P.J. Alexander, New Mexico State University

• my focus has changed a bit since the abstract
• I’ll be talking about:
• the role of operationality in species controversies
• ideological disagreements lead us astray
• criticism of the phylogenetic species concept

Goldstein & Desalle, 2000:
“If, as most would argue, our species delimitations are to reflect reality of some kind in nature--reality that is either independent of our understanding or takes the form of a historical entity--then their discovery is not easily forwarded by either strictly operational discussions or by the generation of new vocabularies.”

• stated most explicitly by de Queiroz, 1998
• species concept: what species are (in some ± non-empirical/non-operational sense)
• species criterion: operational method for identifying species

• disagreement is primarily in operational criteria
• agreement conceptually that species are lineages (1998)

“Operational” criterion from species as lineages:
• all previously suggested methods for identifying species sufficient, but none necessary
• separate lineages are species whether identifiable, divergent, reproductively isolated, etc., or not (2005)

• what kind of conceptual agreement is it to say that species are lineages? one bad term for another...
• does screening off operational disagreement help us?
• what kind of “operationality” does de Queiroz give us?

• they focus research in speciation? (Wiens, 2004)
• they state common or necessary attributes of species? (Dobzhansky, 1935)
• they justify species criteria? (Nixon & Wheeler 1990)
• or are they too vague to do anything? (de Queiroz, 1998)

• species concepts unrelated to criteria are not interesting in systematics
• BSC & PSC contain both conceptual and criterial aspects

• concept: groups of actually or potentially interbreeding organisms
• criterion: direct breeding data generally unavailable or unusable
(Darwin, Dobzhansky, Mayr, etc.) instead we have a “morphological yardstick” (Mayr, 1942)

• poor ability of the morphological criterion to predict characteristics implied by the conceptual aspect
➤ “potential” interbreeding?
• poor applicability in asexual or hybridizing taxa

• concept: largest groups of tokogenetically-related organisms terminals in phylogeny; identified prior to phyl. analysis
• criterion: direct data on tokogenetic relationships may be possible
(e.g., microsatellites), but generally not used instead we have diagnosability (Nixon & Wheeler 1990)

• continuum from tokogenetic to phylogenetic relations
• so what connects disjunct populations? potential tokogenetic relationships?
from Christin Slaughter

• asexual & hybridizing taxa? same problems as for BSC!
• there is no reticulate/divergent boundary in asexuals
• how much hybridization is too much?

• poor ability of the morphological criterion to predict characteristics implied by the conceptual aspect
➤ “potential” tokogeny?
• poor applicability in asexual or hybridizing taxa
BSC ⇒ PSC: a change in emphasis; the same problems!
• but I haven’t talked about phylogenetic terminals yet!

• diagnosable groups of populations
➤ always appropriate terminals?
from Flora of North America, 1993

• do we need to identify terminals prior to phylogenetics?
• we can be misled by interpreting tokogeny as phylogeny
• but under what circumstances?

• example using population aggregation analysis (PAA)
Doyle, 1995 from Davis & Nixon, 1992

species = terminals? when are we misled?
• same data in a phylogeny; root added
• are we misled?
• the two diagnosable groups are still diagnosable groups
(but not clades)
• there is no spurious resolution out
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A
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B

species = terminals? when are we misled?
• ah, but what if we had a dataset that gave a single fully-resolved tree?
• well, with this information we can’t do better out
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species = terminals? when are we misled?
• if we add population information...
➤ it is perfectly obvious when we aren’t looking at divergent relationships between populations!
• if we can delimit species, we can also identify spurious resolution out
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• both require the same kind of grouping information
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species = terminals? when are we misled?
• identifying/diagnosing evidence of reticulation is important
➤ not insistence that terminals must be species, nor application of any particular species definition out
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species monophyly?
• I’m not advocating a topological species criterion
• species need not be characterized by apomorphies in each species
➤ and thus need not appear as ‘monophyletic’ clades
(Nixon & Wheeler, 1990) out
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• does this mean species can be paraphyletic?
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A
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B

species monophyly?
• what does paraphyly mean at this level?
• relationships here are tokogenetic, right?
• yes, within species; but between?
out
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species monophyly?
• two representations of the same pattern...
• there are several ways to view this
A B out
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species monophyly?
• species delimited by character difference only
• B diverged from an unchanged
A; A is paraphyletic
A B
• species delimited by inferred nodes
• A has the same characters as ancestral C; A is not paraphyletic
A B
A C

species monophyly?
• which is implied by the PSC?
A B A B
A C

• purely ideological disagreement is irrelevant; different approaches are important when they yield different results
• change from BSC to PSC is largely a change in focus
➤ conceptual & criterial aspects are largely unchanged
➤ problems faced are the same
➤ except that species are terminals under PSC
• insistence that species are the only appropriate terminals is primarily ideological
• insistence that “monophyly” and “paraphyly” are not applicable to species is primarily ideological
• instead, our focus should be on finding solutions to problems common across approaches, like hybridization
& asexual taxa

NMSU Dept of Biology and NSF EF-0542228 (CDB) for financial assistance; Dr. C.D. Bailey for discussion and many helpful comments.