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James TY. Sex Without Sexes: Can the Cost of Finding a Mate Explain Diversity in Fungal Mating Systems? Integr Comp Biol 2023; 63:922-935. [PMID: 37218718 DOI: 10.1093/icb/icad037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 05/14/2023] [Accepted: 05/17/2023] [Indexed: 05/24/2023] Open
Abstract
Eukaryotes have evolved myriad ways of uniting gametes during sexual reproduction. A repeated pattern is the convergent evolution of a mating system with the fusion of larger gametes with smaller gametes (anisogamy) from that of fusion between morphologically identical gametes (isogamy). In anisogamous species, sexes are defined as individuals that produce only one gamete type. Although sexes abound throughout Eukarya, in fungi there are no biological sexes, because even in anisogamous species, individuals are hermaphroditic and produce both gamete types. For this reason, the term mating types is preferred over sexes, and, thus defined, only individuals of differing mating types can mate (homoallelic incompatibility). In anisogamous fungal species, there is scant evidence that there are more than two mating types, and this may be linked to genetic constraints, such as the use of mating types to determine the inheritance of cytoplasmic genomes. However, the mushroom fungi (Agaricomycetes) stand out as having both large numbers of mating types within a species, which will allow nearly all individuals to be compatible with each other, and reciprocal exchange of nuclei during mating, which will avoid cytoplasmic mixing and cyto-nuclear conflicts. Although the limitation of mating types to two in most fungi is consistent with the cyto-nuclear conflicts model, there are many facets of the Agaricomycete life cycle that also suggest they will demand a high outbreeding efficiency. Specifically, they are mostly obligately sexual and outcrossing, inhabit complex competitive niches, and display broadcast spore dispersal. Subsequently, the Agaricomycete individual pays a high cost to being choosy when encountering a mate. Here, I discuss the costs of mate finding and choice and demonstrate how most fungi have multiple ways of reducing these costs, which can explain why mating types are mostly limited to two per species. Nevertheless, it is perplexing that fungi have not evolved multiple mating types on more occasions nor evolved sexes. The few exceptions to these rules suggest that it is dictated by both molecular and evolutionary constraints.
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Affiliation(s)
- Timothy Y James
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
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2
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Wilson AM, Wingfield MJ, Wingfield BD. Structure and number of mating pheromone genes is closely linked to sexual reproductive strategy in Huntiella. BMC Genomics 2023; 24:261. [PMID: 37179314 PMCID: PMC10182648 DOI: 10.1186/s12864-023-09355-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 05/05/2023] [Indexed: 05/15/2023] Open
Abstract
BACKGROUND Huntiella resides in the Ceratocystidaceae, a family of fungi that accommodates important plant pathogens and insect-associated saprotrophs. Species in the genus have either heterothallic or unisexual (a form of homothallism) mating systems, providing an opportunity to investigate the genetic mechanisms that enable transitions between reproductive strategies in related species. Two newly sequenced Huntiella genomes are introduced in this study and comparative genomics and transcriptomics tools are used to investigate the differences between heterothallism and unisexuality across the genus. RESULTS Heterothallic species harbored up to seven copies of the a-factor pheromone, each of which possessed numerous mature peptide repeats. In comparison, unisexual Huntiella species had only two or three copies of this gene, each with fewer repeats. Similarly, while the heterothallic species expressed up to 12 copies of the mature α-factor pheromone, unisexual species had up to six copies. These significant differences imply that unisexual Huntiella species do not rely on a mating partner recognition system in the same way that heterothallic fungi do. CONCLUSION While it is suspected that mating type-independent pheromone expression is the mechanism allowing for unisexual reproduction in Huntiella species, our results suggest that the transition to unisexuality may also have been associated with changes in the genes governing the pheromone pathway. While these results are specifically related to Huntiella, they provide clues leading to a better understanding of sexual reproduction and the fluidity of mating strategies in fungi more broadly.
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Affiliation(s)
- Andi M Wilson
- Forestry and Agricultural Biotechnology Institute (FABI), Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, 0028, South Africa.
| | - Michael J Wingfield
- Forestry and Agricultural Biotechnology Institute (FABI), Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, 0028, South Africa
| | - Brenda D Wingfield
- Forestry and Agricultural Biotechnology Institute (FABI), Department of Biochemistry, Genetics and Microbiology, University of Pretoria, Pretoria, 0028, South Africa
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3
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Martinossi-Allibert I, Ament-Velásquez SL, Saupe SJ, Johannesson H. To self or not to self? Absence of mate choice despite costly outcrossing in the fungus Podospora anserina. J Evol Biol 2023; 36:238-250. [PMID: 36263943 PMCID: PMC10092876 DOI: 10.1111/jeb.14108] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2022] [Revised: 09/16/2022] [Accepted: 09/20/2022] [Indexed: 01/11/2023]
Abstract
Fungi have a large potential for flexibility in their mode of sexual reproduction, resulting in mating systems ranging from haploid selfing to outcrossing. However, we know little about which mating strategies are used in nature, and why, even in well-studied model organisms. Here, we explored the fitness consequences of alternative mating strategies in the ascomycete fungus Podospora anserina. We measured and compared fitness proxies of nine genotypes in either diploid selfing or outcrossing events, over two generations, and with or without environmental stress. We showed that fitness was consistently lower in outcrossing events, irrespective of the environment. The cost of outcrossing was partly attributed to non-self recognition genes with pleiotropic effects on fertility. We then predicted that when presented with options to either self or outcross, individuals would perform mate choice in favour of the reproductive strategy that yields higher fitness. Contrary to our prediction, individuals did not seem to avoid outcrossing when a choice was offered, in spite of the fitness cost incurred. Our results suggest that, although functionally diploid, P. anserina does not benefit from outcrossing in most cases. We outline different explanations for the apparent lack of mate choice in face of high fitness costs associated with outcrossing, including a new perspective on the pleiotropic effect of non-self recognition genes.
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Affiliation(s)
- Ivain Martinossi-Allibert
- Systematic Biology, Department of Organismal Biology, Uppsala University, Uppsala, Sweden.,Institut de Biochimie et de Génétique Cellulaire, UMR 5095 CNRS, Université de Bordeaux, Bordeaux CEDEX, France.,Department of Biology, Realfagbygget, Norwegian University of Science and Technology, Trondheim, Norway
| | | | - Sven J Saupe
- Institut de Biochimie et de Génétique Cellulaire, UMR 5095 CNRS, Université de Bordeaux, Bordeaux CEDEX, France
| | - Hanna Johannesson
- Systematic Biology, Department of Organismal Biology, Uppsala University, Uppsala, Sweden
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4
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Seike T, Niki H. Pheromone Response and Mating Behavior in Fission Yeast. Microbiol Mol Biol Rev 2022; 86:e0013022. [PMID: 36468849 PMCID: PMC9769774 DOI: 10.1128/mmbr.00130-22] [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] [Indexed: 12/12/2022] Open
Abstract
Most ascomycete fungi, including the fission yeast Schizosaccharomyces pombe, secrete two peptidyl mating pheromones: C-terminally modified and unmodified peptides. S. pombe has two mating types, plus and minus, which secrete two different pheromones, P-factor (unmodified) and M-factor (modified), respectively. These pheromones are specifically recognized by receptors on the cell surface of cells of opposite mating types, which trigger a pheromone response. Recognition between pheromones and their corresponding receptors is important for mate discrimination; therefore, genetic changes in pheromone or receptor genes affect mate recognition and cause reproductive isolation that limits gene flow between populations. Such genetic variation in recognition via the pheromone/receptor system may drive speciation. Our recent studies reported that two pheromone receptors in S. pombe might have different stringencies in pheromone recognition. In this review, we focus on the molecular mechanism of pheromone response and mating behavior, emphasizing pheromone diversification and its impact on reproductive isolation in S. pombe and closely related fission yeast species. We speculate that the "asymmetric" system might allow flexible adaptation to pheromone mutational changes while maintaining stringent recognition of mating partners. The loss of pheromone activity results in the extinction of an organism's lineage. Therefore, genetic changes in pheromones and their receptors may occur gradually and/or coincidently before speciation. Our findings suggest that the M-factor plays an important role in partner discrimination, whereas P-factor communication allows flexible adaptation to create variations in S. pombe. Our inferences provide new insights into the evolutionary mechanisms underlying pheromone diversification.
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Affiliation(s)
- Taisuke Seike
- Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, Suita, Osaka, Japan
| | - Hironori Niki
- Microbial Physiology Laboratory, Department of Gene Function and Phenomics, National Institute of Genetics, Mishima, Shizuoka, Japan
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5
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Auxier B, Czárán TL, Aanen DK. Modelling the consequences of the dikaryotic life cycle of mushroom-forming fungi on genomic conflict. eLife 2022; 11:75917. [PMID: 35441591 PMCID: PMC9084891 DOI: 10.7554/elife.75917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/14/2022] [Indexed: 11/21/2022] Open
Abstract
Generally, sexual organisms contain two haploid genomes, one from each parent, united in a single diploid nucleus of the zygote which links their fate during growth. A fascinating exception to this is Basidiomycete fungi, where the two haploid genomes remain separate in a dikaryon, retaining the option to fertilize subsequent monokaryons encountered. How the ensuing nuclear competition influences the balance of selection within and between individuals is largely unexplored. We test the consequences of the dikaryotic life cycle for mating success and mycelium-level fitness components. We assume a trade-off between mating fitness at the level of the haploid nucleus and fitness of the fungal mycelium. We show that the maintenance of fertilization potential by dikaryons leads to a higher proportion of fertilized monokaryons, but that the ensuing intradikaryon selection for increased nuclear mating fitness leads to reduced mycelium fitness relative to a diploid life cycle. However, this fitness reduction is lower compared to a hypothetical life cycle where dikaryons can also exchange nuclei. Prohibition of fusion between dikaryons therefore reduces the level of nuclear parasitism. The number of loci influencing fitness is an important determinant of the degree to which average mycelium-level fitness is reduced. The results of this study crucially hinge upon a trade-off between nucleus and mycelium-level fitness. We discuss the evidence for this assumption and the implications of an alternative that there is a positive relationship between nucleus and mycelium-level fitness.
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Affiliation(s)
- Benjamin Auxier
- Laboratory of Genetics, Wageningen University, Wageningen, Netherlands
| | | | - Duur K Aanen
- Laboratory of Genetics, Wageningen University, Wageningen, Netherlands
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6
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Shuker DM, Kvarnemo C. The definition of sexual selection. Behav Ecol 2021; 32:781-794. [PMID: 34695172 PMCID: PMC8528540 DOI: 10.1093/beheco/arab055] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 05/05/2021] [Accepted: 05/11/2021] [Indexed: 11/13/2022] Open
Abstract
Sexual selection is a key component of evolutionary biology. However, from the very formulation of sexual selection by Darwin, the nature and extent of sexual selection have been controversial. Recently, such controversy has led back to the fundamental question of just what sexual selection is. This has included how we incorporate female-female reproductive competition into sexual or natural selection. In this review, we do four things. First, we examine what we want a definition to do. Second, we define sexual selection: sexual selection is any selection that arises from fitness differences associated with nonrandom success in the competition for access to gametes for fertilization. An important outcome of this is that as mates often also offer access to resources, when those resources are the targets of the competition, rather than their gametes, the process should be considered natural rather than sexual selection. We believe this definition encapsulates both much of Darwin's original thinking about sexual selection, and much of how contemporary biologists use the concept of sexual selection. Third, we address alternative definitions, focusing in some detail on the role of female reproductive competition. Fourth, we challenge our definition with a number of scenarios, for instance where natural and sexual selection may align (as in some forms of endurance rivalry), or where differential allocation means teasing apart how fecundity and access to gametes influence fitness. In conclusion, we emphasize that whilst the ecological realities of sexual selection are likely to be complex, the definition of sexual selection is rather simple.
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Affiliation(s)
- David M Shuker
- School of Biology, Harold Mitchell Building, University of St. Andrews, St. Andrews, UK
| | - Charlotta Kvarnemo
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, SE, Sweden
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7
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Vos M, Buckling A, Kuijper B. Sexual Selection in Bacteria? Trends Microbiol 2019; 27:972-981. [PMID: 31493990 DOI: 10.1016/j.tim.2019.07.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Revised: 07/03/2019] [Accepted: 07/24/2019] [Indexed: 01/05/2023]
Abstract
A main mechanism of lateral gene transfer in bacteria is transformation, where cells take up free DNA from the environment which subsequently can be recombined into the genome. Bacteria are also known to actively release DNA into the environment through secretion or lysis, which could aid uptake via transformation. Various evolutionary benefits of DNA uptake and DNA release have been proposed but these have all been framed in the context of natural selection. Here, we interpret bacterial DNA uptake and release in the context of sexual selection theory, which has been central to our understanding of the bewildering diversity of traits associated with sexual reproduction in the eukaryote world but has never been applied to prokaryotes. Specifically, we explore potential scenarios where bacteria releasing DNA into the environment could compete for successful uptake by other cells, or where bacteria could selectively take up DNA to enhance their fitness. We conclude that there is potential for sexual selection to act in bacteria, and that this might in part explain the considerable diversity in transformation-related behaviours.
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Affiliation(s)
- Michiel Vos
- European Centre for Environment and Human Health, University of Exeter Medical School, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK.
| | - Angus Buckling
- Department of Biosciences, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK
| | - Bram Kuijper
- Department of Biosciences, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK
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8
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Seike T, Maekawa H, Nakamura T, Shimoda C. The asymmetric chemical structures of two mating pheromones reflect their differential roles in mating of fission yeast. J Cell Sci 2019; 132:jcs.230722. [PMID: 31186279 DOI: 10.1242/jcs.230722] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 06/03/2019] [Indexed: 02/01/2023] Open
Abstract
In the fission yeast Schizosaccharomyces pombe, the mating reaction is controlled by two mating pheromones, M-factor and P-factor, secreted by M- and P-type cells, respectively. M-factor is a C-terminally farnesylated lipid peptide, whereas P-factor is a simple peptide. To examine whether this chemical asymmetry in the two pheromones is essential for conjugation, we constructed a mating system in which either pheromone can stimulate both M- and P-cells, and examined whether the resulting autocrine strains can mate. Autocrine M-cells responding to M-factor successfully mated with P-factor-lacking P-cells, indicating that P-factor is not essential for conjugation; by contrast, autocrine P-cells responding to P-factor were unable to mate with M-factor-lacking M-cells. The sterility of the autocrine P-cells was completely restored by expressing the M-factor receptor. These observations indicate that the different chemical characteristics of the two types of pheromone, a lipid and a simple peptide, are not essential; however, a lipid peptide might be required for successful mating. Our findings allow us to propose a model of the differential roles of M-factor and P-factor in conjugation of S. pombeThis article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Taisuke Seike
- Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan
| | - Hiromi Maekawa
- Yeast Genetic Resources Laboratory, Graduate School of Engineering, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Taro Nakamura
- Department of Biology, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Chikashi Shimoda
- Department of Biology, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
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9
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Nieuwenhuis BPS, Aanen DK. Nuclear arms races: Experimental evolution for mating success in the mushroom-forming fungus Schizophyllum commune. PLoS One 2018; 13:e0209671. [PMID: 30589876 PMCID: PMC6320016 DOI: 10.1371/journal.pone.0209671] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 12/10/2018] [Indexed: 12/21/2022] Open
Abstract
When many gametes compete to fertilize a limited number of compatible gametes, sexual selection will favour traits that increase competitive success during mating. In animals and plants, sperm and pollen competition have yielded many interesting adaptations for improved mating success. In fungi, similar processes have not been shown directly yet. We test the hypothesis that sexual selection can increase competitive fitness during mating, using experimental evolution in the mushroom-forming fungus Schizophyllum commune (Basidiomycota). Mating in mushroom fungi occurs by donation of nuclei to a mycelium. These fertilizing 'male' nuclei migrate through the receiving 'female' mycelium. In our setup, an evolving population of nuclei was serially mated with a non-evolving female mycelium for 20 sexual generations. From the twelve tested evolved lines, four had increased and one had decreased fitness relative to an unevolved competitor. Even though only two of those five remained significant after correcting for multiple comparisons, for all five lines we found a correlation between the efficiency with which the female mycelium is accessed and fitness, providing additional circumstantial evidence for fitness change in those five lines. In two lines, fitness change was also accompanied by increased spore production. The one line with net reduced competitive fitness had increased spore production, but reduced fertilisation efficiency. We did not find trade-offs between male reproductive success and other fitness components. We compare these findings with examples of sperm and pollen competition and show that many similarities between these systems and nuclear competition in mushrooms exist.
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Affiliation(s)
- Bart P. S. Nieuwenhuis
- Division of Evolutionary Biology, Faculty of Biology II, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany
- Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands
- * E-mail:
| | - Duur K. Aanen
- Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands
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10
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Rogers DW, McConnell E, Miller EL, Greig D. Diminishing Returns on Intragenic Repeat Number Expansion in the Production of Signaling Peptides. Mol Biol Evol 2017; 34:3176-3185. [PMID: 28961820 PMCID: PMC5850478 DOI: 10.1093/molbev/msx243] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Signaling peptides enable communication between cells, both within and between individuals, and are therefore key to the control of complex physiological and behavioral responses. Since their small sizes prevent direct transmission to secretory pathways, these peptides are often produced as part of a larger polyprotein comprising precursors for multiple related or identical peptides; the physiological and behavioral consequences of this unusual gene structure are not understood. Here, we show that the number of mature-pheromone-encoding repeats in the yeast α-mating-factor gene MFα1 varies considerably between closely related isolates of both Saccharomyces cerevisiae and its sister species Saccharomyces paradoxus. Variation in repeat number has important phenotypic consequences: Increasing repeat number caused higher pheromone production and greater competitive mating success. However, the magnitude of the improvement decreased with increasing repeat number such that repeat amplification beyond that observed in natural isolates failed to generate more pheromone, and could actually reduce sexual fitness. We investigate multiple explanations for this pattern of diminishing returns and find that our results are most consistent with a translational trade-off: Increasing the number of encoded repeats results in more mature pheromone per translation event, but also generates longer transcripts thereby reducing the rate of translation—a phenomenon known as length-dependent translation. Length-dependent translation may be a powerful constraint on the evolution of genes encoding repetitive or modular proteins, with important physiological and behavioral consequences across eukaryotes.
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Affiliation(s)
- David W Rogers
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany.,Department of Evolutionary Theory, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Ellen McConnell
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany.,Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Biology, Plön, Germany
| | - Eric L Miller
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany.,Department of Veterinary Medicine, Cambridge Veterinary School, University of Cambridge, Cambridge, United Kingdom
| | - Duncan Greig
- Experimental Evolution Research Group, Max Planck Institute for Evolutionary Biology, Plön, Germany.,Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
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11
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Beekman M, Nieuwenhuis B, Ortiz-Barrientos D, Evans JP. Sexual selection in hermaphrodites, sperm and broadcast spawners, plants and fungi. Philos Trans R Soc Lond B Biol Sci 2016; 371:20150541. [PMID: 27619704 PMCID: PMC5031625 DOI: 10.1098/rstb.2015.0541] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/23/2016] [Indexed: 11/12/2022] Open
Abstract
Darwin was the first to recognize that sexual selection is a strong evolutionary force. Exaggerated traits allow same-sex individuals to compete over access to mates and provide a mechanism by which mates are selected. It is relatively easy to appreciate how inter- and intrasexual selection work in organisms with the sensory capabilities to perceive physical or behavioural traits that signal mate quality or mate compatibility, and to assess the relative quality of competitors. It is therefore not surprising that most studies of sexual selection have focused on animals with separate sexes and obvious adaptations that function in the context of reproductive competition. Yet, many sexual organisms are both male and female at the same time, often lack sexual dimorphism and never come into direct contact at mating. How does sexual selection act in such species, and what can we learn from them? Here, we address these questions by exploring the potential for sexual selection in simultaneous hermaphrodites, sperm- and broadcast spawners, plants and fungi. Our review reveals a range of mechanisms of sexual selection, operating primarily after gametes have been released, which are common in many of these groups and also quite possibly in more familiar (internally fertilizing and sexually dimorphic) organisms.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.
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Affiliation(s)
- Madeleine Beekman
- School of Life and Environmental Sciences, University of Sydney, 2006 New South Wales, Australia
| | - Bart Nieuwenhuis
- Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden
| | | | - Jonathan P Evans
- Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, 6009 Western Australia, Australia
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12
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Nieuwenhuis BPS, Immler S. The evolution of mating-type switching for reproductive assurance. Bioessays 2016; 38:1141-1149. [DOI: 10.1002/bies.201600139] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
| | - Simone Immler
- Department of Evolutionary Biology; Uppsala University; Uppsala Sweden
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13
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Banderas A, Koltai M, Anders A, Sourjik V. Sensory input attenuation allows predictive sexual response in yeast. Nat Commun 2016; 7:12590. [PMID: 27557894 PMCID: PMC5007329 DOI: 10.1038/ncomms12590] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Accepted: 07/14/2016] [Indexed: 12/22/2022] Open
Abstract
Animals are known to adjust their sexual behaviour depending on mate competition. Here we report similar regulation for mating behaviour in a sexual unicellular eukaryote, the budding yeast Saccharomyces cerevisiae. We demonstrate that pheromone-based communication between the two mating types, coupled to input attenuation by recipient cells, enables yeast to robustly monitor relative mate abundance (sex ratio) within a mixed population and to adjust their commitment to sexual reproduction in proportion to their estimated chances of successful mating. The mechanism of sex-ratio sensing relies on the diffusible peptidase Bar1, which is known to degrade the pheromone signal produced by mating partners. We further show that such a response to sexual competition within a population can optimize the fitness trade-off between the costs and benefits of mating response induction. Our study thus provides an adaptive explanation for the known molecular mechanism of pheromone degradation in yeast. Cells of the yeast Saccharomyces cerevisiae can mate with other cells of opposite mating type. Here, the authors show that the combination of a pheromone and a pheromone-degrading enzyme allows yeast cells to monitor relative mate abundance within a population and adjust their commitment to sexual reproduction.
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Affiliation(s)
- Alvaro Banderas
- Max Planck Institute for Terrestrial Microbiology &LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch-Str. 16, D-35037 Marburg, Germany.,Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany
| | - Mihaly Koltai
- Max Planck Institute for Terrestrial Microbiology &LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch-Str. 16, D-35037 Marburg, Germany
| | - Alexander Anders
- Max Planck Institute for Terrestrial Microbiology &LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch-Str. 16, D-35037 Marburg, Germany
| | - Victor Sourjik
- Max Planck Institute for Terrestrial Microbiology &LOEWE Research Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch-Str. 16, D-35037 Marburg, Germany
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14
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Tang-Martínez Z. Rethinking Bateman's Principles: Challenging Persistent Myths of Sexually Reluctant Females and Promiscuous Males. JOURNAL OF SEX RESEARCH 2016; 53:532-559. [PMID: 27074147 DOI: 10.1080/00224499.2016.1150938] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In 1948, Angus Bateman published a paper on fruit flies that tested Charles Darwin's ideas of sexual selection. Based on this one fruit fly study, Bateman concluded that because males are able to produce millions of small sperm, males are likely to behave promiscuously, mating with as many females as possible. On the other hand, because females produce relatively fewer, larger, and presumably more expensive eggs, females are likely to be very discriminating in selecting only one high-quality sexual partner. He also posited that a male's reproductive success increases linearly with the number of females he is able to mate with, but that a female's reproductive success peaks after she mates with only one male. Consequently, in almost all organisms, sexual selection acts most strongly on males. These ideas became a recurring theme in attempts to explain wide-ranging differences in male and female behavior not only in nonhuman animals but also in humans. As such, Bateman's conclusions and predictions have become axiomatic and, at times, have gone unquestioned even when modern empirical data do not conform to this model. This article reviews the origins and history of these ideas and uses modern data to highlight the current and growing controversy surrounding the validity and general applicability of this paradigm.
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16
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Gladieux P, Ropars J, Badouin H, Branca A, Aguileta G, Vienne DM, Rodríguez de la Vega RC, Branco S, Giraud T. Fungal evolutionary genomics provides insight into the mechanisms of adaptive divergence in eukaryotes. Mol Ecol 2014; 23:753-73. [DOI: 10.1111/mec.12631] [Citation(s) in RCA: 151] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Accepted: 12/04/2013] [Indexed: 12/15/2022]
Affiliation(s)
- Pierre Gladieux
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
- Department of Plant and Microbial Biology University of California Berkeley CA 94720‐3102 USA
| | - Jeanne Ropars
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
| | - Hélène Badouin
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
| | - Antoine Branca
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
| | - Gabriela Aguileta
- Center for Genomic Regulation (CRG) Dr, Aiguader 88 Barcelona 08003 Spain
- Universitat Pompeu Fabra (UPF) Barcelona 08003 Spain
| | - Damien M. Vienne
- Center for Genomic Regulation (CRG) Dr, Aiguader 88 Barcelona 08003 Spain
- Universitat Pompeu Fabra (UPF) Barcelona 08003 Spain
- Laboratoire de Biométrie et Biologie Evolutive Université Lyon 1 CNRS UMR5558 Villeurbanne 69622 France
| | - Ricardo C. Rodríguez de la Vega
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
| | - Sara Branco
- Department of Plant and Microbial Biology University of California Berkeley CA 94720‐3102 USA
| | - Tatiana Giraud
- Ecologie, Systématique et Evolution UMR8079 University of Paris‐Sud Orsay 91405 France
- Ecologie, Systématique et Evolution CNRS UMR8079 Orsay 91405 France
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17
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Nieuwenhuis BPS, Aanen DK. Sexual selection in fungi. J Evol Biol 2013; 25:2397-411. [PMID: 23163326 DOI: 10.1111/jeb.12017] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2012] [Revised: 09/07/2012] [Accepted: 09/07/2012] [Indexed: 12/14/2022]
Abstract
The significance of sexual selection, the component of natural selection associated with variation in mating success, is well established for the evolution of animals and plants, but not for the evolution of fungi. Even though fungi do not have separate sexes, most filamentous fungi mate in a hermaphroditic fashion, with distinct sex roles, that is, investment in large gametes (female role) and fertilization by other small gametes (male role). Fungi compete to fertilize, analogous to 'male-male' competition, whereas they can be selective when being fertilized, analogous to female choice. Mating types, which determine genetic compatibility among fungal gametes, are important for sexual selection in two respects. First, genes at the mating-type loci regulate different aspects of mating and thus can be subject to sexual selection. Second, for sexual selection, not only the two sexes (or sex roles) but also the mating types can form the classes, the members of which compete for access to members of the other class. This is significant if mating-type gene products are costly, thus signalling genetic quality according to Zahavi's handicap principle. We propose that sexual selection explains various fungal characteristics such as the observed high redundancy of pheromones at the B mating-type locus of Agaricomycotina, the occurrence of multiple types of spores in Ascomycotina or the strong pheromone signalling in yeasts. Furthermore, we argue that fungi are good model systems to experimentally study fundamental aspects of sexual selection, due to their fast generation times and high diversity of life cycles and mating systems.
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Affiliation(s)
- B P S Nieuwenhuis
- Laboratory of Genetics, Wageningen University, Wageningen, The Netherlands.
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18
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Reding LP, Swaddle JP, Murphy HA. Sexual selection hinders adaptation in experimental populations of yeast. Biol Lett 2013; 9:20121202. [PMID: 23485874 DOI: 10.1098/rsbl.2012.1202] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sexual selection, the suite of processes that lead to differential mating success among individuals, probably influences the evolutionary trajectory of populations. Because sexual selection often shifts traits away from their survival optima, strong sexual selection pressures are thought to increase potential for population extinction, especially during environmental change. Sexual selection pressures may also increase the opportunity for speciation by accelerating the generation of pre-zygotic isolation among populations. These relationships remain largely untested experimentally. Here, we allow populations of baker's yeast, Saccharomyces cerevisiae, to evolve for approximately 250 generations with altered sex ratios in order to test the effect of the strength of sexual selection on the fate of populations. We find that populations experiencing stronger sexual selection are less able to adapt to a novel environment compared with populations experiencing weaker sexual selection or no sex, and that strong sexual selection erases the benefits of sexual reproduction. This pattern persists when fitness is assayed in a closely related environment. We also identify a trend that may suggest the beginning of pre-zygotic isolation between populations experiencing stronger sexual selection, though this is not statistically significant. These results highlight the importance of sexual selection in shaping macroevolutionary patterns and biodiversity.
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Affiliation(s)
- L P Reding
- Department of Biology, College of William and Mary, , Williamsburg, VA 23187, USA
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19
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Nygren K, Wallberg A, Samils N, Stajich JE, Townsend JP, Karlsson M, Johannesson H. Analyses of expressed sequence tags in Neurospora reveal rapid evolution of genes associated with the early stages of sexual reproduction in fungi. BMC Evol Biol 2012. [PMID: 23186325 PMCID: PMC3571971 DOI: 10.1186/1471-2148-12-229] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Background The broadly accepted pattern of rapid evolution of reproductive genes is primarily based on studies of animal systems, although several examples of rapidly evolving genes involved in reproduction are found in diverse additional taxa. In fungi, genes involved in mate recognition have been found to evolve rapidly. However, the examples are too few to draw conclusions on a genome scale. Results In this study, we performed microarray hybridizations between RNA from sexual and vegetative tissues of two strains of the heterothallic (self-sterile) filamentous ascomycete Neurospora intermedia, to identify a set of sex-associated genes in this species. We aligned Expressed Sequence Tags (ESTs) from sexual and vegetative tissue of N. intermedia to orthologs from three closely related species: N. crassa, N. discreta and N. tetrasperma. The resulting four-species alignments provided a dataset for molecular evolutionary analyses. Our results confirm a general pattern of rapid evolution of fungal sex-associated genes, compared to control genes with constitutive expression or a high relative expression during vegetative growth. Among the rapidly evolving sex-associated genes, we identified candidates that could be of importance for mating or fruiting-body development. Analyses of five of these candidate genes from additional species of heterothallic Neurospora revealed that three of them evolve under positive selection. Conclusions Taken together, our study represents a novel finding of a genome-wide pattern of rapid evolution of sex-associated genes in the fungal kingdom, and provides a list of candidate genes important for reproductive isolation in Neurospora.
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Affiliation(s)
- Kristiina Nygren
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 D, SE-752 36, Uppsala, Sweden
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20
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21
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Kawecki TJ, Lenski RE, Ebert D, Hollis B, Olivieri I, Whitlock MC. Experimental evolution. Trends Ecol Evol 2012; 27:547-60. [PMID: 22819306 DOI: 10.1016/j.tree.2012.06.001] [Citation(s) in RCA: 477] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2012] [Revised: 06/03/2012] [Accepted: 06/13/2012] [Indexed: 12/26/2022]
Abstract
Experimental evolution is the study of evolutionary processes occurring in experimental populations in response to conditions imposed by the experimenter. This research approach is increasingly used to study adaptation, estimate evolutionary parameters, and test diverse evolutionary hypotheses. Long applied in vaccine development, experimental evolution also finds new applications in biotechnology. Recent technological developments provide a path towards detailed understanding of the genomic and molecular basis of experimental evolutionary change, while new findings raise new questions that can be addressed with this approach. However, experimental evolution has important limitations, and the interpretation of results is subject to caveats resulting from small population sizes, limited timescales, the simplified nature of laboratory environments, and, in some cases, the potential to misinterpret the selective forces and other processes at work.
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Affiliation(s)
- Tadeusz J Kawecki
- Department of Ecology and Evolution, University of Lausanne, CH 1015 Lausanne, Switzerland.
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22
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Rogers DW, McConnell E, Greig D. Molecular quantification of Saccharomyces cerevisiae α-pheromone secretion. FEMS Yeast Res 2012; 12:668-74. [PMID: 22672638 DOI: 10.1111/j.1567-1364.2012.00817.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 05/29/2012] [Accepted: 05/31/2012] [Indexed: 11/29/2022] Open
Abstract
Saccharomyces cerevisiae yeast cells court each other by producing an attractive sex pheromone specific to their mating type. Cells detect the sex pheromone from potential mates using a well-defined intracellular signalling cascade that has become a model for studying signal transduction. In contrast, the factors contributing to the production of pheromone itself are poorly characterized, despite the widespread use of the S. cerevisiae α-pheromone secretion pathway in industrial fungal protein expression systems. Progress in understanding pheromone secretion has been hindered by a lack of a precise and quantitative pheromone production assay. Here, we present an ELISA-based method for the quantification of α-pheromone secretion. In the absence of pheromone from the opposite mating type, we found that each cell secretes over 550 mature α-pheromone peptides per second; 90% of this total was produced from MF α1. The addition of a-pheromone more than doubled total α-pheromone secretion. This technique offers several improvements on current methods for measuring α-pheromone production and will allow detailed investigation of the factors regulating pheromone production in yeast.
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Affiliation(s)
- David W Rogers
- Max Planck Institute for Evolutionary Biology, Plön, Germany.
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23
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Tazzyman SJ, Seymour RM, Pomiankowski A, Greig D. Mate choice among yeast gametes can purge deleterious mutations. J Evol Biol 2012; 25:1463-71. [PMID: 22594920 DOI: 10.1111/j.1420-9101.2012.02539.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Meiosis in Saccharomyces yeast produces four haploid gametes that usually fuse with each other, an extreme form of self-fertilization among the products of a single meiosis known as automixis. The gametes signal to each other with sex pheromone. Better-quality gametes produce stronger signals and are preferred as mates. We suggest that the function of this signalling system is to enable mate choice among the four gametes from a single meiosis and so to promote the clearance of deleterious mutations. To support this claim, we construct a mathematical model that shows that signalling during automixis (i) improves the long-term fitness of a yeast colony and (ii) lowers its mutational load. We also show that the benefit to signalling is greater with larger numbers of segregating mutations.
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Affiliation(s)
- S J Tazzyman
- CoMPLEX, University College London, Gower St., London, UK.
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24
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Sefc KM. Mating and Parental Care in Lake Tanganyika's Cichlids. INTERNATIONAL JOURNAL OF EVOLUTIONARY BIOLOGY 2011; 2011:470875. [PMID: 21822482 PMCID: PMC3142683 DOI: 10.4061/2011/470875] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 12/30/2010] [Revised: 03/22/2011] [Accepted: 05/02/2011] [Indexed: 11/20/2022]
Abstract
Cichlid fishes of Lake Tanganyika display a variety of mating and parental care behaviors, including polygamous and monogamous mouthbrooding and substrate breeding, cooperative breeding, as well as various alternative reproductive tactics such as sneaking and piracy. Moreover, reproductive behaviors sometimes vary within species both in space and in time. Here, I survey reports on mating and parenting behaviors of Lake Tanganyika cichlid species and address the evolution of mating and parental care patterns and sexual dimorphism. Notes on measures of sexual selection intensity and the difficulties of defining mating systems and estimating selection intensities at species level conclude the essay.
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Affiliation(s)
- Kristina M. Sefc
- Department of Zoology, Karl-Franzens University Graz, Universitätsplatz 2, 8010 Graz, Austria
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25
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Hollis B, Houle D. Populations with elevated mutation load do not benefit from the operation of sexual selection. J Evol Biol 2011; 24:1918-26. [PMID: 21658188 DOI: 10.1111/j.1420-9101.2011.02323.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Theory predicts that if most mutations are deleterious to both overall fitness and condition-dependent traits affecting mating success, sexual selection will purge mutation load and increase nonsexual fitness. We explored this possibility with populations of mutagenized Drosophila melanogaster exhibiting elevated levels of deleterious variation and evolving in the presence or absence of male-male competition and female choice. After 60 generations of experimental evolution, monogamous populations exhibited higher total reproductive output than polygamous populations. Parental environment also affected fitness measures - flies that evolved in the presence of sexual conflict showed reduced nonsexual fitness when their parents experienced a polygamous environment, indicating trans-generational effects of male harassment and highlighting the importance of a common garden design. This cost of parental promiscuity was nearly absent in monogamous lines, providing evidence for the evolution of reduced sexual antagonism. There was no overall difference in egg-to-adult viability between selection regimes. If mutation load was reduced by the action of sexual selection in this experiment, the resultant gain in fitness was not sufficient to overcome the costs of sexual antagonism.
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Affiliation(s)
- B Hollis
- Department of Biological Science, Florida State University, Tallahassee, FL, USA.
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26
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Abstract
The handicap principle holds that costly sexual signals can reliably indicate mate quality. Only individuals of high quality can afford a strong signal--the cost of signaling is relatively lower for high-quality signalers than for low-quality signalers. This critical property is difficult to test experimentally because the benefit of signaling on mating success, and cost of signaling on other components of fitness, cannot easily be separated in obligate sexual organisms. We therefore studied the facultatively sexual yeast Saccharomyces cerevisiae, which produces pheromones to attract potential mates. To precisely measure the cost of signaling, the signal was reduced or removed by deleting one or both copies of the pheromone-encoding genes and measuring asexual growth rate in competition with a wild-type signaler. We manipulated signaler quality either by changing the quality of the assay environment or by changing the number of deleterious mutations carried. For both types of treatment, we found that the cost of signaling decreased as the quality of the signaler increased, demonstrating that the yeast pheromone signal has the key property required for selection under the handicap principle. We found that cells of high genetic quality produce stronger signals than low-quality cells, verifying that the signal is indeed honest.
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Affiliation(s)
- Carl Smith
- The Galton Laboratory, Research Department of Genetics, Evolution, and Environment, University College London, 4 Stephenson Way, London NW1 2HE, United Kingdom
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27
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From preferred to actual mate characteristics: the case of human body shape. PLoS One 2010; 5:e13010. [PMID: 20885953 PMCID: PMC2946385 DOI: 10.1371/journal.pone.0013010] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Accepted: 08/31/2010] [Indexed: 11/25/2022] Open
Abstract
The way individuals pair to produce reproductive units is a major factor determining evolution. This process is complex because it is determined not only by individual mating preferences, but also by numerous other factors such as competition between mates. Consequently, preferred and actual characteristics of mates obtained should differ, but this has rarely been addressed. We simultaneously measured mating preferences for stature, body mass, and body mass index, and recorded corresponding actual partner's characteristics for 116 human couples from France. Results show that preferred and actual partner's characteristics differ for male judges, but not for females. In addition, while the correlation between all preferred and actual partner's characteristics appeared to be weak for female judges, it was strong for males: while men prefer women slimmer than their actual partner, those who prefer the slimmest women also have partners who are slimmer than average. This study therefore suggests that the influences of preferences on pair formation can be sex-specific. It also illustrates that this process can lead to unexpected results on the real influences of mating preferences: traits considered as highly influencing attractiveness do not necessarily have a strong influence on the actual pairing, the reverse being also possible.
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Abstract
We expect that sexual selection may play an important role in the evolution of mushroom-forming basidiomycete fungi. Although these fungi do not have separate sexes, they do play female and male roles: the acceptance and the donation of a nucleus, respectively. The primary mycelium (monokaryon) of basidiomycete fungi, growing from a germinating sexual spore, is hermaphroditic, but it loses female function upon the acceptance of a second nucleus. The resulting dikaryon with two different nuclei in each cell retains a male potential as both nuclei can fertilize receptive mycelia. We tested the occurrence of sexual selection in the model species of mushroom-forming basidiomycetes, Schizophyllum commune, by pairing monokaryons with fully compatible dikaryons. In most pairings, we found a strong bias for one of the two nuclei although both were compatible with the monokaryon when paired alone. This shows that sexual selection can occur in mushroom-forming basidiomycetes. Since the winning nucleus of a dikaryon occasionally varied depending on the receiving monokaryon, we infer that sexual selection can operate through choosiness of the receiving individual (analogous to female choice). However, in other cases the same nucleus won, irrespective of the receiving monokaryon, suggesting that competition between the two nuclei of the donating mycelium (analogous to male–male competition) might also play a role.
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31
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Kassen R. Toward a general theory of adaptive radiation: insights from microbial experimental evolution. Ann N Y Acad Sci 2009; 1168:3-22. [PMID: 19566701 DOI: 10.1111/j.1749-6632.2009.04574.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The history of life has been punctuated by unusually spectacular periods of evolutionary diversification called adaptive radiation. Darwin's finches in the Galapagos, cichlid fishes in African Rift and Nicaraguan crater lakes, and the emergence of mammals at the end of the Cretaceous are hallmark examples. Although we have learned much from these and other case studies about the mechanisms thought to drive adaptive radiations, convincing experimental tests of theory are often lacking for the simple reason that it is usually impossible to "rewind the tape of life," as Stephen Jay Gould was fond of saying, and run it again. This situation has changed dramatically in recent years with the increasing emphasis on the use of microbial populations which, because of their small size and rapid generation times, make possible the construction of replicated, manipulative experiments to study evolution in the laboratory. Here I review the contributions that microbial experimental evolution has made to our understanding of the ecological and genetic mechanisms underlying adaptive radiation. I focus on three major gaps in the theory of adaptive radiation--the paucity of direct tests of mechanism, the genetics of diversification, and the limits and constraints on the progress of radiations--with the aim of pointing the way toward the development of a more general theory of adaptive radiation.
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Affiliation(s)
- Rees Kassen
- Department of Biology and Center for Advanced Research in Environmental Genomics, University of Ottawa, Ottawa, Ontario, Canada.
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32
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Current awareness on yeast. Yeast 2009. [DOI: 10.1002/yea.1622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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33
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Yeast reveals sexual selection in action. Nature 2008. [DOI: 10.1038/news.2008.1168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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