Selden R et al. (2009), Waterborne cues from crabs induce thicker skele...

ECB-ART-43244

Mar Biol 2009 Jan 01;1565:1057-1071. doi: 10.1007/s00227-009-1150-0.

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Waterborne cues from crabs induce thicker skeletons, smaller gonads and size-specific changes in growth rate in sea urchins.

Selden R , Johnson AS , Ellers O .

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Indirect predator-induced effects on growth, morphology and reproduction have been extensively studied in marine invertebrates but usually without consideration of size-specific effects and not at all in post-metamorphic echinoids. Urchins are an unusually good system, in which, to study size effects because individuals of various ages within one species span four orders of magnitude in weight while retaining a nearly isometric morphology. We tracked growth of urchins, Strongylocentrotus droebachiensis (0.013-161.385 g), in the presence or absence of waterborne cues from predatory Jonah crabs, Cancer borealis. We ran experiments at ambient temperatures, once for 4 weeks during summer and again, with a second set of urchins, for 22 weeks over winter. We used a scaled, cube-root transformation of weight for measuring size more precisely and for equalizing variance across sizes. Growth rate of the smallest urchins (summer: <17 mm diameter; winter: <7 mm diameter) decreased by 40-42% in response to crab cues. In contrast, growth rate of larger urchins was unaffected in the summer and increased in response to crab scent by 7% in the winter. At the end of the 22-week experiment, additional gonadal and skeletal variables were measured. Cue-exposed urchins developed heavier, thicker skeletons and smaller gonads, but no differences in spine length or jaw size. The differences depended on urchin size, suggesting that there are size-specific shifts in gonadal and somatic investment in urchins.

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Genes referenced: LOC100887844 LOC100893907 LOC583082 ran span

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	Fig. 1. Strongylocentrotus droebachiensis. Nominal diameter change (mm) as a function of initial nominal diameter (mm) for urchins grown in the presence (black circles, solid lines) or absence (open circles, dashed lines) of waterborne cues from the crab Cancer borealis. Growth is shown for a four and b 20 weeks. Lines indicate least squares linear regressions for: i small urchins in the lag region, ii middle-sized urchins in the steadily declining region; and iii larger urchins in the tail region. For clarity, the scale is expanded for the lag region in the 20-week period. Separate lines for each treatment indicate that an ANCOVA analysis indicates that a one slope, two intercept model best fit these data; a single dot-dash line for both treatments indicates that a one slope, one intercept model best fit these data. See Table 1 for statistics
	Fig. 2. Strongylocentrotus droebachiensis.a Gonad equivalent length (cm) and b gonad index (%) both as a function of final nominal diameter (mm), c gonadal AFDW equivalent length (cm) as a function of total AFDW equivalent length (cm) and d gonadal AFDW index (%) as a function of total AFDW (g) for urchins grown for 22 weeks in the presence (black circles, solid lines) or absence (open circles, dashed lines) of waterborne cues from the crab Cancer borealis. Lines in a, b, c and d indicate the fit of Eqs. 6, 8, 7 and 9, respectively, to each treatment. All lines are significantly different between treatments. See Table 2 for statistics
	Fig. 3. Strongylocentrotus droebachiensis.a Skeletal ashed weight (g), b skeletal index (%), c ambital plate thickness (mm) and d aboral plate thickness (mm) each as a function of final nominal diameter (mm) for urchins grown for 22 weeks in the presence (black circles, solid lines) or absence (open circles, dashed lines) of waterborne cues from the crab Cancer borealis. For a the lines indicate least squares linear regressions on the log transformed data; for b the lines indicate fit of Eq. 10; for c and d the lines indicate least squares linear regressions. Separate lines for each treatment indicate significant differences between treatments. See Table 3 for statistics
	Fig. 4. Strongylocentrotus droebachiensis. a maximum spine length (mm), b mean spine length (mm), c mean demipyramid length (mm) and d demipyramid weight (g) all as a function of final nominal diameter (mm) for urchins grown for 22 weeks in the presence (black circles, solid lines) or absence (open circles, dashed lines) of waterborne cues from the crab Cancer borealis. For a–c the lines indicate least squares linear regressions on the axes variables shown; for d the line indicates the least squares linear regression fit for the cube root of demipyramid weight as the dependent variable shown transformed back to demipyramid weight. The single dot-dash line indicates no significant difference between treatments. See Table 3 for statistics

References [+] :

Appleton, Water-borne stimuli released by predatory crabs and damaged prey induce more predator-resistant shells in a marine gastropod. 1988, Pubmed