Things fall apart: biological species form unconnected parsimony networks

Abstract

The generality of operational species definitions is limited by problematic definitions of betweenspecies divergence. A recent phylogenetic species concept based on a simple objective measure of statistically significant genetic differentiation uses between-species application of statistical parsimony networks that are typically used for population genetic analysis within species. Here we review recent phylogeographic studies and reanalyse several mtDNA barcoding studies using this method. We found that (i) alignments of DNA sequences typically fall apart into a separate subnetwork for each Linnean species (but with a higher rate of true positives for mtDNA data) and (ii) DNA sequences from single species typically stick together in a single haplotype network. Departures from these patterns are usually consistent with hybridization or cryptic species diversity.

Cryptic mitochondrial lineages in the widespread pycnogonid Colossendeis megalonyx Hoek, 1881 from Antarctic and Subantarctic waters

“…Third, a statistical parsimony analysis using TCS yielded completely separated networks for the six clades at a 95% as well as a 90% connection limit. In previous analyses, this level of separation has frequently been shown to be in accordance with the definition of biological species (Hart and Sunday 2007).…”

Whole-community DNA barcoding reveals a spatio-temporal continuum of biodiversity at species and genetic levels

“…We first established a hierarchical grouping scheme from the mtDNA variation using Templeton's (1987) algorithm to generate nested clades of n steps according to the number of mutational steps between increasingly more distant haplotypes incorporated into a network 17 . Based on the 2,183 unique haplotypes, the method defined 268 networks, closely matching the number and extent of GMYC groups, as seen elsewhere 18 . Each network contained genealogies of up to five hierarchical levels.…”

Worms without borders: genetic diversity patterns in four Brazilian Ototyphlonemertes species (Nemertea, Hoplonemertea)

“…This pattern should be consistent with the model of recurring adaptive radiations taking place at small geographic scales in allopatrically distributed sister taxa. Delimiting species boundaries in marine taxa is a challenging task (Knowlton 1993(Knowlton , 2000Hart and Sunday 2007), and this is especially true for nemerteans, due to the scarcity of discrete morphological traits. Several of the traits used to distinguish varieties among established species are plastic and would rather diagnose ecological morphs than represent monophyletic units (Envall and Sundberg 1998;Envall and Norenburg 2001).…”