EVALUATING THE COSTS OF MOSQUITO RESISTANCE TO MALARIA PARASITES
Open Access
- 1 December 2005
- Vol. 59 (12), 2560-2572
- https://doi.org/10.1111/j.0014-3820.2005.tb00969.x
Abstract
Costly resistance mechanisms have been cited as an explanation for the widespread occurrence of parasitic infections, yet few studies have examined these costs in detail. A malaria‐mosquito model has been used to test this concept by making a comparison of the fitness of highly susceptible lines of mosquitoes with lines that are resistant to infection. Malaria infection is known to cause a decrease in fecundity and fertility of mosquitoes; were thus predicted to be fitter than susceptible ones. >o?Anopheles gambiae were selected for refractoriness/resistance or for increased susceptibility to infection by Plasmodium yoelii nigeriensis. Additional lines that acted as controls for inbreeding depression were raised in parallel but not exposed to selection pressure. Selections were made in triplicate so that founder effects could be detected. Resistance mechanisms that were selected included melanotic encapsulation of parasites within 24 h postinfection and the complete disappearance of parasites from the gut. Costs of immune surveillance were assessed after an uninfected feed, and costs of immune deployment were assessed after exposure to infection and to infection and additional stresses. Mosquito survivorship was unaffected by either resistance to infection or by an increased burden of infection when compared with low levels of infection. In most cases reproductive fitness was equally affected by refractoriness or by infection. Resistant mosquitoes did not gain a fitness advantage by eliminating the parasites. Costs were consistently associated with larval production and egg hatch rate but rarely attributed to changes in blood feeding and never to changes in mosquito size. No advantages appeared to be gained by the offspring of resistant mosquitoes. Furthermore, we were unable to select for refractoriness in groups of mosquitoes in which 100% or 50% of the population were exposed to infection every generation for 22 generations. Under these selection pressures, no population had become completely refractory and only one became more resistant. Variations in fitness relative to control lines in different groups were attributed to founder effects. Our conclusion from these findings is that refractoriness to malaria is as costly as tolerance of infection.Keywords
This publication has 56 references indexed in Scilit:
- Mosquito–malaria interactions: a reappraisal of the concepts of susceptibility and refractorinessInsect Biochemistry and Molecular Biology, 2004
- Physiology of Immunity in the Water Flea Daphnia magna: Environmental and Genetic Aspects of Phenoloxidase ActivityPhysiological and Biochemical Zoology, 2003
- The costs of mounting an immune response are reflected in the reproductive fitness of the mosquito Anopheles gambiaeOikos, 2002
- Three Mechanisms of Host Resistance to Microparasites—Avoidance, Recovery and Tolerance—Show Different Evolutionary DynamicsJournal of Theoretical Biology, 1999
- The effects of infection withPlasmodium yoelii nigeriensison the reproductive fitness of the mosquitoAnopheles gambiaeInvertebrate Reproduction & Development, 1999
- Decreased immune response as a proximate cost of copulation and oviposition in a damselflyPhysiological Entomology, 1998
- The effect of Plasmodium yoelii nigeriensis infection on ovarian protein accumulation by Anopheles stephensiZeitschrift für Parasitenkunde, 1997
- Estimation of the infectious reservoir of Plasmodium falciparum in natural vector populations based on oocyst sizeTransactions of the Royal Society of Tropical Medicine and Hygiene, 1996
- Ecological immunology: costly parasite defences and trade-offs in evolutionary ecologyTrends in Ecology & Evolution, 1996
- Interactions between bloodfeeding, fecundity and infection in mosquitoesParasitology Today, 1995