Anti-predatory responses of two native gastropods to an invasive predator

As native prey species lack a co-evolutionary history with invasive predators, they often have limited capacity to identify and respond to the threat of predation. This phenomenon has led to the prey naivety hypothesis. Invasive predators can have devastating impacts on native prey populations. Thus, there is a need to better understand the ability of native species to respond to invasive predators. Here, laboratory behavioural experiments tested the anti-predatory responses of two gastropods, Cominella lineolata and Dicathais orbita, against an invasive predator, Asterias amurensis, and a native predator, Coscinasterias muricata. There was no chemical exudate released by any D. orbita to either species of seastar or a wax seastar control. Only a small percentage of D. orbita individuals fled from the invasive (12.5%) and native (17%) seastars. The overall separation distance between D. orbita and the two seastars was recorded for a further three minutes. While the measured distance between the invasive seastar and D. orbita was greater (61 ± 7 mm) than the distance between the native seastar (39 ± 10 mm), this was not statistically significant. In contrast, C. lineolata exhibited strong responses to the native seastar, but less strongly to the invasive seastar. Only 50% of snails fled and 15% released an exudate in response to A. amurensis, compared to 80% of snails fleeing and releasing an exudate to the native seastar. In contrast to expectations, C. lineolata collected from naïve populations tended to respond less frequently (25% of snails) by fleeing from the invasive seastar than snails collected from exposed (50% of snails), however this was not significant. This same trend was observed for C. muricata with 70% and 90% of snails fleeing from exposed and naïve populations, respectively. After recording the behavioural responses of both seastars and snails for three minutes, the release of exudate resulted in an increased separation distance between C. lineolata and C. muricata of 122 mm (± 31 mm) compared with just 28 mm (± 16 mm) when the snails failed to release the exudate, whereas the separation distances between C. lineolata and A. amurensis was 143 mm (± 31 mm) and 87 mm (± 10 mm) with and without exudate release, respectively. This latter result indicates that while the exudate appears to be an effective anti-predatory mechanism against the native seastar, it appears less effective against the invasive seastar.