Evolutionary stasis despite selection on a heritable trait in an invasive zooplankton

Abstract

Invasive species are one of the greatest threats to ecosystems, and there is evidence that evolution plays an important role in the success or failure of invasions. Yet, few studies have measured natural selection and evolutionary responses to selection in invasive species, particularly invasive animals. We quantified the strength of natural selection on the defensive morphology (distal spine) of an invasive zooplankton, Bythotrephes longimanus, in Lake Michigan across multiple months during three growing seasons. We used multiple lines of evidence, including historic and contemporary wild-captured individuals and palaeoecology of retrieved spines, to assess phenotypic change in distal spine length since invasion. We found evidence of temporally variable selection, with selection for decreased distal spine length early in the growing season and selection for increased distal spine length later in the season. This trend in natural selection is consistent with seasonal changes in the relative strength of non-gape-limited and gape-limited fish predation. Yet, despite net selection for increased distal spine length and a known genetic basis for distal spine length, we observed little evidence of an evolutionary response to selection. Multiple factors likely limit an evolutionary response to selection, including genetic correlations, trade-offs between components of fitness, and phenotypic plasticity.

Is earlier reproduction associated with higher or lower survival? Antagonistic results between individual and population scales in the blue tit

“…Another explanation behind common evolutionary stasis in heritable selected traits is the spatio-temporal fluctuations of selection (e.g. Miehls et al, 2015). In our study population, the only case in which selection on survival was inversed was in harsh condition years (early median laying date and high population density), whereby later laying individuals had higher survival rates: If the frequency of such years were to increase in the context of climate change, the selection regime of the focal population might face significant changes.…”

Local differentiation in the defensive morphology of an invasive zooplankton species is not genetically based

“…Despite this adaptive potential, and significant differences in selection among lakes, we found no evidence of genetic differentiation for distal spine length among populations of Bythotrephes . Previous work on Bythotrephes used historic and contemporary wild-caught animals and remnant distal spines retrieved from sediment cores to test for a response to selection on distal spine length since Bythotrephes invasion of Lake Michigan, and found little evidence of phenotypic change through time (Miehls et al 2015). Together, our results and those of Miehls et al (2015) provide clear examples of selection on a heritable trait not leading to an evolutionary response temporally (in Lake Michigan) or spatially (in these Canadian Shield lakes).…”

“…For example, temporal fluctuations in selection can influence the direction and strength of selection overall (Siepielski et al 2009; Bell 2010; Kingsolver and Diamond 2011). In GLP lakes, predation risk for Bythotrephes increases through the growing season because juvenile gape-limited fish grow from sizes too small to consume any Bythotrephes to sizes that can consume some Bythotrephes depending on gape-size (Straile and Halbich 2000; Branstrator 2005; Pothoven et al 2012; Miehls et al 2015). Our study only looked at a single snapshot of selection for each study lake, but previous work on Bythotrephes in Lake Michigan found strong temporal variation in selection within a growing season, which reduced net selection (Miehls et al 2015).…”

“…Lastly, we measured selection between first and second instar individuals, but selection on later instar stages is likely to occur on the length of the total spine, rather than just the distal spine (Fig. 1), which might reduce the strength of selection on distal spine length if selection on the total spine is weaker or in the opposite direction (see Miehls et al 2015 for further discussion of potential causes of stasis in Bythotrephes ).…”

Environmental variability and the evolution of the glucocorticoid receptor (Nr3c1) in African starlings

“…; Miehls et al . ). Frequent and rapid changes in environmental conditions may therefore result in genetic canalisation that reduces sensitivity to environmental change (Gibson & Wagner ; Kawecki ; Flatt ).…”