(23% vs. 1.6%). Also, a significantly lower percentage of larvae derived from self-fertilized eggs metamorphose, and the growth of the colonies derived from their metamorphosis is significantly lower. These findings suggest that self-fertilization gives rise to inbreeding depression associated with developmental deficits that are likely caused by expression of deleterious recessive mutations. Asexual reproduction Many colonial sea squirts are also capable of asexual reproduction, although the means of doing so are highly variable between different families. In the simplest forms, the members of the colony are linked only by rootlike projections from their undersides known as stolons. Buds containing food storage cells can develop within the stolons and, when sufficiently separated from the 'parent', may grow into a new adult individual. In other species, the postabdomen can elongate and break up into a string of separate buds, which can eventually form a new colony. In some, the pharyngeal part of the animal degenerates, and the abdomen breaks up into patches of germinal tissue, each combining parts of the epidermis, peritoneum, and digestive tract, and capable of growing into new individuals. In yet others, budding begins shortly after the larva has settled onto the substrate. In the family Didemnidae, for instance, the individual essentially splits into two, with the pharynx growing a new digestive tract and the original digestive tract growing a new pharynx. DNA repair Apurinic/apyrimidinic (AP) sites are a common form of DNA damage that inhibit DNA replication and transcription. AP endonuclease 1 (APEX1), an enzyme produced by C. intestinalis, is employed in the repair of AP sites during early embryonic development. Lack of such repair leads to abnormal development. C. intestinalis also has a set of genes that encode proteins homologous to those employed in the repair of DNA interstrand crosslinks in humans. Ecology The exceptional filtering capability of adult sea squirts causes them to accumulate pollutants that may be toxic to embryos and larvae as well as impede enzyme function in adult tissues. This property has made some species sensitive indicators of pollution. Over the last few hundred years, most of the world's harbors have been invaded by non-native sea squirts that have clung to ship hulls or to introduced organisms such as oysters and seaweed. Several factors, including quick attainment of sexual maturity, tolerance of a wide range of environments, and a lack of predators, allow sea squirt populations to grow rapidly. Unwanted populations on docks,