Edition 5, June 2010
Fast-moving Species Leave Pathogens And Parasites For Dead
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June 18th, 2010
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Species that move fast under climate change may initially outpace the damaging parasites and pathogens that normally inhibit population numbers, as the cane toad (Bufo marinus) has done at its invasion front in Australia.
Modelling the relationship dynamics between hosts increasing their range and their pathogens/parasites, Ben Phillips and colleagues have found that parasites and pathogens are likely to be absent at the front-end of the host’s expansion.
Evidence comes from the lack of lungworms (Rhabdias pseudosphaerocephala) in invasive cane toads in newly-invaded areas in northern Australia. The lungworms catch up after 1-3 years. Until then, the toads at the invasion front are virtually pathogen-free, which can lead to very high toad densities at first.
Release from parasites and pathogens is thought to be one of the primary reasons for the “spectacular success” of many introduced species. They are often introduced in small numbers with only a small subset of their native pathogens and parasites to stymie growth and reproduction.
The same process could occur with native species expanding under climate change, as low densities of hosts at the expansion front limit transmission or increase the chances of random (stochastic) events causing local extinction of parasites and pathogens.
One example may be the brown argus butterfly (Aricia agestis), which has expanded northward in Britain over the past 30 years. Rosa Menendez and colleagues found that it had fewer parasites at its northern edge and larvae suffered lower mortality from parasites in newly-colonised areas.
The pathogen-free honeymoon phase for both invasive species and species expanding under climate change may lead to accelerated rates of range expansion by the host and affect the evolution of both hosts and their parasites and pathogens.
Hosts that don’t have to deal with pathogens and parasites may change their immune traits and life history, and parasites or pathogens may evolve increased dispersal ability.
References
Phillips BL, Kelehear C, Pizzatto L, Brown GP, Barton D and Shine R. 2010. Parasites and pathogens lag behind their host during periods of host range advance. Ecology 91(3): 872-881.