Are there more female octopuses than male?

Discussion in 'Physiology and Biology' started by Octavarium, Mar 15, 2008.

  1. Octavarium

    Octavarium Wonderpus Registered

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    I wonder, because it seems like so many people describe their octopuses laying eggs, it seems like the population is dominated by females. Is their any evidence of this in the progeny, or is it just a coincidence.
     
  2. Nancy

    Nancy Titanites Staff Member Moderator

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    Interesting question, but you also have to ask whether females are more likely to be captured as wild caught octopuses than males.

    I remember reading a few years ago that female octopuses are more likely to crawl into pots, but I've also heard the opposite. I wonder whether any research has been done in this area.

    Nancy
     
  3. robyn

    robyn Vampyroteuthis Supporter

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    I've heard that female nautiluses supposedly comprise 75% of the population, can't remember where I heard it, but that could also be a trapping bias. Interesting question..
     
  4. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

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    In the Tropic Shale of Southern Utah you only find the female dimorph of Metoicoceras geslinianum, yet in New Mexico the ratio is about 1:1, biogeographical bias?
     
  5. gholland

    gholland Haliphron Atlanticus Supporter

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    You also have to keep in mind that not many people will write to report about their octopus NOT laying eggs. :wink: Baited pots might be more likely to attract gravid females when they are in their food binging period right before laying.
     
  6. L8 2 RISE

    L8 2 RISE Haliphron Atlanticus Registered

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    Could it have something to do with temperature? For example, in Caretta caretta, if the temperature of incubation is ~24-26 C the egg will most likely be male, if the temperature of incubation is ~32-34 C the egg will most likely be female, in between those 2 temperatures is neutral and usually results in a 1:1 ratio. Is this the case with octo eggs? If this is the case, could climate change have anything to do with a higher population of female octos?
     
  7. monty

    monty Colossal Squid Staff Member Supporter

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    I've been trying to figure out what drives sex determination in cephalopods, and as far as I've been able to tell, it's not known. There are no species of cephs that ever change sex or hermaphrodites, so a genetic determination seems likely, but hardly proven... temperature would certainly be a factor to look at in any studies. One more reason we need an octopus genome project (and a cuttlefish genome project, and a squid genome project, and a nautilus genome project, and especially vampyroteuthis/argonaut/spirula genome projects!)
     
  8. gjbarord

    gjbarord Sepia elegans Staff Member Moderator

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    Good discussion. Some of my thoughts.

    I would guess that female octopus are just more likely to be caught than their male counterparts. Many are caught already at the end of their life and the pot would be an enticing den, while males would be more active at this point and probably fall victim to predation. I would think that the sex ratios in the wild are fairly balanced given that most octopus will die shortly after mating. There would be no advantage to having more males than females, or the reverse. Although, sperm competition has been noted in cuttlefish so perhaps more males exist in the wild??? I would not believe there to be more females based on anecdotal evidence.

    The nautilus statement sounds intriguing. Perhaps in that case, the fact that nautilus have much slower maturity rates than other cephalopods and are able to reproduce more than once, having more females would allow the greatest chance for population expand.

    Greg
     
  9. monty

    monty Colossal Squid Staff Member Supporter

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    Great comments, but I'm confused by this part:

    I think I'm missing something here... since most male octos (AFAIK all except argonauta, where the hectocotylus breaks off during mating, and I don't know if it is regrown, but even if it is, it's hight cost) can mate numerous times once they reach maturity, even with immature females that can store spermatophores for months, doesn't the "die shortly after mating" argument only apply if the male can't roam a lot looking for multiple mates?

    It seems like, looking at large numbers of animals, most have a pretty even sex ratio, which certainly seems good for the whole population (if you believe in group selection) in that it keeps the gene pool shuffled. This would seem to apply to most cephs, and pretty much most animals, but there's certainly a number of exceptions... I know lion pride structure is one male and many females, but I don't know if that's maintained by an uneven birth sex ratio, or of males kill each other off, or there are just a lot of wandering unattached males. Similarly with deer and pinnipeds, IIRC, at least deer when it's OK for the locals to shoot bucks but not does... I wonder if anyone's done genetic diversity studies of deer populations comparing "hunting allowed" and "no hunting" (like national parks)?

    What I'm getting at is that there seem to be more exceptions than rules in terms of looking at the diversity in animals in sex ratio's impact on reproductive strategy, so "there would be no advantage" doesn't seem to show obvious universal rules in animals that are easier to sex by observation...

    I'd almost say sex ratio and reproductive strategy seems to have different selective advantage or disadvantage based on context, and is often neutral enough that animals have drifted into a diverse set of strategies. And it seems like cephs have a fairly wide variety of strategies, ranging from the single event schooling mating behavior followed by egg-laying and death common in shallow-water squids like Loligo and seen in Sepia apama to the more spread-over-time we see in captive bandensis to Nautilus laying eggs over years, to most octopus having a fairly long window for females to mate and store sperm, but then having a single brooding event just before senescence (except for chierchiae) to Steve's reconstruction of Architeuthis having infrequent encounters (squids passing in the night) needing extensive sperm storage rather like octopuses.

    I'm not meaning this to be a counter-argument, more of a brain-dump of things I'm finding confusing, interesting, or both in this discussion...
     
  10. Octavarium

    Octavarium Wonderpus Registered

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    Excellent input so far, it seems I learn more on these boards then i did in BIO 430 (marino bio)!
     
  11. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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    Mark, Henk Hoving published a VERY interesting paper on hermaphrodite (I recall male and female structures, but not sure if fully functional) squid off South Africa. Brain is too exhausted to recall the details, but it came out last year in 'Reviews in Fish Biology and Fisheries' (I think the title was). Tomorrow I'll cite more, with literature at hand.
     
  12. monty

    monty Colossal Squid Staff Member Supporter

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    Fascinating! I suppose that's what I get for pretending there are any rules without exceptions in biology... I wonder if this is a reversion to an earlier evolutionary state (I know hermaphrodite non-ceph molluscs aren't too unusual) or something that developed on its own.
     
  13. Jean

    Jean Colossal Squid Supporter

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    It's interesting that if we pot for an octopus (for the aquarium) 9 times out of 10 we'll get a male, if we want a female (not terribly likely, they're more strongly nocturnal than the males! Not good in a display animal) we have to dredge! this is for P. cordiformis.

    J
     
  14. Steve O'Shea

    Steve O'Shea Colossal Squid Supporter

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  15. monty

    monty Colossal Squid Staff Member Supporter

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    fooey, I don't have full-text access to that one. It looks like the abstract pretty much says it all, though, right?

    This actually is starting to sound familiar, I wonder if you've mentioned it before and I'd forgotten. It's certainly interesting, and I wonder what its evolutionary implications are... I could imagine it being just an activation of some useful sexual characteristics, in the "why do men have nipples?" sense, or a throwback to a Cambrian hermaphrodite mollusc's genes being re-enabled. Very curious indeed. And quite possibly a Rosetta stone for "how is sex determined on cephalopods" research!
     
  16. Fujisawas Sake

    Fujisawas Sake Larger Pacific Striped Octopus Supporter Registered

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    Grrr.. that abstract was pretty abstract. There's difference between intersexuality and actual sexual reassignment. I would like to read this paper to see if there was any environmental factors (i.e. hormones in the water, etc.). The genes for hermaphrodism are there, I would bet, buried in countless millenia of evolutionary pathways. Yes, cephs are usually gonochoristic and all, but more about these oddball males would be nice - at least to see if there is a reproductive effect here.

    It seems more like the paper should focus on identifying and describing the pseudohermaphroditism rather than postulate on the distribution of the anomaly(?) across the entire population unless the sample size was really significant and covered the entire oceanographic range.

    "Why do men have nipples?" - besides them being functional in rare cases of gynecomastia, plus that some species of male bats actually functionally lactate, its also because all vertebrate embryos are inherently female, but recieve the male "trigger" during development. You probably already knew that.

    I can't imagine the sex being determined by temperature (great nod to Caretta by the way - I've worked with that species and I have a soft spot in my heart for sea turtles) in octos, but then again who knows?

    - John
     
  17. gholland

    gholland Haliphron Atlanticus Supporter

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    If sex were temperature dependent, wouldn't we have seen a bunch of single-sex hatches in captivity?
     
  18. Neogonodactylus

    Neogonodactylus Haliphron Atlanticus Staff Member Moderator

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    Ramblings on deviation from primary 1:1 sex ratio

    This is from my lecture on primary sex ratio and some circumstances that may cause it to deviate from 1:1.

    Roy

    IV. There are circumstances that will cause the primary sex ratio to vary from 1:1 investment. These are particularly instructive pointing out why the rule is so general. Let me give you five circumstances that will produce a shift in primary sex ratio.

    A. Local Mate Competition. Suppose that two or more sons compete only among themselves for opportunities to mate. The mother would do better to put reproductive effort into producing daughters since one son can do all the mating necessary. This typically happens in species where there is little opportunity for dispersal outside of the family unit.

    1. Acarophenox: viviparous mite. The female produces one son and about 20 daughters. The male mates with his sisters before they are even born from the brood pouch. (Note: This doesn't produce clones because females may occasionally mate after birth.)

    2. Parasitoid Wasp, Nasonia vitripennis: females lay eggs in fly larvae. If only one female parasitizes a fly larvae, all daughters will be fertilized by sons. We would expect extreme local mate competition. Only 8% of brood is male. Remember, these are wasps and females can control sex of offspring by whether or not they fertilize the egg. If a second female lays eggs in same fly, she can detect the presence of eggs from another female and begins by laying more males, but then switches to females.

    B. Local Resource Competition. In Galago, male biased investment in offspring. Why? As in many mammals, females disperse less than males. Daughters end up competing with mother and sisters for limited food (gum and fruit). Severe limitation so that usually only one female can survive to replace her mother and breed. Additional investment in daughters is wasted since the environment is pretty much saturated with breeding females, so it is better to make more sons. They have a chance of dispersing and each finding a breeding female.

    In birds, helpers at the nest occur in some species. These are often males since the females are the sex that disperses. If males really can increase reproductive success, then more males should be produced. This appears to happen in a few species.

    C. Maternal Condition. In the red deer studied by Clutton-Brock, males compete with one another to fertilize females. Bigger, stronger males do better. A mother's ability to nurse affects her ability to produce big sons. If she has lots of milk, she can produce larger offspring. A female's dominance status within the herd of females influences her ability to forage and thus her production of milk. Dominant females produce more sons. Subordinate females produce more daughters as would be predicted. We don't know the mechanism.

    Some have tried to apply this same argument to human societies. Powerful clans should produce sons since they can take many wives. Weak families should produce daughters since a son would have little chance of taking a wife. A daughter has a better chance of reproducing.

    Kakapo Parrots of New Zealand. This is a nocturnal, flightless parrot that is extremely threatened. There are only 83 birds left. They have a lek breeding system where male Kakapos clear a display arena and call for females. There is strong competition and a lot of reproductive skew with the biggest males getting the most copulations. In a situation such as this, sex allocation theory predicts that fit females should produce sons; small, low weight females should produce daughters. However, conservationists had intervened and were feeding the kakapo females trying to get them to reproduce more. Typically, female kakapos only breed every few years when the Rimu trees bear fruit. If the females reach a weight over 1.5 kg, they breed. The thinking was that if the females were fed and brought to reproductive weight, they might reproduce more often. Unfortunately, because of this, the fed females were producing more young, but they were 70% males – not a good way to make more kakapos. Beginning five years ago, the fat females were put on a diet and all females were kept just over 1.5 kg. It worked. The sex ratio came back slightly in favor of females. Provisioning still occurs, but only after the eggs are laid and the sex ratio determined.

    D. Population Sex Ratio. When the population sex ratio deviates from 1:1, an individual that could engage in a compensatory shift would be favored. In Polistes, when queens die, the colony can still produce some males (unfertilized eggs) in the hope that they will reproduce. Since this happens frequently, queen right colonies produce slightly more queens to compensate for this over production of males.

    In white-tailed deer, if males are scarce, females produce more males. If males are common, they produce more females. This is determined by how long it is after ovulation that a female is fertilized. If the female is mated within 24 hrs, 14% of the offspring are male. If she mates after 96 hrs, 80% are male.

    E. Population Growth. If a species periodically experiences opportunities for population explosion, might favor more females because this will favor more rapid growth. This happens in wood lemmings. Primary sex ratio is 3:1 female. Species is diploid. Female is XX, Male is XY, but there is a second kind of X, X*. XX* is female, but X*Y is also female because genes on X* suppress the effects of the Y. Also, genes on X* prevent the formation of Y eggs. The result is that X*Y produce only daughters. If X and X* are in equal frequency, only 1/4 of the individuals will be XY and thus male.
     
  19. Taollan

    Taollan Vampyroteuthis Supporter

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    I wonder if the apparent skew towards females showing up in the pet trade could be related to seasonality of the location of different sexes. I have noticed in in some of my collection sites for O. rubescens that during certain parts of the year (summer and fall) about 90% of the octopuses I collect will be male, while during the winter and spring many more will be female (about 80%). If there were people collecting these octopuses for the pet trade, and if they were only collecting during certain seasons (perhaps avoiding the harsh weather during the Salish Sea winter) they may conclude the population is dominated by males.
     
  20. Paradox

    Paradox Haliphron Atlanticus Supporter

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    Great post for Ive been thinking about this in relation to cuttlefish.

    In every batch of Bandensis that I have raised from eggs, I always had many more males then females. This was also the case for Rich. I believe Cuttlegirl also had 2 males and a single female. All these were raised from wild caught eggs. However, the eggs had time to develop in our systems. Im curious to know if this is coincidence, relates to temperature, thier ability to develop hunting skills, or some other factor. There are often runts in the litter that die younger probably from starvation. Perhaps these are all females?

    Knowing the answer to this question would be very helpful for future breeding attempts.
    Any thoughts?
     

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