Juliana Valencia

Disposable-soma senescence mediated by sexual selection in an ungulate.

Senescence may result from an optimal balance between current reproductive investment and bodily repair processes required for future reproduction, a theoretical prediction difficult to prove especially in large, long-lived animals. Here we propose that teeth that have fixed dimensions early in life, but that wear during chewing, can be taken as a measure of total lifetime ‘repair’, and their wear rate as a measure of current expenditure in performance. Our approach also considers the sexual selection process to investigate the advance of senescence in males compared with females, when selection favouring competition over mates reduces the reproductive lifespan of males. We studied carcasses of 2,141 male and 739 female red deer (Cervus elaphus) of different ages, finding that male molariform teeth emerged at a far smaller size than expected from body size dimorphism. This led to higher workload, steeper wear rate and earlier depletion of male teeth than in females, in concordance with sex-specific patterns of lifetime performance and reproduction. These findings provide the empirical support for the disposable-soma hypothesis of senescence, which predicts that investment in bodily repair will decrease when the return from this investment may not be realized as a result of other causes that limit survival or reproduction.

Space use by red deer in a Mediterranean ecosystem as determined by radio-tracking

Abstract Space use, movements and activity rhythms of radio-tagged red deer were studied in a Mediterranean environment. The deer were found to be mainly crepuscular, nocturnal activity being higher than diurnal activity, which differs from studies of northern European populations of the species. Home ranges were smaller than most reported in the literature, that of the male being about two or three times larger than those of the females. Daily movements ranged from 3 to 4 km day −1 according to the size of the home range. Vegetation cover was used more by the male and by all individuals during the summer, whilst open areas were used during the winter and spring, probably because of the high grass production in these seasons. The differences found with respect to other populations indicate that further studies in Mediterranean ecosystems are required to provide a basis of knowledge for management decisions.

Fluctuating asymmetry of red deer antlers negatively relates to individual condition and proximity to prime age

After about 50 years of research on fluctuating asymmetry (FA) as a reliable indicator of both individual quality and environmental stress, the enthusiasm is beginning to decline. The findings of many studies are inconsistent and the relationship between FA and stress appears both weaker and more complex than first thought. To provide clarification of the debate, new studies should use more efficient and unified statistical protocols, large sample sizes and joint analysis of several related traits. In addition, fitnesseFA associations should be tested at the individual level, in different populations and under different environmental conditions. To achieve these criteria, we describe a 9-year study in which we measured six antler traits of 3 000 Iberian red deer, Cervus elaphus hispanicus, from three study areas in southwest Spain. Males were harvested during hunting activities and measured, weighed and aged post mortem. We found evidence of correlations between traits in FA, an association between asymmetry and stress conditions and a weak but significant negative relationship between FA and fitness surrogates (body mass and antler size), thus supporting some assumptions of the FA hypothesis. As also predicted by theory, antler traits of less functional importance were more asymmetric and more sensitive to stress than those directly used in fighting behaviour. The relationship between age and antler asymmetry was U-shaped, suggesting an effect of sexual selection on antler development in favour of larger and more symmetrical antlers during prime age.

Testosterone and helping behavior in the azure-winged magpie (Cyanopica cyanus): natural covariation and an experimental test

In this study, we investigated patterns of natural covariation between testosterone and reproductive status in a cooperatively breeding bird species, the azure-winged magpie (Cyanopica cyanus). To assess the relationship between testosterone and breeding behavior, we also manipulated testosterone (T) levels early in the season (before breeding started) using testosterone-filled or empty implants. Our results do not support the hypothesis that circulating testosterone levels affect the occurrence of helping behavior in the azure-winged magpie. Helping males had similar T levels to breeding males. Furthermore, experimentally augmented plasma T did not affect the likelihood of becoming either a helper or a breeder. Overall, these results are consistent with previous findings in other bird species and only give some support to the behavioral suppression hypothesis, suggesting that helping in the azure-winged magpie is a flexible behavioral option moderated in the short-term by social and ecological factors. Experimentally elevated testosterone levels, however, reduced the reproductive success of male breeders because of markedly lower levels of paternal care, had similar effects on their mates, but had the contrary effect on helpers, which raised levels of parental effort. We suggest increases in the share of paternity and in social prestige as possible explanations for these results.

Positive correlation between helpers at nest and nestling immune response in a cooperative breeding bird

In cooperatively breeding species, helpers may contribute to the success of the brood by increasing the number of independent offspring, but also, they may affect offspring condition and, hence, their survival and recruitment into the breeding population. This second type of benefits is rarely included in theoretical models or assessed in field studies. Immune response is a good proxy of individual quality and fitness, and there is good evidence that the performance of the immune system of chicks during the nestling phase is related to their chances of survival and future reproduction. However, no study has so far explored whether helpers at the nest might contribute to enhance immune functioning of nestlings in species with a cooperative breeding system. Here we investigate this issue in the azure-winged magpie (Cyanopica cyanus) and found for the first time a positive correlation between the number of helpers at nest and the cell-mediated immune response of nestlings. This effect was not explained by a general improvement of body condition of chicks because it was independent of individual variation in body mass or tarsus length. Our results suggest that helping can have subtle effects on the quality of offspring that may influence their survival and future reproduction.

Sex determination of Iberian Azure-winged Magpies Cyanopica cyanus cooki by discriminant analysis of external measurements

Like all corvids, the Azure‐winged Magpie Cyanopica cyanus is sexually monomorphic in plumage, making it difficult to distinguish between males and females in the field. We examined sexual size dimorphism in a population of Iberian Azure‐winged Magpies C.c. cooki and used a discriminant function analysis based on five morphological characters to determine the sex of first‐year and adult individuals. Females were significantly smaller than males for all tested variables within each age class except for keel length of first‐year individuals. In both sexes, wing length of adults was greater than that of yearlings, but only males showed significant differences in tail length between age classes (longer in first‐year birds). Stepwise discriminant analysis indicated that tail length and head plus bill length were the most accurate variables in a discriminant function model, predicting the sex of yearlings with about 90% accuracy. Adding wing length to the model yielded the same level of accuracy for adults. We propose a simple system to sex Iberian Azure‐winged Magpies, using only two or three variables easily measured in the field, which provides classification with a high level of accuracy.

No brood parasitism by the Great Spotted Cuckoo Clamator glandarius on the Azure-winged Magpie Cyanopica cyanus

Capsule No case of parasitic interaction was found after 12 years of intensive monitoring of a marked population in Spain where both species are sympatric. Aims To evaluate whether the Azure-winged Magpie is parasitized, and suggest possible causes that affect its relationship with the Great Spotted Cuckoo. Methods Data from a long-term field study of marked individuals in a population of Azure-winged Magpie in Spain, were collected from about 60 nests per year over 12 years. Results Although common in the area, no eggs or young of the Great Spotted Cuckoo were found in an Azure-winged Magpie nest. Conclusion The Great Spotted Cuckoo does not appear to parasitize the Azure-winged Magpie, and we suggest that elevated predation rates on nests may be an important, overlooked factor potentially affecting the choice of host species by this brood parasite.

Exploratory behaviour modulates the relationship between colony familiarity and helping in a cooperative bird.

Individuals within animal groups may differ in personality and degree of familiarity raising the question of how this influences their social interactions. In Iberian magpies Cyanopica cooki, a portion of first-year males engage in cooperative behaviours and dispersal, allowing addressing this question. In this study, we first investigate the relationship between colony familiarity (native versus foreign) and reproductive status (breeding versus helping) of males during 21 years. Secondly, we measure the exploratory behaviour and monitor reproductive status of a sample of individuals with different colony familiarity during 2 years. Long-term monitoring revealed that foreign individuals were more likely breeders. The analysis on the subset of individuals in which exploratory behaviour was measured revealed a mediatory effect of exploratory behaviour in the association between colony familiarity and helping behaviour. Specifically, among foreign individuals, higher explorative males were more frequently involved in helping behaviour than lower explorative ones. Conversely, among native males, breeders were more explorative than helpers. Our results suggest that aspects of personality may mediate the value of familiarity in reproductive tasks in social species.