Cronberg, N., R. Natcheva, and K. Hedlund. 2006. Microarthropods Mediate Sperm Transfer in Mosses Science 313: 1255.
I was tidying up my computer desktop today and came across a really cool article about moss sperm. Yes, mosses have sperm. They are flagellated and get around by swimming in water. This fact can limit the distance that sperm can travel since they need a film of water to swim through. This is not an issue for plants such as pine trees and dandelions, because their equivalent dispersal units are pollen. Pollen is more easily dispersed since it can be transported long distances via wind or animal pollinators.
There are some interesting ways that bryophytes can disperse their sperm. One of them is a type of liverwort that explosively sends its sperm into the air, thus sending it farther from the parent plant. I discussed this Airborne Sperm Dispersal and the associated video in a previous post. Click here for a link to that blog post.
Getting back to the paper at hand, researchers hypothesized that sperm could be dispersed via small arthropods such as springtails and mites. Animals act as pollinators for many flowering plants, maybe they interact with the sperm of mosses as well?
They tested this hypothesis in an experiment where they placed the male and female mosses at different distances from each other and with or without microarthropods. They found that the mosses that were separated without a film of water connecting them could not reproduce. The sperm could not travel to the eggs without the water and no sporophytes were produced. When the microarthropods were added to containers under these same conditions ... (drumm-roll) ... sporophytes were produced! They are not sure exactly how, but the sperm were able to catch a ride on the arthropods and to be transported from the male to female mosses. It is a pretty amazing feat if you ask me and I think that it would be great to see a SEM photo of the sperm attached to the microarthropods.
In case you have never before seen one, this is a photo of some moss antheridia of Funaria hygrometrica that I took. Sperm are made inside of the brown antheridia. My former officemate always describes them as 'corn dog-shaped' when teaching. The green structures intermingled with them are hairs with swollen apical cells.Check out the original article too see their data and figures. It is a short, but good, read.
Great find, this paper! One of the items burned into my brain in basic biology was that mosses need water to reproduce, precisely so there is sperm transport. How neat to find that wee animals - which we figured only came into the picture with flowering plants - can be involved. In fact, does this cast a new light on the evolution of flowering plants? At any rate, thanks for bringing this new information to light. It may be years before it makes it to the textbooks!
ReplyDeleteThanks for the comment.
ReplyDeleteIt is unfortunate that there is such a lag time between research being published in scientific research journals and the information making it into textbooks. That places the burden on teachers to keep up on the latest literature and than pass the cutting edge information along to their students. Sometimes that means that teachers will contradict what is in the textbook with the updated research. Having taught freshman biology laboratory classes, students have a hard time recognizing that science is in a constant state of discovery and with new data old ideas can be overturned. The ever-present mantra they repeat is, "But that's not what the textbook says."
I hope to combat that type of stagnant thinking with cool research papers such as this one. I am glad that you enjoyed it!