Seed yield, seed size and germination behaviour in the annualPogogyne abramsii

Abstract

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.

Maternal fecundity does not affect offspring germination – An empirical test of the sibling competition hypothesis

“…For example, Hyatt and Evans (1998) found only marginal support for the sibling competition hypothesis with a study of a short-lived perennial desert species. On the other hand, Zammit and Zedler (1990) found a negative correlation between seed family size and germination fractions in the semi-aquatic Pogogyne abramsii that confirmed the sib competition hypothesis. Cheplick (1996) interpreted reduced germination fractions of seeds collected from the most basal tiller nodes of two species of grass as a means to avoid excessive competition among siblings.…”

The effect of temperature and water stress on laboratory germination of Eucalyptus globulus Labill. seeds of different sizes

“…Reports on the effect of seed size on germination in eucalypts are contradictory [23,27]. In this study seedsize effects were significant for several temperatures, demonstrating that sorting is essential to achieve germination uniformity in E. globulus, and that seed size has operational importance.…”

Influence of energetic status on ontogenetic niche shifts: emergence from the redd is linked to metabolic rate in brown trout

“…Indeed, it would seem likely that selection might favor females that can adjust offspring emergence to decrease the level of kin competition. Such control over offspring emergence has been theorized in plant species where variable seed dormancy is expected to reduce sibling competition (Ellner 1986;Nilsson et al 1994), and some empirical support has been found in Pogogyne abramsii (Zammit and Zedler 1990) and Lepidium lasiocarpum (Philippi 1993). However, such a relationship has not been investigated in mobile organisms, such as salmonids, where it may be a causal mechanism driving the evolution of within-family variation at emergence time.…”