Abstract
Reproductive interference can shape regional distribution patterns in closely related species, if prezygotic isolation barriers are weak. The study of such interaction could be more challenging in nuptial gift‐giving species due to the direct nutritional effects on both sexes of both species during copulation. We mapped the distribution of two sister bush‐cricket species, Pholidoptera aptera and Pholidoptera transsylvanica, at the northern margin of their overlapping ranges in Europe, and with a behavioral experiment, we tested the possibility of heterospecific mating. We found a very rare coexistence of species locally (0.5%, n = 391 sites) with mostly mutually exclusive distribution patterns, resulting in a mosaic pattern of sympatry, whereas they occupied the same climate niche in forest‐dominated mountain landscape. Over 14 days of a mating experiment with seven mixed groups of conspecifics and heterospecifics (n = 56 individuals in total), the number of received spermatophores per female was 3–6 in P. aptera and 1–7 in P. transsylvanica. In total, we found 8.1% of heterospecific copulations (n = 99 transferred spermatophores with genetic identification of the donor species), while we also confirmed successful transfer of heterospecific sperms into a female's reproductive system. Because bush‐cricket females also obtain required nutrition from a heterospecific spermatophylax what should increase their fitness and fecundity, we suggest that their flexibility to mate with heterospecifics is beneficial and drives reproductive interference. This may substantially limit the reproductive success of the less frequent species (P. transsylvanica), coupled with eventual detrimental effects from hybridization, and result in the competitive exclusion of that species from their areas of coexistence.
Highlights
The study of interactions between closely related taxa which occupy a sympatric range is important for understanding the evolutionary adaptations and isolation mechanisms that lead to their coexistence or divergence (Chesson, 2000; Hewitt, 2001)
To learn how regional distribution patterns of such species are shaped, we should be interested in both the barriers that prevent coexistence and the factors that result in the competitive exclusion of the inferior species (Grether, Losin, Anderson, & Okamoto, 2009; Gröning & Hochkirch, 2008; Kyogoku, 2015; Wellenreuther, Larson, & Svensson, 2012)
Heterospecific mating, ranging from mating attempts to hybridization between sister species, has been demonstrated in a wide range of animal taxa (Gröning & Hochkirch, 2008), and it is known in different genera of Orthoptera (e.g., Allonemobius, Gregory & Howard, 1993; Pterophylla, Barrientos-Lozano, 1998; Orchelimum, Shapiro, 2000; Tetrix, Hochkirch, Deppermann, & Gröning, 2006, Gröning et al, 2007, Chorthippus, Vedenina, Kulygina, & Panyutin, 2007; Poecilimon, Lehmann, Siozios, Bourtzis, Reinhold, & Lehmann, 2011; Aglaothorax, Cole, 2016; Phaneroptera, own unpublished data)
Summary
The study of interactions between closely related taxa which occupy a sympatric range is important for understanding the evolutionary adaptations and isolation mechanisms that lead to their coexistence or divergence (Chesson, 2000; Hewitt, 2001). Copulation between related species shows no obvious behavioral differences to conspecific mating, as spermatophores, including sperms, are successfully transferred (Lehmann et al, 2011).
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