Sex ratio adjustment and kin discrimination in malaria parasites

• Published in: Nature 2008-05, Vol.453 (7195), p.609-614
• Main Authors: Reece, Sarah E., Drew, Damien R., Gardner, Andy
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Apoptosis; Biological and medical sciences; Biological Evolution; Conspecifics; Cues; Demecology; Evolutionary biology; Female; Females; Fertility - genetics; Fertility - physiology; Fundamental and applied biological sciences. Psychology; Genetic aspects; Genetic diversity; Genetic engineering; Genetic Variation; Genotype; Health aspects; Humanities and Social Sciences; Humans; Immunization; Infectious diseases; Life cycle. Host-agent relationship. Pathogenesis; Livestock; Malaria; Malaria - parasitology; Male; Models, Biological; multidisciplinary; Parasites; Plant reproduction; Plasmodium chabaudi; Plasmodium chabaudi - genetics; Plasmodium chabaudi - physiology; Protozoa; Protozoa. Invertebrata; Science; Science (multidisciplinary); Sex Ratio; Tropical diseases; Vector-borne diseases; Wildlife
• ISSN: 0028-0836; 1476-4687; 1476-4679
• DOI: 10.1038/nature06954

Malaria parasites and related Apicomplexans are the causative agents of the some of the most serious infectious diseases of humans, companion animals, livestock and wildlife. These parasites must undergo sexual reproduction to transmit from vertebrate hosts to vectors, and their sex ratios are consistently female-biased. Sex allocation theory, a cornerstone of evolutionary biology, is remarkably successful at explaining female-biased sex ratios in multicellular taxa, but has proved controversial when applied to malaria parasites. Here we show that, as predicted by theory, sex ratio is an important fitness-determining trait and Plasmodium chabaudi parasites adjust their sex allocation in response to the presence of unrelated conspecifics. This suggests that P. chabaudi parasites use kin discrimination to evaluate the genetic diversity of their infections, and they adjust their behaviour in response to environmental cues. Malaria parasites provide a novel way to test evolutionary theory, and support the generality and power of a darwinian approach. Sex and the malaria parasite Malaria parasites need to reproduce sexually before they can transmit to vectors, but despite extensive research on ways of blocking transmission, little is known about their reproductive strategies. Reece et al . use novel experiments to show that the assumptions of sex-allocation theory, previously controversial when used to explain sex ratios in malaria parasites, are in fact valid. As predicted by this plank of evolutionary theory, Plasmodium chabaudi parasites adjust their sex-allocation in response to the presence of unrelated conspecifics. By means of this kin discrimination they evaluate the genetic diversity of their infections, and adjust their behaviour in response to environmental cues. Malaria parasites must reproduce sexually to transmit to vectors, but very little is understood about their reproductive strategies. This paper details that malaria parasites adjust their sex ratios in response to unrelated conspecifics, as predicted by evolutionary theory.