DOI: 10.5061/dryad.3tx95x6c3
title: Evolutionary and plastic changes in a native annual plant after a historic drought

description: Severe droughts are forecast to increase with global change. Approaches
 that enable the study of contemporary evolution, such as resurrection
 studies, are valuable for providing insights into the responses of
 populations to global change. In this study, we used a resurrection
 approach to study the evolution of the California
 native Leptosiphon bicolor (true babystars,
 Polemoniaceae) across populations differing in precipitation in response
 to the state’s recent prolonged drought (2011-2017). In the
 Mediterranean-climate region in which L. bicolor grows,
 this historic drought effectively shortened its growing season. We used
 seeds collected both before and after this drought from three populations
 found along a moisture availability gradient to assess contemporary
 evolution in a common garden greenhouse study. We coupled this with a
 drought experiment to examine plasticity. We found evolution toward
 earlier flowering after the historic drought in the wettest of the three
 populations, while plasticity to experimental drought was observed across
 all three. We also observed trade-offs associated with earlier flowering.
 In the driest population, plants that flowered earlier had lower intrinsic
 water-use efficiency than those flowering later, which was an expected
 pattern. Unexpectedly, earlier flowering plants had larger flowers. Two
 populations exhibited evolution and plasticity toward smaller flowers with
 drought. The third exhibited evolution toward larger flowers, but
 displayed no plasticity. Our results provide valuable insights into
 differences among native plant populations in response to drought.
description: These data were collected as part of a resurrection type study to
 examine contemporary evolution in response to drought. Seeds were
 collected from three field populations of <em>Leptosiphon
 bicolor </em>(Polemoniaceae) varying in moisture availability both
 before and after a multi-year historic drought in California. Seeds were
 grown together in a greenhouse in a "refresher" generation to
 remove maternal and storage effects, and allowed to set seed. These seeds
 were then planted in a greenhouse experiment in which plants were given
 one of two watering treatments (low- and well-watered). We monitored
 plants daily to record germination date and flowering date. On the first
 flowering date, flower size was measured and plants were collected to
 measure aboveground biomass and perform stable carbon isotope analyses to
 assess intrinsic water-use efficiency. Date of death was recorded for any
 plants that died before flowering
description: All tests were analyzed using SPSS (v.25, IBM Corp., NY, USA). To test for evidence of earlier flowering time, we used a Cox proportional hazards model. Our analyses included generation (ancestral or descendant), population, watering treatment, and block (planting date), as well as all 2- and 3-way interaction terms between generation, population, and treatment. The test generates a Wald chi-square test statistic, which is a one-tailed test with alpha = 0.10. After our initial analysis indicated significant differences between populations, we ran post-hoc pairwise models to compare populations, using the Sidak-corrected alpha = 0.034 (Tripathi and Pandey 2017). Finally, we ran individual analyses of flowering time for each population.  We used mixed models to examine how physiological and morphological traits (intrinsic WUE, flower size, and aboveground vegetative mass) varied among populations over time and with watering treatment using MIXED in SPSS. We first ran the full model including all 2- and 3-way interactions between population, generation, and treatment. We then ran subsequent models, eliminating non-significant interaction terms, one at a time, selecting the model with the lowest value of Aikike’s Information Criteria. When a significant population effect was detected, we used estimated marginal means with a Bonferroni correction to make pairwise comparisons between populations. Finally, intra-population models were run to determine the effect of generation and watering treatment within each population.  We used pairwise Pearson correlations to examine the relationship between flowering time and the other measured traits. Correlations were analyzed within each population, generation, and treatment combination.             We assessed survival of plants through the study using the non-parametric chi square-test of independence. We compared survival both across the generations and between the watering treatments. We followed these tests with an analysis that compared survival in the low water treatment between generations of each population.