Reproductive and habitat isolation between two populations of the striated spined loach

Synopsis This study deals with ecological differences influencing reproductive isolation between two sympatric populations, the small and middle forms, of the striated spined loach. As natural hybrids are rare, isolation between these populations must be complete. There are some differences in their reproduction and early life history. Both reproduce in temporary waters flooded in summer, but their spawning sites are isolated from each other. The small form spawns in shallow areas of still water around irrigation creeks or fens. On the other hand, the middle form spawns in slow-flowing ditches. Spawning site segregation between them is an important isolating mechanism, and is a by-product of adaptation in their early life history.