To disperse between isolated waterbodies, freshwater organisms must often cross terrestrial barriers and many freshwater animals that are incapable of flight must rely on transport via flooding events, other animals or anthropogenic activity. Decapods such as crayfish, on the other hand, can disperse to nearby waterbodies by walking on land, a behaviour that has facilitated the spread of invasive species. Overland movement could play a key role in the management of non-native crayfish, though to what extent terrestrial emigration occurs in different species is poorly understood. Here, we directly compared the terrestrial emigration tendency of two non-native crayfish species in Great Britain; red swamp (Procambarus clarkii) and signal (Pacifastacus leniusculus) crayfish. We found that both species emigrated from the water and that there was no significant difference in terms of their terrestrial emigration tendency, suggesting that there is a risk both of these species will migrate overland and disperse to new habitats. This study shows that terrestrial emigration is an important behavioural trait to consider when preventing the escape of crayfish from aquaculture and further spread of invasive species.
The spread of invasive, non-native species is a key threat to biodiversity. Parasites can play a significant role by influencing their invasive host's survival or behaviour, which can subsequently alter invasion dynamics. The North American signal crayfish (Pacifastacus leniusculus) is a known carrier of Aphanomyces astaci, an oomycete pathogen that is the causative agent of crayfish plague and fatal to European crayfish species, whereas North American species are considered to be largely resistant. There is some evidence, however, that North American species, can also succumb to crayfish plague, though how A. astaci affects such ‘reservoir hosts’ is rarely considered. Here, we tested the impact of A. astaci infection on signal crayfish, by assessing juvenile survival and adult behaviour following exposure to A. astaci zoospores. Juvenile signal crayfish suffered high mortality 4-weeks post-hatching, but not as older juveniles. Furthermore, adult signal crayfish with high-infection levels displayed altered behaviours, being less likely to leave the water, explore terrestrial areas and exhibit escape responses. Overall, we reveal that A. astaci infection affects signal crayfish to a much greater extent than previously considered, which may not only have direct consequences for invasions, but could substantially affect commercially harvested signal crayfish stocks worldwide.
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 nonnative 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.
This is the report of a new species of catfish, Kryptoglanis shajii nov. gen. and nov. sp., distinguished from all other genera of siluriform fishes by the combination of the following morphological characters: viz. the absence of dorsal fin; the presence of four pairs of barbels; an upwardly directed mouth, with a distinctly projecting lower jaw; subcutaneous eyes; anal fin completely confluent with the caudal fin; anal and caudal fins together carry 70-74 fin rays; and no spines in any of the fins. Kryptoglanis, which has a maximum recorded size of 59.1 mm in standard length, was collected from a well fed by subterranean springs. The type locality is a well located at the extreme western part of Western Ghats, near Chalakudy in Thrissur district, Kerala State, India.
Global climate change continues to impact fish habitat quality and biodiversity, especially in regard to the dynamics of invasive non-native species. Using individual aquaria and an open channel flume, this study evaluated the effects of water temperature, flow velocity and turbulence interactions on swimming performance of two lentic, invasive non-native fish in the UK, pumpkinseed (
Lepomis gibbosus
) and topmouth gudgeon (
Pseudorasbora parva
). Burst and sustained swimming tests were conducted at 15, 20 and 25°C. Acoustic Doppler velocimetry was used to measure the flume hydrodynamic flow characteristics. Both
L. gibbosus
and
P. parva
occupied the near-bed regions of the flume, conserving energy and seeking refuge in the low mean velocities flow areas despite the relatively elevated turbulent fluctuations, a behaviour which depended on temperature. Burst swimming performance and sustained swimming increased by up to 53% as temperature increased from 15 to 20°C and 71% between 15 and 25°C. Furthermore, fish test area occupancy was dependent on thermal conditions, as well as on time-averaged velocities and turbulent fluctuations. This study suggests that invasive species can benefit from the raised temperatures predicted under climate change forecasts by improving swimming performance in flowing water potentially facilitating their further dispersal and subsequent establishment in lotic environments.
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