Effects of rearing environment and population origin on responses to repeated behavioural trials in cane toads (Rhinella marina)

Climate match is key to predict range expansion of the world's worst invasive terrestrial vertebrates

Understanding the determinants of the range expansion of invasive alien species is crucial for developing effective prevention and control strategies. Nevertheless, we still lack a global picture of the potential factors influencing the invaded range expansion across taxonomic groups, especially for the world's worst invaders with high ecological and economic impacts. Here, by extensively collecting data on 363 distributional ranges of 19 of world's worst invasive terrestrial vertebrates across 135 invaded administrative jurisdictions, we observed remarkable variations in the range expansion across species and taxonomic groups. After controlling for taxonomic and geographic pseudoreplicates, model averaging analyses based on generalized additive mixed-effect models showed that species in invaded regions having climates more similar to those of their native ranges tended to undergo a larger range expansion. In addition, as proxies of propagule pressure and human-assisted transportation, the number of introduction events and the road network density were also important predictors facilitating the range expansion. Further variance partitioning analyses validated the predominant role of climate match in explaining the range expansion. Our study demonstrated that regions with similar climates to their native ranges could still be prioritized to prevent the spread of invasive species under the sustained global change.

Captivity induces large and population-dependent brain transcriptomic changes in wild-caught cane toads (Rhinella marina)

Gene expression levels are key molecular phenotypes at the interplay between genotype and environment. Mounting evidence suggests that short-term changes in environmental conditions, such as those encountered in captivity, can substantially affect gene expression levels. Yet, the exact magnitude of this effect, how general it is, and whether it results in parallel changes across populations are not well understood. Here, we take advantage of the well-studied cane toad, Rhinella marina, to examine the effect of short-term captivity on brain gene expression levels, and determine whether effects of captivity differ between long-colonized and vanguard populations of the cane toad's Australian invasion range. We compared the transcriptomes of wild-caught toads immediately assayed with those from toads captured from the same populations but maintained in captivity for seven months. We found large differences in gene expression levels between captive and wild-caught toads from the same population, with an over-representation of processes related to behaviour and the response to stress. Captivity had a much larger effect on both gene expression levels and gene expression variability in toads from vanguard populations compared to toads from long-colonized areas, potentially indicating an increased plasticity in toads at the leading edge of the invasion. Overall, our findings indicate that short-term captivity can induce large and population-specific transcriptomic changes, which has significant implications for studies comparing phenotypic traits of wild-caught organisms from different populations that have been held in captivity.