloración de los animales. Sin embargo, en los Squamata se desconoce la identidad molecular de los pigmentos melánicos (i.e., eumelanina y feomelanina) responsables de las coloraciones negras, marrones y azules. Basado en estudios anteriores en aves y mamíferos, cabría esperar que la feomelanina fuera el pigmento mayoritario en coloraciones marrones y que la eumelanina sea el pigmento mayoritario en las coloraciones negras y azules de los Squamata. Para caracterizar los pigmentos responsables de la coloración melánica en lagartos hemos analizado la piel de nueve géneros de lacértidos usando espectroscopía Raman dispersiva. Nuestros resultados sugieren que no se puede predecir el tipo de melanina pigmentaria presente en la piel de los lácertidos basándonos solo en la tonalidad de la muestra. De hecho, en los patrones de color marrón de la piel de lagartos de los géneros Psammodromus, Gallotia, Acanthodactylus y Algyroides están presentes ambas formas químicas de la melanina pigmentaria, es decir, eumelanina y feomelanina. En los patrones melánicos del género Zootoca y en las manchas ultravioleta (UV)-azules de lagartos en los géneros Podarcis, Iberolacerta, Lacerta, y Timon el espectro Raman sugirió que la forma eumelánica debe de ser el pigmento mayoritario en estas manchas. La espectroscopía Raman es una técnica no destructiva que es aplicable para identificar las formas melánicas presentes en la piel de los lagartos y demostró que los Squamata pueden sintetizar feomelanina.

Prey availability, prey selection, and trophic niche width in the lizard Psammodromus algirus along an elevational gradient

Abstract Mountains imply enormous environmental variation, with alpine habitats entailing harsh environments, especially for ectotherms such as lizards. This environmental variability also may imply variation in prey availability. However, little is known about how lizard trophic ecology varies with elevation. In this study, we analyze diet, prey availability, prey selection, and trophic niche width in the lacertid lizard Psammodromus algirus along a 2,200-m elevational gradient in the Sierra Nevada (SE Spain). The analysis of fecal samples has shown that Orthoptera, Formicidae, Hemiptera, Coleoptera, and Araneae are the main prey, although, according to their abundance in pitfall traps, Formicidae and Coleoptera are rejected by the lizard whereas Orthoptera, Hemiptera, and Araneae are preferred. Prey abundance and diversity increase with elevation and diet subtly varies along with the elevational gradient. The consumption of Coleoptera increases with elevation probably as a consequence of the lizard foraging more in open areas while basking. The electivity for Araneae increases with elevation. Araneae are rejected in the lowlands—where they are relatively abundant—whereas, at high elevation, this lizard positively selects them, despite they being less abundant. The lizard trophic niche width expands with elevation due to concomitant greater prey diversity and hence this lizard feeds on more prey types in highlands. Although no sex difference in diet has been found, the trophic niche is broader in females than males. As a whole, alpine lizards show a trophic niche similar to that found at lower elevations, suggesting that P. algirus is well adapted to the harsh environment found in alpine areas.

Female Reproduction in Thamnophis scaliger: The Significance of Parturition Timing

Abstract Reproduction involves costs and benefits to a female snake. Costs include increased predation risk as well as lower future survival and reproduction probability, whereas benefits are the current production of offspring. Reproduction also is highly energy demanding: at each reproductive event, a female must decide between the allocation of energy to female condition or to reproductive output. Moreover, energy allocation linked to reproduction may be influenced by environmental features, especially climate and food availability. During 2008 and 2009, we studied the female reproductive tactics of Thamnophis scaliger, a viviparous and earthworm-eating snake distributed at rather high altitudes in central México. Gravid females were collected in the field and maintained in captivity until giving birth. The low percentage of females that were gravid each year suggested they did not reproduce annually. This result probably was driven by the seasonal constrained availability and low-energy content of earthworms, which preclude females from acquiring sufficient energy to fuel more frequent reproduction. Females also produced rather large litter sizes, implying a significant investment in reproduction. Univariate and multivariate analyses (path analysis) found the expected relationships between maternal body size and litter size and mass, and there was no trade-off of energy allocation between postpartum females and their litters. We found, however, a noteworthy relationship between parturition date and postpartum female body condition. Females that reproduced later benefited most from foraging opportunities during the short rainy and high prey-availability period and remained in better body condition. Resumen La reproducción implica costes y beneficios para una hembra de ofidio. Los costes incluyen el aumento del riesgo a ser depredada, así como la disminución de la probabilidad de supervivencia y reproducción en el futuro, mientras que los beneficios son la producción de descendencia en el presente. La reproducción también demanda mucha energía, y cada vez que una hembra se reproduce, debe decidir entre la asignación de energía a su condición corporal postparto o al rendimiento reproductivo. Estas tácticas en la reproducción de los ofidios pueden estar condicionadas por factores medioambientales, especialmente el clima y la disponibilidad de alimento. En 2008 y 2009, estudiamos la táctica reproductiva de las hembras de Thamnophis scaliger, un ofidio vivíparo, especialista en el consumo de lombrices, distribuido a bastante altitud en el centro de México. Se colectaron hembras grávidas que se mantuvieron en cautividad hasta el parto. El bajo número de hembras grávidas cada año sugirió que no se reproducían anualmente. Este resultado estuvo probablemente condicionado por la estacionalmente limitada disponibilidad y el bajo contenido energético de las lombrices, que impiden a las hembras adquirir suficiente energía para una reproducción más frecuente. Además, las hembras produjeron camadas relativamente numerosas, lo que implica elevada inversión en reproducción. Análisis univariantes y multivariantes (análisis de vías) encontraron la esperada relación entre tamaño corporal materno, y el tamaño y peso de la camada, pero no hubo una compensación entre la energía asignada a las hembras postparto y sus camadas. Si encontramos una notable relación entre la fecha de parto y la condición postparto de las hembras. Las hembras que se reproducían más tarde se beneficiaban de mayor oportunidad de forrajeo durante el corto periodo lluvioso y de alta disponibilidad de presas, por lo que quedaban con mejor condición corporal.

Multiple color patches and parasites in Sceloporus occidentalis: differential relationships by sex and infection

Abstract Parasites generally have a negative influence on the color expression of their hosts. Sexual selection theory predicts resistant high-quality individuals should show intense coloration, whereas susceptible low-quality individuals would show poor coloration. However, intensely colored males of different species of Old and New World lizards were more often infected by hemoparasites. These results suggest that high-quality males, with intense coloration, would suffer higher susceptibility to hemoparasites. This hypothesis remains poorly understood and contradicts general theories on sexual selection. We surveyed a population of Sceloporus occidentalis for parasites and found infections by the parasite genera Lankesterella and Acroeimeria. In this population, both males and females express ventral blue and yellow color patches. Lankesterella was almost exclusively infecting males. The body size of the males significantly predicted the coloration of both blue and yellow patches. Larger males showed darker (lower lightness) blue ventral patches and more saturated yellow patches that were also orange-skewed. Moreover, these males were more often infected by Lankesterella than smaller males. The intestinal parasite Acroeimeria infected both males and females. The infection by intestinal parasites of the genus Acroeimeria was the best predictor for the chroma in the blue patch of the males and for hue in the yellow patch of the females. Those males infected by Acroeimeria expressed blue patches with significantly lower chroma than the uninfected males. However, the hue of the yellow patch was not significantly different between infected and uninfected females. These results suggest a different effect of Lankesterella and Acroeimeria on the lizards. On the one hand, the intense coloration of male lizards infected by Lankesterella suggested high-quality male lizards may tolerate it. On the other hand, the low chroma of the blue coloration of the infected males suggested that this coloration could honestly express the infection by Acroeimeria.