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Are sick individuals weak competitors? Competitive ability of snails parasitized by a gigantism-inducing trematode.

Seppälä O, Karvonen A, Kuosa M, Haataja M, Jokela J - PLoS ONE (2013)

Bottom Line: In such systems, alternatively to reduced competitive ability due to negative effects of parasitism on host performance, larger size could allow more efficient resource acquisition and thus increase the relative competitive ability of host individuals.However, growth of the snails was faster when competing with parasitized individuals compared to unparasitized snails indicating reduced competitive ability due to parasitism.The latter effect, however, was relatively weak suggesting that the effects of the parasite on snail physiology may partly override each other in determining competitive ability.

View Article: PubMed Central - PubMed

Affiliation: Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland ; Department of Aquatic Ecology, Eawag, Dübendorf, Switzerland.

ABSTRACT
Parasitized individuals are often expected to be poor competitors because they are weakened by infections. Many trematode species, however, although extensively exploiting their mollusc hosts, also induce gigantism (increased host size) by diverting host resources towards growth instead of reproduction. In such systems, alternatively to reduced competitive ability due to negative effects of parasitism on host performance, larger size could allow more efficient resource acquisition and thus increase the relative competitive ability of host individuals. We addressed this hypothesis by testing the effect of a trematode parasite Diplostomum pseudospathaceum on the competitive ability of its snail host Lymnaea stagnalis. We experimentally examined the growth of snails kept in pairs in relation to their infection status and intensity of resource competition (i.e. food availability). We found that parasitized snails grew faster and their reproduction was reduced compared to unparasitized individuals indicating parasite-induced gigantism. However, growth of the snails was faster when competing with parasitized individuals compared to unparasitized snails indicating reduced competitive ability due to parasitism. The latter effect, however, was relatively weak suggesting that the effects of the parasite on snail physiology may partly override each other in determining competitive ability.

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Related in: MedlinePlus

Growth rate of Lymnaea stagnalis snails during the experiment.Bars (size-adjusted mean ± SE) show the specific growth rate of focal individuals with different infection status (unexposed, exposed but unparasitized, exposed and parasitized; parasite: Diplostomum pseudospathaceum) maintained together with another snail individual [competitor; unexposed (white), exposed but unparasitized (grey), exposed and parasitized (black); parasite: D. pseudospathaceum] under (A) ad libitum food supply and (B) reduced food supply (i.e. half of the average food consumption) for ten weeks.
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pone-0079366-g001: Growth rate of Lymnaea stagnalis snails during the experiment.Bars (size-adjusted mean ± SE) show the specific growth rate of focal individuals with different infection status (unexposed, exposed but unparasitized, exposed and parasitized; parasite: Diplostomum pseudospathaceum) maintained together with another snail individual [competitor; unexposed (white), exposed but unparasitized (grey), exposed and parasitized (black); parasite: D. pseudospathaceum] under (A) ad libitum food supply and (B) reduced food supply (i.e. half of the average food consumption) for ten weeks.

Mentions: Food limitation reduced the growth of snails (focal individuals) during the experiment (Figure 1, Table 1). Thus, we were able to manipulate the amount of external resources for snails using feeding treatments so that resource competition among them should be intensified under reduced food supply compared to ad libitum food supply.


Are sick individuals weak competitors? Competitive ability of snails parasitized by a gigantism-inducing trematode.

Seppälä O, Karvonen A, Kuosa M, Haataja M, Jokela J - PLoS ONE (2013)

Growth rate of Lymnaea stagnalis snails during the experiment.Bars (size-adjusted mean ± SE) show the specific growth rate of focal individuals with different infection status (unexposed, exposed but unparasitized, exposed and parasitized; parasite: Diplostomum pseudospathaceum) maintained together with another snail individual [competitor; unexposed (white), exposed but unparasitized (grey), exposed and parasitized (black); parasite: D. pseudospathaceum] under (A) ad libitum food supply and (B) reduced food supply (i.e. half of the average food consumption) for ten weeks.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814966&req=5

pone-0079366-g001: Growth rate of Lymnaea stagnalis snails during the experiment.Bars (size-adjusted mean ± SE) show the specific growth rate of focal individuals with different infection status (unexposed, exposed but unparasitized, exposed and parasitized; parasite: Diplostomum pseudospathaceum) maintained together with another snail individual [competitor; unexposed (white), exposed but unparasitized (grey), exposed and parasitized (black); parasite: D. pseudospathaceum] under (A) ad libitum food supply and (B) reduced food supply (i.e. half of the average food consumption) for ten weeks.
Mentions: Food limitation reduced the growth of snails (focal individuals) during the experiment (Figure 1, Table 1). Thus, we were able to manipulate the amount of external resources for snails using feeding treatments so that resource competition among them should be intensified under reduced food supply compared to ad libitum food supply.

Bottom Line: In such systems, alternatively to reduced competitive ability due to negative effects of parasitism on host performance, larger size could allow more efficient resource acquisition and thus increase the relative competitive ability of host individuals.However, growth of the snails was faster when competing with parasitized individuals compared to unparasitized snails indicating reduced competitive ability due to parasitism.The latter effect, however, was relatively weak suggesting that the effects of the parasite on snail physiology may partly override each other in determining competitive ability.

View Article: PubMed Central - PubMed

Affiliation: Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland ; Department of Aquatic Ecology, Eawag, Dübendorf, Switzerland.

ABSTRACT
Parasitized individuals are often expected to be poor competitors because they are weakened by infections. Many trematode species, however, although extensively exploiting their mollusc hosts, also induce gigantism (increased host size) by diverting host resources towards growth instead of reproduction. In such systems, alternatively to reduced competitive ability due to negative effects of parasitism on host performance, larger size could allow more efficient resource acquisition and thus increase the relative competitive ability of host individuals. We addressed this hypothesis by testing the effect of a trematode parasite Diplostomum pseudospathaceum on the competitive ability of its snail host Lymnaea stagnalis. We experimentally examined the growth of snails kept in pairs in relation to their infection status and intensity of resource competition (i.e. food availability). We found that parasitized snails grew faster and their reproduction was reduced compared to unparasitized individuals indicating parasite-induced gigantism. However, growth of the snails was faster when competing with parasitized individuals compared to unparasitized snails indicating reduced competitive ability due to parasitism. The latter effect, however, was relatively weak suggesting that the effects of the parasite on snail physiology may partly override each other in determining competitive ability.

Show MeSH
Related in: MedlinePlus