Ontogenic Sex Ratio Variation in Nazca Boobies Ends in Male-Biased Adult Sex Ratio

Estimates of the intensity and abundance of species provide essential data for ecological, evolutionary and epidemiological studies of gastrointestinal nematode communities. These estimates are typically derived from the species composition of adult males when only males have readily scorable species-specific morphological traits. Such estimation assumes that all species in the community have the same adult sex ratio. We evaluated this assumption for the trichostrongyle nematodes Ostertagia gruehneri and Marshallagia marshalli in infracommunities in Svalbard reindeer by identifying to species adult females using a polymerase chain reaction assay. The proportion of males was found to be slightly higher in O. gruehneri than in M. marshalli. Evidence for seasonal variation and density dependence in the adult sex ratio was only found for O. gruehneri. Possible demographic mechanisms for such sex ratio variation are discussed, and stochastic models that generate density-dependent sex ratios proposed. Sex ratio variation caused substantial bias in some male-based estimates of intensity of infection, while substantial and consistent bias in estimates of abundances was only evident in late winter samples. Our results suggest that estimating sex ratios can be particularly important in individual host level studies of nematode species of low abundance.

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Demographic causes of adult sex ratio variation and their consequences for parental cooperation

Nature Communications ◽

10.1038/s41467-018-03833-5 ◽

2018 ◽

Vol 9 (1) ◽

Cited By ~ 21

Author(s):

Luke J. Eberhart-Phillips ◽

Clemens Küpper ◽

María Cristina Carmona-Isunza ◽

Orsolya Vincze ◽

Sama Zefania ◽

...

Keyword(s):

Sex Ratio ◽

Ratio Variation ◽

Adult Sex Ratio

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Sex ratio variation as a function of host size inPseudacteonflies (Diptera: Phoridae), parasitoids ofSolenopsisfire ants (Hymenoptera: Formicidae)

Biological Journal of the Linnean Society ◽

10.1006/bijl.1998.0265 ◽

1999 ◽

Vol 66 (2) ◽

pp. 257-267 ◽

Cited By ~ 3

Author(s):

L MORRISON

Keyword(s):

Sex Ratio ◽

Host Size ◽

Ratio Variation

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Effects of phytoseiid predators on the sex ratio of the spider mite Panonychus ulmi

Canadian Journal of Zoology ◽

10.1139/z91-031 ◽

1991 ◽

Vol 69 (1) ◽

pp. 208-212 ◽

Cited By ~ 3

Author(s):

Dan L. Johnson ◽

Heather C. Proctor

Keyword(s):

Population Density ◽

Sex Ratio ◽

Spider Mite ◽

Total Population ◽

Panonychus Ulmi ◽

Encounter Rate ◽

Male Mortality ◽

Adult Sex Ratio ◽

Biased Sex Ratio ◽

Male Activity

The effect of predator presence on the adult sex ratio of a spider mite (Panonychus ulmi) was examined in a field experiment. Phytoseiid predators (chiefly Typhlodromus occidentalis) were removed from 32 trees harboring P. ulmi populations, and allowed to remain at natural levels on 32 other trees. Both total population density and proportion of males in the prey population were significantly higher in predator-free trees. Mechanisms that could explain the increase in the proportion of males are examined. The most probable is that greater male activity results in a higher encounter rate between predator and prey, and that subsequent higher male mortality when predators are present exaggerates the female-biased sex ratio. The theoretical effects of sex-biased predation on diplo-diploid and haplo-diploid organisms are discussed.

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Population sex ratio variation in a monogamous long-lived bird, the wandering albatross

Journal of Animal Ecology ◽

10.1111/j.1365-2656.2005.00922.x ◽

2005 ◽

Vol 74 (2) ◽

pp. 285-291 ◽

Cited By ~ 81

Author(s):

HENRI WEIMERSKIRCH ◽

JOELLE LALLEMAND ◽

JULIEN MARTIN

Keyword(s):

Sex Ratio ◽

Ratio Variation ◽

Wandering Albatross

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Sex ratio effects on reproductive strategies in humans

Royal Society Open Science ◽

10.1098/rsos.140402 ◽

2015 ◽

Vol 2 (1) ◽

pp. 140402 ◽

Cited By ~ 53

Author(s):

Ryan Schacht ◽

Monique Borgerhoff Mulder

Keyword(s):

Sexual Selection ◽

Sex Ratio ◽

Ethnic Group ◽

Reproductive Strategies ◽

Situational Factors ◽

Male Mating ◽

Mating Effort ◽

Short Term ◽

Adult Sex Ratio ◽

Using Data

Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.

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