Experiment 2: the effect of relatedness on survival, growth, and reproduction
The second experiment ran from March to June of 2022. Individual colonies were arranged into two treatments, related and unrelated, each with 10 replicate On each replicate dish, there were 10 colonies randomly assigned to a position in a 3 × 4 cm grid, reflecting a common density in the field at times when the population is large, and at the middle density used in Experiment 1. Overall, there were 21 maternal families. In the “related” treatment, 10 of these maternal families were used, where each of the 10 replicates comprised offspring from a different maternal family (i.e., replicate 1 had 10 offspring from family X, replicate 2 had 10 offspring from family Y, and so on). In the “unrelated” treatment, each of the 10 replicates comprised one offspring randomly chosen from one of the 21 maternal families, such that the 10 maternal families in the related treatment were also used in the unrelated treatments, plus an additional 11 maternal families to achieve the desired density. Petri dishes were randomly assigned to PVC poles. There were 10 replicate Petri dishes in each treatment at the start of the experiment; however, two dishes were lost after deployment, resulting in eight Petri dishes in the unrelated treatment.
After 20 days in the field, individual colonies were collected and returned to the laboratory. The surviving individuals were preserved in 95% ethanol. Survival (present or absent), size (number of zooids), and reproductive output (total number of ovicells) were recorded for each individual colony under a dissecting microscope. The number of ovicells is considered proportional to the production of sperm and eggs and the potential number of brooded larvae.