Variation in Resistance to the Invasive Crayfish Plague and Immune Defence in the Native Noble Crayfish

Abstract

Emerging diseases, such as the crayfish plague, are a worldwide problem with serious ecological and economic impacts. Under the framework of ecological immunology, we investigated whether variation in crayfish plague resistance, the indicators of immune defence (encapsulation response, phenoloxidase and lytic activity), and the exploration behaviour among four subpopulations of noble crayfish is explained by potential local adaptation through differences in crayfish plague history, or alternatively by geographical divergence in a large watershed. We examined whether the strength of immune defence is associated with survival and exploration behaviour. Survival time after experimental crayfish plague infection and phenoloxidase activity differed among the subpopulations of the watershed but did not reveal local adaptation to the disease. Increased investment in immune defence (i.e. encapsulation response) compromised survival time after infection, suggesting the self-reactivity costs of mounting a strong immune response. Exploration behaviour was negatively associated with phenoloxidase activity before and after immune challenge. IntroductionEvolving and maintaining parasite resistance and variation in immune defence are essential for host population persistence, since parasites and pathogens can reduce host growth, reproductive success and survival prospects (Goater & Holmes 1997, Zuk & Stoehr 2002). Due to a long co-evolutionary history, parasites often show low virulence and host populations high levels of resistance (see Schmid-Hempel 2011). In contrast to local, familiar parasites, nonnative parasites are often highly virulent, causing heavy host mortality and population crashes, as observed in fish and crayfish (Bakke & Harris 1998, Bangyeekhun 2002, Edgerton et al. 2004). The evolvability of resistance or tolerance is a key mechanism for understanding and forecasting the dynamics of host populations in response to emerging diseases caused by non-native parasites and pathogens. Host genetic diversity in immune defence can play an important role in evolving resistance in a population (Altizer et al. 2003). The evolution of resistance should be favoured when parasites and pathogens pose a strong selection pressure on hosts but is only possible when some of the hosts survive and remain able to reproduce (Duncan & Little 2007, Duffy & Forde 2009. Recent studies have shown that disease resistance against pathogens in Drosophila melanogaster can evolve in less than ten generations under laboratory conditions (Ye et al. 2009), and natural populations of Daphnia magna planktonic crustaceans are able to evolve immune defence in less than a decade (Pauwels et al. 2010). Whether hosts in the wild can evolve fast enough in response to emerging diseases is still uncertain. Emerging diseases resulting from the introduction of non-native parasites and pathogens are often well documented and offer the opportunity to investigate evolutionary processes, such as the evolving resistance and immune defences of the new host in th...

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