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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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Observations (% of time; mean + SEM, n = 20 except small Elysia viridis from Codium fragile and Cladophora sericea where n = 16 and 19 respectively) of A) large and B) small E. viridis individuals from different original algal hosts (C. sericea, Cladophora rupestris, and C. fragile) on different algal diet species (Chaetomorpha melagonium, C. fragile, C. sericea, and C. rupestris) in 40 h multiple-choice assays.Different letters above bars within each original host species indicate significant differences at α = 0.05 (Friedman's PHC). The no choice category denotes observations where E. viridis were not on an algal diet species, these are not included in statistical analyses.
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pone-0102752-g001: Observations (% of time; mean + SEM, n = 20 except small Elysia viridis from Codium fragile and Cladophora sericea where n = 16 and 19 respectively) of A) large and B) small E. viridis individuals from different original algal hosts (C. sericea, Cladophora rupestris, and C. fragile) on different algal diet species (Chaetomorpha melagonium, C. fragile, C. sericea, and C. rupestris) in 40 h multiple-choice assays.Different letters above bars within each original host species indicate significant differences at α = 0.05 (Friedman's PHC). The no choice category denotes observations where E. viridis were not on an algal diet species, these are not included in statistical analyses.

Mentions: E. viridis from different original hosts demonstrated statistically significant preferences for different algal diet species (Friedman's test, large E. viridis from C. sericea: χ2 = 14.08, df = 3, P = 0.003; C. rupestris: χ2 = 25.00, df = 3, P<0.001; and C. fragile: χ2 = 36.99, df = 3, P<0.001; small E. viridis from C. rupestris: χ2 = 9.72, df = 3, P = 0.021; and C. fragile: χ2 = 20.29, df = 3, P<0.001), except for small E. viridis from C. sericea (Friedman's test, χ2 = 2.221, df = 3, P = 0.528). Large E. viridis from the two Cladophora hosts preferred the septate filamentous species C. melagonium, C. sericea and C. rupestris and were observed <1% of the time on the siphonous fleshy C. fragile, while large E. viridis collected from C. fragile showed a strong preference for C. fragile (Friedman's PHC, P<0.05; Fig. 1a). Small E. viridis collected from C. rupestris preferred C. rupestris, and small E. viridis from C. fragile preferred C. fragile (Friedman's PHC, P<0.05; Fig. 1b), although the preference was not as pronounced as for large slugs.


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

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

Observations (% of time; mean + SEM, n = 20 except small Elysia viridis from Codium fragile and Cladophora sericea where n = 16 and 19 respectively) of A) large and B) small E. viridis individuals from different original algal hosts (C. sericea, Cladophora rupestris, and C. fragile) on different algal diet species (Chaetomorpha melagonium, C. fragile, C. sericea, and C. rupestris) in 40 h multiple-choice assays.Different letters above bars within each original host species indicate significant differences at α = 0.05 (Friedman's PHC). The no choice category denotes observations where E. viridis were not on an algal diet species, these are not included in statistical analyses.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0102752-g001: Observations (% of time; mean + SEM, n = 20 except small Elysia viridis from Codium fragile and Cladophora sericea where n = 16 and 19 respectively) of A) large and B) small E. viridis individuals from different original algal hosts (C. sericea, Cladophora rupestris, and C. fragile) on different algal diet species (Chaetomorpha melagonium, C. fragile, C. sericea, and C. rupestris) in 40 h multiple-choice assays.Different letters above bars within each original host species indicate significant differences at α = 0.05 (Friedman's PHC). The no choice category denotes observations where E. viridis were not on an algal diet species, these are not included in statistical analyses.
Mentions: E. viridis from different original hosts demonstrated statistically significant preferences for different algal diet species (Friedman's test, large E. viridis from C. sericea: χ2 = 14.08, df = 3, P = 0.003; C. rupestris: χ2 = 25.00, df = 3, P<0.001; and C. fragile: χ2 = 36.99, df = 3, P<0.001; small E. viridis from C. rupestris: χ2 = 9.72, df = 3, P = 0.021; and C. fragile: χ2 = 20.29, df = 3, P<0.001), except for small E. viridis from C. sericea (Friedman's test, χ2 = 2.221, df = 3, P = 0.528). Large E. viridis from the two Cladophora hosts preferred the septate filamentous species C. melagonium, C. sericea and C. rupestris and were observed <1% of the time on the siphonous fleshy C. fragile, while large E. viridis collected from C. fragile showed a strong preference for C. fragile (Friedman's PHC, P<0.05; Fig. 1a). Small E. viridis collected from C. rupestris preferred C. rupestris, and small E. viridis from C. fragile preferred C. fragile (Friedman's PHC, P<0.05; Fig. 1b), although the preference was not as pronounced as for large slugs.

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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