Stressed out Sperm

What happens when you stress out moss sperm? That was one of the questions that researchers asked in this study.

Todd N. Rosenstiel and Sarah M. Eppley. 2009. Long-lived sperm in the geothermal bryophyte Pohlia nutans. Biology Letters 5: 857-860. 

Not only did they look at the impact of high temperature, but they also looked at sperm concentration, rainwater vs. deionized water, and the addition of sugar on sperm survival. 

In general they found that moss sperm are pretty long-lived, relatively speaking, with 20% survival after 100 hours for all dilution levels. This is pretty cool because the sperms may then be able to be transported by animal vectors or survive in a small drop of water until more water forms a film that they can use to swim to a female.

They found that sperm lived longer when sucrose was added. You might not think that moss sperm would have access to external supplies of sugar. It is not like they swim through maple syrup, but when dry bryophytes are rehydrated they release sugars into the surrounding water and these could be used by swimming sperm. Thus they could live longer and have more energy to swim to females that are further away.

The sperm were unaffected by temperature and survived at the same levels at both 22 and 60 C (~72 and 140 F). This is a pretty dramatic thermo-tolerance. Imagine the difference between room temperature and slightly hotter than the record temperature for Death Valley. I can't quite imagine being somewhere that hot, but it seems pretty extreme! The species they studied (Pohlia nutans) grows in geothermal areas and thus may be unique in terms of its tolerance for high heat.

Overall I think that it is a really cool study!