Evidence of Matrotrophy in the Viviparous Holothuroid Echinoderm Synaptula hydriformis

Synaptula hydriformis is a holothuroid echinoderm that retains its young in the adult perivisceral coelom. It is also a simultaneous hermaphrodite and is probably self-fertilizing. Eggs are released from the germinal epithelium into the lumen of the ovotestis tubule, and from there into the perivisceral coelom. S. hydriformis is viviparous: eggs are never released to the outside of the adult organism, but develop internally until juveniles are released. It is also matrotrophic: the young rely on the parent to supply nutrition in excess of that supplied by yolk in the egg. Th e increase in both dry and organic weight from egg to 8-mm juvenile is in excess of 100 X. The additional nutrition is supplied as coelomocytes and molecules present in adult coelomic fluid. Brooded juveniles consume naturally occurring particulates and experimentally introduced 50-nm and l-jLm microspheres from the adult perivisceral coelom. 14Cpalmitic acid was also ingested by brooded juveniles and was incorporated into juvenile tissue, indicating that consumed nutrients are metabolized. Additional key words: reproduction, hermaphrodite,viviparity, ovoviviparity, holothurian Synaptula hydriformis ([smLesueur[nm 1824) broods its young in the perivisceral coelom and eventually gives birth to juveniles. In this paper, "young" is used collectively to describe all stages of brooded development: from egg to juvenile. "Juvenile" (as per Smiley et al. 1991) refers to those brooded young, adult-like in form, with five or more tentacles. Because juveniles can achieve a large body size while being brooded within the body of the adult (Clark 1898; Estabrooks 1984; Frick 1995), provisioning of the developing young with additional nutrients supplied by the parent seems likely. Nutrient provisioning of offspring is classified in vertebrates as either lecithotrophy or matrotrophy. Lecithotrophic young depend solely on yolk laid down in the egg for their nutritional requirements during development, whereas matrotrophic young depend on additional nutrients, other than those in the yolk, that are supplied by the parent (Wourms 1981). In invertebrate literature, these contrasting terms, though useful, generally have not been adopted (but see Wourms 1987). A direct test of whether nutrient supplementation to the young (matrotrophy) occurs is a comparison of egg mass and juvenile mass. If the dry weight of the juvenile is equal to or greater than the dry weight of the egg, then yolk supplies within the egg are insufficient a E-mail: jefrick@clemson.edu to account for the increase in weight of the juvenile (Wourms 1981). In such cases, an additional source of nutrition, other than that of yolk, is supplied. Some of the dry weight gain of juvenile echinoderms may result from the sequestration of calcium carbonate in the form of skeletal ossicles common to all echinoderms (Hyman 1955; Ruppert & Barnes 1994). Since yolk reserves are not transformed directly into calcium carbonate, calcium carbonate is removed from consideration of organic weight (Jaeckle & Manahan 1989). It should be noted, however, that because the young of S. hydriformis produce ossicles while being brooded inside the body of the adult, the adults may have the opportunity to regulate the supply of ossicle-forming calcium carbonate to the young. Organic weight determinations do not address this aspect of parental care. The principal objective of this research was to test the hypothesis that matrotrophy occurs in S. hydriformis, and, if so, to determine some of the sources and routes of the nutrients. Dry weight and organic weight of eggs and juveniles are used to determine the degree of parental investment. In addition, observations of ovulation and fertilization are reported. Terminology of parity mode is discussed to clarify the ambiguous use of the terms viviparity and ovoviviparity, and a refined definition of viviparity that acknowledges invertebrate diversity is proposed. This content downloaded from 207.46.13.145 on Sun, 03 Jul 2016 04:50:23 UTC All use subject to http://about.jstor.org/terms