ZSL reveals seahorse sperm secrets
Friday 19 January 2007
ZSL scientists have revealed the secrets of the yellow seahorse’s fertilisation strategy. The scientists have discovered that the male produces two different types of sperm which are released outside the body and not directly into the pouch as previously thought.
The ZSL research reveals that the male seahorse cannot put his sperm directly into his brood pouch (the organ in which the growing baby seahorses develop) but releases them outside the pouch, from where they must travel a significant distance outside his body into the pouch. This directly contradicts the commonly accepted theory that sperm travel into the pouch without any contact with seawater. The study was published today in The Journal of Experimental Biology.
Lead author of the paper, ZSL scientist Dr Katrien Van Look, commented, “We were delighted to finally be able to uncover the male seahorse’s fertilisation mechanism, a fascinating area of seahorse reproduction that has been neglected until now. Seahorses are highly unusual in the animal kingdom, as the male broods the eggs rather than the female, as is the case in most species.”
The research found that the male seahorse produced a surprisingly small number of sperm, indicating a high degree of efficiency and an absence of sperm competition, which is often seen in other fish species. Approximately two thirds of the sperm produced was Type 1 sperm, suggesting that the fertilisation process occurs internally, ruling out the possibility of sperm competition. The research suggests that the Type 2 sperm does not take part in the fertilisation process, but that they are a relic of a previous reproductive strategy in which the male seahorse fertilised the eggs in the water before they entered the his brood pouch.
Professor Bill Holt, Head of Science at ZSL and co-author of the paper, commented, “This exciting discovery is particularly important to conservation, as it furthers our knowledge of the reproduction of this vulnerable species. This helps us to understand the implications of environmental change, including global warming and pollution, on the ability of the seahorse to reproduce.”
The yellow seahorse (Hippocampus kuda) has an IUCN Red List status of Vulnerable and is therefore considered to have a high risk of extinction in the wild. The species is marine and is distributed through South-East Asia, Australia and Japan. The yellow seahorse faces threats from habitat degradation, by catch and hunting for use in traditional medicines and aquaria, and as curios.