Mossive Disjunctions are from the Birds

Though we may not think about it, plants have migratory capacity. Their migrations are not like those of a wildebeest or neotropical warblers. Instead of moving as individuals, plants migrate via seeds, spores, or pieces of the parent plant that can then grow into a new, albeit genetically identical individual. Either way, long distance dispersal events have long puzzled ecologists. It has been demonstrated time and again that even modest barriers can inhibit propagule movement. Still, it would seem that over the course of time, plants have managed to overcome such boundaries. One way or another, plants have made some impressive migrations.

Some species have really managed to confuse ecologists. Certain mosses and lichens have very curious distributions. There are species that are found only in the Arctic and the very southern tip of South America. Nowhere in between. Why is this? There have been hypotheses regarding wind currents but the genera to which these plants belong originated in the Miocene and Pleistocene, while the Intertropical Convergence Zone (a major barrier between northern and southern wind currents) was already in place.

Recently, researchers have looked towards long-distance fliers like plovers to explain these distributions. These birds breed in the Arctic and overwinter in South America. Could these be the vessels by which these plants migrate? It has long been known that seeds passing through the gut of a bird often have high germination rates. Many plant species gear their fruit specifically for this reason. Birds travel great distances in their search for food and breeding territory, much greater than the average plant can. But birds aren't necessarily eating mosses and lichens. However, they do use them in their nests. Spores and bits of vegetative material can then get stuck in their feathers. After breeding, the birds migrate to South America and begin their molt. The feathers containing spores and plant material are now shed into the wild where they can germinate and grow.

Considering the size of these migrations, it is likely that these migratory shore birds, and possibly many other species of migratory birds, play a significant role in the dispersal of these plant species.

Photo Credit: barloventomagico (http://bit.ly/1p1X2WC)

Further Reading:
https://peerj.com/articles/424/

Poop Moss

Coming this month to a bog near you...

Splachnum moss!

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Splachnum has to be one of the most interesting genera of mosses in the world. When we think about habitat specificity, we usually think of some sort of endangered or rare habitat type. The mind definitely would not go to poop. Yet, this is exactly where Splachnum grow.

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These mosses are specialists on animal dung. What's more, since different animals produce different kinds of poop with different chemical makeups and different textures, different species of Splachnum specialize on different kinds of poop. Deer poop is a favorite haunt of Splachnum ampullulceum whereas coyote or wolf poop will be inhabited by Splachnum luteum. 

If this ecology wasn't specific enough, Splachnum cannot inhabit poop anywhere it lands. These mosses can only be found on poop which has landed in either a bog or a fen. As one can probably guess, poop quickly breaks down. Its ephemeral nature, especially in a wet bog, means that Splachnum mosses can't be bothered with a chance encounter via wind-borne spores. Instead, these mosses utilize other poop specialists, flies. 

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Splachnum spores are produced at the tip of very long, very ornate sporophytes. They are large, colorful, and some even produce a fetid odor in hopes of attracting their winged spore dispersers. Once a fly lands to investigate, it becomes covered in sticky Splachnum spores. When it lands on another pile of poop, some of the spores will fall off and find a new pile of rotting dung to colonize. Because poop decomposes rather quickly, the Splachnum mosses don't bother with lots of vegetative growth. A small gametophyte quickly produces a grandiose display of sporophytes so that the next generation can get a head start before the fecal substrate decomposes out from underneath the parent. Also, Splachnum colonies actively skew their sex ratio to favore females over males 2:1. This ensures that there is as much spore production as possible. 

July is the perfect time of summer in the North to go looking for Splachnum. Keep an eye out and tread lightly. These lovely little mosses with their peculiar natural history are a real gem to discover. They are a wonderful reminder of how complex of a world we live in. 

Photo Credits: caspar s (http://bit.ly/1H7P4pf), madcowcult (Wikimedia Commons), and Biopix: A Neumann (http://bit.ly/1HFoUh0)

Further Reading:

http://www.bbsfieldguide.org.uk/sites/default/files/pdfs/mosses/Splachnum_sphaericum.pdf

http://www.bbsfieldguide.org.uk/sites/default/files/pdfs/mosses/Splachnum_ampullaceum.pdf

http://www.jstor.org/stable/3243620?seq=1#page_scan_tab_contents

http://link.springer.com/article/10.1007/s11240-006-9176-1#page-1

Moss Matriarchy

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Mosses have been around for a long time. They also retain some interesting features of early land plants. Like their algal precursors, mosses have motile sperm that must literally swim their way to a female gamete. Of course, this process requires water. For some mosses, living on land makes reproduction difficult, even at the scale of a few centimeters. Distance is not the friend of diminutive, sexually reproducing mosses.

There are some groups of mosses that have evolved an interesting way around the issue of distance. Though it occurs in plenty of other genera, I would like to focus attention on one genus in particular, the Dicranum mosses. You can find these hairy-looking mosses growing in tufts or mats in forests throughout North America. Like all bryophytes, they exhibit an alternation of generations. The green gametophytes house the sexual organs and, after fertilization, give rise to the stalked sporophytes that produce and disseminate their spores. 

An inspection of Dicranum patches in the wild may reveal that all of the gametophytes seem to be female. Despite this observation, there would seem to be no shortage of sporophyte stalks poking above the mat. How is this possible? How does sperm make it from some undisclosed male population to fertilize the eggs of these entirely female mats? The answer is to be found only after you observe the females under a microscope. 

Dwarf males growing on the stem tomentum of  Dicranum polysetum

Dwarf males growing on the stem tomentum of Dicranum polysetum

Under magnification, you will notice that many of the female gametophytes appear to have hairy little outgrowths scattered around their tiny leaves. Under a higher powered lens you may then notice that these hairy outgrowths contain antheridia, the sperm producing organs of males. What is going on here? Are these mosses hermaphroditic? Nope! What you are seeing are indeed the males of this species. 

Spores of Dicranum don't start out as either sex. Instead, their fate in the environment determines what they eventually develop into. If a spore makes it to new terrain, it will become a female. Females are larger and can handle the rigors of establishing new territory. If a spore lands on another clump of moss, something different happens. The female gametophytes emit hormones which direct the development of that spore into one of these dwarfed males. Settled in among a forest of females, this tiny male individual is now primed and ready to release sperm. They are essentially live-in sperm donors.

For this genus, it doesn't make sense fore males to grow into full blown adults in such situations. The bigger a male gets, the more distance separates his sperm from the eggs of females. A reduction in size allows the males to insert themselves into colonies made entirely of females to serve as the reproductive agent for that grouping. Quite a fascinating life history trait if you ask me. Mosses have also been at the survival game much longer than pretty much all other forms of life we encounter on land. I think it goes without saying that they certainly deserve a greater recognition. 

Photo Credit: [1] [2]

Further Reading: [1] [2]

Time

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There is something very special about old plants. They offer us a way of appreciating a timescale that we can never fully understand. I am especially fond of finding people who have had house plants in their family for generations. I grew up with a few that had already been around for decades before I was born. Here is a wonderful example of what I am talking about. This Acronia titan orchid has been blooming for years and has acquired a wonderful little moss patch in the crux of its leaf. Out of that moss grows a fern.

This photo comes to us courtesy of Kevin Holcomb. You can find him on instagram via @orchid_beard