RAPID EVOLUTION OF REPRODUCTIVE ISOLATION BETWEEN INCIPIENT OUTCROSSING AND SELFING<i>CLARKIA</i>SPECIES

Runquist, Ryan D. Briscoe; Chu, Eric; Iverson, Justin L.; Kopp, Jason C.; Moeller, David A.

doi:10.1111/evo.12488

Cited by 72 publications

(80 citation statements)

References 81 publications

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“…), pollinator preference (Briscoe Runquist et al. ) and constancy (Kennedy et al. ), and extrinsic postzygotic isolation (Melo et al.…”

Section: Resultsmentioning

confidence: 99%

“…Many case studies of RI are conducted across short time spans, yet shifting environmental conditions can affect the relative importance of different pre‐pollination barriers in different years (Briscoe Runquist et al. ; Roccaforte et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…Recent work has sometimes focused on taxa that have diverged extremely recently (e.g., Briscoe Runquist et al. ; Sobel and Streisfeld ; Ostevik et al. ), as young taxa offer the best opportunity to identify factors shaping initial divergence (Sobel et al.…”

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confidence: 99%

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Reproductive isolation and the maintenance of species boundaries in two serpentine endemic Jewelflowers

Christie

Strauss

2019

Evolution

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Speciation occurs when reproductive barriers substantially reduce gene flow between lineages. Understanding how specific barriers contribute to reproductive isolation offers insight into the initial forces driving divergence and the evolutionary and ecological processes responsible for maintaining diversity. Here, we quantified multiple pre‐ and post‐pollination isolating barriers in a pair of closely related California Jewelflowers (Streptanthus, Brassicaceae) living in an area of sympatry. S. breweri and S. hesperidis are restricted to similar serpentine habitats; however, populations are spatially isolated at fine‐scales and rarely co‐occur in intermixed stands. Several intrinsic postzygotic barriers were among the strongest we quantified, yet, postzygotic barriers currently contribute little to overall reproductive isolation due to the cumulative strength of earlier‐acting extrinsic barriers, including spatial isolation, and flowering time and pollinator differences. Data from multiple years suggest that pre‐pollination barriers may have different strengths depending on annual environmental conditions. Similarly, crossing data suggest that the strength of intrinsic isolation may vary among different population pairs. Estimates of total reproductive isolation in S. breweri and S. hesperidis are robust to uncertainty and variability in individual barrier strength estimates, demonstrating how multiple barriers can act redundantly to prevent gene flow between close relatives living in sympatry.

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“…), pollinator preference (Briscoe Runquist et al. ) and constancy (Kennedy et al. ), and extrinsic postzygotic isolation (Melo et al.…”

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Reproductive isolation and the maintenance of species boundaries in two serpentine endemic Jewelflowers

Christie

Strauss

2019

Evolution

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“…Variable levels of attractiveness between selfing and outcrossing species may cause asymmetries in pollinator mediated pollen flow and can result into higher risks of heterospecific pollen deposition in the more selfing species (Briscoe Runquist et al . ; Brys et al . ).…”

Section: Discussionmentioning

confidence: 99%

The importance of autonomous selfing in preventing hybridization in three closely related plant species

2016

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Summary In plants that are able to self‐fertilize, autonomous selfing has been hypothesized to function as an effective mechanism that prevents heterospecific mating. However, there have only been few studies that have assessed the relative and absolute contribution of different modes of selfing to total reproductive isolation acting between species. Because selfing can be expected to increase fitness costs when offspring are sired from more outcrossing sister taxa, it can be hypothesized that the contribution of post‐zygotic barriers to total reproductive isolation becomes stronger in selfing than in more outcrossing relatives. To assess the efficiency of different modes of selfing against heterospecific mating, we conducted mixed‐pollination experiments in three Centaurium species showing strong differences in mating system (i.e. delayed selfing in Centaurium erythraea, competing selfing in C. littorale and prior selfing in C. pulchellum). The contribution of selfing to total reproductive isolation was further examined by quantifying the strength of three pre‐zygotic (flowering phenology, pollinator fidelity and pollen production) and four intrinsic post‐zygotic (seed set and germination, survival and flowering capacity) barriers for each of the six species pair combinations. Although autonomous selfing as a reproductive barrier was unable to completely impede gene flow, its efficiency as a mechanism to prevents heterospecific pollination strongly depended on the mode of selfing, with prior selfing being by far the most efficient mechanism and delayed selfing only offering a limited protection against hybrid fertilization at the end of a flower's lifetime. Apart from the prevention effect of selfing, differences in pollinator fidelity and pollen production also contributed substantially to total reproductive isolation. Post‐zygotic hybrid costs were high and most prevalent for seed production and germination success. Reductions in hybrid vigour were significantly associated with the mating system of the maternal species, with the highest reductions in the most selfing C. pulchellum and the lowest reductions in predominant outcrossing C. erythraea. Synthesis. Our findings indicate that selfing may prevent species from interspecific gene flow and hybridization. The association between the capacity to self‐autonomously and hybrid vigour further suggests that selfing may foster post‐zygotic costs following hybridization.

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“…; Briscoe Runquist et al. ). This may be achieved when divergent natural selection in contrasting environments generates isolation barriers, a process now referred to as “ecological speciation” (Schluter , ).…”

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confidence: 99%

Strong cryptic prezygotic isolation despite lack of behavioral isolation between sympatric host races of the leaf beetleLochmaea capreae

2016

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One of the major goals in speciation research is to understand which isolation mechanisms form the first barriers to gene flow. This requires examining lineages that are still in the process of divergence or incipient species. Here, we investigate the presence of behavioral and several cryptic barriers between the sympatric willow and birch host races of Lochmaea capreae. Behavioral isolation did not have any profound effect on preventing gene flow. Yet despite pairs mating indiscriminately, no offspring were produced from the heterospecific matings between birch females and willow males due to the inability of males to transfer sperm to females. We found evidence for differences in genital morphology that may contribute to failed insemination attempts during copulation. The heterospecific matings between willow females and birch males resulted in viable offspring. Yet fecundity and hatchability was remarkably reduced, which is likely the result of lower efficiency in sperm transportation and storage and lower survival of sperm in the foreign reproductive tract. Our results provide evidence for the contribution of several postmating-prezygotic barriers that predate behavioral isolation and act as primary inhibitors of gene flow in this system. This is a surprising, yet perhaps often overlooked feature of barriers acting early in sympatric speciation process.

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RAPID EVOLUTION OF REPRODUCTIVE ISOLATION BETWEEN INCIPIENT OUTCROSSING AND SELFINGCLARKIASPECIES

Cited by 72 publications

References 81 publications

Reproductive isolation and the maintenance of species boundaries in two serpentine endemic Jewelflowers

Reproductive isolation and the maintenance of species boundaries in two serpentine endemic Jewelflowers

The importance of autonomous selfing in preventing hybridization in three closely related plant species

Strong cryptic prezygotic isolation despite lack of behavioral isolation between sympatric host races of the leaf beetleLochmaea capreae

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