DOI: 10.5061/dryad.rfj6q57cg
title: Thermal plasticity of setae of the second limb of Daphnia

description: These data are associated with a study that tests the hypothesis of
 thermal plasticity in the rigid setae of the second limb of Daphnia. The
 data are body size and length measurements (mm) of three limb setae (limb
 2; endite 2). The second seta is often called the "rigid" seta
 because it is heavily chitinized. In all, 300 specimens of Daphnia
 (including Daphnia umbra and Daphnia galeata) were dissected from four
 sets of clonal thermal transfers and seasonal variants from nature.
 Specimens of D. galeata were cultured under identical conditions save
 temperature (10 and 20◦C). Clonal neonates were reciprocally transferred
 across temperature regimes to determine the degree of postnatal
 plasticity.
description: Midsummer and Midwinter samples of Daphnia galeata were collected
 by a zooplankton throw net (30 cm dia., 200-250 um mesh size) from Guelph
 Lake, a eutrophic reservoir in Guelph Ontario, Canada, and Lake Ontario
 near Rochester, New York. Midwinter specimens were collected when the lake
 was covered with ice. We used ethanol preserved specimens of Daphnia umbra
 from a pond on the northern Melville Peninsula, Nunavut, Canada in
 August. To quantify the seasonal differences in seta
 lengths, midsummer and midwinter specimens (i.e., the coldest and warmest
 lake temperatures) were collected and mature females (ovigerous females)
 were photographed in lateral view and then dissected to remove and mount
 the second thoracic limbs. To test for phenotypic plasticity of the rigid
 setae, ovigerous specimens of D. galeata from cold water conditions
 (winter; 4–5◦C) were transferred to individual glass vials at 20◦C and
 24-h light photoperiod until they released their embryos. The first mature
 adults were then preserved for measurement and dissection (Zuykova and
 Bochkarev, 2010). The clonal offspring were raised in vials at a constant
 20◦C until maturity. One mature clonal offspring per vial was used for
 morphological measurements. Selenastrum capricornutum algae were provided
 daily (1.9 104 cells per single Daphnia) to the vials. The third set of
 experiments tested the hypothesis that temperature change alone (in both
 directions) is sufficient to induce phenotypic plasticity. The hypothesis
 of postembryonic induction of phenotypic plasticity was also tested in
 this experiment. Clones from Lake Ontario (collected in midsummer) were
 cultured individually in 7-dram borosilicate glass vials (Kimble Glass
 Inc.) and 20mL of culturing solution in 20◦C experimental chambers. Broods
 were split and clonal juveniles haphazardly assigned to either 20◦C or
 10◦C vials with otherwise identical growth conditions (24-h light
 photoperiod and 100 μL algal food +50 μL homogenized fish food per vial
 every 3 days). Vials from both treatments were examined for mature females
 (with eggs)—when detected, such females were removed and preserved in 50%
 at −20◦C for dissection. A similar experiment was run in the other thermal
 direction with the seed specimens here grown at 10◦C for more than one
 generation. The culturing solution was made by mixing
 10-mL synthetic freshwater (96mgNaHCO3, 60mgCaSO4 2H2O, 60 mg MgSO4, and 4
 mg KCl in 1 L of double distilled water) (EPA, 2002) with 100 μL algal (S.
 capricornutum) solution (4.8 106 cells per mL) and 50 μL homogenized fish
 food. Homogenized fish food was made by blending 10 g of Tetrafin™
 Goldfish flakes in 1 L of double distilled water (Baldwin and LeBlanc,
 1994; Olmstead and LeBlanc, 2000). Solids were settled out overnight and
 the resulting supernatant was used as homogenized fish food. The dry
 weight of 1 mL of homogenized fish food is 4 mg.
 Experimental animals were killed in 50% ethanol and stored at
 −20◦C. Microphotographs were taken using a Leica MZ16 motor-focus
 microscope equipped with a Leica DC480 camera. The initial pictures of the
 entire specimen were used for measurements of body length. Specimens were
 then transferred into a drop of distilled water and dissected to separate
 the second thoracic limbs from the body. Minuten needles (from WARDS, item
 # 14-0185) were used for the dissection. Pictures of one thoracic limb II
 were then taken for measurement (Fig. 1). Body length was measured as the
 distance (mm) between the anterior margin of the eye and the inflection
 point of the curve formed by the posteroventral margin of the valves at
 the base of the tail-spine in mature females (Dodson, 1988). The rigid
 seta of Endopodite 4 (seta 2) thoracic limb II has adjacent setae (seta
 1and seta 3). Each seta was measured in ImageJ by tracing the arc of the
 curved seta from base to tip.
description: Table of measurements from experiments to test the hypothesis of
 thermal plasticity of the rigid seta of the second endite, second limb, in
 Daphnia. Daphnia galeata was collected from Glen Haven Park, Irondequoit
 Bay, Lake Ontario, Rochester, NY and Guelph Lake, Ontario, Canada. The
 columns are: body (body length from lateral view of adult females in mm),
 seta 1 length (mm), seta 2 length (rigid seta), seta 3 length (mm), group
 number in the manuscript, temp (growth temp warm &gt;20C or cold
 &lt;10C), source (wild type from nature, F1 or multigenerational
 culture), and transfer (life stage of transfer to temperature
 treatment).