Natural history and ecology go together like flowers and pollinators

I've only very recently returned from Victoria, where I attended CSEE2017 and gave a talk. CSEE2017 was fantastic, but I will save my commentary thereupon for another post. I'm only mentioning my visit to Victoria now because I went to the Butchart Gardens while there. To be perfectly honest, these days as a plant ecologist I often get grumpy visiting ornamental gardens, as they generally have few or no native plants, usually have virtually no pollinators to watch, and just lack ecological interest. Certainly I found the gardens beautiful, and if I were a horticulture aficionado I might have found more to interest my curiosity while there, but what actually caught my attention was this:

Tulip showing stem fasciation and an abnormal number of flowers.

Fasciation: an abnormal condition of growth tissues, wherein in the meristem (area of actively dividing, growing, and differentiating cells), rather than having its normal domed/round shape, is elongated in one dimension, resulting in thick, wide organs and distorted growth. For a more detailed discussion of fasciation, I invite you to read my previous blog post on the topic (linked below).

I have talked about fasciation before, in context of a rather awesome monster thistle that displayed multiple levels of fasciation plus homeosis (substitution of one organ for another), so that was an individual with a lot of issues. But this fasciated  tulip is rather intriguing to me because it exhibits only stem fasciation, with no other visible abnormalities. The photo below shows the fasciated stem clearly.

Fasciated tulip stem

Now, the fasciation of just the stem is interesting to me because it is specifically accompanied by a subsequent splitting of the fasciated stem and the production of multiple otherwise normal flowers, as seen in the first photo and even the one below, where there are two tulips rather too close to one another, but they are not fused (i.e. they grew on separate meristems) and they seem to be anatomically normal. You may have noticed that the photo below is a different plant -- at the gardens I saw three cases of this kind of stem fasciation in tulips with an abnormally large number of otherwise anatomically normal flowers.

Fasciated tulip again

Since I saw it three times, it may well have been more common than that at the garden. Possibly this is a heritable fasciation (i.e. fasciation resulting from a genetic mutation); the probability of this option depends a bit on how the garden acquires and maintains their tulip population -- if they breed their own tulips, then it is possible that these fasciated individuals are actually related to each other, which increases the probability of this being a heritable genetic mutation.

Fasciated tulip!

However, as with the thistle, there are other reasonable possibilities, among them the possibility that the fasciation has an environmental cause (e.g. a pesticide or fertilizer applied to all the tulips), or that it results from a bacterial or fungal pathogen transmitted through the garden by gardening activities like watering and weeding.

My friend and travelling companion, Kayleigh, also found a case of fasciation in Bellis perennis (english daisy) in Victoria. First, here's a normal one:

Bellis perennis normal specimen -- photo taken by K.G. Nielson and used with permission

And our weird mutant showing floral fasciation (this is what is not seen in the tulips above; with them, the stem is fasciated but the flowers normal; with this one, the stem is normal but the flower is fasciated):

Bellis perennis fasciated individual -- photo taken by K.G. Nielson and used with permission

So you might be wondering when I'm going to get to the point. The point is this: an ecologist should also be a natural historian! There was an interesting opinion piece recently published about the importance ecologists place on natural history (the largely observational study of organisms, particularly their traits, their interactions with their environment, and their history), and how ill-equipped many young ecologists feel to teach natural history.

This story resonates with me, because I adore natural history but make no pretensions to having great skill or knowledge in the area; I am largely self-taught on this subject. I run this blog partly to share the beauty and wonder and amazing scientific appeal of nature, and partly to remind myself to root my ideas firmly in the reality (read: natural history) of the organisms and communities I study.

I believe that natural history is where it all begins: a couple of ecologists on a walk notice a bunch of fasciated plants, and this spurs all sorts of wonderful lines of inquiry about how the fasciation comes about, how the condition might spread in a population, the particular mechanisms of function, the possible associations between assorted fasciation types, etc etc etc.

Darwin is a particularly notable example of beginning ecology with natural history: his work starts with incisive observation and proceeds from there into testable hypotheses and experiments.

When it comes down to it, everything we do as ecologists starts in with natural history.

I don't have enough experience or expertise to weigh in on whether natural history training is lacking in many universities as suggested in the article I linked. I can't even say whether my own lack of extensive natural history training is due to my own neglect of my options, or due to an absence of options available to me. But at the personal heart of it, I'm an ecologist because it allows me to blend my deep and abiding love of natural history with the elegance, logic, and rigour of the scientific approach. I'm sure I'm not alone.

The best ecological questions and hypotheses happen because ecologists are also natural historians.

Besides, it's better for our health to get outside and wander around once in a while with our eyes wide open.

Attack of the mutant thistle: homeotic genes and how a cell knows what organ to become

Over the weekend, I was looking around for some populations of Cirsium vulgare (bull thistle) for my research, and while wandering, I noticed a rather remarkable individual that displays several physiological abnormalities.

For context, here's a full-plant view of a reasonably normal (i.e., representative) individual, which was only about 2m away from our plant of interest.

Cirsium vulgare, structurally representative individual

It clearly has a central stalk from which numerous branches emerge, each topped with one to three (ish) flower buds. Most individuals were not yet actively blooming this weekend.

To understand what's going on here, some knowledge of plant development is required. This is not my area of expertise, so I apologize for any minor inaccuracies which may be found in the descriptions below.

When a plant is developing normally, the cells can be broadly split into two categories: differentiated cells, and meristematic cells. Meristematic cells are found in the areas of the plant experiencing active growth: root tips, stem tips, and flower buds. These cells have not yet become differentiated, that is to say that they are not yet assigned to a particular organ type (e.g. stem, leaf, petal, etc.). The areas where these cells are found are the places of active growth and development in a plant.

There are a regulatory genes which are responsible for determining which cells become which types of organs (they tell the meristematic cells what to become), which are broadly referred to as homeotic genes. The proper functioning of these genes is essential to the accurate physiological (anatomical) development of an organism. When homeotic genes are not functioning correctly, the consequence is usually a non-viable organism (i.e. an organism which cannot live). Sometimes, however, disruption of homeotic genes can be survivable. Generally, when something is seriously wrong with the physiology or anatomy of an organism, there's a good chance that a malfunctioning homeotic gene is responsible.

Homeotic genes are not exclusively found in kindom Plantae; indeed, quite a lot of research has been conducted on the function of homeotic genes in kingdom Animalia, especially with flies. There's quite a lot of interesting research about homeotic gene mutations or gene knockouts resulting in abnormal physiological development in many organisms, such as this study in mice which found that the silencing of one homeotic gene resulted in a continuation of anterior (front-body) anatomy development further along the body of mice -- basically, extra ribs.

A lot of studies have been conducted in this area for plants, as well, particularly using Arabidopsis thaliana, the world's most popular plant research organism. Manipulations of homeotic genes of this plant have isolated the particular genes responsible for the development of assorted organs in plants.

Now let's take a look at our unusual individual.

Whaaaaa-? Abnormal Cirsium vulgare

The most obvious oddity about this particular individual, from a distance, is the exceptionally thick stalk and lack of branching. It looks rather like a small tree from a distance (my husband mistook it for one at first).

If we get in closer, we can see that the stalk seems to be many fused stalks (note the vertical striations, and the strangely wide & flat shape). This is either because all the branching stalks have failed to separate from the trunk (possible), or because the apical meristem (developing portion of the vegetative part of the plant) is fasciated (misshapen, resulting in elongation along one plane). Hard to decide. I'm tempted to say fasciated, but the total lack of branching stems is throwing me off on that conclusion.

Close-up of the abnormal C. vulgare's central stalk; note the vertical striations and odd shape

The next weird thing about this particular individual only becomes obvious once one gets in a bit closer to take a look at the top of the plant, where we expect to see flower buds. Instead of normal C. vulgare flower buds, we see this:

Huh? Flower buds of abnormal C. vulgare

Cirsium vulgare flowers normally have a rather large receptacle (the lowest part of the flower, essentially a swelling of the stalk, which is often seen as a bulbous portion below the organs we more readily recognize as 'flower'), covered with spikes. In place of this spiky receptacle, this abnormal individual has an abundance of leaves. When cells which should have developed into one organ instead become another, we call this homeosis.

Finally, if you look closely at the flower bud in the lower right of the above picture, you can see that it is not classically round, instead looking strangely comma-shaped. This is called floral fasciation, where the floral apical meristem (portion of the plant actively developing into floral organs) becomes misshapen, so instead of round it gets stretched out like this.

You might be wondering at this point -- is this common? Well, no, such abnormalities are quite rare in natural populations, although it may be more accurate to say that such they are rarely found in living, viable individuals in natural populations (most of the time such abnormalities mean that the organism is nonviable and so never grows/develops, or dies extremely young).

You may also be wondering -- how did this happen? Well, that's a bigger question. I can't establish from observation of the plant, for example, whether the problem is that the homeotic genes themselves are altered (i.e. the genetic code is wrong; this is what we call "mutation"), or whether the homeotic genes are simply malfunctioning. The anatomical oddness of the individual could be the consequence of viral infection, fungal infection, parasitism, hormonal abnormalities, or genetic changes. Unfortunately, I don't have the tools necessary to determine how the mutant individual pictured above came about.

Given the sheer number of obvious abnormalities on this individual, I suspect that there is an external cause (i.e. that the mutations are induced), because this would be the simplest explanation. All the abnormalities being the product of a fungal, viral, or parasitic infection is a simpler scenario than the idea that each abnormality has a separate cause (which would be the case if this were a product of actual genetic changes). Of course, they may also be a product of a hormonal abnormality resulting from a single genetic mutation. I have no means of determining the cause, so unfortunately my speculation will remain speculation and I shall have to leave my curiosity unsatisfied on this score.

Of course, this individual will not be used in my research. It is entirely too non-representative. Despite being unsuitable for my work, at least it was an interesting specimen!