Field identification of ‘types’ A and B of the ascidian Ciona intestinalis in a region of sympatry
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 differences, 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 differences are shown to be inherited.
KeywordsCryptic Species Natural Hybrid Body Colour Hybrid Cross Orange Pigment
We thank Chris Wood, Linda Noble, Colin Brownlee and other staff of the Marine Biological Association of the UK for generous hospitality during work on C. intestinalis. We also thank Seb Shimeld for valuable comments and laboratory space and resources for genotyping, Marie Nydam for advice on genotyping, Andy Griffiths for advice in genome extraction, and Takeshi Kawashima, Takeshi Nakashima and Mayuko Hamada for helpful discussion. This research was funded by a Ray Lankester Investigatorship from the Marine Biological Association of the UK, the AXA Research Fund, the Okinawa Institute of Science and Technology, and a JSPS Fellowship for Study Abroad to A.S.
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