A possible mechanism for the displacement of Austropotamobius pallipes by Pacifastacus leniusculus

Mechanisms behind the displacement of native species by invasive species are not fully understood. This paper examines the effect of the chemical presence of an invasive species of crayfish (Pacifastacus leniusculus) on Austropotamobius pallipes, a native British species of crayfish, and visa versa. Water was conditioned with juvenile and mature life stages of male and female Pacifastacus leniusculus inside (IBS) and outside (OBS) of the breeding season. Conditioned water was tested on male and female Austropotamobius pallipes of both juvenile and mature life stage IBS and OBS. The animal’s behaviour was recorded on a scale of response from 0 (no action) to 4 (tail-flip). Water was conditioned in a similar manner using mature male and female A. pallipes IBS and OBS, which was tested on P. leniusculus. The behaviour of P. leniusculus was recorded on a different behavioural scale of 0 (no action) to 3 (most attractive). Austropotamobius pallipes was found to be repelled when presented with water conditioned by both mature male and female Pacifastacus leniusculus IBS and OBS. The animals used in the experiment had no previous contact with the other species. Juvenile A. pallipes showed a greater response than adults to water conditioned IBS by adult male P. leniusculus. Water conditioned by Austropotamobius pallipes had little effect on Pacifastacus leniusculus, other than water conditioned by adult female A. pallipes IBS which attracted adult male P. leniusculus. It was unclear whether this was a feeding or a sexual response. This paper highlights chemical signals as a possible mechanism involved in the displacement of the British native species of crayfish (Austropotamobius pallipes) by the invasive crayfish Pacifastacus leniusculus.