Geographic Variation in Sexual Selection Among Populations of an Iguanid Lizard, Sauromalus Obesus (=ater)

Abstract

Geographic variation in selection pressures may result in population divergence and speciation, especially if sexual selection varies among populations. Yet spatial variation in targets and intensity of sexual selection is well studied in only a few species. Even more rare are simultaneous studies of multiple populations combining observations from natural settings with controlled behavioral experiments. We investigated how sexual selection varies among populations of the chuckwalla, Sauromalus obesus. Chuckwallas are sexually dimorphic in color, and males vary in coloration among populations. Using field observations and multiple regression techniques, we investigated how sexual selection acts on various male traits in three populations in which males differed in coloration. The influence of sexual selection on male coloration was then investigated in more detail using controlled experiments. Results from field observations indicate that phenotypic selection was acting on territory quality in all three populations. In two populations, selection was also acting either directly or indirectly on male coloration. Male color likely functions as an indicator of food resources to females because male color is based partly on carotenoid pigments. In controlled experiments, significantly more females from these two populations chose males with brighter colors over dull males, a result consistent with studies on carotenoid pigments in other taxa. In a third population, no evidence of sexual selection on male coloration was found in either the field study or controlled experiment. Lack of female preferences for male color in this population, in which chuckwalla densities are low and home ranges are large, may result from searching costs to females.

Variation in polyandry and its fitness consequences among populations of the red flour beetle, Tribolium castaneum

“…A number of examples have been documented in the literature on the variation in traits associated with reproduction among populations (e.g., Boake and Wade 1984;Endler and Houde 1995;Uy and Borgia 2000;Arnaud et al 2001;Kwiatkowski and Sullivan 2002) and the fitness consequences of mating behavior (e.g., Gilburn and Day 1994;Lesna and Sabelis 1999). Our results strongly suggest that generalizations about the fitness effects of polyandry should be made with caution.…”

Parasites and health affect multiple sexual signals in male common wall lizards, Podarcis muralis

“…In other populations of P. muralis, there are different color morphs, which also differ in average immune responses (Sacchi et al 2007). Male color variability may be important because, for example, color brightness seems to be preferred by females in several lizard species (e.g., Baird et al 1997;Kwiatkowski and Sullivan 2002), which may use coloration as a signal of male condition.…”

“…In birds, hue and saturation of feathers are positively correlated with the total carotenoid content of the feathers (Saks et al 2003b). In chuckwalla lizards, Sauromalus obesus, male color likely functions as an indicator of food resources to females because male color is based partly on carotenoid pigments (Kwiatkowski and Sullivan 2002). It is likely that only those male lizard P. muralis with less parasites and a greater immune response were able to find or defend more food resources and allocate more yellow carotenoids to their Similarly, chemicals used in secretions of lizards may be important in many physiological functions and can only be allocated to secretions if they are diverted from general metabolism.…”

“…Accordingly, some species have evolved a variety of colorful sexually dimorphic ornaments that are used in intraspecific relationships (reviewed in Cooper and Greenberg, 1992). For example, the size and color characteristics of male visual badges may determine success in male-male competition (Thompson and Moore 1991;Olsson 1994) or mate acquisition (Baird et al 1997;Kwiatkowski and Sullivan 2002;Anderholm et al 2004). However, chemical signals also play prominent roles in social relationships of many lizards (reviewed in Mason 1992;Alberts 1993).…”

Gradual evolution of male genitalia in a sibling species complex of millipedes (Diplopoda : Spirobolida : Rhinocricidae : Anadenobolus)

“…Because genitalic features are not usually 'adaptive' in the traditional sense, they are unlikely subject to the same selective forces operating on other phenotypic attributes. However, selection resulting from geographic variation in environmental conditions can indirectly drive divergence of mating signals and preferences (Schluter 2001;Kwiatkowski and Sullivan 2002) such that genitalia, or other premating and postmating barriers, evolve as a secondary consequence of ecological divergence. Moreover, speciation is considered by some to be inevitable for allopatric populations maintained over extended periods of time; thus, mating isolation is sometimes thought to evolve, facilitated by random genetic drift (Lande 1981), simply in response to the absence of forces maintaining reproductive compatibility (Turelli et al 2001).…”