SEXUAL REPRODUCTION

The sexual stage of T. democratica begins as a chain of genetically identical buds; a stolon, coiled around the stomach of the asexual ‘parent’ (Heron, 1972, Henschke, 2009, Kremer, 2002). Upon release, buds take on a female form, each containing a single ovary with one egg (Miller and Cosson, 1997). After release, sperm present in the water column fertilize female buds (Heron, 1972). Sperm penetrate and fertilize eggs through a fertilizing duct; a conduit like strand of tissue extending from the outer lining of the body to the ovary (Miller and Cosson, 1997). After fertilization, growth of the embryo begins inside the female (Henschke, 2009, Miller and Cosson, 1997). Once the developing embryo reaches approximately 1.5mm in size, it is born through the atrial excurrent canal into the water column. At this stage the female ‘parent’ individual develops testes and functions as a male in the fertilization of other recently released aggregates. After fertilizing one clutch of aggregates males die and sink to the sea bottom, a process fundamentally important in storage of free carbon in the ocean (Deibel, 1982). Individuals released from sexual generations are solitary stage individuals, and represent the alternation of sexual to asexual generations. Due to the strict asexual andsexual intervals in the life cycle of T. democratica prevents self-fertilization, further promoting genetic diversity within the species (Miller and Cosson, 1997)