Interaction between host phenotype and microbiome composition inA. mexicanus
Some studies have shown that age and sex can impact fish microbiome composition . Although not significantly different, the field-collected surface fish were larger on average compared to Pachón cavefish and were all sexually differentiated suggesting they may be older (Figure S1 ). Due to limited availability of samples, we were not able to test how these variables may impact microbiome composition. However, in the laboratory we collected fish that were the same age (6-months-old). The lab-raised morphotypes were not significantly different in weight at the time of collection, although Pachón and Tinaja cavefish weighed more than surface fish and Molino cavefish on average (Figure S1 ). Interestingly, most Tinaja and Pachón cavefish had undefined sex compared to surface fish and Molino cavefish (Figure S1 ). The impact of growth rate and delayed sexual maturation on microbiome composition can be explored in future studies using A. mexicanus .