Eco-evolutionary dynamics of Great Lakes percid fishes
A burgeoning field of research is developing around the theory that evolutionary change can occur much more rapidly than expected, driving population responses to anthropogenic stressors and creating feedbacks on ecological timescales. Many of these rapidly evolving traits represent important life history characteristics, such as maturation, growth, reproductive investment, and offspring size. This dissertation focused on two important aspects of fish reproductive ecology: the process of maturation and the mechanisms driving variation in offspring size and fitness. These traits appear to vary on both spatial and temporal scales, and this variation can be driven by a complex interplay of phenotypically plastic responses to local environments and genetically-based adaptation to changing selection pressures. My research addressed: 1) temporal variation in maturation schedules of Great Lakes yellow perch, with special attention to potential changes in maturation due to commercial fishing; 2) how tradeoffs between growth, mortality, and maturation influenced sex-specific variation in maturation schedules among populations of Great Lakes yellow perch in recent time; 3) the influence of adaptation, plastic responses to thermal conditions, and maternal effects on egg size and intra-female egg size variation among walleye (Sander vitreus) populations, 4) the importance of genetic diversity to early life growth and survival in yellow perch, and 5) how maternal effects may influence life history trait evolution in response to and during recovery from fisheries exploitation. Yellow perch maturation schedules exhibited surprisingly rapid recovery toward maturity at larger sizes and older ages in Lake Michigan during a fishing moratorium, suggesting recovery from fisheries-induced evolution is possible in some fish stocks. Female and male maturation schedules exhibited dimorphic relationships with growth and mortality rates, highlighting how sex-specific variation in life history tradeoffs influences their evolution. Walleye exhibited consistently positive maternal effects on egg size and marked among-population variation in egg size related to average thermal conditions, suggesting adaptation of offspring size to local environments, while intra-female egg size varied plastically with annual temperatures, suggesting conditions regulating both energy acquisition and allocation to eggs influence offspring size in this species. Heterozygosity was significantly correlated with increased size in juvenile yellow perch under harsh environmental conditions, and the largest individuals were also most related to one another, further highlighting the importance of local environments to offspring size and fitness. Finally, an eco-genetic model testing the evolutionary response of life history traits to fishing mortality over various levels of maternal effect showed that positive maternal effects can increase the rate of evolutionary recovery of these traits when fishing is ceased. This research identified important factors that drive life history shifts in fish stocks; vital information as management agencies seek to restore or maintain the valuable fisheries and ecosystem services these species provide. More broadly, analyses of plastic and adaptive change of life history traits in populations experiencing several anthropogenic stressors could improve predictions of population responses to future change.
Hook, Purdue University.
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