INTRODUCTION

Why males should mate exclusively with one partner and after mating abstain from searching for additional females is difficult to understand in mammalian species, and several hypotheses have been proposed to explain the evolution of monogamy (Clutton-Brock, 1989). Widely accepted explanations for the evolution of monogamy in mammals include female dispersion, with female ranges being too large or too dispersed to allow males to defend more than one female, or the need for biparental care (e.g., Kleiman, 1977; Wittenberger & Tilson, 1980; Kleiman & Malcolm, 1981; Clutton-Brock, 1989). However, a recent phylogenetic analysis indicates that monogamy evolved significantly more often in the absence of paternal care than in its presence (Komers & Brotherton, 1997). Females were not widely dispersed and obligate monogamy without paternal care was found in a small antelope (Kirk's dik-dik, Madoqua kirki: Brotherton & Rhodes, 1996; Komers, 1996; Brotherton & Komers, chapter 3).

Biparental care appears to improve offspring survival in most monogamous fish (Barlow, 1984), birds (Lack, 1968; Wittenberger & Tilson, 1980), and mammals (Kleiman, 1977; Clutton-Brock, 1989). For example, substantial improvement in offspring survival was found in the monogamous, biparental California mouse (Peromyscus californicus: Gubernick & Teferi, 2000) and in the obligate monogamous Djungarian hamster (Phodopus campbelli: Wynne-Edwards, 1987). It is generally assumed that the fitness benefits gained by pair-living males should outweigh the costs of lost mating opportunities (Trivers, 1972; Kleiman & Malcolm, 1981).