Friday, 20 September 2013

Fishy Fossil Monogamy

Coelacanths give birth to live young
Image: Peter Shunula
Zoologger: The fossil fish that's a serial monogamist - life - 20 September 2013 - New Scientist

Following close on my blog about so-called 'living fossils', our closest living fishy relative, the Coelacanth, is back in the news once again, with this New Scientist article by Andy Coghlan. As so often with science, the answer to one question leads to a couple more questions.

Female coelacanths give birth to a large number of large live young after a gestation lasting three years. This represents an enormous investment for the female, so we would expect her to use a spread bet strategy and mate with several males rather than risk all on a small number of mates. However, DNA analysis of two pregnant Latimeria chalumnae females caught in 1991 and 2007 respectively by Kathrin Lampert and colleagues of Ruhr University Bochum in Germany, showed that all the young had the same male parent.

Coelacanths are carnivorous and live mainly on squid and small fish. The reason for a long gestation and live birth of relatively large young could be because, living together in caves would put small young at risk of being quickly eaten by parents and other coelacanths. Being large and immediately independent would give them a fighting chance of escaping.

So, we now know that females are monogamous, admittedly based on just two examples, but that raises a couple of questions:

  1. Why monogamy when polygamy would be expected?
  2. How does internal mating occur when males don't appear to have the necessary apparatus for penetration?

These massive fish - up to 1.5 meters (nearly five feet) long - live in deep ocean volcanic caves in what are believed to be colonies of a few individuals. It is believed that there are only a few hundred coelacanths still alive, so it could be that males are in short supply. It could also be the mating is a prolonged process, maybe involving mating rituals intended to bring the male and female cloaca into the right alignment for sperm transfer to occur.

But the real answer is that we don't yet know and can only hazard educated guesses.

I wonder if one of my keen creationist readers could suggest an 'Intelligent' Design explanation for males not have the required equipment for internal fertilisation and why females put all their eggs in one basket as a mating strategy. Could it be that a slow lingering extinction is what the benevolent Intelligent Designer had in mind all along when he created coelacanths?

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