DOI: 10.5061/dryad.j3tx95x9p
title: Size, not temperature, drives cyclopoid copepod predation of invasive mosquito larvae

description: During range expansion, invasive species can experience new thermal
 regimes. Differences between the thermal performance of local and invasive
 species can alter species interactions, including predator-prey
 interactions. The Asian tiger mosquito, Aedes albopictus, is a known
 vector of several viral diseases of public health importance. It has
 successfully invaded many regions across the globe and currently threatens
 to invade regions of the UK where conditions would support seasonal
 activity. We assessed the functional response and predation efficiency
 (percentage of prey consumed) of the cyclopoid copepods Macrocyclops
 albidus and Megacyclops viridis from South East England, UK against
 newly-hatched French Ae. albopictus larvae across a relevant temperature
 range (15, 20, and 25ºC). Predator-absent controls were included in all
 experiments to account for background prey mortality. We found that both
 M. albidus and M. viridis display type II functional response curves, and
 that both would therefore be suitable biocontrol agents in the event of an
 Ae. albopictus invasion in the UK. No significant effect of temperature on
 the predation interaction was detected by either type of analysis.
 However, the predation efficiency analysis did show differences due to
 predator species. The results suggest that M. viridis would be a
 superior predator against invasive Ae. albopictus larvae due to the larger
 size of this copepod species, relative to M. albidus. Our work highlights
 the importance of size relationships in predicting interactions between
 invading prey and local predators.
description: <strong>Tire data</strong>: We
 measured the temperature of rainwater collected in six used car tires that
 were divided between an urban London area and a nearby suburban area.
 These temperature data provided rough guidelines for our choice of the
 three temperatures to be tested in our functional response and predation
 efficiency experiments. <strong>Functional
 response data</strong>: Adult non-gravid female
 copepods, identified by larger relative size, were removed from their
 culture and each was placed in a Petri dish (diameter: 50 mm, height: 20.3
 mm) holding 20 mL of spring water. The copepods were placed in three
 different controlled environments set to 15 ± 1, 20 ± 1, and 25 ± 1°C, all
 at a 12:12 light/dark cycle, to begin a 24 h starvation and
 temperature-acclimation period for the predators. Each combination of
 copepod species (<i>M. albidus</i> or <i>M.
 viridis</i>) and temperature had 28 copepods, each one held in its
 own Petri dish; there were 168 copepods in total. 
 Groups of 87 newly-hatched <i>Ae. albopictus</i>
 larvae were each pipetted into a small plastic tub containing 150 mL of
 spring water to strongly dilute any residual food from the hatching media.
 Each tub of 87 larvae was then split into seven Petri dishes each
 containing 20 mL of spring water and the following larval densities: 1, 2,
 4, 8, 16, 24, and 32. All larvae were counted into dishes at room
 temperature and then divided into the three different controlled
 environments, allowing a 12 h temperature acclimation period before
 predator introduction. For each of six combinations of copepod species and
 temperature, there were 35 Petri dishes containing a total of 435
 newly-hatched <i>Ae. albopictus</i> larvae, with a total of
 2,610 larvae used across all predator treatments and controls. This sample
 size allowed for four replicates of each larval density and one
 predator-absent control at each density, for each combination of copepod
 species and temperature. The next day, the copepod
 predators held at three different temperatures were introduced to larval
 Petri dishes of matching controlled temperatures. The copepods were
 removed after a 6 h period of predation, which follows the schedule of
 similar experiments. Each copepod was preserved in 80% ethanol so that its
 body size could later be measured and matched to the larval count data.
 Immediately following the removal of the copepods, the number of surviving
 larvae in each Petri dish was counted and recorded. In addition, the body
 lengths of the 10 gravid females selected from each species of copepod, as
 well as the body lengths of all copepods included as predators in the
 functional response experiments, were measured from the front of the
 cephalosome to the end of the last urosomite.
 <strong>Predation efficiency data</strong>:
 <i>Ae. albopictus</i> larvae were hatched, and any
 residual food was diluted in spring water following the same procedure
 used for the functional response experiments. Adult non-gravid female
 copepods were each placed in a Petri dish for a 24 h period of starvation
 and acclimation to three different temperature settings: 15 ± 1, 20 ± 1,
 and 25 ± 1°C, all at a 12:12 light/dark cycle. The largest non-gravid
 copepods of each species were selected to minimize the risk of selecting
 males or immature stages. The Petri dishes containing larvae were split
 into the three different temperature settings 12 h prior to the
 introduction of copepod predators, and there was a 6 h period of
 predation. At the end of the 6 h period, the copepods were removed, and
 each was stored individually in 80% ethanol so that predator body lengths
 could later be measured. The number of surviving larvae in each Petri dish
 was recorded immediately after removing the copepods.
 At each of the three temperature settings, there was a total of
 24 Petri dishes, each containing 24 larvae (1,728 larvae across all
 temperatures); the 24 dishes were divided into three groups (n = 8): one
 with <i>M. albidus</i> predation, one with <i>M.
 viridis</i> predation, and one as a control. Every predator
 treatment was matched to a control that had been held at the same
 temperature. Each temperature setting had a total of 192 control larvae. A
 total of 24 <i>M. albidus</i> and 24 <i>M.
 viridis</i> copepods were used in this experiment.
description: Please refer to information
 provided in "ReadMe.pdf".