Testosterone and the dark ventral patch of male red deer: the role of the social environment

Abstract

The expression of male sexual traits, which is stimulated by testosterone, entails significant costs for individuals. Consequently, natural selection is expected to favour the modulation of sexual trait development according to the balance between its costs and benefits. The proportion of rivals in a population may affect this balance by increasing or decreasing the reproductive benefits associated with the development of sex traits. Here, we explore the relationship between testosterone level and sex-trait size under two populational conditions of mate competition: fenced (i.e. high male-male competition; all male age groups are present) and unfenced (i.e. low competition; most males present are juveniles). Our model species is the Iberian red deer (Cervus elaphus hispanicus) and the sex trait is the dark ventral patch that males exhibit during the rutting season. Our results showed that the positive relationship between testosterone levels and the size of the dark ventral patch depends on the environmental level of malemale competition. Only in populations where the operational sex ratio was high (i.e., high proportion of rival males), individuals with high levels of testosterone developed the sex trait. Conversely, when mate competition was low, there was no significant relationship between testosterone level and trait size. This result reinforces the idea that the effect of testosterone in promoting the development of sex traits may be mediated by the intensity of mate competition in the population, as well as the role of sexual selection in the evolution of the dark ventral patch in red deer. Keywords Dark ventral patch • Trait expression • Faecal testosterone metabolites •Male-male competition • Cervus elaphus hispanicus helpful comments. We thank the autonomous governments of Andalucía (Junta de Andalucía) and Extremadura (Junta de Extremadura) and the owners of the hunting estates that provided permissions and facilities for fieldwork. Jose Manuel Seoane and students from the University of Córdoba helped in fieldwork and samples collection.We are indebted to P. Capilla-Lasheras for his advice on the statistical approach.Funding: Financial support came from projects CGL2013-48122-P and CGL2016-77052-P to JC.

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

“…Males with larger antlers in HC environment showed low testosterone levels in agreement with the expectation, while variation in antler size and testosterone were higher among LC males. Results for the dark ventral patch in Iberian red deer populations showed a positive relationship between this trait and testosterone, but only in HC populations (de la Peña et al 61 ) Both results suggest that the relationship between testosterone and sex traits may be weaker when sexual competition is lower, but further research is needed.…”

Temporal and spatial dynamics of gastrointestinal parasite infection in Père David’s deer

“…The four measurements of parasites defined in this study were: (1) Prevalence, the number of hosts infected with one or more individuals of a particular parasitic species (or taxonomic group), divided by the number of hosts examined for that parasitic species ( Bush et al, 1997 ). (2) Parasite burden was estimated as the number of a parasitic form (oocysts, eggs or larvae) in a single faecal sample ( Bush et al, 1997 ; De la Peña et al, 2020a ). In this study the parasite burden was assessed by calculating the faecal oocyst or egg counts.…”

“…Parasite dynamics can be affected by abiotic factors (such as season and climatic conditions); for example, precipitation caused significant changes in the gastrointestinal parasites of eastern chimpanzees ( Gillespie et al, 2010 ) and temperature had a significant impact on the transmission of parasites in the gastrointestinal tracts of Arctic ungulates ( Kafle et al, 2018 ). Alpine chamois and red deer parasite burden was affected by various biotic factors, including reproduction and immune status ( Corlatti et al, 2012 ; De la Peña et al, 2020a ). The host often faces a life history trade-off between reproduction and immunity ( Corlatti et al, 2012 ; De la Peña et al, 2020a ).…”

“…Alpine chamois and red deer parasite burden was affected by various biotic factors, including reproduction and immune status ( Corlatti et al, 2012 ; De la Peña et al, 2020a ). The host often faces a life history trade-off between reproduction and immunity ( Corlatti et al, 2012 ; De la Peña et al, 2020a ).…”

The dark ventral patch: A bimodal flexible trait related to male competition in red deer

“…Regarding the frequency histogram of the dark ventral patch size (see Fig 1 ), we checked for unimodality or multimodality, estimating the distribution underlying this trait by Hartigans’ dip test using the package diptest [ 41 ]. In previous assessments, the frequency histogram of the size of the dark ventral patch showed a data gap in values between 40 and 50 cm [ 42 , 43 ]. Thus, we maintained here the cut point used in previous analyses that followed the distribution gap appearing in previous data sets, and defined two groups: low trait expression males, those that had between 0 and 50 cm of darkness area in their bellies, and those that had more than 50 cm, even the whole ventral area dark, high trait expression males.…”