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Re: KillieTalk Digest V3 #1273
>> Subject: RE: Sex Ratio? -A working hypothesis- NEEDS
>> YOUR HELP!!!!!!
>> A possible alternative hypothesis: It could also be
>> that fish that are
>> growing faster opt to be male since faster growth is
>> needed to be a
>Just a couple of thoughts, maybe more males is mother
>natures of insureing the survival of a species.
*non-directed soap box mode on*
Some interesting thoughts, although as an evolutionary ecologist, I have to
put in a plug about "just-so" stories. There's a very common phenomenon of
making up theories that seem to make some sense and then accepting them
without ever looking at the ecology of the organisms. Without any evidence
fron looking at the beasties in the wild, we have no clue why or how things
might be adaptive. It's common to accept little stories about adaptation
as being true without evidence, but it's a very bad habit!
In this case, perhaps bright colors and finnage may increase
vulnerability to predators, but it may also turn out that there aren't
important predators, or that the predators are mostly color blind (like
many frogs that sense motion rather than color) . We can speculate
reasonably about mechanisms (i.e. fast growing fish become male) without
having to speculate why such a mechanism may have evolved. For all we
know, it might be some "side effect" of being in an aquarium, because I
suspect that a lot of fry in our tanks grow much faster than what is seen
in nature, so it may be the growth rates that trigger a switch to being
male never or rarely occur in nature, so they can't be adaptive in any way.
This is particularly common with humans. I'm sure you've all see them,
like "X is adaptive because it helped humans do Y". No one has yet
invented a time machine to go back to see if trait X actually helped
humans do Y at the time when X actually evolved. Until then we won't have
a clue why some of these traits arose.
*soap box mode off*
In this case we have some testable hypotheses! yippee!
>Very colourful species that are easy to breed and are
>an important part of the food chain. Should give a
>high percentage of males to females, 80-90% males.
>Colourful species that is part of the food chain but
>not as important as the first, 70-80% males
I suspect that you're probably spot on in your intuition that the sex
ratios differ depending on the ecology and the lineage of the fish. I
particularly think the point about annuals with perhaps fewer predators are
likely to have different mechanisms/behavior than non-annuals with maybe
more fish/amphibian predators around. One thing though: the importance of
floating plants in calming killies make me wonder if they might not be also
susceptible to predation by birds in the wild.
1821 S. Maxwell St.
Bloomington, IN 47401
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