Environmental change is predicted to accelerate into the future and will exert strong selection pressure on biota. While many species may be fated to extinction, others may survive through their capacity to evolve rapidly at highly localized (i.e. microgeographic) scales. Yet, even as new examples have been discovered, the limits to such evolutionary responses have not often been evaluated. One of the first examples of microgeographic variation involved pond populations of wood frogs (Rana sylvatica). Although separated by just tens to hundreds of meters, these populations exhibited countergradient variation in intrinsic embryonic development rates when reared in a common garden. We repeated this experiment 17 years (approx. 6-9 generations) later and found that microgeographic variation persists in contemporary populations. Furthermore, we found that contemporary embryos have evolved to develop 14% to 19% faster than those in 2001. Structural equation models indicate that the predominant cause for this response is likely due to changes in climate over the intervening 17 years. Despite potential for rapid and fine-scale evolution, demographic declines in populations experiencing the greatest changes in climate and habitat imply a limit to the species’ ability to mitigate extreme environmental change.

Embryonic development and size:

In the spring of 2018, we conducted a common garden experiment following the methods in Skelly (2004). We collected embryos from 13 wood frog breeding ponds at Yale Myers Forest, Connecticut, USA within 24 hours of oviposition between 31 March and 14 April 2018. We excised embryos from the egg mass, being careful not to puncture the vitelline membrane, and placed them individually into wells of 6-well culture plates with 15 ml reconstituted distilled water so that each plate contained 6 full-sib embryos. We split clutches across two temperature treatments (high: 13.7°C; low: 11.7°C). Incubator temperatures were set to replicate the original study and represent a large portion of the range in temperatures measured at wood frog oviposition sites. We stocked one plate from each clutch into each light controlled incubator treatment with a 12:12 H photoperiod centered at 1200 EST. The incubators (I-36VL (Percival Scientific, Inc.)) were the same units used in the original study. Plates were placed randomly in the incubators and rotated daily. In total, we included 888 embryos representing 74 clutches in the experiment.We monitored embryos daily and estimated hatching as the moment when a larva breaks through the vitelline membrane. Embryos that died or exhibited abnormal development were noted and excluded from further analysis. These data are included in “EmbPer2018_YMF_20190910.csv”. See ReadMe files for data column descriptions.

Data from the original experiment (Skelly, D. K. (2004). Microgeographic countergradient variation in the wood frog, Rana sylvatica. Evolution, 58(1), 160–165.) are included in “EmbVol2001_YMF_20190822.csv” and “EmbPer2001_YMF_20190820.csv”. See ReadMe files for data column descriptions.

Raw images for both the 2001 and 2018 experiment are included in the directory “Images”.

Incubator temperatures recorded from Hobo Pendant temperature loggers for the 2001 experiment (directory “2001_IncLogger”) and 2018 experiment (“IncubatorTemps_20180507.csv”) are included. Further details are included in the Supplementary Materials and inline in the R code.

Microhabitat:

We extracted daily meteorological data, including maximum and minimum temperature, precipitation, and snowpack (quantified as snow water equivalent) from the DayMet database (v.3 (Thornton et al. 2016)). The Daymet algorithm uses daily meteorological observations from ground stations to interpolate estimates at 1km square cells across North America between 1980 and 2018. We extracted estimates for the cell centered nearest the geographical center of our site (tile: 11754, N 41.9198 W -72.1604). This data file “DAYMET_YMF_20200402.csv “ originated in Arietta, A. Z. Andis (2020), Data from: Phenological delay despite warming in wood frog (Rana sylvatica) reproductive timing: a 20-year study, Dryad, Dataset, https://doi.org/10.5061/dryad.dv41ns1vs

We recorded water temperatures in a subset of the 60 wood frog breeding ponds at our field site. We recorded water temperature at the deepest point in the pond every 0.5 or 1 h with submersible temperature loggers (HOBO 8K Pendant (Onset Computer Corporation)) suspended 10 cm below the surface. Loggers were deployed within days of oviposition and removed after larvae had metamorphosed or the pond dried. The data file “Master_PondLoggerTemps20200403.csv“ contains daily average temperature data. See ReadMe files for data column descriptions.

We estimated canopy and understory light from repeated hemispherical photos taken in 1999-2001 and 2017-2018. Briefly, five hemispherical photographs were take along the shore at each cardinal point and at the center of each pond during leaf-off and leaf-on seasons. We used Gap Light Analyzer (Frazer 1999) to estimate average leaf-on and leaf-off global site factor (GSF; the ratio of above-canopy radiation to under-canopy radiation (Anderson 1964)) and a weighted GSF value integrated over the duration of wood frog larval and embryonic life cycle (Halverson et al. 2003). Additionally, we included the within-pond variance in GSF values, which captures important components of the canopy shape and structure above and surrounding the ponds. Data from 2017-2018 are included in “YMF_canopy_Master_10Mar2018.csv”. Data from 1999-2001 (“RAWradiation_2000data.csv”) are from: Halverson (2003. Forest mediated light regime linked to amphibian distribution and performance. Oecologia. 134: 360-364). Further details are included in the Supplementary Materials and inline in the R code.

Population size:

These data (“YMF_EggSurveyData_00to19_CLEANED.csv“) include records of annual egg-mass surveys collected between 2000 and 2019 for 64 wood frog breeding ponds at Yale Myers Forest, a 3,213 ha research forest in northeastern Connecticut, USA. During surveys, the entire pond was closely searched by observers. If eggs were found, the observers independently counted and then averaged the estimates (or, in cases of surveys by a single observer, egg masses were counted twice and averaged). This data file originated in Arietta, A. Z. Andis (2020), Data from: Phenological delay despite warming in wood frog (Rana sylvatica) reproductive timing: a 20-year study, Dryad, Dataset, https://doi.org/10.5061/dryad.dv41ns1vs

Site data:

These data include locational and geographic information for wood frog pond populations at Yale Myers Forest, Connecticut, USA. “YMF_Pond_GeoInfo.csv” includes point values for aspect and elevation estimated from the USGS National Elevation Dataset (U.S Geological Survey 2002). “YM_Pond_Coords.csv” includes geographic coordinates for the center point of wood frog breeding ponds. A data file for converting pond names to standard letter codes (“YMFpondID.csv”) and a directory containing shape files of Yale Myers Forest property (“YMF_shapefiles”) are included.

ReadMe files and notes on data use are included in the data, inline in the R code, and in the Supplementary Materials.