Social environment modulates investment in sex trait versus lifespan: red deer produce bigger antlers when facing more rivalry.

Theory predicts that the plastic expression of sex-traits should be modulated not only by their production costs but also by the benefits derived from the presence of rivals and mates, yet there is a paucity of evidence for an adaptive response of sex-trait expression to social environment. We studied antler size, a costly and plastic sex trait, and tooth wear, a trait related to food intake and longevity, in over 4,000 male Iberian red deer (Cervus elaphus hispanicus) from 56 wild populations characterized by two contrasting management practices that affect male age structure and adult sex-ratio. As a consequence, these populations exhibit high and low levels of male-male competition for mating opportunities. We hypothesized that males under conditions of low intra-sexual competition would develop smaller antlers, after controlling for body size and age, than males under conditions of high intra-sexual competition, thus reducing energy demands (i.e. reducing intake and food comminution), and as a consequence, leading to less tooth wear and a concomitant longer potential lifespan. Our results supported these predictions. To reject possible uncontrolled factors that may have occurred in the wild populations, we carried out an experimental design on red deer in captivity, placing males in separate plots with females or with rival males during the period of antler growth. Males living with rivals grew larger antlers than males living in a female environment, which corroborates the results found in the wild populations. As far as we know, these results show, for the first time, the modulation of a sexual trait and its costs on longevity conditional upon the level of intra-sexual competition.

Phylogenetic analysis of stomach adaptation in digestive strategies in African ruminants.

The stomach morphology of 28 species of artiodactyls that differ in feeding style (browser, mixed feeder, grazer) was analysed using a multivariate approach and phylogenetic correction in order to test whether stomach morphology was correlated with feeding style when body mass was controlled for. A total of 25 morphological traits of the stomach were used in the analysis. After the effects of body mass and phylogeny on stomach morphology were taken into account, there was no significant grouping of species according to feeding style. When information about the feeding style of each species was included in the analysis, the set of morphological traits separated the mixed feeders from the other two feeding styles, but grazers and browsers had similar morphological features. Most of the variance in stomach morphology was explained by body mass and a lesser proportion by phylogeny. The main morphological features that have previously been proposed as being adaptations in grazing species, namely, lengthening of the retention time of ingesta to achieve an increase in their fibre digestion capability by means of a larger relative stomach capacity, a greater subdivision of chambers and smaller openings, are not supported by the findings of this study. Thus, there is no consistent evidence to support a significant adaptive effect of stomach morphology to different diets in the Artiodactyla.