Sex Determination as a Bottleneck to Species Development
6Garrett Baker
2Dacyn
1Morpheus
2leerylizard
1Morpheus
New Comment
For Mississippi alligators at least, while the determining factor for sex is temperature, this is likely more a proxy for birth location than it is climate or weather patterns. If the nest is on leaves, then the egg temperature is about 34 C, and if its in a marsh, then the egg temperature is 30 C, meaning the leaf nests produce males and the marsh nests produce females.
This information comes from (an old edition of) Gilbert's Developmental Biology.
1So if the climate is moving out of the optimal temperature for the species, it might make sense for you to produce more females, because they are a lower risk strategy?
This seems confused to me. In general, males are more risk-seeking than females because (inclusive) fitness is not a linear function of successfulness at endeavors, with the function being closer to linear for males and more like linear-with-a-cutoff for females. But males and females are still both perfectly risk-neutral when measured in the unit of fitness, since that follows from the definition of expected fitness which is what needs to be greater than average in order for a mutation to propagate throughout a population.
I would expect that if a species has more females than males in some circumstances, then either it is because females are cheaper to raise for some reason, or else that it is due to a fact of biology that the DNA can't really control directly.
Yes! For the individual, it does not make sense to adjust the sex ratio with changes in climate, but for the species overall it's not that bad or even positive. Sex chromosomes do a much better job for the individual here (And would be selected for if temperature changes were happening too often). I do think I had confused thinking at the time, because I also had just read about a theory in humans that high status females supposedly produce more males (so payoff could be different between low and high status, but that doesn't apply in this case, and it's not born out well empirically anyway).
What I do think is true: It might not be that much of a coincidence that climate change would lead to more females. If it was the other way around, there is a higher likelihood the species would have gone extinct from a meteor, and we wouldn't observe it today. Having 1% females and 99% males is going to lead to a really bad population bottleneck, but having 1% males and 99% females just means the remaining males have little competition (the effective population is still reduced to some extent). The fact that turtles don't fit this pattern and look like they should have gone extinct with the last meteor tells you how weak and slow selection between species is.
I was thinking of this when I saw these articles complaining how sex ratios are supposedly endangering sea turtles. It doesn't seem obvious to me that the sex ratios alone should be a problem (although 1/99 is probably bad).
Haplodiploidy in hymenopterans (ants and wasps) has a huge impact on eusociality: All daughters of the queen get half their genes from their father's entire genome (the father's sperm are all identical), which means they share 75% of their genes with their sisters rather than the 50% in others like termites. For this reason, Eusociality has evolved independently multiple times in hymenopterans.
I would speculate that the colony is more cohesive for this reason, and this may have an impact on why ants are so successful in so many niches.
Termites, on the other hand, have one key thing going for them: the ability to digest wood. This allows them to fill their specific niche well.
I thought about this a bunch of years ago, and I am not quite sure how much this matters. Often ants get sperm from multiple fathers, and then they'd be less related than siblings (although maybe they only start doing that once they are out of the unstable intermediate period between being not eusocial and being eusocial). Also, this leads to colonies producing fewer males than would be game theoretically optimal for the queen and to conflict between queen and workers (50/50 would be optimal), although that might be helpful on the species level? So I think most of the cohesion benefits from 75% kinship between daughters is offset by the 25% kinship between brothers and sisters and if the queen mates with 2 males instead of 1, then the kinship is actually less than with monogamous termites (which is most termites, while I think most ant queens mate with multiple males).
I do think the difference in kinship could make it easier to develop eusociality, but I think my above argument that you just need a queen, so adapting behaviour is a simpler program might explain better how ants got through the unstable period between being individualistic and being sort of eusocial better (also if you start out with two parents there is less marginal returns to another worker for the nest, so that might also explain why it happened so often in Hymenoptera rather than other nest building insects). There are some wasp species that sometimes decide to build nests together and do division of labour (protect nest, search food) even though they are unrelated, but I forgot their name (Most of my opinion above is informed by the Superorganism book from EO Wilson. He has some idiosyncratic beliefs when it comes to group selection, but I think when it comes to his analysis that the kinship seems marginally important, he seems right). The kinship could explain why ants developed it multiple times, but it doesn't explain why termites even after developing eusociality didn't expand further.