Causes and Consequences of Cooperative Construction in the Mice Mus spicilegus and Peromyscus polionotus

Abstract

The cooperative construction of shared dwellings is a phylogenetically-widespread evolutionary puzzle. Shared shelters are common goods – all individuals in the shelter benefit, at the expense of those individuals that contribute to the construction. The evolution of cooperation requires existing variation for selection to act upon and genetic benefits to cooperators, through inclusive fitness or direct rewards. This study focuses on two genera of mice, Mus and Peromyscus, to examine shared construction and social monogamy as potential transitions to more sophisticated forms of sociality, such as cooperative breeding. The mound-building mouse (Mus spicilegus) is named for the large mounds that groups of mice build and beneath which they overwinter. Variation in mtDNA and 14 microsatellites show limited genetic structure across the geographic range of M. spicilegus. Mice from the same mound are more genetically related than mice from different mounds, and males and females associated with a mound are equally likely to be relatives. However in spring, when breeding begins, male kin are more likely to share a territory than are female kin. One possible interpretation is that males associate with kin to minimize the costs of being cuckolded, as this study finds evidence of multiple paternity in every litter genotyped. By increasing the chances of the cuckold being a brother, a male still gains inclusive fitness benefits from paternal care to extra-pair offspring in this socially monogamous species. Behavioral experiments show that another socially monogamous mouse species, the oldfield mouse (Peromyscus polionotus), can coordinate construction with unfamiliar, unrelated conspecifics. In contrast, two other closely related Peromyscus species do not dig longer burrows in pairs than they would have as individuals. Male-female P. polionotus pairs tend to dig longer burrows than pairs of the same sex, but males within opposite sex pairs do most of the digging, particularly when paired with an unfamiliar female. Male burrowing could be the product of female choice in this monogamous species. In M. spicilegus and P. polionotus, shared parental care and construction shed light on the evolution of cooperation and conflict.