Natural history collections document biological responses to climate change

Abstract

All organisms experience a series of transitions across their lives, from birth to juvenile, to reproductive adult, and finally to death. Selection operates strongly on the timing of these transitions, as advancing or delaying any of these stages can reduce lifetime fitness (e.g., Munguía-Rosas, Ollerton, Parra-Tabla, & De-Nova, 2011). Along with other abiotic and biotic agents of selection, climatic factors such as temperature and water availability can elicit pheno-logical shifts and shape the evolution of these transitions. Climate change has disrupted the timing of life history events for plants and animals in a diversity of ecosystems. In response to climate change, many species are emerging and reproducing earlier in the spring and going dormant later in the fall (Parmesan & Yohe, 2003). Other species have delayed the transition to reproduction (Sherry et al., 2007). Recent technological advances have increased our ability to detect and track these phenological changes on the scales of individuals to whole ecosystems. However, natural history museums and herbaria remain a relatively untapped resource which allows us to track past phenological patterns. In this issue of Global Change Biology, DeLeo et al. (2019) leverage long-term herbarium records spanning over 200 years to identify historical changes in phenology and physiology across the native range of Arabidopsis thaliana (Brassicaceae). DeLeo et al. (2019) document striking shifts in phenology in this model species. Here, we discuss their results and highlight ways in which herbarium and museum collections can shed light on crucial biological processes, especially in the context of climate change. DeLeo et al. (2019) analyzed a suite of phenological and physiological traits to determine the extent in which these traits vary temporally and spatially. They found significant shifts in each of their focal traits over time. For example, their analyses revealed a significant delay in flowering time across the range, which is surprising as warmer temperatures associated with climate change have accelerated flowering phenology in other species. The Leaf Economic Spectrum predicts a continuum of fast to slow life history strategies across climate gradients, with lower leaf N content and thicker leaves in arid and warmer regions as a means of protecting against drought stress. However, DeLeo et al.'s (2019) results did not conform to expectations under the Leaf Economic Spectrum, as the responses of C:N, Δ 13 C, and δ 15 N to climatic variation differed across the range. Instead, temporal changes in foliar C:N and δ 15 N could have resulted from increased atmospheric CO 2 concentration and shifting land use patterns over the two centuries. Collectively, these results could signify that some Arabidopsis populations are shifting from a slow-growing, overwintering annual life cycle to a strategy of rapid spring germination and summer flowering with changing climate. Interestingly, phenology did not change uniformly across the range. These contrasting shifts in flowering across the range demonstrate Arabidopsis does not employ a single strategy to cope with climatic variation. DeLeo and colleagues' analyses suggest that divergent selection could be acting on different strategies for drought response, life history, and phenology. 1 | MUS EUM COLLEC TI ON S TE S TIF Y TO S PECIE S' RE S P ON S E S TO CLIMATE CHANG E Reproductive phenology may be the best studied trait in plants: a large and growing body of literature examines the genetics, This article is a commentary on DeLeo et al, 26, 523-538.