REPLICATED ORIGIN OF FEMALE-BIASED ADULT SEX RATIO IN INTRODUCED POPULATIONS OF THE TRINIDADIAN GUPPY (POECILIA RETICULATA)

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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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Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated.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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Is biasing offspring sex ratio adaptive? A test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2018.1251 ◽

2018 ◽

Vol 285 (1891) ◽

pp. 20181251 ◽

Cited By ~ 1

Author(s):

Andrea E. Wishart ◽

Cory T. Williams ◽

Andrew G. McAdam ◽

Stan Boutin ◽

Ben Dantzer ◽

...

Keyword(s):

Sex Ratio ◽

Tamiasciurus Hudsonicus ◽

Red Squirrels ◽

Offspring Sex Ratio ◽

Offspring Sex ◽

Adult Sex Ratio ◽

Secondary Sex Ratio ◽

North American Red Squirrels ◽

Negative Frequency Dependent Selection ◽

Fisher’S Principle

Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1 : 1 owing to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have more grandoffspring. In a wild population of North American red squirrels ( Tamiasciurus hudsonicus ) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1 : 1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, the adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring at their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.

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