Self- and Cross-Fertilization in the Solitary Ascidian Ciona savignyi

• Published in: The Biological bulletin (Lancaster) Vol. 209; no. 2; pp. 107 - 112
• Main Authors: Jiang, Di, Smith, William C.
• Format: Journal Article
• Language: English
• Published: United States Marine Biological Laboratory 01.10.2005; University of Chicago Press
• Subjects: Animal populations; Animal reproduction; Animals; Aquatic life; Ascidiacea; California; Chorion; Ciona intestinalis; Ciona savignyi; Development and Reproduction; Female; Fertilization; Gametes; Genetics; Green Fluorescent Proteins; Hermaphroditism; Inbreeding; Invertebrates; Male; Mutation - genetics; Ova; Ovotesticular Disorders of Sex Development; Sea squirts; Sea water; Self fertilization; Sexual behavior; Sexual Behavior, Animal - physiology; Species Specificity; Sperm competition; Spermatozoa; Spermatozoa - physiology; Tadpoles; Urochordata - genetics; Urochordata - physiology; California; United States; Santa Barbara California; INE, USA, California
• ISSN: 0006-3185; 1939-8697
• DOI: 10.2307/3593128

Solitary ascidians are hermaphrodites that release sperm and eggs simultaneously. However, many species are self-sterile, owing to a self/non-self recognition system operating at the outer surface of the chorion during sperm-egg interaction. In Ciona intestinalis, self-incompatibility is thought to have a genetic basis. Here, we report a survey of the self-fertilization potential of a Santa Barbara, California, population of Ciona savignyi, a close relative of C. intestinalis. We found that, in contrast to reports on C. intestinalis, C. savignyi is highly self-fertile. However, using two nonlethal recessive mutant strains, aimless (aim) and immaculate (imc), and a stable transgenic strain that expresses green fluorescent protein (GFP) in the notochord to follow offspring genotype, we demonstrate that non-self sperm outcompete self-sperm in fertilization competition assays. When the chorion was removed, both self- and non-self sperm performed equally well in the competition assay. Thus the non-self/self gamete recognition in C. savignyi is not absolute but relative, and is mediated by one or more components in the chorion. We discuss the significance of this finding in the context of natural populations in the wild, where individuals of C. savignyi are typically found growing in large groups that spawn in unison and where self-fertilization would be expected to be very rare.