A genetic perspective on rapid evolution in cane toads (Rhinella marina)

Abstract

The process of biological invasion exposes a species to novel pressures, in terms of both the environments it encounters and the evolutionary consequences of range expansion. Several invaders have been shown to exhibit rapid evolutionary changes in response to those pressures, thus providing robust opportunities to clarify the processes at work during rapid phenotypic transitions. The accelerating pace of invasion of cane toads (Rhinella marina) in tropical Australia during its 80-year history has been well characterized at the phenotypic level, including common-garden experiments that demonstrate heritability of several dispersal-relevant traits. Individuals from the invasion front (and their progeny) show distinctive changes in morphology, physiology and behaviour that, in combination, result in far more rapid dispersal than is true of conspecifics from long-colonized areas. The extensive body of work on cane toad ecology enables us to place into context studies of the genetic basis of these traits. Our analyses of differential gene expression from toads from both ends of this invasion-history transect reveal substantial upregulation of many genes, notably those involved in metabolism and cellular repair. Clearly, then, the dramatically rapid phenotypic evolution of cane toads in Australia has been accompanied by substantial shifts in gene expression, suggesting that this system is well suited to investigating the genetic underpinnings of invasiveness.

Costs of immunity and their role in the range expansion of the house sparrow in Kenya

“…Surprisingly, we still know little about what traits comprise successful invaders, especially for vertebrates. Perhaps the best-studied introduced vertebrate species is the cane toad (Rhinella marina), which spread across Australia in ∼80 years (Phillips et al, 2006;Kolbe et al, 2009;Brown and Shine, 2014;Brown et al, 2015a,b;Rollins et al, 2015). Other non-native vertebrates, particularly rodents and songbirds (Losos et al, 1997;Kolbe et al, 2004;Lee et al, , 2005Fassbinder-Orth et al, 2013;Vilcinskas et al, 2013;White et al, 2013;Morand et al, 2015;Tian et al, 2015), have gained some recent attention, but the diversity of research approaches makes generalizations about facilitators of range expansions premature.…”

Selecting for invasive tendencies: the evolution of morphological, physiological, and movement behaviour traits associated with dispersal

“…Resting MR has been previously found to be higher in individuals with greater movement propensity (Niitepõld et al 2009;Myles-Gonzalez et al 2015) and a recent study found that genes underlying metabolic processes are upregulated in dispersive cane toads (Rollins et al 2015). Given the potential involvement of genetic and epigenetic mechanisms, and potential metabolome differences between dispersive and non-dispersive individuals (Rollins et al 2015;Van Petegem et al 2015;2016b), it may be worth exploring the association between MR and movement in other systems. Burton et al 2011;Killen et al 2012;Killen et al 2013;Lebeau et al 2016;Metcalfe et al 2016).…”

“…If differences in these traits are apparent between resident and disperser larvae (which seems highly probable), then it would be insightful to examine the expression of genes involved in metabolic processes and their regulation. Recent studies have found that the genetics, epigenetics, and metabolomics can differ between resident and disperser toads (Rollins et al 2015) and spider mites (Van Petegem et al 2016b). …”

“…Subsequent studies have found numerous species that express different levels of PKG vary in locomotion behaviour and performance, suggesting it is conserved across diverse taxa (Wheat 2012). A recent genetic study on invasive cane toads has found differential expression of genes involved in metabolism and immune function between individuals from range edge and range core populations (Rollins et al 2015). Those at the range edge display substantial upregulation genes involved with metabolism and activity (Rollins et al 2015), which contrasts with findings from metabolomics of invasive spider mites (Tetranychus urticae) that have undergone a range expansion (Van Petegem et al 2016b).…”

“…A recent genetic study on invasive cane toads has found differential expression of genes involved in metabolism and immune function between individuals from range edge and range core populations (Rollins et al 2015). Those at the range edge display substantial upregulation genes involved with metabolism and activity (Rollins et al 2015), which contrasts with findings from metabolomics of invasive spider mites (Tetranychus urticae) that have undergone a range expansion (Van Petegem et al 2016b). Individuals from the expanding range edge potentially downregulate metabolic pathways associated with protein synthesis and also show differential use of amino acids to those individuals from the range core (Van Petegem et al 2016b).…”