#i have no idea what saskia’s normal body temperature is i am still bouncing wildly between ‘runs hot bc dragon’ and ‘runs cold bc lizard’

[laurelnose]

being mean to Roche is Iorveth’s thing!!

right, so for temperature-dependent sex determination, the temp of the egg is what matters. there’s a critical period midway through incubation, about 1-2 weeks long, where gonad development becomes fixed, called the TSP (thermosensitive period). after this period, it doesn’t matter what temperature the egg is, the phenotypic sex is unaffected. (phenotypic sex being: sex defined by which reproductive organs are present. notably, some people say for a species to be truly considered to have temperature-dependent sex determination, they need to not have genotypic sex. that is, no X, no Y, no Z or W, no sex chromosomes period. this isn’t really relevant I just think it’s kind of fascinating.)

during the TSP, consistent temperature above or below certain thresholds will definitely produce either a male or female hatchling. for instance in American alligators 30°C and below produces all girls, 34°C and above produces all boys. eggs incubated at a consistent temperature between these cutoffs may produce male or female hatchlings. (also in some species high and low temperatures both produce females, while median temps produce males.) you can see these temps are pretty similar; this is the case in all species. differences of 1-3 degrees can have huge impacts on development. this is probably because there’s not exactly a massive range of temperatures that an egg can safely be at to begin with. if it’s too hot or too cold for too long, egg dies.

the trick, though, is if the temperature is not consistent. (in nature it never is! for instance, even in the hypothetical perfect world where the weather is constant, it tends to be colder at night.) there is no short answer to this tho. what happens when the temperature varies is wildly different between species, and it depends a lot on what the average temperature is and how much the temperature varies. also it’s a little understudied because uh, it is way easier to do experiments where you keep your eggs at a constant temperature.

(in one 1974 study on turtles, fluctuating the temperature daily produced intersex turtlets (i.e. turtlets that developed ovaries and testes) but his results haven’t been replicated and in general hatchlings like this are extremely rare and I don’t think we have a very good understanding of what, if any, effect temperature has on the occurrence of that kind of intersex condition in reptiles. now, some reptiles, such as the alpine skink Bassiana duperreyi, DO have sex chromosomes AND can be influenced by temperature in development, producing XX hatchlings with testes. this is considered a type of intersexuality in humans but apparently is not in reptiles because all these papers keep insisting “intersex hatchlings” are vanishingly rare sometimes while mentioning it is totally normal in alpine skinks to have “XX females” and both “XX males” and “XY males.” herpetologists explain.)

but! if, hypothetically, Iorveth spends his nights during the egg’s TSP cuddling with someone warmer than he is, yes, it will affect the hatchling’s sex. regular large fluctuations in temperature like this make the hatchling more likely to be female. if the fluctuation is large enough (8° hotter and colder than the mean) the likelihood can go from 0% girls to 100% girls. but regularly being 8° hotter than normal sounds pretty hellish to me.

(though—there was a REALLY INTERESTING hypothesis—some reptile embryos react to temperature changes by moving within the egg, and scientists thought it might be possible that they could moderate their own temperature this way, possibly allowing embryos to exhibit some control over sex development. this has been disproven for real reptiles but I’m considering stealing it for dragons. dragons decide in the egg which sex they’re gonna be, why not?)

today’s doodle from curbside: a Sassy. but mostly contemplation of echidnas. and alligators. and the possibility of dragons having system where incubation temperature determines the sex of the hatchling

[transcript of my handwriting:

- assume Iorveth has the basal body temperature of an echidna (30.7°C ± 1.03 / 87.3°F ± 2.4)

- operative active temp of echidnas is ~32°C / 89°F

- conveniently this is approximately the incubation temperature that produces females in American alligators (~30°C / 86°F) provided he doesn’t do anything too strenuous

- not like anyone could stop him tho so it’d really be like

IORVETH: do you think it’ll be a boy or girl

SASKIA: if you had any chill we would definitely be having a daughter but you don’t so it’s 50/50 at this point

- OR POSSIBLY: SASKIA: it’s going to be a dragon.]