1
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McKermitt JT, Foquet B, Kuna W, Hunt J, Sadd BM, Sakaluk SK. Experimental evolution under varying sex ratio and behavioral plasticity in response to perceived competitive environment independently affect calling effort in male crickets. Evolution 2024; 78:453-462. [PMID: 38124480 DOI: 10.1093/evolut/qpad224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 11/29/2023] [Accepted: 12/17/2023] [Indexed: 12/23/2023]
Abstract
The operational sex ratio (OSR) is a key component influencing the magnitude of sexual selection driving the evolution of male sexual traits, but males often also retain the ability to plastically modulate trait expression depending on the current environment. Here we employed an experimental evolution approach to determine whether the OSR affects the evolution of male calling effort in decorated crickets, a costly sexual trait, and whether plasticity in calling effort is altered by the OSR under which males have evolved. Calling effort of males from 2 selection regimes maintained at different OSRs over 18-20 generations (male vs. female biased) was recorded at 2 different levels of perceived competition, in the absence of rivals or in the presence of an experimentally muted competitor. The effect of the OSR on the evolution of male calling effort was modest, and in the opposite direction predicted by theory. Instead, the immediate competitive environment strongly influenced male calling effort as males called more in the presence of a rival, revealing considerable plasticity in this trait. This increased calling effort came at a cost, however, as males confined with a muted rival experienced significantly higher mortality.
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Affiliation(s)
- Jack T McKermitt
- School of Biological Sciences, Behavior, Ecology, Evolution and Conservation Section, Illinois State University, Normal, IL, United States
| | - Bert Foquet
- School of Biological Sciences, Behavior, Ecology, Evolution and Conservation Section, Illinois State University, Normal, IL, United States
| | - Will Kuna
- School of Biological Sciences, Behavior, Ecology, Evolution and Conservation Section, Illinois State University, Normal, IL, United States
| | - John Hunt
- School of Science, Western Sydney University, Penrith, NSW, Australia
| | - Ben M Sadd
- School of Biological Sciences, Behavior, Ecology, Evolution and Conservation Section, Illinois State University, Normal, IL, United States
| | - Scott K Sakaluk
- School of Biological Sciences, Behavior, Ecology, Evolution and Conservation Section, Illinois State University, Normal, IL, United States
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2
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Kappeler PM, Benhaiem S, Fichtel C, Fromhage L, Höner OP, Jennions MD, Kaiser S, Krüger O, Schneider JM, Tuni C, van Schaik J, Goymann W. Sex roles and sex ratios in animals. Biol Rev Camb Philos Soc 2023; 98:462-480. [PMID: 36307924 DOI: 10.1111/brv.12915] [Citation(s) in RCA: 19] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 10/12/2022] [Accepted: 10/14/2022] [Indexed: 11/29/2022]
Abstract
In species with separate sexes, females and males often differ in their morphology, physiology and behaviour. Such sex-specific traits are functionally linked to variation in reproductive competition, mate choice and parental care, which have all been linked to sex roles. At the 150th anniversary of Darwin's theory on sexual selection, the question of why patterns of sex roles vary within and across species remains a key topic in behavioural and evolutionary ecology. New theoretical, experimental and comparative evidence suggests that variation in the adult sex ratio (ASR) is a key driver of variation in sex roles. Here, we first define and discuss the historical emergence of the sex role concept, including recent criticisms and rebuttals. Second, we review the various sex ratios with a focus on ASR, and explore its theoretical links to sex roles. Third, we explore the causes, and especially the consequences, of biased ASRs, focusing on the results of correlational and experimental studies of the effect of ASR variation on mate choice, sexual conflict, parental care and mating systems, social behaviour, hormone physiology and fitness. We present evidence that animals in diverse societies are sensitive to variation in local ASR, even on short timescales, and propose explanations for conflicting results. We conclude with an overview of open questions in this field integrating demography, life history and behaviour.
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Affiliation(s)
- Peter M Kappeler
- Behavioral Ecology and Sociobiology Unit, German Primate Center - Leibniz Institute of Primatology, Kellnerweg 4, 37077, Göttingen, Germany
- Department of Sociobiology/Anthropology, University of Göttingen, Kellnerweg 6, 37077, Göttingen, Germany
| | - Sarah Benhaiem
- Department of Ecological Dynamics, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Strasse 17, D-10315, Berlin, Germany
| | - Claudia Fichtel
- Behavioral Ecology and Sociobiology Unit, German Primate Center - Leibniz Institute of Primatology, Kellnerweg 4, 37077, Göttingen, Germany
| | - Lutz Fromhage
- Department of Biological and Environmental Science, Ambiotica, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland
| | - Oliver P Höner
- Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Strasse 17, D-10315, Berlin, Germany
| | - Michael D Jennions
- Division of Ecology & Evolution, Research School of Biology, ANU College of Science, The Australian National University, RN Robertson Building, 46 Sullivans Creek Road, Canberra, ACT, 2600, Australia
| | - Sylvia Kaiser
- Department of Behavioural Biology, University of Münster, Badestr. 13, 48149, Münster, Germany
| | - Oliver Krüger
- Department of Animal Behavior, Bielefeld University, Morgenbreede 45, 33615, Bielefeld, Germany
| | - Jutta M Schneider
- Department of Biology, Institute of Zoology, Universität Hamburg, Martin-Luther-King Platz 3, 20146, Hamburg, Germany
| | - Cristina Tuni
- Department of Biology II, Ludwig Maximilians University of Munich, Großhaderner Str 2, 82152, Planegg-Martinsried, Germany
| | - Jaap van Schaik
- Applied Zoology and Nature Conservation, University of Greifswald, Loitzer Str. 26, 17489, Greifswald, Germany
| | - Wolfgang Goymann
- Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Str. 6a, D-82319, Seewiesen, Germany
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3
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Driscoll JG, Alo FM, Paoli A, Weladji RB, Holand Ø, Kumpula J, Soveri T. Influence of operational sex ratio and male age on mating competition intensity in reindeer (Rangifer tarandus). ETHOL ECOL EVOL 2022. [DOI: 10.1080/03949370.2021.1975997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Jeffrey G. Driscoll
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Franco M. Alo
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Amélie Paoli
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Robert B. Weladji
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Øystein Holand
- Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, Ås 1432, Norway
| | - Jouko Kumpula
- Natural Resources Institute of Finland (Luke), Ecosystems and Ecology, Saarikoskentie 99910, Finland
| | - Timo Soveri
- Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Paroninkuja 20, 04920 Saarentaus, Finland
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4
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Driscoll JG, Alo FM, Paoli A, Weladji RB, Holand Ø, Kumpula J, Soveri T. Influence of operational sex ratio and male age on mating competition intensity in reindeer ( Rangifer tarandus). ETHOL ECOL EVOL 2021. [DOI: 10.1080/03949370.2021.1989054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Jeffrey G. Driscoll
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Franco M. Alo
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Amélie Paoli
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Robert B. Weladji
- Department of Biology, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec H4B1R6, Canada
| | - Øystein Holand
- Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Jouko Kumpula
- Ecosystems and Ecology, Natural Resources Institute of Finland (Luke), 99910, Finland
| | - Timo Soveri
- Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, P.O. Box 66, Helsinki, Finland
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5
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Bath E, Edmunds D, Norman J, Atkins C, Harper L, Rostant WG, Chapman T, Wigby S, Perry JC. Sex ratio and the evolution of aggression in fruit flies. Proc Biol Sci 2021; 288:20203053. [PMID: 33726599 PMCID: PMC8059548 DOI: 10.1098/rspb.2020.3053] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Aggressive behaviours are among the most striking displayed by animals, and aggression strongly impacts fitness in many species. Aggression varies plastically in response to the social environment, but we lack direct tests of how aggression evolves in response to intra-sexual competition. We investigated how aggression in both sexes evolves in response to the competitive environment, using populations of Drosophila melanogaster that we experimentally evolved under female-biased, equal, and male-biased sex ratios. We found that after evolution in a female-biased environment—with less male competition for mates—males fought less often on food patches, although the total frequency and duration of aggressive behaviour did not change. In females, evolution in a female-biased environment—where female competition for resources is higher—resulted in more frequent aggressive interactions among mated females, along with a greater increase in post-mating aggression. These changes in female aggression could not be attributed solely to evolution either in females or in male stimulation of female aggression, suggesting that coevolved interactions between the sexes determine female post-mating aggression. We found evidence consistent with a positive genetic correlation for aggression between males and females, suggesting a shared genetic basis. This study demonstrates the experimental evolution of a behaviour strongly linked to fitness, and the potential for the social environment to shape the evolution of contest behaviours.
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Affiliation(s)
- Eleanor Bath
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Danielle Edmunds
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Jessica Norman
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Charlotte Atkins
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Lucy Harper
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Wayne G Rostant
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Tracey Chapman
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Stuart Wigby
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK.,Department of Evolution, Ecology, and Behaviour, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, UK
| | - Jennifer C Perry
- Department of Zoology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK.,School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
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6
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Yamashita J, Takeuchi A, Hosono K, Fleming T, Nagahama Y, Okubo K. Male-predominant galanin mediates androgen-dependent aggressive chases in medaka. eLife 2020; 9:59470. [PMID: 32783809 PMCID: PMC7423395 DOI: 10.7554/elife.59470] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 07/29/2020] [Indexed: 12/26/2022] Open
Abstract
Recent studies in mice demonstrate that a subset of neurons in the medial preoptic area (MPOA) that express galanin play crucial roles in regulating parental behavior in both sexes. However, little information is available on the function of galanin in social behaviors in other species. Here, we report that, in medaka, a subset of MPOA galanin neurons occurred nearly exclusively in males, resulting from testicular androgen stimulation. Galanin-deficient medaka showed a greatly reduced incidence of male-male aggressive chases. Furthermore, while treatment of female medaka with androgen induced male-typical aggressive acts, galanin deficiency in these females attenuated the effect of androgen on chases. Given their male-biased and androgen-dependent nature, the subset of MPOA galanin neurons most likely mediate androgen-dependent male-male chases. Histological studies further suggested that variability in the projection targets of the MPOA galanin neurons may account for the species-dependent functional differences in these evolutionarily conserved neural substrates.
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Affiliation(s)
- Junpei Yamashita
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Akio Takeuchi
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Kohei Hosono
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Thomas Fleming
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Yoshitaka Nagahama
- Division of Reproductive Biology, National Institute for Basic Biology, Okazaki, Japan
| | - Kataaki Okubo
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
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7
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Naretto S, Chiaraviglio M. Factors driving sexual dimorphism and colour variability in the Achala Copper Lizard (Pristidactylus achalensis), an endemic species to the highland mountains in central Argentina. CAN J ZOOL 2020. [DOI: 10.1139/cjz-2019-0293] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intensity of mating competition varies according to the temporal and spatial distribution of individuals. Measuring sexual dimorphism over time and interpreting the association between individuals is therefore important if we aim to understand how sexual traits are influenced. We examined sex differences in the Achala Copper Lizard (Pristidactylus achalensis (Gallardo, 1964)), an endemic species from the highest part of mountains of central Argentina. Over 4 years, we explored sex-specific variation in body size, head size, interlimb length, and body colouration. Furthermore, we evaluated how these traits varied temporally, and we also explored whether the spatial distribution of individuals is explained by variation in these traits. We found that P. achalensis is a species with sexual dimorphism in multiple characters, including body size, head size, and colouration. Interestingly, some traits related to mating, such as head width, show a temporal variability in both sexes, whereas other traits, such as colouration, varies seasonally only in males. Our results underline the intriguing possibility of seasonal morphological changes related to mating, and more broadly that sex differences are influenced by sexual selection pressures mediated by temporal variation in mate competition.
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Affiliation(s)
- S. Naretto
- Laboratorio de Biología del Comportamiento, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sársfield 299, CP X5000JJC, Córdoba, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
- Laboratorio de Biología del Comportamiento, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sársfield 299, CP X5000JJC, Córdoba, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
| | - M. Chiaraviglio
- Laboratorio de Biología del Comportamiento, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sársfield 299, CP X5000JJC, Córdoba, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
- Laboratorio de Biología del Comportamiento, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Vélez Sársfield 299, CP X5000JJC, Córdoba, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
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8
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Hare RM, Simmons LW. Sexual selection and its evolutionary consequences in female animals. Biol Rev Camb Philos Soc 2018; 94:929-956. [DOI: 10.1111/brv.12484] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 10/31/2018] [Accepted: 11/02/2018] [Indexed: 01/01/2023]
Affiliation(s)
- Robin M. Hare
- Centre for Evolutionary Biology, School of Biological Sciences University of Western Australia 35 Stirling Highway, Perth, 6009 Australia
| | - Leigh W. Simmons
- Centre for Evolutionary Biology, School of Biological Sciences University of Western Australia 35 Stirling Highway, Perth, 6009 Australia
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9
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Reedy AM, Pope BD, Kiriazis NM, Giordano CL, Sams CL, Warner DA, Cox RM. Female anoles display less but attack more quickly than males in response to territorial intrusions. Behav Ecol 2017. [DOI: 10.1093/beheco/arx095] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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10
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Chuard PJ, Brown GE, Grant JW. The effects of adult sex ratio on mating competition in male and female guppies (Poecilia reticulata) in two wild populations. Behav Processes 2016; 129:1-10. [DOI: 10.1016/j.beproc.2016.05.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 05/03/2016] [Accepted: 05/05/2016] [Indexed: 10/21/2022]
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11
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Aronsen T, Berglund A, Mobley KB, Ratikainen II, Rosenqvist G. SEX RATIO AND DENSITY AFFECT SEXUAL SELECTION IN A SEX-ROLE REVERSED FISH. Evolution 2013; 67:3243-57. [DOI: 10.1111/evo.12201] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Accepted: 06/13/2013] [Indexed: 11/30/2022]
Affiliation(s)
- Tonje Aronsen
- Department of Biology, Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; NO-7491 Trondheim Norway
| | - Anders Berglund
- Department of Ecology and Genetics/Animal Ecology; Uppsala University; SE-752 36 Uppsala Sweden
| | - Kenyon B. Mobley
- Department of Evolutionary Ecology; Max Planck Institute for Evolutionary Biology; 24306 Plön Germany
| | - Irja I. Ratikainen
- Department of Biology, Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; NO-7491 Trondheim Norway
| | - Gunilla Rosenqvist
- Department of Biology, Centre for Biodiversity Dynamics; Norwegian University of Science and Technology; NO-7491 Trondheim Norway
- University of Gotland; SE-621 67 Visby Sweden
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12
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Aronsen T, Mobley K, Berglund A, Sundin J, Billing A, Rosenqvist G. The operational sex ratio and density influence spatial relationships between breeding pipefish. Behav Ecol 2013. [DOI: 10.1093/beheco/art019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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13
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Fernandez-Duque E, Huck M. Till death (or an intruder) do us part: intrasexual-competition in a monogamous primate. PLoS One 2013; 8:e53724. [PMID: 23372665 PMCID: PMC3553134 DOI: 10.1371/journal.pone.0053724] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2012] [Accepted: 12/05/2012] [Indexed: 11/28/2022] Open
Abstract
Polygynous animals are often highly dimorphic, and show large sex-differences in the degree of intra-sexual competition and aggression, which is associated with biased operational sex ratios (OSR). For socially monogamous, sexually monomorphic species, this relationship is less clear. Among mammals, pair-living has sometimes been assumed to imply equal OSR and low frequency, low intensity intra-sexual competition; even when high rates of intra-sexual competition and selection, in both sexes, have been theoretically predicted and described for various taxa. Owl monkeys are one of a few socially monogamous primates. Using long-term demographic and morphological data from 18 groups, we show that male and female owl monkeys experience intense intra-sexual competition and aggression from solitary floaters. Pair-mates are regularly replaced by intruding floaters (27 female and 23 male replacements in 149 group-years), with negative effects on the reproductive success of both partners. Individuals with only one partner during their life produced 25% more offspring per decade of tenure than those with two or more partners. The termination of the pair-bond is initiated by the floater, and sometimes has fatal consequences for the expelled adult. The existence of floaters and the sporadic, but intense aggression between them and residents suggest that it can be misleading to assume an equal OSR in socially monogamous species based solely on group composition. Instead, we suggest that sexual selection models must assume not equal, but flexible, context-specific, OSR in monogamous species.
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Affiliation(s)
- Eduardo Fernandez-Duque
- Department of Anthropology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
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14
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Weir LK. Male–male competition and alternative male mating tactics influence female behavior and fertility in Japanese medaka (Oryzias latipes). Behav Ecol Sociobiol 2012. [DOI: 10.1007/s00265-012-1438-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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15
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Kokko H, Klug H, Jennions MD. Unifying cornerstones of sexual selection: operational sex ratio, Bateman gradient and the scope for competitive investment. Ecol Lett 2012; 15:1340-1351. [PMID: 22925080 DOI: 10.1111/j.1461-0248.2012.01859.x] [Citation(s) in RCA: 128] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2012] [Revised: 05/10/2012] [Accepted: 07/23/2012] [Indexed: 11/28/2022]
Abstract
What explains variation in the strength of sexual selection across species, populations or differences between the sexes? Here, we show that unifying two well-known lines of thinking provides the necessary conceptual framework to account for variation in sexual selection. The Bateman gradient and the operational sex ratio (OSR) are incomplete in complementary ways: the former describes the fitness gain per mating and the latter the potential difficulty of achieving it. We combine this insight with an analysis of the scope for sexually selected traits to spread despite naturally selected costs. We explain why the OSR sometimes does not affect the strength of sexual selection. An explanation of sexual selection becomes more logical when a long 'dry time' ('time out', recovery after mating due to e.g. parental care) is understood to reduce the expected time to the next mating when in the mating pool (i.e. available to mate again). This implies weaker selection to shorten the wait. An integrative view of sexual selection combines an understanding of the origin of OSR biases with how they are reflected in the Bateman gradient, and how this can produce selection for mate acquisition traits despite naturally selected costs.
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Affiliation(s)
- Hanna Kokko
- Centre of Excellence in Biological Interactions, Division of Ecology, Evolution & Genetics, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
| | - Hope Klug
- Department of Biological & Environmental Sciences, University of Tennessee Chattanooga, 215 Holt Hall, Dept 2653, 615 McCallie Aven, Chattanooga, TN, 37403, USA
| | - Michael D Jennions
- Centre of Excellence in Biological Interactions, Division of Ecology, Evolution & Genetics, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
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16
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de Jong K, Forsgren E, Sandvik H, Amundsen T. Measuring mating competition correctly: available evidence supports operational sex ratio theory. Behav Ecol 2012. [DOI: 10.1093/beheco/ars094] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AbstractCentral to sexual selection theory is the question of when individuals should compete for mates. Theory predicts that the sex ratio of ready-to-mate individuals (operational sex ratio; OSR) affects male and female mating competition. In accordance with this, the strength of mating competition, measured by agonistic behaviors and courtship displays, has been found to co-vary with the OSR in field populations of several species. However, laboratory experiments have often produced results that seemingly contradict OSR theory, especially for courtship behavior. We argue that this may be because experiments typically measure frequencies of competitive behaviors. Frequencies of courtship and agonistic behavior are not only affected by the level of mating competition, but also by the number of potential mates or competitors encountered. In contrast, the propensity to behave competitively at a given encounter represents a behavioral response, and thus directly reflects mating competition. We show in 2 simple models that 1) courtship frequency can be expected to respond differently from courtship propensity to changes in OSR and 2) an increase in frequency of agonistic behaviors could occur even if the propensity is not affected by the OSR. In a meta-analysis of studies on courtship competition, we show that frequency measures produced largely opposite results to propensity measures, as predicted by our model. Moreover, courtship propensity increased when the OSR became more biased toward competitors. This presents strong evidence that the OSR affects competition, in the form of courtship, as predicted by OSR theory.
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Affiliation(s)
- Karen de Jong
- Department of Biology, Norwegian University of Science and Technology (NTNU) 7491 Trondheim, Norwayand
| | - Elisabet Forsgren
- The Norwegian Institute for Nature Research (NINA) 7485 Trondheim, Norway
| | - Hanno Sandvik
- Department of Biology, Norwegian University of Science and Technology (NTNU) 7491 Trondheim, Norwayand
| | - Trond Amundsen
- Department of Biology, Norwegian University of Science and Technology (NTNU) 7491 Trondheim, Norwayand
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17
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18
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Weir LK, Grant JWA, Hutchings JA. The influence of operational sex ratio on the intensity of competition for mates. Am Nat 2011; 177:167-76. [PMID: 21460553 DOI: 10.1086/657918] [Citation(s) in RCA: 188] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The evolution and maintenance of secondary sexual characteristics and behavior are heavily influenced by the variance in mating success among individuals in a population. The operational sex ratio (OSR) is often used as a predictor of the intensity of competition for mates, as it describes the relative number of males and females who are ready to mate. We investigate changes in aggression, courtship, mate guarding, and sperm release as a function of changes in the OSR using meta-analytic techniques. As the OSR becomes increasingly biased, aggression increases as competitors attempt to defend mates, but this aggression begins to decrease at an OSR of 1.99, presumably due to the increased costs of competition as rivals become more numerous. Sperm release follows a similar but not significant trend. By contrast, courtship rate decreases as the OSR becomes increasingly biased, whereas mate guarding and copulation duration increase. Overall, predictable behavioral changes occur in response to OSR, although the nature of the change is dependent on the type of mating behavior. These results suggest considerable flexibility of mating system structure within species, which can be predicted by OSR and likely results in variation in the strength of sexual selection.
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Affiliation(s)
- Laura K Weir
- Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
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Intrasexual competition and courtship in female and male Japanese medaka, Oryzias latipes: effects of operational sex ratio and density. Anim Behav 2010. [DOI: 10.1016/j.anbehav.2010.07.007] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Abstract
Sexual selection is among the most powerful of all evolutionary forces. It occurs when individuals within one sex secure mates and produce offspring at the expense of other individuals within the same sex. Darwin was first to recognize the power of sexual selection to change male and female phenotypes, and, in noting that sexual selection is nonubiquitous, Darwin was also first to recognize the importance of mating system--the "special circumstances" in which reproduction occurs within species. Analyses of mating systems since Darwin have emphasized either the genetic relationships between male and female mating elements, usually among plants, or the numbers of mates males and females may obtain, usually among animals. Combining these schemes yields a quantitative methodology that emphasizes measurement of the sex difference in the variance in relative fitness, as well as phenotypic and genetic correlations underlying reproductive traits that may arise among breeding pairs. Such information predicts the degree and direction of sexual dimorphism within species, it allows the classification of mating systems using existing genetic and life history data, and with information on the spatial and temporal distributions of fertilizations, it may also predict floral morphology in plants. Because this empirical framework identifies selective forces and genetic architectures responsible for observed male-female differences, it compliments discoveries of nucleotide sequence variation and the expression of quantitative traits. Moreover, because this methodology emphasizes the process of evolutionary change, it is easier to test and interpret than frameworks emphasizing parental investment in offspring and its presumed evolutionary outcomes.
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Independent effects of male and female density on sexual harassment, female fitness, and male competition for mates in the western mosquitofish Gambusia affinis. Behav Ecol Sociobiol 2007. [DOI: 10.1007/s00265-007-0365-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Smith CC, Sargent RC. Female fitness declines with increasing female density but not male harassment in the western mosquitofish, Gambusia affinis. Anim Behav 2006. [DOI: 10.1016/j.anbehav.2005.06.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Price AC, Helen Rodd F. The Effect of Social Environment on Male-Male Competition in Guppies (Poecilia reticulata). Ethology 2006. [DOI: 10.1111/j.1439-0310.2006.01142.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Abstract
Hypotheses for the adaptive significance of extreme female-biased sexual size dimorphism (SSD) generally assume that in dimorphic species males rarely interfere with each other. Here we provide the first multivariate examination of sexual selection because of male-male competition over access to females in a species with 'dwarf' males, the orb-weaving spider Argiope aurantia. Male A. aurantia typically try to mate opportunistically during the female's final moult when she is defenceless. We show that, contrary to previous hypotheses, the local operational sex ratio (males per female on the web) is male-biased most of the season. Both interference and scramble competition occur during opportunistic mating, the former leading to significant selection for large male body size. Male condition and leg length had no effect on mating success independent of size. We discuss these findings in the context of the evolution of extreme female-biased SSD in this clade.
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Affiliation(s)
- M W Foellmer
- Department of Biology, Concordia University, Montreal, Canada.
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