Competitive habitat utilization in the damselfly,Mnais nawai (Zygoptera: Calopterygidae) coexisting with a related species,Mnais pruinosa

Reproductive interference explains persistence of aggression between species

Interspecific territoriality occurs when individuals of different species fight over space, and may arise spontaneously when populations of closely related territorial species first come into contact. But defence of space is costly, and unless the benefits of excluding heterospecifics exceed the costs, natural selection should favour divergence in competitor recognition until the species no longer interact aggressively. Ordinarily males of different species do not compete for mates, but when males cannot distinguish females of sympatric species, females may effectively become a shared resource. We model how reproductive interference caused by undiscriminating males can prevent interspecific divergence, or even cause convergence, in traits used to recognize competitors. We then test the model in a genus of visually orienting insects and show that, as predicted by the model, differences between species pairs in the level of reproductive interference, which is causally related to species differences in female coloration, are strongly predictive of the current level of interspecific aggression. Interspecific reproductive interference is very common and we discuss how it may account for the persistence of interspecific aggression in many taxonomic groups.

Niche partitioning in three sympatric congeneric species of dragonfly, Orthetrum chrysostigma, O. coerulescens anceps, and O. nitidinerve: the importance of microhabitat

Habitat heterogeneity has been shown to promote co-existence of closely related species. Based on this concept, a field study was conducted on the niche partitioning of three territorial congeneric species of skimmers (Anisoptera: Libellulidae) in Northeast Algeria during the breeding season of 2011. According to their size, there is a descending hierarchy between Orthetrum nitidinerve Sélys, O. chrysostigma (Burmeister), and O. coerulescens anceps (Schneider). After being marked and surveyed, the two latter species had the same breeding behavior sequence. Knowing that they had almost the same size, such species could not co-occur in the same habitat according to the competitive exclusion principle. The spatial distribution of the three species was investigated at two different microhabitats, and it was found that these two species were actually isolated at this scale. O. chrysostigma and O. nitidinerve preferred open areas, while O. c. anceps occurred in highly vegetated waters. This study highlights the role of microhabitat in community structure as an important niche axis that maintains closely related species in the same habitat.

Interspecific barriers between salmonids when hybridisation is due to sneak mating

Male sneaking behaviour can lead to interspecific hybridisation if sneakers attempt to fertilise ova in heterospecific mating, contributing to break down of interspecific barriers. In south European rivers, sneaking Atlantic salmon males fertilise an important proportion of ova from adult females in heterospecific crosses, up to 65%. In a south French flow-controlled stream, we found that they were able to naturally fertilise brown trout ova in absence of brown trout males. Aggressiveness of brown trout males towards sneaking salmon males and low survival of hybrids issued from salmon sneakers are found to be interspecific barriers.