EERNISSE, D.J.; Calif. State Univ., Fullerton: Similar but independent origins of selfing in two West Coast hermaphroditic chiton brooders.

Two small chitons species that can brood embryos when isolated in the lab are relatively distantly related within a West Coast clade of chitons. These two, Lepidochitona fernaldi Eernisse, 1986 and L. caverna Eernisse, 1986, are the only known hermaphroditic chiton species and are most likely regular selfers. New 16S rDNA and cox-I mtDNA comparisons confirm earlier estimates based on morphology and allozymes: the two hermaphroditic selfers are not sister taxa, so their similarities are unlikely due to common ancestry. Instead, selfing more likely arose independently, perhaps because both are brooders with potential for �crawl away� dispersal. A third brooder, L. thomasi (Pilsbry, 1898), has separate sexes and is an obligate cross fertilizer. L. thomasi is now resolved as the likely sister taxon of the hermaphroditic L. fernaldi. Together with allozyme evidence that L. thomasi is highly inbred, a multi-part hypothesis first proposed in 1984 by Strathmann et al. (Am. Nat. 123: 796-818) is supported: 1) if hermaphroditic selfers arise, they should gain a reproductive advantage relative to cross-fertilizers, provided they can also emphasize female over male gamete production; 2) despite its potential advantage, the loss of fitness due the inbreeding depression probably explains why selfing is rare in the sea; 3) an exception might occur if a population is already highly inbred, because deleterious alleles might have long since been �purged� so that any additional inbreeding depression due to selfing might be minimal; 4) brooding leads to inbreeding because progeny can crawl away, and thus brooding can be a pre-condition for any selfers that arise to gain at least a short-term reproductive advantage.