Female-biased sex ratio, polygyny, and persistence in the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus)

AbstractUsing molecular-genetic techniques, we determined the gender of 202 Southwestern Willow Flycatcher (Empidonax traillii extimus) nestlings from 95 nests sampled over a five-year period. Overall nestling sex ratio did not vary significantly from 50:50 among years, by clutch order, or by mating strategy (monogamous vs. polygamous pairings). However, we did observe significant differences among the four sites sampled, with sex ratios biased either toward males or females at the different sites. Given the small population sizes and geographic isolation of many of the endangered subspecies' breeding populations, sex-ratio differences may have localized negative impacts.Cociente de Sexos en Polluelos de Empidonax traillii extimusResumen. Utilizando técnicas moleculares determinamos el sexo de 202 polluelos de Empidonax traillii extimus pertenecientes a 95 nidos que fueron muestreados durante un período de cinco años. En general, el cociente de sexos no varió significativamente de 50:50 entre años, ya sea por orden de la nidada o por estrategia de apareamiento (monogamia vs. poligamia). Sin embargo, observamos diferencias significativas entre los cuatro sitios muestreados, en los cuales la razón de sexos estuvo sesgada hacia los machos o las hembras dependiendo del sitio. Dados los pequeños tamaños poblacionales y el aislamiento geográfico de muchas de las poblaciones reproductivas de esta subespecie en peligro, las diferencias en el cociente de sexos pueden tener un impacto negativo a nivel local.

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Willow Flycatcher (Empidonax traillii)

10.2173/bna.wilfly.02 ◽

2000 ◽

Author(s):

James A. Sedgwick

Keyword(s):

Willow Flycatcher ◽

Empidonax Traillii

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Willow Flycatcher (Empidonax traillii)

10.2173/bow.wilfly.01 ◽

2020 ◽

Author(s):

James A. Sedgwick

Keyword(s):

Willow Flycatcher ◽

Empidonax Traillii

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No room for males in caves: Female‐biased sex ratio in subterranean amphipods of the genus Niphargus

Journal of Evolutionary Biology ◽

10.1111/jeb.13917 ◽

2021 ◽

Author(s):

Ester Premate ◽

Špela Borko ◽

Simona Kralj‐Fišer ◽

Michael Jennions ◽

Žiga Fišer ◽

...

Keyword(s):

Sex Ratio ◽

Biased Sex Ratio

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Male-biased sex ratio in Argulus canadensis Wilson, 1916 (Crustacea: Branchiura) ectoparasitic on sticklebacks

Canadian Journal of Zoology ◽

10.1139/z89-296 ◽

1989 ◽

Vol 67 (8) ◽

pp. 2078-2080 ◽

Cited By ~ 3

Author(s):

Robert Poulin ◽

Gerard J. FitzGerald

Keyword(s):

Salt Marsh ◽

Sex Ratio ◽

Laboratory Experiments ◽

Fish Predation ◽

Reproductive Behaviour ◽

Egg Deposition ◽

Alternative Hypotheses ◽

Biased Sex Ratio ◽

The Difference ◽

Fish Hosts

Females of the ectoparasitic crustacean Argulus canadensis must leave their fish hosts at least temporarily to deposit their eggs on the substrate. To test the hypothesis that this difference in reproductive behaviour between the two sexes could result in male-biased sex ratios on their stickleback hosts, we sampled sticklebacks in tide pools of a Quebec salt marsh from early July to early September 1986. During this period, fish harboured significantly more male than female A. canadensis. Laboratory experiments were done to test two alternative hypotheses offered to explain this biased sex ratio. The first hypothesis was that male A. canadensis were more successful than females in attacking their stickleback hosts; however, we found no differences in attack success on their hosts between the two parasite sexes. The second hypothesis was that sticklebacks ate more female than male A. canadensis. Although males were less vulnerable to fish predation than females, the difference was not significant. We conclude that sexual differences in reproductive behaviour, i.e., egg deposition behaviour of females, can account for the male-biased sex ratio of A. canadensis on sticklebacks.

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Female-Biased Sex Ratio at Hatching in the Green Woodhoopoe

The Auk ◽

10.2307/4088009 ◽

1990 ◽

Vol 107 (4) ◽

pp. 765-771 ◽

Cited By ~ 35

Author(s):

J. David Ligon ◽

Sandra H. Ligon

Keyword(s):

Sex Ratio ◽

Biased Sex Ratio

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Variably male-biased sex ratio in a marine bird with females larger than males

Oecologia ◽

10.1007/s004420050698 ◽

1999 ◽

Vol 118 (1) ◽

pp. 16-22 ◽

Cited By ~ 54

Author(s):

Roxana Torres ◽

Hugh Drummond

Keyword(s):

Sex Ratio ◽

Marine Bird ◽

Biased Sex Ratio

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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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Polygyny and Extra-Pair Paternity in a Population of Southwestern Willow Flycatchers

The Condor ◽

10.1093/condor/108.3.571 ◽

2006 ◽

Vol 108 (3) ◽

pp. 571-578

Author(s):

Talima Pearson ◽

Mary J. Whitfield ◽

Tad C. Theimer ◽

Paul Keim

Keyword(s):

Reproductive Success ◽

Microsatellite Markers ◽

Mating Strategy ◽

Male Reproductive Success ◽

Offspring Survival ◽

Extra Pair Paternity ◽

Study Population ◽

Willow Flycatcher ◽

Empidonax Traillii ◽

Disproportionate Number

Abstract Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extra-pair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 ± 0.35 offspring per season, compared to 1.15 ± 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extra-pair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.

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