Compensatory adaptation and diversification subsequent to evolutionary rescue in a model adaptive radiation.
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ABSTRACT:
SUBMITTER: Zhou DH
PROVIDER: S-EPMC8293784 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The warmer regions harbour more species, attributable to accelerated speciation and increased ecological opportunities for coexistence. While correlations between temperature and energy availability and habitat area have been suggested as major drivers of these biodiversity patterns, temperature can theoretically also have direct effects on the evolution of diversity. Here, we experimentally studied the evolution of diversity in a model adaptive radiation of the bacterium Pseudomonas fluorescens across a temperature gradient. Diversification increased at higher temperatures, driven by both faster generation of genetic variation and stronger diversifying selection. Specifically, low temperatures could limit the generation of diversity, suggested by the observation that supply of genetic variation through immigration increased diversity at low, but not high temperatures. The two major determinants of mutation supply, population size and mutation rate, both showed a positive temperature dependence. Stronger diversifying selection in warmer environments was suggested by promoted coexistence, and further explicitly inferred by the ability of evolved phenotypes to invade the ancestral type from rare. We discuss possible physiological and environmental mechanisms underlying the findings, most of which are likely to be general.
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Project description:BackgroundDiet is a key component of a species ecological niche and plays critical roles in guiding the trajectories of evolutionary change. Previous studies suggest that dietary evolution can influence the rates and patterns of species diversification, with omnivorous (animal and plant, 'generalist') diets slowing down diversification compared to more restricted ('specialist') herbivorous and carnivorous diets. This hypothesis, here termed the "dietary macroevolutionary sink" hypothesis (DMS), predicts that transitions to omnivorous diets occur at higher rates than into any specialist diet, and omnivores are expected to have the lowest diversification rates, causing an evolutionary sink into a single type of diet. However, evidence for the DMS hypothesis remains conflicting. Here, we present the first test of the DMS hypothesis in a lineage of ectothermic tetrapods-the prolific Liolaemidae lizard radiation from South America.ResultsAncestral reconstructions suggest that the stem ancestor was probably insectivorous. The best supported trait model is a diet-dependent speciation rate, with independent extinction rates. Herbivory has the highest net diversification rate, omnivory ranks second, and insectivory has the lowest. The extinction rate is the same for all three diet types and is much lower than the speciation rates. The highest transition rate was from omnivory to insectivory, and the lowest transition rates were between insectivory and herbivory.ConclusionsOur findings challenge the core prediction of the DMS hypothesis that generalist diets represent an 'evolutionary sink'. Interestingly, liolaemid lizards have rapidly and successfully proliferated across some of the world's coldest climates (at high elevations and latitudes), where species have evolved mixed arthropod-plant (omnivore) or predominantly herbivore diets. This longstanding observation is consistent with the higher net diversification rates found in both herbivory and omnivory. Collectively, just like the evolution of viviparity has been regarded as a 'key adaptation' during the liolaemid radiation across cold climates, our findings suggest that transitions from insectivory to herbivory (bridged by omnivory) are likely to have played a role as an additional key adaptation underlying the exceptional diversification of these reptiles across extreme climates.
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Project description:Competitors are known to be important in governing the outcome of evolutionary diversification during an adaptive radiation, but the precise mechanisms by which they exert their effects remain elusive. Using the model adaptive radiation of Pseudomonas fluorescens, we show experimentally that the effect of competition on diversification of a focal lineage depends on both the strength of competition and the ability of the competitors to diversify. We provide evidence that the extent of diversification in the absence of interspecific competitors depends on the strength of resource competition. We also show that the presence of competitors can actually increase diversity by increasing interspecific resource competition. Competitors that themselves are able to diversify prevent diversification of the focal lineage by removing otherwise available ecological opportunities. These results suggest that the progress of an adaptive radiation depends ultimately on the strength of resource competition, an effect that can be exaggerated or impeded by the presence of competitors.
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Project description:(1) Background: Adaptive diversification of complex traits plays a pivotal role in the evolution of organismal diversity. In the freshwater snail genus Tylomelania, adaptive radiations were likely promoted by trophic specialization via diversification of their key foraging organ, the radula. (2) Methods: To investigate the molecular basis of radula diversification and its contribution to lineage divergence, we used tissue-specific transcriptomes of two sympatric Tylomelania sarasinorum ecomorphs. (3) Results: We show that ecomorphs are genetically divergent lineages with habitat-correlated abundances. Sequence divergence and the proportion of highly differentially expressed genes are significantly higher between radula transcriptomes compared to the mantle and foot. However, the same is not true when all differentially expressed genes or only non-synonymous SNPs are considered. Finally, putative homologs of some candidate genes for radula diversification (hh, arx, gbb) were also found to contribute to trophic specialization in cichlids and Darwin's finches. (4) Conclusions: Our results are in line with diversifying selection on the radula driving Tylomelania ecomorph divergence and indicate that some molecular pathways may be especially prone to adaptive diversification, even across phylogenetically distant animal groups.
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Project description:Since deleterious mutations may be rescued by secondary mutations during evolution, compensatory evolution could identify genetic solutions leading to therapeutic targets. Here, we tested this hypothesis and examined whether these solutions would be universal or would need to be adapted to one's genetic and environmental make-ups. We performed experimental evolutionary rescue in a yeast disease model for the Wiskott-Aldrich syndrome in two genetic backgrounds and carbon sources. We found that multiple aspects of the evolutionary rescue outcome depend on the genotype, the environment, or a combination thereof. Specifically, the compensatory mutation rate and type, the molecular rescue mechanism, the genetic target, and the associated fitness cost varied across contexts. The course of compensatory evolution is therefore highly contingent on the initial conditions in which the deleterious mutation occurs. In addition, these results reveal biologically favored therapeutic targets for the Wiskott-Aldrich syndrome, including the target of an unrelated clinically approved drug. Our results experimentally illustrate the importance of epistasis and environmental evolutionary constraints that shape the adaptive landscape and evolutionary rate of molecular networks.
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Project description:"Explosive" adaptive radiations on islands remain one of the most puzzling evolutionary phenomena and the evolutionary genetic processes behind such radiations remain unclear. Rapid morphological and ecological evolution during island radiations suggests that many genes may be under fairly strong selection, although this remains untested. Here, we report that during a rapid recent diversification in the Hawaiian endemic plant genus Schiedea (Caryophyllaceae), 5 in 36 studied genes evolved under positive selection. Positively selected genes are involved in defence mechanisms, photosynthesis, and reproduction. Comparison with eight mainland plant groups demonstrates both the relaxation of purifying selection and more widespread positive selection in Hawaiian Schiedea. This provides compelling evidence that adaptive evolution of protein-coding genes may play a significant role during island adaptive radiations.
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Project description:The causes and mechanisms of evolutionary diversification are central issues in biology. Geographic isolation is the traditional explanation for diversification, but recent theoretical and empirical studies have shown that frequency-dependent selection can drive diversification without isolation and that adaptive diversification occurring in sympatry may be an important source of biological diversity. However, there are no empirical examples in which sympatric lineage splits have been understood at the genetic level, and it is unknown how predictable this process is-that is, whether similar ecological settings lead to parallel evolutionary dynamics of diversification. We documented the genetic basis and the evolutionary dynamics of adaptive diversification in three replicate evolution experiments, in which competition for two carbon sources caused initially isogenic populations of the bacterium Escherichia coli to diversify into two coexisting ecotypes representing different physiological adaptations in the central carbohydrate metabolism. Whole-genome sequencing of clones of each ecotype from different populations revealed many parallel and some unique genetic changes underlying the derived phenotypes, including changes to the same genes and sometimes to the same nucleotide. Timelines of allele frequencies extracted from the frozen "fossil" record of the three evolving populations suggest parallel evolutionary dynamics driven at least in part by a co-evolutionary process in which mutations causing one type of physiology changed the ecological environment, allowing the invasion of mutations causing an alternate physiology. This process closely corresponds to the evolutionary dynamics seen in mathematical models of adaptive diversification due to frequency-dependent ecological interactions. The parallel genetic changes underlying similar phenotypes in independently evolved lineages provide empirical evidence of adaptive diversification as a predictable evolutionary process.
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Project description:The vangas of Madagascar exhibit extreme diversity in morphology and ecology. Recent studies have shown that several other Malagasy species also are part of this endemic radiation, even as the monophyly of the clade remains in question. Using DNA sequences from 13 genes and representatives of all 15 vanga genera, we find strong support for the monophyly of the Malagasy vangids and their inclusion in a family along with six aberrant genera of shrike-like corvoids distributed in Asia and Africa. Biogeographic reconstructions of these lineages include both Asia and Africa as possible dispersal routes to Madagascar. To study patterns of speciation through time, we introduce a method that can accommodate phylogenetically non-random patterns of incomplete taxon sampling in diversification studies. We demonstrate that speciation rates in vangas decreased dramatically through time following the colonization of Madagascar. Foraging strategies of these birds show remarkable congruence with phylogenetic relationships, indicating that adaptations to feeding specializations played a role in the diversification of these birds. Vangas fit the model of an 'adaptive radiation' in that they show an explosive burst of speciation soon after colonization, increased diversification into novel niches and extraordinary ecomorphological diversity.
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