Chemosensory assessment of rival competitive ability and scent-mark function in a lizard, Podarcis hispanica

Recent studies have stressed the role of scent marks as signals potentially mediating competitor assessment. According to this view, receivers may use scent marks to derive information about the costs of exploiting a given area, but few studies have directly addressed this hypothesis. One of its main predictions is that scent marks should reflect a signaller's competitive ability. We simulated the situation faced by an intruding male when entering the scent-marked territories of rival males of varying competitive ability to test predictions about the role of scent marks in a lizard, Podarcis hispanica. We report that males were attracted to areas marked by males of similar or higher competitive ability (i.e. larger size), but not to areas scent marked by males of lower competitive ability, and that this preference disappeared towards the end of the breeding season. Our results show that (1) male lizards can assess rival competitive ability (i.e. rival size) on the basis of scent marks alone, (2) scent marks do not function as chemical barriers to deter intruders, and (3) male response to marked areas varies throughout the breeding season, suggesting a shift in the cost-to-benefit balance of entering a scent-marked area. We propose that male assessment of rival competitive ability may function as an indirect assessment mechanism of territory resource quality in this species, and thus that scent marks may convey information not only about costs but also about the benefits of exploiting a scent-marked area.