All organisms face two allocation trade-offs: one between many small versus a few large offspring; and the second between present and future reproduction. Nowhere are these allocation trade-offs more apparent than in the vast range of variation in egg, offspring, and clutch size exhibited among species of marine invertebrates. It has become increasingly clear that, in many taxa of marine and terrestrial organisms, there is substantial intraspecific variation for egg and hatching size. This project focuses on a rarely considered, but potentially widespread, source of variation in egg and offspring size, namely, the inevitable conflicts of interest that arise over the optimal distribution of parental resources among siblings. The reproductive pairing system - because of its effects on the relatedness of interacting siblings - can have a decisive impact on the magnitude and resolution of these conflicts. This research characterizes how variation in the pairing system of a marine snail (Nucella ostrina) accounts for variation in maternal provisioning and offspring size. The work will also establish whether shifts in the reproductive pairing system correspond to patterns and modes of maternal provisioning across the entire genus of Nucella.
This project has several broad scientific implications: 1) Polyandry and encapsulation of offspring are widespread in marine organisms, angiosperms, and matrotrophic animals; however, few studies have considered their evolutionary ramifications, especially their costs. 2) Reproductive pairing system and parental-offspring conflict may also drive the evolution of post-zygotic reproductive isolation. This research brings to light a novel and potentially widespread mechanism causing such isolation in marine systems. 3) This study examines consequence of the links between oceanographic processes that affect recruitment of prey species, such as barnacles and mussels, and their predators. Unlike other well-studied predators such as seastars, Nucella has limited dispersal potential, hence is far more likely to exhibit spatially constrained population dynamics as well as adaptations that reflect varying food supplies. 4) The research will advance our understanding of the scale of ecological and evolutionary connections among members of marine communities, providing the foundation for scientifically informed design of marine reserve networks that sustain both species and genetic diversity. The snail, Nucella, has similarities to marine animal predators on commercially important marine resource species.
The project will interface with three outreach/training programs, including a collaborative program for undergraduates working at the interface of math and biology, an REU program that recruits a diverse population of local high-school students to collaborate on faculty research projects, and a program that provides Ph.D. students with hands-on experience in K-12 classrooms, and K-12 teachers and students experience with in the latest technical and conceptual advances in ocean science. This project will support a molecular ecology website and associated workshops, and a multi-user DNA facility to train these students, postdocs, and K-12 teachers in state-of-the-art molecular genetic analysis. It will support a number of young scientists, giving them multidisciplinary training at the interface of behavior, ecology, evolution, and marine biology.
Families are a unique arena where conflicts of interest often arise between males and females, between parents and offspring, and among siblings. The theory of kin selection, which underlies much of our understanding of the evolution of coopertation and conflict in non-human biological systems, predicts that the magnitude of these conflicts fundamentally depends on a species' mating system, specifically how many times a female mates, and with how many different males. When females mate with a single male, offspring will be full siblings and levels of conflict relatively low. At the other extreme, when females mate with multiple males, offspring are more likely to be half-sibs, and more likely to harm each other, either directly or indirectly. In addition, conflcts between parents and offspring over allocation of parental resources are also greatest when offspring are half-, rather than full-, sibs. These core predictions have rarely been rigorosuly tested, despite their importance for understanding ecologically and economically important traits, including seed size in crop plants, offspring size in many animals, and levels of parental investment in offspring. Using experiments and comparisons of natural populations that have different mating systems, this project demonstrated for the first time how variation in the mating system, through its effects on family conflict, accounts for variation in offspring size of an ecologically important, predatory marine snail (Nucella ostrina). As predicted, we found a strong positive relationship between the number of males a female mated with and levels of variation in the size of her offspring: the more fathers, the greater the variation. In addition, when we experimentally crossed snails from populations with different mating systems, few hybrid offspring were produced. Therefore, differences in mating systems may be an important engine driving biodiveristy in the sea. Overall, this project generated novel insights into the complex forces, notably family conflict, that drive the evolution of ecologically critical traits, in this case ofspring size. The project also provided training and professional development for 9 high-school biotechnology interns; >20 undergraduate researchers, including 2 female African American research fellows from Howard University and 3 Hispanic women; 2 Ph.D. students; and 2 postdoctoral fellows, both of whom are now faculty members at major research universities. Beyond the research community, the project's findings have been disseminated to the public through press releases, public forums, and coverage by national media.
