Variation and Hybridization in Southern California Populations of Diplacus (Scrophulariaceae)

Beeks, Richard M.

doi:10.5642/aliso.19620502.02

Cited by 25 publications

(44 citation statements)

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“…Perhaps regional differences in relative abundance of each pollinator contribute to variation in the rate of successful pollination by each floral type (Beeks 1962;Grant 1993a;M. Streisfeld, pers.…”

Section: Discussionmentioning

confidence: 99%

“…For the first analysis, we performed separate AMOVAs that individually tested each of the three nearby Diplacus subspecies against a group that contained the red, yellow, and hybrid populations to determine whether the San Diego populations were more highly differentiated from these other subspecies than they were from each other. We also tested these same San Diego populations against a group of red, yellow, and hybrid populations from north of San Diego County to examine Beeks' (1962) assertion that these regions reflected distinct population series. These analyses were performed using only the cpDNA and SNP data sets, as AFLP data were collected only from red-and yellow-flowered populations within San Diego County.…”

Section: Discussionmentioning

confidence: 99%

“…These forms are distributed throughout San Diego, Orange, and Riverside Counties in extreme southern California, but according to Beeks (1962), there is greater discontinuity in floral traits and more extreme geographical structure found among San Diego County populations than elsewhere. Therefore, we focused our sampling on populations from the San Diego series (sensu Beeks 1962), but we also sampled five populations from the more northern regions of southern California (i.e., Orange and Riverside Counties) and three other nearby subspecies from the section Diplacus for comparison with the San Diego group (see Table S1 available online only at http://dx.doi.org/10.1554/05-514.1.s1). Further taxonomic difficulties surround the entire section Diplacus, and to avoid confusion over the nomenclature of these forms, we simply refer to the San Diego series of populations as the red and yellow floral races, but refer to the other subspecies as defined by Munz (1973).…”

Section: Methodsmentioning

confidence: 99%

“…These perennial subshrubs of the section Diplacus show extensive geographic variation in floral traits (McMinn 1951;Beeks 1962;Beardsley et al 2004). They have been described in detail for the variation that they exhibit not only in flower color, but also in floral shape, nectar volume, and ecology (McMinn 1951;Beeks 1962;Waayers 1996;Tulig 2000). In particular, there is a steep gradient in flower color between coastal and inland regions in San Diego County, California, with coastal populations containing red flowers, and inland populations containing yellow flowers.…”

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confidence: 99%

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Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

Streisfeld

Kohn

2005

Evolution

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Abstract. Steep clines in ecologically important traits may be caused by divergent natural selection. However, processes that do not necessarily invoke ongoing selection, such as secondary contact or restricted gene flow, can also cause patterns of phenotypic differentiation over short spatial scales. Distinguishing among all possible scenarios is difficult, but an attainable goal is to establish whether scenarios that imply selection need to be invoked. We compared the extent of morphological and genetic differentiation between geographically structured red and yellow floral races of Mimulus aurantiacus (bush monkeyflower; Phrymaceae). Flower color was assessed in a common garden as well as in the field to determine whether variation was genetic and to quantify the extent of geographical differentiation. Population genetic differentiation at marker loci was measured for both chloroplast and nuclear genomes, and the degree of population structure within and among the floral races was evaluated. Flower color shows both a strong genetic basis and a sharp geographic transition, with pure red-flowered populations in western San Diego County and pure yellow-flowered populations to the east. In the zone of contact, both pure and intermediate phenotypes occur. Patterns of genetic differentiation at marker loci are far less pronounced, as little of the variation is partitioned according to the differences in flower color. Phenotypic differentiation (Q ST ) between populations with different flower colors is much greater than neutral genetic differentiation (F ST ). When comparisons are made between populations of the same flower color, the opposite trend is evident. Limited neutral genetic structure between the floral races, combined with sharp differentiation in flower color, is consistent with the hypothesis that current or recent natural selection maintains the cline in flower color.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

Streisfeld

Kohn

2005

Evolution

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“…A pair of florally isolated species may remain reproductively isolated in one area of sympatric contact but hybridize in another area. This pattern has been reported in a number of genera: Aquilegia (Ranunculaceae) (1)(2)(3)(4), Epimedium (Berberidaceae) (5), Ipomopsis (Polemoniaceae) (4,(6)(7)(8), Penstemon (Scrophulariaceae) (9), Diplacus (Scrophulariaceae) (10), Rhinanthus (Scrophulariaceae) (11), Salvia (Labiatae) (12), and Platanthera (Orchidaceae) (13).…”

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confidence: 99%

Effects of hybridization and selection on floral isolation.

Grant

1993

Proc. Natl. Acad. Sci. U.S.A.

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This paper examines the case of natural hybridization between two angiosperm species (A and B) which are mechanically and ethologically isolated (or florally isolated). What is the effect of hybridization on the pollination system, and conversely, what is the effect of the pollinators on the outcome of the hybridization? The original floral isolation is based on an interspecific differentiation in floral characters, the floral mechanisms of the parental species being specialized for pollination by different types of pollinators with different body forms and behavioral traits. F1 hybrids of A x B have intermediate floral characters and serve as bridges for interspecific cross-pollination. The problem next shifts to the changes in floral characters and mode of pollination that are likely to occur in later generations in the hybrid population.The pollinators of species A and species B exert selective pressures on the hybrid population. If the normal pollinator of A is more abundant, active, and effective in the hybrid population than the pollinator of B, selection is expected to favor a reversion toward the floral characters and pollination system of A. The opposite condition, in which the pollinator of B is predominant, leads to the reciprocal result, reversion toward B. If the two types of pollinators are more or less the same in number of flower visits and pollination effectiveness, their combined selective pressure should produce latergeneration derivatives with intermediate floral characters suited for both pollinators. Three western North American plant groups containing florally isolated species that hybridize (Ipomopsis, Diplacus, and Aquilegia) are examined in relation to these predictions. The evidence in the three groups is generally in agreement with the hypothesis.Mechanical and ethological isolation often occur together in angiosperms and are referred to collectively as floral isolation. The floral isolation is frequently incomplete. A pair of florally isolated species may remain reproductively isolated in one area of sympatric contact but hybridize in another area. This pattern has been reported in a number of genera: Aquilegia (Ranunculaceae) (1-4), Epimedium (Berberidaceae) (5), Ipomopsis (Polemoniaceae) (4,(6)(7)(8), Penstemon (Scrophulariaceae) (9), Diplacus (Scrophulariaceae) (10), Rhinanthus (Scrophulariaceae) (11), Salvia (Labiatae) (12), and Platanthera (Orchidaceae) (13).We understand why the floral isolation breaks down locally. Floral isolation operates in conjunction with ecological isolation (4). Both modes of isolation are sensitive to manmade or natural disturbances of the original habitat differences between the related sympatric species. We have descriptive and analytical studies of the hybrids between florally isolated species in various plant groups. The initial hybridization is known to be followed by introgression in the species groups in six of the genera listed above: Aquilegia (1), Ipomopsis (6, 7), Diplacus (10, 14), Rhinanthus (11), Salvia (12), and Platanthera (13)....

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Pollen Morphology in the Genus Mimulus (Scrophulariaceae) and Its Taxonomic Significance

Argue

1980

American J of Botany

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The pollen morphology of 117 species and varieties of Mimulus was examined by light and scanning electron microscopy. Five major and 8 more tentative, minor types were found based on the differential correlation of aperture type, exine morphology, pollen grain diameter and other characters: type 1—synaperturate, usually ±spiraperturate, exine perforate to microreticulate with supratectal processes; type II—trocolporate, exine microreticulate (IIa and IIb, supratectal processes absent; IIa, mean polar axis 16–19 μm; IIb, mean polar axis 25–35 μrn; IIc, supratectal processes present); type III—tricolpate, colpus membrane ±psilate. exine with supratectal processes (IIIa, exine microreticulate and 1.4–2.0 μm thick, polar axis ≥ 30 μm; 111b, exine densely perforate and 2.2–2.8 μm thick, polar axis ≤ 23 μm); type IV—tricolpate, colpus covered with spinulose granules (operculate), exine microreticulate with supratectal processes; type V—5–7 stephanocolpate (Va and Vb, colpus margins ±straight and nongranular; Va, exine microreticulate with supratectal spinules; Vb, exine perforate with supratectal spinules or spinulose verrucae; Vc, colpus margins ragged and granular, exine microreticulate with supratectal processes). The pollen data correlate well with geographical and macromorphological data and, where the latter are ambiguous, often provide important clues toward the resolution of conflicting interpretations of infrageneric classification and generic delimitation.

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Variation and Hybridization in Southern California Populations of Diplacus (Scrophulariaceae)

Cited by 25 publications

References 14 publications

Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

Contrasting Patterns of Floral and Molecular Variation Across a Cline in Mimulus Aurantiacus

Effects of hybridization and selection on floral isolation.

Pollen Morphology in the Genus Mimulus (Scrophulariaceae) and Its Taxonomic Significance

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