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Individual specialization to non-optimal hosts in a polyphagous marine invertebrate herbivore.

Baumgartner FA, Pavia H, Toth GB - PLoS ONE (2014)

Bottom Line: E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits.Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles.We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological and Environmental Sciences-Tjärnö, University of Gothenburg, Strömstad, Sweden.

ABSTRACT
Factors determining the degree of dietary generalism versus specialism are central in ecology. Species that are generalists at the population level may in fact be composed of specialized individuals. The optimal diet theory assumes that individuals choose diets that maximize fitness, and individual specialization may occur if individuals' ability to locate, recognize, and handle different food types differ. We investigate if individuals of the marine herbivorous slug Elysia viridis, which co-occur at different densities on several green macroalgal species in the field, are specialized to different algal hosts. Individual slugs were collected from three original algal host species (Cladophora sericea, Cladophora rupestris and Codium fragile) in the field, and short-term habitat choice and consumption, as well as long-term growth (proxy for fitness), on four algal diet species (the original algal host species and Chaetomorpha melagonium) were studied in laboratory experiments. Nutritional (protein, nitrogen, and carbon content) and morphological (dry weight, and cell/utricle volume) algal traits were also measured to investigate if they correlated with the growth value of the different algal diets. E. viridis individuals tended to choose and consume algal species that were similar to their original algal host. Long-term growth of E. viridis, however, was mostly independent of original algal host, as all individuals reached a larger size on the non-host C. melagonium. E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits. Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles. We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT.

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Tissue A) protein (% dry weight, mean + SEM, n = 3–5), B) nitrogen (% dry weight, mean + SEM, n = 5), and C) carbon content (% dry weight, mean + SEM, n = 5), D) C:N ratio, E) dry weight (% wet weight, mean + SEM, n = 5), and F) cell/utricle volume (nl, mean + SEM, n = 5) of the four algal diet species (Chaetomorpha melagonium, Codium fragile, Cladophora rupestris and Cladophora sericea) during the four week growth experiment with Elysia viridis.Different letters above bars indicate significant differences at α = 0.05 (R-E-G-W F procedure) between mean values for the different algal diet species.
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pone-0102752-g004: Tissue A) protein (% dry weight, mean + SEM, n = 3–5), B) nitrogen (% dry weight, mean + SEM, n = 5), and C) carbon content (% dry weight, mean + SEM, n = 5), D) C:N ratio, E) dry weight (% wet weight, mean + SEM, n = 5), and F) cell/utricle volume (nl, mean + SEM, n = 5) of the four algal diet species (Chaetomorpha melagonium, Codium fragile, Cladophora rupestris and Cladophora sericea) during the four week growth experiment with Elysia viridis.Different letters above bars indicate significant differences at α = 0.05 (R-E-G-W F procedure) between mean values for the different algal diet species.

Mentions: All measured algal traits varied significantly between algal diet species and/or between collection weeks (Table 1). Nutritional traits (tissue P, N, and C content) showed fairly similar patterns between different algal diets (Fig. 4a–c). C. rupestris demonstrated the highest tissue P, N and C content followed by C. melagonium, C. sericea and C. fragile (R-E-G-W F, P<0.05; Fig. 4a–c). C. fragile consistently had the lowest nutritional content (Fig. 4a–c) although its' P content was similar to C. sericea (R-E-G-W F, P<0.05; Fig. 4a). There were no significant differences in the mean C:N ratio between algal diets (Table 1d, Fig. 4d). Percent dry weight followed a fairly similar pattern to algal nutritional traits with C. rupestris having the highest, C. fragile the lowest, and C. sericea, and C. melagonium intermediate values (Fig. 4e). Cell/utricle volumes of C. melagonium were on average 2.4 times larger than those of C. fragile across weeks (Fig. 4f), whereas Cladophora species had much smaller mean cell/utricle volumes that were fairly similar across sampling weeks (Fig. 4f). Decreases in mean cell/utricle volumes of approximately 25–40% from week 2 compared to weeks 3 and 4 occurred for both C. melagonium and C. fragile diets, which did not occur for the Cladophora diets (Fig. 4f), were the likely cause of the significant interaction term (Table 1f).


Individual specialization to non-optimal hosts in a polyphagous marine invertebrate herbivore.

Baumgartner FA, Pavia H, Toth GB - PLoS ONE (2014)

Tissue A) protein (% dry weight, mean + SEM, n = 3–5), B) nitrogen (% dry weight, mean + SEM, n = 5), and C) carbon content (% dry weight, mean + SEM, n = 5), D) C:N ratio, E) dry weight (% wet weight, mean + SEM, n = 5), and F) cell/utricle volume (nl, mean + SEM, n = 5) of the four algal diet species (Chaetomorpha melagonium, Codium fragile, Cladophora rupestris and Cladophora sericea) during the four week growth experiment with Elysia viridis.Different letters above bars indicate significant differences at α = 0.05 (R-E-G-W F procedure) between mean values for the different algal diet species.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4121074&req=5

pone-0102752-g004: Tissue A) protein (% dry weight, mean + SEM, n = 3–5), B) nitrogen (% dry weight, mean + SEM, n = 5), and C) carbon content (% dry weight, mean + SEM, n = 5), D) C:N ratio, E) dry weight (% wet weight, mean + SEM, n = 5), and F) cell/utricle volume (nl, mean + SEM, n = 5) of the four algal diet species (Chaetomorpha melagonium, Codium fragile, Cladophora rupestris and Cladophora sericea) during the four week growth experiment with Elysia viridis.Different letters above bars indicate significant differences at α = 0.05 (R-E-G-W F procedure) between mean values for the different algal diet species.
Mentions: All measured algal traits varied significantly between algal diet species and/or between collection weeks (Table 1). Nutritional traits (tissue P, N, and C content) showed fairly similar patterns between different algal diets (Fig. 4a–c). C. rupestris demonstrated the highest tissue P, N and C content followed by C. melagonium, C. sericea and C. fragile (R-E-G-W F, P<0.05; Fig. 4a–c). C. fragile consistently had the lowest nutritional content (Fig. 4a–c) although its' P content was similar to C. sericea (R-E-G-W F, P<0.05; Fig. 4a). There were no significant differences in the mean C:N ratio between algal diets (Table 1d, Fig. 4d). Percent dry weight followed a fairly similar pattern to algal nutritional traits with C. rupestris having the highest, C. fragile the lowest, and C. sericea, and C. melagonium intermediate values (Fig. 4e). Cell/utricle volumes of C. melagonium were on average 2.4 times larger than those of C. fragile across weeks (Fig. 4f), whereas Cladophora species had much smaller mean cell/utricle volumes that were fairly similar across sampling weeks (Fig. 4f). Decreases in mean cell/utricle volumes of approximately 25–40% from week 2 compared to weeks 3 and 4 occurred for both C. melagonium and C. fragile diets, which did not occur for the Cladophora diets (Fig. 4f), were the likely cause of the significant interaction term (Table 1f).

Bottom Line: E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits.Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles.We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological and Environmental Sciences-Tjärnö, University of Gothenburg, Strömstad, Sweden.

ABSTRACT
Factors determining the degree of dietary generalism versus specialism are central in ecology. Species that are generalists at the population level may in fact be composed of specialized individuals. The optimal diet theory assumes that individuals choose diets that maximize fitness, and individual specialization may occur if individuals' ability to locate, recognize, and handle different food types differ. We investigate if individuals of the marine herbivorous slug Elysia viridis, which co-occur at different densities on several green macroalgal species in the field, are specialized to different algal hosts. Individual slugs were collected from three original algal host species (Cladophora sericea, Cladophora rupestris and Codium fragile) in the field, and short-term habitat choice and consumption, as well as long-term growth (proxy for fitness), on four algal diet species (the original algal host species and Chaetomorpha melagonium) were studied in laboratory experiments. Nutritional (protein, nitrogen, and carbon content) and morphological (dry weight, and cell/utricle volume) algal traits were also measured to investigate if they correlated with the growth value of the different algal diets. E. viridis individuals tended to choose and consume algal species that were similar to their original algal host. Long-term growth of E. viridis, however, was mostly independent of original algal host, as all individuals reached a larger size on the non-host C. melagonium. E. viridis growth was positively correlated to algal cell/utricle volume but not to any of the other measured algal traits. Because E. viridis feeds by piercing individual algal cells, the results indicate that slugs may receive more cytoplasm, and thus more energy per unit time, on algal species with large cells/utricles. We conclude that E. viridis individuals are specialized on different hosts, but host choice in natural E. viridis populations is not determined by the energetic value of seaweed diets as predicted by the ODT.

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