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Summary The mechanisms underlying trait conservation over long evolutionary time scales are poorly known. These mechanisms fall into the two broad and nonmutually exclusive categories of constraint and selection. A variety of factors have been hypothesized to constrain trait evolution. Alternatively, selection can maintain similar trait values across many species if the causes of selection are also relatively conserved, while many sources of constraint may be overcome over longer periods of evolutionary divergence. An example of deep trait conservation is tetradynamy in the large family Brassicaceae, where the four medial stamens are longer than the two lateral stamens. Previous work has found selection to maintain this difference in lengths, which we call anther separation, in wild radish,Raphanus raphanistrum.Here, we test the constraint hypothesis using five generations of artificial selection to reduce anther separation in wild radish.We found a rapid linear response to this selection, with no evidence for depletion of genetic variation and correlated responses to this selection in only four of 15 other traits, suggesting a lack of strong constraint.Taken together, available evidence suggests that tetradynamy is likely to be conserved due to selection, but the function of this trait remains unclear.
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Can disease resistance evolve independently at different ages? Genetic variation in age‐dependent resistance to disease in three wild plant species
Abstract Juveniles are typically less resistant (more susceptible) to infectious disease than adults, and this difference in susceptibility can help fuel the spread of pathogens in age‐structured populations. However, evolutionary explanations for this variation in resistance across age remain to be tested.One hypothesis is that natural selection has optimized resistance to peak at ages where disease exposure is greatest. A central assumption of this hypothesis is that hosts have the capacity to evolve resistance independently at different ages. This would mean that host populations have (a) standing genetic variation in resistance at both juvenile and adult stages, and (b) that this variation is not strongly correlated between age classes so that selection acting at one age does not produce a correlated response at the other age.Here we evaluated the capacity of three wild plant species (Silene latifolia,S. vulgarisandDianthus pavonius) to evolve resistance to their anther‐smut pathogens (Microbotryumfungi), independently at different ages. The pathogen is pollinator transmitted, and thus exposure risk is considered to be highest at the adult flowering stage.Within each species we grew families to different ages, inoculated individuals with anther smut, and evaluated the effects of age, family and their interaction on infection.In two of the plant species,S. latifoliaandD. pavonius, resistance to smut at the juvenile stage was not correlated with resistance to smut at the adult stage. In all three species, we show there are significant age × family interaction effects, indicating that age specificity of resistance varies among the plant families.Synthesis. These results indicate that different mechanisms likely underlie resistance at juvenile and adult stages and support the hypothesis that resistance can evolve independently in response to differing selection pressures as hosts age. Taken together our results provide new insight into the structure of genetic variation in age‐dependent resistance in three well‐studied wild host–pathogen systems.
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- Award ID(s):
- 1936334
- PAR ID:
- 10371126
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 110
- Issue:
- 9
- ISSN:
- 0022-0477
- Page Range / eLocation ID:
- p. 2046-2061
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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