Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls

Matthias Tschumi; Jolanda Humbel; Joscha Erbes; Julien Fattebert; Jochen Fischer; Gerhard Fritz; Barbara Geiger; Ronald van Harxen; Bernd Hoos; Johanna Hurst; Lars Bo Jacobsen; Herbert Keil; Werner Kneule; Vanja T. Michel; Heinz Michels; Leander Möbius; Marco Perrig; Philip Rößler; Dieter Schneider; Siegfried Schuch; Pascal Stroeken; Beat Naef-Daenzer; Martin U. Grüebler

doi:10.1007/s00265-019-2694-8

Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls

Matthias Tschumi^*, Jolanda Humbel, Joscha Erbes, Julien Fattebert, Jochen Fischer, Gerhard Fritz, Barbara Geiger, Ronald van Harxen, Bernd Hoos, Johanna Hurst, Lars Bo Jacobsen, Herbert Keil, Werner Kneule, Vanja T. Michel, Heinz Michels, Leander Möbius, Marco Perrig, Philip Rößler, Dieter Schneider, Siegfried SchuchPascal Stroeken, Beat Naef-Daenzer, Martin U. Grüebler

^*Corresponding author for this work

3 Citations (Scopus)

Abstract

Abstract: Although biased offspring sex ratios are common in species with sexual size dimorphism, the proximate causes are often unresolved. This is because two general mechanisms operating in different ways and in various periods of reproduction can lead to the bias: sex-biased survival or parental sex-allocation. We examined nestling sex ratio patterns between hatching and fledging, sexual size dimorphism, and factors affecting nestling survival using growth and survival data of 846 individual little owl Athene noctua nestlings with known sex from 307 broods from Germany, the Netherlands and Denmark. Nestling sex ratio was female-biased, mainly due to a significant female bias in the first-hatched chicks. Females showed a higher body weight than male nestlings at ringing and body weight of nestlings decreased with hatching sequence. Nestling survival was higher in females (Φ = 0.91) than in males (Φ = 0.85), and survival rates were positively related to body mass and negatively to brood size. Although the observed lower survival of males can cause an overall female-biased sex ratio, the sex dimorphism and survival patterns found here are unlikely to explain the conspicuous sex ratio pattern with a female bias in the first-hatched nestlings and the increase in female bias across the season. Thus, these results point towards interacting mechanisms of parental sex allocation strategies and sex-specific survival. As the female bias was allocated to the first rank that is most likely to survive, the female bias will increase under suboptimal breeding conditions. We therefore suggest that under suboptimal ecological conditions, higher investment into females is adaptive in little owls. Significance statement: Biased sex ratios can have severe effects on the social behaviour and population dynamics of endangered species. However, the existence of subtle sex ratio bias is often unknown and its proximate mechanisms and ultimate consequences often remain unclear. Small sample sizes make the detection of subtle effects unlikely and often fail to disentangle diverging mechanisms such as sex-biased survival and parental sex allocation. We used a large dataset of 846 little owl nestlings from 307 broods from three countries to investigate offspring sex ratio patterns, sexual size dimorphism and nestling survival simultaneously. Our findings suggest interacting mechanisms of parental sex allocation strategies and sex-specific survival to drive biased offspring sex ratios in little owls. The context dependence of the sex ratio bias indicates that offspring sex ratio bias in little owls is both, a consequence of—and an adaptation to—suboptimal breeding conditions.

Original language	English
Article number	85
Journal	Behavioral Ecology and Sociobiology
Volume	73
Issue number	6
Number of pages	10
ISSN	0340-5443
DOIs	https://doi.org/10.1007/s00265-019-2694-8
Publication status	Published - 1 Jun 2019

Keywords

Birds
Hatching order
Nestling survival
Parental investment
Sex-specific mortality
Sexual size dimorphism

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10.1007/s00265-019-2694-8

Cite this

Tschumi, M., Humbel, J., Erbes, J., Fattebert, J., Fischer, J., Fritz, G., Geiger, B., van Harxen, R., Hoos, B., Hurst, J., Jacobsen, L. B., Keil, H., Kneule, W., Michel, V. T., Michels, H., Möbius, L., Perrig, M., Rößler, P., Schneider, D., ... Grüebler, M. U. (2019). Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls. Behavioral Ecology and Sociobiology, 73(6), Article 85. https://doi.org/10.1007/s00265-019-2694-8

Tschumi, M, Humbel, J, Erbes, J, Fattebert, J, Fischer, J, Fritz, G, Geiger, B, van Harxen, R, Hoos, B, Hurst, J, Jacobsen, LB, Keil, H, Kneule, W, Michel, VT, Michels, H, Möbius, L, Perrig, M, Rößler, P, Schneider, D, Schuch, S, Stroeken, P, Naef-Daenzer, B & Grüebler, MU 2019, 'Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls', Behavioral Ecology and Sociobiology, vol. 73, no. 6, 85. https://doi.org/10.1007/s00265-019-2694-8

@article{04dc7f42a9af4267ba80f27f27dcccd8,

title = "Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls",

abstract = "Abstract: Although biased offspring sex ratios are common in species with sexual size dimorphism, the proximate causes are often unresolved. This is because two general mechanisms operating in different ways and in various periods of reproduction can lead to the bias: sex-biased survival or parental sex-allocation. We examined nestling sex ratio patterns between hatching and fledging, sexual size dimorphism, and factors affecting nestling survival using growth and survival data of 846 individual little owl Athene noctua nestlings with known sex from 307 broods from Germany, the Netherlands and Denmark. Nestling sex ratio was female-biased, mainly due to a significant female bias in the first-hatched chicks. Females showed a higher body weight than male nestlings at ringing and body weight of nestlings decreased with hatching sequence. Nestling survival was higher in females (Φ = 0.91) than in males (Φ = 0.85), and survival rates were positively related to body mass and negatively to brood size. Although the observed lower survival of males can cause an overall female-biased sex ratio, the sex dimorphism and survival patterns found here are unlikely to explain the conspicuous sex ratio pattern with a female bias in the first-hatched nestlings and the increase in female bias across the season. Thus, these results point towards interacting mechanisms of parental sex allocation strategies and sex-specific survival. As the female bias was allocated to the first rank that is most likely to survive, the female bias will increase under suboptimal breeding conditions. We therefore suggest that under suboptimal ecological conditions, higher investment into females is adaptive in little owls. Significance statement: Biased sex ratios can have severe effects on the social behaviour and population dynamics of endangered species. However, the existence of subtle sex ratio bias is often unknown and its proximate mechanisms and ultimate consequences often remain unclear. Small sample sizes make the detection of subtle effects unlikely and often fail to disentangle diverging mechanisms such as sex-biased survival and parental sex allocation. We used a large dataset of 846 little owl nestlings from 307 broods from three countries to investigate offspring sex ratio patterns, sexual size dimorphism and nestling survival simultaneously. Our findings suggest interacting mechanisms of parental sex allocation strategies and sex-specific survival to drive biased offspring sex ratios in little owls. The context dependence of the sex ratio bias indicates that offspring sex ratio bias in little owls is both, a consequence of—and an adaptation to—suboptimal breeding conditions.",

keywords = "Birds, Hatching order, Nestling survival, Parental investment, Sex-specific mortality, Sexual size dimorphism",

author = "Matthias Tschumi and Jolanda Humbel and Joscha Erbes and Julien Fattebert and Jochen Fischer and Gerhard Fritz and Barbara Geiger and {van Harxen}, Ronald and Bernd Hoos and Johanna Hurst and Jacobsen, {Lars Bo} and Herbert Keil and Werner Kneule and Michel, {Vanja T.} and Heinz Michels and Leander M{\"o}bius and Marco Perrig and Philip R{\"o}{\ss}ler and Dieter Schneider and Siegfried Schuch and Pascal Stroeken and Beat Naef-Daenzer and Gr{\"u}ebler, {Martin U.}",

year = "2019",

month = jun,

day = "1",

doi = "10.1007/s00265-019-2694-8",

language = "English",

volume = "73",

journal = "Behavioral Ecology and Sociobiology",

issn = "0340-5443",

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TY - JOUR

T1 - Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls

AU - Tschumi, Matthias

AU - Humbel, Jolanda

AU - Erbes, Joscha

AU - Fattebert, Julien

AU - Fischer, Jochen

AU - Fritz, Gerhard

AU - Geiger, Barbara

AU - van Harxen, Ronald

AU - Hoos, Bernd

AU - Hurst, Johanna

AU - Jacobsen, Lars Bo

AU - Keil, Herbert

AU - Kneule, Werner

AU - Michel, Vanja T.

AU - Michels, Heinz

AU - Möbius, Leander

AU - Perrig, Marco

AU - Rößler, Philip

AU - Schneider, Dieter

AU - Schuch, Siegfried

AU - Stroeken, Pascal

AU - Naef-Daenzer, Beat

AU - Grüebler, Martin U.

PY - 2019/6/1

Y1 - 2019/6/1

N2 - Abstract: Although biased offspring sex ratios are common in species with sexual size dimorphism, the proximate causes are often unresolved. This is because two general mechanisms operating in different ways and in various periods of reproduction can lead to the bias: sex-biased survival or parental sex-allocation. We examined nestling sex ratio patterns between hatching and fledging, sexual size dimorphism, and factors affecting nestling survival using growth and survival data of 846 individual little owl Athene noctua nestlings with known sex from 307 broods from Germany, the Netherlands and Denmark. Nestling sex ratio was female-biased, mainly due to a significant female bias in the first-hatched chicks. Females showed a higher body weight than male nestlings at ringing and body weight of nestlings decreased with hatching sequence. Nestling survival was higher in females (Φ = 0.91) than in males (Φ = 0.85), and survival rates were positively related to body mass and negatively to brood size. Although the observed lower survival of males can cause an overall female-biased sex ratio, the sex dimorphism and survival patterns found here are unlikely to explain the conspicuous sex ratio pattern with a female bias in the first-hatched nestlings and the increase in female bias across the season. Thus, these results point towards interacting mechanisms of parental sex allocation strategies and sex-specific survival. As the female bias was allocated to the first rank that is most likely to survive, the female bias will increase under suboptimal breeding conditions. We therefore suggest that under suboptimal ecological conditions, higher investment into females is adaptive in little owls. Significance statement: Biased sex ratios can have severe effects on the social behaviour and population dynamics of endangered species. However, the existence of subtle sex ratio bias is often unknown and its proximate mechanisms and ultimate consequences often remain unclear. Small sample sizes make the detection of subtle effects unlikely and often fail to disentangle diverging mechanisms such as sex-biased survival and parental sex allocation. We used a large dataset of 846 little owl nestlings from 307 broods from three countries to investigate offspring sex ratio patterns, sexual size dimorphism and nestling survival simultaneously. Our findings suggest interacting mechanisms of parental sex allocation strategies and sex-specific survival to drive biased offspring sex ratios in little owls. The context dependence of the sex ratio bias indicates that offspring sex ratio bias in little owls is both, a consequence of—and an adaptation to—suboptimal breeding conditions.

AB - Abstract: Although biased offspring sex ratios are common in species with sexual size dimorphism, the proximate causes are often unresolved. This is because two general mechanisms operating in different ways and in various periods of reproduction can lead to the bias: sex-biased survival or parental sex-allocation. We examined nestling sex ratio patterns between hatching and fledging, sexual size dimorphism, and factors affecting nestling survival using growth and survival data of 846 individual little owl Athene noctua nestlings with known sex from 307 broods from Germany, the Netherlands and Denmark. Nestling sex ratio was female-biased, mainly due to a significant female bias in the first-hatched chicks. Females showed a higher body weight than male nestlings at ringing and body weight of nestlings decreased with hatching sequence. Nestling survival was higher in females (Φ = 0.91) than in males (Φ = 0.85), and survival rates were positively related to body mass and negatively to brood size. Although the observed lower survival of males can cause an overall female-biased sex ratio, the sex dimorphism and survival patterns found here are unlikely to explain the conspicuous sex ratio pattern with a female bias in the first-hatched nestlings and the increase in female bias across the season. Thus, these results point towards interacting mechanisms of parental sex allocation strategies and sex-specific survival. As the female bias was allocated to the first rank that is most likely to survive, the female bias will increase under suboptimal breeding conditions. We therefore suggest that under suboptimal ecological conditions, higher investment into females is adaptive in little owls. Significance statement: Biased sex ratios can have severe effects on the social behaviour and population dynamics of endangered species. However, the existence of subtle sex ratio bias is often unknown and its proximate mechanisms and ultimate consequences often remain unclear. Small sample sizes make the detection of subtle effects unlikely and often fail to disentangle diverging mechanisms such as sex-biased survival and parental sex allocation. We used a large dataset of 846 little owl nestlings from 307 broods from three countries to investigate offspring sex ratio patterns, sexual size dimorphism and nestling survival simultaneously. Our findings suggest interacting mechanisms of parental sex allocation strategies and sex-specific survival to drive biased offspring sex ratios in little owls. The context dependence of the sex ratio bias indicates that offspring sex ratio bias in little owls is both, a consequence of—and an adaptation to—suboptimal breeding conditions.

KW - Birds

KW - Hatching order

KW - Nestling survival

KW - Parental investment

KW - Sex-specific mortality

KW - Sexual size dimorphism

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U2 - 10.1007/s00265-019-2694-8

DO - 10.1007/s00265-019-2694-8

M3 - Journal article

AN - SCOPUS:85066292566

SN - 0340-5443

VL - 73

JO - Behavioral Ecology and Sociobiology

JF - Behavioral Ecology and Sociobiology

IS - 6

M1 - 85

ER -

Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls

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Keywords

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