Abstract
Variation in seed size and dormancy can take the form of seed heteromorphism, i.e., production of different kinds of seeds by a single individual. In this paper, I tested for the effect of seed position within a spikelet on its germination over time, and the contribution of this effect to population differentiation along an aridity gradient in an annual grass, Triticum dicoccoides. The results show that the upper grain in a spikelet is larger than the bottom grain, and either germinates in the season following dispersal, or dies. In contrast, a substantial fraction of the bottom grains do not germinate in the first season, but remain dormant in the soil seed bank for 1 and, very rarely, 2 years. This pattern was observed in seeds of all origins, but the bottom grains from the most arid location had the lowest, and from the least arid location, the highest germination fraction in the 1st year and vice versa in the 2nd year. This difference in germination fraction was observed under controlled irrigation conditions but not in the field experiment. These mixed results suggest that seed dimorphism is a life history trait with a complicated evolutionary history and wide adaptive implications. Seed dimorphism in T. dicoccoides could initially be an adaptation for reducing competition in productive (i.e., high precipitation) environments. In addition to this, seed dimorphism under increasing aridity could become a bet-hedging trait allowing a population to survive periods of insufficient rainfall through dormancy.
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Acknowledgments
The current study was supported by the Israel Academy of Sciences (ISF 958/07) and the CAS/SAFEA International Partnership Program for Creative Research Teams. The experiments conducted comply with the current laws of Israel in which the experiments were performed. I would like to thank Asher Dvir and Lev Burdeniy for help with the fieldwork and greenhouse experiments, Linda Olsvig-Whittaker for editing the English, and two anonymous reviewers for constructive comments.
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S. V. conceived, designed and performed the experiments, analyzed the data and wrote the manuscript.
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Communicated by Anne Worley.
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Volis, S. Seed heteromorphism in Triticum dicoccoides: association between seed positions within a dispersal unit and dormancy. Oecologia 181, 401–412 (2016). https://doi.org/10.1007/s00442-016-3576-7
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DOI: https://doi.org/10.1007/s00442-016-3576-7