The immunocompetence handicap hypothesis posits that androgens in males can be a ‘double-edged sword’, actively promoting reproductive success, while also negatively impacting health. Because there can be both substantial androgen concentrations in females and significant androgenic variation among them, particularly in species portraying female social dominance over males or intense female–female competition, androgens might also play a role in mediating female health and fitness. We examined this hypothesis in the meerkat ( Suricata suricatta ), a cooperatively breeding, social carnivoran characterized by aggressively mediated female social dominance and extreme rank-related reproductive skew. Dominant females also have greater androgen concentrations and harbour greater parasite loads than their subordinate counterparts, but the relationship between concurrent androgen concentrations and parasite burdens is unknown. We found that a female's faecal androgen concentrations reliably predicted her concurrent state of endoparasitism irrespective of her social status: parasite species richness and infection by Spirurida nematodes, Oxynema suricattae , Pseudandrya suricattae and coccidia were greater with greater androgen concentrations. Based on gastrointestinal parasite burdens, females appear to experience the same trade-off in the costs and benefits of raised androgens as do the males of many species. This trade-off presumably represents a health cost of sexual selection operating in females.
Studies of mate choice in vertebrates have focused principally on birds, in which male ornaments are often highly developed, and have shown that females commonly select mates on the basis of particular phenotypic characteristics that may reflect their genetic quality. Studies of female mate choice in mammals are less highly developed, and they have commonly focused on female mating preferences that are likely to be maintained by benefits to the female's own survival or breeding success. However, recent experimental studies of mate choice in mammals—especially rodents—provide increasing evidence of consistent female preferences that appear likely to generate benefits to the fitness of offspring. As yet, there is no compelling evidence that female mating preferences are less highly developed in female mammals than in female birds, although these preferences may more often be masked by the effects of male competition or of attempts by males to constrain female choice.
48 patients over 6 years of age with strictly defined cerebral malaria were randomised to receive either a single intramuscular injection of phenobarbitone (3·5 mg/kg) or placebo in a double-blind, placebo-controlled study. Phenobarbitone significantly reduced the incidence of subsequent convulsions from 54% to 12·5%, without adverse effects. A single intramuscular injection of phenobarbitone is a simple, cheap, and effective method for prevention of convulsions in cerebral malaria.
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Methaemoglobin results from the oxidation of ferrous to ferric iron in the centre of the haem moiety of haemoglobin. The production of dose-dependent methaemoglobinaemia by 8-aminoquinoline antimalarial drugs appears to be associated with, but is not directly linked to, therapeutic efficacy against latent Plasmodium vivax and Plasmodium ovale malarias (radical cure). Iatrogenic methaemoglobinaemia may be a useful pharmacodynamic measure in 8-aminoquinoline drug and dose optimization.
Where a maternal trait influences the fitness of sons or daughters, mothers would be expected to bias the sex ratio towards the sex whose fitness they are more able to increment. In many polygynous species, maternal characteristics affect the fitness of sons more than that of daughters, but, in meerkats, variance in female reproductive success exceeds variance in male reproductive success and maternal rank affects the success of daughters more than sons. Dominant females would therefore be expected to produce an excess of daughters, a reversal of the hypothesis' usual predictions. In a long-term data set, despite a strong effect of maternal rank on daughters' success, we found no indication that dominant females produce female-biased litters. Offspring sex ratios did not deviate significantly from equality, and were also unaffected by maternal mass, age or number of previous litters produced in the same season. We suggest that potential advantages to both mother and offspring of producing and developing in mixed litters may result in the adaptive maintenance of an equal offspring sex ratio.
