A comparison of pollen-siring ability and life history between males and hermaphrodites of subdioecious Silene acaulis

TY - JOUR

T1 - A comparison of pollen-siring ability and life history between males and hermaphrodites of subdioecious Silene acaulis

AU - Philipp, Marianne

AU - Jakobsen, Ruth Bruus

AU - Nachman, Gøsta Støger

N1 - Keywords: Arctic, gynodioecy, pollen competition, Silene acaulis, subdioecy.

PY - 2009

Y1 - 2009

N2 - Background: Silene acaulis is an evergreen, very long-lived cushion plant. Populations ofis an evergreen, very long-lived cushion plant. Populations of S. acaulis in Greenland are subdioecious, consisting of female, hermaphrodite, and malein Greenland are subdioecious, consisting of female, hermaphrodite, and male individuals. The sex expression of males and hermaphrodites can vary over years for the sameindividual, while females are always females. Previous studies have shown that outcrossedseeds from females become seedlings with higher survival and growth rates than those fromoutcrossed seeds from hermaphrodites.Questions: (1) Do pollen grains from males exhibit some advantage over pollen from(1) Do pollen grains from males exhibit some advantage over pollen from hermaphrodites? In particular, do they sire more seeds than hermaphrodites? (2) Is thereproductive system of S. acaulis stable or is it evolving towards one with fewer morphs(i.e. dioecy or gynodioecy)?Hypothesis: Pollen from male plants is better at siring seeds on females than pollen fromPollen from male plants is better at siring seeds on females than pollen from hermaphrodites.Study system: A subdioecious population of S. acaulis in Greenland, containing maleA subdioecious population of in Greenland, containing male individuals that produce pollen and rarely or never set seed, hermaphrodites that produce bothpollen and seeds, and females that produce only seeds.Methods: A pollen-competition experiment was performed in which females were handA pollen-competition experiment was performed in which females were hand pollinated with a mixture of pollen from males and hermaphrodites, all with known isozymealleles, which allowed determination of who sired each seed. We recorded plant size, flowermorphology, fruit and seed set, as well as pollen per anther for the individuals used in theexperiment, as well as for a large number of other individuals to allow us to make comparisonsbetween the three types of individuals.Conclusions: Well-developed pollen grains from males or hermaphrodites did not differ inWell-developed pollen grains from males or hermaphrodites did not differ in their seed-siring capacity, although males had significantly more well-developed pollen grainsper anther than hermaphrodites. Hence, on a per flower basis, males would be predictedto sire more seeds than hermaphrodites. However, given that males and hermaphroditesproduce similar numbers of flowers per square centimetre of cushion and that male plantswere significantly smaller than hermaphrodites, hermaphrodites have the potential tocontribute relatively more to the seed pool than males. Calculations based on our quantitativeresults suggest that the dynamics of the population should develop slowly towards gynodioecy.However, this conclusion applies only as long as the population does not experience asignificant change in the environmental conditions over time.

AB - Background: Silene acaulis is an evergreen, very long-lived cushion plant. Populations ofis an evergreen, very long-lived cushion plant. Populations of S. acaulis in Greenland are subdioecious, consisting of female, hermaphrodite, and malein Greenland are subdioecious, consisting of female, hermaphrodite, and male individuals. The sex expression of males and hermaphrodites can vary over years for the sameindividual, while females are always females. Previous studies have shown that outcrossedseeds from females become seedlings with higher survival and growth rates than those fromoutcrossed seeds from hermaphrodites.Questions: (1) Do pollen grains from males exhibit some advantage over pollen from(1) Do pollen grains from males exhibit some advantage over pollen from hermaphrodites? In particular, do they sire more seeds than hermaphrodites? (2) Is thereproductive system of S. acaulis stable or is it evolving towards one with fewer morphs(i.e. dioecy or gynodioecy)?Hypothesis: Pollen from male plants is better at siring seeds on females than pollen fromPollen from male plants is better at siring seeds on females than pollen from hermaphrodites.Study system: A subdioecious population of S. acaulis in Greenland, containing maleA subdioecious population of in Greenland, containing male individuals that produce pollen and rarely or never set seed, hermaphrodites that produce bothpollen and seeds, and females that produce only seeds.Methods: A pollen-competition experiment was performed in which females were handA pollen-competition experiment was performed in which females were hand pollinated with a mixture of pollen from males and hermaphrodites, all with known isozymealleles, which allowed determination of who sired each seed. We recorded plant size, flowermorphology, fruit and seed set, as well as pollen per anther for the individuals used in theexperiment, as well as for a large number of other individuals to allow us to make comparisonsbetween the three types of individuals.Conclusions: Well-developed pollen grains from males or hermaphrodites did not differ inWell-developed pollen grains from males or hermaphrodites did not differ in their seed-siring capacity, although males had significantly more well-developed pollen grainsper anther than hermaphrodites. Hence, on a per flower basis, males would be predictedto sire more seeds than hermaphrodites. However, given that males and hermaphroditesproduce similar numbers of flowers per square centimetre of cushion and that male plantswere significantly smaller than hermaphrodites, hermaphrodites have the potential tocontribute relatively more to the seed pool than males. Calculations based on our quantitativeresults suggest that the dynamics of the population should develop slowly towards gynodioecy.However, this conclusion applies only as long as the population does not experience asignificant change in the environmental conditions over time.

M3 - Journal article

SN - 1522-0613

VL - 11

SP - 787

EP - 801

JO - Evolutionary Ecology Research

JF - Evolutionary Ecology Research

IS - 5

ER -