title: Mechanism of the block to hybridization and selfing between the sympatric ascidians Ciona intestinalis and Ciona savignyi.
abstract: 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 < 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 < 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 < 0.0001) and concanavalin A (P < 0.0001), and wheat germ agglutinin inhibits fertilization in C. intestinalis (P < 0.0001) but is without effect on C. savignyi fertilization. Self and hybrid blocks employ different mechanisms including glycoside composition and acid sensitivity.
authors.affiliation: Biological Science, California State University Fullerton, Fullerton, California, USA.
authors.forename: J
authors.initials: J
authors.lastname: Byrd
authors.forename: C C
authors.initials: CC
authors.lastname: Lambert
mesh_terms: D000818:Animals; D002938:Ciona intestinalis / Q000196:embryology* / Q000502:physiology; D005260:Female; D005306:Fertilization / Q000187:drug effects / Q000502:physiology; D005990:Glycerol / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000494:pharmacology; D037102:Lectins / Q000378:metabolism; D008297:Male; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D013045:Species Specificity; D013084:Sperm-Ovum Interactions / Q000187:drug effects; D013094:Spermatozoa / Q000378:metabolism*; D014561:Urochordata / Q000196:embryology* / Q000502:physiology; D014817:Vitelline Membrane / Q000187:drug effects / Q000502:physiology
chemical_list: D007211:Indoles; D037102:Lectins; C007293:DAPI; D005990:Glycerol