Intrinsic postzygotic barriers constrain cross‐fertilisation between two hybridising sibling rotifer species of the <i>Brachionus calyciflorus</i> species complex

Abstract Brachionus calyciflorus is a recently described monogonont rotifer species complex that comprises four species. The observation of hybridisation between two these challenges this delimitation. mechanisms reproductive isolation essential to the maintenance integrity remain unclear. Here, we conducted upscaled experiments obtain large numbers hybrid and non‐hybrid dormant propagules. Through hatching assays, compared zygote viability with Furthermore, investigated populations F1 clones assessed their clonal growth rate ability reproduce sexually. Our results demonstrated higher rates morphological abnormality associated mortality in propagules hybrids non‐hybrids yet healthy‐looking proved similar. exhibited high population rates, nevertheless, also observed strong differences influence parental genotype identity. Two‐thirds showed low incidence sexual reproduction almost never produced Clones seemed invest less reproduction. clearly demonstrate existence intrinsic postzygotic barriers caused by relatively most engage may reduce long‐term fitness clones. These probably impede genetic exchange contribute integrity.