Male gametocyte fecundity and sex ratio of a malaria parasite, Plasmodium mexicanum

Parasitology ◽  
2011 ◽  
Vol 138 (10) ◽  
pp. 1203-1210 ◽  
Author(s):  
A. T. NEAL
Keyword(s):  
Genetic Variation ◽  
Sex Ratio ◽  
Evolutionary Theory ◽  
Malaria Parasite ◽  
Clonal Diversity ◽  
Male Gametes ◽  
A Value ◽  
Parasite Plasmodium ◽  
Sex Ratio Theory ◽  
Few Data

SUMMARYEvolutionary theory predicts that the sex ratio of Plasmodium gametocytes will be determined by the number of gametes produced per male gametocyte (male fecundity), parasite clonal diversity and any factor that reduces male gametes' ability to find and combine with female gametes. Despite the importance of male gametocyte fecundity for sex ratio theory as applied to malaria parasites, few data are available on gamete production by male gametocytes. In this study, exflagellating gametes, a measure of male fecundity, were counted for 866 gametocytes from 26 natural infections of the lizard malaria parasite, Plasmodium mexicanum. The maximum male fecundity observed was 8, but most gametocytes produced 2–3 gametes, a value consistent with the typical sex ratio observed for P. mexicanum. Male gametocytes in infections with higher gametocytaemia had lower fecundity. Male fecundity was not correlated with gametocyte size, but differed among infections, suggesting genetic variation for fecundity. Fecundity and sex ratio were correlated (more female gametocytes with higher fecundity) as predicted by theory. Results agree with evolutionary theory, but also suggest a possible tradeoff between production time and fecundity, which could explain the low fecundity of this species, the variation among infections, and the correlation with gametocytaemia.

Gametocyte sex ratio in single-clone infections of the malaria parasite Plasmodium mexicanum

Parasitology ◽  
2010 ◽  
Vol 137 (13) ◽  
pp. 1851-1859 ◽  
Author(s):  
A.T. NEAL ◽  
J.J. SCHALL
Keyword(s):  
Genetic Variation ◽  
Sex Ratio ◽  
Malaria Parasite ◽  
Sex Ratios ◽  
Experimental Studies ◽  
Life History Trait ◽  
Gametocyte Density ◽  
Male Gametes ◽  
Single Clone ◽  
Sex Ratio Theory

SUMMARYSex ratio theory predicts that malaria parasites should bias gametocyte production toward female cells in single-clone infections because they will experience complete inbreeding of parasite gametes within the vector. A higher proportion of male gametocytes is favoured under conditions that reduce success of male gametes at reaching females such as low gametocyte density or attack of the immune system later in the infection. Recent experimental studies reveal genetic variation for gametocyte sex ratio in single-clone infections. We examined these issues with a study of experimental single-clone infections for the lizard malaria parasite Plasmodium mexicanum in its natural host. Gametocyte sex ratios of replicate single-clone infections were determined over a period of 3–4 months. Sex ratios were generally female biased, but not as strongly as expected under simple sex ratio theory. Gametocyte density was not related to sex ratio, and male gametocytes did not become more common later in infections. The apparent surplus of male gametocytes could be explained if male fecundity is low in this parasite, or if rapid clotting of the lizard blood reduces male gamete mobility. There was also a significant clone effect on sex ratio, suggesting genetic variation for some life-history trait, possibly male fecundity.

Gametocyte sex ratio of a malaria parasite: response to experimental manipulation of parasite clonal diversity

Parasitology ◽  
2004 ◽  
Vol 128 (1) ◽  
pp. 23-29 ◽  
Author(s):  
S. M. OSGOOD ◽  
J. J. SCHALL
Keyword(s):  
Sex Ratio ◽  
Malaria Parasite ◽  
Clonal Diversity ◽  
Experimental Manipulation ◽  
Sceloporus Occidentalis ◽  
Infected Blood ◽  
Single Donor ◽  
Mixed Blood ◽  
Sex Ratio Theory ◽  
Male To Female

Sex ratio theory posits that the adaptive proportion of male to female gametocytes of a malaria parasite within the vertebrate host depends on the degree of inbreeding within the vector. Gametocyte sex ratio could be phenotypically flexible, being altered based on the infection's clonal diversity, and thus likely inbreeding. This idea was tested by manipulating the clonal diversity of infections of Plasmodium mexicanum in its lizard host, Sceloporus occidentalis. Naive lizards were inoculated with infected blood from a single donor or 3 pooled donors. Donors varied in their gametocyte sex ratios (17–46% male), and sex ratio theory allowed estimation of the clonal diversity within donor and recipient infections. Phenotypic plasticity would produce a correlation between donor and recipient infections for infections initiated from a single donor, and a less female-biased gametocyte sex ratio in recipients that received a mixed blood inoculum (with predicted higher clonal diversity) than recipients receiving blood from a single donor. Neither pattern was observed. Gametocyte sex ratio of most infections ranged from 35 to 42% male, expected if clonal diversity was high for all infections. Alternative explanations are suggested for the observed variation of gametocyte sex ratio among P. mexicanum infections.

Using Meta-analysis to Test Ecological and Evolutionary Theory

2013 ◽  
Author(s):  
Michael D. Jennions ◽  
Christopher J. Lortie ◽  
Julia Koricheva
Keyword(s):  
Sexual Selection ◽  
Sex Ratio ◽  
Case Studies ◽  
Evolutionary Theory ◽  
Meta Analysis ◽  
Basic Research ◽  
Fighting Behavior ◽  
Main Research ◽  
Sex Ratio Theory

This chapter describes nine case studies that illustrate how meta-analysis has contributed to theoretical developments in basic research in ecology and evolution. The main research topics cover are maintenance of biodiversity (Case 1); sexual selection (mate choice/fighting behavior) (cases 2, 8, 9); sex ratio theory (Case 3); allometric scaling (Case 4); the invasiveness of exotic plants (Case 5); seed size and plant abundance (Case 6); and the role of competition and predation in structuring communities (Case 7). It is hoped that these case studies will resonate with the reader and provide “templates” for ways to conduct comparable tests on analogous controversies in their own fields of research.

Clonal diversity within infections and the virulence of a malaria parasite,Plasmodium mexicanum

Parasitology ◽  
2008 ◽  
Vol 135 (12) ◽  
pp. 1363-1372 ◽  
Author(s):  
A. M. Vardo-ZALIK ◽  
J. J. Schall
Keyword(s):  
Malaria Parasite ◽  
Blood Clotting ◽  
Haemoglobin Concentration ◽  
Clonal Diversity ◽  
Sceloporus Occidentalis ◽  
Glucose Levels ◽  
Blood Glucose Levels ◽  
Parasite Plasmodium ◽  
Blood Haemoglobin ◽  
The Cost

SUMMARYBoth verbal and mathematical models of parasite virulence predict that genetic diversity of microparasite infections will influence the level of costs suffered by the host. We tested this idea by manipulating the number of co-existing clones ofPlasmodium mexicanumin its natural vertebrate host, the fence lizardSceloporus occidentalis. We established replicate infections ofP.mexicanummade up of 1, 2, 3, or >3 clones (scored using 3 microsatellite loci) to observe the influence of clone number on several measures of parasite virulence. Clonal diversity did not affect body growth or production of immature erythrocytes. Blood haemoglobin concentration was highest for the most genetically complex infections (equal to that of non-infected lizards), and blood glucose levels and rate of blood clotting was highest for the most diverse infections (with greater glucose and more rapid clotting than non-infected animals). Neither specific clones nor parasitaemia were associated with virulence. In this first experiment that manipulated the clonal diversity of a naturalPlasmodium-host system, the cost of infection with 1 or 2 clones ofP.mexicanumwas similar to that previously reported for infected lizards, but the most complex infections had either no cost or could be beneficial for the host.

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