Evolution in eternal triangles: a dynamic landscape for driving rapid changes in reproduction
Lead Research Organisation:
University of East Anglia
Department Name: Biological Sciences
Abstract
The interplay between males and females over reproduction can ultimately lead to the evolution of spectacular diversity in reproductive behaviour, morphology and physiology. This can range from the stunning peacock's tail to elaborate and bizzare penis morphology. The interactions are particularly strong when females mate with multiple males (polyandry) and when there is internal fertilization and sperm storage for long periods within females. This is because there are then frequent, intense and continuing competitions between males for matings and for fertilizations even after matings have occurred.
In the last few decades it has been realized that interactions between females and males can often be antagonistic rather than co-operative. This 'sexual conflict' occurs because each sex can increase their reproductive success in a way that can result in the expression of costs in the other sex. It is often the case, for example, that males but not females increase their reproductive success through increasing their mating frequency.
When this happens, changes in one sex lead to counter changes in the other, as in an arms race. This continual back and forth between males and females, otherwise known as 'antagonistic coevolution', is a widespread and potent force for driving evolutionary change. Because its effects are focussed on changes to reproductive genes it can lead to reproductive incompatibilities. This can then lead to the creation of new species.
Therefore, sexual conflict is important because it represents a potent and eternal fuel for generating biodiversity through increasing variation in genes and ultimately the number of species.
Sexual conflict should be particularly strong when relatively minor differences in phenomena such as how often to mate result in large effects on the reproductive success of males in comparison to females. This will be particularly intense in the typical situation in which more than one male is involved in a reproductive bout with a single female (the 'eternal triangle' where one females mates with two or more males in series). Hence there can often be three- (or more) way 'disagreements' about reproductive decisions such as how often to mate, since the interests of the two males are served by very different outcomes. For example, the first male to mate would benefit if females never mated again.
Although we currently have predictions, we lack actual measurements of the extent of these evolutionary disagreements and we also lack any understanding of the underlying mechanisms. This is therefore an important gap to fill.
Our first aim is therefore to work with the fruitfly and measure for the first time the magnitude of disagreements in (i) normal flies and (ii) in those in which the 'sex peptide (SP)' pathway - which we know mediates sexual conflict - has been manipulated in both sexes. We will use natural and engineered versions of SP pathway genes, to fully pin down their causal effects.
Our supporting background work shows that in principle this is a valid and promising way to proceed. Our work provides proof of principle (a) that there are differences in reproductive success for normal males and females within eternal triangles, and (b) that inactivation of sex peptide receptor (SPR) in females significantly alters the patterns seen, party through changes in how the sperm of different males are stored and used for fertilisation. The latter could increase the chance of reproductive failure for males. Our second aim is therefore to test how sexual conflict within the eternal triangle could lead to reproductive isolation via a break down in competitions between sperm.
Overall, the research work will show the extent, basis and significance of evolutionary disagreements over reproductive decisions in males and females that can drive evolutionary change, and their potential contribution to reproductive isolation and the generation of biodiversity.
In the last few decades it has been realized that interactions between females and males can often be antagonistic rather than co-operative. This 'sexual conflict' occurs because each sex can increase their reproductive success in a way that can result in the expression of costs in the other sex. It is often the case, for example, that males but not females increase their reproductive success through increasing their mating frequency.
When this happens, changes in one sex lead to counter changes in the other, as in an arms race. This continual back and forth between males and females, otherwise known as 'antagonistic coevolution', is a widespread and potent force for driving evolutionary change. Because its effects are focussed on changes to reproductive genes it can lead to reproductive incompatibilities. This can then lead to the creation of new species.
Therefore, sexual conflict is important because it represents a potent and eternal fuel for generating biodiversity through increasing variation in genes and ultimately the number of species.
Sexual conflict should be particularly strong when relatively minor differences in phenomena such as how often to mate result in large effects on the reproductive success of males in comparison to females. This will be particularly intense in the typical situation in which more than one male is involved in a reproductive bout with a single female (the 'eternal triangle' where one females mates with two or more males in series). Hence there can often be three- (or more) way 'disagreements' about reproductive decisions such as how often to mate, since the interests of the two males are served by very different outcomes. For example, the first male to mate would benefit if females never mated again.
Although we currently have predictions, we lack actual measurements of the extent of these evolutionary disagreements and we also lack any understanding of the underlying mechanisms. This is therefore an important gap to fill.
Our first aim is therefore to work with the fruitfly and measure for the first time the magnitude of disagreements in (i) normal flies and (ii) in those in which the 'sex peptide (SP)' pathway - which we know mediates sexual conflict - has been manipulated in both sexes. We will use natural and engineered versions of SP pathway genes, to fully pin down their causal effects.
Our supporting background work shows that in principle this is a valid and promising way to proceed. Our work provides proof of principle (a) that there are differences in reproductive success for normal males and females within eternal triangles, and (b) that inactivation of sex peptide receptor (SPR) in females significantly alters the patterns seen, party through changes in how the sperm of different males are stored and used for fertilisation. The latter could increase the chance of reproductive failure for males. Our second aim is therefore to test how sexual conflict within the eternal triangle could lead to reproductive isolation via a break down in competitions between sperm.
Overall, the research work will show the extent, basis and significance of evolutionary disagreements over reproductive decisions in males and females that can drive evolutionary change, and their potential contribution to reproductive isolation and the generation of biodiversity.
Planned Impact
The School of Biological Sciences at UEA is committed to raising the economic and societal impact of its research (for further details, see Pathways to Impact).
1. WHO WILL BENEFIT FROM THIS RESEARCH
We anticipate 4 main areas for potential impact:
(i) The battle of the sexes. The interplay between males and females is powerful in evolutionary terms. Such interactions can be mutualistic, with both males and females benefitting, or selfish, with one sex benefitting at the expense of the other. There is intuitive and public appeal in the study of adaptations that are good for males and bad for females, and vice versa.
(ii) Husbandry practices for insect control: There is an applied context of this research in terms of increasing the reproductive performance of insect pests that are mass reared for control.
(iii) Communication between signals and receivers: The way in which signals are generated and received or misunderstood is a topic of broad importance and also of public interest.
(iv) Sperm competition dynamics: The proposed work aims to examine the dynamics of the sperm in storage inside females using 'glow in the dark' sperm. These provide visually arresting images that we have already used on public visit days.
The main beneficiaries with whom we aim to maximise the impacts of the research above are:
1. Academia: we aim to maximise impact of the research described above through open access papers, reviews, commentaries, lab research web sites etc. For this project, we plan a research blog to which the research team and particularly the PDRA would contribute.
2. Private sector: we aim to investigate the potential for conflicts of interest to impact upon husbandry and rearing regimes of insects used for pest control. For instance, sexual conflicts that can disrupt the normal fertility patterns for males are of obvious concern if the aim is to breed maximally fertile pest insects for release in sterile insect programmes. We are already developing in the private sector the application of knowledge to fruitfly pests in a NERC-funded CASE studentship together with Oxford insect technologies (Oxitec). We plan to further increase impact by attending the next Fruit flies of Economic Importance conference in 2014 (in Bangkok, Thailand) and offer a talk (TC) and poster (DS) outlining fundamental principles of relevance to control, drawn from the non pest fruitfly model systems.
3. General public, schools: We have recently devised new exhibition materials for open days and visit days at UEA. We also aim to develop these materials following 'road testing', for the SET for success exhibition at the Royal Society in the summer of 2013. We are also developing teaching resources for use in the Teacher Scientist Network (TSN) scheme. Together with our engagement Director in the School, we are tailoring these resources to the National Science Curriculum, for taking into schools via the TSN. We plan to base these around the concepts of 'the eternal love (or not) triangle' and to utilize the visual impact of the 'glow in the dark' fluorescent sperm.
2. HOW WILL THEY BENEFIT FROM THIS RESEARCH
The beneficiaries named above will benefit through:
(i). Increased economic competitiveness of UK plc through increased visibility of research outputs and increased engagement with the private sector.
(ii). The impacts are likely to be primarily of academic and public interest. Here the beneficiaries will gain through enhanced effectiveness in the transmission of research findings.
(iii). Increased learning and awareness (through school visits) of the opportunities, relevance and range career choices available through academia.
(iv). An increased range of career options (DS) through training in media, communication, business and private sector practices, which could be employed in a range of employment sectors.
1. WHO WILL BENEFIT FROM THIS RESEARCH
We anticipate 4 main areas for potential impact:
(i) The battle of the sexes. The interplay between males and females is powerful in evolutionary terms. Such interactions can be mutualistic, with both males and females benefitting, or selfish, with one sex benefitting at the expense of the other. There is intuitive and public appeal in the study of adaptations that are good for males and bad for females, and vice versa.
(ii) Husbandry practices for insect control: There is an applied context of this research in terms of increasing the reproductive performance of insect pests that are mass reared for control.
(iii) Communication between signals and receivers: The way in which signals are generated and received or misunderstood is a topic of broad importance and also of public interest.
(iv) Sperm competition dynamics: The proposed work aims to examine the dynamics of the sperm in storage inside females using 'glow in the dark' sperm. These provide visually arresting images that we have already used on public visit days.
The main beneficiaries with whom we aim to maximise the impacts of the research above are:
1. Academia: we aim to maximise impact of the research described above through open access papers, reviews, commentaries, lab research web sites etc. For this project, we plan a research blog to which the research team and particularly the PDRA would contribute.
2. Private sector: we aim to investigate the potential for conflicts of interest to impact upon husbandry and rearing regimes of insects used for pest control. For instance, sexual conflicts that can disrupt the normal fertility patterns for males are of obvious concern if the aim is to breed maximally fertile pest insects for release in sterile insect programmes. We are already developing in the private sector the application of knowledge to fruitfly pests in a NERC-funded CASE studentship together with Oxford insect technologies (Oxitec). We plan to further increase impact by attending the next Fruit flies of Economic Importance conference in 2014 (in Bangkok, Thailand) and offer a talk (TC) and poster (DS) outlining fundamental principles of relevance to control, drawn from the non pest fruitfly model systems.
3. General public, schools: We have recently devised new exhibition materials for open days and visit days at UEA. We also aim to develop these materials following 'road testing', for the SET for success exhibition at the Royal Society in the summer of 2013. We are also developing teaching resources for use in the Teacher Scientist Network (TSN) scheme. Together with our engagement Director in the School, we are tailoring these resources to the National Science Curriculum, for taking into schools via the TSN. We plan to base these around the concepts of 'the eternal love (or not) triangle' and to utilize the visual impact of the 'glow in the dark' fluorescent sperm.
2. HOW WILL THEY BENEFIT FROM THIS RESEARCH
The beneficiaries named above will benefit through:
(i). Increased economic competitiveness of UK plc through increased visibility of research outputs and increased engagement with the private sector.
(ii). The impacts are likely to be primarily of academic and public interest. Here the beneficiaries will gain through enhanced effectiveness in the transmission of research findings.
(iii). Increased learning and awareness (through school visits) of the opportunities, relevance and range career choices available through academia.
(iv). An increased range of career options (DS) through training in media, communication, business and private sector practices, which could be employed in a range of employment sectors.
Publications
Bretman A
(2016)
Effect of competitive cues on reproductive morphology and behavioral plasticity in male fruitflies.
in Behavioral ecology : official journal of the International Society for Behavioral Ecology
Bretman A
(2017)
The role of species-specific sensory cues in male responses to mating rivals in Drosophila melanogaster fruitflies.
in Ecology and evolution
Godwin JL
(2017)
Experimental evolution reveals that sperm competition intensity selects for longer, more costly sperm.
in Evolution letters
Edward DA
(2014)
Sexual conflict and interacting phenotypes: a quantitative genetic analysis of fecundity and copula duration in Drosophila melanogaster.
in Evolution; international journal of organic evolution
Fricke C
(2014)
MicroRNAs influence reproductive responses by females to male sex peptide in Drosophila melanogaster.
in Genetics
Fricke C
(2017)
Variation in the post-mating fitness landscape in fruit flies.
in Journal of evolutionary biology
Morimoto J
(2019)
Sex peptide receptor-regulated polyandry modulates the balance of pre- and post-copulatory sexual selection in Drosophila.
in Nature communications
Mohorianu I
(2017)
Comparison of alternative approaches for analysing multi-level RNA-seq data.
in PloS one
Fowler EK
(2018)
Small RNA populations revealed by blocking rRNA fragments in Drosophila melanogaster reproductive tissues.
in PloS one
Brockhurst MA
(2014)
Running with the Red Queen: the role of biotic conflicts in evolution.
in Proceedings. Biological sciences
| Description | The interplay between males and females over reproduction can ultimately lead to the evolution of spectacular diversity in reproductive behaviour, morphology and physiology. In the last few decades it has been realized that interactions between females and males can often be antagonistic rather than co-operative. This 'sexual conflict' occurs because each sex can increase their reproductive success in a way that can result in the expression of costs in the other sex. When this happens, changes in one sex lead to counter changes in the other, as in an arms race. This continual back and forth between males and females is a widespread and potent force for driving evolutionary change. So far theory and empirical studies have tended to focus on thinking of sexual conflict as a two way interaction between a male and a female. However this ignores the typical situation in which more than one male may be involved in a reproductive bout with a single female (the 'eternal triangle' where one females mates with two or more males in series). Hence there can often be three- (or more) way disagreements' about reproductive decisions such as how often to mate, since the interests of the two males are served by very different outcomes. Our aims are to measure for the first time the magnitude of disagreements in (i) normal flies and (ii) in those in which the 'sex peptide (SP)' pathway - which we know mediates sexual conflict - has been manipulated in both sexes. Our second aim is to test how sexual conflict within the eternal triangle could lead to reproductive isolation via a break down in competitions between sperm. Prior to starting the project, our background data showed that: (a) that there are differences in reproductive success for normal males and females within eternal triangles, and (b) that inactivation of sex peptide receptor (SPR) in females significantly alters the patterns seen, party through changes in how the sperm of different males are stored and used for fertilisation. These data are important and showed that conflict of interest between players in mating traingles could be reduced by elimination of the sex peptide pathway. So far since October 2012 when the project started, we have analysed further data on manipulations of the interests of all parties in eternal triangles. These interesting findings are broadly consistent with our earlier results and we have now published these data. We have also realised that it is important to understand which sex peptide alleles we have in our wild type populations and so we have also screened those. We linked up with Professor Scott Pitnick's laboratory in Syracuse University to obtain lines of flies with either green or red fluorescing sperm for our sperm competition experiments. Overall, the research work revealed the extent, basis and significance of evolutionary disagreements over reproductive decisions in males and females that can drive evolutionary change, and their potential contribution to reproductive isolation and the generation of biodiversity. The foillowing will be a key output arising from this research: Smith DT*, Mohorianu I*, Fowler EK*, Xu P, Dalmay T & Chapman T. Temporal regulation of post mating responses by mRNAs and sRNAs in female fruitflies. For imminent submission to Genetics. |
| Exploitation Route | The way in which signals are generated and received or misunderstood is a topic of broad importance and also of public interest. The proposed work also aims to examine the dynamics of the sperm in storage inside females using 'glow in the dark' sperm. These provide visually arresting images that we have been using on public visit days. We have also developed teaching resources around the concepts of 'the eternal love triangle' and by utilizing the visual impact of the 'glow in the dark' fluorescent sperm. There is potential to use the findings of this research to explore the development of husbandry practices for insect control - to increase the reproductive performance of insect pests that are mass reared for control. For instance, sexual conflicts that can disrupt the normal fertility patterns for males are of obvious concern if the aim is to breed maximally fertile pest insects for release in sterile insect programmes. We are already developing in the private sector the application of knowledge to fruitfly pests in a NERC-funded CASE studentship together with Oxford insect technologies (Oxitec). |
| Sectors | Agriculture Food and Drink Environment |
| Title | Revealing small RNA populations using blocking oligos |
| Description | We developed a method to use blocking oligonucleotides to soak up abundant ribosomal RNAs that sometime swamp small RNA sequencing libraries. The use of these allows the underlying small RNAs to emerge and to be compared. |
| Type Of Material | Technology assay or reagent |
| Year Produced | 2018 |
| Provided To Others? | Yes |
| Impact | None yet, but we hope that this method may be adopted and will facilitate comparative analysis of small RNAs. |
| Title | Data from: Effect of competitive cues on reproductive morphology and behavioural plasticity in male fruitflies |
| Description | Phenotypic plasticity will be favored whenever there are significant fitness benefits of responding to environmental variation. The extent and nature of the plasticity that evolves depends on the rate of environmental fluctuations and the capacity to track and respond to that variability. Reproductive environments represent one arena in which changes can be rapid. The finding that males of many species show morphological, physiological, and behavioral plasticity in response to premating and postmating reproductive competition (RC) suggests that plasticity is broadly beneficial. The developmental environment is expected to accurately predict the average population level of RC but to be a relatively poor indicator of immediate RC at any particular mating. Therefore, we predict that manipulation of average RC during development should cause a response in plasticity "set" during development (e.g., size of adult reproductive structures), but not in flexible plasticity determined by the immediate adult environment (e.g., behavioral plasticity in mating duration). We tested this prediction in Drosophila melanogaster males by manipulating 2 independent cues of average RC during development: 1) larval density and 2) the presence or absence of adult males within larval culture vials. Consistent with the prediction, both manipulations resulted in the development of males with significantly larger adult accessory glands (although testis size decreased when males were added to culture vials). There was no effect on adult plasticity (mating duration, extended mating in response to rivals). The results suggest that males have evolved independent responses to long- and short-term variation in RC. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2016 |
| Provided To Others? | Yes |
| URL | https://datadryad.org/stash/dataset/doi:10.5061/dryad.c633k |
| Title | Data from: Experimental evolution reveals that sperm competition intensity selects for longer, more costly sperm |
| Description | It is the differences between sperm and eggs that fundamentally underpin the differences between the sexes within reproduction. For males, it is theorized that widespread sperm competition leads to selection for investment in sperm numbers, achieved by minimizing sperm size within limited resources for spermatogenesis in the testis. Here, we empirically examine how sperm competition shapes sperm size, after more than 77 generations of experimental selection of replicate lines under either high or low sperm competition intensities in the promiscuous flour beetle Tribolium castaneum. After this experimental evolution, populations had diverged significantly in their sperm competitiveness, with sperm in ejaculates from males evolving under high sperm competition intensities gaining 20% greater paternity than sperm in ejaculates from males that had evolved under low sperm competition intensity. Males did not change their relative investment into sperm production following this experimental evolution, showing no difference in testis sizes between high and low intensity regimes. However, the more competitive males from high sperm competition intensity regimes had evolved significantly longer sperm and, across six independently selected lines, there was a significant association between the degree of divergence in sperm length and average sperm competitiveness. To determine whether such sperm elongation is costly, we used dietary restriction experiments, and revealed that protein-restricted males produced significantly shorter sperm. Our findings therefore demonstrate that sperm competition intensity can exert positive directional selection on sperm size, despite this being a costly reproductive trait. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| URL | https://datadryad.org/stash/dataset/doi:10.5061/dryad.22rh6 |
| Title | Data from: Sexual conflict over remating interval is modulated by the sex peptide pathway |
| Description | Sexual conflict, in which the evolutionary interests of males and females diverge, shapes the evolution of reproductive systems across diverse taxa. Here, we used the fruit fly to study sexual conflict in natural, three-way interactions comprising a female, her current and previous mates. We manipulated the potential for sexual conflict by using sex peptide receptor (SPR) null females and by varying remating from 3 to 48 h, a period during which natural rematings frequently occur. SPR-lacking females do not respond to sex peptide (SP) transferred during mating and maintain virgin levels of high receptivity and low fecundity. In the absence of SPR, there was a convergence of fitness interests, with all individuals gaining highest productivity at 5 h remating. This suggests that the expression of sexual conflict was reduced. We observed an unexpected second male-specific advantage to early remating, resulting from an increase in the efficiency of second male sperm use. This early window of opportunity for exploitation by second males depended on the presence of SPR. The results suggest that the SP pathway can modulate the expression of sexual conflict in this system, and show how variation in the selective forces that shape conflict and cooperation can be maintained. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| URL | https://datadryad.org/stash/dataset/doi:10.5061/dryad.h5346 |
| Title | Data from: The role of species-specific sensory cues in male responses to mating rivals in Drosophila melanogaster fruitflies |
| Description | Complex sets of cues can be important in recognising and responding to conspecific mating competitors and avoiding potentially costly heterospecific competitive interactions. Within Drosophila. melanogaster, males can detect sensory inputs from conspecifics to assess the level of competition. They respond to rivals by significantly extending mating duration and gain significant fitness benefits from doing so. Here, we tested the idea that the multiple sensory cues used by D. melanogaster males to detect conspecifics also function to minimise 'off-target' responses to heterospecific males that they might encounter (D. simulans, D. yakuba. D. pseudoobscura or D. virilis). Focal D. melanogaster males exposed to D. simulans or D. pseudoobscura subsequently increased mating duration, but to a lesser extent than following exposure to conspecific rivals. The magnitude of rivals responses expressed by D. melanogaster males did not align with genetic distance between species and none of the sensory manipulations caused D. melanogaster to respond to males of all other species tested. However, when we removed or provided 'false' sensory cues, D. melanogaster males became more likely to show increased mating duration responses to heterospecific males. We suggest that benefits of avoiding inaccurate assessment of the competitive environment may shape the evolution of recognition cues. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2018 |
| Provided To Others? | Yes |
| URL | https://datadryad.org/stash/dataset/doi:10.5061/dryad.4vs00 |
| Title | Data from: Variation in the post-mating fitness landscape in fruitflies |
| Description | Sperm competition is pervasive and fundamental to determining a male's overall fitness. Sperm traits and seminal fluid proteins (Sfps) are key factors. However, studies of sperm competition may often exclude females that fail to remate during a defined period. Hence, the resulting datasets contain fewer data from the potentially fittest males that have most success in preventing female remating. It is also important to consider a male's reproductive success before entering sperm competition, which is a major contributor to fitness. The exclusion of these data can both hinder our understanding of the complete fitness landscapes of competing males and lessen our ability to assess the contribution of different determinants of reproductive success to male fitness. We addressed this here, using the Drosophila melanogaster model system, by (i) capturing a comprehensive range of intermating intervals that define the fitness of interacting wild type males, and (ii) analysing outcomes of sperm competition using selection analyses. We conducted additional tests using males lacking the sex peptide (SP) ejaculate component versus genetically matched (SP+) controls. This allowed us to assess the comprehensive fitness effects of this important Sfp on sperm competition. The results showed a signature of positive, linear selection in wild type and SP+ control males on the length of the intermating interval and on male sperm competition defense. However, the fitness surface for males lacking SP was distinct, with local fitness peaks depending on contrasting combinations of remating intervals and offspring numbers. The results suggest that there are alternative routes to success in sperm competition and provide an explanation for the maintenance of variation in sperm competition traits. |
| Type Of Material | Database/Collection of data |
| Year Produced | 2017 |
| Provided To Others? | Yes |
| URL | https://datadryad.org/stash/dataset/doi:10.5061/dryad.j2n46 |
| Description | Animation |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Media (as a channel to the public) |
| Results and Impact | Made youtube animation of the research project. |
| Year(s) Of Engagement Activity | 2016 |