Predation rate and prey preference by <i>Cercopagis pengoi</i> offered pigmented and unpigmented <i>Eurytemora affinis</i> in feeding trials (Experiments 1 and 2).

<p>(A) predation rate (PR) in single-prey incubations (Experiment 1; mean ±SD; n = 12), and (B) prey preference index (Manley’s α) estimated from the mixed-prey incubations (Experiment 2; Tukey’s box and whisker plot, n = 12); the index ranges from 0 to 1, with higher values indicating greater preference. Shown are the median value (horizontal line), 25% to 75% response ranges (top and bottom lines of boxes) and minima and maxima (whiskers). Asterisk indicate a significant difference (p<0.05) in preference for the pigmented copepods when compared to those without visible pigmentation.</p

Trade-Offs between Predation Risk and Growth Benefits in the Copepod <i>Eurytemora affinis</i> with Contrasting Pigmentation

<div><p>Intraspecific variation in body pigmentation is an ecologically and evolutionary important trait; however, the pigmentation related trade-offs in marine zooplankton are poorly understood. We tested the effects of intrapopulation phenotypic variation in the pigmentation of the copepod <i>Eurytemora affinis</i> on predation risk, foraging, growth, metabolic activity and antioxidant capacity. Using pigmented and unpigmented specimens, we compared (1) predation and selectivity by the invertebrate predator <i>Cercopagis pengoi</i>, (2) feeding activity of the copepods measured as grazing rate in experiments and gut fluorescence <i>in situ</i>, (3) metabolic activity assayed as RNA:DNA ratio in both experimental and field-collected copepods, (4) reproductive output estimated as egg ratio in the population, and (5) total antioxidant capacity. Moreover, mitochondrial DNA (mtDNA) COI gene variation was analysed. The pigmented individuals were at higher predation risk as evidenced by significantly higher predation rate by <i>C. pengoi</i> on pigmented individuals and positive selection by the predator fed pigmented and unpigmented copepods in a mixture. However, the antioxidant capacity, RNA:DNA and egg ratio values were significantly higher in the pigmented copepods, whereas neither feeding rate nor gut fluorescence differed between the pigmented and unpigmented copepods. The phenotypic variation in pigmentation was not associated with any specific mtDNA genotype. Together, these results support the metabolic stimulation hypothesis to explain variation in <i>E. affinis</i> pigmentation, which translates into beneficial increase in growth via enhanced metabolism and antioxidant protective capacity, together with disadvantageous increase in predation risk. We also suggest an alternative mechanism for the metabolic stimulation via elevated antioxidant levels as a primary means of increasing metabolism without the increase in heat absorbance. The observed trade-offs are relevant to evolutionary mechanisms underlying plasticity and adaptation and have the capacity to modify strength of complex trophic interactions.</p></div

Eurytemora affinis.

<p>Eurytemora affinis.</p

Eurytemora affinis.

<p>Eurytemora affinis.</p

Minimum spanning tree showing relationships among haplotypes of pigmented (black) and unpigmented (white) <i>Eurytemora affinis</i>.

<p>Size of circle is proportional to the frequency of the haplotype. Slash marks indicate the number of nucleotide substitutions between haplotypes; no slash marks present indicates a single substitution separating haplotypes.</p

Details on sampling dates, locations, sample usage and preservation.

<p>Details on sampling dates, locations, sample usage and preservation.</p

Correlation plots of the redundancy analysis (RDA) on the relationship between environmental parameters (vectors) and plankton variables during 1979–2008.

<p>Asterisks indicate statistical significance (<i>p</i><0.05) of environmental variables. The plots display 15.5, 15.6 and 26.2% of the variance in the plankton data in the NBP, GF and ÅS, respectively, and eigenvalues of the first two axes are indicated by λ₁ and λ₂. Bac  =  Bacillariophyceae, Chl  =  Chlorophyceae, Chr  =  Chrysophyceae, Cry  =  Cryptophyceae, Cya  =  Cyanophyceae, Dino  =  Dinophyceae, Eug  =  Euglenophyceae, Pra  =  Prasinophyceae, Pry  =  Prymnesiophyceae, ACA  =  <i>Acartia</i> spp., EUB  =  <i>Eubosmina</i> spp., EUR  =  <i>Eurytemora</i> spp., EVA  =  <i>Evadne</i> spp., KER  =  <i>Keratella</i> spp., POD  =  <i>Podon</i> spp., SYN  =  <i>Synchaeta</i> spp.</p

Significant trends (<i>p</i><0.05) in environmental (squares) and zooplankton parameters (triangles) in the northern Baltic proper from 1979 to 2011, and in phytoplankton (circles) from 1979 to 2008.

<p>A Loess curve (solid line) is fitted, with a 95% confidence interval (dashed line).</p

Mann-Kendall trend test results for cladoceran and copepod abundance data divided into adults and juveniles or copepodites, respectively.

<p>(<i>S</i>  =  Kendall score, <i>p</i>  =  significance, <i>n</i>  =  number of observations). Data of <i>Podon</i> and <i>Evadne</i> spp. (GF, ÅS) were not tested due to small number of observations (<10) of juveniles. Significant trends are marked in bold.</p

Results of the Mann-Kendall test for detection of long-term trends.

<p>Significant trends in the environmental factors, phytoplankton biomass and zooplankton abundance data (for cladocerans and copepods, sum of adults and juveniles or copepodites, respectively) are marked in bold. <i>S</i>  =  Kendall score, <i>p</i>  =  significance, <i>n</i>  =  number of observations.</p