Promiscuous tendencies in the round-eared sengi: a male’s perspective

Abstract

Although monogamy is interpreted as riskadverse strategy by reducing intra-sexual conflicts, most pair-living males increase their reproductive success by engaging in extra-pair copulations. However, little is known about costs involved in such extra-pair attempts from the male's perspective. We investigated promiscuous tendencies of paired Macroscelides proboscideus (roundeared elephant-shrew or round-eared sengi), a pair-living small mammal occurring in southern Africa. In particular, we measured potential costs of extra-pair attempts for the males. For this, we conducted laboratory experiments, involving interactions between neighbouring male-female pairs. Data collection included direct behavioural observations and establishing the morphological and physiological characteristics of males. Both sexes intruded into the neighbouring area, and initiated sexual behaviour with neighbours of the opposite sex. Males which displayed a higher marking frequency in the neighbouring area received more sexually motivated behaviour from neighbouring females. Resident males attacked intruding males. Aggression experienced by and marking behaviour of intruding males was positively correlated with body mass losses. Furthermore, glucocorticoid levels, determined from analyses of faeces and urine samples, correlated positively with body mass losses and marking behaviour of intruding males, indicating costs of intruding. We conclude that male as well as female round-eared sengis have promiscuous tendencies. Although interactions with neighbouring females may offer potential benefits for males in terms of enhanced reproductive success, males also seem to pay substantial costs, as indicated by body mass losses and elevated stress hormone levels.

Revisiting the components of Macroscelidea social systems: Evidence for variable social organization, including pair‐living, but not for a monogamous mating system

“…A male Rhynchocyon chrysopygus chased the female and then copulated with her during 2 s with five rapid copulations. Schubert et al (2012) found in captive experiments that female Macroscelides proboscideus showed as many sexual interactions with a neighboring male as with her pair partner, and that males actively aimed to mate with non‐pair neighboring females. In an unpublished poster on a study using micro‐satellites to determine paternity in Macroscelides proboscideus , Peffley et al (2009) found for the population studied by Schubert et al (2009) that only two out of six mother‐offspring families resulted from serially monogamous mating.…”

“…Moreover, both sexes defend a territory and are very aggressive towards conspecifics of the same sex (FitzGibbon, 1997; Rathbun, 1979). Schubert et al (2012) found in captive experiments no evidence for pair‐bonding, but individuals of both sexes readily interacted with opposite sex conspecifics with which they were not paired.…”

“…In several species, aggression towards young was observed around weaning. Some species tolerated their weaned offspring for periods ranging from 21 to 40 days old (Rathbun, 1979; Schubert et al, 2012) while in Elephantulus rufescens , parents tolerated one of their young for the entire period of 193 days. In Elephantulus rufescens , some offspring can remain in their parents’ territory long after reaching adulthood (Rathbun, 1979).…”

“…In Macroscelidea, individuals of a pair spend little time together (Fitzgibbon, 1997; Koontz & Roeper, 1983; Rathbun, 1979) apart from the period when the female is receptive (Fitzgibbon, 1997; Schubert et al, 2012). This represents the behavioral pattern of many solitary living species (Schülke & Kappeler, 2003).…”

“…Females defend territories against other females and males against other males (Rathbun, 1979). Mate guarding has been observed in several elephant‐shrew species (FitzGibbon, 1997; Rathbun, 1979; Sauer, 1973; Schubert et al, 2012). This tactic consists of a male keeping within a short distance to a female as long as she is receptive, possibly to prevent male competitors to have access to that female (Huck et al, 2004).…”