An evolutionary process that assembles phenotypes through space rather than time

School of Biological Sciences A08, University of Sydney, Sydney, NSW 2006, Australia.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 03/2011; 108(14):5708-11. DOI: 10.1073/pnas.1018989108
Source: PubMed

ABSTRACT In classical evolutionary theory, traits evolve because they facilitate organismal survival and/or reproduction. We discuss a different type of evolutionary mechanism that relies upon differential dispersal. Traits that enhance rates of dispersal inevitably accumulate at expanding range edges, and assortative mating between fast-dispersing individuals at the invasion front results in an evolutionary increase in dispersal rates in successive generations. This cumulative process (which we dub "spatial sorting") generates novel phenotypes that are adept at rapid dispersal, irrespective of how the underlying genes affect an organism's survival or its reproductive success. Although the concept is not original with us, its revolutionary implications for evolutionary theory have been overlooked. A range of biological phenomena (e.g., acceleration of invasion fronts, insular flightlessness, preadaptation) may have evolved via spatial sorting as well as (or rather than) by natural selection, and this evolutionary mechanism warrants further study.

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Available from: Richard Shine, Sep 28, 2015
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    • "competition with conspecifics is low, but are less successful when placed in competition with conspecifics (Burton et al. 2010; Shine et al. 2011). These shifts in dispersal are increasingly observed in invasions, with examples ranging from cane toads, to birds, to damselflies (Phillips & Suarez 2012). "
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    ABSTRACT: Anthropogenic threats often impose strong selection on affected populations, causing rapid evolutionary responses. Unfortunately, these adaptive responses are rarely harnessed for conservation. Here, we suggest that conservation managers should pay close attention to adaptive processes and geographic variation, with an eye to using them for conservation goals. Translocating pre-adapted individuals into recipient populations is currently considered a potentially important management tool in the face of climate change. Here we point out that targeted gene flow could have much broader application in conservation, with uses ranging from the management of invasive species and their impacts to controlling the impact and virulence of pathogens. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Conservation Biology 08/2015; DOI:10.1111/cobi.12623 · 4.17 Impact Factor
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    • "We worked in the wet–dry tropics of the Northern Territory, where the predominant habitat is savannah woodland. In this region, cane toads are inactive during the long annual dry-season (broadly, May to November) and disperse only when monsoonal rains provide moist soil (Brown, Kelehear & Shine, 2011a). "
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    ABSTRACT: At an invasion front, energetic and physiological trade-offs may differ from those at the range-core as a result of selection for enhanced dispersal, combined with a low density of conspecifics (which reduces pathogen transmission and competition for food). We measured traits related to energy stores and immunity in wild cane toads (Rhinella marina) across a 750-km transect from their invasion front in tropical Australia, back into sites colonized 21 years earlier. Several traits were found to vary with population age; some linearly and others in a curvilinear manner. The relative size of spleens and fat bodies was highest in the oldest and newest populations, where rates of lungworm infection were lowest. Toads from older populations produced more corticosterone in response to a standardized stressor, and had higher lymphocyte counts (but lower basophil counts). The amount of skin swelling elicited by phytohaemagglutinin injection did not vary geographically, although recruitment of leukocytes to the injected tissue was higher in toads from long-colonized areas. Because this was a field-based study, we cannot differentiate the effects of population age, toad density or pathogen pressure on our measures of stress and immune responses, nor can we distinguish whether the causation involves hard-wired adaptive processes or phenotypically plastic responses. Nonetheless, our data demonstrate substantial variation in immune systems among toads at varying distances from an invasion front, showing that a biological invasion imposes strong pressures on physiological systems of the invader.
    Biological Journal of the Linnean Society 08/2015; DOI:10.1111/bij.12623 · 2.26 Impact Factor
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    • "For example, deleterious mutations may accumulate at expanding range edges (Burton & Travis, 2008; Peischl, Kirkpatrick & Excoffier, 2015), and the low reproductive output could be a result of non-adaptive accumulation of reproductionreducing mutations. Alternatively, successive generations of interbreeding among the fastest-dispersing toads at the invasion front every generation ('spatial sorting'; Shine et al., 2011) may have caused inbreeding effects. Another possibility is that environmental conditions experienced prior to capture "
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    ABSTRACT: The rapid evolution of increased dispersal rate during a population's range expansion provides a unique opportunity to detect trade-offs between dispersal and reproduction. If a high reproductive rate slows down an individual's dispersal, vanguard individuals should exhibit a lower reproductive output than conspecifics from long-colonized areas. In the present study, we demonstrate a reduction in reproductive rate in highly dispersive invasion-front populations of cane toads in tropical Australia.
    Biological Journal of the Linnean Society 07/2015; DOI:10.1111/bij.12618 · 2.26 Impact Factor
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