Spatial behavior in relation to mating systems: movement patterns, nearest-neighbor distances, and mating success in diploid and polyploid frog hybrids ( Pelophylax esculentus )

Mating success depends not only on genetic and phenotypic characteristics of males and females but also on their spatial position relative to other individuals, which influences the chances for interactions. Hence, any behavior that affects proximity to other individuals can potentially translate into fitness gain or loss. Here, we investigate the effects of genotype on male movement and distance to nearest neighbor (DNN) in three populations of the edible frog Pelophylax esculentus , a natural hybrid between its parental species Pelophylax ridibundus (genotype RR) and Pelophylax lessonae (LL). The system is particularly suited for such an analysis because the fitness differences between mating with a certain genotype are particularly strong. Moreover, which genotype should be preferred differs among populations where diploid hybrids (LR) live in sympatry with P. lessonae (L–E system) and those where diploid hybrids occur in all-hybrid populations together with triploids (LLR and/or LRR) (E–E system). Hence, we expected differences among genotypes in movement patterns and spatial arrangement within the breeding pond. We did, indeed, find such differences. They were predominantly due to density differences between populations, followed by size and condition differences between males. Most relevant for our question was a difference in DNN: in the E–E system, distances between all three hybrid types were equal, whereas in the L–E system LR hybrids tended to stay closer to LL than to other LR. The results are discussed in relation to previous mate choice experiments and theoretical models about mating preferences in the two systems.