Determinants of immigration strategies in male crested macaques (Macaca nigra).

Pascal R Marty,Antje Engelhardt,Muhammad Agil,Keith Hodges

doi:10.1038/srep32028

Abstract

Immigration into a new group can produce substantial costs due to resistance from residents, but also reproductive benefits. Whether or not individuals base their immigration strategy on prospective cost-benefit ratios remains unknown. We investigated individual immigration decisions in crested macaques, a primate species with a high reproductive skew in favour of high-ranking males. We found two different strategies. Males who achieved low rank in the new group usually immigrated after another male had immigrated within the previous 25 days and achieved high rank. They never got injured but also had low prospective reproductive success. We assume that these males benefitted from immigrating into a destabilized male hierarchy. Males who achieved high rank in the new group usually immigrated independent of previous immigrations. They recieved injuries more frequently and therefore bore immigration costs. They, however, also had higher reproductive success prospects. We conclude that male crested macaques base their immigration strategy on relative fighting ability and thus potential rank in the new group i.e. potential reproductive benefits, as well as potential costs of injury.

Highlights

In gregarious species, dispersal of individuals evolved as a consequence of selective pressures from within group competition and inbreeding avoidance[1,2,3]
A change-point analysis revealed that immigrations occurred non-randomly with 74% of all males immigrating within 25 days of another male (Fig. 1)
Our results show that immigrations by male crested macaques typically occur during immigration periods whereby several males immigrate around the same time

Summary

Introduction

Dispersal of individuals evolved as a consequence of selective pressures from within group competition and inbreeding avoidance[1,2,3]. In species in which male mating competition is mostly scrambled and male reproductive skew low, male rank is of relatively little and the number of females in a group of relatively high importance for a male’s individual reproductive success Dispersing males of such species are supposed to base their decision on a group’s sex ratio rather than on the characteristics of group males[33]. In species with high reproductive skew, escalated fights are common and costs of immigration in terms of injuries high (e.g. Hanuman langurs, Semnopithecus entellus[33,35]) In these species, males can be expected to develop strategies that potentially reduce immigration costs

Methods

Results

Conclusion