Reproductive phenological shifts and other phylogenetic trait changes in the Arbutoideae (Ericaceae) in the context of drought, seed predation, and fire

V Thomas Parker,Morgan A Stickrod

doi:10.1139/cjb-2021-0163

Abstract

Phenology is an ecologically critical attribute that is commonly coordinated with other plant traits. Phenological shifts may be the result of evolutionary adjustments to persistently new conditions, or they may be transitory, varying with annual fluxes in abiotic conditions. In summer-dry, fire-prone Mediterranean-type climates, for example, many plant lineages have historically migrated from forests to more arid shrublands resulting in adaptive trait changes. These shifts in habitat abiotic conditions and biotic interactions influence morphology of flowers and fruits and interact with phenological timing. The Arbutoideae (Ericaceae) is one lineage that illustrates such modifications, with fruit characters evolving among genera from fleshy to dry fruit, thin to stony endocarps, and bird to rodent dispersal, among other changes. We scored herbarium collections and used ancestral trait analyses to determine phenological shifts among the five Arbutoid genera found in semi-arid climates. Our objective was to determine if phenology shifts with the phylogenetic transition to different reproductive characters. Our results indicate that phenological shifts began with some traits, like the development of a stony endocarp or dry fruits, but not with all significant trait changes. We conclude that early phenological shifts correlating with some reproductive traits were permissive for the transition to other later character changes.

Highlights

Phenological changes that occur in coordination with fruit types is an understudied dimension of fruit evolution compared with dispersal or other traits (Forrest and Miller-Rushing 2010)
American Arbutoideae reflect their ecological and phylogenetic history as this lineage expanded from relatively mesic forests to drier woodlands and semi-arid shrublands (Stevens 1971, 1995)
Large phenological shifts correlated with morphological trait changes involving seed predation and especially the change from fleshy to dry fruit, but not with other trait changes

Summary

Introduction

Phenological changes that occur in coordination with fruit types is an understudied dimension of fruit evolution compared with dispersal or other traits (Forrest and Miller-Rushing 2010). The focus on dispersal agents and abiotic factors is important, but in the context of climate change, reproductive phenology is one trait likely to be influenced significantly by warming temperatures, either in terms of flowering time or fruit maturation (Menzel et al 2006; Gordo and Sanz 2010; Piao et al 2019). We selected the Arbutoideae, an early diverging, monophyletic subfamily in the Ericaceae (Kron et al 2002; Freudenstein et al 2016) comprising six morphologically distinct genera (Stevens 1995) Most species of this subfamily are found in summer-dry, fire-prone Mediterranean-climates (Parker et al 2016) or otherwise strongly seasonal climates (Stevens 1995; Hileman et al 2001). Different fruit types occur in this subfamily and we ask if phenological differences in flowering and fruit maturation are coordinated with changes in fruit types

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Conclusion