Seed size, fecundity and postfire regeneration strategy are interdependent in Hakea.

Sh-Hoob Mohamed El-Ahmir,Sim Lin Lim,Tianhua He,Byron B Lamont

doi:10.1371/journal.pone.0129027

Abstract

Seed size is a key functional trait that affects plant fitness at the seedling stage and may vary greatly with species fruit size, growth form and fecundity. Using structural equation modelling (SEM) and correlated trait evolution analysis, we investigated the interaction network between seed size and fecundity, postfire regeneration strategy, fruit size, plant height and serotiny (on-plant seed storage) among 82 species of the woody shrub genus, Hakea, with a wide spectrum of seed sizes (2–500 mg). Seed size is negatively correlated with fecundity, while fire-killed species (nonsprouters) produce more seeds than resprouters though they are of similar size. Seed size is unrelated to plant height and level of serotiny while it scales allometrically with fruit size. A strong phylogenetic signal in seed size revealed phylogenetic constraints on seed size variation in Hakea. Our analyses suggest a causal relationship between seed size, fecundity and postfire regeneration strategy in Hakea. These results demonstrate that fruit size, fecundity and evolutionary history have had most control over seed size variation among Hakea species.

Highlights

Seed size is a key trait in the life history of plants that affects fitness at the seedling stage and is often correlated with other attributes important in their evolution and ecology [1]
Structural equation modelling and Bayesian Monte Carlo Markov Chain (MCMC) analysis showed that seed size was most significantly associated, in a co-evolutionary sense, with fruit size where larger fruits support larger seeds (H6)
This relationship is clearly causal as a) the number of seeds per fruit is fixed so that only seed size can vary, b) the pericarp acts directly as a source of nutrients for seed filling [33], c) larger fruits have a better vascular supply for seed filling [53], and d) larger fruits are an adaptive response to the greater vulnerability of larger seeds to granivores [32]

Summary

Introduction

Seed size is a key trait in the life history of plants that affects fitness at the seedling stage and is often correlated with other attributes important in their evolution and ecology [1]. By analysing seed mass data for 13,000 species, Moles et al [8] concluded that there is a close association between seed size and plant height that is likely the result of the scaling of seed size to plant height [9]. Seed size variation may be subject to phylogenetic constraints on seed development, such that closely related species may have similar seed sizes [9]. Recent research points to a significant role for fire in shaping the evolution of plant functional traits in these fire-prone ecosystems [10, 11]. Studies of how fire might have influenced seed size variation are scarce

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