Large Male Advantage: Phenotypic and Genetic Correlates of Territoriality in Tuatara JENNIFER A. MOORE, 1 CHARLES H. DAUGHERTY, AND NICOLA J. NELSON Allan Wilson Centre for Molecular Ecology and Evolution, School of Biological Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand ABSTRACT.—In reptiles, phenotypic measures such as body size usually predict a male’s success in territorial interactions. Recent evidence from fish, birds, and mammals has shown that genetic heterozygosity also has a strong influence on competitive ability and territory quality. Here, we provide a comprehensive assessment of the social structure and factors affecting male territory quality and aggressive behavior in a dense population of Tuatara, a long-lived reptile that maintains long-term territories, on Stephens Island, New Zealand. The only significant predictor of female access and competitive ability was male body size, and there was no relationship between male body size or condition and individual genetic heterozygosity. Body size, body condition, and heterozygosity did not predict territory size. Also, heterozygosity, body condition, and territory size had no relationship with the number of females to which a male had access. Large males were more effective at (1) monopolizing areas where females were most dense and (2) guarding females by consistently winning aggressive encounters with other males. Our finding of no relationship between territoriality and heterozygosity probably reflects the genetic background of this large, outbred population or that behavioral attributes or neutral heterozygosity are not appropriate individual fitness correlates for these long-lived reptiles. Knowing the factors that affect individual success in territorial interactions is a critical first step in understanding the evolution of mating systems and reproductive strategies. Territori- ality is common in many reptiles (particularly lizards, reviewed in Stamps, 1983), but most studies cite the distribution of ecological attri- butes, such as habitat characteristics and food quantity, as the driving force behind the observed spatial structure (Maher and Lott, 2000). Food resources in many territorial reptile species are evenly distributed; many females nest outside of breeding territories; and paternal care is absent. Territory structure and quality may depend more on the distribution of mates and competitors than on other ecological attri- butes (Stamps, 1983). However, few studies consider the distribution of potential mates as the driving force (Stamps, 1983; Stamps, 1994) because conspecific interactions are often diffi- cult to observe and quantify in cryptic species (but see M’closkey et al., 1987; Wikelski et al., 1996). For many vertebrates, including reptiles, male phenotypic measures, such as body size or condition, predict territory size and access to females (e.g., Shine et al., 2000; Candolin and Voigt, 2001; Va ¨ lima ¨ ki et al., 2007). Consequent- ly, these characteristics could result in a bias in reproductive success toward larger males (Abell, 1997; Lewis et al., 2000; Lebas, 2001). Where dominance hierarchies are formed, it is the smaller males that assume subordinate roles or adopt alternative reproductive strategies (e.g., ‘‘satellites’’ or ‘‘floaters,’’ Andersson, 1994; Maher and Lott, 1995). Male phenotypic measures are not the only predictors of territory quality. Genetic hetero- zygosity, a measure of inbreeding, affects standard fitness measures such as survival, hatching success, and disease resistance (e.g., Hansson and Westerberg, 2002; Keller and Waller, 2002; Reed and Frankham, 2003). Grow- ing evidence shows that genetic heterozygosity can also have an indirect effect on competitive behavior and territoriality (Ho ¨glund et al., 2002; Tiira et al., 2003; Lieutenant-Gosselin and Bernatchez, 2006). Seddon et al. (2004) found that heterozygosity was the best predictor of territory quality in a group living bird (Monias benschi). Likewise, individual competitive abil- ity is more strongly correlated with heterozy- gosity than body size or learning in Common Shrews (Sorex araneus; Va ¨ lima ¨ki et al., 2007). In many fish, birds, and mammals, acquisition of seasonal breeding territories is critical for individual survival and fitness. These examples provide strength for the argument that aggres- siveness and territoriality are reliable fitness correlates. In this study, we investigate the social structure and individual male territoriality in 1 Corresponding Author. E-mail: moore.jennifer@ gmail.com Journal of Herpetology, Vol. 43, No. 4, pp. 570–578, 2009 Copyright 2009 Society for the Study of Amphibians and Reptiles