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Re: Hybrid sunnies (fwd)

J. L. Wiegert
 Dubotchugh yIpummoH.                      bI'IQchugh Yivang!
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---------- Forwarded message ----------
Date: Sat, 03 Oct 1998 19:41:29 -0400
From: David E. Boruchowitz <editor at tfh_com>
To: nfc at actwin_com
Subject: Re: Hybrid sunnies

Hi, all!

I usually lurk here, but this is one of my favorite topics.  Hybrids almost
always grow faster/bigger than either parent species. This is true for
strains within a species, too, and is called "hybrid vigor" or heterosis.
It's one reason Americans tend to be taller than Europeans or
Asians---there's a lot of genetic mixing going on in the States!

As for the species concept, it is partly a human construct. Birds and fish
especially are prone to hybridization between species---usually in
captivity, where all the normal behavioral and territorial controls are
absent, but occasionally in the wild. When the parent species are close,
the offspring are often fertile. There are even some bird hybrids where
only one sex is fertile in the F1!

>   The best breaks to the Bioloigcal Species Concept truly come in the
>fishes.  Think of Rivulus marmoratus: A "hermaphrodite" fish.  Or again,
>to invoke the livebearers, the Amazon Molly... which will only breed with
>males of another speies, and has no males in its own!  A truly bizzare
>species, indeed.  

Hermaphrodite species are not really a problem for the species concept.
Many fish species are hermaphrodites which change sex at different stages
of life--very common in coral reef fishes. The marmoratus is the only one I
know of that is both sexes at the same time and fertilizes its own eggs.

Parthenogenetic species, like the Amazon molly, are almost always the
result of an interspecies cross. There are a few among the reptiles, too.
BTW recent evidence suggests that the sperm of the other species male MIGHT
make some genetic contribution to the Amazon molly fry. Up until now it was
believed that the sperm was only necessary to "jump start" the egg into
developing. Parthenogenetic species are typically short-lived (in
evolutionary timescales).

There are a few hybrids whose parent species are not definitely known. The
society finch is a combination of at least two mannikin species, and its
origin is lost in antiquity--it exists only in captivity. The domestic goat
is another domestic-only species with uncertain hybrid origin. Domestic
platies and swordtails, which were already mentioned, are a mix of at least
three species, often more, and they do not normally occur in the wild.

A very common hybrid in captivity is the convict cichlid with the blue-eye
(Archocentrus nigrofasciatum x A. spilurum). It does not usually occur,
however, in nature, even where both species inhabit the exact same locales.
This is surprising, since in captivity convicts will hybridize with quite
distant relatives--I've heard it said they'll mate with a can of tuna!  :)

A question for everyone collecting Lepomis. Just how frequent are these
hybrids? One in a 1000? More? Less?


David E. Boruchowitz
Editor, TFH Magazine
editor at tfh_com