NARROW HYBRID ZONE BETWEEN TWO SUBSPECIES OF BIG SAGEBRUSH (<i>ARTEMISIA TRIDENTATA</i>: ASTERACEAE). IV. RECIPROCAL TRANSPLANT EXPERIMENTS

Wang, Han; McArthur, E. Durant; Sanderson, Stewart C.; Graham, John H.; Freeman, D. Carl

doi:10.1111/j.1558-5646.1997.tb02391.x

Cited by 107 publications

(137 citation statements)

References 41 publications

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“…For example, both favorable and unfavorable cytonuclear interactions have been shown in Iris hybrids to contribute to short-term survival in the greenhouse (Burke et al 1998). Environment-dependent selection has been suggested by other reciprocal transplant studies, for example, in an Artemisia hybrid zone where there is evidence for adaptation of the parental types to their own habitat (Wang et al 1997). Our results are novel because they demonstrate asymmetric effects on fitness of hybrids under natural, rather than greenhouse, conditions.…”

Section: Discussionsupporting

confidence: 54%

“…This gap is all the more surprising given that natural hybridization is so common in flowering plants. Renewed interest in plant hybridization has recently generated a few reciprocal transplant studies in natural hybrid zones (Levin and Schmidt 1985;Wang et al 1997). Renewed interest in plant hybridization has recently generated a few reciprocal transplant studies in natural hybrid zones (Levin and Schmidt 1985;Wang et al 1997).…”

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confidence: 99%

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Genotype-by-Environment Interaction and the Fitness of Plant Hybrids in the Wild

Campbell

Waser

2001

Evol

139

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Natural hybrid zones between related species illustrate processes that contribute to genetic differentiation and species formation. A common viewpoint is that hybrids are essentially unfit, but they exist in a stable tension zone where selection against them is balanced by gene flow between the parent species. An alternative idea is that selection depends on the environment, for example, by favoring opposite traits in the two parental habitats or favoring hybrids within a bounded region. To determine whether selection of hybrids is environment dependent, we crossed plants of naturally hybridizing Ipomopsis aggregata and I. tenuituba in the Colorado Rocky Mountains and reciprocally planted the seed offspring into a suite of natural environments across the hybrid zone. All types of crosses produced similar numbers and weights of seeds. However, survival of the offspring after 5 years differed markedly among cross types. On average, the F1 hybrids had survival and growth rates as high as the average for their parents. But hybrid survival depended strongly on the direction of a cross, that is, on which species served as the maternal parent. This fitness difference between reciprocal hybrids appeared only in the parental environments, suggesting cytonuclear gene interactions that are environment specific. These results indicate that complex genotype-by-environment interactions can contribute to the evolutionary outcome of hybridization.

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Section: Discussionsupporting

confidence: 54%

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confidence: 99%

Genotype-by-Environment Interaction and the Fitness of Plant Hybrids in the Wild

Campbell

Waser

2001

Evol

139

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“…These consequences can include a stable hybrid zone, disappearance or reinforcement of species differences, or production of a new hybrid species (Arnold, 1997). Only recently has variation in physiological performance been examined in natural hybrid systems (Wang et al, 1997;Johnston et al, 2001;Schwarzbach et al, 2001;Ludwig et al, 2004). Only recently has variation in physiological performance been examined in natural hybrid systems (Wang et al, 1997;Johnston et al, 2001;Schwarzbach et al, 2001;Ludwig et al, 2004).…”

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Leaf physiology reflects environmental differences and cytoplasmic background inIpomopsis(Polemoniaceae) hybrids

Campbell²

2007

American J of Botany

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Natural hybridization can produce individuals that vary widely in fitness, depending upon the performance of particular genotypes in a given environment. In a hybrid zone with habitat heterogeneity, differences in physiological responses to abiotic conditions could influence the fitness and spatial distribution of hybrids and parental species. This study compared gas exchange physiology of Ipomopsis aggregata, I. tenuituba, and their natural hybrids in situ and assessed whether physiological differences were consistent with their native environmental conditions. We also produced reciprocal F2s in a greenhouse study to test for cytonuclear effects on water-use efficiency (WUE). The relative performance of natural hybrids and parentals was consistent with their native habitats: I. aggregata at the coolest, wettest locations had the lowest WUE, while hybrids from the most xeric sites had the highest WUE. In hybrids, the mechanism by which both natural and experimental hybrids achieved this high WUE depended on cytotype: those with I. tenuituba cytoplasm had reduced transpiration, while those with I. aggregata cytoplasm had an increased photosynthetic rate, consistent with patterns in the cytoplasmic parent. The high WUE in hybrids may contribute to their high survival in the dry center of the natural hybrid zone, consistent with environment-dependent models of hybrid zone dynamics.

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“…Although reduced hybrid fitness relative to pure-species types is common (reviewed in Barton and Hewitt 1989;Howard 1993), hybridization can sometimes be beneficial (reviewed in Arnold and Hodges 1995;Arnold 1997; see also Semlitsch and Reyer 1992;Semlitsch 1993;Burke et al 1998;Parris 1999Parris , 2001aVeen et al 2001). Moreover, the fitness consequences of hybridization may vary across environments or fitness components (Semlitsch and Reyer 1992;Emms and Arnold 1997;Wang et al 1997;Burke et al 1998;Pearson 2000;Parris 2001a,b). For instance, hybrids may outperform pure-species types early in ontogeny but may suffer lower fecundity as adults (e.g., Simovich 1985;Simovich et al 1991;Parris et al 1999).…”

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Differential Selection to Avoid Hybridization in Two Toad Species

Pfennig¹,

Simovich

2002

Evol

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Abstract.— The fitness consequences of hybridization critically affect the speciation process. When hybridization is costly, selection favors the evolution of prezygotic isolating mechanisms (e.g., mating behaviors) that reduce heter‐ospecific matings and, consequently, enhance reproductive isolation between species (a process termed reinforcement). If, however, selection to avoid hybridization differs between species, reinforcement may be impeded. Here, we examined both the frequency and fitness effects of hybridization between plains spadefoot toads (Spea bombifrons) and New Mexico spadefoot toads (S. multiplicata). Hybridization was most frequent in smaller breeding ponds that tend to be ephemeral, and heterospecific pairs consisted almost entirely of S. bombifrons females and S. multiplicata males. Moreover, in controlled experimental crosses, hybrid offspring from crosses in which S. multiplicata was maternal had significantly lower survival and longer development time than pure S. multiplicata offspring. By contrast, hybrid offspring from crosses in which S. bombifrons was maternal outperformed pure S. bombifrons offspring by reaching metamorphosis faster. These data suggest that, although S. multiplicata females are under selection to avoid hybridization, selection might favor those S. bombifrons females that hybridize with S. multiplicata if their breeding pond is highly ephemeral. Generally, the strength of selection to avoid hybridization may differ for hybridizing species, possibly impeding reinforcement.

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NARROW HYBRID ZONE BETWEEN TWO SUBSPECIES OF BIG SAGEBRUSH (ARTEMISIA TRIDENTATA: ASTERACEAE). IV. RECIPROCAL TRANSPLANT EXPERIMENTS

Cited by 107 publications

References 41 publications

Genotype-by-Environment Interaction and the Fitness of Plant Hybrids in the Wild

Genotype-by-Environment Interaction and the Fitness of Plant Hybrids in the Wild

Leaf physiology reflects environmental differences and cytoplasmic background inIpomopsis(Polemoniaceae) hybrids

Differential Selection to Avoid Hybridization in Two Toad Species

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