Advanced

Infrequent sporophyte production maintains a female-biased sex ratio in the unisexual clonal moss Hylocomium splendens

Rydgren, Knut; Halvorsen, Rune and Cronberg, Nils LU (2010) In Journal of Ecology 98(5). p.1224-1231
Abstract
P>1. Sex ratios in unisexual bryophytes are most often female biased, whereas male-biased sex ratios predominate in unisexual seed plants. This 'bryophyte paradox', i.e. that sex ratios are biased in favour of the sex associated with the highest reproductive costs, has remained unexplained. 2. Analysis of sex-ratio patterns via the influence of sex distribution on population growth rates (lambda) has not previously been carried out for bryophytes. We used this method to model how variation in sex ratio and sporophyte frequency influences lambda in the clonal bryophyte Hylocomium splendens. We obtained lambda by matrix modelling of synthetic experimental populations derived from demographic field data, using a linear two-sex model. 3. In... (More)
P>1. Sex ratios in unisexual bryophytes are most often female biased, whereas male-biased sex ratios predominate in unisexual seed plants. This 'bryophyte paradox', i.e. that sex ratios are biased in favour of the sex associated with the highest reproductive costs, has remained unexplained. 2. Analysis of sex-ratio patterns via the influence of sex distribution on population growth rates (lambda) has not previously been carried out for bryophytes. We used this method to model how variation in sex ratio and sporophyte frequency influences lambda in the clonal bryophyte Hylocomium splendens. We obtained lambda by matrix modelling of synthetic experimental populations derived from demographic field data, using a linear two-sex model. 3. In our set of experimental populations lambda varied between 1.13 and 1.27 in response to variation in sex ratio and sporophyte frequency, with the highest lambda obtained for the combination of a very low sporophyte frequency and a slightly female-biased sex ratio. 4. Our results explain the female-biased sex ratio of H. splendens by the slightly lower survival of and production of vegetative offspring by males than by non-sporophytic females. 5. Synthesis. According to our models, female dominance is the predicted outcome of low to moderate fertilization success and male performance intermediate between that of sporophytic and of non-sporophytic females. Our results therefore explain how a female-biased sex ratio can be maintained despite higher costs of reproduction in females than in males. In dioecious bryophytes, males and females must grow in close contact for fertilization to take place. Better performance of male ramets than of the female ramets they fertilize also explains how male clones can expand into female clones. A similar performance hierarchy of males and females may occur in unisexual clonal seed plants, but more efficient fertilization systems by pollination prevents the selective advantage of unfertilized females from being realized. This explains why vascular plant populations tend to be male biased. We hypothesise difference in fertilization distance range between sperm and pollen as a simple explanation why ramet level sex ratios are in general male dominated in clonal seed plants and female dominated in clonal bryophytes. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
sex-ratio, dynamics, sporophyte frequency, population growth rate, matrix model, linear two-sex model, Hylocomium splendens, cost of reproduction, bryophytes, clonality
in
Journal of Ecology
volume
98
issue
5
pages
1224 - 1231
publisher
Wiley-Blackwell
external identifiers
  • wos:000280667200026
  • scopus:77955375188
ISSN
1365-2745
DOI
10.1111/j.1365-2745.2010.01639.x
language
English
LU publication?
yes
id
b1668d41-e89c-47f7-beb0-76ba2e735a5b (old id 1678267)
date added to LUP
2010-09-21 09:53:32
date last changed
2018-05-29 11:31:32
@article{b1668d41-e89c-47f7-beb0-76ba2e735a5b,
  abstract     = {P>1. Sex ratios in unisexual bryophytes are most often female biased, whereas male-biased sex ratios predominate in unisexual seed plants. This 'bryophyte paradox', i.e. that sex ratios are biased in favour of the sex associated with the highest reproductive costs, has remained unexplained. 2. Analysis of sex-ratio patterns via the influence of sex distribution on population growth rates (lambda) has not previously been carried out for bryophytes. We used this method to model how variation in sex ratio and sporophyte frequency influences lambda in the clonal bryophyte Hylocomium splendens. We obtained lambda by matrix modelling of synthetic experimental populations derived from demographic field data, using a linear two-sex model. 3. In our set of experimental populations lambda varied between 1.13 and 1.27 in response to variation in sex ratio and sporophyte frequency, with the highest lambda obtained for the combination of a very low sporophyte frequency and a slightly female-biased sex ratio. 4. Our results explain the female-biased sex ratio of H. splendens by the slightly lower survival of and production of vegetative offspring by males than by non-sporophytic females. 5. Synthesis. According to our models, female dominance is the predicted outcome of low to moderate fertilization success and male performance intermediate between that of sporophytic and of non-sporophytic females. Our results therefore explain how a female-biased sex ratio can be maintained despite higher costs of reproduction in females than in males. In dioecious bryophytes, males and females must grow in close contact for fertilization to take place. Better performance of male ramets than of the female ramets they fertilize also explains how male clones can expand into female clones. A similar performance hierarchy of males and females may occur in unisexual clonal seed plants, but more efficient fertilization systems by pollination prevents the selective advantage of unfertilized females from being realized. This explains why vascular plant populations tend to be male biased. We hypothesise difference in fertilization distance range between sperm and pollen as a simple explanation why ramet level sex ratios are in general male dominated in clonal seed plants and female dominated in clonal bryophytes.},
  author       = {Rydgren, Knut and Halvorsen, Rune and Cronberg, Nils},
  issn         = {1365-2745},
  keyword      = {sex-ratio,dynamics,sporophyte frequency,population growth rate,matrix model,linear two-sex model,Hylocomium splendens,cost of reproduction,bryophytes,clonality},
  language     = {eng},
  number       = {5},
  pages        = {1224--1231},
  publisher    = {Wiley-Blackwell},
  series       = {Journal of Ecology},
  title        = {Infrequent sporophyte production maintains a female-biased sex ratio in the unisexual clonal moss Hylocomium splendens},
  url          = {http://dx.doi.org/10.1111/j.1365-2745.2010.01639.x},
  volume       = {98},
  year         = {2010},
}