ENERGETIC
REQUIREMENTS DURING GONAD MATURATION AND SPAWNING IN SCALLOPS: SEX
DIFFERENCES IN CHLAMYS ISLANDICA (MULLER 1776)
K.B.
Brokordt, H.E. Guderley-2004
Journal of Shellfish Research, 23(1): 25-32
Abstract:
Reproduction in scallops, as in many
broadcast-spawning invertebrates, involves the production of a gonad that
can become the largest tissue in the body. Gonad maturation leads to
mobilization of macromolecular reserves from somatic tissues in many
scallops. Because ovaries typically contain higher energetic contents than
testes, we examined whether the energetic investment in gonad production and
spawning and the impact on somatic tissues was greater in female than male
Iceland scallops, Chlamys
islandica. In
males and females, maturation led to accumulation of carbohydrate and
protein in the gonads, whereas lipids only accumulated in the ovary. In both
sexes, the increase in gonad mass was accompanied by decrease of
carbohydrate in muscle and the remaining tissues, but testes maturation was
also paralleled by loss of carbohydrates and lipids from the digestive
gland. Although spawning led to a greater energy loss in the female than in
the male gonads (73
vs. 49 kJ in
gonad energy content), less mobilization of somatic energy was observed
during gametogenesis and spawning in females than males (14.5 kJ vs. 36.7). Most of the energy requirements for maturation and
spawning in females must have been covered by feeding, whereas somatic
reserve mobilization could have covered most of these costs in males. As in
most scallop species, lipids account for a major part of the ovarian energy
content. Direct deposition of dietary lipids in the eggs could minimize the
impact on somatic tissues of female scallops. The costs of protein synthesis
during testes maturation could decrease the aerobic scope available for
feeding by males. In light of our previous demonstration of the impact of
gonad maturation in C.
islandica on
recuperation from exhaustive exercise, our results suggest that the survival
of males may be decreased more by their reproductive investment than that of
females. The bioenergetic strategies of female scallops seem to favor
survival and hence future reproduction more than those of male scallops.
(Departement de Biologie and Quebec- Ocean, Universite
Laval, Quebec City, Quebec GIK 7P4, Canada, e-mail of H.E. Guderley: