[Taxacom] The 'reality' of species boundaries -- Once Again (UGHHH!)

[Richard Pyle]

> By FREELY INTERBREED, I mean more than just a bit of 
> hybridisation around the edges! If the Centropyge FREELY 
> INTERBRED, then hybrids would take over the whole range and 
> the whole darn lot would become one. 

So...at what proportion of hybridization does it stop being hybridization
(between two different species), and start being freely inter-breeding
morphotypes (within the same species)?  Is that threshold established
through "real", "natural" values that exist independent of human
subjectivity?

> If you think that is 
> (slowly) happening (and you are correct), then they are the 
> same species. If you think the bulk of them are retaining 
> integrity, with just a bit of mixing at the border (and you 
> are correct), then they are distinct species.

You're approaching a point I had raised years ago in this same discussion on
this list (BTW, have you had a chance to read the archives yet -- as several
of us have recommended you do?).  The "reality" (or not) of species
boundaries depends on future events.  Right now, the proportion of
hybridization between these two morphotypes in Centropyge is low enough that
we would call them distinct species.  If this proportion changes in the
future (e.g., through alterations in oceanic current patterns and their
effect on larval dispersal, resulting from global climate change) such that
it *increases*, then today's populations retroactively become the same
species.  But if the proportion stays the same or decreases in the future,
then today's populations retroactively become different species.

Thus, today's "reality" is contingent upon future events. No?

> Many parasitic Hymenoptera are so sexually dimorphic that 
> there are no morphological features to match up males with 
> females. Why are they still males and females of the same 
> species? Because they FREELY INTERBREED!

This is a COMPLETELY different situation. One hundred percent of male
morphotypes are born from female-morphotype mothers, and 100% female
morphotypes are sired by male-morphotype fathers.  If you had some
geographic regions where ONLY males existed and reproduced with each other,
and produced fertile offspring; and other geographic regions where ONLY
females existed and reproduced with each other, and produced fertile
offspring; and a few places where both males and females occurred together,
and reproduced with each other, and produced fertile offspring; then it
would be a meaningful comparison.

Aloha,
Rich