Abstract
Distinct behaviours can co-vary within individuals. As such, the magnitude of certain behaviours may be partly predicted by other behaviours, rather than the environment. This can constrain behaviours, potentially reducing behavioural variability. Pre-copulatory sexual cannibalism, the consumption of potential mates before copulation, can lead to females remaining unmated, particularly if males are rare. One possible explanation for the persistence of pre-copulatory cannibalism is that sexual cannibalism is correlated with high levels of aggression towards prey. Here, we test this in two species of praying mantis: the highly cannibalistic Miomantis caffra and the less cannibalistic Orthodera novaezealandiae. If cannibalism in M. caffra is linked to aggression towards prey, we predicted that (1) M. caffra would be more aggressive towards prey than O. novaezealandiae, (2) female M. caffra would be more aggressive than males, (3) aggression towards prey would be correlated across juvenile and adult instars for M. caffra but not O. novaezealandiae, and (4) aggression towards prey would be associated with a propensity for sexual cannibalism among individual M. caffra. We found evidence supporting predictions one and two, but not predictions three and four. Surprisingly, aggression was shown to be repeatable and correlated across instars for O. novaezealandiae but not M. caffra. Our results suggest sexual cannibalism is not a product of behavioural co-variation, even in clades where sexual cannibalism is common. This suggests that sexual cannibalism evolves due to the direct benefits it brings to females, rather than being a by-product of high aggression towards heterospecific prey.Significance statementIn some animals, different behaviours co-vary within individuals. This may lead to the emergence of costly behaviours and reduce behavioural plasticity. It is theorized that pre-copulatory cannibalism is a costly behavioural by-product of selection for high levels of aggression towards prey. However, there are very few studies that explicitly test this. Here, we provide a behavioural comparison between two species of praying mantis that vary in their propensity to cannibalize and tested whether general aggression is linked cannibalism. We found that aggression towards prey in adults can be linked to juvenile aggression but not a propensity for cannibalism. Although cannibalism rates were higher in the species that was more aggressive towards prey, aggression towards prey was not linked to cannibalism within individuals. This suggests that pre-copulatory cannibalism is not a behavioural by-product but a result of direct selection.
Highlights
Evidence from certain species suggests that some behaviours are consistent within individuals across ecological contexts and correlate with different behaviours among individuals (Sih et al 2004)
We found no correlation between juvenile aggression and adult aggression in M. caffra and very little evidence for behavioural repeatability, showing that consistency in aggression across time is not linked to the high frequency of sexual cannibalism in M. caffra
The aggressive spillover theory for pre-copulatory cannibalism proposes that aggression in some species is linked across developmental and ecological contexts and that sexual cannibalism is a byproduct of this aggression
Summary
Evidence from certain species suggests that some behaviours are consistent within individuals across ecological contexts and correlate with different behaviours among individuals (Sih et al 2004) This has the potential to restrict behavioural variation within individuals (Pruitt et al 2008), which may have implications for species’ ecology (Pruitt and Riechert 2012). Individual variation in aggression is known to be consistent across developmental and environmental contexts in certain species (Arnqvist and Henriksson 1997; Dingemanse et al 2007) and can correlate with a variety of other behaviours that determine fitness (Smith and Blumstein 2008). Studies across several spider families have shown that aggression towards prey is positively correlated with a propensity for pre-copulatory cannibalism: the killing and eating of potential mates prior to copulation (Arnqvist 1992; Riechert and Hedrick 1993; Arnqvist and Henriksson 1997; Johnson and Sih 2005; Pruitt et al 2008; Rabaneda-Bueno et al 2014)
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