Estimating reproductive effort in small aquatic invertebrates from lipid dynamics

Invertebrates that brood eggs or offer parental care to developing embryos incur a cost of reproduction in addition to that associated with the production of eggs. This additional cost is difficult to quantify but it is important in shaping the reproductive strategy of organisms and for evaluating their life history trade-offs. I used lipid analyses to determine the energy expended by female amphipods during the incubation of eggs. Lipid levels in female Gammarus lacustris during incubation of eggs dropped from 18.2% after egg deposition into the brood pouch to 8.4% when young were released. This decrease equalled 13.0 J and was similar to the 14.6 J in lipid energy in the eggs.