What makes a male anglerfish evolve into a tiny parasitic attachment on its mate?

Embargoed until: Publicly released: 2026-07-22 09:01

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They're well known for their weird looks, and some anglerfish species have pretty weird mating arrangements too, with the male shrinking down to a tiny size and becoming little more than a parasitic attachment on the larger female, but why has such an unusual reproductive system evolved in this group, and why is it only found in certain species? Japanese scientists investigated anglerfish using computer simulations, and found that parasitic males are favoured when females are in short supply, so encounters are rare, and the costs of being a parasitic appendage on the female's body are low. On the flipside, when mates are plentiful and the costs of being a parasitic male are high, the males remain free-living. The findings help explain why only some anglerfish species have evolved this odd mating system, the authors conclude.