In the article, the authors studied how short-term exposure to carcinogenic pollutant affects the behaviour of Girardia tigrina planaria. The study consists of a two-phase experiment involving a 7-day exposure to cadmium followed by a 7-day recovery period. The authors employ a double hierarchical generalised linear model framework, which not only considers the population's mean and variance but also explicitly addresses intraindividual variability.
The study results reveal that planaria exposed to the carcinogen exhibited reduced activity levels compared to their unexposed counterparts. Notably, the planaria were able to recover to their pre-exposure activity patterns during the recovery phase, albeit with a reduced variance in daily activity changes. Additionally, the authors note that planaria displaying high activity levels were less predictable, displaying larger daily activity variations and higher residual variance.

These findings have important implications for understanding how exposure to cancer risk factors impacts wildlife behaviour. However, the study currently requires revision before being considered for publication. I have outlined major concerns in my specific comments below.

In general, I found the methods section is not reproducible at its current state—further information on the planaria life history, housing, exposure days, and experimental setup is necessary. The statistical calculation needs further clarification, and in some stages, terminological changes. The readers would also benefit from the accessibility of statistical codes used in constructing the double hierarchical generalised mixed effect model or a full model syntax provided in the supplementary material. There are numerous typos present throughout the manuscript, which need to be revised.

Specific comments

Introduction

Line 93: Please briefly mention what level of cadmium and how, if, the concentration is environmentally/toxicologically relevant.

Methods

Line 136-139: Please provide sufficient details on their housing condition, i.e., if They were housed individually or as a group. Were they provided food on the days of activity measurements?
Line 134: Is this lagoon free from cadmium contamination? How did you ensure the planaria were free from Cd exposure prior to the experiment?
Line 143: remove the dots after DNA repair mechanisms or add relevant examples
Line 146: rewrite: … and as a result, bioaccumulates... or split the sentence into two.
Line 151, Line 176: G. tigrina
Line 160: what’s the relevant concentration of Cd found in the environment?
Line 164-167: Why seven days? Is it relevant to their lifespan?
Line 202: Does the day of the experiment account for the 14 experimental days? From the output in the supplementary section, it looks like it was modelled as a continuous variable and not a factor. Please briefly clarify how it was modelled in the experiment.
Line 217: Place this sentence higher up in the paragraph.

Results

Line 252: Figure 2, b: does the y-axis denote to mean activity?
Line 266: were the variances between the two groups significantly different from each other? You can calculate the magnitude difference in variance following
Royauté, R., Dochtermann, N.A. Comparing ecological and evolutionary variability within datasets. Behav Ecol Sociobiol 75, 127 (2021). https://doi.org/10.1007/s00265-021-03068-3
Line 267: Fix the typo in Figure 3B heading.
Line 287: again, the variances with very large CIs don’t tell us much about the magnitude of differences between the two groups unless we test for differences in variances between each potential pair. I highly recommend testing for that. Check this paper on applying a similar stats tool to answer relevant questions in the interdisciplinary field of behavioural ecology and ecotoxicology: https://doi.org/10.1093/beheco/arad065
Line 257: all the group-level estimates are calculated as standard deviation (SD) units (Supplementary Material, Table 2). Your model output should also indicate if the sigma is calculated in a log scale. Please consider transforming them into variances or being transparent about the prediction scales.
Line 315: Figure 5 is missing any blue line.

Discussion
Line 321: For readers in Proceedings B, it would be beneficial to have a summarising, broad-scale sentence at the end of the introductory paragraph.
Lines 331-333: As mentioned above, your description might strengthen if there was information on the inhabiting water being tested for Cd concentration.
Lines 342-345: please split this sentence into two.
Lines 347-348: I am unsure how this interpretation is relevant for this study. Could you clarify if the planaria were starved during this study?
Lines 351-352: do you mean the target molecule the contaminant as on? Please elaborate.
Line 373: remove- range
Line 388: rewrite: …using a combination of…
Line 392: remove- a

The authors seem to have addressed most of my comments in their revision, I therefore have no further suggestions.