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1 This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institutionand sharing with uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal , institutional or third partywebsites are most cases authors are permitted to post their version of thearticle ( in Word or Tex form) to their personal website orinstitutional repository. authors requiring further informationregarding Elsevier s archiving and manuscript policies areencouraged to visit: 's personal copyAnother genetically promiscuous polygynous mammal: mating systemvariation inNeotoma McEacherna,*, Richard L.

2 McElreathb,1, Dirk H. Van Vurena,2, John M. Eadiea,2aDepartment of Wildlife Fish and Conservation Biology, University of California, DavisbDepartment of Anthropology, University of California, Davisarticle infoArticle history:Received 29 July 2008 Initial acceptance 4 September 2008 Final acceptance 17 October 2008 Published online 6 December 2008MS. number: A08-00486 Keywords:dusky-footed woodratgenetic mating systemmonogamyNeotoma fuscipespromiscuityparentage analysisPolygyny is widely thought to be the dominant mating system in mammals. However, more recentgenetic work casts doubt on this view. Variation in mating systems has been found in both males andfemales within and across mammalian species. The causes and consequences of mating system variationhave important implications for understanding the population and evolutionary dynamics of species.

3 Tobetter understand mating system variation, both in mammals and more generally, this study analysesgenetic mating system variation in dusky-footed woodrats,Neotoma fuscipes. Contrary to expectation,there was little support for polygyny at the genetic level. Instead, the study populations were charac-terized by promiscuity and monogamy, in both males and females. At higher densities, variance in thenumbers of mates and offspring were higher in breeding males than in females, as is often , this trend was reversed in low-density, coniferous forest habitat. Model selection revealed thatthe best model of successfully mated pairs includes population density, operational sex ratio and indi-vidual pairwise distances as predictors.

4 Higher densities coupled with male-biased sex ratios appear todecrease the probability of mating and decrease opportunities for polygamy, particularly in woodrats display sexual size dimorphism, male body size had no detectable effect on matingsuccess. This study questions the prevalence of polygyny in mammals and demonstrates the need formore detailed, genetic investigations of mating systems. Future studies are needed to explore thecomplex interactions among mating system determinants and test hypotheses of sex-specific matingsystem variation. 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights of mating influence the amount of genetic variation,strength of sexual selection and overall rate of evolution in pop-ulations (Wright 1951; Bush et ; Emlen & Oring 1977; Bessa-Gomes et al.)

5 2004). One evolutionarily important contrast is thedistinction between polygyny and promiscuity. Polygyny, a matingsystem in which single males monopolize and exclusively matewith multiple females, has very different population geneticconsequences than a promiscuous mating system, defined asa mating system in which both males and females mate non-exclusively with multiple partners in a breeding season. A strictlypolygynous mating system increases genetic relatedness withingroups, reduces the effective population size (Ne), and increasesgenetic differentiation among groups relative to monogamous orpromiscuous mating systems. These differences have importantimplications for our understanding of how mating system variationinfluences population viability and evolution via kin and sexualselection (Sugg et al.

6 1996; Parker & Waite 1997).Given its evolutionary importance, the empirical literature onmating system variation (MSV) is highly incomplete. Observationalstudies of mating systems have often focused on males (Clutton-Brock 1989; Shuster & Wade 2003), in particular, their ability tomonopolize and control access to multiple resources and matesunder variable environmental conditions. While such studies havesignificantly advanced our understanding of mating systems,revealing their inherent flexibility both temporally and spatially,within and among species, there is a relative lack of data fromcryptic, solitary mammals that are difficult to study addition, the female perspective has often been overshadowedby a male-dominated focus, resulting in a relative paucity ofinformation on the determinants of female MSV and matingsuccess (Clutton-Brock 1989; Wolff & Macdonald 2004).

7 Despite these gaps in knowledge, the idea that polygyny is thepredominant mating system in mammals continues to pervade theliterature (Krebs & Davies 1993; Birkhead 2000; Storz et al. 2001;Eberle & Kappeler 2004). It remains unclear whether this idea will*Correspondence and present address: M. B. McEachern, Department ofAnthropology, University of Utah, Salt Lake City, UT 84112, McEachern).1 Richard L. McElreath is in the Graduate Group in Ecology, Department ofAnthropology, University of California, Davis, CA 95616, H. Van Vuren & John M. Eadie are in the Graduate Group in Ecology,Department of Wildlife Fish and Conservation Biology, University of California,Davis, CA 95616, lists available atScienceDirectAnimal Behaviourjournal homepage: $ 2008 The Association for the Study of Animal Behaviour.

8 Published by Elsevier Ltd. All rights Behaviour 77 (2009) 449 455 Author's personal copyhold once females are fully integrated into mating system theoryand a more complete inventory of species is (1989)noted the lack of data on females and on solitarymammals, which make up a large portion of mammalian , solitary females may be more difficult to monopolize thansocial gregarious ones, and recent studies have pointed out theways in which females, solitary or gregarious, can benefit frommating with multiple partners (Soltis & McElreath 2001; Wolff &Macdonald 2004). Thus, a more thorough investigation of matingsystems with detailed genetic data on both male and female matingsuccess could reveal that promiscuity is more common in mammalsthan previously thought.

9 Indeed, behavioural ecologists studyingsolitary rodents have long suspected that promiscuity characterizesthe mating systems of their subjects (Waterman 2007), but thegenetic evidence to support this claim has been sparse. Moreevidence is mounting, however, with a recent review suggestingthat promiscuous mating in mammals is quite common, occurringin 133 species, 33 families and 9 orders (Wolff & Macdonald 2004).To generate a better understanding of MSV in females and theextent to which polygyny characterizes mammalian matingsystems, we used spatial and genetic data to investigate male andfemale mating behaviour in the dusky-footed woodrat,Neotomafuscipes. Dusky-footed woodrats are solitary, nocturnal rodents(200 350 g) that build conspicuous stick houses in the coastal andmountainous regions of northern California.

10 Male-biased dispersalcoupled with spatial clusters of related females, or matrilines, arethought to generate a predominantly polygynous mating system inthe genusNeotoma(Kelly 1989). However, monogamy, promiscuityand polyandry have been reported anecdotally (Linsdale & Tevis1951; Kelly 1989). Observational studies of woodrats suggest thatfemales tend to mate with spatially proximate males that overlap inhome range. However, the extent to which observational studiesreliably predict MSV inN. fuscipeshas not been verified withgenetic test for ecological and demographic correlates of MSV inwoodrats, we studied woodrats in three distinct habitats thatsupported different spatial distributions, densities and sex , we examined the degree to which differences in thesevariables affect the number of mates with which individualssuccessfully breed, from both the male and female a maximum likelihood model selection approach andfollowingEmlen & Oring s (1977)ecological framework, we testedthe general prediction that clumped spatial distributions, increasedpopulation densities and biased sex ratios increase frequencies ofpolygamous matings (polygyny, promiscuity, polyandry).