Fast and Cheap in the Fall: Phylogenetic determinants of late flowering phenologies in Himalayan Rhododendron.

Abstract

Biotic and abiotic pressures affect the beginning and end of phenologies differently, but little is known about how these temporal components may be determined by phylogeny. We tested for phylogenetic signal in the phenological components and related traits among Himalayan Rhododendron species. We constructed a phylogeny with trnL-trnL-trnF, atpH-I, RPB2-I (3F-4R), and ITS 4-5, and examined it in combination with trait data recorded for a nine-species assemblage on Mt. Yulong, Yunnan, China. Uniquely among phenological traits, 'last flowering day' had a significant phylogenetic signal. Last flowering day was latest in the clade with the smallest fruits. A similar association between the end of flowering and reproductive investment existed in data from Flora of China (Wu et al., 2005) for 160 Yunnan Rhododendron species, for which last flowering month was correlated with fruit size. Phylogenetic determinants of last flowering day and fruit size may be driven by limited time for fruit development before the onset of cold temperatures in autumn-a temporal niche that only small-fruited species can occupy. This strategy is analogous to 'fast and cheap' spring ephemerals. More may be gained from late-phenology studies, both within and among species and across seasons.