Abstract
Animal behaviour is increasingly recognised as critical to the prediction of non-native species success and impacts. Rainbow trout and brown trout have been introduced globally, but there appear to be differences in their patterns of invasiveness and ecological impact. Here, we investigated whether diploid rainbow trout and diploid and triploid brown trout differ among several key behavioural measures linked to invasiveness and impact. We assessed activity, boldness, aggression, and feeding, using open field, novel object, shelter, mirror, feeding, and functional response experiments. We also tested within each fish type for behavioural syndromes comprising correlations among activity, boldness and aggression. Rainbow trout were more active and aggressive but less bold than diploid and triploid brown trout. In small groups, however, rainbow trout were bolder than both types of brown trout. Diploid brown trout were more active and bolder than triploids when tested individually, and had a higher functional response than both rainbow trout and triploid brown trout. In terms of behavioural syndromes, there was no association between activity and boldness in rainbow trout, however, there was in both brown trout types. The increased activity and aggression of rainbow trout may reflect an increased stress response to novel situations, with this response reduced in a group. These results suggest that rainbow trout do not manage their energy budgets effectively, and may explain why they have limited survival as invaders. In addition, the lower functional response of rainbow trout may explain why they are implicated in fewer ecological impacts, and the triploidy treatment also appears to lower the potential impact of brown trout. Comparative analyses of multiple behaviours of invasive species and genetic variants may thus be key to understanding and predicting invader success and ecological impacts.
Highlights
Animal behaviour is increasingly recognised as critical to the prediction of non-native species success and impacts
There was no difference between rainbow trout and diploid brown trout in latency to begin swimming, but rainbow trout were significantly faster than triploids (t = 4.05, df = 66, p < 0.001) as were diploid brown trout (t = 2.39, df = 66, p < 0.05) (Fig. 1C)
Several reports show increased levels of invasiveness and impact of brown trout compared with rainbow trout
Summary
Animal behaviour is increasingly recognised as critical to the prediction of non-native species success and impacts. Rainbow trout and brown trout are both economically and ecologically valuable native species and are among the most impactful invasive species worldwide, with a long history of introductions in many different countries[19,20,21] Both species have successfully established invading populations in Australasia22, Japan[23], South Africa[24], the U SA25, and elsewhere. The success of rainbow trout in Europe (where brown trout is native) is, limited, and in the British Isles, for example, despite many large escapes/releases, there is currently only one known self-sustaining rainbow trout population (in the River Wye, Derbyshire[26]) Where both trout species have been introduced as non-native species, brown trout appears to be a more successful invader with a greater ecological impact on native species. In Chilean Patagonia, rainbow trout were found to successfully invade a greater area than brown trout[28], brown trout were still found to have a greater ecological impact on the native galaxiids
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