Hey Kyle! I don't think there is anything that stops you from having those 4 classes. The only thing you need to consider is to have enough samples for each category and that they are well balanced among them (more or less the same number of samples on each category).

For the other question, I also think you can do it but the method for the analysis will depend on if it your samples are the from the same individuals over the two seasons or if they are non-related groups (e.g., t-test or same sample repeated-measures ANOVA). I would also plot everything and see if the behavior of the two groups match, it could be that one sex is heavier when the other isn't, or that the changes in weight occur at different months. In both cases keeping them separately would be better

Hope this helps. I would like to see what other people think about this.

Hey Jose, thanks for you advice. Since the study species is mole-rats, there's only 1 reproductive female per social group and therefore a much smaller sample size for reproductive females compared to other categories, and also much higher sample sizes for non-reproductive males and females. My initial gut feeling was to split by both sex and reproductive status, but another lab mate grouped them together in their studies.

Hello Kyle , you can only estimate a linear regression between body mass and reproductive class, if the reproductive class is a continuous variable, otherwise you cannot use it. As for the test of difference in body mass during the season, it is interesting. But I advise you to do the test comparing male and female in each season (t-test), it would be more interesting. Hope this helps