Allozyme variation in Louisiana irises: a test for introgression and hybrid speciation

Arnold, Michael L.; Hamrick, J. L.; Bennett, Bobby D.

doi:10.1038/hdy.1990.99

Cited by 95 publications

(77 citation statements)

References 27 publications

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“…I. nelsonii flowers are dark red in color and morphologically intermediate between I. fulva and I. hexagona for some traits, while extreme to the means of the purported progenitors for others (Randolph, 1966). The hybrid origin of I. nelsonii was later confirmed with allozyme (Arnold et al, 1990) and nuclear (Arnold, 1993) data that suggested that a majority of the I. nelsonii genome was derived from I. fulva with contributions of loci from I. hexagona and I. brevicaulis.…”

Section: Introductionmentioning

confidence: 58%

Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona

Taylor

Rojas

et al. 2012

Heredity

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Hybrid speciation represents a relatively rapid form of diversification. Early models of homoploid hybrid speciation suggested that reproductive isolation between the hybrid species and progenitors primarily resulted from karyotypic differences between the species. However, genic incompatibilities and ecological divergence may also be responsible for isolation. Iris nelsonii is an example of a homoploid hybrid species that is likely isolated from its progenitors primarily by strong prezygotic isolation, including habitat divergence, floral isolation and post-pollination prezygotic barriers. Here, we used linkage mapping and quantitative trait locus (QTL) mapping approaches to investigate genomic collinearity and the genetic architecture of floral differences between I. nelsonii and one of its progenitor species I. hexagona. The linkage map produced from this cross is highly collinear with another linkage map produced between I. fulva and I. brevicaulis (the two other species shown to have contributed to the genomic makeup of I. nelsonii), suggesting that karyotypic differences do not contribute substantially to isolation in this homoploid hybrid species. Similar to other studies of the genetic architecture of floral characteristics, at least one QTL was found that explained 420% variance in each color trait, while minor QTLs were detected for each morphological trait. These QTLs will serve as hypotheses for regions under selection by pollinators.

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Section: Introductionmentioning

confidence: 58%

Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona

Taylor

Rojas

et al. 2012

Heredity

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“…Electrophoretic analysis Between 6 and 12 seeds from each fruit were assayed for six electrophoretic loci using previously described methods (Arnold et al, 1990b). The loci examined (fluorescent esterase, FE-i; glutamate oxaloacetate transaminase, GOT-3; isocitrate dehydrogenase, IDH-2; 6-phosphate dehydrogenase, 6P-2 and 6P-3; phospho-glucoisomerase, PGI-2) were polymorphic in both species.…”

Section: Methodsmentioning

confidence: 99%

Mating system variation in hybridizing irises: Effects of phenology and floral densities on family outcrossing rates

et al. 1994

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The frequency of outcrossing in two hybridizing species of Iris was estimated for populations and for individual fruits. Effects of floral phenology and the local densities of flowers on outcrossing rates were examined and the potential for hybrid seed formation under different pollen environments was assessed. The populations examined differed with respect to the spatial distribution of plants and the level of genetic structure; the I. fulva population consisted of a number of low density patches and appeared to have some genetic differentiation whereas the I. hexagona population consisted of a single high-density experimental plot of randomly distributed genotypes. Population outcrossing rate estimates were relatively high (0.67-0.90) for both species. The distribution of family outcrossing rates tended to be bimodal for both species with individual fruits either having the majority of seeds fertilized by outcrossed donors or being almost entirely selfed. fulva may have been a consequence of higher levels of vegetative reproduction and genetic structure and the behaviour of pollen vectors. Differences in pollen prepotency and the higher selfing rates observed at low floral densities in I. hexagona may have contributed to the observed patterns of hybrid seed formation. The analyses of family outcrossing rates provide important information on factors responsible for mating system variation and evolution.

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“…Such hybrid associations between these three species have been reported previously (Randolph et a!., 1967). Furthermore, hybridization between these three species is thought to have resulted in the production of the hybrid species I. nelsonii (Randolph, 1966;Arnold et a!., 1990a;1991). Figure 3 summarizes the cpDNA and allozyme data for each of 47 individuals from such a hybrid population.…”

Section: Discussionmentioning

confidence: 99%

“…These populations include two populations identified as I. brevicaulis, and one population that had allozyme markers characteristic of I. brevicaulis, 1. fulva and 1. hexagona (Arnold et aL, 1990a DNA isolation was carried out using leaf material and the procedure described by Arnold et a!. (1990b). This resulted in the collection of both nuclear and cytoplasmic DNA.…”

Section: Methodsmentioning

confidence: 99%

“…These data were used to test for the presence of maternal lineages originating from these three species. By comparing data for biparentally transmitted nuclear markers (Arnold et a!., 1990a, b;1991) with the maternally transmitted cpDNA markers, we were able to test for introgression resulting from pollen flow between allopatric populations versus introgression due to seed dispersal into populations of the alternate species, followed by pollen transfer. It was also possible to test for any restriction on which species may act as the maternal parent in interspecific crosses.…”

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confidence: 99%

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Pollen dispersal and interspecific gene flow in louisiana irises

et al. 1992

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An analysis of chloroplast DNA (cpDNA) variation was carried out for 106 individual plants from three natural populations of Louisiana irises. Two of the samples (59 individuals) represented I. brevicaulis populations. The third sample was from a population defined by allozyme markers as an area of contact between I. fidva, I. hexagona and I. brevicaulis. The cpDNA acts as a seed-specific genetic marker because it is inherited from the maternal parent. cpDNA markers were thus used to discriminate between (i) introgressive hybridization due to seed movement followed by pollen transfer and, (ii) introgression resulting from direct transfer of pollen between allopatric populations of the hybridizing taxa. Furthermore, the concurrent analysis of biparental and maternal markers for the same individuals allowed a test for any directionality in the introgression. A comparison of cpDNA results with data from previous nuclear analyses led to the conclusion that pollen flow occurred from allopatric populations of I. hexagona into an area of sympatry involving I. fulva and I. brevicaulis. In addition, the genotypes detected in the hybrid population indicate that 1. fulva and I. brevicaulis have acted as both pollen and seed parents to produce introgressant individuals. The results of the present study and those of previous nuclear and cpDNA analyses suggest that pollen dispersal is the most important avenue for gene flow between these Iris species.

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Allozyme variation in Louisiana irises: a test for introgression and hybrid speciation

Cited by 95 publications

References 27 publications

Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona

Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona

Mating system variation in hybridizing irises: Effects of phenology and floral densities on family outcrossing rates

Pollen dispersal and interspecific gene flow in louisiana irises

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