sex determination in cephalopods

Discussion in 'Physiology and Biology' started by monty, Sep 18, 2007.

  1. monty

    monty Colossal Squid Staff Member Supporter

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    I've been stumped on this on google scholar (maybe because I don't know the right keywords):

    What determines sex in cephalopods. I know some molluscs are hermaphroditic, but cephs are not... they are born with a gender that doesn't change. How is this determined? I know in a lot of animals, such as humans, there's a heterogametic sex (XY are men) and a homogametic sex (XX are women) but that even among vertebrates (and the occasional outlying mammal) this doesn't apply, and there are heterogametic female komodo dragons, for example.

    I also know there are some fish that change gender based on age or environmental conditions. And colony insects have cases where the queen suppresses sexual development in all other females.

    I found an 1959 paper trying to count chromosomes in octopus that said they couldn't find a sex chromosome, but technology was pretty primitive back then. But I seem to not know the right keywords to search for to get much information on this (or chromosome counts, for that matter, although I found a side reference that chromosome number varies pretty widely in cephs, with octopus and nautilus having 20-some-odd and squids and cuttles having 50-something.)

    Anybody know this sort of stuff off the top of their heads? (or in handy books on their bookshelves? My books have failed me so far....)

    This suggests nobody understands this sort of stuff in molluscs at all: http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1691630&blobtype=pdf
     
  2. Cephalopodia

    Cephalopodia O. bimaculoides Supporter

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    Good question- something that I have been pondering for a long time. I might have to correct you on the 'cephs don't change sex' part. I don't know if this would actually answer your question or not but I found this article that talks about intersexuality in male Ancistrocheirus lesueurii, a squid from South African waters.
    http://www.blackwell-synergy.com/doi/abs/10.1111/j.1469-7998.2006.00093.x

    In addition to sexual dimorphism between males and females where females are typically larger, intersexual males are exhibiting pseudohermaphrotidism leading to larger testis and spermatophores in addition to having nidemental glands but no oocytes and oviducts.

    Also I think if you type keywords such as genetic sex determination in cephalopods on Google scholar, it might come up with more relevant results. You just need to play around with words.
    If someone can come up with more recent journals regarding this, I would be happy to know about it :smile:
     
  3. monty

    monty Colossal Squid Staff Member Supporter

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    Thanks. Sadly, Caltech no longer subscribes to the Journal of Zoology, so I can't read the whole thing... from the abstract, it sounds interesting, but it doesn't mention a genetic tie. My inclination is to say that it's something worth looking into, but in some ways it boils down to the "why do men have nipples?" question... it's not evolutionarily unheard-of for sexual traits to be expressed in the other sex if it's a neutral or advantageous mutation, and it sounds like the authors hypothesize that the larger size that goes along with this mutation is a selective advantage. Does the paper say if they've shown that these males are fertile? It seems to be pretty clear that they're not functional as females...

    It's of course still very relevant to the original question, since it does give a great case study of "what's genetically or hormonally different about these squids from other cephs that don't show this?" which probably goes somewhat hand-in-hand with "why did the mostly-hermaphrodite non-ceph molluscs branch off from the two-sexed cephs?" It's noteworthy than nautilus and the coleoida are both two-sexed, and that there's fossil evidence that at least a lot of ammonoids and nautiloids showed sexual dimorphism (although I suppose that's only indirect evidence for a lack of hermaphrodites or gender-switching...)
     
  4. Cephalopodia

    Cephalopodia O. bimaculoides Supporter

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    Unfortunately I can't access the entire paper as well but judging from the abtract, the pseudohermaphroditism hasn't affected the male functionality in any way and they are very much fertile. Yes it does sway towards a selective advantage( large testis, spermatophores= fitter next generation ?!). I still don't understand why they need to undergo feminization to achieve a larger size...:confused:

    In-depth genealogical studies would be able to reveal the deviation of hermaphrodite cephs from two-sexed cephs. Correct me if I'm wrong but I wouldn't be surprised if the reason turns out to be more due to environmental factors and a bit of 'climate change' in the past. I would think any organism faced with changing abiotic factors would have to adapt itself for survival, even if it means becoming intersexual!
     
  5. monty

    monty Colossal Squid Staff Member Supporter

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    Assuming it's genetic at all: maybe it's caused by some environmental factor (pesticide run-off from farms can cause developmental and hormonal problems in some areas, perhaps something similar is going on in the area where these squids were sampled...)

    Another interesting question might be whether the ancestral protomollusc was 2-sexed and the non-cephs developed their hermaphrodite aspects after the split, or whether the cephs lost that? Since most molluscs, even ones that seem to be similar to the hypothetical first cephalopod, are hermaphrodites, it seems plausible that the cephs lost that... at least some limpets and chitons are hermaphrodites, and I think cephs are believed to have split from the gastropod sometime after the chitons diverged, but I may be remembering that wrong (the kooky segmented chiton shell seems pretty radically different from the gastropods and shelled cephs).
     

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