Self-fertilization as an alternative mode of reproduction in the solitary tunicate Pyura chilensis

Abstract

The hermaphroditic broadcasting tunicate Pyura chilensis Molina, 1782 is a sessile filter-feeder organism that occurs in intertidal and subtidal habitats 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 selfing and highly successful settlement and metamorphosis of progeny originating from reproductively-isolated specimens suggest that even though outcrossing predominates, selfing is an advantageous alternative when sources of allosperm are scarce.

Fertilization efficiency and gamete viability in the ascidian Pyura praeputialis in Chile

“…Unlike similar studies conducted in Pyura chilensis (Manríquez & Castilla 2005), our manipulated fertilization using strip-spawned gametes of P. praeputialis failed to record significant levels of self fertilization, which is in agreement with the published evidence for this species (Clarke et al 1999). In our study, fertilization failures ended as eggs with no cleavage or with an abnormal cleavage pattern, which were counted as unfertilized eggs or the result of polyspermy respectively.…”

“…Counts were expressed as number per specimen and volume of seawater sampled from the aquarium during the sampling period (30 min). Sperm counts (see Manríquez et al 2001, Manríquez & Castilla 2005 were made from 20 ml samples collected every 30 min from the container in which the sieve was submerged. Spawning episodes during the experiment were counted, assigned to the immersion or emersion phase of each cycle, averaged and expressed as a function of elapsed time.…”

No effect of group size on sex allocation in a protandric-simultaneous hermaphroditic shrimp

“…In protandric-simultaneous hermaphrodites, individuals invariably reproduce as males first and later in life as simultaneous hermaphrodites. This sexual system has been confirmed in a polychaete worm (Premoli & Sella, 1995), a land snail (Tomiyama, 1996), a tunicate (Manríquez & Castilla, 2005) and shrimps from the genus Lysmata (Baeza, 2006).…”

Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

“…Current understanding of the evolutionary and ecological significance of self-fertilization versus outcrossing is mainly derived from investigation of terrestrial plant species (reviewed in Jarne and Charlesworth, 1993;Hedrick and Kalinowski, 2000;Goodwillie et al, 2005). The importance of such mating systems in animals has, however, rarely been investigated (reviewed in Jarne and Auld, 2006), though information on the importance of selfing in pulmonate snails (Jarne and Charlesworth, 1993;Jarne et al,1996Jarne et al, , 2000Trouvé et al, 2003;Henry et al, 2005), ascidians (Ryland and Bishop, 1990;Bishop and Ryland, 1993;Cohen, 1996;Jiang and Smith, 2005;Manríquez and Castilla, 2005) and platyhelminthes (Trouvé, et al, 1996) is starting to emerge.…”