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Re: Monster Tadpoles

James Purchase wrote:
>There was a show on the Discovery Channel recently (within the past 2 weeks)
>about life in a freshwater pond and they focused on tadpoles and how most of
>them exist happily on algae while others become cannibalistic monsters which
>devour their smaller cousins (and any other aquatic creatures they can
>catch). They didn't go into much detail as to the exact mechanism of what
>triggers this sort of change, but said that it was an evolutionary attempt
>to get at least some tadpoles (the mean ones) to grow quickly and reach
>adulthood before the temporary pools they lived in dried up. The monsters
>became weaker adults than the normal tadpoles, but during droughts they
>ensured that at least some tadpoles reached adulthood before the water in
>the pools evaporated.
I remember seeing the "monster tadpoles" on Nature, on our educational TV
station.  This is a different mechanism that is employed by desert toads,
as I recall. The temporary ponds formed by heavy desert rains dry up so
quickly, that often the tadpoles don't have time to make it to adulthood
unless they turn carnivorous.  Some do, and the others provide enough food
for them so that they can make it in the short time available.

I am quite sure that Merill Rose's tadpoles were not that kind, but were
Rana pipiens tadpoles, or a related species.  The mechanism here is suited
for a small overcrowded pond that is not going to dry up quickly, but which
may have more tadpoles than the amount of available food can support.
Rather than them all starving or only growing very slowly, a few inhibit
the others from eating.  The lucky few mature rapidly with all the food
available, and when they undergo metamorphosis and leave, another one or
two "get on top" and, in turn, inhibit the others.  It is, again, a
mechanism that insures that some mature into adults rapidly, rather than
all being food-limited.

Paul Krombholz, in cool, breezy central Mississippi,