DOI: 10.5061/dryad.n5tb2rc06
title: Lake water chemistry and population of origin interact to shape fecundity and growth in Daphnia ambigua

description: Freshwater environments vary widely in ion availability, owing to both
 natural and anthropogenic drivers. Field and laboratory work point to the
 importance of overall salinity as well as cation depletion, in shaping the
 physiology, behavior, and ecology of freshwater taxa. Yet, we currently
 have a poor understanding of the degree to which populations may vary in
 response to ion availability. Using Daphnia collected from three lakes
 that differ greatly in salinity and calcium availability, we conducted a
 laboratory reciprocal transplant experiment to assess how animals
 representing these populations vary in fecundity, body size, and survival
 when reared in lake water from each environment. The lake water
 environment and population of origin strongly interacted to shape Daphnia
 growth and reproduction. Surprisingly, we found only modest evidence that
 lake water with abundant calcium (5.5 mg/L vs. 1.2-2.3 mg/L) increased
 Daphnia growth or reproduction. In contrast, water from a relatively
 ion-rich lake (400 µS/cm specific conductance) strongly boosted Daphnia
 fecundity over lower-ion lake water (20-50 µS/cm), especially for the
 population originating from the high-ion environment. Our results suggest
 that ion-poor conditions common in regions around the world may exert
 stress on freshwater organisms, even for populations inhabiting these
 environments. Meanwhile, moderate salt enrichment may not prove harmful
 but could even benefit freshwater taxa in these ion-poor regions. The
 context dependence of how and when lake water chemistry affects Daphnia
 and other freshwater taxa deserves greater attention, in both ion-depleted
 and ion-rich conditions. Daphnia are key members of lake food webs and
 serve as an important model for ecology, evolution, and toxicology
 research. Consideration of how lake water chemistry may influence how
 Daphnia populations respond to abiotic and biotic stress may improve the
 ability to evaluate and predict ecological and evolutionary dynamics in
 lakes of varying chemical composition.
description: We reared <em>Daphnia</em> from three lakes in lake
 water from each of these lakes. We included 4 clonal lineages per lake and
 4-13 replicates per clonal lineage/ lake/ treatment. We measured body size
 at 7 days and noted whether <em>Daphnia</em> reproduced by
 that time. We noted survival to maturity. We counted offspring over 21
 days and measured <em>Daphnia</em> again at 21 days.
 If Daphnia did not survive to 7 or 21 Days, 7-day and/or 21-day
 length is NA.  If Daphnia did not survive to reproduce,
 totaloffspring = NA and rep_by_day7 = NA Column headers
 are: Lake: Lake of origin (from Egypt,
 Hall, or Sewell Pond) Trt: Lake water rearing
 conditions (E: Egypt, S: Sewell, H: Hall) Clone:
 clonal lineage (one of four from each lake)
 Replicate: experimental replicate for a given lake x treatment x
 clone Died_before_mature: did the animal die before
 reproducing? 0: no, 1: yes rep_by_day7: reproduced by
 day 7 (0: no, 1: yes) totaloffspring: total offspring
 produced over the 21 day trial Day7_length_mm: body
 length measured on day 7 in mm Day21_length_mm: body
 length measured on day 21 in mm (NA if died between days 7 and
 21)