https://phys.org/news/2018-07-animals-muscle-internal-source.html

"We know about the importance of fat reserves to fuel the energetic costs of reproduction. But what about water? Our study shows that during reproduction, muscle metabolism is linked to the water requirements of developing offspring. Fat is only about 10 percent water, whereas muscle is closer to 75 percent, so burning muscle will release extra water," said George Brusch IV, lead investigator for the project and doctoral student at Arizona State University. "From an evolutionary perspective, the concept of capital breeding—or using stored resources to fuel reproduction—is currently restricted to energetic needs. We propose that this should extend to a broader, multi-resource strategy that also includes water allocation."

The researchers looked into this concept by studying the effects of water deprivation on the reproductive efforts of female Children's pythons, a medium-sized snake that reproduces during the dry-season in Australia, where natural water sources are extremely limited. They found that muscles play an important role in providing water to the body when none is available.