The good news: I’m getting roughly one new egg sac every week, so I’ve had one produced on 27 December, another on 4 January, and another this week, on 7 January. I can make progress with that level of production.
Except the bad news: that egg sac from December should have hatched out by now. I opened it up: mostly dead. There were a total of 35 eggs in it; 6 had made it to the postembryo stage, and then died; 4 had made it past the first instar, and then croaked; 24 were arrested in an earlier embryonic stage, and were clearly not going to make it any further. There was ONE second instar survivor, waving its legs weakly in the midst of the charnel house of its siblings. That’s not very good. I’m not even certain the survivor is going to make it — I put it in a little chamber of its own with a fruit fly it can try to eat.
The other egg sacs…well, I’ll have to wait and see. I isolated the one from 4 January, and like the December clutch, put it in a petri dish on a cotton pad, which I spritz with water daily. Unfortunately, I’m finding that the pad doesn’t seem to help, acting more as a dessicant, I think. So I threw out the cotton on that second clutch. I’m leaving the 7 Jan sac with its mommy, in a large vial. We’ll compare outcomes under those two conditions.
Another hypothesis for this problem is that my original wild caught stock produced vigorous clutches of spiderlings, where the majority were healthy and fine…and cannibalistic, which contributed to a rapid culling. All of the egg sacs recently have been the product of inbreeding between progeny of the extraordinarily fecund Gwyneth. So I’ve placed my sole remaining male, a son of Gwyneth, in the company of a daughter of Xena, and will, I hope, get a new outbred clutch to compare. Or maybe Xena1 will consume the puny male. It was tough to get Xena0 to put up with any mates at all.
It would be interesting if Parasteatoda were sensitive to genetic inbreeding, rather than this low output being a result of my poor spider husbandry skills. I’m so used to zebrafish and flies that don’t care if you cross an individual with its sibling, its offspring, its parents, its grandparents (The Aristocrats!), but it is possible that wild species that engage in more mixing might be carrying a higher load of recessive lethals…although I’d also think there’d be limits to how much mixing there’d be in a synanthropic species with limited mobility in adults. Maybe there’s a lot of juvenile ballooning going on that I’ve missed? I’ll have to keep my eyes open in the spring, and see how my garage gets repopulated.
I’ve also noticed something strange going on in my brain. The questions I’ve been asking myself have been shifting from the generally embryological to something more ecological — I might turn into an eco-devo guy yet.