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Gonatodes albogularis is a small diurnal gecko that lives in Central and northern South America and whose behaviour has been rarely analysed. This study describes the behaviour patterns occurring during agonistic encounters between male geckos, assesses the effect of morphological and behavioural traits on aggressive intensity and contest outcome, and tests predictions of the sequential assessment and self-assessment models of animal contests. We staged encounters between randomly paired wild-caught males in a neutral arena. The behaviour of both males was recorded and a winner was determined for most encounters. Aggressive patterns exhibited during the contests included 'throat depression', 'push-ups', three types of 'tail display', 'whole body waving' and 'bites'. Contest winners did not differ from losers in any of the morphological variables examined. However, winners performed longer or more frequent aggressive behaviours than losers, and frequency of 'throat depression' and duration of 'whole body waving' significantly predicted final status of geckos. These results show that some behaviours are good predictors of the outcome of aggressive encounters in G. albogularis. Moreover, winner SVL significantly predicted the aggressive intensity of the contest. Early theoretical models hypothesized that there should be mutual assessment between contestants, but our results for G. albogularis agree more with a recent model of 'self-assessment only' of intrasexual competition.

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Body coloration is sexually dimorphic in many vertebrate species, including lizards, in which males are often more conspicuous than females. A detailed analysis of the relative size of coloured patches and their reflectance, including the ultraviolet (UV) range, has rarely been performed. In the present work we quantified sexual dimorphism in body traits and surface area of all lateral patches from adult females and males of two subspecies of Gallotia galloti (G. g. galloti and G. g. eisentrauti). We also analysed the magnitude of sexual dichromatism in the UV-visible reflectance of such patches and the changes in patch size and brightness during the reproductive season (April-July). Males had significantly larger patch areas (relative to their snout-vent length) and higher brightness (mainly in the UV-blue range) than did females in both subspecies. The comparison of relative patch areas among months did not reach statistical significance. However, patch brightness significantly changed during the breeding season: that of the UV-blue (300-495 nm) range from lizards of the two subspecies was significantly larger in June than in April, while brightness in the 495-700 nm range in G. g. galloti was larger in May, June, and July than in April. A different pattern of dichromatism was also detected in the two populations, with G. g. eisentrauti being more sexually dichromatic than G. g. galloti. We discuss the results in terms of possible evolutionary causes for the sexual dichromatism related to different ecological characteristics of the habitats where each subspecies live.

In lizards, site selection is related to the acquisition of resources such as refuges, mates or prey, but also to the exploitation of sites suitable for thermoregulation. The latter process may be affected by lizard posture and body axis orientation in relation to the sun as a way to optimize heat exchange throughout the day. Specific postures and body orientations could also contribute to more efficient signal transmission in social contexts. In this paper we analyze activity and body axis orientation of adult males and females of the lacertid Gallotia galloti in two localities of Tenerife with different structural habitats. We performed transects at both sampling localities in the morning and at midday during May and June of three years (2002)(2003)(2004). The numbers of lizards detected per unit time during transects at both localities were similar; however, significantly more males than females were detected. Moreover, more lizards were found oriented parallel or perpendicular to the sun than in alternative (oblique) orientations. Heating rates were not different for copper lizard models oriented parallel or perpendicular to the sun, neither in the morning nor at midday, and there was no significant relationship between air temperature and lizard body orientation. This suggests that lizard body orientation is not constrained by thermoregulatory requirements. We discuss alternative hypotheses and conclude that body axis orientation in G. galloti lizards may reflect a compromise between the conflicting demands imposed by thermoregulation and social communication.