Temporal variation in allele frequencies in the pollen pool of Eucalyptus rhodantha

Sampson, Jane; Hopper, Stephen D.; James, S. H.

doi:10.1038/hdy.1990.87

Cited by 15 publications

(6 citation statements)

References 22 publications

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“…A number of studies have, however, documented temporal shifts in allele frequencies in the pollen pool (e.g. Fripp et al 1987;Sampson et al 1990). These shifts imply genetic differences among plants flowering at different times, but they do not confirm IBT because individual plants can contribute disproportionately to the pollen pool.…”

Section: Empirical Evidencementioning

confidence: 99%

Population structure attributable to reproductive time: isolation by time and adaptation by time

2005

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Many populations are composed of a mixture of individuals that reproduce at different times, and these times are often heritable. Under these conditions, gene flow should be limited between early and late reproducers, even within populations having a unimodal temporal distribution of reproductive activity. This temporal restriction on gene flow might be called 'isolation by time' (IBT) to acknowledge its analogy with isolation by distance (IBD). IBD and IBT are not exactly equivalent, however, owing to differences between dispersal in space and dispersal in time. We review empirical studies of natural populations that provide evidence for IBT based on heritabilities of reproductive time and on molecular genetic differences associated with reproductive time. When IBT is present, variation in selection through the reproductive season may lead to adaptive temporal variation in phenotypic traits [adaptation by time (ABT)]. We introduce a novel theoretical model that shows how ABT increases as (i) selection on the trait increases; (ii) environmental influences on reproductive time decrease; (iii) the heritability of reproductive time increases; and (iv) the temporal distribution of reproductive activity becomes increasingly uniform. We then review empirical studies of natural populations that provide evidence for ABT by documenting adaptive temporal clines in phenotypic traits. The best evidence for IBT and ABT currently comes from salmonid fishes and flowering plants, but we expect that future work will show these processes are more widespread.

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Section: Empirical Evidencementioning

confidence: 99%

Population structure attributable to reproductive time: isolation by time and adaptation by time

2005

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“…Eighty-three plants (41.4%) are estimated to have been capable of flowering in the entire population during the 1992 flowering season, but the number releasing pollen at any one time would be considerably less, because large-flowered eucalypts have staggered flowering over long seasons. In E. rhodantha for example, although most plants had buds, no more than 50% of plants were flowering at the peak of the season (Sampson et al, 1990). Indeed, some plants may finish flowering before others begin.…”

Section: Discussionmentioning

confidence: 99%

Multiple paternity in Eucalyptus rameliana (Myrtaceae)

Sampson

1998

Heredity

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Estimates of the level of multiple paternity/correlated outcrossing within and between fruits in a predominantly outbreeding population of the bird-pollinated mallee, Eucalyptus rameliana, were made using six allozyme loci. The correlation of outcrossed paternity (r p ) was positive and significant within fruits (0.26) and the effective number of mates for a single fruit was estimated to be 3.85. This correlation was attributed to the low number of potential male parents and pollen-bearing flowers available at any one time in the population. Although consistent with suggestions that correlation of paternity may be a general feature of animal-pollinated plants, the level in E. rameliana was remarkably low considering its population size and phenology. There was no significant correlation of paternity between fruits, probably because flowers were pollinated at different times during the long season. Individual plants differed greatly in both male and female contributions to the next generation, with a small proportion of genotypes located in a small area contributing at least half of the gene pool of the seeds stored in the canopy. In contrast, the male contribution is probably from a wider area. The specialization of floral structure and phenology in E. rameliana for bird-pollination has probably contributed to correlation of paternity within fruits because there are fewer male parents available at any one time than in mass-flowering species. However, the behaviour of the bird pollinators also promotes pollen dispersal and multiplicity of paternity, factors which would be particularly significant when the female contribution to the gene pool is concentrated in a few plants.

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“…However, since the StAMOVA is a general linear model, any number of additional external factors and interactions among external factors can be easily added to the model just as in a multiple regression analysis. For example, in addition to the density of local pollen donors, the degree of phenological overlap has also been shown to influence pollen pool composition significantly (eg, Sampson et al, 1990;Adams and Birkes, 1991). By sampling across a range of densities in the degrees of phenological overlap, one could isolate the importance of each of these factors as well as their interaction in shaping the distribution of genetic structure within spatially separated pollen pools.…”

Section: Discussionmentioning

confidence: 99%

“…Further, several studies of forest tree mating systems have reported the effects of local pollen donor density on pollen pool composition (eg, Farris and Mitton, 1984;Knowles et al, 1987;Shea, 1987;Murawski and Hamrick, 1991). Additional factors such as flowering phenology (Sampson et al, 1990), adult allele frequency gradients (Dyer and Sork, 2002), elevation gradients (Loechelt and Franke, 1996), and inbreeding and spatial autocorrelation among adult individuals (Austerlitz and Smouse, 2001b) also act to increase the genetic divergence among sampled pollen pools. If any of these factors have a significant influence on pollen pool composition, then estimates of pollen dispersal distance will be biased downward.…”

Section: Introductionmentioning

confidence: 99%

Two-generation analysis of pollen flow across a landscape V: a stepwise approach for extracting factors contributing to pollen structure

et al. 2004

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Patterns of pollen dispersal are central to both the ecology and evolution of plant populations. However, the mechanisms controlling either the dispersal process itself or our estimation of that process may be influenced by site-specific factors such as local forest structure and nonuniform adult genetic structure. Here, we present an extension of the AMOVA model applied to the recently developed TWOGENER analysis of pollen pool structure. This model, dubbed the Stepwise AMOVA (StAMOVA), focuses on determining to what extent ecological, demographic, and/or environmental factors influence the observed genetic variation in spatially separated pollen pools. The analysis is verified for efficacy, using an extensive battery of simulations, illustrating: (1) how nonuniform adult genetic structure influences the differentiation of spatially separated pollen pools, and (2) how effectively the Stepwise analysis performs in carrying out the appropriate corrections. Finally, the model is applied to a Quercus alba data set, from which we have prior evidence that the adult genetic structure is nonuniformly distributed across the sampling landscape. From this data set, we show how the Stepwise model can be applied to remove the effects of spatial adult genetic structure on pollen pool differentiation and contrast these results with those derived from the original TWOGENER analysis.

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Temporal variation in allele frequencies in the pollen pool of Eucalyptus rhodantha

Cited by 15 publications

References 22 publications

Population structure attributable to reproductive time: isolation by time and adaptation by time

Population structure attributable to reproductive time: isolation by time and adaptation by time

Multiple paternity in Eucalyptus rameliana (Myrtaceae)

Two-generation analysis of pollen flow across a landscape V: a stepwise approach for extracting factors contributing to pollen structure

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