1) The study examined maternal effects in 29 annual plant species native to California or Spain that commonly face drought. Plants were grown in wet or dry conditions and their seeds were analyzed. 2) Maternal effects on seed mass or number were found in 5 and 7 species respectively, but the direction of effects varied. Seed number generally increased in wet conditions while seed mass responses were mixed. 3) Neither phylogeny nor geographical origin appeared to influence drought responses significantly, except some seed mass effects were grouped in the Poales order. Many species favored one environment for either seed mass or number, with unclear trade-offs between the two.

1. 1. Riginos, C., M.S. Herschel, and J. Schmitt. 2007. Am. J. Bot. 94(12): 1984-1991
2. Sultan, S.E., K. Barton, and A.M. Wilczek. 2009. Ecology 90(7): 1831-1839
3. Sultan, S.E. 1996. Ecology 77(6): 1791-1807
4. Weiner, J., S. Martinez, H. Muller-Scharer, P. Stoll, and B. Schmid. 1997. J. Ecol. 85(2): 133-142
5. Jakobsson, A. & Eriksson, O 2000.. Oikos 88: 494-502.
Experiment Conclusions
Results
In plants, ‘maternal effects’ refer to the effect of the maternal
environment on offspring phenotype. For example, some
studies have shown that parents in good environments produce
larger, healthier seeds.
Despite clear examples of maternal effects in some species,
there has been no systematic study of their importance for a
broad suite of species1,2. In addition, the type of maternal effect
can differ – species have shown differences in terms of the
quality and quantity of offspring, but the potential trade-off in
these responses has not been tested.
In our study, we examined the generality of maternal effects for
Mediterranean annual plants found in California. This large
group of species commonly faces drought conditions, with
highly variable rainfall from one year to the next. Our goal was
to test the generality of maternal effects among these species,
using ecologically relevant conditions. In this study, we asked:
1) Are drought induced maternal effects still prevalent at
the community level?
2) Does phylogeny and area of origin (native to California
or Spain) account for any variation in maternal effects?
Drought
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C. Seed mass vs. number (negative values indicate a trade-off)
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B. Number of seeds per plant
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A. Seed mass
Figure 2: a) t-values for mass per seed testing null hypothesis μDry – μWet = 0, b) t-values for total number of seeds per plant testing
null hypothesis μDry – μWet = 0, c) t-values testing null hypothesis that the linear relationship between seed mass and number is equal
to zero. All tests showed significant species x environment interactions, indicating different responses among species.
* Significant P-value with 0.05 significance level
Native species
Non-Native species
Performanceindry-wetenvironments(t-values)
Maternal effects to drought were negligible for 58% of the
species, with five and seven species responding significantly
through seed mass and seed number, respectively (Fig. 2)
Seed mass varied in direction. However, seed number was
mainly increased in wet compared to dry environments.
Phylogeny and area of origin does not appear to play a
significant role in species’ drought responses, except for some
grouping of significant seed mass effects in the Poales order.
Many species had one favourable environment (seed mass or
seed number effect with a positive or no relationship between the
two). However, for those species that do show a trade-off, it is
unclear if gain in seed size offsets loss in seed number, and vice
versa, in response to the environment.
Despite many studies showing the importance of maternal
effects on specific species, these effects are not consistent in
magnitude or direction within a community4.
Maternal effects are expressed at several nodes across a
diverse phylogeny, suggesting that their expression is not
constrained by recent evolutionary relationships.
Similarly, maternal effects do not seem to be related to the
geographical origin of the plant.
The importance of different types of effects (seed size and
seed number) and their trade-offs remains an important area of
research5. Our ongoing study is designed to address these
questions.
ACKNOWLEDGMENTS
Ecological community: 29 species from Mediterranean climates
native to California or Spain comprising taxonomic orders
Asterales, Lamiales, Fabales, Caryophyllales, Ranunculales and
Poales
Maternal plants were grown in dry (5.8 % soil moisture) or wet
(11.1% soil moisture) greenhouse conditions, which are known to
be important to Mediterranean species3. Seeds were counted and
weighed, and a subset were planted to examine seedling
performance (Fig. 1).
We used generalized linear models to examine the effect of
maternal environment on seed size, seed number and any
potential trade-off.
Figure 1: Growing plants and processing seeds.
Hvulg Vmyur Pcamp
Figure 3: Seed morphology of three species used in this experiment.