Seed yield,seed size and germination behaviour in the annualPogogyne abramsii |
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Authors: | Charles Zammit Paul H Zedler |
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Institution: | (1) Biology Department, San Diego State University, 92182 San Diego, CA, USA;(2) Present address: Ecosystem Dynamics Group, Research School of Biological Sciences, The Australian National University, P.O. Box 475, 2601 Canberra, ACT, Australia |
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Abstract: | Summary Models of the evolution of seed dormancy reveal that dormancy is favoured either when opportunities for establishment vary
over time and when there is wide variation in the probability of success, or when the probability of success is limited by
frequency dependence. Empirical evidence supporting the temporal heterogeneity hypothesis exists, but there is scant evidence
for dormancy being favoured by frequency dependent competition among seedlings. We test the hypothesis that the intensity
of between-sib competition should favour a positive relationship between maternal fecundity and seed dormancy. This hypothesis
is supported for the rare, vernal pool annual,Pogogyne abramsii: the proportion of dormant offspring was significantly higher among high fecundity mothers than among other mothers. Dormancy
inP. abramsii is controlled by the seed coat, a maternal tissue, so delaying germination favours the inclusive fitness of mothers by reducing
the potential for competition among siblings. Seed weight and time to first germination varied significantly amongP. abramsii plants and mean seed weight increased linearly with plant biomass. Seed weight and seed number are independently regulated
by plant size. Overall, seed weight varied 10-fold and variability in seed weight within mothers was not explained by plant
biomass, seed yield or mean seed weight. GerminableP. abramsii seeds were significantly heavier than dormant seeds, and germinable seeds heavier than 0.20 mg germinated more rapidly than
those smaller than 0.20 mg. |
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Keywords: | Dormancy Germination Seed size Seed number Sibling competition |
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