Kin Selection in Plants

October 15, 2015

Apparently some plants can recognize their relatives...

The plant world is highly competitive. Since they can't move around, plant have gotten quite creative in terms of defense and competition. From brute force to chemical warfare, plants are not the static entities that most write them off as. And, while most of what we see is going on above ground, underground, things get even more crazy.

Recent evidence shows that the sea rocket (Cakile edentula) seems to be able to distinguish between plants that it shares DNA with and plants that it doesn't. According to a study done by researchers at McMaster University in Hamilton, Canada, plants that grow around genetic relatives allocated less to root growth than those around non-relatives. Basically, when planted near a non-relative, the sea rocket will expand its root system to try and get the most out of its surroundings. When planted near a relative, the plant limits this expansion. So what does this mean? Well, they believe that the plants are recognizing their relation to other plants and attempting to limit the amount of competition for nutrients and water to genetically related individuals.

So, is this altruism? Not exactly. According to evolutionary geneticist John Kelly, its more along the lines of reduced antagonism. Sea rockets tend to grow in high disturbance beach habitats and because of their short lifespan they frequently self-pollinate. Their seed capsules also tend to stay on the mother plant and because of this, groups of clones tend to be found within close proximity to each other.

If they were to be as aggressive to their relatives as they would be with non-relatives, then they would be essentially competing with copies of their own DNA. From an evolutionary standpoint, preserving copies of your DNA, even in individuals other than yourself, is a boost to overall fitness. The researchers make it a point to note that, in this study, they were not looking at overall lifetime fitness of the plants in question. They do not know if reduced root mass, in this situation, incurs any positive or negative fitness to individuals overall. It should be noted that studies have shown that, at least in some plant species, reduced root mass seems to incur greater reproductive efforts. It is possible that sea rocket, in the presence of related individuals, can produce more seed.

How do the plants recognize their relation to their neighbors? The mechanism is not known at this point. My guess is that there is some form of chemical signature that the plants can recognize. How this information is processed is another story entirely. More and more we are discovering how complex the botanical world really is. According to the researchers, they feel that this type of relationship is not unique to this species alone. Research like this is opening new doors into uncharted and exciting territory.

Further Reading:
http://plants.usda.gov/java/profile?symbol=caed

http://rsbl.royalsocietypublishing.org/content/3/4/435.full

Rusty Mustards

May 4, 2015

Believe it or not, what you are seeing here is the same species of plant. The one on the left is the normal reproductive state of a Boechera (Arabis) mustard while the one on the right is the same species of mustard that has been infected by a rust fungus known as Puccinia monoica.

The interaction of these two species is interesting on so many levels. I spent an entire summer, along with my botanical colleagues, completely stumped as to what this strange orange-colored plant could be only to eventually find out that it was a mustard that has been hijacked! The fungus in question, P. monoica, is part of a large complex of interrelated rust fungi who are quite fond of mustards. The reason for this all boils down to reproduction.

The lifecycle of P. monoica begins when spores land on a young mustard plant and invade the host tissue. As they grow, they gain more and more nutrients from the mustard. Eventually the fungi effectively sterilizes the mustard and causes it to begin forming what are referred to as "pseudoflowers." The pseudoflowers are basically leaves that have been mutated by the fungus to look and smell a lot like other plants blooming in early summer.

The pseudoflowers produce a sticky, nectar-like substance that is very attractive to pollinators. The mimicry even goes as far as to produce yellowish pigments that reflect UV light, making them an even more irrisistable target for passing insects. On each pseudoflower are hundreds of small cups known as spermatogonia. These house the sex cells of the fungus. Visiting insects get covered in these sex cells, which they will then transfers to other infected plants thus achieving sexual reproduction for the fungus.

Still with me?

At this point, the pseudoflowers stop producing color and nectar and instead, the fused sex cells germinate into hyphae that begin to form specialized structures called "aecia." The aceia house the spores that will be responsible for infecting their secondary host plants, which are grasses. Spores blow about on the wind and, with a little luck, a few will land on a blade of grass. The spores germinate and infect the grass. From there, structures called "uredia" are formed that go on to produce even more spores to infect even more grass. Eventually, structures called "telia" are formed on the grass and the cycle finally comes full circle. The telia produce the spores that will go on to infect the original mustard host plants.

Whew! To have stumbled across an evolutionary drama such as this serves as a reminder of just how much in nature goes largely unnoticed every day.

Further Reading: [1] [2] [3] [4]

A Tenacious Little Mustard

March 16, 2015

If you are looking to place a bet on what the first flower sighting of early spring will be, then a safe pick would be Draba verna. Known commonly as early Whitlow grass, the small stature of this tenacious mustard is quite deceiving. It is one tough cookie, certainly one of the toughest little plants I know. Though it is originally native to parts of Eurasia, encountering this little beauty after a long winter is a welcome treat.

If you want to find this species, you have to look where humans are. It excels in disturbance. I most often see it growing along the edges of gravel parking lots. It is quite variable in appearance but is nonetheless recognizable due to its early flowering period and bright white, four petaled flowers. It is not uncommon for there to be plenty of snow still on the ground when these little plants begin throwing up flower buds.

Like most winter weary denizens of the northern hemisphere, the flowers of Draba verna only seem to open on during bright, sunny days. There is good reason for this too. For starters, the few pollinators active this early in the season are only really out on fair weather days. Also, since dark and cloudy spring days are often cold and full of precipitation, it isn't worth the risk of damaging sensitive flower parts from wind, rain, or frost. Plants set seed by late spring but by that time ambient temperatures are too high for successful germination. Instead, seeds require a warm summer dormancy before they will begin germinating later in the fall. Sometimes the most interesting things come in very small packages.