Delayed benefits for fallow bucks: more fights decrease same day mating success, but may increase matings the next day

Abstract

Dominance hierarchies help to reduce unnecessary fights and associated costs during the mating season. Fallow deer (Dama dama) typically have high levels of male-male competition and strong reproductive skew. Nevertheless, how male dominance and daily fight rates affect mating success remains unknown. We used a two-year dataset from a large population of tagged fallow deer (620-689 individuals), to calculate male dominance ranks based on their agonistic interactions prior to the mating season ( prerut), in order to then examine how rank is related to fight rates and mating success during the mating season ( rut). Overall, higher-ranked males fought at least twice a day on a higher proportion of days during the rut and secured more matings. Males engaging in more than 10 fights per day were less likely to secure a mating that same day, and those males exceeding 15 fights per day secured no matings at all. Nevertheless, males with the highest numbers of fights (i.e. 15-21 fights per day) on a given day had higher mating success on subsequent days. Although higher-ranked males secured most matings during the rut, their fight rates decreased towards the end. We propose that engaging in more fights negatively affects daily individual mating success, but may benefit mating success on subsequent days, and potentially increase long-term fitness benefits. Additionally, engaging in more fights as the rut progresses probably allows lower-ranked males to secure some matings before the availability of oestrous females ends for almost a year. SIGNIFICANCE STATEMENTFighting carries a risk of injury and high energetic costs. Male fallow deer establish dominance hierarchies, that help reduce unnecessary fights among individuals of different competitive abilities. However, whether high-ranked males fight more or less is yet unknown. By calculating social ranks of fallow bucks before the start of their mating period, we show that males of higher social status do fight and mate more during the mating season (rut). Furthermore, by investigating how investment in fights affects individual mating success that same day and the next day, we find that males that fight more cause a decrease in their immediate daily mating success, but can potentially increase their chances of mating in subsequent days. Thus, to fight more may allow males to climb the hierarchical social ladder, hence increasing longer-term fitness benefits associated to higher ranks.