Self-fertilization as an alternative mode of reproduction in the solitary tunicate <i>Pyura chilensis</i>
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2005
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Abstract
The hermaphroditic broadcasting tunicate Pyura chilensis Molina, 1782 is a sessile filter-feeder organism that occurs in intertidal and subtidal habitat s along the Chilean and Peruvian coast. In natural populations, P. chilensis form dense aggregations, small patches or occur as isolated individuals. This suggests that self-fertilization could be a potential insurance against adverse conditions for cross-fertilization. In this study, P. chilensis were reared in the laboratory as isolated and paired individuals, to assess occurrence and success of fertilization, settlement and metamorphosis. Occurrence of self-fertilization was also compared between specimens forced to cross-fertilize and specimens maintained in reproductive isolation for different periods. We also manipulated cross- and self-fertilization using strip-spawned gametes. Our study shows that P. chilensis is a hermaphroditic species with adolescent gonochorism; that is, individuals first developed male function and then later male and female functions simultaneously as specimens increased in size (protandrous hermaphroditism). The results also show more frequent fertilization in paired specimens and in manipulated fertilization involving cross sperm. Moreover, no perceptible differences in fertilization, settlement, and metamorphosis success among self and outcross progeny were found. Prolonged periods of reproductive isolation resulted in more frequent self-fertilization. Occurrence of selling and highly successful settlement and metamorphosis of progeny originating from reproductively-isolated specimens suggest that even though outcrossing predominates, selling is an advantageous alternative when sources of allosperm are scarce.
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hermaphroditism, broadcast spawner, self-fertilization, settlement, metamorphosis, inbreeding, reproductive success