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Life-cycle complexity in helminths: What are the benefits?
Daniel P Benesh1,2, Geoff Parker3, James C Chubb3
1Molecular Parasitology, Humboldt University, Berlin, Germany.
Evolution; International Journal of Organic Evolution
|June 29, 2021
Summary
Complex helminth life cycles benefit parasitic worms by using small intermediate hosts for transmission and large, endothermic final hosts for growth and reproduction. This strategy maximizes parasite survival and fecundity across multiple hosts.
Area of Science:
- Parasitology
- Evolutionary Biology
- Ecology
Background:
- Parasitic worms (helminths) often have complex life cycles involving multiple hosts.
- Each transmission step presents a risk of parasite death before reproduction.
Purpose of the Study:
- To investigate the benefits of complex helminth life cycles.
- To determine if early hosts facilitate transmission and late hosts enhance growth and fecundity.
Main Methods:
- Analysis of a dataset comprising 973 species of trophically transmitted helminths (acanthocephalans, cestodes, nematodes).
- Examination of host size, predator-prey mass ratios, and parasite growth and maturation in relation to life cycle length.
Main Results:
- Helminths with longer life cycles infected smaller first hosts and slightly larger final hosts.
- Parasites exploited trophic links with lower predator-prey mass ratios.
- Parasite growth and fecundity were highest in larger, endothermic definitive hosts, achieved through later maturation.
Conclusions:
- Complex helminth life cycles are advantageous because the optimal hosts for transmission (small) differ from those for growth and reproduction (large, endothermic).
- This strategy balances the risks of transmission with the potential for high reproductive output.
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