WITHIN-SEASON REPRODUCTIVE AND SOMATIC ENERGY ALLOCATION IN A FRESH-WATER CLAM, ANODONTA-PISCINALIS

The effect of a change in the environment on reproductive and somatic energy allocation in an iteroparous freshwater clam Anodonta piscinali s was studied at different times of the seasonal reproductive cycle. E nvironmental change was produced by reciprocal transplant experiments among sites of varying productivity. In addition, clams were caged at high density to reduce the availability of resources. Transplanting fe males before fertilization (from May to June), or during the early dev elopment of the brood (from July to August) had no detectable effect o n reproductive output. Early-season environment, however, affected bod y mass and percent fat content of females from two populations. This s uggests that maintaining the level of reproductive allocation when res ources are reduced early in the season leads to lower allocation to so matic growth and biochemical storage. Transplanting females late in th e season (from September to November) had a substantial effect on repr oductive output and body mass, but not on fat content, suggesting that late in the season allocation to biochemical energy storage is import ant. Hence, late in the season reproductive allocation may be adjusted to prevailing conditions in preparation for winter. Indeed, over-wint ering site had a significant effect on percent fat content, body mass and shell growth when females were kept in a new environment from Sept ember to March. Variation among transplant sites in female body mass m atched the estimated productivity of the sites, suggesting that it occ urred in response to differences in the productivity of the habitats. The results emphasize the importance of taking seasonal changes in the priorities of energy allocation and the seasonality of reproductive p rocesses into account when developing or testing models of optimal ene rgy allocation.