A negative association between horn length and survival in a weakly dimorphic ungulate

Abstract

While all models of sexual selection assume that the development and expression of enlarged secondary sexual traits are costly, males with larger ornaments or weapons generally show greater survival or longevity. These studies have mostly been performed in species with high sexual size dimorphism, subject to intense sexual selection. Here, we examined the relationships between horn growth and several survival metrics in the weakly dimorphic Pyrenean chamois (Rupicapra pyrenaica). In this unhunted population living at high density, males and females were able to grow long horns without any apparent costs in terms of longevity. However, we found a negative relationship between horn growth and survival during prime age in males. This association reduces the potential evolutionary consequences of trophy hunting in male chamois. We also found that females with long horns tended to have lower survival at old ages. Our results illustrate the contrasting conclusions that may be drawn when different survival metrics are used in analyses. The ability to detect trade‐off between the expression of male secondary sexual traits and survival may depend more on environmental conditions experienced by the population than on the strength of sexual selection.

Brains vs Brawn: Relative brain size is sexually dimorphic amongst weapon-bearing ruminants

“…Across twenty-nine species and three weapon types (horns, tusks, antlers), as males evolved to invest relatively more than conspecific females in building larger weapons, they invested relatively less than conspecific females in building larger brains. Past studies support physiological and behavioral tradeoffs when males possess large, exaggerated weapons (e.g., reduced limbs (Emlen, 2001;Simmons & Tomkins, 1996), reduced efforts in nuptial gift giving (Liu et al, 2015), survival rate (Douhard et al, 2020;Garratt et al, 2015) or increased grooming time (Allen & Levinton, 2007;McCullough et al, 2020)) but this is the first study to show that males may suffer reductions in relative brain size for the development and maintenance of elaborate sexual weapons.…”

Is horn length crucial for Alpine chamois?

“…However, such studies have often failed to provide a full understanding of the actual benefits associated with larger weapons in these species. Only recently researchers have assumed that, in these species, weapon size has a reduced or null effect on life history traits, for example individual survival (Corlatti et al., 2017; Douhard et al., 2020), thus suggesting to downscale the role of size.…”