Morphological variability in propagules of a desert annual as a function of rainfall patterns at different temporal and spatial scales

1.Organisms living in highly variable environments have to display integrated strategies to deal with both systematic and random variation occurring at different temporal and spatial scales. Two predictions were tested by analysing geographic-scale patterns of seed size and seed retention (serotiny) in Chorizanthe rigida, a strict winter desert annual that delays seed dispersal and releases propagules after rainfall events: (a) Adaptation to systematic environmental cues occurs by means of changes in morphology, and (b) within-individual variation in seed size allows a differential response to rainfall cues: while some seeds germinate rapidly others are retained for future rainfall events.
2.We quantified morphological variation and performed germination experiments on C. rigida propagules (involucres + achenes) from six populations distributed throughout the Mojave and Sonoran deserts covering: (a) a systematic, west-to-east, winter-to-bi-seasonal (summer and winter) precipitation gra...