Genetic Networking of the Bemisia tabaci Cryptic Species Complex Reveals Pattern of Biological Invasions

Paul De Barro,Muhammad Z Ahmed,Barry L Williams

doi:10.1371/journal.pone.0025579

Abstract

BackgroundA challenge within the context of cryptic species is the delimitation of individual species within the complex. Statistical parsimony network analytics offers the opportunity to explore limits in situations where there are insufficient species-specific morphological characters to separate taxa. The results also enable us to explore the spread in taxa that have invaded globally.Methodology/Principal FindingsUsing a 657 bp portion of mitochondrial cytochrome oxidase 1 from 352 unique haplotypes belonging to the Bemisia tabaci cryptic species complex, the analysis revealed 28 networks plus 7 unconnected individual haplotypes. Of the networks, 24 corresponded to the putative species identified using the rule set devised by Dinsdale et al. (2010). Only two species proposed in Dinsdale et al. (2010) departed substantially from the structure suggested by the analysis. The analysis of the two invasive members of the complex, Mediterranean (MED) and Middle East – Asia Minor 1 (MEAM1), showed that in both cases only a small number of haplotypes represent the majority that have spread beyond the home range; one MEAM1 and three MED haplotypes account for >80% of the GenBank records. Israel is a possible source of the globally invasive MEAM1 whereas MED has two possible sources. The first is the eastern Mediterranean which has invaded only the USA, primarily Florida and to a lesser extent California. The second are western Mediterranean haplotypes that have spread to the USA, Asia and South America. The structure for MED supports two home range distributions, a Sub-Saharan range and a Mediterranean range. The MEAM1 network supports the Middle East - Asia Minor region.Conclusion/SignificanceThe network analyses show a high level of congruence with the species identified in a previous phylogenetic analysis. The analysis of the two globally invasive members of the complex support the view that global invasion often involve very small portions of the available genetic diversity.

Highlights

An enduring challenge within the context of cryptic species is the delimitation of individual species within the complex [1,2,3]
Of the remaining six putative species three, AsiaI (Fig. 1), AsiaII_6 (Fig. 2) and MED (Fig. 3) each consisted of a network plus one unconnected haplotype and Middle East – Asia Minor 1 (MEAM1) (Fig. 4) split into one network plus two unconnected haplotypes (Table 1)
The statistical parsimony analysis showed that of the 352 unique haplotypes, all but 15 belonged to the network that corresponded to one of the 24 putative species identified in Dinsdale et al (2010) [27]

Summary

Introduction

An enduring challenge within the context of cryptic species is the delimitation of individual species within the complex [1,2,3]. Using mitochondrial cytochrome oxidase 1 (mtCOI) and the software TCS v1.21 [22] they calculated the maximum number of mutational steps needed to make a parsimonious connection between two haplotypes with the probability of 95% These haplotypes were linked using cladogram estimation analyses to form a network [23]. Where the number of steps needed to form a link exceeded the likelihood of 5%, those haplotypes remained unconnected This method is appropriate for population level analysis as it does not involve many of the assumptions of phylogenetic reconstruction methods e.g. it does not assume that the ancestral sequence is missing and does not require bifurcating relationships [24]. The results enable us to explore the spread in taxa that have invaded globally

Methods

Results

Conclusion