Mechanism of the block to hybridization and selfing between the sympatric ascidians Ciona intestinalis and Ciona savignyi

✍ Scribed by Jennifer Byrd; Charles C. Lambert

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 282 KB
• Volume: 55
• Category: Article
• ISSN: 1040-452X
• DOI: 10.1002/(sici)1098-2795(200001)55:1<109::aid-mrd15>3.0.co;2-b

✦ Synopsis

The solitary ascidians Ciona intestinalis and Ciona savignyi co-occur in southern California harbors, but no hybrids have been recognized in nature. Numerous differences in their egg morphology were detected. Homologous (normal outcross) fertilization yielded 96-99% cleavage, where autologous (self) fertilization showed 3% and heterologous (hybrid) fertilization showed 0-1%. Acid treatment (pH 3.2) removed the block to selfing (P Ͻ 0.0001) but not hybridization for both species. Heterologous sperm bind to the vitelline coat (VC), but fail to penetrate. Enzymatic removal of the VC resulted in 91-97% cleavage with autologous and heterologous sperm (P Ͻ 0.0001). The vitelline coats of the two species differ in lectin binding to surface glycosides. Fertilization in both species is significantly inhibited by the lectins, fucose binding protein (P Ͻ 0.0001) and concanavalin A (P Ͻ 0.0001), and wheat germ agglutinin inhibits fertilization in C. intestinalis (P Ͻ 0.0001) but is without effect on