Doug Von Gausig wrote:
> Good luck! There is precedent in birds (and probably frogs/toads, too?) for
> separation of a species because the calls, and therefore the breeding
> selection, are different. This arises from sympatric evolution - where one
> species becomes two without the benefit of physical separation. The calls
> are necessarily different to help keep the two species separate. The
> opposite is allopatry/allopatric - in which a species differentiates to two
> after a physical separation, like a mountain range, ocean, etc. In
> allopatry the two species (at least in birds) often retain their
> plesiomorphic (ancestral) calls, since the physical barrier serves to
> separate them sexually.
>
> I love sympatry, because it means that the new species has found a new
> niche - a new way to exploit the resources in the area. The new species
> necessarily is a "renegade" that no longer follows the rules of the species
> from which it arose - evolution in action!
>
> Great stuff, Walt!
>
> (Sorry for the biology lesson, it's just I find this sort of thing very,
> very exciting!)
One to think about is the Cope's Gray Treefrog (Hyla chrysoscelis) and
the Common Gray Treefrog (Hyla versicolor). Only field character that
differs is the call. And the true genetic difference is that H.
versicolor has twice the chromosome count of H. chrysoscelis. It arose
as a failure of full cell division from H. chrysoscelis.
The plot thickens more in that modern testing has indicated that this
mutation is not a single event, but multiple events in different areas.
There are groups of H. versicolor closely connected with a group of H.
chrysoscelis genetically in each case.
And still more elaboration I got involved in when I found a frog that
called like H. versicolor. We thought we had confirmed the first record
of this species in Georgia until genetic testing was done. My version
was of the lower chromosome number of H. chrysoscelis but also sterile.
Farther testing (by the same woman involved in the current frog)
confirmed that what we had was a hybrid. H. chrysoscelis X H. avivoca
(the bird-voiced treefrog). I've recorded instances of this hybrid on a
fair number of times, always at sites with both species. So far we have
still not confirmed H. versicolor anywhere in Georgia.
Note that since the chromosome number differs that H. chrysoscelis and
H. versicolor don't hybridize.
Another one of note is that Green Treefrogs and Barking Treefrogs
hybridize. The hybrid has a call that differs from either, somewhere
intermediate. I've recorded this call a number of times.
As a side note modern genetic testing is making the species tag a bit
murky with some frogs. A current study underway seems to indicate more
genetic diversity between various groups of Northern Cricket Frogs than
there is between them and Southern Cricket Frogs. That's unclear where
it's going to lead us and is still a work in progress. John and I had
already noted that the characters used to ID these two visually were all
unreliable, though they can be fairly easily separated by call.
Tricky business recording frogcalls sometimes. It pays to note any
different things you find. They may have hidden meaning.
Walt
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