Alteration of cleaner wrasse cognition and brain morphology under marine heatwaves
Data files
Feb 21, 2025 version files 46.45 KB
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brain_data.csv
2.84 KB
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data_cognition.csv
751 B
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README.md
4.58 KB
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Water_parameters.xlsx
38.28 KB
Abstract
Heatwaves, exacerbated by global warming, are progressively affecting various ecosystems, with coral reefs among the most susceptible. Within these ecosystems, cleaner wrasses (Labroides dimidiatus), engage in cooperative interactions with client fish by removing ectoparasites, and play an essential role in sustaining client abundance and diversity. In 2016, the northern section of the Great Barrier Reef experienced widespread and intense bleaching due to unparalleled ocean temperatures associated with a marine heatwave. While prior studies have connected changes in fish densities following this heatwave to modifications in cleaner fish cognitive performance, the immediate impact of heatwave exposure on cleaner fish cognition and brain structure has yet to be investigated. Here, we exposed cleaner wrasses to a laboratory-simulated Category 1 marine heatwave for 55 days, mirroring the 2016 Great Barrier Reef event. Cleaners’ cognitive performance was evaluated through a visual discrimination task during the heatwave and after a 14-day recovery phase. This was followed by analysis of brain development 30 days after the cessation of the marine heatwave. Our results demonstrate that although heatwave exposure temporarily hindered cognitive performance, these deficits were recoverable. Interestingly, cleaner fish brain morphology, measured after recovery, underwent significant changes. Specifically, despite cleaners exposed to heatwaves having notably larger brains, their telencephalon was substantially smaller, while their brainstem was enlarged. These findings indicate that while some cognitive effects may be reversible, marine heatwave exposure leads to lasting alterations in brain morphology, particularly in regions associated with higher cognitive functions and social behaviour. This raises questions about the potential impact on more complex tasks that rely on these brain regions. We argue that the significant disruptions in cleaners' cognitive performance observed months after the 2016 due to neurological impairments linked to brain morphological changes. If so, a mere recovery of fish densities may not necessarily lead to a restoration of cognitive performance, as experiencing marine heatwaves might induce life-long morphological alterations in fish. Our results underscore marine heatwaves' intricate and enduring impact on cleaner fish, emphasising the need for comprehensive strategies to safeguard these vital components of coral reef ecosystems.
https://doi.org/10.5061/dryad.9zw3r22rn
Description of the data and file structure
In this study, we investigate whether the response to environmental stress in a laboratory setting would parallel the observations of diminished strategic sophistication in cleaners, as reported by Triki et al. (2018) in the field. To explore this, individuals were subjected to a simulated Category 1 marine heatwave lasting 55 days, replicating the conditions of the 2016 El Niño event. Cleaners’ cognitive performance was evaluated through a visual discrimination task during the heatwave and after a 14-day recovery phase. This was followed by analysis of brain development 30 days after the cessation of the marine heatwave. The potential alignment of our laboratory findings with the field observations would imply that the impairment of cleaners’ cognitive abilities could be linked to the direct consequences of a temperature peak affecting their physiological mechanisms.
Files and variables
File 1: brain_data.csv
Description: Brain development data
Variables
- ID: fish ID
- Treatment: experimental treatment (Control or Marine Heatwave I)
- body: body weight (g)
- sl: standard length (cm)
- brain: total brain weight (g)
- bs: brainstem weight (g)
- cer: cerebelum weight (g)
- die: diencephalum weight (g)
- ot: optic tetum weight (g)
- tel: telencephalum weight (g)
- bbo: brain/body ration
- bsb: brain-stem/body ration
- cb: cerebelum/body ration
- db: diencephalum/body ration
- otb: optic tetum/body ration
- tb: telencephalum/body ration
File 2: data_cognition.csv
Description: cognitive performance data (associative learning task results)
Variables
- ID: fish ID
- Treatment: experimental treatment (Control or Marine Heatwave I)
- trials_1: trials at the end of exposure period
- solved_1: task solved (yes/no)
- colour_1: color of the correct plate for trial 1
- colour_2: color of the correct plate for trial 2
- trials_2: trials after 14-day recovery period
- solved_2: task solved (yes/no)
File 3: Water_parameters.xlsx
Description: This file contains seawater parameter data collected during an experiment assessing the effects of marine heatwaves.
Structure:
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Page 1: Control treatment
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Page 2: Marine Heatwave I treatment
Experimental periods: Acclimation, ramp period, exposure to MHW, recovery period, and brain sampling
Date: Represents the experimental days corresponding to each period
Seawater parameters: Temperature (ºC), Oxygen (mg), pH, Salinity
Replication & Labeling: Each parameter was measured across four replicates, labeled as follows:
- Temperature: T(ºC)_1, T(ºC)_2, T(ºC)_3, T(ºC)_4
- Oxygen: O2(mg)_1, O2(mg)_2, O2(mg)_3, O2(mg)_4
- pH: pH_1, pH_2, pH_3, pH_4
- Salinity: salinity_1, salinity_2, salinity_3, salinity_4
Averaged Values: Represents the daily mean of each parameter across the four replicates.
File 4: Statistical_Analysis.pdf
Description: This file provides details on the statistical methods used to analyze data_cognition.csv and brain_data.csv
- The file includes information on data processing, statistical tests, and significance levels.
- To analyze the data, the free and open-source software R (Version 3.4.3, RStudio Team, 2022) was used.
- R packages used:
- survival (for survival analysis and Cox proportional hazards models): Used to analyze time-to-event data from the learning task.
- survminer (for survival curve visualization): Utilized for plotting Kaplan-Meier survival curves.
- car (for analysis of variance): Applied to test the homogeneity of variances in experimental models.
- performance (for model diagnostics): Used to assess normality and homogeneity of residuals in linear models.
- dplyr (for data manipulation): Applied to filter, group, and summarize data efficiently during preprocessing.
- stats (for statistical modeling): Used to perform weighted general linear models and hypothesis testing.
- ggthemes (for plot aesthetics): Provided additional themes and color palettes to enhance ggplot2 visualizations.
- ggplot2 (for data visualization): Used to generate plots and graphs for exploratory data analysis and presentation.
- HighstatLibV10 (for data exploration and validation): Applied to detect collinearity, outliers, and heteroscedasticity in data.
The dataset was collected from a laboratory experiment involving Bluestreak cleaner wrasses (Labroides dimidiatus; n=20), which were wild-caught in the Maldives and housed in flow-through aquaria at Laboratório Marítimo da Guia, Cascais, Portugal. Cleaners were exposed to two experimental treatments: control (28.8°C) and a simulated Category I marine heatwave (29.8°C). After a 5-day acclimation period, temperature was increased over 6 days to reach the target temperature for the heatwave treatment, and exposure lasted for 55 days. Afterward, a 30-day recovery period followed before brain dissection.
Behavioral trials, using an associative learning task (FAP test), were conducted at the end of the heatwave exposure and after a 14-day recovery period. Cleaners were tested individually on their ability to learn colour cues to locate a food reward, with up to 100 trials per fish.
Brain development was analyzed 30-days post exposure, with brains dissected into five regions and weighed for further analysis. Statistical analyses were performed using R, including survival analysis for learning tasks and weighted linear models for brain development.
The dataset includes variables on experimental treatments, task performance, body weight, brain weight, and brain region measurements.