Overlap in the form of sexual signals such as pheromones raises the possibility of reproductive interference by invasive species on similar, yet naive native species. Here, we test the potential for reproductive interference through heterospecific mate attraction and subsequent predation of males by females of a sexually cannibalistic invasive praying mantis. Miomantis caffra is invasive in New Zealand, where it is widely considered to be displacing the only native mantis species, Orthodera novaezealandiae, and yet mechanisms behind this displacement are unknown. We demonstrate that native males are more attracted to the chemical cues of introduced females than those of conspecific females. Heterospecific pairings also resulted in a high degree of mortality for native males. This provides evidence for a mechanism behind displacement that has until now been undetected and highlights the potential for reproductive interference to greatly influence the impact of an invasive species.

Inclusive fitness theory predicts that cannibalism should be more likely to arise if close relatives can be avoided, suggesting that cannibalistic species will possess mechanisms for minimizing predation on kin. Juvenile Miomantis caffra are good candidates for the possession of such traits because; (1) groups of siblings hatch together into the same locale, (2) they are aggressive hunters, and (3) they are strongly cannibalistic. In this study, the possibility of kin recognition or avoidance in M. caffra is investigated by laboratory comparison of cannibalism rates between groups of differing relatedness. In order to examine the likelihood of encounters between early instar siblings, the extent of dispersal away from the ootheca in the days following hatching is also observed. Nymphs did not rapidly disperse after hatching, so the chances of full siblings encountering one another in the wild appear to be high. Despite this, cannibalism was equally high in groups of full siblings and groups of mixed parenthood. We suggest that for M. caffra, a generalist ambush predator, the benefits of indiscriminate aggression may outweigh any inclusive fitness benefits that would be gained from kin discrimination.

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Mate guarding is a widespread behaviour resulting from sperm competition and conflict over optimal remating rates. It is a key way in which males exhibit differential mating investment, and represents a complex interplay between mating effort, intrasexual competition, opportunity costs and sexual conflict. Nevertheless, although there are many examples of exaggerated male structures used to fight rivals, few animals have developed specialized male morphological adaptations for directly sheltering females from disturbance by non-rivals. Here we report on the use of sexually dimorphic, elongated male hind legs, which are used to guard females in the New Zealand cave wētā (Orthoptera: Rhaphidophoridae). We found that male hind legs alongside the female failed to deter rivals from accessing her or disrupting copulation. However, they did reduce the disturbance to females from other, non-rival animals such as juveniles and heterospecifics. Males with longer hind legs were more effective in reducing disturbance, and remained with females for longer. Longer guarding periods also led to higher numbers of matings between pairs. Models of males with artificially altered hind leg dimensions also showed a benefit to greater leg length, and artificially altering the disturbance rate to females also had a significant effect on pair duration. Our results indicate that nuisance disturbance to females may play an important role in driving sexual selection on male leg length and its exaggeration in this species.