Preference for Local Mates in a Recently Diverged Population of the Lesser Earless Lizard (Holbrookia maculata) at White Sands

—When divergent selection favors different phenotypes in different environments, a preference for resident mates can help ensure that offspring are well suited to local conditions, thus increasing an individual’s lifetime fitness. Here I use both field and laboratory experiments to investigate the potential for mate choice in a unique color morph of the Common Lesser Earless Lizard, Holbrookia maculata, which inhabits the gypsum dune fields of White Sands in southern New Mexico. I demonstrate that light-colored H. maculata, which have evolved within the last 6,000 years, can discriminate between potential mates. In the field, simultaneous choice experiments revealed that White Sands males in their natural habitat courted females from White Sands sooner than females from a nearby population occupying dark substrate. The use of paint treatments to reverse female dorsal coloration showed that male choice was not based on dorsal coloration alone, if at all. The only variable measured in field trials that correlated strongly with male courtship behavior was female display activity. Resident females displayed in more trials than nonresident females, and males preferentially courted actively displaying females suggesting that behavioral cues may be important in this system. In the lab, sequential choice experiments on an intermediate substrate color showed that preference for local mates was reciprocal, with males of both color morphs preferentially addressing courtship behavior to potential mates from their same locality. By integrating field and lab experiments, I demonstrate that male preference for local mates in the recently diverged White Sands population is robust to experimental design. Although mate choice is common for many groups of vertebrates, (e.g., Andersson, 1994; Ptacek, 2000), choosiness appears to be less widespread for squamates (lizards and snakes) (Tokarz, 1995). A number of studies have looked for and failed to find any evidence for mate choice in this group (e.g., Olsson, 2001; Lailvaux and Irshick, 2006). However, even without direct parental care, costs associated with reproduction for female squamates can be high because of increased predation and compromised overall body condition (Angilletta and Sears, 2000; Miles et al., 2000; Webb, 2004). Although female choice is certainly not as ubiquitous for squamates as for other vertebrates, theoretical (e.g., Alonzo and Sinervo, 2001) and empirical studies (e.g., Hews, 1990; Lopez et al., 2003; Hamilton and Sullivan, 2005) have suggested a role for female choice in at least some squamate species. Male squamates also may suffer a higher price during the breeding season than previously considered because of energetic costs and predation exposure associated with competitive and territorial behavior (Marler and Moore, 1989; Aldridge and Brown, 1995; Bonnet et al., 1999). A handful of studies have demonstrated that male lizards and snakes can discriminate among potential mates (e.g., Olsson, 1993; Orrell and Jenssen, 2002; Shine et al., 2004), but again evidence for male choice in this group is limited. For those squamate species that do exhibit mate choice, a variety of cues have been shown to influence mating decisions. Potential mates may be assessed by visual cues (e.g., coloration or body size), behavioral displays, olfactory signals, and territory quality (e.g., Hews, 1990; Censky, 1997; Martin and Lopez, 2000). Given the diverse repertoire of signals used, squamates represent a potentially rich group in which to study the conditions that promote the use of specific mating cues. Therefore, it is necessary to identify systems in which a priori predictions can be made about which signals are likely important in particular populations. The rapid divergence of two distinct color morphs of the Common Lesser Earless Lizard, Holbrookia maculata, in southern New Mexico provides an opportunity to evaluate the potential for mate discrimination in recently diverged lizard populations. White Sands is a dramatic and geologically recent landscape of stark white hydrous calcium sulfate (gypsum) dunes deposited during the last 6,000 years (Kocurek et al., 2007; S. G. Fryberger, unpubl. data). The 275 square miles of gypsum contrast dramatically with the dark colors of adjacent substrate. A 1 Present address: Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844, USA; Email: [email protected] Journal of Herpetology, Vol. 42, No. 3, pp. 572–583, 2008 Copyright 2008 Society for the Study of Amphibians and Reptiles