Alex Mustard - Egg Trading
A black hamlet (Hypoplectrus nigricans) and a yellowbelly hamlet (Hypoplectrus aberrans) spawn at dusk.
And Yes, I am cheating this month with two pictures instead of one. But this pair of pictures are perfect for showing the really fascinating biology of hamlet fish in the Caribbean. The 10 species of hamlets are really in the grip of speciation. The different types are so recently evolved that they are not really full differentiated into different species. There are actually no consistent genetic differences between then – although the 10 species can be easily recognised by their colours. They greatly prefer to mate with their own species, although hybridisation, like this, is possible when they don’t have the option of their own species.
Each time they spawn with their own kind they take a step towards being fully distinct genetically. Every time they hybridise they take a step back. It is expected that over time hybridisation will become less and less common and eventually the 10 species will have differentiated enough to be incompatible. It is a fascinating glimpse into one of the processes of speciation.
These photos also show another highly unusual aspect of hamlet biology. Hamlets are one of the few vertebrates that are true hermaphrodites. Both functioning male and female at the same time. Hamlets take it in turns to play both roles. Usually this is hard to spot when both fish look so similar. But in a hybrid spawning it is much clearer. The female fish holds her body straight, while the male curls around. You can see the roles are reversed on these two spawning clasps in the two photos.
Location: Grand Cayman, Cayman Islands. Caribbean Sea
Tags: black hamlet, Caribbean Sea, Cayman Islands, hybrid, Hypoplectrus aberrans, Hypoplectrus nigricans, spawning, yellow belly hamlet