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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?
Two is a pair for purposes of an exhibition or show. This was specified by a
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.
Please don't stop with my summary after a quick perusal. That site deserves
much more attention.
Turner's bibliographic essay mentions variation between populations in terms
of their gender make up. Most populations have no males, just hermaphrodites
(with all of the allure of most Rivulus females). Other collections show as
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 species).
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 can
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 and
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 characteristics
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 ovarian
pretty much "disappeared".
A 1971 study by R.W. Harrington (the scientist who did so much to bring this
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
All the best!
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