Zebra mussels' phenotype expression changes with predation risk.

<p>Anti-predator responses of zebra mussels from the four experimental treatments: either a single crayfish (crayfish symbol), a single roach (fish symbol), both predators combined (both symbols next to each other) or no predator at all (minus symbol). Different lower case a and b letters denote significant differences for p<0.05 after post-hoc tests. Error bars denote 95% confidence intervals <b>A</b>: shell shape expressed as a principal component PC1 explaining 77% of the total variation in the contour shape of all analyzed mussels (the contours on the y-axis depict ±2SD of the mean of PC1). <b>B</b>: shell strength as resistance to crushing in the form of the residuals from the correlation between mussel size and strength. <b>C</b>: growth measured in mm increase in the three shell dimensions length, height, and width compared to the start of experiment. <b>D</b>: Attachment strength as inferred from the number of byssus threads with which individual zebra mussels were attached to the surface.