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Effects of body size divergence on male mating tactics in the ground beetle Carabus japonicus


Okuzaki, Yutaka (2021), Effects of body size divergence on male mating tactics in the ground beetle Carabus japonicus, Dryad, Dataset,


Animal body size is involved in reproduction in various ways. Carabus japonicus exhibits considerable variation in adult body size across geographical locations depending on the larval environment. To investigate the effects of body size divergence on male mating traits, spermatophore deposition and weight, copulation duration, and post-copulatory mounting were observed using male-female pairs from C. japonicus populations with different body sizes. Then, variables with high predictive power on the mating traits were identified from individual characteristics. When the male was slightly smaller than his mate, spermatophore deposition likely succeeded, suggesting that mechanical size-assortative insemination determined male body size. Although male reproductive organ size was positively correlated with male body size, spermatophore weight was not significantly affected by male body size, whereas copulation duration decreased with increasing male body size. Enlarged males, with a high capacity for spermatophore production, could increase paternity by decreasing copulation duration and increasing mating frequency. Such shifts in mating tactics would alter selection pressures of intra- and intersexual interactions (e.g., sperm competition and sexual conflict). Genital dimensions also affected mating traits other than copulatory duration. Thus, ecological heterogeneity has the potential to lead to divergences in sexual traits, such as genital morphology, through body size divergence.