Does anyone know of information about desiccation resistance in Hydra eggs, please? A few years ago I collected mud from a dried-up pond, aiming to rear crustaceans, and found I got green hydra, H. viridissima, too. I can’t remember just how dry the mud was, but certainly no standing water left.
Wikipedia mentions the eggs having a tough coating and sinking to the bottom of the pond, but not being resistant to drying out. Most of what is on the web about Hydra eggs seems to involve wizards.
I don’t really have any information on this but I have a pond in my garden which is completely dry for most of the year. Whenever the pond fills up with water Hydra viridissima becomes very common. I assume it must survive in the pond somehow while dry rather than recolonise regularly. Interestingly I sometimes find brown hydra species in nearby, more permanent, ponds but only ever the green ones in this particular pond.
Looks like there haven’t been many studies of Hydra survival in situations like that. The following paper is one of the few that directly addresses the question:
Our findings lead us to hypothesize that Hydra evolved in an unstable freshwater habitat in which survival required that its life cycle include the use of a bet-hedging reproductive strategy and the formation of an embryo that is desiccation resistant and that can remain dormant for long periods of time.
Yes this is a very interesting phenomenon that we are aware of but don’t know much about. I’ve been doing research with freshwater hydroids for a little while now, and we know some people who would be very interested in getting samples of Hydra eggs if anyone is able to find any. All part of Hydra getting attention for being immortal.
Yes. I worked with Hydra in the lab. They can be hatched from dried eggs, and I have done so. Drying of their ponds in fact induces them to switch to sexual reproduction, and one likely advantage of this is that the eggs can survive drying but the polyps cannot. Organisms that reproduce sexually only some of the time are called cyclical parthenogens, and in many freshwater cyclical parthenogens, it is the eggs that survive through dry spells.
Thanks very much for those responses, especially for the paper.
John
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