Abstract
Sexual and asexual reproduction and associated population dynamics were investigated in the colonial ascidian Didemnum rodriguesi Rocha & Monniot, 1993 (Didemnidae) in southern Brazil. Investment in sexual (production of new individuals) and asexual (colony growth) reproduction was compared between seasons. Permanently marked quadrats were repeatedly photographed to measure changes in colonies. Eggs and larvae were counted monthly in collected colonies. This species alternates seasonally between sexual (summer) and asexual (winter) reproduction. In summer, colonies were smaller, brooded eggs and larvae and recruitment rates were greater, while in winter, colony size was larger and eggs and larvae were absent. There is a relationship between fecundity and colony area. Fragmentation and fusion of colonies were similar in summer and winter, as well as mortality. In conclusion, D. rodriguesi has a lifecycle usual for high latitude ascidians with a limited time length for sexual reproduction and alternate investment in sexual and asexual reproduction along the year.
Highlights
Sexual reproduction in colonial ascidians is through the production of male and female gametes, with internal fertilization that follows the release of sperm to the environment that is subsequently taken in by other individuals
Asexual reproduction in colonial forms occurs in many ways: a colony may divide into smaller units or zooids may replicate within a colony through budding
Colony growth has been studied in a number of ascidians, revealing complex patterns of growth and fission (BAK et al, 1981), influence of neighbors (STOCKER & UNDERWOOD, 1991), or a strong seasonal component coupled with alternating sexual and asexual reproduction (GROSBERG, 1988; TURON & BECERRO, 1992; TURON, 2005)
Summary
Colony growth has been studied in a number of ascidians, revealing complex patterns of growth and fission (BAK et al, 1981), influence of neighbors (STOCKER & UNDERWOOD, 1991), or a strong seasonal component coupled with alternating sexual and asexual reproduction (GROSBERG, 1988; TURON & BECERRO, 1992; TURON, 2005). These patterns suggest that demographic parameters of modular organisms may be a function of organism size rather than age (LINACRE & KEOUGH, 2003)
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