Journal Article An artesunate pharmacometric model to explain therapeutic responses in falciparum malaria—authors' response Get access Sompob Saralamba, Sompob Saralamba Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand https://orcid.org/0000-0002-5460-8447 Search for other works by this author on: Oxford Academic PubMed Google Scholar Julie A Simpson, Julie A Simpson Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria, Australia https://orcid.org/0000-0002-2660-2013 Search for other works by this author on: Oxford Academic PubMed Google Scholar Nicholas J White Nicholas J White Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand Corresponding author. E-mail: nickw@tropmedres.ac https://orcid.org/0000-0002-1897-1978 Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Antimicrobial Chemotherapy, Volume 79, Issue 3, March 2024, Page 692, https://doi.org/10.1093/jac/dkad411 Published: 22 January 2024
Attempts to account for observed variation in the degree of reproductive skew among cooperative breeders have usually assumed that subordinate breeding has fitness costs to dominant females. They argue that dominant females concede reproductive opportunities to subordinates to retain them in the group or to dissuade them from challenging for the dominant position or that subordinate females breed where dominants are incapable of controlling them. However, an alternative possibility is that suppressing subordinate reproduction has substantive costs to the fitness of dominant females and that variation in these costs generates differences in the net benefits of suppression to dominants which are responsible for variation in the frequency of subordinate breeding that is not a consequence of either reproductive concessions or limitations in dominant control. Here, we show that, in wild Kalahari meerkats (Suricata suricatta), the frequency with which dominants evict subordinates or kill their pups varies with the costs and benefits to dominants of suppressing subordinate breeding, including the dominants' reproductive status, the size of their group, and the relatedness of subordinates. We review evidence from other studies that the suppression of reproduction by subordinates varies with the likely costs of subordinate breeding to dominants.
In social mammals, grooming may be used in care of offspring, to maintain pair bonds, or to placate dominant individuals. We examined grooming patterns in groups of the cooperatively breeding meerkat, Suricata suricatta. Dominant females produce over 80% of litters, but older subordinate females occasionally breed. Grooming between dominant individuals was the most common and symmetrical interaction. The dominant female received more and gave less in grooming interactions with subordinates. The dominant female groomed younger subordinates more frequently than older subordinates, suggesting that grooming by dominant females represents parental care, and also reflects the reproductive conflict between females. Older subordinates groomed the dominant female more frequently than did younger subordinates. Subordinates that were frequently attacked by the dominant female groomed her for longer durations than those that were not, and the duration of dominant female grooming by subordinates increased as birth of the dominant female's pups approached. These results support the idea that subordinates use grooming to placate the dominant female. Analysis of ‘immediate reciprocity’ (whether the groomee returned grooming of the groomer within the grooming bout) showed that subordinate females reciprocated more frequently than subordinate males when the dominant female initiated grooming. However, the dominant female reciprocated subordinate females less frequently than she did subordinate males. This suggests that the need to placate the dominant female may be higher for subordinate females than for subordinate males, possibly because of the risk of eviction caused by reproductive conflict between females.
Kin selection theory suggests that altruistic behaviors can increase the fitness of altruists when recipients are genetic relatives. Although selection can favor the ability of organisms to preferentially cooperate with close kin, indiscriminately helping all group mates may yield comparable fitness returns if relatedness within groups is very high. Here, we show that meerkats (Suricata suricatta) are largely indiscriminate altruists who do not alter the amount of help provided to pups or group mates in response to their relatedness to them. We present a model showing that indiscriminate altruism may yield greater fitness payoffs than kin discrimination where most group members are close relatives and errors occur in the estimation of relatedness. The presence of errors in the estimation of relatedness provides a feasible explanation for associations between kin discriminative helping and group relatedness in eusocial and cooperatively breeding animals.
In cerebral malaria, the use of currently recommended doses of intravenous quinine may result in subtherapeutic plasma concentrations during the critical first 24 hours of treatment. A loading dose of quinine (20 mg/kg quinine dihydrochloride, equivalent to 16.7 mg/kg base, infused over 4 hours) proved a rapid and safe method of achieving plasma concentrations above the high minimum inhibitory concentrations for Plasmodium falciparum prevalent in Eastern Thailand.
We have measured the plasma concentrations of sex steroids and sex hormone-binding globulin (SHBG) in twenty-three massively obese women and ten age-matched lean female volunteers. In the obese women increased plasma testosterone (obese 3.2 +/- 0.5 nmol/l controls 1.7 +/- 0.5 nmol/l, P less than 0.3) and androstenedione concentrations (obese 9.7 +/- 1.2 nmol/l, controls 4.4 +/- 0.6 nmol/l, P = less than 0.01) an increased ratio of oestrone:oestradiol (obese 2.4 +/- 0.4, controls 1.0 +/- 0.1, P = less than 0.1) and decreased SHBG levels (obese 30 +/- 4 nmol/l, controls 60 +/- 8 nmol/l, P = less than 0.001) were found. Obesity differed from the polycystic ovary syndrome (in which a similar pattern of changes of sex steroid concentrations and binding are seen) in that it was associated with normal increases in serum luteinizing hormone (LH) follicle stimulating hormone (FSH) levels in response to the administration of LHRH. We conclude that the common occurrence of menstrual abnormalities in obesity results from abnormal secretion and binding of sex steroids. In addition, the unaltered secretion of LH and FSH in the presence of such changes is evidence for a disorder of hypothalamic function.
Throughout the tropical world antimalarial drug resistance is increasing, particularly in the potentially lethal malaria parasite Plasmodium falciparum. In some parts of Southeast Asia, parasites which are resistant to chloroquine, pyrimethamine-sulfadoxine, and mefloquine are prevalent. The characteristics of a drug that make it vulnerable to the development of resistance are a long terminal elimination half-life, a shallow concentration-effect relationship, and that one or two base-pair mutations confer a marked reduction in susceptibility. The development of resistance can be delayed or prevented by drug combinations. The artemisinin derivatives are the most potent of all antimalarial drugs. They reduce the infecting parasite biomass by approximately 10 000-fold per asexual life cycle. There are good arguments for combining, de novo, an artemisinin derivative with all newly introduced antimalarial drugs.
In cooperative animal societies, dominant females typically show higher breeding success than subordinates, and are commonly believed to control the extent of reproductive sharing. However, studies of social insect societies reveal that subordinates too can interfere with the breeding attempts of others, with important implications for the distribution of fitness within colonies. Here, we show that subordinate females in a high-skew vertebrate (the meerkat, Suricata suricatta ), also exert a substantial influence over the reproductive attempts of others. In meerkat societies, pregnant dominants are known to kill subordinate litters, but we show that pregnant subordinates also kill pups; not only those of other subordinates but the dominant's as well. Litters born to females of any rank were half as likely to survive their first 4 days if a subordinate was pregnant. However, dominant females were more likely than subordinates to give birth when no other females were pregnant, and so lost fewer litters to infanticide than subordinates. This is probably due in part to dominants employing counter-tactics to reduce the incidence of subordinate pregnancy. We discuss the broad implications of subordinates having a degree of control over reproductive sharing for future attempts to understand the distribution of reproduction in animal societies.
