Locomotory mimicry in ant-like jumping spiders (Salticidae)
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The jumping spider genus Myrmarachne (Salticidae) contains many different morphological ant mimics that resemble a wide variety of ant species. This mimicry enables Myrmarachne to evade ant-averse predators that confuse the spiders with ants. A conspicuous trait of Myrmarachne, which is frequently mentioned in the literature but has been overlooked experimentally, is locomotory mimicry. In this thesis, I quantified, for the first time, the locomotory pattern of non-ant-like salticids, Myrmarachne, and their presumed models. Indeed, I found that the locomotion of the mimics resembles that of ants, but not of other salticids. I then attempted to identify whether this behavioural mimicry enhances the morphological component of the mimicry signal. The locomotion component was tested by modelling a 3D computer animation based on the morphology of Myrmarachne, and then applying either non-ant-like salticid motion characteristics or ant-like locomotion to the models. These animations were presented to ant-eating salticid predators, which are known to have acute vision, in order to identify any differences in how the predators reacted to each virtual prey type based solely on differences in locomotory behaviour. No significant effect was identified for enhancing the deception, but there was a non-significant trend that hinted at an enhancement of the mimicry signal, suggesting that a more robust finding would be found with a larger sample size. Additionally, ant mimics are unusual in their relationship to their model organism, as the ant models are also potential predators of the mimic. Predation by visual ant species may exert selection pressure on Myrmarachne across some aspects of morphological or behavioural mimicry. In turn, this may select for traits that improve Myrmarachne’s survival in close proximity to their highly aggressive models. Consequently, I investigated whether ant-like locomotion is salient to a visual ant species, Oecophylla smaragdina. I found that the locomotion typical of ants and Myrmarachne is more attractive to ants than non-ant-like salticid locomotion. This suggests that the trade-off of increased resemblance to ants is not just towards being categorised as prey by ant-eating species, but also by being more attractive to ant species. This may place them at greater risk of predation by the model. As a whole, these results suggest that there is selection pressure on Myrmarachne for increased resemblance to a model by locomotory mimicry, despite associated costs when faced with ant-eating predators and when living in proximity to models that are both aggressive and visual.