Effects of Growth Rate on Variation in Breeding Coloration in Male Sand Lizards (Lacerta agilis: Sauria)

Abstract

Sand lizards (Lacerta agilis) have color vision which is most sensitive in the wavelengths that correspond to the male breeding coloration (Swiezawska, 1949), and males with more green lateral breeding coloration (i.e., with larger badges) are more likely to win staged contests in the laboratory and have higher mating success in the wild (Olsson, 1992a, 1992b, 1993). Olsson and Madsen (1995) demonstrated that female sand lizards do not choose males, so breeding colors are not sexually selected via female choice. Instead, males seem to use the green badge to facilitate the judgment of a rival's fighting ability (Olsson 1994a). An interesting question is therefore, What factor(s) determine(s) badge size and prevent(s) males from cheating? (i.e., developing a too large or too bright badge to, ultimately, obtain more matings; see e.g., Maynard Smith, 1982). In other lizard species, androgens affect male breeding coloration (e.g., Cooper and Greenberg, 1992; Rand, 1992; Hews and Moore, 1994), which, hence, may influence mating success (Olsson 1994a). However, androgens may be costly to maintain at high plasma concentrations (Marler and Moore, 1989), and growth rate declines with body size and age (Olsson, 1994a). Thus, young, sexually mature males may allocate most energy and nutrients to growth rather than to reproduction and its associated expenditures. The aim of this study was to investigate whether growth rate affects breeding coloration, independent of testosterone and body size. Once sand lizard males emerge from hibernation in mid-April, they begin to develop breeding coloration and about two to three weeks later begin mating. The badge is temporally labile in sand lizards, and sexually mature males develop a badge that increases allometrically in relation to body size (Olsson, 1994a). When males are castrated after developing breeding coloration, they maintain their green color that year but fail to develop green coloration the following year (Regamy, 1935). We performed analyses on lizards kept in the laboratory and on which we monitored testosterone levels. This enabled us to tease apart the independent effect of growth rate on a component of breeding coloration while we statistically held plasma testosterone concentration constant at its mean in partial correlations.