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Re: Two Riv marmoratus

Thank you for the link and information, I have studied that site and heard
about that show incident, I had just left that site, which was the reason
for the inquiry. I was only trying to make light of an otherwise fascinating
fish, I have just recently acquired a set from Al Castro's collection and
was seeking some otherwise unknown sources of information.
----- Original Message -----
From: "Scott Davis" <unclescott at prodigy_net>
To: <killietalk at aka_org>
Sent: Monday, July 22, 2002 2:40 PM
Subject: Two Riv marmoratus

> > if Rivulus marmoratus are
> > hermaphrodite and I have two fish, does that mean I have two pair or one
> > pair that are capable of being switch hitters?
> > Patrick
> Two is a pair for purposes of an exhibition or show. This was specified by
> couple of groups after some wise acres showed one as a breeding pair. :)
> Bruce Turner's site discusses this. I'm quite sure I didn't understand
> everything he said.
> http://www.bsi.vt.edu/rivmar/
> Please don't stop with my summary after a quick perusal. That site
> much more attention.
> Turner's bibliographic essay mentions variation between populations in
> of their gender make up. Most populations have no males, just
> (with all of the allure of most Rivulus females). Other collections show
> many as 10 to 25% of the specimens collected could be male.
> From a key in Belize, "Significant levels of outcrossing detected on one
> Belize key, Twin Cays, by progeny testing of field-caught hermaphrodites,
> using DNA fingerprinting; all hermaphrodites tested were heterozygous
> (Lubinski et al., 1995). This is the only record of field-caught
> heterozygotes in the species. Progeny testing thus far has detected only
> homozygotes in other populations..."
> One experiment generated a number of males were the eggs were incubated a
> degree or two under 20 degrees C. (the comfortable minimum for the
> Dr. Turner alludes to a study in Copeia  (1997 pages 596-600 - now you've
> got me wanting to run over to the local college and look that baby up) by
> Cole and Noakes where they contend that under some conditions young fish
> develop into "regular males or females". I vaguely remember a TFH article
> (Feb. 1998?), possibly by the same two researchers.
> At least one of the studies Turner reviewed did show field evidence of
> sexual reproduction among the marmoratus.
> One of the studies on self-fertilizing individuals noted that every now
> again, a viable eggs was released, but not fertilized. That would leave an
> opening for fertilization by a male.
> Presumably young females which hadn't yet taken one the dual
> of older marmoratus could also spawn with those males.
> And then there are the cases of secondary males - which had been
> hermaphrodites!!!! In time, a research team found that those fish's
> pretty much "disappeared".
> A 1971 study by R.W. Harrington (the scientist who did so much to bring
> unique animal to the world's attention) showed that one or more short day
> seasons or elevated temperatures could cause some hermaphrodites "undergo
> sex transformation ("sex succession" or "inversion") to secondary males".
> Yurner also suggested that more work in that area needs to be done.
> That article also mentions marmoratus flipping across land 100 feet from
> water and being able to survive 60 days in wet leaves. What a survivor!
> So yes Patrick, if you consider their ability to evidentally (in some
> instances) change from more conventional males and females into
> self-fertilizing hermaphrodites and then in some cases into males after
> having been self-fertilizing hermaphrodites, yes they could be considered
> switch hitters.
> All the best!
> Scott
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