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OUP accepted manuscript. J Mammal 2022. [DOI: 10.1093/jmammal/gyac041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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2
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Toni P, Forsyth DM, Festa-Bianchet M. Determinants of offspring sex in kangaroos: a test of multiple hypotheses. Behav Ecol 2021. [DOI: 10.1093/beheco/araa131] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Abstract
When the fitness costs and benefits of sons and daughters differ, offspring sex ratio manipulation could be an important reproductive tactic. We explored the effects of environment and maternal caring ability on offspring sex to test four adaptive sex ratio modification hypotheses: the extrinsic modification hypothesis (EMH), carrying capacity hypothesis (CCH), Trivers-Willard hypothesis (TWH), and cost-of-reproduction hypothesis (CRH). The EMH and CCH propose that environmental conditions shape offspring sex ratios, directly or in interaction with maternal condition. The TWH and CRH predict a positive relationship between maternal condition and production of the costlier sex. The TWH predicts that mothers with superior caring ability should produce more of the sex that can provide the greatest fitness returns from additional maternal allocation, and the CRH proposes that females with limited caring ability should reduce fitness costs by producing the cheaper sex. Repeated measures on 83 known-age eastern gray kangaroos, polygynous marsupials with strong sexual dimorphism, revealed that offspring sex ratio was independent of per capita forage, supporting neither the EMH nor CCH, but was dependent on maternal mass, consistent with the TWH and CCH. Our results, however, cannot clearly identify the ultimate cause of the relationship between maternal mass and greater production of sons. One of the three assumptions of the TWH could not be verified, and mothers of sons suffered only marginal additional fitness costs. Sex ratios in higher vertebrates are likely not solely explained by factors dependent on maternal control.
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Affiliation(s)
- Pauline Toni
- Université de Sherbrooke, 2500 boulevard de l’Université, J1K2R1 Sherbrooke, Quebec, Canada
| | - David M Forsyth
- Vertebrate Pest Research Unit, New South Wales Department of Primary Industries, Orange, NSW, Australia
| | - Marco Festa-Bianchet
- Université de Sherbrooke, 2500 boulevard de l’Université, J1K2R1 Sherbrooke, Quebec, Canada
- Research School of Biology, The Australian National University, Canberra, ACT, Australia
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3
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Douhard M, Geffroy B. Males can adjust offspring sex ratio in an adaptive fashion through different mechanisms. Bioessays 2021; 43:e2000264. [PMID: 33594712 DOI: 10.1002/bies.202000264] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 01/26/2021] [Accepted: 01/26/2021] [Indexed: 01/15/2023]
Abstract
Sex allocation research has primarily focused on offspring sex-ratio adjustment by mothers. Yet, fathers also benefit from producing more of the sex with greater fitness returns. Here, we review the state-of-the art in the study of male-driven sex allocation and, counter to the current paradigm, we propose that males can adaptively influence offspring sex ratio through a wide variety of mechanisms. This includes differential production and motility of X- versus Y-bearing sperms in mammals, variation in seminal fluid composition in haplo-diploid invertebrates, and epigenetic mechanisms in some fish and lizards exhibiting environmental sex determination. Conflicts of interest between mothers and fathers over offspring sex ratios can emerge, although many more studies are needed in this area. While many studies of sex allocation have focused on adaptive explanations with little attention to mechanisms, and vice versa, the integration of these two topics is essential for understanding male-driven sex allocation.
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Affiliation(s)
- Mathieu Douhard
- Laboratoire de Biométrie & Biologie Evolutive, Université Lyon 1, Villeurbanne, France
| | - Benjamin Geffroy
- MARBEC, Univ Montpellier, Ifremer, CNRS, IRD, Palavas-Les-Flots, France
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4
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Lavoie MD, Tedeschi JN, Garcia‐Gonzalez F, Firman RC. Exposure to male-dominated environments during development influences sperm sex ratios at sexual maturity. Evol Lett 2019; 3:392-402. [PMID: 31388448 PMCID: PMC6675145 DOI: 10.1002/evl3.123] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 04/15/2019] [Accepted: 05/21/2019] [Indexed: 11/18/2022] Open
Abstract
Different stages during development are important when it comes to phenotypic adjustments in response to external stimuli. Critical stages in mammals are the prenatal phase, where embryos are exposed to a milieu of sex steroid hormones, and the early-postnatal phase, where littermates interact and experience their incipient social environment. Further, the postmaternal environment will influence the development of traits that are linked to reproductive success in adulthood. Accumulated evidence of male-driven sex allocation establishes the currently untested hypothesis that the sperm sex ratio is a plastic trait that can be mediated to align with prevailing social conditions. Here, we used natural variation in the maternal environment and experimentally manipulated the postmaternal environment to identify the importance of these developmental phases on sperm sex ratio adjustments in wild house mice (Mus musculus domesticus). We found that male density in both environments was predictive of sperm sex ratios at sexual maturity: males from more male-biased litters and males maturing under high male density produced elevated levels of Y-chromosome-bearing sperm. Our findings indicate that the sperm sex ratio is a variable phenotypic trait that responds to the external environment, and highlight the potential that these adjustments function as a mechanism of male-driven sex allocation.
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Affiliation(s)
- Misha D. Lavoie
- School of Biological Sciences (M092), Centre for Evolutionary BiologyThe University of Western AustraliaCrawleyWA6009Australia
| | - Jamie N. Tedeschi
- School of Biological Sciences (M092), Centre for Evolutionary BiologyThe University of Western AustraliaCrawleyWA6009Australia
| | - Francisco Garcia‐Gonzalez
- School of Biological Sciences (M092), Centre for Evolutionary BiologyThe University of Western AustraliaCrawleyWA6009Australia
- Estacion Biológica de DoñanaCSICSevillaSpain
| | - Renée C. Firman
- School of Biological Sciences (M092), Centre for Evolutionary BiologyThe University of Western AustraliaCrawleyWA6009Australia
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5
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Vanthournout B, Busck MM, Bechsgaard J, Hendrickx F, Schramm A, Bilde T. Male spiders control offspring sex ratio through greater production of female-determining sperm. Proc Biol Sci 2019; 285:rspb.2017.2887. [PMID: 29563266 DOI: 10.1098/rspb.2017.2887] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2017] [Accepted: 02/26/2018] [Indexed: 01/07/2023] Open
Abstract
Sex allocation theory predicts that when sons and daughters have different reproductive values, parents should adjust offspring sex ratio towards the sex with the higher fitness return. Haplo-diploid species directly control offspring sex ratio, but species with chromosomal sex determination (CSD) were presumed to be constrained by Mendelian segregation. There is now increasing evidence that CSD species can adjust sex ratio strategically, but the underlying mechanism is not well understood. One hypothesis states that adaptive control is more likely to evolve in the heterogametic sex through a bias in gamete production. We investigated this hypothesis in males as the heterogametic sex in two social spider species that consistently show adaptive female-biased sex ratio and in one subsocial species that is characterized by equal sex ratio. We quantified the production of male (0) and female (X) determining sperm cells using flow cytometry, and show that males of social species produce significantly more X-carrying sperm than 0-sperm, on average 70%. This is consistent with the production of more daughters. Males of the subsocial species produced a significantly lower bias of 54% X-carrying sperm. We also investigated whether inter-genomic conflict between hosts and their endosymbionts may explain female bias. Next generation sequencing showed that five common genera of bacterial endosymbionts known to affect sex ratio are largely absent, ruling out that endosymbiont bacteria bias sex ratio in social spiders. Our study provides evidence for paternal control over sex allocation through biased gamete production as a mechanism by which the heterogametic sex in CSD species adaptively adjust offspring sex ratio.
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Affiliation(s)
- Bram Vanthournout
- Department of Bioscience, Section for Genetics, Ecology and Evolution, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark.,Biology Department, Evolution and Optics of Nanostructures Group, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium
| | - Mette Marie Busck
- Department of Bioscience, Section for Microbiology, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark
| | - Jesper Bechsgaard
- Department of Bioscience, Section for Genetics, Ecology and Evolution, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark
| | - Frederik Hendrickx
- Biology Department, Terrestrial Ecology Unit, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium.,Entomology Department, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, 1000 Brussels, Belgium
| | - Andreas Schramm
- Department of Bioscience, Section for Microbiology, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark
| | - Trine Bilde
- Department of Bioscience, Section for Genetics, Ecology and Evolution, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark
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6
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Malo AF, Gilbert TC, Riordan P. Drivers of sex ratio bias in the eastern bongo: lower inbreeding increases the probability of being born male. Proc Biol Sci 2019; 286:20190345. [PMID: 31064305 PMCID: PMC6532524 DOI: 10.1098/rspb.2019.0345] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Accepted: 04/14/2019] [Indexed: 01/13/2023] Open
Abstract
Parent sex ratio allocation has consequences for individual fitness, population dynamics, and conservation. Theory predicts that parents should adjust offspring sex ratio when the fitness returns of producing male or female offspring varies. Previous studies have assumed that only mothers are capable of biasing offspring sex ratios, but have neglected fathers, given the expectation of an equal proportion of X- and Y-chromosome-bearing (CBS) sperm in ejaculates due to sex chromosome segregation at meiosis. This assumption has been recently refuted and both paternal fertility and paternal genetic quality have been shown to bias sex ratios. Here, we simultaneously test the relative contribution of paternal, maternal, and individual genetic quality, as measured by inbreeding, on the probability of being born a son or a daughter, using pedigree and lifelong offspring sex ratio data for the eastern bongo ( Tragelaphus eurycerus isaaci). Our models showed first, that surprisingly, as individual inbreeding decreases the probability of being born male increases, second, that paternal genetic effects on sex ratio were stronger than maternal genetic effects (which were absent). Furthermore, paternal effects were opposite in sign to those predicted; father inbreeding increases the probability of having sons. Previous paternal effects have been interpreted as adaptive due to sex-specific inbreeding depression for reproductive traits. We argue that in the eastern bongo, the opposite sign of the paternal effect on sex ratios results from a reversed sex-specific inbreeding depression pattern (present for female but not male reproductive traits). We anticipate that this research will help stimulate research on evolutionary constraints to sex ratios. Finally, the results open a new avenue of research to predict sex ratio allocation in an applied conservation context. Future models of sex ratio allocation should also include the predicted inbreeding level of the offspring and paternal inbreeding levels.
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Affiliation(s)
- Aurelio F. Malo
- GLOCEE - Global Change Ecology and Evolution Group, Department of Life Sciences, Universidad de Alcalá, 28871, Spain
- Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
| | - Tania C. Gilbert
- Marwell Wildlife, Thompsons Lane, Winchester, Hampshire SO21 1JH, UK
- School of Biological Sciences, Faculty of Environmental and Life Sciences, University of Southampton, Southampton SO17 1BJ, UK
| | - Philip Riordan
- Marwell Wildlife, Thompsons Lane, Winchester, Hampshire SO21 1JH, UK
- School of Biological Sciences, Faculty of Environmental and Life Sciences, University of Southampton, Southampton SO17 1BJ, UK
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7
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Edwards AM, Cameron EZ, Deakin JE, Ezaz T, Pereira JC, Ferguson‐Smith MA, Robert KA. Sexual conflict in action: An antagonistic relationship between maternal and paternal sex allocation in the tammar wallaby, Notamacropus eugenii. Ecol Evol 2019; 9:4340-4348. [PMID: 31031909 PMCID: PMC6476839 DOI: 10.1002/ece3.4813] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 11/22/2018] [Indexed: 01/29/2023] Open
Abstract
Sex ratio biases are often inconsistent, both among and within species and populations. While some of these inconsistencies may be due to experimental design, much of the variation remains inexplicable. Recent research suggests that an exclusive focus on mothers may account for some of the inconsistency, with an increasing number of studies showing variation in sperm sex ratios and seminal fluids. Using fluorescent in-situ hybridization, we show a significant population-level Y-chromosome bias in the spermatozoa of wild tammar wallabies, but with significant intraindividual variation between males. We also show a population-level birth sex ratio trend in the same direction toward male offspring, but a weaning sex ratio that is significantly female-biased, indicating that males are disproportionately lost during lactation. We hypothesize that sexual conflict between parents may cause mothers to adjust offspring sex ratios after birth, through abandonment of male pouch young and reactivation of diapaused embryos. Further research is required in a captive, controlled setting to understand what is driving and mechanistically controlling sperm sex ratio and offspring sex ratio biases and to understand the sexually antagonistic relationship between mothers and fathers over offspring sex. These results extend beyond sex allocation, as they question studies of population processes that assume equal input of sex chromosomes from fathers, and will also assist with future reproduction studies for management and conservation of marsupials.
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Affiliation(s)
- Amy M. Edwards
- Department of Ecology, Environment and Evolution, School of Life SciencesLa Trobe UniversityMelbourneVictoriaAustralia
| | - Elissa Z. Cameron
- School of Biological SciencesUniversity of CanterburyChristchurchNew Zealand
| | - Janine E. Deakin
- Institute for Applied EcologyUniversity of CanberraCanberraAustralian Capital TerritoryAustralia
| | - Tariq Ezaz
- Institute for Applied EcologyUniversity of CanberraCanberraAustralian Capital TerritoryAustralia
| | - Jorge C. Pereira
- Department of Veterinary MedicineUniversity of CambridgeCambridgeUK
- Cytocell Ltd.CambridgeUK
| | | | - Kylie A. Robert
- Department of Ecology, Environment and Evolution, School of Life SciencesLa Trobe UniversityMelbourneVictoriaAustralia
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9
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Edwards AM, Cameron EZ. Cryptic male choice: experimental evidence of sperm sex ratio and seminal fluid adjustment in relation to coital rate. Reprod Fertil Dev 2017; 29:1401-1404. [DOI: 10.1071/rd16123] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 05/16/2016] [Indexed: 11/23/2022] Open
Abstract
The differential allocation hypothesis suggests that a mother should adjust the sex of offspring in relation to her mate’s attractiveness, thereby increasing future reproductive fitness when her sons inherit the attractive traits. More attractive males have been shown to sire more sons, but it is possible that the sex ratio skew could be a result of paternal rather than maternal manipulation, which would be a more parsimonious explanation. We manipulated coital rate (an indicator of attractiveness) in laboratory mice and showed that males that mate more often have higher levels of glucose in their semen despite lower blood glucose levels. Since peri-conceptual glucose levels in utero increase male conceptus survival, this could result in male-biased sex ratios. The males that mated most also had more remaining X-chromosome-bearing-spermatozoa, suggesting depletion of Y-chromosome-bearing-spermatozoa during mating. We hypothesise that males may alter both seminal fluids and X : Y ratios in an ejaculate to influence subsequent sex ratios. Our results further support a paternal role in sex allocation.
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10
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Cameron EZ, Edwards AM, Parsley LM. Developmental sexual dimorphism and the evolution of mechanisms for adjustment of sex ratios in mammals. Ann N Y Acad Sci 2016; 1389:147-163. [PMID: 27862006 DOI: 10.1111/nyas.13288] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Revised: 09/28/2016] [Accepted: 10/05/2016] [Indexed: 12/15/2022]
Abstract
Sex allocation theory predicts biased offspring sex ratios in relation to local conditions if they would maximize parental lifetime reproductive return. In mammals, the extent of the birth sex bias is often unpredictable and inconsistent, leading some to question its evolutionary significance. For facultative adjustment of sex ratios to occur, males and females would need to be detectably different from an early developmental stage, but classic sexual dimorphism arises from hormonal influences after gonadal development. Recent advances in our understanding of early, pregonadal sexual dimorphism, however, indicate high levels of dimorphism in gene expression, caused by chromosomal rather than hormonal differences. Here, we discuss how such dimorphism would interact with and link previously hypothesized mechanisms for sex-ratio adjustment. These differences between males and females are sufficient for offspring sex both to be detectable to parents and to provide selectable cues for biasing sex ratios from the earliest stages. We suggest ways in which future research could use the advances in our understanding of sexually dimorphic developmental physiology to test the evolutionary significance of sex allocation in mammals. Such an approach would advance our understanding of sex allocation and could be applied to other taxa.
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Affiliation(s)
- Elissa Z Cameron
- School of Biological Sciences, University of Tasmania, Hobart, Australia.,School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
| | - Amy M Edwards
- School of Biological Sciences, University of Tasmania, Hobart, Australia
| | - Laura M Parsley
- School of Biological Sciences, University of Tasmania, Hobart, Australia
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11
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Edwards AM, Cameron EZ, Pereira JC, Wapstra E, Ferguson-Smith MA, Horton SR, Thomasson K. Gestational experience alters sex allocation in the subsequent generation. ROYAL SOCIETY OPEN SCIENCE 2016; 3:160210. [PMID: 27493776 PMCID: PMC4968468 DOI: 10.1098/rsos.160210] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 06/08/2016] [Indexed: 06/06/2023]
Abstract
Empirical tests of adaptive maternal sex allocation hypotheses have presented inconsistent results in mammals. The possibility that mothers are constrained in their ability to adjust sex ratios could explain some of the remaining variation. Maternal effects, the influence of the maternal phenotype or genotype on her developing offspring, may constrain sex allocation through physiological changes in response to the gestational environment. We tested if maternal effects constrain future parental sex allocation through a lowered gestational stress environment in laboratory mice. Females that experienced lowered stress as embryos in utero gave birth to female-biased litters as adults, with no change to litter size. Changes in offspring sex ratio was linked to peri-conceptual glucose, as those females that had increasing blood glucose peri-conceptionally gave birth to litters with a higher male to female sex ratio. There was, however, no effect of the lowered prenatal stress for developing male embryos and their sperm sex ratio when adult. We discuss the implications of maternal effects and maternal stress environment on the lifelong physiology of the offspring, particularly as a constraint on later maternal sex allocation.
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Affiliation(s)
- A. M. Edwards
- School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia
- Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
| | - E. Z. Cameron
- School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia
| | - J. C. Pereira
- Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
- Cytocell Ltd., Cambridge Technopark, Newmarket Road, Cambridge, UK
| | - E. Wapstra
- School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia
| | | | - S. R. Horton
- School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia
| | - K. Thomasson
- School of Biological Sciences, University of Tasmania, Hobart, Tasmania, Australia
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