Environmental change from anthropogenic activities threatens individual organisms, the persistence of populations, and entire species. Rapid environmental change puts organisms in a double bind, they are forced to contend with novel environmental conditions but with little time to respond. Phenotypic plasticity can act quickly to promote establishment and persistence of individuals and populations in novel or altered environments. In typical environmental conditions, fitness-related traits can be buffered, reducing phenotypic variation in expression of traits, and allowing underlying genetic variation to accumulate without selection. In stressful conditions, buffering mechanisms can break down, exposing underlying phenotypic variation and permitting the expression of phenotypes that may allow populations to persist in the face of altered or otherwise novel environments. Using reciprocal transplant experiments of freshwater snails, we demonstrate that novel conditions induce higher variability in growth rates and, to a lesser degree, morphology (area of the shell opening) relative to natal conditions. Our findings suggest a potentially important role of phenotypic plasticity in population persistence as organisms face a rapidly changing, human-altered world.

File 1: site information

At three time intervals during the experiment at least two days apart, we measured temperature, conductivity, flow rate, and dissolved oxygen with a sonde (Yellow Springs Instrument, model 85) adjacent to the containers containing the experimental snails. Midway through the experiment, we measured pH (Corning pH meter, Model 430), magnesium and calcium carbonate hardness (Hach Test Kit, Model 5-EP), and ammonia (Hach Test Kit, Model NI-8) from water samples adjacent to the platforms. To analyze food quality and quantity, we collected epiphyton samples at each site by scrubbing an equivalent surface area of submerged macrophytes from the same locations where we collected macrophytes to feed the snails.

File 2: snail_measurements

Before and after each pair of experimental trials, we measured specific growth rate. We estimated specific growth rate by measuring shell length with an ocular micrometer (Leica S6E). To obtain consistent measurements, we used the same orientation and angle for all snails with the aperture facing upwards and the shell slightly rotated to measure maximum shell length. 

File 3: Physella_morphology

Before and after each pair of experimental trials, we measured three defense-related traits that are commonly induced by crayfish and can protect snails from predation by crayfish (Crowl and Covich, 1990; Dewitt et al., 2000; Stevison et al., 2016): specific growth rate, aperture shape and aperture area.  To obtain consistent measurements, we used the same orientation and angle for all snails with the aperture facing upwards and the shell slightly rotated to measure maximum shell length. We used an image-processing microscope (Olympus SZX2-ILLT) and ImageJ software (Schneider et al., 2012) to analyze shell morphology for each snail.