MCCURDY, D.G.*; COOK, K.A.; FORBES, M.R.; Albion College; Carleton Univ.: Brood sizes and egg sizes of the intertidal amphipod Corophium volutator in relation to season and density

Life-history theory predicts that females will invest in offspring optimally- that is, in ways that result in the highest recruitment of new reproductive individuals into populations. We investigated the brood size-egg size relations in an intertidal amphipod, Corophium volutator (Pallas) in relation to season. We expected that female amphipods at sites in the Bay of Fundy would allocate more resources to offspring later in the breeding season, if increased competition among amphipods was present at that time, and because of reduced time available for juveniles to grow before winter. While average egg size carried by females was inversely associated with brood size, it was not influenced by size of mothers. Furthermore, brood size of females declined seasonally, but season did not account for variation in egg size, after factoring out the effect of brood size and location of sampling. Density of juvenile amphipods increased seasonally; however, overall amphipod density was inconsistently related to season across sites. Thus, our results show that female amphipods carry smaller broods later in the season, but that this adjustment is not necessarily associated with larger egg size. Other work is needed to determine costs associated with carrying broods of various sizes, and to assess whether such costs vary seasonally or affect future survival and reproductive output of females.