Rhea Wong, Kyle Parks, Keelan Lang, Keon Mook Seong
I. Introduction
Diapause is common in insects. Below Rhea and Kyle discuss what diapause actually is and how it is regulated by the endocrine systems. Oh, and nematodes 😉
II. Podcast
Click here to listen to the audio file via SoundCloud.
III. Transcript
Rhea: what is this diapause thing exactly?
Kyle: So diapause is a state of arrested development. It’s very common in insects. So what happens is at a specific point in development the animal can stop growing, so tissues just stop developing until conditions change. It’s usually to get through a rough patch of environmental pressure. So…winter or summer, if you live in a really hot area, and the things that trigger it usually are not direct associated with that condition. So if you’re diapausing to get through winter, it’s not the cold that cues you in to start diapause. It’s usually shortening of photoperiod or scarcity of food.
Rhea: You wouldn’t want to have to wait for an ice storm for you to go into diapause.
Kyle: That would be bad.
Rhea: Diapause in insects is largely controlled by the endocrine system. All the typical hormones we know of and love; PTTH, JH, ecdysteroids. Like in Manduca, when they are going into their pupal state to overwinter, it is due to a lack of ecdysteroids, which is in turn due to the prothoracic gland not producing enough ecdysteroids. It just stops off and goes to sleep. The odd thing is that, for most species that have overwintering diapause, it actually ends in midwinter. So I guess it takes a little bit for them to wake up.
Kyle: So what happens actually is the specific physiological state of being in diapause ends, but they remain in a senescence. So they remain inactive and they remain sort of hibernating in a sense but they’re susceptible to cues that will allow them to be active in that state. So diapause ends before the condition that is the reason for them being in diapause goes away and it’s kind of like REM sleep. Like, you sleep a while, and then you go into REM sleep, and then you exit REM sleep and you stay sleeping a while. So if you think of diapause like the REM sleep it’s hard to get jolted out of that.
Rhea: You need to be in a special sort of state to actually wake up, to cue into being woken up.
Kyle: The other cool thing is that the pathways that mediate diapause seem to be involved in aging in general. So in some animals, where they’ve like cut out the Corpora Allata all together, they live twice as long for some reason. Some research suggests that, even when you reach adulthood, it’s still a developmental state, and that aging is a controlled process and not just the degradation of tissues. So diapause you usually think of happening to an egg or larva or pupa that’s still growing larger or developing, but there’s a special kind of diapause called “reproductive diapause,” and this is a lot different than the regular diapause we think of because the animal’s up and about and its moving around, but what happens is that it stops producing all sorts of things associated with its reproductive system. So some of the most well-known animals that do that are like locust and monarch butterfly.
Rhea: Migration…you don’t want to have to bother with all those nit-picky things when you’re trying to just get someplace.
Kyle: You’re spending most of your energy flying, so you don’t have energy to spare building eggs that you’re not going to use ’til you get where you’re going. Nematodes do this really weird thing called a “dauer” state, which is kind of like an extreme diapause. It’s most well known in C. elegans. Usually C. elegans molt four times and then become adults. If the population density is too high, or if food source is too scarce, they can go into this thing called “dauer” state, which roughly translates to “resilient” or “permanent” in German. And they basically make like a little cyst, and they almost completely arrest their metabolic development and they can stay in that cyst for a long time.
Rhea: So you said like crowding or lack of food. Do you think maybe it’s just lack of food and crowding has contributed to that? Or can they actually sense, like, chemicals from other nematodes and that also contributes?
Kyle: Yeah so there are these things called “small molecules.” They’re molecules that other C. elegans are producing and giving off in their environment and, like, if things are good, a lot of times those small molecules are used by C. elegan to find each other. So like a male C. elegan that’s looking for a nice hermaphrodite C. elegans to settle down with. They don’t have females, they just have males and hermaphrodites.
Rhea: That’s bizarre.
Kyle: He can sense these small molecules and go and find the hermaphrodite. When there’s lots of crowding and there’s, like, lots of these small molecules slipping around the C. elegans’ environment, they go: “Holy crap, there’s a lot of people here I better duck down and chill out for a little bit!” So they can go into the dauer state until the population disperses a little and the food source comes back.
Rhea: Why are we talking about nematodes again?
Kyle: The interesting thing for insects about the dauer state is it seems to be mediated by an insulin signaling pathway, which, if you do RNAi and knock that down in mosquitos…
Rhea: Would they go into diapause then? Is it the same pathway?
Kyle: So when the insulin signaling pathway that controls the dauer state in nematodes was knocked down in mosquitos, the tissues where it was knocked down with RNAi in went into arrested development, and a sort of diapause. It seems like the pathway that controls dauer state in nematodes and diapause in insects might be a conserved pathway.
Rhea: Okay cool.
Insect Physiology at Illinois 
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