Exaggerated male genitalia intensify interspecific reproductive interference by damaging heterospecific female genitalia.

Male-male competition over fertilization can select for harmful male genital structures that reduce the fitness of their mates, if the structures increase the male's fertilization success. During secondary contact between two allopatrically formed, closely related species, harmful male genitalia may also reduce the fitness of heterospecific females given interspecific copulation. We performed a laboratory experiment to determine whether the extent of genital spine exaggeration in Callosobruchus chinensis males affects the fitness of C. maculatus females by injuring their reproductive organs. We found that males with more exaggerated genital spines were more likely to injure the females via interspecific copulation and that the genital injury translated into fecundity loss. Thus, as predicted, reproductive interference by C. chinensis males on C. maculatus females is mediated by exaggeration of the genital spine, which is the evolutionary consequence of intraspecific male-male competition. Harmful male traits, such as genital spines, might generally affect the extent of interaction between closely related species.

Strong plastic responses in aerenchyma formation in F1 hybrids of Imperata cylindrica under different soil moisture conditions.

Hybrids can express traits plastically, enabling them to occupy environments that differ from parental environments. However, there is insufficient evidence demonstrating how phenotypic plasticity in specific traits mediates hybrid performance. Two parental ecotypes of Imperata cylindrica produce F1 hybrids. The E-type in wet habitats has larger internal aerenchyma than the C-type in dry habitats. This study evaluated relationships between habitat utilisation, aerenchyma plasticity, and growth of I. cylindrica accessions. We hypothesize that plasticity in expressing parental traits explains hybrid establishment in habitats with various soil moisture conditions. Aerenchyma formation was examined in the leaf midribs, rhizomes and roots of two parental ecotypes and their F1 hybrids in their natural habitats. In common garden experiments, we examined plastic aerenchyma formation in leaf midribs, rhizomes and roots of natural and artificial F1 hybrids and parental ecotypes and quantified vegetative growth performance. In the natural habitats where soil moisture content varied widely, the F1 hybrids showed larger variation in aerenchyma formation in rhizomes than their parental ecotypes. In the common garden experiments, F1 hybrids showed high plasticity of aerenchyma formation in rhizomes, and their growth was similar to that of C-type and E-type under drained and flooded conditions, respectively. The results demonstrate that F1 hybrids of I. cylindrica exhibit plasticity in aerenchyma development in response to varying local soil moisture content. This characteristic allows the hybrids to thrive in diverse soil moisture conditions.