DOI: 10.5061/dryad.280gb5mzs
title: Captive rearing reduces the sensitivity of Acartia tonsa copepods to predator cues

description: Captive populations are often subject to different selective pressures
 than their wild counterparts, which could result in trait differences
 between these populations. This study investigates the effect of captive
 rearing on the swimming behavior and escape responses of Acartia tonsa, a
 species of marine copepod zooplankton that use hydromechanical signal
 detection to aid in finding food, locating mates, and avoiding predation.
 As captive populations of A. tonsa experience reduced interspecific
 predation and higher population densities compared to wild populations, it
 was hypothesized that these differences may drive adaptive evolution of
 swimming behavior in this species. Several components of routine swimming
 were compared (swimming speed, number of hops, distance of hops, frequency
 of hops) for groups of captive-reared and wild-caught A. tonsa, revealing
 that wild-caught copepods swim faster and hop more frequently than
 captive-reared copepods. However, when the escape responses of the
 captive-reared and wild-caught populations were compared using an
 artificial predator mimic, no significant differences were found in the
 number of sequential hops performed during the escape response, the
 maximum velocity of the response, or the total distance traveled during
 the response. Although the escape responses performed by the
 captive-reared and wild-caught copepods were similar, the captive-reared
 individuals often showed no response to the artificial predator mimic (34%
 of individuals responded to the predator mimic), whereas wild individuals
 almost always showed a response (96% responded). This suggests that
 captive rearing may have resulted in reduced sensitivity to
 hydromechanical signals in captive copepods compared to wild copepods, as
 responding to these signals in a predator-free captive environment would
 impose an unnecessary energy cost. This study offers new insight into how
 captive-rearing may impact copepod populations and provides evidence of
 how predator-driven evolution and density dependent selection may
 influence the behavior of copepod species.
description: Wild <em>A. tonsa </em>were collected from Ballast
 Point Park, Tampa Bay using a 30 cm diameter, 150 µm mesh zooplankton net.
 Captive copepods were obtained from Aquaculture Nursery Farms, based in
 Charlotte County, Florida.  Copepod swimming behavior
 was recorded using an Edgertronic high speed imaging camera with a Nikon
 AF micro NIKKOR 105 mm lens. Each water sample contained approximately 100
 copepods. Videos of the copepods swimming were recorded for 9 seconds at a
 resolution of 1280 x 1024 pixels, with 6400 ISO sensitivity, 1/10000
 shutter speed, and 60 frames per second. 14 videos were recorded for the
 captive populations and 30 videos were recorded for the wild
 populations. To collect the escape response data, an
 artificial predator mimic was generated using a piezoelectric actuator.
 This was generated using a BK Precision 4030 10MHz pulse generator. The
 piezoelectric actuator was used to rapidly move a narrow aluminum rod in a
 vertical orientation to create a strong, radiating hydromechanical signal
 to trigger escape behavior in copepods (methodology from Gemmell
 <em>et al., </em>2013). Video recordings spanned immediately
 before and after this predator cue was administered, with a pre trigger
 frame rate of 500 frames per second and a post trigger rate of 500 frames
 per second. 31 videos were recorded for the captive populations and 21
 videos were recorded for the wild populations, with approximately 100
 copepods per water sample. The video recordings were
 analyzed using ImageJ (version 1.54i) image analysis software, using the
 tracking plugin to track and record the movement of the copepods. The
 video was analyzed frame by frame, with each frame representing 0.02
 seconds of the total recording. 200 copepods were randomly selected for
 tracking (50 per group – captive routine swimming, wild routine swimming,
 captive escape response, wild escape response). For the routine swimming
 videos, a random coordinate generator was used to select the copepods that
 were tracked (the copepod closest to the random coordinates was tracked),
 and for the escape response data the copepods within several body lengths
 to the piezoelectric needle were selected to be tracked. As we were
 working with two-dimensional video recordings, we only tracked copepods
 that remained clear and in focus (copepod swimming is three-dimensional,
 so loss of focus indicates that the copepod has moved out of the X-Y focal
 plane). 
description: # Captive rearing reduces the sensitivity of Acartia tonsa copepods to
 predator cues
 [https://doi.org/10.5061/dryad.280gb5mzs](https://doi.org/10.5061/dryad.280gb5mzs) ## Description of the data and file structure This is a study on copepod swimming behavior by Muir et al. (2025). The research compares swimming behavior and escape responses between wild-caught and captive-reared Acartia tonsa copepods. The data include measurements of swimming speed, hop frequency, hop distance, and escape responses when exposed to an artificial predator mimic. The data for the wild copepods are from a copepod population collected from Tampa Bay, Florida, while data for the captive-reared copepods are obtained from a copepod population raised in aquaculture. ### Files and variables #### File: Muir\_Acartia\_tonsa\_manuscript\_jumpanalysis\_escape.csv **Description:** Escape response data for both wild-caught and captive-reared copepods ##### Variables * ID: Unique identifier for each copepod individual * Total Response Hops: Number of hops performed during the escape response sequence * Maximum Escape Velocity: Maximum velocity achieved during escape response (measured in body lengths/second) * Total Escape Distance: Total distance traveled during the escape response (measured in body lengths in mm) * Response: Binary indicator of whether the copepod responded to the predator mimic (yes/no) #### File: Muir\_Acartia\_tonsa\_manuscript\_jumpanalysis\_routine.csv **Description:** Routine swimming data for both wild-caught and captive-reared copepods ##### Variables * ID: Unique identifier for each copepod individual * TotalHops: Total number of hops performed during the 9-second recording period * MaxDist: Maximum distance traveled in a single hop (measured in body lengths) * AvgPauseDuration: Average time spent stationary between hops (seconds) * AvgHopDist: Average distance traveled in a single hop (body lengths) #### File: Muir\_Acartia\_tonsa\_manuscript\_speedanalysis\_captiveescape.csv **Description:** Swimming speed measurements during escape responses for captive-reared copepods ##### Variables * ID: Unique identifier for each captive-reared copepod individual * Average: Average swimming speed during escape response (body lengths/second) * SD: Standard deviation of swimming speed measurements (body lengths/second) #### File: Muir\_Acartia\_tonsa\_manuscript\_speedanalysis\_wildescape.csv **Description:** Swimming speed measurements during escape responses for wild-caught copepods ##### Variables * ID: Unique identifier for each wild-caught copepod individual * Average: Average swimming speed during escape response (body lengths/second) * SD: Standard deviation of swimming speed measurements (body lengths/second) #### File: Muir\_Acartia\_tonsa\_manuscript\_speedanalysis\_wildroutine.csv **Description:** Routine swimming speed measurements for wild-caught copepods ##### Variables * ID: Unique identifier for each wild-caught copepod individual * Average: Average routine swimming speed (body lengths/second) * SD: Standard deviation of swimming speed measurements (body lengths/second) #### File: Muir\_Acartia\_tonsa\_manuscript\_speedanalysis\_captiveroutine.csv **Description:** Routine swimming speed measurements for captive-reared copepods ##### Variables * ID: Unique identifier for each captive-reared copepod individual * Average: Average routine swimming speed (body lengths/second) * SD: Standard deviation of swimming speed measurements (body lengths/second) ## Code/software * **R (version 4.2.2)** with base packages for statistical analysis * **ImageJ (version 1.54i)** with tracking plugin for video analysis Included scripts: * **Muir_Acartia_tonsa_manuscript_speedanalysis.R**: Calculates average copepod swimming speed for each individual from the raw coordinate data * **Muir_Acartia_tonsa_manuscript_jumpanalysis.R**: Analyzes jumps performed by copepods during routine swimming and escape responses Workflow: 1. Processing video with ImageJ to track copepod movements (data exported coordinate data as a csv file) 2. Running the R scripts to calculate swimming metrics and analyze hop patterns from the csv coordinate data 3. Statistical comparison using Mann-Whitney U Tests and Fisher's Exact Tests