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Tuesday, March 1, 2016

Vavilovian Mimicry

Vavilovian mimicry is a form of mimicry where an agricultural weed begins to take on characteristics of a domesticated agricultural crop due to the selective forces present in the agricultural system.

The first example is involving wheat. Well, really, it involves both wheat and barley. During the early phases of domestication of these grains, they weren't distinguished as separate plants. Initially, the large seeded grasses were collected from the wild and planted closer to home. The now-farmers would then collect the large seeds from the grasses they grew, eat most and protect some, and then plant what was left the following year. You could say that wheat and barley are Vavilovian mimics of each other, because we really don't know which was the first grass to enter domestication.

At some point while the wheat/barley agricultural system was developing, other weedy grasses invaded the prime growing habitat found in the fields. Two of these weeds evolved to become what we call "rye" and "oats". They developed larger, non-shattering seed heads and an annual life-cycle. This allowed their seeds to be collected, saved, and planted as contaminants to the main crop. Both rye and oats are more tolerant of cold conditions and poor soils. Because they had become mimics (and contaminants) of the major crop, when farmers tried to establish the crop system in marginal conditions, these mimics can come to predominate as the major crop.
Wheat/Barley -> Wheat (Triticum spp.)
Wheat/Barley -> Barley (Hordeum vulgare)
Wheat/Barley -> Rye (Secale cereale)
Wheat/Barley -> Oats (Avena sterilis)

Another often-cited case of Vavilovian mimicry is found in the agriculture of lentils (Lens culinaris). A common weed in lentil fields is the Common Vetch (Vicia sativa). The Common Vetch seeds are bitter, so farmers are able to sell their crop for less if there is too much vetch contamination. As farmers have increased the selection pressure on the vetch by mechanical (and computer-vision) assisted seed sorting, strains of the vetch have evolved so that their seeds mimic the lentils in color and size, as well as the characteristic flattened lens-shape.

A. Lens culinaris. B. Vicia sativa, wild and mimic.
(from: www4.ncsu.edu/~fgould/pdfs/Gould1991.pdf)
Lentil (Lens culinaris) -> Common-Vetch (Vicia sativa)
Lentil (Lens culinaris) -> Black-Pod-Vetch (Vicia sativa subsp. nigra)
If farmers could impart some selective force on the mimic vetches such that they would lose their bitter flavor, they would have effectively created a new crop. This new crop might grow better in some conditions where lentils don't thrive, thus spreading the useful area of agriculture.


The selection force involved in the development of Vavilovian mimicry can be mechanical (as in Flax weeds) or manual (as in Rice weeds). What is key is that the selection force separating weeds from the crop has to progressively get more and more stringent over time. This allows the weed population to always have some individuals that will escape the selection force applied to them.
Flax -> False-Flax (Camelina sativa linicola)
Flax -> Flax-Dodder (Cuscuta epilinum)
Rice (Oryza sativa) -> Early-Baryard-Grass (Echinochloa oryzoides)

An interesting case that I think is related to Vavilovian mimicry is the complex of Andean tuber crops. I don't know which crop was first domesticated in this region, but since before modern history, five species of tuberous crops have been traditionally grown together in fields. Growing several different crops together in this agricultural system mean that there will always be production, even if any given plant doesn't produce in some year (due to weather, disease, or other factors).
Potato (Solanum tuberosum) -> Maca (Lepidium meyenii)
Potato (Solanum tuberosum) -> Oca (Oxalis tuberosa)
Potato (Solanum tuberosum) -> Mashua (Tropanolum tuberosum)
Potato (Solanum tuberosum) -> Ullucus (Ullucus tuberosus)
Though I doubt any of these species entered the agricultural system as weeds, I expect that each species will undoubtedly have evolved towards a set of traits similar to those of the most common plant grown in the fields. Any individual plants that didn't prosper in the agricultural system would have contributed less to the next generation and the species would shift to a form that did prosper. This shifting of the traits of one species to align with another, due to the selection forces favoring the majority plant species, is a characteristic common between Vavilovian mimicry and whatever this case should be referred to as.


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Tuesday, February 23, 2016

From Weeds to Trees and Back Again

The evolution of the first plants into the modern trees included the incorporation of numerous evolutionary novelties. I'm going to focus on the ones that I think are important for the story I'm trying to tell, though I'll likely get them in the wrong order. It has been many years since I took a course emphasizing this topic and it is likely I also won't be able to find links discussing all the fossils from which this knowledge originally came. In the end, this first section below is really about setting context.


The first novelty was water transporting tissue (tracheids) that let plants grow taller (a few inches) than water diffusing through previous tissues would reach. The size of these early plants was then limited by how thick their stems could grow from their apical meristems (called primary growth). The ability to restart growth from tissue previously laid down by the apical meristems, called secondary growth, allowed plants to grow thicker (and taller, since the thicker stems could support greater height). Eventually the plants were again limited in size by their strength. The evolution of the first true wood (thick cellulose cell walls reinforced with lignin) allowed what we would first recognize as trees to develop.

The trunks of these first trees could only grow to a certain size, however, because of a quirk of their secondary growth. They grew outwards by dividing their outer cells parallel to the outer surface (periclinal division). As the trunk grew, the outer cells got thinner and and wider. Eventually the cells were too thin to divide further. The growth of the trunks slowed to a stop. Eventually, a group of trees developed the ability for its outer cells to divide in half from side to side (anticlinal division). By mixing periclinal and anticlinal divisions, these trees could grow beyond the limited size of their ancestors with only periclinal divisions. They could grow thicker, stronger, and thus taller.

from: www.mun.ca/biology/desmid/brian/BIOL3530/DEVO_07/devo_07.html

At this stage we effectively have modern trees. There are lots of other interesting developments to talk about (vessel cells, seeds, leaves, flowers, etc.), but for some other time.


So, now that I've discussed the context...  what is the main topic I want to discuss?

Modern flowering plants (angiosperms) all count some of those ancient trees as ancestors. They range from the exceedingly tiny (Wolffia borealis), to the stupendously huge (Ficus benghalensis, others). Though most families of flowering plants don't range to such extremes, they generally count trees and small herbaceous plants among their members.

The milkweed family (Asclepiadaceae) is mostly small herbaceous species (such as Cynanchum barbigerum and Asclepias involucrata), but includes at least one moderately sized tree (Calotropis Procera). The dogwood family (Cornaceae) is most woody shrubs and trees (such as Cornus florida and C. kousa), but includes at least one herbaceous weed (C. canadensis).

If a tiny weed is introduced to an island, it can in a reasonably short time (from an evolutionary perspective) evolve into shrubs and large trees. This isn't just a story, an idea that sounds nice. The ecologies of isolated islands are often filled with very closely related plants filling wildly divergent ecological roles. Early on the geologic history of the Hawaiian islands, a tarweed seed managed to find a foothold and grow. It's descendants now fill the island in the form of weeds, vines, shrubs, and trees. On the Galapagos islands, a member of the common cactus genus Opuntia has evolved into a tree (Opuntia megasperma). On the channel islands, a member of the common herbaceous weedy genus Coreopsis has evolved into a tree (Coreopsis gigantea).

Coreopsis gigantea (from plants.usda.gov/core/profile?symbol=COGI)

Numerous other examples can likely be found where a tree has quickly evolved from an herbaceous group (or an herbaceous plant from a tree group) by examining the flora of the various isolated islands around the world.

Though the evolution of a flowering herbaceous plant into a tree or the reverse is interesting (and would make for really neat garden specimens), it doesn't require any dramatic evolutionary changes. Every flowering plant inherited the genetic/developmental toolkit necessary for growing as an herbaceous plant or as a tree from its ancestors among the very first trees. If an organism is missing some trait that its ancestors had, it is likely that the organism still carries most of the genetic tools needed to quickly evolve that trait in the future.


References
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Tuesday, February 16, 2016

The Impermanence of Being (a Fossil)

A fossil you find may have existed hidden away underground for millions of years, but they have a very short lifespan once uncovered and exposed to the elements. Rain, snow, wind, animals, plants, and people (not just collectors) all wear away at exposed fossils that are almost invariably fragile. Within a relatively few years of becoming exposed, they crumble away to unrecognizable gravel. Good fossil exposures are transient things.

Because of the temporary nature and physically limited size of fossil sites, many fossil-hounds develop a habit of being somewhat vague when describing where they've found a really nice specimen (at least until they have gotten to know you well). If you widely spread the news about some interesting site you found, you're more likely to find the site completely picked over the next time you visit. These days, I can imagine fossils being quickly stripped from a site for sale online. I don't have a problem with someone selling fossils, but I would definitely despair at finding an interesting site emptied between one visit and the next. Much of the value of an interesting fossil in the context. (The geologic era, what species were found with it, etc.) This information can easily be lost if a site is picked over with too much haste.

The former fossil site, now a movie theater.
I recently checked in on a site where I once found numerous wonderful fossils. The site was directly behind my high-school in San Antonio, Tx. Thanks to GoogleMaps, I now know it to be the parking lot for a movie theater. I have no problem with telling the wider world exactly where the site is located. There is no further damage over-exposure can do to it.

Previously, there had been a wide, flat hilltop covered with multi-pound specimens of Exogyra ponderosa (a reef-forming oyster), along with the numerous shells from several smaller relatives. The fossiliferous layer was the very top of the hill, so one could walk along and easily visualize how the ecosystem was organized back in the Cretaceous era when this hilltop was the floor of a shallow sea. Though all the animals had been extinct for 60 million years, the fossils were comprehensive enough to clearly be a well-populated oyster reef. The site was impressive. I expect ecological studies could have been done there. The nearby area of undeveloped land probably contains fossils, since much of Cretaceous limestone does, but the oyster reef did not extend into that area. The reef no longer exists and only the few fossils remaining from the site in the hands of collectors like myself (and the biology teacher who pointed me towards the site) are evidence for it having ever existed.

A ~6in long Exogyra ponderosa from the oyster reef.


I always meant to spend more time exploring the area, but the classes and drama of high-school always seemed to get in the way. When I graduated and moved on to college in Austin-Tx, my parents moved out of state. I no longer had any connection to the neighborhood. It wasn't until years later, when I too had moved out of state, that I got my first car and with it the freedom to go wandering around looking for fossils and the like.

Now I have other fossil sites to visit and keep quiet about. (For example, where I found another mollusk... the-biologist-is-in.blogspot.com/2014/05/a-gastropods-lesson.html).


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Tuesday, February 9, 2016

"Chauncy"

The University of Minnesota just had the rare event of a blooming specimen of Amorphophallus titanum. The flower structure grows to nearly 6 feet tall, then opens to reveal a scent that befits one of its common names, the "Corpse Flower". I was able to stop by for a visit on 08-Feb-2016, a day after the bloom had first fully opened. From discussion around campus, it seems the scent produced by the flower was so overpowering for the first day that nobody was willing to go near it.

The structure isn't actually a single botanical flower. Instead it is a contains hundreds of relatively tiny and nondescript flowers along the base of the large spire, hidden inside the prominent shroud-like bract. The greenhouse staff cut a small window through the bract, so that visitors could see the inner structure (as well as get a very close sniff, for the brave).

The university staff had named the plant "Chauncy" and had posted some paper for people write their descriptions of the flower's scent. One description that caught my eye and well fit my experience of the flower's scent was, "A dead racoon 3 days old". The scent wasn't over-powering by the time I visited, but it did linger in my nose for about half an hour after I left the greenhouse.

In a neighboring pot to "Chauncy" was another specimen of A. titanum that isn't blooming this year. This plant was about 12 feet tall and appeared as a small tree with a few branches and luxuriant leaves. I use the word "appeared" because the entire above-ground structure of this plant is botanically a single leaf. It is somewhat like the leaf of a tomato plant, with stem-like structures, branches, and leaflets. Only in this case, the single leaf grows to tower overhead. After some time, the leaf will die and fall, only to be replaced by a new and larger leaf (if the plant is happily growing). The persistent body of the plant is a large tuber, securely hidden underground.



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Tuesday, January 19, 2016

Micro insects

I haven't been feeling up to writing much lately. Most of my free time has been occupied with working on an academic project in meta-genomics. I'm aiming for this to be published in a science journal, so I won't be discussing the details of it here (for now). I'm also experiencing some anxiety surrounding what my job currently is, where it is going, and where I want it to go.

All together, this is leading to a pretty solid writer's block. I've got a collection of interesting topics that I haven't managed to pull together into full posts, so I'll probably be posting a few of these over the next several weeks. Today, I want to point you towards some readings about extremely, bizarrely, tiny insects.



Micro-wasp with aneucleate nerves
Micro beetle.
Features found in both micro-insects.
  1. Reduced number of neurons, but a relatively larger nervous system.
  2. Reduction in number of organ parts. Reduction in Malpigian tubules, spicules, etc.
References:
  1. Polilov, A. (2008). Anatomy of the smallest coleoptera, featherwing beetles of the tribe nanosellini (Coleoptera, Ptiliidae), and limits of insect miniaturization. Entomological Review 88:26-33.
  2. Polilov, A. (2011). The smallest insects evolve anucleate neurons. Arthropod Structure & Development In press. doi:10.1016.j.asd.2011.09.001
  3. Niven, J. E., and S. M. Farris (2012). Miniaturization of Nervous Systems and Neurons. Current Biology 22:R323-R329.
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Tuesday, January 12, 2016

The Poison-Apple Tree

Most residents of the USA are familiar with Poison Ivy (or Poison Oak), but we're generally not familiar with a farm more poisonous tree that also lives here. The Manchineel tree (Hippomane mancinella) grows in Florida (as well as more tropical areas of the Americas) and is considered one of the most poisonous trees on the planet.

H. mancinella belongs to the Euphorbiacea, a plant family which is crowded with poisonous representatives. This tree stands out in the crowd, however. You can be poisoned by eating the fruit, touching the leaves, breathing smoke from burned wood, or even by rain splashing off upper branches. Locals tend to place large hazard signs on any tree that they know about. This doesn't stop the occasional tourist from finding one without appropriate signage, and even eating some of the sweet smelling (and tasting) fruit, before the poison begins to have its effect. Extreme pain, lesions, intestinal damage, etc. are common. Death isn't unheard of as a side effect of all this damage.

Before you go tromping around in the woods on some tropical Caribbean island, you should make a point to study up on how to identify this tree from a distance.


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Tuesday, January 5, 2016

Doom of the Fruit Fly

The red-eyed fruit-fly familiar to biology students everywhere (Drosophila melanogastor) likes to lay eggs in recently spoiled fruit, where its larvae can consume the fruit sugars and the yeasts that grow on them. If you have an infestation of D. melanogastor in your kitchen, the first step is to get rid of whatever they're breeding in. The second step is to get rid of all the adults that are flying around. You could spray some poison, get skilled with a fly-swatter, or buy some commercial traps... but it is a pretty simple task to make your own trap without needing any poison. Make a paper cone with a small hole in the tip, then put it point-down into small jar with a bit of over-ripe fruit in the bottom as bait

The inverted cone prevents the fruit flies from finding their way out once they've crawled inside. If you don't have an inverted cone, you'll just be breeding more fruit flies to infest your kitchen. The bait can be whatever rotten fruit was attracting the flies.


One species of fruit-flies that doesn't like recently spoiled fruit is the Spotted-Wing Fruit Fly (Drosophila suzukii). This species lays its eggs in ripe soft fruit (raspberries, strawberries, blueberries, etc.). They are able to do this because the females have a saw-edged ovipositor that lets them cut into soft fruit to lay their eggs. They don't have to wait for fruit to begin rotting like the typical fruit flies and their infestation will result in the rapid destruction of fruit that would otherwise go to market. This has become a big problem for people trying to grow berries without pesticides. There are traps for these flies, but they're only really useful as a surveillance tool. The traps alone will not protect your fruit.


Image from blogs.cornell.edu post.
Another group of fruit-flies that don't like recently spoiled fruit are the dark-eyed fruit flies. D. repleta, D. hydei, and D. robusta are slightly larger and prefer their food source to be far more degraded. What this often means is the grimy collection of goo in floor drains or between/underneath cracked floor tiles in restaurant kitchens. It also can mean chicken poop in a barn, a mostly rotted compost pile, or the litter of a reptile tank (that I really probably should have cleaned already).

Once I noticed the existence of the flies, I cleaned up the source of the problem and my gecko is happy with her spiffy new home. The fruit-fly trap I described for D. melanogastor would work equally well for these flies if I could figure out a bait that they would be attracted to. I could scoop some of the old rotted reptile media into the jar, but I discovered something a bit more interesting (and effective).

S. integrifolium "Pumpkin Tree" fruit.
I had the branches and fruit from a Solanum integrifolium "Pumpkin Tree" plant I grew this year hanging up in our kitchen to dry. I first noticed the dark-eyed fruit-flies because they were hanging out on the branches when I checked on how the dry the fruit was. As an experiment, I put a couple of the fruit into the previously described fruit-fly trap and put the remainder of the plant outside.

The next morning, all of the flies from the kitchen were having a party -inside- the trap. I scattered all the flies outside and reset the trap beside the (now clean) reptile tank. The next morning, all the fruit-flies in that area were also inside the trap. The dark-eyed fruit-flies (of whichever species I have here; D. repleta, D. hydei, or D. robusta) really, really, love the fruit of the "Pumpkin Tree" plant.

I've dehydrated and powdered the remaining fruit to save them for later use as a bait. If the dark-eyed fruit-flies ever reappear, I'll mix some of the powder with some water as bait and continue the experiment. I could also do some experiments outside next summer, as the dark-eyed fruit flies are likely to prosper in my compost pile again.

I've saved seeds from the "Pumpkin Tree" plant and will definitely be growing it again for its decorative and fly-trapping features.


References:
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