Spontaneous Occurrence in Lythrum salicaria of Plants Duplex for the Short-style Gene

Fisher, Ronald Aylmer; Martin, V. C.

doi:10.1038/160541a0

Cited by 12 publications

(4 citation statements)

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“…Data from Ontario after Eckert and Barrett (1992). tetrasomic inheritance of tristyly at both loci (Fisher and Martin 1947;Fisher 1949;Fyfe 1953), we simulated a diploid genetic system for the sake of generality. Ploidy, however, does not affect the theoretical dynamics of tristylous populations because, with only two alleles per locus and strong disassortative mating among morphs, autotetraploid tristyly loci effectively behave as diploid loci (Heuch and Lie 1985;Eckert and Barrett 1992).…”

Section: Computer Simulationsmentioning

confidence: 99%

GENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT,LYTHRUM SALICARIA(LYTHRACEAE)

1996

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Abstract.-There are few convincing examples of genetic drift at loci under selection in natural populations. The plant sexual polymorphism tristyly provides an opportunity to investigate genetic drift because stochastic processes interacting with frequency-dependent selection give rise to a diagnostic pattern of morph-frequency variation. A previous study of 102 Ontario populations of the introduced tristylous wetland herb Lythrum salicaria provided evidence for the role of stochastic processes during colonization. However, whether stochastic effects are greater in these recently introduced populations compared to native Eurasian populations remains unclear. The propensity of this species to invade disturbed habitats suggests that episodes of colonization and periods of small population size must also occur in the native range. A survey of 102 populations in southwestern France indicated reduced stochastic effects in native populations. Populations exhibited significantly lower morph loss than in Ontario (5% vs. 23%) and significantly higher values of morph evenness. The greater incidence of trimorphism in French populations was not associated with larger population sizes; populations were significantly smaller than those in Ontario (means: 266 vs. 487). Morph evenness was positively correlated with population size among French but not Ontario populations, providing further evidence of nonequilibrium conditions in introduced compared to native populations. The incidence of trimorphism was unexpectedly high in small native populations (N:S 25; 22 of 27 populations trimorphic). Computer simulations indicated that levels of gene flow on the order of m 2: 0.05 can account for the maintenance of tristyly in small populations. The high connectivity of populations within the agricultural landscape typical of southwestern France may facilitate levels of gene flow sufficient to maintain trimorphism in small populations.

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Section: Computer Simulationsmentioning

confidence: 99%

GENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT,LYTHRUM SALICARIA(LYTHRACEAE)

1996

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“…These specifics of the inheritance are of importance for the predictions of the stochastic models. In L. salicaria, the inheritance of both style morph loci is tetrasomic, with no linkage or dosage effects (Fisher and Mather 1943;Fisher and Martin 1947).…”

Section: The Speciesmentioning

confidence: 99%

Population Structure and Morph-Specific Fitness Differences in Tristylous Lythrum salicaria

Ågren¹,

Ericson²

1996

Evolution

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In tristylous plant populations, style-morph frequencies are governed by an interaction between frequencydependent selection due to disassortative mating and stochastic processes. Provided that there are no inherent fitness differences among morphs, frequency-dependent selection should result in equal morph frequencies at equilibrium. Stochastic models indicate that the short-styled morph has the highest and the long-styled morph the lowest probability of being lost from local populations as a result of random processes. We surveyed the morph composition of 82 populations of the tristylous, self-incompatible herb Lythrum salicaria in two archipelagos, one in central and one in northern Sweden, located close to the range-margin of the species. To examine whether deviations from even morph frequencies can be explained by among-rnorph differences in reproductive success, we quantified flower and seed production in six and three populations in the northern and southern archipelago, respectively, and we recorded segregation ratios in offspring produced in six trimorphic populations in the northern area. Seed germination and offspring growth were studied in the greenhouse.Ninety percent of the populations in the southern archipelago (N = 31) and 69% of the populations in the northern archipelago (N = 35) were trimorphic; the remaining populations were dimorphic (only populations consisting of at least three flowering plants considered). Dimorphic populations were smaller than trimorphic populations, as predicted by stochastic models. There was a striking difference in the morph composition of L. salicaria populations between the two archipelagos. In the southern archipelago, there was a slight excess of the long-styled morph and a corresponding deficiency of the short-styled morpho In contrast, the northern populations were characterized by a marked deficiency of the mid-styled morph: the average frequency of the mid-styled morph in trimorphic populations was 0.21, and nine of eleven dimorphic populations lacked the mid-styled morpho In both archipelagos, the long-styled morph (the most common morph) produced about 20% fewer seeds per fruit than the other morphs. The long-styled morph also tended to produce fewer seeds per plant. A hand-pollination experiment performed in two of the northern populations indicated that seed production per flower was pollen-limited in the long-styled morph but not in the other two morphs. Seed germination and offspring size after 24 weeks of growth did not differ among morphs. The mid-styled morph tended to have a higher representation in the offspring than in the parental generation in all six trimorphic populations studied further indicating that the deficiency of the mid-styled morph in the northern archipelago does not represent an equilibrium. Taken together, the results do not support the hypothesis that morph-specific differences in reproductive success can account for deviations from even morph frequencies in L. salicaria. It is suggested that among-morph differences in other com...

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“…Sm/sM, SsMM, SSmm, SSMm, or SSMM. Lythrum salicaria exhibits tetrasomic inheritance at both style morph loci, with no linkage or dosage effects (Fisher and Mather, 1943;Fisher and Martin, 1947). Double reduction has been estimated at 10% for the S locus (Fyfe, 1953) and 2.5% for the M locus (Fisher, 1949).…”

Section: Computer Modelsmentioning

confidence: 99%

STOCHASTIC LOSS OF STYLE MORPHS FROM POPULATIONS OF TRISTYLOUSLYTHRUM SALICARIAANDDECODON VERTICILLATUS(LYTHRACEAE)

Eckert¹,

Barrett²

1992

Evolution

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Despite the theoretical importance of stochastic processes in evolution there have been few empirical studies of the interaction between genetic drift and selection on the maintenance of polymorphisms in plant populations. We used computer models to investigate the interaction between drift and frequency-dependent selection in affecting style morph frequencies in populations of tristylous species. Drift produces a distinct pattern of morph frequency variation involving: 1) the loss of the S morph and, to a lesser extent, the M morph; 2) no consistent bias in frequencies within populations; 3) a restricted pattern of variation involving a deficiency of one morph and equal excesses of the other two. Morph frequencies were surveyed in 137 populations of Lythrum salicaria from both its native range in Europe (N = 35) and recent adventive range in Ontario (N = 102), and 133 populations of Decodon verticillatus from four regions in eastern North America with different glacial histories to assess these theoretical predictions. There was a negative relationship between morph loss and population size in both species; the relationship was weaker in D. verticillatus than in L. salicaria. Morph loss was more frequent in the adventive than native range of L. salicaria, and in populations of D. verticillatus from glaciated northern regions compared with the unglaciated southern portion of its range. Simulations incorporating variation in life history, regeneration strategy and mating patterns revealed that the degree of morph loss was strongly influenced by year to year survival, clonal propagation, self-fertilization and departures from disassortative mating. Comparing the pattern of morph frequency variation between species supported these predictions. Morph loss was lower in self-incompatible L. salicaria (0% in Europe; 23% in Ontario), which reproduces through seed compared to self-compatible, clonal D. verticillatus (52%). A stochastic model provides the most parsimonious explanation for observed patterns of morph frequency variation in both species.

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Spontaneous Occurrence in Lythrum salicaria of Plants Duplex for the Short-style Gene

Cited by 12 publications

References 4 publications

GENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT,LYTHRUM SALICARIA(LYTHRACEAE)

GENETIC DRIFT AND FOUNDER EFFECT IN NATIVE VERSUS INTRODUCED POPULATIONS OF AN INVADING PLANT,LYTHRUM SALICARIA(LYTHRACEAE)

Population Structure and Morph-Specific Fitness Differences in Tristylous Lythrum salicaria

STOCHASTIC LOSS OF STYLE MORPHS FROM POPULATIONS OF TRISTYLOUSLYTHRUM SALICARIAANDDECODON VERTICILLATUS(LYTHRACEAE)

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