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Abstract Background Biological invasions are a principal threat to global biodiversity and identifying the determinants of non-native species’ success is a conservation priority. Through their ability to regulate host populations, parasites are increasingly considered as important in determining the outcome of species’ invasions. Here, we present novel evidence that the common crayfish ecto-symbiont, Xironogiton victoriensis (Annelida: Clitellata) can affect the behaviour of a widespread and ecologically important invader, the signal crayfish (Pacifastacus leniusculus). Methods To assess the signal crayfish–X. victoriensis relationship naïve crayfish were infested with an intensity of worms typically observed under natural conditions. Over a 10-week period the growth rate and survivorship of these animals was monitored and compared to those of uninfested counterparts. Complementary dyadic competition and foraging experiments were run to assess the behaviour of infested compared to uninfested animals. These data were analysed using General Linear Models and Generalized Linear Mixed Models. Results Whilst X. victoriensis did not affect the growth rate or survivorship of signal crayfish under laboratory conditions, infested animals were significantly less aggressive and poorer foragers than uninfested individuals. Conclusions Through reducing aggression and foraging efficiency, infestation with X. victoriensis may disrupt the social structure, and potentially growth rate and/or dispersal of afflicted crayfish populations, with potential effects on their invasion dynamics. This is important given the widespread invasive range of crayfish and their functional roles as ecosystem engineers and keystone species.

Symbionts are a fundamental component of biological systems, and their survival is highly dependent on transmission and host movement. Ectosymbionts of amphibious animals face the added challenge of having to survive dramatic environmental changes as their hosts cross ecosystem boundaries. Within freshwaters, crayfish are amongst the most widespread invasive species that readily disperse overland and are host to a wide range of ectosymbionts. Relatively little is known about the transmission of these ectosymbionts, including their ability to survive overland host migration. Here, we assessed terrestrial emigration and both inter- and intra-specific transmissions of Xironogiton victoriensis, a non-native branchiobdellidan (Annelida: Clitellata) recently found on invasive signal crayfish (Pacifastacus leniusculus) in the UK. These branchiobdellidans tolerated desiccation and did not alter host terrestrial behaviour. Transmission was rapid between natural signal and novel virile (Orconectes cf. virilis) crayfish hosts, with host interactions facilitating transmission. Thus, branchiobdellidans can disperse via amphibious host behaviour and readily infect novel hosts. These traits facilitate symbionts’ survival and provide access to additional dispersal pathways that are likely to aid transmission. [ABSTRACT FROM AUTHOR]

The impact of invasive species on the recipient ecosystem can be strongly influenced by the presence of associated symbionts. It is therefore important to evaluate the likelihood of co-introduced symbiont establishment, and this requires an understanding of their life history traits. Here, we investigate survival, reproduction and competition in two non-native branchiobdellidan ectosymbionts (Xironogiton victoriensis and Cambarincola aff. okadai) on invasive signal crayfish (Pacifastacus leniusculus). In vivo, X. victoriensis established viable infrapopulations within 10 weeks, whereas C. aff. okadai went extinct within 2 weeks. Both X. victoriensis and C. aff. okadai deposited cocoons in vivo that hatched in 10–27 and 10–11 days, respectively. In vitro, X. victoriensis and C. aff. okadai survived for over 13 and 15 weeks respectively, although both were negatively affected by increased temperature and nitrate, and were absent from kick samples taken in the field. Only C. aff. okadai deposited cocoons in vitro, and this larger species readily predated on X. victoriensis but not vice versa. Both branchiobdellidans possess traits associated with colonisation success, including a relatively fast reproductive rate and extended off-host survival. Given its survival in vivo and known detrimental effect on signal crayfish X. victoriensis is perhaps more likely to influence host invasion dynamics, although its persistence may be affected by the presence of co-occurring symbionts.

Background: Biological invasions are a principal threat to global biodiversity and identifying the determinants of non-native species' success is a conservation priority. Through their ability to regulate host populations, parasites are increasingly considered as important in determining the outcome of species' invasions. Here, we present novel evidence that the common crayfish ecto-symbiont, Xironogiton victoriensis (Annelida: Clitellata) can affect the behaviour of a widespread and ecologically important invader, the signal crayfish (Pacifastacus leniusculus). Methods: To assess the signal crayfish-X. victoriensis relationship naïve crayfish were infested with an intensity of worms typically observed under natural conditions. Over a 10-week period the growth rate and survivorship of these animals was monitored and compared to those of uninfested counterparts. Complementary dyadic competition and foraging experiments were run to assess the behaviour of infested compared to uninfested animals. These data were analysed using General Linear Models and Generalized Linear Mixed Models. Results: Whilst X. victoriensis did not affect the growth rate or survivorship of signal crayfish under laboratory conditions, infested animals were significantly less aggressive and poorer foragers than uninfested individuals. Conclusions: Through reducing aggression and foraging efficiency, infestation with X. victoriensis may disrupt the social structure, and potentially growth rate and/or dispersal of afflicted crayfish populations, with potential effects on their invasion dynamics. This is important given the widespread invasive range of crayfish and their functional roles as ecosystem engineers and keystone species. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are particularly vulnerable to the effects of alien species and decapod crustaceans, notably crayfish, are a principal threat. Although symbiotic fauna may influence the impact and dispersal of introduced species, this is often overlooked. Here we provide the first record of non-native ecto-symbiotic branchiobdellidan worms on invasive signal crayfish (Pacifastacus leniusculus Dana, 1852) in the British Isles. Using morphological and molecular techniques we identified and re-described two branchiobdellidan species new to the UK, Xironogiton victoriensis Gelder and Hall, 1990 and Cambarincola aff. okadai Yamaguchi, 1933, both of which were found at a single location in the Gavenny River, South Wales. The prevalence of X. victoriensis and C. aff. okadai was 75.34% and 71.23% respectively. Although the level of X. victoriensis and C. aff. okadai co-infection was high at 75.41% of all infected animals, the two species exhibited different micro-habitat preferences on the host with the former being found predominantly on the chelae and walking legs and the latter on the carapace and abdomen. For both branchiobdellidan species, worm burdens were positively correlated with crayfish size. The lack of branchiobdellidan records from signal crayfish in nearby water bodies, and the reports of native white clawed crayfish (Austropotamobius pallipes) in the Gavenny as recently as 2000, indicates that introduction of this worm infested population occurred relatively recently, despite stringent legislation banning the import and transportation of non-native crayfish into the UK. [ABSTRACT FROM AUTHOR]