Sex
Ratio Evolution in Malaria & Other Protozoan Parasites
Hamilton's local
mate competition (LMC) theory provides an explanation for female biased
sex ratios in malaria and other protozoan (apicomplexan) parasites. LMC
theory predicts the proportion of the transmission stages (gametocytes)
that should be female. We have been: (a) developing sex ratio theory
for protozoan parasites; (b) testing comparative predictions for how
sex ratios should vary across species; (c) carrying out experimental
work on malaria parasites species.
Our main findings include:
- The evolutionary stable gametocyte sex ratio of
population (r*; proportion
female) is given by the pleasingly simple equation r*=(1-F)/2, where F is the inbreeding rate. This
equation is extremely robust and general when considering the
population mean sex ratio. Gametocyte sex ratios therefore offer a
cheap and easy way of estimating the inbreeding rate of a population
(Nee et al. 2002 Proc. Roy. Soc.).
- LMC theory can explain broad variation in
gametocyte sex ratios across the apicomplexan parasites (West et al.
2000 Proc. Roy. Soc.; West et
al. 2001 Trends in Parasitology).
- If there is possibility that all female gametes
will not be fertilised then there a less female biased sex ratio can be
favoured as a form of fertility insurance. This can occur for a variety
of
reasons, such as low gametocyte density, low numbers of gametes per
male gametocyte, immune pressure (West et al. 2002 J. of Parasitology; Gardner et al.
2003 J. Theor. Biol.).
Our major future aims are to test whether malaria
parasites adjust the gametocyte sex ratio facultatively in response to
variation in: (a) the inbreeding rate (i.e. number of lineages per
host),
and (b) the need for fertility insurance. This work is being led by Sarah
Reece. It involves collaboration with Andrew Read, Sean Nee, Andy
Gardner
and Todd Smith.
Related Publications
- Reece, S.E, Duncan, A.B., West, S.A. & Read, A.F. (2005) Host cell preference and variable
transmission strategies in malaria parasites. Proceedings of
the Royal Society London Series B 272, 511-517.
- Gardner, A., Reece, S.E. & West, S.A. (2003) Even more extreme fertility
insurance and the sex ratios of protozoan blood parasites. Journal
of Theoretical Biology, 223, 515-521.
- Reece, S.E., Duncan, A.B., West, S.A. & Read, A.F. (2003) Sex ratios in the rodent malaria
parasite, Plasmodium chabaudi. Parasitology, 127,
419-425. {Supplementary
Info}
- Nee, S., West, S.A. & Read, A.F. (2002) Inbreeding and parasite sex ratios. Proceedings
of the Royal Society London Series B.
269, 755-760.
- Read, A.F., Smith, T.G. Nee, S. & West,
S.A. (2002) Sex ratios of malaria parasites and related protozoa, pp
314-332.. In Sex ratios: concepts and research methods (ed. by
I.C.W. Hardy). Cambridge University Press
- West, S.A., Smith, T.G., Nee, S. & Read, A.F. (2002) Fertility insurance and
the sex ratios of malaria and related hemospororin blood parasites.
Journal of Parasitology, 88, 258-263.
- West, S.A., Reece, S.E. & Read, A.F. (2001) The evolution of gametocyte sex
ratios in malaria and related apicomplexan (protozoan) parasites. Trends
in Parasitology, 17, 525-531.
- Pickering, J., Read, A.F., Guerrero, S. & West, S.A. (2000) Sex ratio and virulence in two species of
lizard malaria parasites. Evolutionary Ecology Research, 2,
171-184.
- West, S.A., Herre, E.A. & Sheldon, B.C. (2000) The benefits of allocating
sex. Science, 290, 288-290.
- West, S.A., Smith, T.G. & Read, A.F. (2000) Sex allocation and population
structure in Apicomplexan (protozoa) parasites. Proceedings of
the Royal Society London Series B, 267, 257-264.
- West, S.A., Reece, S.E. & Read, A.F. (2003) Toxoplasma gondii, sex and premature
rejection. Trends in Parasitology, 19, 155-157. {This was a reply to Ferguson 2002}
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