Reproductive Biology
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Reproductive Biology

A two-minute refresher on genetics.


Methods, Phase (1)


Methods, Phase (2)

How I'd do it, but my wife won't let me.

An open letter to the breeders and distributors.

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I’m beginning with the assumption that all MSCGP volunteers are already familiar with the basics of mystery snail biology, including (especially) their unique reproductive adaptations.  The husbandry of egg laying and hatching are not trivial in Pomacea, but the reason I have advertised this project to groups already enthusiastic about mystery snails is that, I trust, you can handle them.  See Stijn Ghesquiere’s page if you need a refresher.

Six important facts to keep in mind:

(1) Sex ratios are not necessarily balanced in Pomacea populations.  In fact, field surveys generally find wild (or naturalized) populations of Pomacea biased toward the females.  There’s been some fascinating research on introduced Asian populations of Pomacea canaliculata that suggests multigenic inheritance of sex, rather than the typical XY chromosomal system everybody is familiar with.  So takeaway point #1 is that, although I don’t know of any good study, I wouldn’t be surprised if most of the mystery snails in the home aquarium today are female.

(2) Essentially all invertebrates with internal fertilization store sperm, typically for their entire lifetimes.  Some model organisms, like fruit flies, are effectively inseminated just once.  The situation is not well studied in gastropods, but multiple insemination is often reported.  Whether the sperm of the first partner prevails, or the last partner, or some combination, is generally not known.

(3) It’s a very good bet that all the mystery snails in all our home aquaria are already inseminated, possibly by multiple partners, when they arrive in the pet shops.  I ran a brief FB poll that returned 14 cases of mixed-phenotype sibships, and only 2 cases of pure-phenotype sibships, from mystery snail egg clutches hatched in the home aquarium.  This implies that the breeders do not keep snail stocks that they mean for the retail market segregated by color, but rather mix them sometime around maturation, possibly in a calculated effort to block the development of pure lines by competitors.  And (to be fair) it’s more fun for hobbyists who might be able to hatch egg masses from females obtained at the retail level if they obtain mixed-phenotype progeny.

(4) Controlled crosses require virgin snails.  So, since there is no good way to predict when maturity might be reached, we will need to isolate any snails we want to use in genetic experiments shortly after they are hatched and rear them in pairs.  But let’s not get ahead of ourselves.  First things first, second things second, and fifth things fifth.

Photomontage from Roberta Rose

(5)* It is possible, although deceptively difficult, to determine the gender of adult mystery snails.  The penis arises as an evagination of the mantle, at the posterior aperture edge, which you can see (sometimes) if you pull a male Pomacea out of the water and hold him aperture up.  There are some helpful illustrations on the web to show you how to do this. 

The problem is that if you can see a penis, you know your snail is a male, but if you cannot see a penis, you don’t know anything.  Your snail could be immature, or sick.  Or the lighting might be bad, or you might be holding him wrong.  That is an especially big problem in photographs, as demonstrated by the photomontage above from Ms. Roberta Rose (Snails, Snails, Snails 1Oct18).

The situation is similar with behavioral cues.  If your mystery snail is in an aquarium with other mystery snails, and you see him on top of a partner, attempting to copulate, you can infer that he is a male.  But if you do not see that behavior, you don’t know anything. 

I would recommend that you do your best to determine the gender of your parental mystery snail or snails.  Pull it out of the water and flip it over and watch as it struggles.  If you can clearly see a penis, that’s a disqualification.  Otherwise, keep it and we’ll see.

The bottom line.  You'll need a teaspoon of luck or a tablespoon of persistence to participate in the MSCG Project.  The more snails you start with, the more likely you are to have a healthy female.  So you can certainly start this experiment with just one ivory snail, but more would be better.

Up next... Two Minute Refresher on Genetics!

Last updated 7 Nov 2018