Fledgling sex-ratio is biased towards the helping sex in a Neotropical cooperative breeder, the brown-and-yellow marshbird (Pseudoleistes virescens)
In: BehaviourDepartamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
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Abstract
In many cooperatively breeding species, helpers increase the breeding success of their parents. The repayment hypothesis predicts a skewed sex-ratio towards the helping sex at population level; at individual level bias would increase in broods attended by a smaller number of helpers. We studied a brown-and-yellow marshbird (Pseudoleistes virescens) population during 11 breeding seasons. We found that 90% of helpers were males and that they increased nestling survival, although this effect disappeared in presence of parasitic shiny cowbirds. Helpers sometimes helped at nests of adults other than their parents. Population sex-ratio of fledglings was highly skewed towards males (1.4:1). At individual level, male-biased sex-ratio of fledglings was more pronounced early in the season and increased with brood losses but was not affected by number of helpers. Marshbirds feed at communal areas so retaining helpers would not be costly. Therefore, a general skew towards males might be the best adaptive strategy.
Resumen
En numerosas especies con cría cooperativa, los ayudantes aumentan el éxito reproductivo de sus padres. La hipótesis del reembolso predice una relación de sexos sesgada hacia el sexo que ayuda a nivel poblacional; a nivel individual, el sesgo sería más pronunciado en aquellas nidadas atendidas por menos ayudantes. Estudiamos una población de Pseudoleistes virescens durante 11 temporadas reproductivas. Encontramos que el 90% de los ayudantes eran machos y que aumentaron la supervivencia de los pichones en ausencia de parásitos de cría Molothrus bonariensis en el nido. Los ayudantes a veces ayudaron en nidos de adultos que no eran sus padres. La relación de sexos en la población de volantones estuvo fuertemente sesgada hacia machos (1.4:1). A nivel individual, la relación de sexos de los volantones estuvo más sesgada hacia machos al inicio de la temporada reproductiva y aumentó con las pérdidas dentro de la nidada, pero no varió con el número de ayudantes. Los P. virescens se alimentan en áreas comunales, por lo que retener ayudantes no sería costoso. Consecuentemente, generalizar en el sesgo hacia machos podría ser la mejor estrategia adaptativa.
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Fledgling sex-ratio is biased towards the helping sex in a Neotropical cooperative breeder, the brown-and-yellow marshbird (Pseudoleistes virescens)
In: BehaviourDepartamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
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, Current address: Instituto de Fisiología, Biología Molecular y Neurociencias (UBA-CONICET), Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
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, Current address: Departamento de Conservación e Investigación, Fundación Temaikèn — B1625 Escobar, Prov. de Buenos Aires, Argentina
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Departamento de Ecología, Genética, y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Intendente Güiraldes 2160 — C1428EGA Ciudad Universitaria, CABA, Argentina
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Abstract
In many cooperatively breeding species, helpers increase the breeding success of their parents. The repayment hypothesis predicts a skewed sex-ratio towards the helping sex at population level; at individual level bias would increase in broods attended by a smaller number of helpers. We studied a brown-and-yellow marshbird (Pseudoleistes virescens) population during 11 breeding seasons. We found that 90% of helpers were males and that they increased nestling survival, although this effect disappeared in presence of parasitic shiny cowbirds. Helpers sometimes helped at nests of adults other than their parents. Population sex-ratio of fledglings was highly skewed towards males (1.4:1). At individual level, male-biased sex-ratio of fledglings was more pronounced early in the season and increased with brood losses but was not affected by number of helpers. Marshbirds feed at communal areas so retaining helpers would not be costly. Therefore, a general skew towards males might be the best adaptive strategy.
Resumen
En numerosas especies con cría cooperativa, los ayudantes aumentan el éxito reproductivo de sus padres. La hipótesis del reembolso predice una relación de sexos sesgada hacia el sexo que ayuda a nivel poblacional; a nivel individual, el sesgo sería más pronunciado en aquellas nidadas atendidas por menos ayudantes. Estudiamos una población de Pseudoleistes virescens durante 11 temporadas reproductivas. Encontramos que el 90% de los ayudantes eran machos y que aumentaron la supervivencia de los pichones en ausencia de parásitos de cría Molothrus bonariensis en el nido. Los ayudantes a veces ayudaron en nidos de adultos que no eran sus padres. La relación de sexos en la población de volantones estuvo fuertemente sesgada hacia machos (1.4:1). A nivel individual, la relación de sexos de los volantones estuvo más sesgada hacia machos al inicio de la temporada reproductiva y aumentó con las pérdidas dentro de la nidada, pero no varió con el número de ayudantes. Los P. virescens se alimentan en áreas comunales, por lo que retener ayudantes no sería costoso. Consecuentemente, generalizar en el sesgo hacia machos podría ser la mejor estrategia adaptativa.
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