Ghost of environments past: investigating plant maternal effects in the presence of drought

stressAlexandra Mushka and Alanna LealeDepartment of Ecology and Evolutionary Biology

Literature Cited:1. Riginos, C., M.S. Herschel, and J. Schmitt. 2007. Am. J. Bot. 94(12): 1984-19912. Sultan, S.E., K. Barton, and A.M. Wilczek. 2009. Ecology 90(7): 1831-18393. Sultan, S.E. 1996. Ecology 77(6): 1791-18074. Weiner, J., S. Martinez, H. Muller-Scharer, P. Stoll, and B. Schmid. 1997. J. Ecol. 85(2): 133-1425. Jakobsson, A. & Eriksson, O 2000.. Oikos 88: 494-502.

Background

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-induced maternal effects vary across species

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C. Seed mass vs. number (negative values indicate a trade-off)

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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

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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.

ROP project supervisors Rachel Germain and Dr. Benjamin Gilbert.

Learn more about the Gilbert Lab at :http://labs.eeb.utoronto.ca/gilbert/people.htm

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.