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