The Female to Male Ratio (FMR) in Hookworm

Roche, Marcel; Patrzek, Donald

doi:10.2307/3276401

Cited by 20 publications

(17 citation statements)

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“…Poulin (1997) examined the relation between sex ratio and prevalence or intensity of infection in nematode species. Roche & Patrzec (1966) showed that the intensity of infection and female/male sex ratio were significantly correlated in infrapopulations of Ancylostoma caninum, obtained experimentally. In experimental populations of nematodes, the intensity of infection was negatively correlated with the sex ratio.…”

Section: Discussionmentioning

confidence: 87%

“…Several authors have demonstrated, or at least hypothesized, the existence of a relationship between density-dependent ecological parameters and reproduction aspects, such as sex ratio, genetic exchange and diversity within parasite populations (Roche & Patrzec, 1966;Tingley & Anderson, 1986;Holmes, 1990;May & Woolhouse, 1993;Rohde, 1994;Stien et al, 1996;Poulin, 1997;Combes & Théron, 2000;Dezfuli et al, 2002). The primary sex ratio of nematode populations is usually 1:1, since, except for the oxiurids, the sexual chromosomes act as the genetic mechanism for determining the sex of these helminths (Tingley & Anderson, 1986;Stien et al, 1996).…”

Section: Discussionmentioning

confidence: 99%

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Biased sex ratio and niche restriction in Baruscapillaria obsignata (Madsen 1945) (Nematoda, Capillariidae) from Columba livia (Aves, Columbidae)

et al. 2011

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In the present study populations of the avian nematode species Baruscapillaria obsignata are described from Columba livia. Male and female individuals were obtained from 27 birds, fixed in alcohol/formalin/acetic acid (AFA) and preserved in 70% ethanol. Nematodes were identified and then counted under a stereoscopic microscope. Baruscapillaria obsignata were much more frequent in the anterior third of the small intestine, and females were more abundant than males in all infra populations. The prevalence was 55.6%, mean intensity was 11.8 (median 11.0; range 1-31) and abundance 6.56. In the present study, we observed an aggregated distribution of parasite infrapopulations, as demonstrated by the value of the exponent of the negative binomial distribution, K = 0.2773; by the discrepancy index, D = 0.656 and by the variance/mean ratio, 12.44. The female/male sex ratios found in all infrapopulations were always greater than 1, showing a bias in favour of female abundance. This tendency was especially marked in infrapopulations containing fewer individuals. The sizes of infrapopulations ranged from 5 to 31 individuals. The mean sex ratio observed was 2.69 ± 3.28 (median 1.83; range 0-11). In infrapopulations with 5-15 individuals, the sex ratios observed varied from 2.6 to 11, while in those with 17-31 individuals, the sex ratios were lower, ranging from 1.7 to 2.4. There was a negative correlation between the intensity of infection and the sex ratio of infrapopulations. Results are discussed in terms of possible factors influencing the processes that lead to niche restriction and biased sex ratios in parasite infrapopulations.

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Section: Discussionmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Biased sex ratio and niche restriction in Baruscapillaria obsignata (Madsen 1945) (Nematoda, Capillariidae) from Columba livia (Aves, Columbidae)

et al. 2011

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“…Female-biased sex ratios among adult worms are commonly reported in both nematodes (see Roche and Patrzek 1966;Seidenberg et al 1974;Guyatt and Bundy 1993) and acanthocephalans (Crompton 1985). In both groups (with the exception of the haplodiploid nematode order Oxyurida; Adamson 1989), sex chromosomes act as the genetic mechanism of sex determination.…”

Section: Introductionmentioning

confidence: 99%

Population abundance and sex ratio in dioecious helminth parasites

Poulin

1997

Oecologia

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Parasite populations are highly fragmented in space and time, and consist of aggregates of genetically similar individuals sharing the same host. To avoid inbreeding, theory predicts that female-biased sex ratios should be strongly favoured when either or both prevalence and intensity of infection are low. Other models indicate that if sex ratios are selected to increase the probability of mating, they should be less biased at a high intensity of infection in polygamous parasites, since at high intensities all females are mated. To test these predictions, the relationship between sex ratio and both the prevalence and intensity of infection was examined in comparative studies across 193 populations of nematode and acanthocephalan parasites. Sex ratios in these two dioecious, polygamous taxa are usually female biased. Among natural populations, no significant relationship was observed once the confounding effects of phylogeny had been removed. However, among experimental populations of nematodes, a negative relationship was found between intensity of infection and sex ratio, even after controlling for phylogeny. In other words, at high intensities, populations of nematodes are less female biased. This result must be treated with caution because of the unusually high numbers of worms per host in experimental infections. Nevertheless, combined with information on the proximate mechanisms regulating sex ratios in these parasites, it suggests a link between the characteristics of parasite populations and their sex ratio.

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“…The primary sex ratio of animals is expected to be balanced (Fisher, 1930) but later events such as differential survival and infection rates may result in biased sex ratios of parasites within hosts. Early mortality of males contributes to the female-biased sex ratio seen in many helminth parasites of vertebrates (Roche and Patrzek, 1966;Stien et al, 2005) while differential invasion rates of cercariae destined to be male or female contributes to the male-biased sex ratio of schistosomes (Boissier and Mone, 2000). Different behaviour of male and female infective stages has received little attention in parasitic nematodes, apart from the entomopathogenic nematodes Steinernema spp.…”

Section: Introductionmentioning

confidence: 99%

Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema

Alsaiyah

Ebssa

Zenner

et al. 2009

International Journal for Parasitology

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a b s t r a c tIn experimentally infected insects, the sex ratio of first generation nematodes of five species of Steinernema was female-biased (male proportion 0.35-0.47). There was a similar female bias when the worms developed in vitro (0.37-0.44), indicating that the bias in these species is not due to a lower rate of infection by male infective juveniles (IJs). Experimental conditions influenced the proportion of males establishing in insects, indicating that male and female IJs differ in their behaviour. However, there was no evidence that males are the colonising sex in any species, contrary to what has previously been proposed. Time of emergence from the host in which the nematodes had developed influenced sex ratios in experimental infections. In three species (Steinernema longicaudum, Steinernema glaseri and Steinernema kraussei), early emerged nematodes had a higher proportion of males than those that emerged later, with the reverse trend for Steinernema carpocapsae and Steinernema feltiae. In a more detailed in vitro study of S. longicaudum, the proportion of males was similar whether or not the nematodes passed through the developmentally arrested IJ stage, indicating that the female bias is not due to failure of males to exit this stage. The sex ratio in vitro was independent of survival rate from juvenile to adult, and was female-biased even when all juveniles developed, indicating that the bias is not explained by failure of males to develop to adults. The female-biased sex ratio characteristic of Steinernema populations appears to be present from at least the early juvenile stage. We hypothesise that the observed female bias is the population optimal sex ratio, a response to cycles of local mate competition experienced by nematodes reproducing within insect hosts interspersed with periods of outbreeding with less closely related worms following dispersal. Ó

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The Female to Male Ratio (FMR) in Hookworm

Cited by 20 publications

References 12 publications

Biased sex ratio and niche restriction in Baruscapillaria obsignata (Madsen 1945) (Nematoda, Capillariidae) from Columba livia (Aves, Columbidae)

Biased sex ratio and niche restriction in Baruscapillaria obsignata (Madsen 1945) (Nematoda, Capillariidae) from Columba livia (Aves, Columbidae)

Population abundance and sex ratio in dioecious helminth parasites

Sex ratios and sex-biased infection behaviour in the entomopathogenic nematode genus Steinernema

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