Re: Sex Ratios

["David A. Youngker" <youngker@bellsouth.net>]

> From: Mike Jacobs
> Sent: Tuesday, January 21, 2003 8:09
>
> Why do we assume that in nature there is a 50/50
> sex ratio?...

Well, actually it's rarely "dead on" to a 1:1 ratio - just close enough to
call it that. There may be a few points toward one side or another, like a
52/48% balance. Apistos and Westies are but two of the types I'm aware of
having such wide ranging disparities.

> I could see an advantage in there being an excess
> number of males........the males being the "brightest
> of the sexes" then does that not lead to them being
> the first caught...

Most animals that display a high degree of "brightness" usually use that
coloration as an indicator of survival success - from Apistos to Peacocks.
The color not only is attractive, but surviving long enough to achieve a
full display instinctively carries with it a measure of intelligence , or
"wilyness", in avoiding predators and other life-threatening situations.

I seem to remember an interesting report from a couple of years back where
wild Guppy females in Trinidad were prone to chosing males who were
predominately blue or red depending on the amount of available vegetative
coverage within their specific habitats. If I remember correctly, one color
had a better chance of survival in the open - but I _don't_ remember which
of the two it was...

> does mother nature really just swing with the wind in
> these cases and whatever happens happens...

As I conjectured previously, I can "see" one reason for such a response in
order to cope with environmental impacts. But that doesn't necessarily mean
I'm all that correct - I'm just groping for some sort of underlying logic
that can conveniently act as a "feedback" mechanism to drive the species
survival and continuation.

> is that randomness part of natural selection.......or is
> natural selection so precise that 26C should be
> maintained or we have problems?...

I'm again merely trying to correlate environment to response, which is the
biggest reason I originally asked about "off season" environmental
measurements. _Something_ is contributing to the recent success of the genus
in evolutionary terms. I can't see the environment holding a stable 26º all
of the time, but it _would_ be interesting to see how long it _does_ hold
there and how much of a "window of opportunity" exists by exploiting a shift
of a couple of degrees to either side.

The other side of that same coin must also consider the predators
themselves. Their own apparent success deals with those temperature ranges
outside of that optimal to the Apistos. How their numbers ebb and flow with
the temperature might also help explain why Apistos throw females on the low
side and males on the high.

> Thanks for the superb e-mail notes..............may I use the
> past thread of e-mails in our Tampa Aquarium bulletin?

As always, anyone who discovers _some_ measure of merit in anything I spout
off is more than welcome to use it (or discard it) as they see fit...


-Y-


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