Age and Gender-Related Differences in the Social Behavior and Mating Success of Free-Living Collared Lizards, Crotaphytus collaris

Abstract

Field studies on collared lizards at Lake Arcadia Dam, Edmond, Oklahoma, revealed that the social and spatial behavior of individuals differed depending on gender and male age. Body size measurements of known lizards over a threeyear period revealed that females > 70 mm SVL at the beginning of the activity season in April become reproductively active in their first year, males > 100 mm in April are two years and older (adults), whereas smaller males (60-90 mm) are in their first full year (yearlings). Experimental introduction of female intruders onto occupied female home ranges elicited aggression in four of 17 trials. However, female home ranges overlapped one another greatly, and intrasexual female aggression occurred infrequently. These results suggest that female collared lizards at Arcadia Lake do not defend exclusive territories but that occasional aggression may play some other role in the social relationships among adjacent females. Areas occupied by adjacent adult males overlapped little and were defended against other adult males primarily by high rates of travel punctuated with frequent display. Yearling males occupied nondefended home ranges within adult male territories by adopting subordinate tactics characterized by low rates of display and travel and rapid retreat from adult males. The home ranges of approximately 60% of the females were overlapped by the territory of a single adult male. In cases of multiple adult male overlap, one of the males overlapped a larger percentage of the female home range and interacted more frequently with these females than did the other adult males. Most female home ranges were also overlapped partially by as many as four yearling males. Adult males initiated encounters with females much more frequently than did yearlings, and females were almost always receptive to adult males whereas they more often withdrew from yearling males. Estimates based on the relative frequencies of interactions of females with each overlapping male indicated that annual male mating success was correlated with age class, snout-vent length, hourly frequency of social acts initiated, and rate of travel, such that mating success of adult males far exceeded that of yearlings. Among adult males alone, one estimate of mating success was weakly correlated only with the number of females on territories. Our results show that, even though male mating success is low during their first year, yearlings remain on adult male territories by adopting subordinate behavior patterns, perhaps because this tactic enhances future opportunities to inherit territories and mates.