Field identification of ‘types’ A and B of the ascidian Ciona intestinalis in a region of sympatry

Abstract

The ascidian species Ciona intestinalis is a major model chordate in developmental and evolutionary biology, and an important fouling organism and invasive species. However, genomic investigation has recently revealed the existence of two cryptic species, genetically distinct yet without obvious morphological diVerences, currently referred to as types A and B. Here, we show that they are externally distinctive in a zone of sympatry in the western English Channel. Examining genotyped specimens, we found that types A and B of C. intestinalis can generally be distinguished by body colour, pigmentation at the distal end of the siphons and the presence or absence of tubercles on the sides of the siphons. Detecting specimens of hybrid descent still requires detailed molecular analysis, but these visual characters in combination will identify living specimens of types A and B with high probability. These diVerences are shown to be inherited.

Co-occurrence and reproductive synchrony do not ensure hybridization between an alien tunicate and its interfertile native congener

“…The nominal species C. intestinalis (Linnaeus 1767) covers a complex of four cryptic species (Zhan et al 2010). Two of them, C. intestinalis species A and C. intestinalis species B (hereafter referred to species A and species B, respectively) are now considered pseudo-cryptic species since the advent of morphological criteria to distinguish them (Sato et al 2012). In addition, very recently, Brunetti et al (2015) showed that species A displays morphological features specific to the formerly described Japanese species Ciona robusta (Hoshino and Tokioka 1967), later synonymized under C. intestinalis, whereas species B fits with the C. intestinalis description by Millar (1953).…”

In the ovary of Ciona intestinalis (Type A), immune-related galectin and phenoloxidase genes are differentially expressed by the follicle accessory cells

“…The type A has also been designate as C. robusta [55] geographically distributed in the Mediterranean, Pacific, and Southern Atlantic coasts of Europe [54,56]. Nonetheless, evidence of incomplete reproductive isolation from the wild population within the shared range of A and B types, raises the taxonomic issue [57].…”

Combining environmental suitability and population abundances to evaluate the invasive potential of the tunicate Ciona intestinalis along the temperate South American coast

“…After removing duplicate records and a few records that presented obvious errors of georeference, the final dataset consisted of 776 from Northern Europe (considered here as the native range) as well as 107 presences registered in Canada, 98 records from the Pacific coast of the United States, 212 from Southern Europe, and 24 records from Japan. Due to their morphological similarity, and the consequent difficulty that involves the identification of each species in the field (but see Sato et al, 2012), we cannot unambiguously attribute to neither of the species of the genetic complex the records that are available at the public database. Therefore, we decided to follow Zhan et al, (2010) and allocate the set of occurrences to the species that dominates a specific area.…”