Plant defense chemistry effects on parasitoid size vs. number tradeoffs: females get smaller but males become fewer

Abstract: The tradeoff between offspring number and offspring size is an important theme in life-history theory.  Given a fixed amount of resources with which to provision offspring, parents must balance the decisions of how many offspring to produce and how much to invest in each offspring.  While this general tradeoff has been repeatedly shown to exist in a wide variety of species, much less is known about how this balance is reached in response to variable, exogenous, environmental conditions.  In many species, empirical work attempting to explore this balance point has been confounded frequently by the existence of parent-offspring or sibling conflict over clutch size, egg vs. time limitation, or trade-offs between current and future reproductive effort.  In this talk, I will discuss the size-number tradeoff in two species of polyembryonic wasps.  Because multiple, genetically identical offspring arise from a single egg, the balance point between offspring number and offspring size is expected to be unburdened by confounding factors mentioned above.  This allows us to examine more clearly how variable exogenous factors, influence competition for host resources and, hence, the balance point in the size-number tradeoff.  I discuss empirical findings regarding how the balance point between offspring number and offspring size responds to two potential sources of environmental stress: variable competition for host resources resulting from different patterns of within-brood relatedness (arising from the polyembryonic divisions of more than one egg) and the variable levels plant defensive chemistry encountered by host herbivores (and to which parasitoids are directly exposed and/or are indirectly affected via reduced host quality).