Most people know that seahorses are unusual in the fact that the males are pregnant and care for the young; but a recent study has shown that they are also suckers for punishment in that they actively select larger females to mate with so that the resulting eggs and young will be bigger.
The team from the University of Zurich studied the mating behaviour of the Pot-bellied seahorse (Hippocampus abdominalis).
Males of this species undertake all post-fertilization care of the offspring but until recently it was thought that they still had unusually ~conventional sex roles in that the males competed for the attention of the females with the females making the ultimate mate choice.
The study used captive bred individuals and gave them a choice of potential mating partners of varying size. It found that females were generally indiscriminate with their choice of partner whilst males spent considerably longer courting larger females.
Previous studies have found that females body sizes relates directly to egg size, egg number and also offspring size so that the larger a female is, the more eggs she will produce and the larger the offspring will be. Whilst this is true to a certain extent with males, small males can still carry exceptionally large broods suggesting that female choice is somewhat limited.
Recent observations in the wild of this species found large breeding aggregations and have also observed a great deal of aggressive female- female interactions during the mating season which would be expected in a mating system where the males select the female.
The authors Beat Mattle and Tony Wilson concluded "The strong male preferences for large females demonstrated here suggest that sexual selection may act strongly on female body size in wild populations of H. abdominalis, consistent with predictions on the importance of female body size for reproductive output in this species. may offer a means to determine the relative importance of intrasexual competition and mate choice in reproductive interactions"
Future studies may include video-playback experiments where the seahorses are shown digitally enhanced videos of potential mates!
H. abdominalis is distributed throughout the temperate marine waters of New Zealand and south-eastern Australia and is currently listed as threatened in the IUCN red list.