Re: Sex Ratios (and E-mail Test)

[Mike & Diane Wise <apistowise@fgn.net>]

David,

I don't know if you can equate plants & animals. Animals are much more mobile &
will not need the delay of 1 sex over the other to disseminate their genetic
material. Römer has not only studied the physical effect, but also the
ecological effect of temperatures on sex determination in apistos - both in the
laboratory & the wild. He found that 26ºC/79ºF was the optimum temperature for
most apistos. Higher & lower temperatures retarded growth & maturity. He also
found that primary predators on apistos tended to prefer higher & lower
temperatures, so for some reason 26ºC has few predators. Römer has a good review
of his study in his book "Cichlid Atlas" (sections 4.2.2.1 through 6). It can
explain his ideas better than I.

Mike Wise

"David A. Youngker" wrote:

> Hey All -
>
> Well, I've suffered my last problem with MindSpring, and I hate having to
> leave an address that's been maintained for so many years, but I'm moving to
> BellSouth as an ISP. Changing addys means testing some of my subscriptions
> for continuity, but in this case it also allows the opportunity to ask a
> general question concerning Apisto biology and biotopes.
>
> Many of the Apistos we keep seem to have a skewed sex ratio within brood
> batches that varies with temperature. Mayland and Bork reported on Uwe
> Romer's studies, and we've bandied them about at times, and the pattern
> seems to follow that the cooler the water the greater the percentage of
> females. I've also noted it within my own breeding efforts, and it's an
> easily observed phenomenon in my tanks as I tend to keep them on the cooler
> side to extend the Apistos' longevity somewhat. And I've been pondering the
> situation a little but can't come to any definite conclusions because I'm
> lacking some fairly basic information that would help lead to an end point.
>
> The evolutionary reason behind the ratios could depend on one of two logical
> factors. It could be an effort to ensure the availability of ripe females
> for the shorter-lived males (whose colors, etc. tend to cause them to become
> snacks more often than females) or it could be a way to extend the genetic
> pool by allowing females more time to expand their territories before
> encountering a male.
>
> I know that some plants with the capability of self-fertilization often have
> their male and female structures mature at different times to prevent
> inbreeding as a rule of habit. This usually means the males first so that
> the pollen can travel some distance from the originating stand and ensure
> genetic diversity. Something along these lines could be at work within the
> genus Apistogramma, leading to the thought of extended territories. In our
> own efforts, when a breeding doesn't "work" we often assume the male isn't
> "ready", but perhaps instead the _females_ (which most often come from the
> same broods and have the same time for development with us) are the true
> culprits.
>
> Is there a source of field collection data that samples the environments at
> times _other_ than prime collection periods? I know that Apistos, like other
> Amazonian fish, are far easier to collect during the dry season when water
> levels are down and populations are concentrated, and conversely the wet
> season makes collection nearly impossible in a lot of areas. But perhaps
> some of the collectors are out there getting "early starts" on the season
> and have some of this data within their field notes.
>
> It would be an interesting exercise (at least to me) to try to see how much
> time the females would normally have to populate and spread through an area
> before the warming waters start to increase the population of the males...
>
> David A. Youngker
> youngker@bellsouth.net
>
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