Ecologically relevant low oxygen levels reduce unfertilized oocyte output in Caenorhabditis elegans

Caenorhabditis elegans naturally inhabits low-oxygen environments but is typically studied at 21% oxygen. We cultured adult C. elegans at 2.5%, 5%, and 21% oxygen during the fertile period, quantifying daily output of hatched larvae, unfertilized oocytes, and abnormal progeny (unhatched embryos, dead or deformed larvae). While we found no evidence for increased fertility at low oxygen levels compared to 21%, we observed a trend towards fewer unfertilized oocytes after peak fertility at 5% oxygen and significantly fewer at 2.5%. Our results indicate that reproductive output differs between laboratory conditions (high oxygen) and moderately low oxygen levels (closer to natural environments).