Ly assigned to obtain correct error terms for repeated-measures (within-subjects) variables (Table two). Assumptions of parametric statistics were checked by examining model residuals; a was set to 0.05. Statistics were run in R and Minitab software program packages.1860.81, <0.001 0.85, 0.472 2.72, <0.001 61.69, <0.001 0.83, 0.ResultsBrown trout sperm swimming velocity showed plasticity to water pH (Table 2, Fig. 3a), but the reaction norm was neither linear nor consistent. The species-level aver-*"Source" is a code for the different terms, "df" is degrees of freedom, "Error" refers to which "Source" is used in the denominator of the F-test. The term pH 9 time 9 individual (population) is not included in the model; this appears as error (Source 11) and is the correct error term for testing five of the other terms. Sperm velocity (VCL) is the mean among procedural replicates of the mean among sperm cells within a procedural replicate. The model explained 98 of the variance.?2012 The Authors. Published by Blackwell Publishing Ltd.C.F. Purchase D.T.R. MoreauPlasticity in Stressful Environments(a)(b)Figure 4. Population-level average reaction norms of brown trout sperm exposed to different environmental pH levels at 10 sec post-activation. Each datum is the mean among 10 individuals, of the mean among five replicates (= 50 microscope procedures), of the mean among moving sperm cells on a slide. Error bars are not shown; individual data are presented in Figure 5.Figure 3. Species-level average reaction norms of brown trout sperm exposed to different environmental pH levels. The two panels are the same data plotted in different ways to aid in interpretation; each line is a (a) time post-activation, (b) pH treatment. Each datum is the mean among 20 individuals, of the mean among five replicates (= 100 microscope procedures), of the mean among moving sperm cells on a slide over a period of 0.5 s. Error bars are not shown; individual data area presented in Figure 5. Numbers inserted on panel (b) are the average percent of sperm that are moving after a given time post-activation (across all procedures, fish, and pH levels).#3 blue, #8 red line), or nearly linear (e.g., #9 blue line) reaction norm. Variance among individuals increased greatly with decreasing pH, a pattern that was similar for both populations (Fig. 5 middle panels). In other words, environments that would be most stressful for reproduction expressed the most variable phenotypes among individuals. For example, individuals labeled #8 and #10 (red lines) have similar phenotypes under optimal pH 8, but are very divergent below pH 6. The pattern is even more pronounced for individuals #3 and #9 (blue lines).DiscussionReaction norms of the plastic expression of phenotypes can vary by genotype, but detecting this can be verydifficult. Furthermore, whether such responses are adaptive depends on the trait and context, and interpretation cannot be extrapolated to environments beyond those tested. We documented phenotypic plasticity in brown trout sperm performance and found the average reaction norm within and between populations to be flat over a broad range in river pH. Without finer resolution for individual fish, we would interpret the canalization of the species- and population-level reaction norms as being adaptive. This conclusion is altered when we examine reaction norms of specific individuals, a level at which the conceptual PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/21178946 MedChemExpress COH29 underpinnings are based, but where data are often lacking (N.