[Taxacom] large animal genera

[Doug Yanega]

Regarding comments on the "arbitrary" or "artifical" nature of genera, 
with implications of personal bias and idiosyncrasies of the responsible 
taxonomists; briefly, in several of the groups I gave examples of (bees 
and wasps), this clearly can't be what's going on. The same taxonomists 
who recognize and create small genera also recognize large genera, USING 
THE SAME CRITERIA. Those criteria pretty much invariably focus on the 
level of morphological variation, and the ability to recognize and 
discriminate groups of species *based on characters*. In certain 
lineages, the levels of morphological variability are so low that there 
are few *reliable characters* that allow for recognition of groups. Look 
at bee genera like Lasioglossum and Andrena, with over 1000 species (and 
Nomada are parasites of Andrena), and Perdita, with around 800; all of 
them have numerous subgenera, and the subgeneric classification of each 
is a dismal morass, with weak and often contradictory characters, giving 
little concrete or confident support for making further divisions, 
ESPECIALLY if one is hoping to follow any sort of monophyletic 
hierarchy. The point is that while many lineages can be partitioned up 
just fine, there are others where there has clearly been extensive 
radiation with little character evolution, and those lineages defy 
anyone's attempts to partition them further - even when they are the 
same taxonomists who DO partition up most of the remaining diversity in 
their respective areas of expertise. This is not lumpers versus 
splitters, so much as it is people who apply the same criteria to a wide 
variety of taxa, sometimes resulting in very large genera that are just 
as "natural" as small or even monotypic genera recognized *by those same 
people*. There are a few exceptions in bee taxonomy (e.g., the recent 
elevation of the subgenera of Trigona to genus level), but by and large, 
this is the pattern. There may be some pressure in the future to split 
some of these huge genera up based on molecular evidence, but here's the 
quandary: from examples I know of, the molecular divisions are not 
matching up very well with the recognized subgenera. In that situation, 
unless one has a sequence of species X, you won't be able to place it. 
Meaning, more than likely, that the genus can't be split, for all 
practical purposes, without leaving over half the described species 
unplaceable (since that's about how many will NOT have fresh specimens 
available for sequencing).

The same cannot be said, for example, about genera like Cicindela, for 
which there are umpteen different historical classifications, ranging 
from some authors who recognize one genus with nearly 2000 species, to 
other authors who split the exact same group into over 100 genera - or 
Carabus, with something around 900 species placed either into one genus 
or around 90 genera. Both these groups are super popular with collectors 
and non-scientists, and have had hundreds of different "experts" 
publishing on them, rather than a handful. That seems to put an entirely 
different sort of pressure in terms of splitting, even if there is no 
solid morphological basis for doing so.

Food for thought,

Sincerely,

-- 
Doug Yanega      Dept. of Entomology       Entomology Research Museum
Univ. of California, Riverside, CA 92521-0314     skype: dyanega
phone: (951) 827-4315 (disclaimer: opinions are mine, not UCR's)
              http://cache.ucr.edu/~heraty/yanega.html
   "There are some enterprises in which a careful disorderliness
         is the true method" - Herman Melville, Moby Dick, Chap. 82