Bimodal colour pattern of individual Pinus halepensisMill. seeds: A new type of crypsis

Abstract

Variation in seed traits is a well-known phenomenon affecting plant ecology and evolution. Here we describe, for the first time, a bimodal colour pattern of individual seeds, proposing an adaptive explanation, using Pinus halepensis as a model. Pinus halepensis disperses its seeds either by wind on hot dry days, from regular cones, or after fires, mainly from serotinous cones. Post-dispersal seeds are exposed to strong predation by passerine birds, making crypsis important for seed survival. Individual seeds from non-serotinous cones have a bimodal colour pattern: one side is light brown and the other black, exposing only one colour when lying on the ground. Serotinous cones from most trees have seeds with similar bimodal colour patterns, whereas seeds from serotinous cones of some trees are light brown on both sides. The dark side provides the seed with better crypsis on dark soils, whereas the light-brown side is better adapted to light-coloured soils, and mainly to light-grey ash-covered soil, which is the natural post-fire regeneration niche of P. halepensis. The relative reflection curves of the black and brown seed colours differ, and their calculated relative chromatic distance is 5: meaning that seed-predating passerine birds see them differently, and probably prefer seeds that present a higher contrast against the soil background. We propose that such a bimodal colour pattern of individual seeds is probably an overlooked general phenomenon mainly linked to seed dispersal in post-fire and other heterogeneous environments. © 2013 The Linnean Society of London.