Sexual size dimorphism of group-living Mongolian gerbils Meriones unguicutalus (Muridae: Gerbillinae)

Abstract

Polygynous mammals often have male-biased sexual size dimorphism due to male-male competition for mates. However, fecundity selection may enlarge female body size. The Mongolian gerbil Meriones unguiculatus (Milne-Edwards, 1867) is a social rodent of promiscuous mating. Male gerbils exhibit social dominance hierarchy, which may differentiate reproductive success among male gerbils with larger males having more reproductive opportunities. This study investigated the hypothesis that social dominance hierarchy would result in male-biased sexual size dimorphism in Mongolian gerbils. We also tested the prediction of fecundity selection, that litter size would be positively related to female body mass of Mongolian gerbils. Body mass, carcass weight and body length of male gerbils were greater than those of females. Therefore, male-biased sexual size dimorphism was supported in Mongolian gerbils. Although litter size of female gerbils increased with increasing carcass weight, ecological constraints (e.g. burrow living and increased energy expenditure during pregnancy) probably kept female body size smaller than male body size of the gerbil. Social interactions may mediate sexual and fecundity selections on the body size of social rodents.

Not playing by the rules: mixed support of ecogeographic rules in an arid‐adapted African ground squirrel

“…Consistent with our results, Matějů & Kratochvíl (2013) tested Rensch's rule in 63 species of ground squirrels (excluding the Cape ground squirrel) and found that ground squirrels generally do not conform to Rensch's rule, nor do they feature high degrees of sexual dimorphism overall. The relatively constant degree of sexual dimorphism, in Cape ground squirrels and other species of ground squirrel, may be attributable to the need for males to be able to fit into burrows dug by females (Matějů & Kratochvíl, 2013; Martínez & Bidau, 2016; Wang, 2017), for refuge or to copulate with females. Similarly, Wang (2017) suggests that female Mongolian gerbils ( Meriones unguicutalus ) may have smaller body sizes than their male conspecifics allowing them to fit into burrows dug by males.…”

“…The relatively constant degree of sexual dimorphism, in Cape ground squirrels and other species of ground squirrel, may be attributable to the need for males to be able to fit into burrows dug by females (Matějů & Kratochvíl, 2013; Martínez & Bidau, 2016; Wang, 2017), for refuge or to copulate with females. Similarly, Wang (2017) suggests that female Mongolian gerbils ( Meriones unguicutalus ) may have smaller body sizes than their male conspecifics allowing them to fit into burrows dug by males. Thus, for semi‐fossorial or fossorial species, burrowing may constrain sexual size dimorphism (Martínez & Bidau, 2016).…”

Sexual dimorphism in external morphology and pelvis of the lesser bandicoot rat, Bandicota bengalensis (Gray, 1835) (Mammalia: Rodentia: Muridae)

“…Moreover, females are less active and are observed gathering food in holes (Parrack and Thomas, 1970). Females with small body sizes could be able to reach small burrows, especially during pregnancy (Gliwicz, 1988;Wang, 2017).…”