Species

Other Species Concepts 259

Another conception, which expands upon Cohan’s bacterial species concept, is

the adaptive divergence species concept of Vos, which employs the McDonald–

Kreitman (MK) test:

Two [microbial] clusters can each be classified as a distinct species when the MK test

yields a significant NI value (<1), whereas they can be considered to belong to the same

species when the two clusters have not diverged as a result of adaptive evolution and

the NI value is nonsignificant.^26

NI is the Neutrality Index, which measures the selectivity of changes in polymorphisms.

Nothospecies

The almost exact conceptual opposite of the agamospecies/quasispecies conception
is pteridophytologist W. H. Wagner’s conception of a nothospecies.^27 Effectively, this
is a species formed from the hybridization of two sexual species (species formed by
the usual method of cladogenesis of sexual species he refers to as orthospecies.^28 As
Hull notes, “According to recent estimates, 47 percent of angiosperms and 95 percent of
pteridophytes (ferns) are allopolyploids”^29 and ferns and their allies continue to cause
problems for isolation conceptions of species.^30 The notion is so generally applicable
in botany that the concept of nothospecies has been written into the botanical rules
for nomenclature.

Compilospecies

Harlan and de Wet proposed a concept of a species that “plunders” (Latin compilo)
the genetic resources of another species through introgressive hybridization (where
the hybrids preferentially interbreed with only one of the parental species, causing a
gene-flow from one to the other, one-way).^31 It is therefore an asymmetric version of
the nothospecies concept. It also applies to some plant species.^32

OTUs and Phenetics (Phenospecies)

Phenetics developed from the work of Sokal and Sneath,^33 who trace their attempt to

produce a “natural” taxonomy back to Adanson, who used a multivariate classifica-

tion scheme in Familles des Plantes.^34 The phenetic view, also called “numerical

(^26) Vos 2011, 2.
(^27) Wag ner 1983.
(^28) Wag ner, pers. comm.
(^29) Hull 1988, 103 citing Verne Grant.
(^30) Barrington et al. 1989, Paris et al. 1989, Yatskievych and Moran 1989, Haufler 1996, Vogel et al. 1996,
Ramsey and Schemske 1998, Wagner and Smith 1999.
(^31) Harlan and De Wet 1963.
(^32) Aguilar et al. 1999.
(^33) Sokal and Sneath 1963, Sneath and Sokal 1973.
(^34) Adanson 1763. Winsor 2004 provides a rebuttal for this claim. Initially, Sokal and Sneath referred to
their view as “neo-Adansonian.”