Germ-Cell Warfare in Ascidians: Sperm from One Species Can Interfere with the Fertilization of a Second Species

• Published in: The Biological bulletin (Lancaster) Vol. 198; no. 1; pp. 22 - 25
• Main Author: Lambert, Charles C.
• Format: Journal Article
• Language: English
• Published: United States Marine Biological Laboratory 01.02.2000; University of Chicago Press
• Subjects: Acetylglucosaminidase - metabolism; Animal reproduction; Animals; Ascidiacea; Biological taxonomies; Body fluids; Competition (Biology); Female; Fertilization; Fertilization (Biology); Follicles; Germ cells; Male; Marine; Marine biology; Ova; Physiological aspects; Polyspermy; Research Notes; Sea squirts; Species; Species Specificity; Sperm competition; Sperm-Ovum Interactions - physiology; Spermatozoa; Spermatozoa - physiology; Urochordata - enzymology; Urochordata - physiology; Zygotes; United States
• ISSN: 0006-3185; 1939-8697
• DOI: 10.2307/1542799

Ascidians (invertebrate chordates) are very abundant in many marine subtidal areas. They often live in dense multispecies clumps; thus, interspecific competition for space may be intense. Although most noncolonial species are broadcast spawners, their eggs can be fertilized only by sperm of the same species (1). Multiple fertilization is lethal and all animals have evolved blocks to polyspermy. Ascidian eggs block polyspermy by enzymatic (2) and electrical mechanisms (3). Sperm bind to N-acetylglucosamine groups on the vitelline coat (4, 5, 6, 7). Follice cells surrounding the vitelline coat release N-acetylglucosaminidase during egg activation (8), preventing the binding of all sperm but a few (2). I show here that this interaction is not species-specific; sperm from one species can cause glycosidase release from follicle cells of a second species. Furthermore, once glycosidase release has been induced, the subsequent addition of sperm from the egg-producing species fails to fertilize a substantial proportion of these eggs. This leads to the hypothesis that sperm from one species of ascidian can interfere with fertilization of a second species. While intraspecific sperm competition has been well documented in several taxa (9, 10), this is the first record of sperm competition between species, or interspecific sperm competition.