Abstract
As is common in biological invasions, the rate at which cane toads (Rhinella marina) have spread across tropical Australia has accelerated through time. Individuals at the invasion front travel further than range-core conspecifics and exhibit distinctive morphologies that may facilitate rapid dispersal. However, the links between these morphological changes and locomotor performance have not been clearly documented. We used raceway trials and high-speed videography to document locomotor traits (e.g. hop distances, heights, velocities, and angles of take-off and landing) of toads from range-core and invasion-front populations. Locomotor performance varied geographically, and this variation in performance was linked to morphological features that have evolved during the toads' Australian invasion. Geographical variation in morphology and locomotor ability was evident not only in wild-caught animals, but also in individuals that had been raised under standardized conditions in captivity. Our data thus support the hypothesis that the cane toad's invasion across Australia has generated rapid evolutionary shifts in dispersal-relevant performance traits, and that these differences in performance are linked to concurrent shifts in morphological traits.
Highlights
To understand the evolutionary processes that have shaped phenotypic variation within and among species, we ideally need information on morphology, and on the ways in which morphological variation translates into effects on performance, and on lifetime reproductive success [1,2,3]
We used raceway trials and high-speed videography to document locomotor traits of toads from range-core and invasion-front populations. This variation in performance was linked to morphological features that have evolved during the toads’ Australian invasion
Variation in morphology and locomotor performance was linked in the cane toads that we studied, and those suites of traits differed between toads from range-core versus invasion-front populations
Summary
To understand the evolutionary processes that have shaped phenotypic variation within and among species, we ideally need information on morphology, and on the ways in which morphological variation translates into effects on performance, and on lifetime reproductive success [1,2,3]. We predicted that range-core and invasion-front toads would differ both in morphology and performance, that these differences would be seen in captiveraised (common-garden experiment) progeny as well as in wild-caught animals, and that morphological and locomotor variables would be significantly correlated. The same was true for our locomotor measures (interaction between invasion category and jumping performance variables for all toads F5,289 = 2.87, p < 0.02; for F0 only, F5,156 = 2.42, p < 0.04; for F1 only F5,120 = 3.94, p < 0.003) so we proceeded to explore geographical variation in each trait separately To clarify these patterns, we used ANOVA with invasion category (range core versus invasion front) and population nested within invasion category as factors, and either morphological or performance measures as dependent variables. JMP v. 14.0 (SAS Institute, Cary, NC, USA) was used for all statistical analyses
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