Dataset DOI: 10.5061/dryad.mkkwh71bg

Description of the data and file structure

This dataset contains data from a 60-day laboratory experiment designed to investigate strategic growth in the polychaete worm Ophryotrocha puerilis in response to the social environment.

Age- and size-matched juveniles were randomly assigned to one of four social environments (Isolation, Pairs, Triplets, or Groups with adults). Individual body size (segment count) and the timing of sex change (male to female) were monitored every 2-5 days throughout the experiment.

We then analysed growth curve parameters to quantify the individual growth trajectories and examine the underlying mechanisms of strategic growth. By fitting a logistic model, we derived parameters (Asymptotic Size, Growth Rate, and Age at Inflection) to correlate the intensity and duration of individual growth adjustments to the level of competition in the social environment. This analysis allowed us to explore how size hierarchies emerge and eventually dissolve upon conflict resolution (onset of reproduction).

Files and variables

File: Strategic_Growth_Data.xls

Description: Longitudinal data tracking the body growth and timing of sex change for all experimental Ophryotrocha puerilis juveniles over 60 days. Each row represents a single measurement point for an individual worm on a specific day.

Variables

• bowl.no  
  Sequential, non-unique bowl identifier specific to each treatment group. This number identifies the replicate bowl within its specific treatment, not across the whole study (i.e., bowl numbers reset per treatment). Worms sharing a bowl (in Pairs and Triplets) share the same bowl.no value.
  Ranges from 1 to a maximum of 30 (number of replicates per treatment).

• unique.ID
  The primary unique identifier for each individual worm that links it to its rank & its social environment. Composite of the bowl, worm designation (see Note), and treatment.
  e.g., 1G_L1 Groups (Worm L1 in Bowl 1, Groups treatment).

  **Note : **Worm Designation L1 L2 L3 : Component of unique.ID
  This label (L1, L2, L3) was assigned to simplify initial tracking based on the worm's starting size relative to others in the bowl.
  L1: The smallest/only juvenile in the bowl. 
  L2: The larger juvenile in Pairs or the intermediate juvenile in Triplets.
  L3: The largest juvenile in Triplets.

• worm.id
  The unique numerical identifier assigned sequentially to each individual experimental worm. This column links data across the main longitudinal data file (Strategic_Growth_Data.xls) and the derived growth parameters file (growth.parameters.xls).
  Ranges from 1 to 270 (total sample size).

• bowl.id 
  A unique, study-wide identifier for the housing bowl. All individuals that were housed together (e.g., in Pairs and Triplets) share the same ID. This links the bowl across both data files.
  Format: [Bowl Number][Treatment First Letter].
  e.g., 2T (Bowl 2 in Triplets treatment).

• replicate 
  The name of the researcher who took the measurements.
  e.g., Pooja or Noé

• treatment
  One of four social environments the individual worm was randomly assigned to at the start of the experiment.
  Isolated, Pair, Triplets, Groups

• exp.day
  The total number of days elapsed since the start of the experiment (Day 0). This variable marks the time point for each measurement (body size, time of sex change).
  0 to 60 days

• rank
  Hierarchical rank of the individual worm (based on size on day 5 of the experiment) within its bowl. This is used for comparative analysis in Pairs and Triplets.
  Rank 1 (Largest), Rank 2 (Second Largest/Intermediate), Rank 3 (Smallest).
  *NA = Not Applicable (used for Isolated and Groups treatments).

• body.size
  The number of chaetigerous body segments counted for every individual worm at each measurement point (exp.day). This is the primary metric used to track individual growth.
  Unit : Integer (number of chaetigerous segments)

• presence.of.eggs 
  Indicates whether the individual had visible oocytes (eggs) on the measurement day, indicating transition to the female sex.
  Column Values: yes (visible yellow oocytes) or no (no oocytes observed).
  
  Note on Visibility: Oocytes are visible due to the worms' transparent bodies and the yellow coloration derived from their spinach diet.

• moment.sex.change
  Indicates the specific experimental day (exp.day) when the sex change to female was first observed (i.e., the exp.day that presence.of.eggs changed from 'no' to 'yes').
  Column Values: 1 (day of sex change), 0 (no sex change observed on this day)

  Note: Each individual worm has only one instance of moment.sex.change = 1 across the entire time series, reflecting the first day of their male-to-female sex change. If no sex change occurred, the value remains 0 for all recorded days.

File: growth.parameters.xls

Description: Derived data containing the fitted growth curve parameters for each juvenile, based on the body size measurements in the Strategic_Growth_Data.xls file. These parameters were derived by fitting a logistic growth model to the body growth data for each individual to quantify individual growth trajectories

Variables

• worm.id
  The unique numerical identifier assigned sequentially to each individual experimental worm. This column links data across the main longitudinal data file (Strategic_Growth_Data.xls) and the derived growth parameters file (growth.parameters.xls).
  Ranges from 1 to 271 (total sample size).

• C
  Age at Inflection (t0): The age (in days) at which the maximum growth rate (growth spurt) begins to slow down.
  Numerical, age at which growth spurt ended.

• B
  Slope (r): The maximum growth rate (steepness of the curve).
  Numerical, maximum growth rate per day

• A
  Asymptotic Body Size (K): The estimated maximum body size (in segments) that the juvenile is expected to reach based on the model fit.
  Integer, number of chaetigerous segments

• treatment
  One of four social environments the individual worm was randomly assigned to at the start of the experiment.
  Isolated, Pair, Triplets, Groups

• bowl.id
  A unique, study-wide identifier for the housing bowl. All individuals that were housed together (e.g., in Pairs and Triplets) share the same ID. This links the bowl across both data files.
  Format: [Bowl Number][Treatment First Letter].
  e.g., 2T (Bowl 2 in Triplets treatment).

• Worm Designation 
  This label (L1, L2, L3) was assigned to simplify initial tracking based on the worm's starting size relative to others in the bowl.

  L1: The smallest/only juvenile in the bowl. 

  L2: The larger juvenile in Pairs or the intermediate juvenile in Triplets.

  L3: The largest juvenile in Triplets.

Code/software

Statistical analyses were performed in R (version 4.3.1).

Required R Packages:

lme4 (Bates et al., 2015) - Used for Generalized Linear Mixed-effects Models (GLMMs) and Linear Mixed-effects Models (LMMs).

drc (Ritz et al., 2015) - Used for fitting non-linear Logistic growth models to individual growth data.

zoo (Zeileis et al., 2020) - Used for interpolation of missing values.