Species Delimitation and Global Biosecurity

Abstract

Species delimitation directly impacts on global biosecurity. It is a critical element in the decisions made by national governments in regard to the flow of trade and to the biosecurity measures imposed to protect countries from the threat of invasive species. Here we outline a novel approach to species delimitation, “tip to root”, for two highly invasive insect pests, Bemisia tabaci (sweetpotato whitefly) and Lymantria dispar (Asian gypsy moth). Both species are of concern to biosecurity, but illustrate the extremes of phylogenetic resolution that present the most complex delimitation issues for biosecurity; B. tabaci having extremely high intra-specific genetic variability and L. dispar composed of relatively indistinct subspecies. This study tests a series of analytical options to determine their applicability as tools to provide more rigorous species delimitation measures and consequently more defensible species assignments and identification of unknowns for biosecurity. Data from established DNA barcode datasets (COI), which are becoming increasingly considered for adoption in biosecurity, were used here as an example. The analytical approaches included the commonly used Kimura two-parameter (K2P) inter-species distance plus four more stringent measures of taxon distinctiveness, (1) Rosenberg’s reciprocal monophyly, (P(AB)),1 (2) Rodrigo’s (P(randomly distinct)),2 (3) genealogical sorting index, (gsi),3 and (4) General mixed Yule-coalescent (GMYC).4,5 For both insect datasets, a comparative analysis of the methods revealed that the K2P distance method does not capture the same level of species distinctiveness revealed by the other three measures; in B. tabaci there are more distinct groups than previously identified using the K2P distances and for L. dipsar far less variation is apparent within the predefined subspecies. A consensus for the results from P(AB), P(randomly distinct) and gsi offers greater statistical confidence as to where genetic limits might be drawn. In the species cases here, the results clearly indicate that there is a need for more gene sampling to substantiate either the new cohort of species indicated for B. tabaci or to detect the established subspecies taxonomy of L. dispar. Given the ease of use through the Geneious species delimitation plugins, similar analysis of such multi-gene datasets would be easily accommodated. Overall, the tip to root approach described here is recommended where careful consideration of species delimitation is required to support crucial biosecurity decisions based on accurate species identification.

Methods and approaches for the management of arthropod border incursions

“…These include an initial high cost of development and set-up, continuing need for expensive equipment and chemicals, sensitivity to different test parameters (Boykin et al 2012), the current paucity of reliable DNA reference libraries for many arthropod species, and misidentification of sequences deposited on public libraries such as Genbank and BOLD (Jinbo et al 2011). …”

Intercepting Aliens: Insects and Mites on Budwood Imported to South Africa

“…The inability to identify a specimen with certainty makes phytosanitary decisions difÞcult. For some organisms, this has been addressed by the development of DNA barcodes, which are used in quarantine species identiÞcation (Boykin et al 2012). Again, most DNA-identiÞcation protocols available are for insects (e.g., Ball 2005, Barcenas et al 2005), with very few published for mites.…”

Diversity and systematics of philinid snails (Gastropoda: Cephalaspidea) in West Africa with remarks on the biogeography of the region

“…We did not include Rodrigo's (RD) parameter because it is not a relevant measure of the degree of distinctness when the underlying tree is not estimated under a strict molecular clock (Masters et al, 2010). Additionally, the measurement may be oversensitive to taxonomic distinctness (Rodrigo et al, 2008;Boykin et al, 2012). The tree for the SDP computations was estimated with the PhyML (Guindon & Gascuel, 2003;Guindon et al, 2010) plugin in Geneious, using the GTR+G+I model and SPR-search with 250 bootstrap replicates for estimating branch support.…”