DOI: 10.5061/dryad.z8w9ghxg1
title: Data for: Temperature effects on growth rates of Daphnia from different populations

description: When comparing somatic growth thermal performance curves (TPCs), higher
 somatic growth across experimental temperatures is often observed for
 populations originating from colder environments. Such countergradient
 variation has been suggested to represent adaptation to seasonality, or
 shorter favorable seasons in colder climates. Alternatively, populations
 from cold climates may outgrow those from warmer climates at low
 temperature, and vice versa at high temperature, representing adaptation
 to temperature. Using modelling, we show that distinguishing between these
 two types of adaptation based on TPCs requires knowledge about (i) the
 relationship between somatic growth rate and population growth rate, which
 in turn depends on the scale of somatic growth (absolute or proportional),
 and (ii) the relationship between somatic growth rate and mortality rate
 in the wild. We illustrate this by quantifying somatic growth rate TPCs
 for three populations of Daphnia magna where population growth scales
 linearly with proportional somatic growth. For absolute somatic growth,
 the northern population outperformed the two more southern populations
 across temperatures, and more so at higher temperatures, consistent with
 adaptation to seasonality. In contrast, for the proportional somatic
 growth TPCs, and hence population growth rate, TPCs tended to converge
 towards the highest temperatures. Thus, if the northern population pays an
 ecological mortality cost of rapid growth in the wild, this may create
 crossing population growth TPCs consistent with adaptation to temperature.
 Future studies within this field should be more explicit in how they
 extrapolate from somatic growth in the lab to fitness in the wild.
description: <em>D. magna</em> ephippia were obtained from three
 populations: a pond in Værøy, Norway (67.687°N 12.672°E), a pond in Park
 Midden-Limburg, Zonhoven, Belgium (50.982°N 5.318°E), and a rice field
 which is flooded and dries out annually in the Delta del Ebro, Riet Vell,
 Spain (40.659°N 0.775°E). In the following, these three populations are
 referred to as the Norway, Belgium and Spain populations, respectively. We
 used 10 clones (originating from 10 different ephippia) from each
 population in the experiments, and these were reared at 17°C with a 16L:8D
 photoperiod for three to four parthenogenetic generations prior to the
 experiment. During this period, individuals were fed three times a week
 with Shellfish Diet 1800 (Reed Mariculture Inc, USA) at final
 concentration of algae 4 × 10<sup>5</sup> cells/ml, and the
 ADaM medium was changed once a week. For the experiment, second or later
 clutch neonates were collected and photographed less than 24 hours after
 birth. After photographing, neonates were placed individually in 50 ml
 tubes containing 17°C ADaM medium. Each tube was placed in a Memmert
 Peltier-cooled incubator IPP 260plus (Memmert, Germany). We used a 16L:8D
 photoperiod and the temperature in different cabinets was set to 12.0,
 15.0, 17.0, 19.0, 22.0, 24.0 and 26.0 °C. Each temperature treatment
 received eight individuals from each of the 10 clones. Animals were fed
 every second day with concentrations that had previously been established
 to represent <em>ad lib</em> rations. Due to logistic
 constraints, the different temperature treatments were run simultaneously
 for one population at a time (Norway May-June 2015, Spain
 December-February 2018, Belgium July-September 2018). All individuals were
 checked daily for mortality and sexual maturity (presence of eggs in the
 brood chamber). Tubes were rotated daily within the climate cabinets
 during the maturity checks to avoid positional effects. Upon maturation
 individuals were photographed and terminated.