[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Killietalk] reproduction in Campellolebias and Cynopoecilus
I wanted to express my thanks to those who wrote me, on list and off-slit, re
my questions/comments last week on internal fertilization in Campellolebias
and Cynopoecilus. I regret that my teaching obligations did not permit me to
reply further until now. I have an unusually large class this semester and it
takes quite a bit more of my time than is usual. Let me comment as follows:
1. It seems that aquarists have established that internal fertilization
occurs in these two genera. However, I am aware of no reports in the
professional research literature on this topic, other than in the original
description of Campellolebias and in Parenti's remarks on Cynopoecilus. I do
not monitor this literature closely, but I suspect that I would have seen
something like such a report if it had appeared. Aquarists who have made
these observations should publish them, even if their accounts are anecdotal.
2. Apparently, in both Campellolebias and Cynopoecilus, internally fertilized
eggs remain stored in the female for some period of time before they are
spawned ("oviposited," to use the technical jargon). In a broad sense, this
could be viewed as a relatively primitive form of viviparity (live-bearing).
Specialists in fish reproduction formerly used the term "ovoviviparity" to
describe this this reproductive mode, and that term has made its way into the
aquarium literature. However, following the work of John Wourms (Clemson),
that term has been more or less abandoned. The existence of (primitive)
viviparity in Campellolebias and Cynopoecilus is further evidence that it can
evolve independently in many different fish groups.
However, there is a more important issue: it seems to me that viviparity,
even in primitive form, is a most unusual and unexpected adaptation for an
annual fish. In general, viviparity is one of those adaptations which enhance
the quality or fitness of progeny at the expense of fecundity (reproductive
output). That is, all else being equal, fishes which produce larger and/or
more advanced progeny at birth produce fewer progeny than related groups which
have external fertilization or lack parental care. The habitats occupied by
annual fishes seem to have a fair amount of unpredictability. In general,
organisms which persist in unstable/unpredictable environments do so by
maximizing fecundity. Ecologists call this type of strategy "r-selection, "
and there seems to be little doubt that most/all annual killifishes are
"r-selected." In this kind of environment. it is very difficult to understand
how viviparity can be advantageous. We are missing something...
Bruce J. Turner
Biology, Va Tech
fishgen at vt_edu
Do not go quietly into that good night, but
rage, rage, RAGE
Against the dying of the light.
The wonderful thing about tiggers...
Is that tiggers are wonderful things!
Tigger (to Winnie the Pooh)
To join the AKA see http://www.aka.org/pages/join.html