Challenging ecogeographical rules: Phenotypic variation in the Mountain Treeshrew (Tupaia montana) along tropical elevational gradients.

Bergmann's and Allen's rules were defined to describe macroecological patterns across latitudinal gradients. Bergmann observed a positive association between body size and latitude for endothermic species while Allen described shorter appendages as latitude increases. Almost two centuries later, there is still ongoing discussion about these patterns. Temperature, the common variable in these two rules, varies predictably across both latitude and elevation. Although these rules have been assessed extensively in mammals across latitude, particularly in regions with strong seasonality, studies on tropical montane mammals are scarce. We here test for these patterns and assess the variation of several other locomotory, diet-associated, body condition, and thermoregulatory traits across elevation in the Mountain Treeshrew (Tupaia montana) on tropical mountains in Borneo. Based on morphological measurements from both the field and scientific collections, we found a complex pattern: Bergmann's rule was not supported in our tropical mountain system, since skull length, body size, and weight decreased from the lowest elevations (<1000 m) to middle elevations (2000-2500 m), and then increased from middle elevations to highest elevations. Allen's rule was supported for relative tail length, which decreased with elevation, but not for ear and hindfoot length, with the former remaining constant and the latter increasing with elevation. This evidence together with changes in presumed diet-related traits (rostrum length, zygomatic breadth and upper tooth row length) along elevation suggest that selective pressures other than temperature, are playing a more important role shaping the morphological variation across the distribution of the Mountain Treeshrew. Diet, food acquisition, predation pressure, and/or intra- and inter-specific competition, are some of the potential factors driving the phenotypic variation of this study system. The lack of variation in body condition might suggest local adaptation of this species across its elevational range, perhaps due to generalist foraging strategies. Finally, a highly significant temporal effect was detected in several traits but not in others, representing the first phenotypic variation temporal trends described on treeshrews.

Habitat-dependent Culicoides species composition and abundance in blue tit (Cyanistes caeruleus) nests.

Wild birds are hosts of Culicoides from as early on as the nesting stage when constrained to their nests. However, the environmental factors which determine the abundance and composition of Culicoides species within each bird nest are still understudied. We sampled Culicoides from Eurasian blue tit (Cyanistes caeruleus) nests found in 2 types of forests located in southern Spain. Firstly, we monitored the abundance of Culicoides species in bird nests from a dry Pyrenean oak deciduous forest and a humid mixed forest comprising Pyrenean and Holm oaks throughout 2 consecutive years. During the 3rd year, we performed a cross-fostering experiment between synchronous nests to differentiate the role of rearing environment conditions from that of the genetically determined or maternally transmitted cues released by nestlings from each forest. We found 147 female Culicoides from 5 different species in the birds' nests. The abundance of Culicoides was higher in the dry forest than in the humid forest. Culicoides abundance, species richness and prevalence were greater when the nestlings were hatched later in the season. The same pattern was observed in the cross-fostering experiment, but we did not find evidence that nestling's features determined by the forest of origin had any effect on the Culicoides collected. These results support the notion that habitat type has a strong influence on the Culicoides affecting birds in their nests, while some life history traits of birds, such as the timing of reproduction, also influence Culicoides abundance and species composition.

Oxidative status of blue tit nestlings varies with habitat and nestling size.

Oxidative status has been proposed as an important ecological and evolutionary force given that pro-oxidant metabolites damage molecules, cells and tissues, with fitness consequences for organisms. Consequently, organisms usually face a trade-off between regulating their oxidative status and other physiological traits. However, environmental stressors and the availability of dietary-derived antioxidants vary according to local conditions and, thus, organisms inhabiting different habitats face different oxidative pressures. Still, there is little information on how different environmental conditions influence the oxidative status of animals inhabiting terrestrial environments. In this work, we examined the variation in oxidative status in the blue tit (Cyanistes caeruleus), a bird species with hatching asynchrony. Specifically, we examined the oxidative status of the largest and the smallest nestlings in the brood, inhabiting four forests differing in food availability and ectoparasite prevalence. We measured lipid peroxidation (malondialdehyde; MDA) as a marker of oxidative damage, total antioxidant capacity (Trolox-equivalent antioxidant capacity; TEAC) and antioxidant enzymatic activity (catalase, glutathione S-transferase, glutathione peroxidase) in blood samples. The glutathione peroxidase (GPX) activity differed among the forests, being the highest in the pine forest and the lowest in a mixed oak (Quercus) forest in the most humid area. Lipid peroxidation was higher in larger nestlings, suggesting higher oxidative damage with an increasing growth rate. Neither brood size, laying date, nor ectoparasites were related to the oxidative status of nestlings. These results suggest that nest rearing conditions might shape the oxidative status of birds, having consequences for habitat-dependent variation in regulation of oxidative status.

Age structure of a lizard along an elevational gradient reveals nonlinear lifespan patterns with altitude.

Lifespan is one of the main components of life history. Shorter lifespans can be expected in marginal habitats. However, in the case of ectotherms, lifespan typically increases with altitude, even though temperature-one of the main factors to determine ectotherms' life history-declines with elevation. This pattern can be explained by the fact that a shorter activity time favors survival. In this study, we analyzed how lifespan and other life-history traits of the lizard Psammodromus algirus vary along a 2,200 m elevational gradient in Sierra Nevada (SE Spain). Populations at intermediate altitudes (1,200-1,700 m), corresponding to the optimal habitat for this species, had the shortest lifespans, whereas populations inhabiting marginal habitats (at both low and at high altitudes) lived longest. Therefore, this lizard did not follow the typical pattern of ectotherms, as it also lived longer at the lower limit of its distribution, nor did it show a longer lifespan in areas with optimal habitats. These results might be explained by a complex combination of different gradients along the mountain, namely that activity time decreases with altitude whereas food availability increases. This could explain why lifespan was maximum at both high (limited activity time) and low (limited food availability) altitudes, resulting in similar lifespans in areas with contrasting environmental conditions. Our findings also indicated that reproductive investment and body condition increase with elevation, suggesting that alpine populations are locally adapted.

Morphological determinants of jumping performance in the Iberian green frog.

Predation is one of the main selective forces in nature, frequently selecting potential prey for developing escape strategies. Escape ability is typically influenced by several morphological parameters, such as morphology of the locomotor appendices, muscular capacity, body mass, or fluctuating asymmetry, and may differ between sexes and age classes. In this study, we tested the relationship among these variables and jumping performance in 712 Iberian green frogs Pelophylax perezi from an urban population. The results suggest that the main determinant of jumping capacity was body size (explaining 48% of variance). Larger frogs jumped farther, but jumping performance reached an asymptote for the largest frogs. Once controlled by structural body size, the heaviest frogs jumped shorter distances, suggesting a trade-off between fat storage and jumping performance. Relative hind limb length also determined a small but significant percentage of variance (2.4%) in jumping performance-that is, the longer the hind limbs, the greater the jumping capacity. Juveniles had relatively shorter and less muscular hind limbs than adults (for a given body size), and their jumping performance was poorer. In our study population, the hind limbs of the frogs were very symmetrical, and we found no effect of fluctuating asymmetry on jumping performance. Therefore, our study provides evidence that jumping performance in frogs is not only affected by body size, but also by body mass and hind limb length, and differ between age classes.

Telomere length mirrors age structure along a 2200-m altitudinal gradient in a Mediterranean lizard.

The timing of organisms' senescence is developmentally programmed but also shaped by the interaction between environmental inputs and life-history traits. In ectotherms, ageing dynamics are still poorly understood even though their body temperature, metabolism, or growth trajectory are very sensitive to environmental changes. Here, we investigated the role of life-history traits such as age, sex, body size, body condition, and tail autotomy (i.e self-amputation) in shaping telomere length in six populations of the Algerian sand lizard (Psammodromus algirus) distributed along an elevational gradient from 300 to 2500 m above the sea level. Additionally, we compiled the available information on reptiles' telomere length in a review table. Our cross-sectional study shows that older lizards have longer telomeres, which might be mostly linked to the selective disappearance of individuals with shorter telomeres or, alternatively, mediated by a higher expression of telomerase across their life. In fact, variation in telomere length across elevation was explained by age structure of lizards; thus, in contrast to our predictions, altitude had no effect on telomere length in this study system. Telomere length was unaffected by tail regeneration and was sex-independent, but positively correlated with body condition, which might be linked to high somatic investment. Hence, our results suggest that life-history traits such as age or body condition can be major drivers of telomere dynamics for this species, whereas environmental conditions apparently had scarce or no effects on lizard telomeres. Our findings emphasize the relevance of understanding species' life histories for fully disentangling the causes and consequences of differences in ageing in ectotherms.

Fitter frogs from polluted ponds: The complex impacts of human-altered environments.

Human-modified habitats rarely yield outcomes that are aligned with conservation ideals. Landscapes that are subdivided by roads are no exception, precipitating negative impacts on populations due to fragmentation, pollution, and road kill. Although many populations in human-modified habitats show evidence for local adaptation, rarely does environmental change yield outright benefits for populations of conservation interest. Contrary to expectations, we report surprising benefits experienced by amphibian populations breeding and dwelling in proximity to roads. We show that roadside populations of the wood frog, Rana sylvatica, exhibit better locomotor performance and higher measures of traits related to fitness compared with frogs from less disturbed environments located further away from roads. These results contrast previous evidence for maladaptation in roadside populations of wood frogs studied elsewhere. Our results indicate that altered habitats might not be unequivocally detrimental and at times might contribute to metapopulation success. While the frequency of such beneficial outcomes remains unknown, their occurrence underscores the complexity of inferring consequences of environmental change.

Early swelling response to phytohemagglutinin is lower in older toads.

The effects of age on performance of life-history traits are diverse, but a common outcome is senescence, an irreversible deterioration of physical and physiological capabilities of older individuals. Immune response is potentially bound to senescence. However, little is known about immune response ageing in amphibians. In this work, we test the hypothesis that amphibian early immune response is reduced in older individuals. To this end, we captured adult natterjack toads (Epidalea calamita) and inoculated them with phytohemagglutinin, an innocuous protein that triggers a skin-swelling immune response whose magnitude is directly proportional to the ability of the individual to mount an immune response. We measured early swelling immune response (corresponding to an innate-response stage) hourly, for six hours, and we calculated the area under the curve (AUC) for each individual's time series, as a measure of immune response magnitude incorporating time. We estimated toad age by means of phalanx skeletochronology. Swelling and AUC decreased with age. Therefore, in accordance with our predictions, early immune response seems subject to senescence in these toads. Reduced ability to get over infections due to senescence of immune respose might be-together with a worse functioning of other organs and systems-among the causes of lower survival of older specimens.

Greater reproductive investment, but shorter lifespan, in agrosystem than in natural-habitat toads.

Global amphibian decline is due to several factors: habitat loss, anthropization, pollution, emerging diseases, and global warming. Amphibians, with complex life cycles, are particularly susceptible to habitat alterations, and their survival may be impaired in anthropized habitats. Increased mortality is a well-known consequence of anthropization. Life-history theory predicts higher reproductive investment when mortality is increased. In this work, we compared age, body size, and different indicators of reproductive investment, as well as prey availability, in natterjack toads (Epidalea calamita) from agrosystems and adjacent natural pine groves in Southwestern Spain. Mean age was lower in agrosystems than in pine groves, possibly as a consequence of increased mortality due to agrosystem environmental stressors. Remarkably, agrosystem toads were larger despite being younger, suggesting accelerated growth rate. Although we detected no differences in prey availability between habitats, artificial irrigation could shorten aestivation in agrosystems, thus increasing energy trade. Moreover, agrosystem toads exhibited increased indicators of reproductive investment. In the light of life-history theory, agrosystem toads might compensate for lesser reproductive events-due to shorter lives-with a higher reproductive investment in each attempt. Our results show that agrosystems may alter demography, which may have complex consequences on both individual fitness and population stability.