Does selection on horn length of males and females differ in protected and hunted populations of a weakly dimorphic ungulate?

Abstract

Weaponry in ungulates may be costly to grow and maintain, and different selective pressures in males and females may lead to sex‐biased natural survival. Sexual differences in the relationship between weapon growth and survival may increase under anthropogenic selection through culling, for example because of trophy hunting. Selection on weaponry growth under different scenarios has been largely investigated in males of highly dimorphic ungulates, for which survival costs (either natural or hunting related) are thought to be greatest. Little is known, however, about the survival costs of weaponry in males and females of weakly dimorphic species. We collected information on horn length and age at death/shooting of 407 chamois Rupicapra rupicapra in a protected population and in two hunted populations with different hunting regimes, to explore sexual differences in the selection on early horn growth under contrasting selective pressures. We also investigated the variation of horn growth and body mass in yearling males (n = 688) and females (n = 539) culled in one of the hunted populations over 14 years. The relationship between horn growth and survival showed remarkable sexual differences under different evolutionary scenarios. Within the protected population, under natural selection, we found no significant trade‐off in either males or females. Under anthropogenic pressure, selection on early horn growth of culled individuals showed diametrically opposed sex‐biased patterns, depending on the culling regime and hunters’ preferences. Despite the selective bias between males and females in one of the hunted populations, we did not detect significant sex‐specific differences in the long‐term pattern of early growth. The relationship between early horn growth and natural survival in either sex might suggest stabilizing selection on horn size in chamois. Selection through culling can be strongly sex‐biased also in weakly dimorphic species, depending on hunters’ preferences and hunting regulations, and long‐term data are needed to reveal potential undesirable evolutionary consequences.

Hunting and evolution: theory, evidence, and unknowns

“…A similar analysis for female chamois, however, found no evidence of selection against individuals with rapidly-growing horns (Rughetti & Festa-Bianchet 2011). In another study of chamois, Corlatti et al (2017) found that early horn growth had strong effects on age at harvest for both sexes where hunters faced few restrictions or age preferences. Effects were weak for males in an area in Austria where hunters mostly harvested old males, and nonexistent for females in an area in Italy with restrictions on harvesting lactating females.…”

“…Red deer management in Hungary, and in central Europe in general, does not strongly select against largeantlered males and includes culling of males with small antlers, which could compensate for a possible evolutionary effect of trophy hunting (Mysterud & Bischof 2010). Decreases in both horn length and mass have been reported for hunted populations of chamois (Rughetti & Festa-Bianchet 2012, Mason et al 2014, Corlatti et al 2017) but those decreases appear more likely due to climate change than to selective hunting. Horn size appears to play a limited role in chamois male mating success (Corlatti et al 2015).…”

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

“…In chamois, if trophy hunting partly reflects natural mortality, this species would be less susceptible to evolutionary consequences of selective harvesting. Temporal declines in both horn length and body mass reported in several populations of chamois (Corlatti et al, ; Mason, Willis, Chirichella, Apollonio, & Stephens, ; Rughetti & Festa‐Bianchet, ) appear to be caused by climate change, rather than selective hunting.…”

“…Density is particularly high in our population of chamois that has been at or close to carrying capacity since the 1980s. A recent study found no significant effect of early horn growth (L1–L2) on longevity in a protected population of Alpine chamois (Corlatti et al, ), possibly because population density relative to resource levels was not high enough. Our results also show that longevity does not necessarily capture the mortality pattern during early adulthood.…”

“…Few studies have investigated similar relationships in species with low sexual size dimorphism, possibly because limited horn length is unlikely to impose major energetic costs. However, recent studies in the weakly dimorphic Alpine chamois ( Rupicapra rupicapra ) showed nonsignificant trends toward decreased longevity with increasing horn growth in males and females (Bleu, Loison, & Toïgo, ; Corlatti, Storch, Filli, & Anderwald, ). Such relationships may be stronger in populations experiencing poor environmental conditions, as reported for survival costs of reproduction (Cohen, Coste, Li, Bourg, & Pavard, ).…”