Evolution of Trophic Linkages in an Invaded Food WebEPA Grant Number: FP916988
Title: Evolution of Trophic Linkages in an Invaded Food Web
Investigators: Miehls, Andrea Lynn-Jaeger
Institution: Michigan State University
EPA Project Officer: Lee, Sonja
Project Period: June 9, 2009 through June 15, 2009
RFA: STAR Graduate Fellowships (2009) RFA Text | Recipients Lists
Research Category: Academic Fellowships
One of the greatest threats to aquatic environments is exotic (nonindigenous) species invasion. The Laurentian Great Lakes of North America have been subject to persistent exotic species invasion for centuries. Recently, a wave of invertebrate invaders, including the predaceous zooplankton Bythotrephes longimanus, has caused pronounced changes in these ecosystems. While the ecology of the Bythotrephes invasion is well studied, the importance of evolutionary processes to the effects of Bythotrephes has received little attention. My research investigates the effects of rapid evolutionary change in Bythotrephes on its food web interactions.
Adaptive evolution results from natural selection acting on heritable traits. For traits to evolve, genetic (i.e. heritable) variation must be phenotypically expressed and result in the differential survival and reproduction (i.e. selection) of an organism. Bythotrephes has a distinctive morphology featuring a prominent tail spine, which is likely a target of selection due to fish predation. The primary hypothesis of my research is that differences in selection pressures between the native and invaded ranges of Bythotrephes have resulted in the evolution of Bythotrephes morphology since invasion. To test this hypothesis, I am: 1) quantifying natural selection on morphology of Lake Michigan Bythotrephes; 2) investigating a quantity-quality reproductive trade-off between clutch size and endowment of morphological defenses in Bythotrephes young; 3) quantifying genetic variation (i.e. heritability) in Bythotrephes morphology; 4) predicting the evolutionary response of Bythotrephes morphology to natural selection and testing the prediction against observed phenotypic and genetic changes in Bythotrephes morphology since invasion; and 5) modeling the consequences of evolutionary change in Bythotrephes on an important fishery species, yellow perch (Perca flavescens).
Results from 2007 data indicate there is natural selection for decreased distal spine length of Bythotrephes during July (selection differential, S = -0.3mm; p<0.01), selection for increased distal spine length during August (S = 0.1mm; p<0.01) and no selection during September (p=0.1; all results based on a morphological comparison between first and second instar Bythotrephes). Yet, despite selection for decreased distal spine length in July, average distal spine length was greater in August and remained similar into September. This suggests that, although selection may be important for determining Bythotrephes morphology, phenotypic plasticity may also play a role. Quantification of genetic variation in Bythotrephes morphology indicates distal spine length is highly heritable (heritability estimate, H2 = 0.75). Together, estimates of selection and genetic variation indicate rapid evolution of Bythotrephes morphology is possible, however the role of phenotypic plasticity in determining Bythotrephes morphology requires further investigation. Future work will examine the effect of environmental cues on Bythotrephes morphology (i.e. measure phenotypic plasticity) as well as potential food web effects of Bythotrephes morphological change on yellow perch. This research will provide a needed evolutionary perspective for understanding exotic species invasion in the Great Lakes and will offer insight into the resilience of these systems to future invasions.