Limits...
Starvation reveals the cause of infection-induced castration and gigantism.

Cressler CE, Nelson WA, Day T, McCauley E - Proc. Biol. Sci. (2014)

Bottom Line: Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them.Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration.These results are consistent with an energetic structure where the parasite uses growth energy as a resource.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada cressler@queensu.ca.

ABSTRACT
Parasites often induce life-history changes in their hosts. In many cases, these infection-induced life-history changes are driven by changes in the pattern of energy allocation and utilization within the host. Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them. Determining the causes and consequences of infection-induced life-history changes requires the ability to experimentally manipulate life history and a framework for connecting life history to host and parasite fitness. Here, we combine a novel starvation manipulation with energy budget models to provide new insights into castration and gigantism in the Daphnia magna-Pasteuria ramosa host-parasite system. Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration. These results are consistent with an energetic structure where the parasite uses growth energy as a resource. This finding gives us new understanding of the role of castration and gigantism in this system, and how life-history variation will affect infection outcome and epidemiological dynamics. The approach of combining targeted life-history manipulations with energy budget models can be adapted to understand life-history changes in other disease systems.

Show MeSH

Related in: MedlinePlus

Observed host and parasite responses to changing energy to host reproduction. (a) Host size increases with increased energy to host reproduction. Points show the observed weight at death, with grey lines showing the expectation based on GAMM fits (figure 2a). (b) Age at castration shows no response to changes in energy to host reproduction. In (a,b), symbol area denotes number of individuals with observed weight or age at castration. (c) Parasite spore load increases with increased energy to host reproduction. Observations of parasite fitness were made at death of the animal. Because the treatments had an influence on survivorship, we corrected parasite fitness for differences in survivorship by scaling each individual to a common age of 42 days using the treatment-specific spore by age-at-death relationships shown in figure 3a. The label Td denotes the feeding interval in days (d) used to manipulate host reproduction. Grey lines show the trends with statistical support across treatment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4150321&req=5

RSPB20141087F5: Observed host and parasite responses to changing energy to host reproduction. (a) Host size increases with increased energy to host reproduction. Points show the observed weight at death, with grey lines showing the expectation based on GAMM fits (figure 2a). (b) Age at castration shows no response to changes in energy to host reproduction. In (a,b), symbol area denotes number of individuals with observed weight or age at castration. (c) Parasite spore load increases with increased energy to host reproduction. Observations of parasite fitness were made at death of the animal. Because the treatments had an influence on survivorship, we corrected parasite fitness for differences in survivorship by scaling each individual to a common age of 42 days using the treatment-specific spore by age-at-death relationships shown in figure 3a. The label Td denotes the feeding interval in days (d) used to manipulate host reproduction. Grey lines show the trends with statistical support across treatment.

Mentions: We can relate our results back to the predictions made by the energy budget models. Host size increased with increasing energy to reproduction (figure 5a). Age at castration was unaffected by treatment (figure 5b; ANOVA, F = 1.14, d.f. = 5.32, p = 0.36), despite the fact that the treatments caused an observable change in pre-castration fecundity (electronic supplementary material, figure S3). Parasite fitness increased with increasing energy to reproduction (figure 5c; ANOVA, F = 18.0, d.f. = 5.32, p = 1.38 × 10−8).Figure 5.


Starvation reveals the cause of infection-induced castration and gigantism.

Cressler CE, Nelson WA, Day T, McCauley E - Proc. Biol. Sci. (2014)

Observed host and parasite responses to changing energy to host reproduction. (a) Host size increases with increased energy to host reproduction. Points show the observed weight at death, with grey lines showing the expectation based on GAMM fits (figure 2a). (b) Age at castration shows no response to changes in energy to host reproduction. In (a,b), symbol area denotes number of individuals with observed weight or age at castration. (c) Parasite spore load increases with increased energy to host reproduction. Observations of parasite fitness were made at death of the animal. Because the treatments had an influence on survivorship, we corrected parasite fitness for differences in survivorship by scaling each individual to a common age of 42 days using the treatment-specific spore by age-at-death relationships shown in figure 3a. The label Td denotes the feeding interval in days (d) used to manipulate host reproduction. Grey lines show the trends with statistical support across treatment.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150321&req=5

RSPB20141087F5: Observed host and parasite responses to changing energy to host reproduction. (a) Host size increases with increased energy to host reproduction. Points show the observed weight at death, with grey lines showing the expectation based on GAMM fits (figure 2a). (b) Age at castration shows no response to changes in energy to host reproduction. In (a,b), symbol area denotes number of individuals with observed weight or age at castration. (c) Parasite spore load increases with increased energy to host reproduction. Observations of parasite fitness were made at death of the animal. Because the treatments had an influence on survivorship, we corrected parasite fitness for differences in survivorship by scaling each individual to a common age of 42 days using the treatment-specific spore by age-at-death relationships shown in figure 3a. The label Td denotes the feeding interval in days (d) used to manipulate host reproduction. Grey lines show the trends with statistical support across treatment.
Mentions: We can relate our results back to the predictions made by the energy budget models. Host size increased with increasing energy to reproduction (figure 5a). Age at castration was unaffected by treatment (figure 5b; ANOVA, F = 1.14, d.f. = 5.32, p = 0.36), despite the fact that the treatments caused an observable change in pre-castration fecundity (electronic supplementary material, figure S3). Parasite fitness increased with increasing energy to reproduction (figure 5c; ANOVA, F = 18.0, d.f. = 5.32, p = 1.38 × 10−8).Figure 5.

Bottom Line: Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them.Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration.These results are consistent with an energetic structure where the parasite uses growth energy as a resource.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada cressler@queensu.ca.

ABSTRACT
Parasites often induce life-history changes in their hosts. In many cases, these infection-induced life-history changes are driven by changes in the pattern of energy allocation and utilization within the host. Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them. Determining the causes and consequences of infection-induced life-history changes requires the ability to experimentally manipulate life history and a framework for connecting life history to host and parasite fitness. Here, we combine a novel starvation manipulation with energy budget models to provide new insights into castration and gigantism in the Daphnia magna-Pasteuria ramosa host-parasite system. Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration. These results are consistent with an energetic structure where the parasite uses growth energy as a resource. This finding gives us new understanding of the role of castration and gigantism in this system, and how life-history variation will affect infection outcome and epidemiological dynamics. The approach of combining targeted life-history manipulations with energy budget models can be adapted to understand life-history changes in other disease systems.

Show MeSH
Related in: MedlinePlus