Flowering and Fitness: Local Adaptation and Plasticity Responses to an Environmental Gradient in Maize Landraces in Chiapas, Mexico.

Plant populations can evolve to differentially adapt in the presence of environmental variation.  Mountainous regions, where elevation creates temperature, UV-B, and other clinal gradients, allow for study of plastic responses of wild and cultivated plants to environmental variation, as well as of local adaptation.  Understanding these phenomena can provide insight for farming systems combatting climate change.  We ask: how does flowering phenology and fitness in maize landraces respond to environmental change?  We used 27 populations collected from farmers at three elevations (600m, 1550m, 2050m) along a transect in Chiapas, Mexico that were reciprocally planted at three gardens approximately at the collection elevations.  Landraces, especially from the highlands, had some minor difficulty flowering out of their elevation of origin, though especially in the lowland and midland gardens in 2012.  Flowering time was mostly influenced by garden with higher elevation (lower growing degree days) increasing time to flower; but the highland landraces also trended towards having the latest flowering, though less so as elevation increased.  By contrast, anthesis-silking interval showed clear patterns of local adaptation (apart from short ASI commercial varieties) with the shortest values in the local types.  Highland types had very low survival to reproduction under lowland conditions and midland types were also challenged there, while improved varieties had generally high survival to reproduction in all locations.  For plants that did reproduce, we saw local adaptation (especially with seed weight, rather than seed number, data) and types were most differentiated under lowland conditions; the highland environment differentiated seed number the least. Stress brought on by being out-of-place was reflected in our fitness metrics and fitness appeared to be linked to flowering responses.  Thus, responses to stresses brought on by climate change will likely affect flowering and thereby affect important fitness traits in maize landraces—and possibly in other crops.