Beastly Bondage: The Costs of Amplexus in Cane Toads (Bufo marinus)
Reproductive activities can impose fitness costs as well as benefits. In most anuran species, males clasp females for prolonged periods prior to gamete release, and intuition suggests that the male's presence may impair the female's ability to move about and to feed. We tested the prediction that female locomotion and feeding would be reduced during amplexus in laboratory experiments with Cane Toads, Bufo marinus. Amplexus reduced the female's locomotor (sprint and swim) performance, with the degree of locomotor impairment (speed and distance per hop) dependent upon the body size of the amplectant male for trials of terrestrial locomotion, but not for aquatic locomotion. Amplexus also reduced feeding rates in females; amplectant males did not feed at all. Overall, our data confirm that amplexus imposes locomotor and feeding costs to female Cane Toads, and suggest that this distinctive posture may generate sexual conflict in at least some anuran species.Abstract
Effects of an amplectant male on terrestrial locomotor speeds of female Cane Toads, Bufo marinus, over a 10 m raceway. The histograms show (A) mean (±SE) sprint speeds and (C) hops/meter by status (non-amplectant, unfilled bars and amplectant, gray bars). See Table 1 for a statistical summary. The graphs on the right show relationships between the degree of physical burdening (ratio of male mass to female mass) and (B) female speed and (D) number of hops per meter. Larger male size impaired female locomotion more significantly than did smaller males.
Effects of an amplectant male on aquatic locomotor speeds of female Cane Toads, Bufo marinus, over four 1.9 m sections (‘lengths’) of a circular test arena. Panel (A) shows mean (±SE) swim speed by status (non-amplectant, unfilled bars and amplectant, gray bars). Statistics are summarized in Table 1. Panel (B) shows the lack of a significant relationship between the degree of physical burdening (ratio of male mass to female mass) and female swimming speed over the first two lengths of the arena.
Effects of amplexus on feeding rates (mean ± SE, calculated from untransformed data) of amplectant and non-amplectant male and female Cane Toads, Bufo marinus, offered crickets in the laboratory. Amplectant males did not feed at all, whereas amplectant females fed less than did non-amplectant females.
Contributor Notes
Associate Editor: J. D. Litzgus.