Award: OCE-1948788

The intellectual merit of this work was the advance in knowledge on some of the processes that affect genetic diversity in biological populations and the consequences of population genetic diversity for individual fitness. Overall, this project was concept-driven research, combined genomic and experimental approaches in lab and field settings, and focused on experimentally tractable and representative marine invertebrate species. By testing broadly applicable hypotheses, the results have relevance beyond the specific species studied. So far, the project has produced five peer-reviewed publications, and at least three papers are currently in press or under review, and all papers have students, technicians, and postdocs supported by the grant as co-authors.

We quantified bryozoan larval dispersal by directly measuring where larvae settled relative to a known source and discovered that most offspring settle within a meter of their maternal parent. We expected this limited dispersal would mean that close kin (e.g., siblings, cousins) would compete and mate with each other, leading to declines in fitness. However, we genotyped individuals from natural populations and found very little evidence that kin are ever close enough to compete, and little genetic evidence for inbreeding. When we experimentally controlled the density and relatedness of neighbors, we found mixed evidence that close kin compete more strongly than unrelated individuals, but we did discover that mating with siblings, or with individuals from different populations, reduced reproductive output compared to random mating within the population. We also discovered that larger than expected sperm dispersal led to high multiple paternity, regardless of the distance to the nearest neighbor.

Overall, there seems to be few disadvantages to the limited larval dispersal that does occur because greater gene flow likely occurs through sperm dispersal rather than larval dispersal, multiple paternity dilutes inbreeding, and cryptic mate choice avoids inbreeding. There also appears to be limited advantages for larvae to disperse further than a few 10s of meters, which is also relevant given that many other marine species can disperse 10’s of kilometers.

Given than some marine species can disperse 10’s of kilometers, we then developed a theoretical model to explore the evolutionarily stable strategies that could explain why such large-scale dispersal occurs. We discovered that large scales of larval dispersal can be evolutionarily maintained as a consequence of the benefits of having many larvae developing offshore and repeated spawning events to utilize stochastic current reversals and offset the losses of larvae in downstream ocean currents.

Research from graduate students supported by this grant discovered that: 1) the capacity for evolutionary change in dispersal traits of a sea squirt (ascidian) were very low, which was an important result given that the focal species has very limited larval dispersal already, and larval size varies greatly among closely related species, 2) hotter water temperatures reduce reproduction in a bryozoan because temperatures reduce growth rates and zooid states, rather than offspring development, which uncovered new pathways by which temperature affects fitness, and 3) multiple mating the crown conch (marine snail) increases genetic diversity in broods, but does not increase the number of offspring produced.

The results of this research had broader impacts that were relevant to understanding the processes that rebuild depleted adult stocks, facilitate changes in species geographic ranges, and modify the potential for adaptation under environmental stress. The project contributed to STEM education by supporting two PhD students and two Masters students. The project contributed to developing a competitive STEM workforce by mentoring one postdoctoral scholar and two research technicians. The project increased participation of the best and brightest in STEM by training and mentoring four women and two people from an underrepresented group. Results of the research were communicated via invited guest lectures in undergraduate classes, hosting interactive displays and touch tanks at the university marine lab Open House days, and incorporating the findings into undergraduate classes on research methods.

Last Modified: 04/30/2025
Modified by: Scott Burgess