Abstract
Abstract Natural populations of primroses containing homostyles were found by Crosby (1940) near Sparkford, Somerset, and in the Chilterns. Homostyle frequencies up to 80% have often been recorded, but few populations containing higher frequencies have been found. In explaining observed configurations of homostyle frequencies Crosby (1949) assumed that they always selffertilized. Bodmer (1958), however, obtained evidence for the occurrence of crossing between the homostyles under natural conditions. The estimated amount of crossing increases with lower viability for the homostyles and the data indicate a frequency of crossing of at least 80 %. Analysis of counts of populations containing homostyles in Somerset made by Professor Sir Ronald Fisher, F.R.S., over the years 1941-54 shows heterogeneity within populations, but no evidence of an upward trend in homostyle frequency. The only significant change detected is a downward trend in the homostyle frequency. There is also a marked deficiency of thrums relative to pins for high homostyle frequencies. Investigation of theoretical models which take into account crossing between homostyles shows that the homostyles will increase in frequency so long as there are no viability disturbances. However, a method for calculating an effective initial selective value for the homostyle gene shows that when the frequency of crossing is high only moderate viability disturbances are needed to prevent the homostyles from increasing in frequency. Numerical investigation of the models indicates that only a slight decrease in viability is needed to decrease the proportion of homostyles in populations where they are already abundant. Moreover, if the decreased viability affects particularly the mature plants it is possible to account for the thrum deficiency and also a possible very rapid decrease in homostyle frequency. With high initial selective values for the homostyle gene, such as are obtained when the homostyles only self-fertilize, even when they have considerably reduced viability, only a few occurrences are needed to make them almost certain to gain a hold and increase in frequency. It does not seem possible, therefore, to explain why the homostyles have occurred only in a few restricted areas, unless the effective initial selection for them is very small or negative, which can only occur when there is a considerable amount of crossing between the homostyles. It thus seems that the tendency of the homostyles, and possibly also of pins and thrums, to cross-fertilize is an essential buffering mechanism against the possible reversal of an outcrossing system to inbreeding.
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Claims 10
Claim · model-written summary
Primula vulgaris populations show heterogeneity in homostyle frequency among populations.
- Taxon
- Primula vulgaris
Primula vulgarist0 - Outcome
- heterogeneity within populationse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e0“shows heterogeneity within populations”
Claim · model-written summary
The only significant change in Primula vulgaris homostyle frequency was a downward trend.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Outcome
- homostyle frequencye1
- Qualifier
- The only significant change detectede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e1“The only significant change detected is a downward trend in the homostyle frequency”
Claim · model-written summary
No evidence was found of an upward trend in homostyle frequency in Primula vulgaris.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Outcome
- upward trend in homostyle frequencye2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e2“no evidence of an upward trend in homostyle frequency”
Claim · model-written summary
Primula vulgaris shows a marked deficiency of thrums relative to pins at high homostyle frequencies.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Outcome
- deficiency of thrums relative to pinse3
- Qualifier
- for high homostyle frequenciese3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e3“There is also a marked deficiency of thrums relative to pins for high homostyle frequencies”
Claim · model-written summary
Model results indicate that homostyles increase in frequency when there are no viability disturbances.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Treatment
- viability disturbancese4
- Outcome
- homostylese4
- Direction
- increasee4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e4“the homostyles will increase in frequency so long as there are no viability disturbances”
Claim · model-written summary
Model results indicate that only moderate viability disturbances are needed to prevent homostyles from increasing when crossing is frequent.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Treatment
- viability disturbancese5
- Outcome
- homostylese5
- Direction
- decreaseinferrede5
- Qualifier
- when the frequency of crossing is highe6
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e5“only moderate viability disturbances are needed to prevent the homostyles from increasing in frequency”
e6“when the frequency of crossing is high”
Claim · model-written summary
Model results indicate that only a slight decrease in viability is needed to decrease the proportion of homostyles where they are abundant.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Treatment
- decrease in viabilitye7
- Outcome
- proportion of homostylese7
- Direction
- decreasee7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e7“only a slight decrease in viability is needed to decrease the proportion of homostyles in populations where they are already abundant”
Claim · model-written summary
Decreased viability of mature plants could account for the thrum deficiency in Primula vulgaris.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Treatment
- decreased viabilitye7
- Outcome
- thrum deficiencye7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e7“if the decreased viability affects particularly the mature plants it is possible to account for the thrum deficiency”
Claim · model-written summary
With high initial selective values, only a few occurrences of homostyles are needed for them to gain a hold and increase in frequency.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Treatment
- only a few occurrencese7
- Outcome
- gain a hold and increase in frequencye7
- Direction
- increasee7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e7“only a few occurrences are needed to make them almost certain to gain a hold and increase in frequency”
Claim · model-written summary
Crossing between homostyles is an essential buffering mechanism against reversal of the outcrossing system to inbreeding.
- Taxon
- Primula vulgarisPrimula vulgarist0
- Outcome
- reversal of an outcrossing system to inbreedinge7
- Qualifier
- essential buffering mechanisme7
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Primula vulgaris”
e7“is an essential buffering mechanism against the possible reversal of an outcrossing system to inbreeding”