DOI: 10.5061/dryad.sqv9s4n52
title: Data from: Increasing temperature weakens the positive effect of genetic diversity on population growth

description: Genetic diversity and temperature increases associated with global climate
 change are known to independently influence population growth and
 extinction risk. Whether increasing temperature may influence the effect
 of genetic diversity on population growth, however, is not known. We
 address this issue in the model protist system Tetrahymena thermophila. We
 test the hypothesis that at temperatures closer to the species’ thermal
 optimum (i.e., the temperature at which population growth is maximal, or
 Topt), genetic diversity should have a weaker effect on population growth
 compared to temperatures away from the thermal optimum. To do so, we grew
 populations of T. thermophila with varying levels of genetic diversity at
 increasingly warmer temperatures and quantified their intrinsic population
 growth rate, r. We found that genetic diversity increases population
 growth at cooler temperatures, but that as temperature increases, this
 effect weakens. We also show that a combination of changes in the amount
 of expressed genetic diversity (G), plastic changes in population growth
 across temperatures (E), and strong GxE interactions, underlie this
 temperature effect. Our results uncover important but largely overlooked
 temperature effects that have implications for the management of small
 populations with depauperate genetic stocks in an increasingly warming
 world. --
description: We sourced five clonal lines (B2086.2,
 A*III, CU438.1, A*V, and CU427.4) of the protist <i>Tetrahymena
 thermophila</i> from the Cornell University Tetrahymena Stock Center
 from across three putatively different genetic backgrounds (A*III and A*V
 have genetic background A, B2086.2 has background B, while CU438.1 and
 CU427.4, have background C). The lines were reared in Carolina Biological
 protist medium® (Burlington, NC) in 200mL autoclaved borosilicate jars,
 and a 16-8 day/night cycle at 22ºC within Percival growth chambers (Perry,
 IA). To determine whether
 temperature alters the effects of genetic diversity on population growth,
 we manipulated the temperature and initial genetic diversity of microcosm
 populations. To manipulate genetic diversity, we started populations with
 a varying number of clonal lines (1, 2, 3, 4 or 5 lines). Monoclonal
 cultures were initialized with 50 individual protists. For all other
 treatments, the initial abundance of each clone depended on the total
 number of clones present, to control for possible effects of initial
 density: 2-clone populations started with 25 individuals/clone, 3-clone
 populations started with ~16 individuals/clone, 4-clone populations
 started with ~12 individuals/clone, and 5-clone populations started with
 10 individuals/clone. Each monoclonal population, and each combination of
 four and five clones, was replicated 4 times. Each combination of two and
 three clones was replicated twice, for a total of 84 experimental
 populations per temperature. All experimental microcosms were reared in
 3mL of growth media in 35 mm petri dishes. We crossed the five genetic diversity
 treatments with four temperature treatments (19, 22, 25, 28 ºC) along the
 rising portion of the thermal performance curve (TPC) of the organism (Fig
 1c), for a total 336 experimental microcosms. The TPC was itself was
 estimated as the intrinsic growth rate, <i>r</i>, of a
 well-mixed population (i.e., comprising the same number of initial
 individuals per clone, all starting at 3 ind/mL in 3mL petri dishes), at
 seven different temperatures (13, 19, 22, 27, 30, 32, 35 and 37 ºC).
 Experimental microcosms were grown in Percival growth chambers with all
 other environmental variables mimicking rearing conditions.
 After a 24-hr incubation period, we
 estimated final population size by sub-sampling each microcosm and
 counting individual cells under a stereomicroscope (Leica, M205 C).
 Assuming exponential growth, the intrinsic growth rate
 (<i>r</i>, which has units of t<sup>-1</sup>) of
 each microcosm population was calculated as [log(Nf)-log(Ni)]/time, with
 time=1 day, <i>N<sub>f</sub></i> being the final
 abundance, and <i>N<sub>i</sub></i> the initial
 density (=50 ind for all experimental microcosms).