Dynamic Patterns of Parasitism and Immunity across Host Development Influence Optimal Strategies of Resource Allocation

Abstract

The integration of physiological mechanisms into life-history theory is an emerging frontier in our understanding of the constraints and drivers of life-history evolution. Dynamic patterns of antagonism between developmental and immunological pathways in juvenile insects illustrate the importance of mechanisms for determining life-history strategy optima in the face of trade-offs. For example, developmental interference occurs when developmental processes transiently take priority over resources or pathway architecture, preventing allocation to immunity or other traits. We designed a within-host model of infected larval development to explore the impact of developmental dynamics on optimal resource mobilization and allocation strategies as well as on larval resistance and tolerance phenotypes. The model incorporates mechanism-inspired functional forms of developmental interference with immunity against parasites that attack specific larval stages. We find that developmental interference generally increases optimal investment in constitutive immunity and decreases optimal resource mobilization rates, but the results are sensitive to the developmental stage at first infection. Moreover, developmental interference reduces resistance but generally increases tolerance of infection. We demonstrate the potential impact of these dynamics on empirical estimates of host susceptibility and discuss the general implications of incorporating realistic physiological mechanisms and developmental dynamics for life-history theory in insects and other organisms.