Ant predation as a selective agent on overwintering eggs in a field cricket mosaic hybrid zone

Abstract

Hybrid zones may serve as arenas for the evolution of barriers to gene exchange while still allowing the exchange of favorable alleles between species. Differential introgression of linkage groups indicate favored, neutral, and disfavored genomic regions with respect to intrinsic (epistatic interactions, linkage to specific genes) and extrinsic (environmental selection, behavior, ecological interactions) environments. Additionally, the ability of alleles to introgress will depend on hybrid zone structure (opportunity for individuals to interact) and maintenance (criteria for favorable traits). Thus, trait differences that influence local distribution within these hybrid zones contribute to species coexistence and persistence in the face of hybridization. The mosaic hybrid zone between two North American field crickets, Gryllus firmus and G. pennsylvanicus, is structured by underlying soil heterogeneity in Connecticut. Despite this, it is not clear what role soil type plays in maintaining this hybrid zone. A companion study demonstrated that abiotic characteristics of different soil types do not cause significant viability selection on diapausing cricket eggs that overwinter in the soil. Instead, other environmental factors, such as winter weather, play larger roles in egg survival. Here I investigated one biotic factor that potentially has a large effect on egg survival — predation by ants. These results show that when ants are present, egg mortality is dramatic, increasing 2.5 fold against areas without ant infestations. Although not significant, there is some indication that ant activity may vary among sites and soils. Hence, this biotic factor may influence the distribution of cricket species in this hybrid zone and consequently the dynamics of their interactions.