Is the Rare Grassland perennial Saxifraga granulata Pollen Limited?
The Effect of Population size on Seed Quantity and Seed Quality
in the Rare Grassland species Saxifraga granulata
Biodiversity and population dynamics of species in many terrestrial ecosystems are
nowadays threatened by habitat loss and fragmentation. Due to the small size and
increased isolation of the remnant habitats populations become smaller and more
isolated, which can increase the risk of local extinction (Lande, 1993). In animalpollinated plants small populations are most likely less attractive to pollinators than
large populations, which might affect the amount of pollen that is being transferred
between plants and between flowers of the same plant. Small populations might also
experience higher levels of genetic drift, leading to a loss of genetic variation, which
in turn, might affect pollen quality. Thus, small populations might face a reduction in
pollen quantity as a result of fewer pollinator visits or less pollen being delivered per
visit and a reduction in pollen quality due to higher amounts of self, genetically
similar or otherwise incompatible pollen being delivered (Ashman et al., 2004).
Saxifraga granulata (meadow saxifrage) is a rare selfcompatible perennial of mesic and dry grasslands.
Habitat destruction and the increasing use of fertilizers in
agriculture have reduced both the number of populations
and the size of the remaining populations in Belgium. In
a previous study a correlation was found between
populations size and seed production, which leads us to
believe that this species might also be pollen limited.
The aim of this project is to find out whether low seed production in small
populations is due to pollen limitation, but more
specifically if this is caused by a low quantity or
low quality of pollen being delivered to the
flowers. Since pollination success might also be
linked to local plant density, the impact of local
plant density on pollen limitation will be
investigated as well. Finally, different measures of
genetic variation within populations will be
related to the strength of pollen limitation.
During spring (May), 15 populations that range in size from 4 up to 5000 flowering
individuals will be visited. In these populations 20 individuals (or all individuals
when there are less than 20 flowering plants) will
be selected and per individual 2 flowers will be
hand-selfed, 2 flowers will be hand-outcrossed
and 2 flowers will be marked for open
pollination. Plant density within the populations
will be measured as the distance to the nearest
flowering neighbors and the amount of flowers
they display. At the same time, leaf material will
be collected for genetic analysis. However, last season I have collected material in
most populations for a meta-populations study of this species, thus we would just
have to add additional samples from populations that have not been sampled before.
All field work will be conducted in the wide vicinity of Leuven.
In June, after the fruits have ripened, fruits and seeds will be collected
and seed production per population will be assessed. To determine the
seed quality we will sow 90 seeds per plant (30 for every treatment)
and measure the germination rate, seedling survival and growth and
compare these between populations of different sizes, plant density and
genetic structure.
Genetic analysis will be done using newly developed highly
polymorphic micro-satellite markers. This way, we can
determine the level of heterozygosity within populations.
The work in this project is related to work that I will be doing on male and female
function and a demographic study of Saxifraga granulata.
What you can expect during this project is a good field-season outdoors, work in the
lab and greenhouse, and interesting results to analyze and write about.
If you are interested in doing this project or a similar Master project at the dept. of
‘Plant Conservation and Population Biology’ (University of Leuven)
please contact me at Sascha.vanderMeer@bio.kuleuven.be
References:
Ashman T.L., Knight, T.M., Steets J.A., Amarasekare P., Burd M., Campbell D.R., Dudash
M.R., Johnston M.O., Mazer S.J., Mitchell R.J., Morgan M.T., and Wilson W.G., (2004). Pollen
limitation of plant reproduction: ecological and evolutionary causes and consequences. Ecology 85(9):
2408-2421.
Lande, R., (1993). Risks of population extinction from demographic and environmental
stochasticity and random catastrophes. The American Naturalist 142(6): 911-927.