Ecological heterogeneity can lead to local adaptation when populations exhibit fitness trade-offs among habitats. However, the degree to which local adaptation is affected by the spatial and temporal scale of environmental variation is poorly understood. A multi-year reciprocal transplant experiment was performed with populations of the annual plant Leptosiphon parviflorus living on adjacent serpentine and non-serpentine soil. Local adaptation over this small geographic scale was observed, but there were differences in the temporal variability of selection across habitats. On serpentine soil, the local population had a consistently large survival advantage, presumably due to the temporal stability in selection imposed by soil cation content. In contrast, a fecundity advantage was observed for the sandstone population on its native soil type, but only in the two years of study with the highest rainfall. A manipulative greenhouse experiment demonstrated that the fitness advantage of the sandstone population in its native soil type depends critically on water availability. The temporal variability in local adaptation driven by variation in precipitation suggests that continued drought conditions have the potential to erode local adaptation in these populations. These results show how different selective factors can influence spatial and temporal patterns of variation in fitness trade-offs.

ReciprocalTransplant.csv:

Reciprocal transplant experiments were conducted at Jasper Ridge Biological Preserve (JRBP) in San Mateo County California during four spring growing seasons between 2012-2015 with populations of Leptosiphon parviflorus. These populations grow on serpentine soil and sandstone soil in close proximity (~100 m.) at JRBP.

Plants were transplanted at the seedling stage. Source seeds were collected from maternal plants grown in common greenhouse conditions that descended from plants collected from both populations at the study locations. After germination, seedlings were first transplanted into plug trays containing either serpentine or sandstone soil collected from the study site, and then transplanted into the field. During the first 1-2 weeks of growth, all plants were watered, after which supplemental watering ceased. Any seedlings that died before establishment (defined as 10 days after field transplant) were excluded from the dataset.

Study plants were censused periodically to count the number of flowers and fruits produced and whenever possible fruits were collected to count the number of seeds per fruit.

SeedPlots.csv:

Seeds from each population were collected from maternal plants grown in a common greenhouse environment, and in mid-December, roughly the time period that plants naturally germinate in the field, five seeds from each source population were placed in 100 cells in randomized order across an 11 x 24 grid. The remaining cells were kept empty to ensure that natural germinants were not being counted.

In March, (approximately 3 months after sowing), plants in each grid position were thinned to leave only one focal seedling to follow for remaining fitness estimates.

Greenhouse.csv:

Greenhouse experiments were performed at Michigan State University using soil collected from JRBP at both field locations. Seeds were germinated using the same methods as described for the field experiment, except after two weeks in an incubator, seedlings were transplanted to containers filled with a mixture of sieved field soil (serpentine or sandstone) and perlite in a 4:1 ratio. Seedlings were top watered for 3 days after transplanting, and then exclusively bottom watered. After one month of growth, plants were randomly assigned to one of two treatments: an unlimited water treatment where plants were continuously bottom watered throughout the duration of the experiment, or a drought treatment, where watering was ceased when the first plant began flowering, which occurred approximately one month after transplanting.

Hydroponic.csv:

Hydroponic experiments were performed at Michigan State University. Seeds from each parental population were sown in randomized order directly into rockwool sheets of 1” x 1” cubes (©Grodan) saturated with deionized water. These were placed in the dark at 4°C for ten days while periodically spraying with nutrient solution. They were then transferred to a growth chamber set at 22°C, 12-hour days and the rockwool was kept moist using 1⁄2 strength Hoagland’s solution and supplemental spraying of deionized water. After five days in the growth chamber, seedling germination and survival were censused. Seedlings were allowed to grow in half-strength Hoagland’s solution for an additional five days before being randomly assigned to one of four treatments with two replicate blocks per treatment. Block location in the growth chamber was randomized twice per week. 

The nutrient solution (1⁄2-strength Hoagland’s) was provided by the MSU growth chamber facility and contained calcium nitrate (3.6 mmole l-1), potassium nitrate (2.5 mmol l-1), potassium phosphate (400 μM l-1), boric acid (24 μM l-1), manganous sulphate (5 μM l-1), zinc sulphate (700 nmol l-1), copper sulphate (263 nmol l-1), and sequestrene iron chelate (38 mg l-1) dissolved in deionized water. The control solution (also used in the initial growth stages of all plants) contained 1 mmol l-1 MgSO4. The treatments consisted of a control treatment (half-strength Hoagland’s containing 1 mmol l-1 MgSO4), and three treatments with increasing amounts of magnesium sulfate (50 mM, 100 mM, 150 mM) added to the nutrient solution.

Solutions were replaced two times per week, which allowed the rock wool to stay moist throughout the experiment. Plants were censused twice a week for flowering and survival and at the end of the experiment, the total lifetime production of flowers was counted for each individual. A leak in one of the flats caused plants in one of the control blocks to dry and senesce prematurely, therefore these plants were excluded from analyses of fecundity and total fitness.

JRPrecipitationData.csv:

Data collected from weather station at Jasper Ridge Biological Preserve. Data also available from Woodside Fire Station from NOAA (used to fill in gaps when precipitation data were missing from JRBP). Data were formatted to make machine-readable (see Precipitation_analyes.R)

Local_Adaptation.zip:

Code used for ASTER analyses (cloned from: https://github.com/EDitt/Local_Adaptation on 4/26/23). Includes data files to recreate results.

Scripts require R