Final Report Summary - BALDWINIAN_BEETLES (The origin of the fittest: canalization, plasticity and selection as a consequence of provisioning during development)
A major outstanding challenge for evolutionary biology is to explain how novel adaptations arise and to account for the evolutionary trajectories by which they diversify.
We addressed this challenge by analysing the importance of parental care in initiating and driving evolutionary change. Most of our work involved experiments with burying beetles (Nicrophorus vespilloides). This insect breeds on small carrion and supplies care to its offspring, but its larvae can survive without the provision of parental care. It also has a relatively short generation time of about 6 weeks and breeds readily in the lab. We exploited burying beetle natural history to determine how parental care contributes to evolutionary change. We found that parents can influence evolution by:
1.Generating phenotypic variation
We manipulated the supply of care during larval development and measured the consequences for larvae, for the rest of their lives. We found that the supply of care changed their morphology and behaviour in adulthood. For example, individuals that received less care were smaller as adults and less good at competing for a carcass breeding resource.
2.Promoting non-genetic inheritance, through parental effects
We found that individuals that were manipulated to receive less care when they were larvae developed into poorer parents, producing smaller offspring but paying a higher fitness cost for doing so. This means that individuals that receive less care as larvae produce offspring that inherit the same qualities non-genetically and become poorer quality parents themselves.
Furthermore, male burying beetles that received less care during development were less effective at sperm competition but more effective at inducing females to lay eggs. Since larvae compete for finite resources on a carcass, females that produce more eggs produce smaller offspring. Thus, smaller males produce smaller offspring non-genetically, simply by inducing the production of more eggs.
3.Facilitating mutualisms
Removing parental care increased the likelihood that the beetles entered into mutualism with a second species. We found that smaller beetles benefited from carrying mites around to a greater degree than larger individuals. This is because the mites warmed up the smaller beetles more, and so improved their chance of winning fights with larger beetles to obtain carrion for breeding.
4.Influencing the direction of evolutionary change
By using artificial selection, we found that increased body size can evolve, but only when parents are allowed to supply care. Likewise, across species, we found that the evolution of larger beetles is associated with the obligate supply of care to larvae. Artificial selection also revealed that a smaller body size can evolve, but only when parents are prevented from supplying care. In general, the experiment showed that parents influence the pace and direction and evolutionary change in body size.
5.Acting as agents of natural selection
In separate work, we established experimental populations in the laboratory. For generation after generation, larvae in these populations were either exposed to post-hatching care (Full Care) or experimentally prevented from receiving any care at all (No Care). Larvae in the No Care populations evolved to become more self-sufficient and less dependent on parental care. They evolved relatively larger mandibles for their body size. They also evolved greater levels of cooperation with their siblings. No Care parents evolved too, by more rapidly preparing a carrion nest for their larvae, and making it more accessible by larvae by biting entry holes before their larvae hatched.
6.Enabling the accumulation of new genetic variants, upon which selection can act.
We found that parental care caused greater levels of (mildly harmful) genetic variation to build up in the Full Care populations than we observed in the No Care populations. Preliminary work suggests that some of this additional genetic variation could be beneficial when individuals encounter a new thermal environment.
We addressed this challenge by analysing the importance of parental care in initiating and driving evolutionary change. Most of our work involved experiments with burying beetles (Nicrophorus vespilloides). This insect breeds on small carrion and supplies care to its offspring, but its larvae can survive without the provision of parental care. It also has a relatively short generation time of about 6 weeks and breeds readily in the lab. We exploited burying beetle natural history to determine how parental care contributes to evolutionary change. We found that parents can influence evolution by:
1.Generating phenotypic variation
We manipulated the supply of care during larval development and measured the consequences for larvae, for the rest of their lives. We found that the supply of care changed their morphology and behaviour in adulthood. For example, individuals that received less care were smaller as adults and less good at competing for a carcass breeding resource.
2.Promoting non-genetic inheritance, through parental effects
We found that individuals that were manipulated to receive less care when they were larvae developed into poorer parents, producing smaller offspring but paying a higher fitness cost for doing so. This means that individuals that receive less care as larvae produce offspring that inherit the same qualities non-genetically and become poorer quality parents themselves.
Furthermore, male burying beetles that received less care during development were less effective at sperm competition but more effective at inducing females to lay eggs. Since larvae compete for finite resources on a carcass, females that produce more eggs produce smaller offspring. Thus, smaller males produce smaller offspring non-genetically, simply by inducing the production of more eggs.
3.Facilitating mutualisms
Removing parental care increased the likelihood that the beetles entered into mutualism with a second species. We found that smaller beetles benefited from carrying mites around to a greater degree than larger individuals. This is because the mites warmed up the smaller beetles more, and so improved their chance of winning fights with larger beetles to obtain carrion for breeding.
4.Influencing the direction of evolutionary change
By using artificial selection, we found that increased body size can evolve, but only when parents are allowed to supply care. Likewise, across species, we found that the evolution of larger beetles is associated with the obligate supply of care to larvae. Artificial selection also revealed that a smaller body size can evolve, but only when parents are prevented from supplying care. In general, the experiment showed that parents influence the pace and direction and evolutionary change in body size.
5.Acting as agents of natural selection
In separate work, we established experimental populations in the laboratory. For generation after generation, larvae in these populations were either exposed to post-hatching care (Full Care) or experimentally prevented from receiving any care at all (No Care). Larvae in the No Care populations evolved to become more self-sufficient and less dependent on parental care. They evolved relatively larger mandibles for their body size. They also evolved greater levels of cooperation with their siblings. No Care parents evolved too, by more rapidly preparing a carrion nest for their larvae, and making it more accessible by larvae by biting entry holes before their larvae hatched.
6.Enabling the accumulation of new genetic variants, upon which selection can act.
We found that parental care caused greater levels of (mildly harmful) genetic variation to build up in the Full Care populations than we observed in the No Care populations. Preliminary work suggests that some of this additional genetic variation could be beneficial when individuals encounter a new thermal environment.