UMD BIOL 608W - Helpers increase the reproductive potential of offspring in cooperative meerkats

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Helpers increase the reproductive potential of offspring in cooperative meerkatsIntroductionMaterial and methodsHelper effects on lifetime reproductive probabilityHelper effects on underlying life-history traitsThe mechanism of helper effectsStatistical analysesResultsHelper effects on lifetime reproductive probabilityHelper effects on underlying life-history traitsThe mechanism of helper effectsDiscussionWe thank Mr and Mrs H. Kotze and the Northern Cape Conservation Services for permission to work at Rus en Vrede; M. Haupt, J. du Toit, E. Cronje (University of Pretoria) and P. Roth (University of Cambridge) for logistical help; G. McIlrath, L. Sharpe,...Referencesdoi: 10.1098/rspb.2006.3698, 513-520274 2007 Proc. R. Soc. B A.F Russell, A.J Young, G Spong, N.R Jordan and T.H Clutton-Brock cooperative meerkatsHelpers increase the reproductive potential of offspring in Supplementary datamlhttp://rspb.royalsocietypublishing.org/content/suppl/2009/03/12/274.1609.513.DC1.ht "Data Supplement"Referenceshttp://rspb.royalsocietypublishing.org/content/274/1609/513.full.html#related-urls Article cited in: http://rspb.royalsocietypublishing.org/content/274/1609/513.full.html#ref-list-1 This article cites 29 articles, 8 of which can be accessed freeEmail alerting service hereright-hand corner of the article or click Receive free email alerts when new articles cite this article - sign up in the box at the top http://rspb.royalsocietypublishing.org/subscriptions go to: Proc. R. Soc. BTo subscribe to This journal is © 2007 The Royal Society on February 17, 2010rspb.royalsocietypublishing.orgDownloaded fromHelpers increase the reproductive potentialof offspring in cooperative meerkatsA. F. Russell1,*, A. J. Young2, G. Spong2,3, N. R. Jordan2and T. H. Clutton-Brock2,41Department of Animal & Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK2Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK3Department of Ecology, Uppsala University, Norby 18, 75236 Uppsala, Sweden4Mammal Research Institute, University of Pretoria, Pretoria 0002, Republic of South AfricaIn both animal and human societies, individuals may forego personal reproduction and provide care to theoffspring of others. Studies aimed at investigating the adaptive nature of such cooperative breeding systemsin vertebrates typically calculate helper ‘fitness’ from relationships of helper numbers and offspring survivalto independence. The aim of this study is to use observations and supplemental feeding experiments incooperatively breeding meerkats, Suricata suricatta, to investigate whether helpers influence the long-termreproductive potential of offspring during adulthood. We show that helpers have a significant and positiveinfluence on the probability that offspring gain direct reproductive success in their lifetimes. This effectarises because helpers both reduce the age at which offspring begin to reproduce as subordinates andincrease the probability that they will compete successfully for alpha rank. Supplemental feedingexperiments confirm the causality of these results. Our results suggest that one can neither discount thesignificance of helper effects when none is found nor necessarily estimate accurately the fitness benefit thathelpers accrue, unless their effects on offspring are considered in the long term.Keywords: early conditions; helper effects; fitness; kin selection; lifetime reproductive success1. INTRODUCTIONUnderstanding the evolution of cooperative breedingsystems, wherein individuals help to rear offspring thatare not their own, relies fundamentally on understandingthe fitness benefits that individuals accrue from helping. Inthe majority of studies on cooperative vertebrates,estimations of helper fitness have been based on theeffects of helper number/investment on offspring survivalto independence (Emlen 1991; Jennions & Macdonald1994; Cockburn 1998; Russell 2004). However, recentevidence from non-cooperative vertebrate species hasrevealed that levels of parental investment not onlyinfluence the survival of dependent offspring, but alsotheir reproductive potential and longevity during adult-hood (Lindstro¨m 1999; Lummaa & Clutton-Brock 2002).Such findings are of importance to our understanding ofthe adaptive nature of vertebrate cooperative breedingsystems, because helper investment can rival or evensucceed the importance of parental investment as theprimary determinant of offspring growth and condition(Hatchwell 1999). If helpers also have long-term survivaland reproductive consequences for the offspring that theyhelp to rear, then calculations of helper fitness based onshort-term measures of offspring survival during depen-dence could lead to underestimations of the fitnessbenefits that individuals accrue from helping, and areduced understanding of the strength of selection on,and the evolution of, breeding cooperatively.The potential for helpers to have positive effects onoffspring beyond the age at which those offspring reachindependence is clear. In humans (Lahdenpera¨ et al.2004) and long-tailed tits, Aegithalos caudatus (Hatchwellet al.2004), non-breeding grandmothers and failed-breeding adults, respectively, are associated with anincrease in the probability that independent offspringsurvive to adulthood. Indeed, the study by Hatchwell et al.(2004) is of particular note because they failed to detect aneffect of helpers on the number of offspring raised toindependence. While other studies have used similarfindings to question the adaptive nature of helping,Hatchwell et al. (2004) found that, by improving offspringmass at fledging, helpers have dramatic effects on theprobability that independent offspring survive to breed.However, whether helpers additionally influence thereproductive potential of offspring that reach adulthood(as studies on non-cooperative vertebrates would suggest)has not been considered previously, although Solomon(1991) demonstrated that helpers influence the weight ofoffspring at weaning in prairie voles (Microtus ochrogaster),and that heavy offspring are preferred as social matesduring adulthood (Solomon 1993) and are more fecund asbreeders (Solomon 1994). The overall aim of this study istherefore to use observational and supplemental feedingdata in free-ranging meerkats (Suricata suricatta)toinvestigate the effect of helpers on the lifetime reproduc-tive success of offspring in a cooperative vertebrate.Meerkats are small (less than 1 kg)


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