Density and the Rate of Apparent Outcrossing in Helianthus annuus (Asteraceae)

Ellstrand, Norman C.; Torres, Andrew M.; Levin, Donald A.

doi:10.2307/2418752

Cited by 121 publications

(61 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Founder effects could operate following seed migration by animal-mediated dispersal and the resultant small population sizes could represent a restricted and different gene pool to the source population. Evidence for nonrandom mating (deficiency in heterozygotes) has been suggested from the positive F value.s found here and in wild populations of H. annuus in Kansas, United States (Ellstrand et al 1978). Finally genetic drift or random fluctuation in the frequencies of specific genes in small populations may rapidly lead to marked differences between different populations.…”

Section: Discussionsupporting

confidence: 51%

Genetic Structure of Natural Populations of Wild Sunflowers (Helianthus annuus L.) in Australia

Dry¹,

Burdon²

1986

Aust. Jnl. Of Bio. Sci.

View full text Add to dashboard Cite

The genetic structure of 11 wild populations of H. annuus occurring in New South Wales and Queensland was determined by isozyme analysis. Considerable isozyme diversity was found among loci within and between populations, with three to five alleles being identified at each of 10 loci. Mean levels of heterozygosity ranged from o· 19 to O· 38 and gene diversity values from 0·29 to O· 52. In all populations Wright's fixation indices were positive (0·09-0· 51) suggesting a degree of inbreeding. Differences in the level of genetic differentiation between populations were not correlated with geographic distance. Indeed, notable genetic diversity was detected between six sites occurring within a 2-km radius of Gunnedah, N.S.W., where the genetic distance relationships were D = 0·13 ± 0'08, the same as those between popUlations throughout the region.There was statistically significant heterogeneity in gene frequency differences between alleles among populations at all loci (115 < JC < 254, d.f. = 30, P < 0'001). The significant diversity found in these populations suggests that there is considerable scope to utilize wild H. annuus in the improvement of commercial sunflowers.

show abstract

Section: Discussionsupporting

confidence: 51%

Genetic Structure of Natural Populations of Wild Sunflowers (Helianthus annuus L.) in Australia

Dry¹,

Burdon²

1986

Aust. Jnl. Of Bio. Sci.

View full text Add to dashboard Cite

show abstract

“…This result closely parallels findings from two other experimental studies. Krueger & Knapp (1991) Although most studies of insect-pollinated species have found a positive relationship between population density and outcrossing rates, negative correlations between density and outcrossing were observed in selfincompatible Helianthus annuus (Ellstrand et a!., 1978) and self-incompatible Phlox drummondii (Watkins & Levin, 1990). In both species, differences among populations resulted from biparental inbreeding, rather than intrafloral or geitonogamous selffertilization.…”

Section: Discussionmentioning

confidence: 98%

“…In several species of animal-pollinated flowering plants, outcrossing rates vary dramatically among populations (Harding & Barnes, 1977;Valdeyron et a!., 1977;Ellstrand et al, 1978;Schoen, 1982;Schemske & Lande, 1985; Ritland & Ganders, 1987a;Waller & Knight, 1989; Barrett & Husband, 1990;Dole, 1991;Godt & Hamrick, 1991). This variation is often attributed to ecological factors, such as population density, that influence pollinator movements (Aide, 1986;Waller, 1986;Brown et al, 1989;Watkins & Levin, 1990;Murawski & Hamrick, 1991;Lloyd & Schoen, 1992).…”

Section: Introductionmentioning

confidence: 99%

The influence of population density on outcrossing rates in Mimulus ringens

et al. 1995

View full text Add to dashboard Cite

The influence of population density on pollinator movements and outcrossing rates was studied in experimental arrays of Mimulus ringens (square-stemmed monkeyflower), a wetland perennial species with a mixed-mating system. Each population was composed of genets with unique multilocus combinations of homozygous genotypes, facilitating determination of outcrossing rates through paternity exclusion. Replicate arrays were cloned from the same set of genets to minimize differences in floral and vegetative morphology among density treatments. Two arrays were planted at each of three spacings typical of the range of densities found in natural M. ringens populations. Both the proportion of pollinator flights between plants and the frequency of outcrossing were significantly greater at high density. These results suggest that ecological and demographic factors, such as population density, can significantly influence levels of inbreeding in species with mixedmating systems.Keywords: density, experimental arrays, geitonogamy, outcrossing rate, paternity analysis, pollinator movements. IntroductionIn several species of animal-pollinated flowering plants, outcrossing rates vary dramatically among populations (Harding & Barnes, 1977;Valdeyron et a!., 1977;Ellstrand et al., 1978;Schoen, 1982;Schemske & Lande, 1985; Ritland & Ganders, 1987a;Waller & Knight, 1989; Barrett & Husband, 1990;Dole, 1991;Godt & Hamrick, 1991). This variation is often attributed to ecological factors, such as population density, that influence pollinator movements (Aide, 1986;Waller, 1986;Brown et al., 1989;Watkins & Levin, 1990;Murawski & Hamrick, 1991;Lloyd & Schoen, 1992). Despite theoretical predictions that outcrossing rates will be positively correlated with population density (Bateman, 1956;Handel, 1983;Brown et a!. 1989), the relationship between these variables remains poorly understood.Most studies documenting intraspecific variation in plant mating systems have involved comparisons of natural populations. However, in nature, population density is often confounded with other demographic variables such as plant size, population shape and population size (Barrett & Eckert, 1990;Kunin, 1993;Karron, 1995). In addition, differences among populations in genetically determined floral traits influencing *Correspondence the mating system (Campbell & Abbott, 1976;Schoen, 1982; Marshall & Abbott, 1984; Wyatt, 1984a,b;Holtsford & Ellstrand, 1989 Barrett & Husband, 1990;Clegg & Epperson, 1988;Morgan & Barrett, 1990) may further limit the utility of descriptive studies correlating population density with outcrossing rate.The influence of density on plant mating systems is well suited to experimental study. Spacing between plants is readily manipulated in population arrays, and recent experiments have examined the effects of density on patterns of pollinator movement and seed set in self-incompatible species (Kunin, 1992(Kunin, , 1993. Artificial arrays have also been used to determine outcrossing rates of distinct floral morphs in polymorphic populations...

show abstract

“…There is a negative correlation between plant density and outcrossing rate in the self-incompatible Helianthus annuus (Ellstrand et a!., 1978), whereas in self-compatible plants, a decrease in density often is accompanied by a decrease in outcrossing rates (Farris and Mitton, 1984;Dommee etaL, 1978;Bateman, 1947Bateman, , 1956Fowler, 1964;Marshall and Abbott, 1982;Burdon et al, 1988;Vaquero et aL, 1989). We are aware of only one other comparison of outcrossing rates in adjacent thinned and unmanipulated populations.…”

Section: Density Manipulation Experimentsmentioning

confidence: 99%

Outcrossing rates as related to plant density in Phlox drummondii

Watkins

Levin

1990

Heredity

View full text Add to dashboard Cite

Outcrossing rates were investigated in 20 populations of Phlox drummondii using polymorphic allozyme loci. The analysis of progeny genotype arrays gave outcrossing estimates which varied from t =069 to 101; the mean was 086.The estimated outcrossing rate deviated significantly from random mating in 13 populations. The deviation was due principally to crossing among relatives. Outcrossing rates were a weak inverse function of density. At one site the density of some subpopulations was artifically reduced; and the outcrossing rates in these subpopulations were significantly greater than in adjacent unmanipulated subpopulations.

show abstract

Density and the Rate of Apparent Outcrossing in Helianthus annuus (Asteraceae)

Cited by 121 publications

References 7 publications

Genetic Structure of Natural Populations of Wild Sunflowers (Helianthus annuus L.) in Australia

Genetic Structure of Natural Populations of Wild Sunflowers (Helianthus annuus L.) in Australia

The influence of population density on outcrossing rates in Mimulus ringens

Outcrossing rates as related to plant density in Phlox drummondii

Contact Info

Product

Resources

About