Larger body size at metamorphosis enhances survival, growth and performance of young cane toads (Rhinella marina)

Abstract

Body size at metamorphosis is a key trait in species (such as many anurans) with biphasic life-histories. Experimental studies have shown that metamorph size is highly plastic, depending upon larval density and environmental conditions (e.g. temperature, food supply, water quality, chemical cues from conspecifics, predators and competitors). To test the hypothesis that this developmental plasticity is adaptive, or to determine if inducing plasticity can be used to control an invasive species, we need to know whether or not a metamorphosing anuran's body size influences its subsequent viability. For logistical reasons, there are few data on this topic under field conditions. We studied cane toads (Rhinella marina) within their invasive Australian range. Metamorph body size is highly plastic in this species, and our laboratory studies showed that larger metamorphs had better locomotor performance (both on land and in the water), and were more adept at catching and consuming prey. In mark-recapture trials in outdoor enclosures, larger body size enhanced metamorph survival and growth rate under some seasonal conditions. Larger metamorphs maintained their size advantage over smaller siblings for at least a month. Our data support the critical but rarely-tested assumption that all else being equal, larger body size at metamorphosis is likely to enhance an individual's long term viability. Thus, manipulations to reduce body size at metamorphosis in cane toads may help to reduce the ecological impact of this invasive species.

Figure 1. Relationships between the body mass of a metamorph cane toad and its performance.

Performance was measured by (A) mean distance of the three first jumps, (B) total distance swum, and (C) total number of termites eaten.

Figure 2. Growth trajectories (changes in mass over time) for metamorph and juvenile cane toads in three trials conducted in outdoor enclosures.

Figure 3. Relationship between initial body mass and growth rate of metamorph and juvenile cane toads during Trial 1 (A), Trial 2 (B), and Trial 3 (C) over different recapture periods.

Figure 4. Effects of initial body mass on survival of cane toad metamorphs in outdoor enclosures in (A) Trial 1, (B) Trial 2, and (C) Trial 3.

For (C) the lower line indicates the first time period (10 days), the second line indicates the second time period (20 days) and the highest line indicates the last period (sixth recapture period: 185 days).