The origin of this clade predates the ages of all known freshwater populations, in most cases by orders of magnitude, suggesting that the original low-armor mutation occurred long ago. We propose that ecological speciation has occurred multiple times in parallel in this group via a “transporter” process in which selection in freshwater environments repeatedly acts on standing genetic variation that is maintained in marine populations by export of freshwater-adapted alleles from elsewhere in the range. Mating success and male courtship behaviors in three populations of the threespine stickleback. 5), alleles from a stream-adapted population are exported to the sea by a hybridization event between individuals from the marine and stream populations. Populations of sticklebacks that evolved under different ecological conditions show strong reproductive isolation, whereas populations that evolved … Genetic structure of the threespine stickleback. and G.L.C. This seasonal difference contributes to strong (although still incomplete) reproductive isolation. Yet, the number of advantageous mutations for a given trait may be restricted, with the result that the same mutations occur and fix repeatedly under parallel selection (39, 40), preventing divergence. We use cookies to help provide and enhance our service and tailor content and ads. In conclusion, core assumptions of sympatric speciation theory seem to be qualitatively reasonable for stickleback, but speciation may nevertheless fail because of (i) quantitative mismatches with theory and (ii) alternative evolutionary outcomes.

Scale: 1 cm. Key Concepts Adaptive diversification and speciation resulting from competition for a broadly distributed resource is thus likely if the niche width is fixed and relatively narrow or free to evolve but subject to costs. However, so far, all genomic reanalyses of classic examples of sympatric speciation indicate secondary gene flow occurred. Copyright © 2020 Elsevier B.V. or its licensors or contributors. It is likely that other traits in freshwater stickleback populations are the result of selection of standing genetic variation brought from the sea. Furthermore, I summarize empirical evidence that disruptive selection in stickleback drives other forms of evolutionary diversification (plasticity, increased trait variance, and sexual dimorphism) instead of speciation. Felsenstein (21) pointed out that in the absence of very strong reproductive isolation between hybridizing populations recombination between genes governing assortative mating and genes under divergent natural selection will cause existing levels of assortative mating between populations to decay and inhibit the evolution of even stronger assortative mating. We present a hypothesis for the repetitive origin of freshwater stickleback species involving natural selection of standing genetic variation. Furthermore, it is unclear if and how speciation-promoting mechanisms such as magic traits, phenotype matching, and physical linkage of coadapted alleles promote rapid bursts of speciation. Theoretical models suggest that resource competition can lead to the adaptive splitting of consumer populations into diverging lineages, that is, to adaptive diversification. Individual marine ecotypes displaying freshwater-adaptive building blocks were discovered at a frequency of less than 2% [7]. Although numerous cases now indicate the importance of ecological speciation in nature, very little is known about the genetics of the process. We acknowledge that the limnetic and benthic habitats in a lake are not discrete and treating them as two distinct habitats is certainly an oversimplification, yet this distinction is a common and fairly reasonable assumption. Here, we summarize the genetics of premating and postzygotic isolation and the role of standing genetic variation in ecological speciation. Today, sticklebacks exist in many different shapes and sizes (fig. Mutations were assumed to be pleiotropic, which means that while they change the population mean for the trait under directional selection in each environment, they have the side-effect of changing the mean in other traits, too. (d) Speciation can occur when disruptive selection and assortment are near the upper end of plausible empirical values (2γ=0.4, r=0.8). Results from this research (formatted as data sheets included in the teaching notes) are provided to students who design experiments and then compare actual data to investigate why benthic and limnetic sticklebacks seldom interbreed in Paxton Lake. 3B). Genome-wide Patterns of Adaptation and Speciation and Demographic Histories of Young Radiations of Cichlids, Divergence and reproductive isolation in the bushcricket Mecopoda elongata, Exploring the origin and maintenance of biodiversity : insights from the bilaterally asymmetrical cichlid fish Perissodus microlepis, Comparing Adaptive Radiations Across Space, Time, and Taxa, Resource diversity promotes among‐individual diet variation, but not genomic diversity, in lake stickleback. Not as many populations have been surveyed as in the case of Eda, but the low-pigmentation alleles present in 3 freshwater populations in British Columbia, Washington state, and California form a monophyletic clade (Fig. One of the most glaring deficiencies is the almost complete absence of information on the genetics of ecological speciation. Because egg isotopes are derived from females, this correlation reflects assortative mating between males and females by diet.

Rundle, H.D. We use cookies to help provide and enhance our service and tailor content and ads. This implies that speciation in Pundamilia used preexisting genetic variation. Haw and apple differ in their peak fruiting times, and accordingly the 2 races have diverged in pupal diapause traits (affecting overwinter dormancy) that also affect their timing of emergence as adults. Interbreeding is reduced when spatial proximity of individuals is required for mating, and when the survival, growth, or reproductive success of immigrant individuals is diminished because their phenotype is less well adapted than the resident population to local conditions. To illustrate, he assumed that divergent selection acted on just a single trait between populations (Fig. Using these powerful replicates of the evolutionary process, research is identifying the common molecular changes underlying adaptation and speciation. The Goldilocks effect of lake size on within-population diversity in stickleback, Evolutionary Implications of Habitat Choice, New criteria for sympatric speciation in the genomic era, Introduction to the evolutionary biology of the threespine stickleback, REINFORCEMENT OF STICKLEBACK MATE PREFERENCES: SYMPATRY BREEDS CONTEMPT, SEXUAL SELECTION AGAINST HYBRIDS BETWEEN SYMPATRIC STICKLEBACK SPECIES: EVIDENCE FROM A FIELD EXPERIMENT, A test of ecological selection against young-of-the-year hybrids of sympatric sticklebacks, Evolution of niche width and adaptive diversification, Evolutionary Branching and Sympatric Speciation Caused by Different Types of Ecological Interactions, Can intraspecific competition drive disruptive selection? In this thesis I show that female phonotaxis to their ‘own’ call has the potential to contribute to behavioural isolation among the song types and in particular between two song types with overlapping temporal call parameters.

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