Barcoding of the cytochrome oxidase I (COI) indicates a recent introduction of Ciona savignyi into New Zealand and provides a rapid method for Ciona species discrimination

Kirsty Smith,Craig Cary,Chrissen Gemmill,Andrew Fidler,Joshua Thia

doi:10.3391/ai.2012.7.3.002

Abstract

Mitochondrial cytochrome oxidase I (COI) gene sequencing (DNA barcoding) of Ciona specimens from New Zealand (NZ) led to the first record of the solitary ascidian Ciona savignyi in the Southern Hemisphere. We sought to quantify C. savignyi COI genetic diversity around the NZ archipelago and to compare this with diversity within C. savignyi’s native range in the north-west Pacific. Ciona savignyi specimens were collected from two NZ sites and from three sites around Japan. COI sequences (595 bp) were amplified and measures of genetic diversity were calculated. Based on differences between their COI sequences we developed a PCR-based assay to distinguish C. savignyi from the morphologically similar C. intestinalis. A total of 12 C. savignyi COI haplotypes were recovered from the 76 samples. Of the four haplotypes observed in NZ, two were unique. From the 10 haplotypes observed in the Japan samples, eight were unique. The C. savignyi populations in Japan were found to contain higher haplotype diversity when compared with those in NZ. The NZ samples contained only a small subset of the haplotype variation of the Japan samples, however, NZ samples did harbor two haplotypes not observed in the Japan samples. A PCR-based assay developed from the COI sequences was able to reliably discriminate the two Ciona species. The low COI genetic diversity within the two NZ C. savignyi populations sampled is consistent with a founder effect associated loss of genetic diversity. The robust PCR-based assay for distinguishing C. savignyi and C. intestinalis may find application in ecological and taxonomic studies and can be applied to both archival materials and live animals.

Highlights

Population genetic theory predicts that the small founding populations associated with many introduced species will contain a reduced portion of the total genetic variation present in the source population (Mayr 1954)
Population genetic analyses using Ciona savignyi mitochondrial cytochrome oxidase I (COI) sequences Partial mitochondrial COI coding sequences (595 bp) were amplified from the 76 C. savignyi specimens collected in New Zealand (NZ) (n = 56) and Japan (n = 20) with 12 distinct haplotypes recovered, denoted Cs1 – Cs12 (Table 1; GenBank accession numbers for COI haplotype Cs1 - Cs12 sequences are JF19699 through JF19710 inclusive)
No missing intermediate haplotypes were apparent in the cladogram generated from haplotypes Cs112 suggesting the genetic diversity of the C. savignyi COI gene has been well sampled in this study (Figure 2)

Summary

Introduction

Population genetic theory predicts that the small founding populations associated with many introduced species will contain a reduced portion of the total genetic variation present in the source population (Mayr 1954). Additional stochastic losses of genetic diversity (i.e. genetic drift; Fisher 1930) are to be anticipated in such small populations (Nei et al 1975; Sakai et al 2001; Roman and Darling 2007; Dlugosch and Parker 2008; Geller et al 2010). Such nonadaptive microevolutionary genetic changes are expected to have biological consequences, including inbreeding depression and a reduced capacity to adaptively evolve (Sakai et al 2001). This in turn may enhance the ability of such invasive species to persist, and even thrive, in novel ecological contexts

Methods

Results

Conclusion