Tuesday, July 10, 2018

It looks like a bee and sounds like a bee... but it's not a bee

I've written about mimicry of bees by flies before, in context of syrphid flies. Syrphid flies are generally considered Batesian mimics, which means, broadly speaking, that they mimic a more harmful creature. In the case of syrphid flies, they are mimicking stinging insects like wasps and bees, and thereby get to piggyback on the anti-predator defenses of those species. This kind of mimicry can only work if the creature being mimicked signals its ability to harm a predator in some way that can be imitated.

What I'm writing about today is a bit different. I managed to snap a picture of a bumble bee-imitating robber fly last week in my local ravine park. Although it's possible that the bumble bee-imitation confers some anti-predation advantages to the robber fly through Batesian mimicry, something else is probably also going on here: Wicklerian-Eisnarian mimicry. The idea with this kind of mimicry is that an organism imitates a less harmful one in order to avoid detection by its prey. Robber flies prey on other insects, including bees; looking a lot like a bumble bee is probably a pretty good way to get close enough to their prey to kill them, since bees are nectar and pollen eaters rather than insect eaters. From the perspective of many insects, a bumble bee is no particular threat, while a robber fly is definitely worth avoiding.

There are many other types of mimicry besides these two, as well. I was rather pleased to get a picture of a bee mimic that isn't a pollinator but rather a predator. Pretty neat! They also sound a lot like bumble bees, interestingly, so the mimicry goes beyond visual cues in the case of this robber fly, which I think is in the genus Laphria, and which has caught an emerald ash borer (Agrilus planipennis). Robber flies consume their prey by piercing their bodies with a hardened tube that serves as their mouth, through which they inject their prey with some digestive enzymes and then suck out the delicious bug juice that results.

Laphria sp. consuming Agrilus planipennis (sorry for the crummy cell phone camera photo)
Mmm, bug juice.

Tuesday, October 24, 2017

There's (bee) love in the air

A couple of weeks ago I came across a rather unconventional-seeming insect gathering on the sidewalk on my way home from the lab:

Bombus sp. mating pair (below), and harassing male (on top)
For many bees, fall is the mating season. The Bombus (bumble bee) life cycle is rather intriguing, so here's the condensed version: in the springtime, queens emerge from diapause (hibernation/overwintering) and begin foraging on the first flowers of the season. Each queen seeks out a suitable nesting site, starts building her nest and stocking it with pollen and nectar, and begins laying her eggs. Once the first brood of hatched larvae mature into workers, these workers take over foraging for the hive and the queen no longer leaves the nest. Instead she focuses her energy on laying more eggs. As the hives grow, workers may specialize further in their roles in the hive, some becoming foragers, others working primarily as nurses of the young brood, etc. For most of the season, the queen will lay eggs fertilized with the sperm she obtained from mating in the previous fall, which she stores in a dedicated sperm storage organ inside her body until she needs it. In bumble bees, fertilized eggs become females. During most of the season, the queen can suppress the sexual development of the females in her hive, so they remain incapable of laying eggs, and they serve as workers. But, toward the end of the season her control over workers starts to fail and the workers start developing their ovaries. During this period the queen will also lay some unfertilized eggs, and these unfertilized eggs become males (referred to as drones), and these drones leave the colony in search of mates. The queen either dies naturally or is killed by her workers, and the colony disbands.

Once the colony disbands, the new queens are looking for a mate and a place to hibernate; the males try to find queens to fertilize. When they do get together to mate, if the queen doesn't find the male distasteful (if she does, she will evade him and even sting him if he gets too pushy about trying to mate with her), then he will attach himself to her and transfer some sperm into her. This part of the process only takes a couple of minutes at most, but a male bumble bee will stay attached to the queen and then produce a mating plug, basically just a sticky sperm-free substance that, if effective, will block the path up to the organ she uses to store sperm, thereby preventing any subsequent males from providing sperm. The process of transferring the mating plug can take up to 80 minutes (average of just under 37 minutes in one species, [Duvoisin et al. 1999]), so for the majority of the time that the queen and male are copulating, really it's just the male hanging on transferring the mating plug to prevent other males from getting a chance to fertilize the queen's eggs.

So I filmed some bee porn. I watched these three on the sidewalk for about 25 minutes before I left because I was getting cold (and because the residents of the houses started giving me pointed, stern looks from their porches, since I was loitering with my camera out on the sidewalk across from an elementary school...). I may have come across them just at the beginning of copulation, so in theory I could have caught the moment when sperm transfer was occurring on camera, but I think it's much more likely that what I have filmed is the period during which the male transfers the mating plug.  Whether or not I did, I would have no way to tell whether the male is transferring sperm or a mating plug just from the video. It's pretty cool for a few minutes, but gets repetitive after  a while, so here's a short clip to give you an idea of what it looked like:

I was aware of the production of mating plugs in Bombus, so I was somewhat confused to see the bee threesome pictured above. If the mating plugs work in the usual way that they are expected to, as a mechanical blockage preventing subsequent males' sperm from entering the reproductive tract of the female, then there would presumably be no benefit in being that harassing male on top; even if he waits until the other male leaves and tries to mate with the female, unless he has some way of overcoming the mating plug, then mating with this female would just waste some of his limited sperm supply. So naturally, I had to wonder what might be going on here that would lead to this kind of behaviour. There were a number of possibilities to consider:

(1) it may be that this is an extremely rare behaviour because it is maladaptive, and I just happened to be in the right place at the right time to witness it;

(2) mating opportunities are so scarce for male Bombus spp. that even a really slim chance to father the next generation by being the second mate to a queen, would be better than trying to find another queen to mate with;

(3) the odds of siring some of the queen's offspring, even as a second (or later) mate to a queen aren't actually as bad as I am presuming based on the presence of the mating plug;

(4) the mating plug doesn't directly or entirely prevent other sperm from entering the running to sire the queen's eggs, but instead serves some other purpose;

(5) some other process or force that hasn't occurred to me.

I won't spend much time on (5) except to say that it's the thing that keeps scientists up at night ("What if the thing I found was actually the result of something else I totally haven't even imagined, that just happens to be associated with the thing I measured???"). This is the unknown unknown. We try to get around this with study designs that reduce the likelihood that this is occurring, but we can't be perfect.

Anyway, witnessing this bee threesome gave me lots of questions and very few answers, so I have been reading up for a few weeks in preparation for this post. I was able to discount (1) as a possibility fairly quickly, as I found a bumble bee mating study which directly references the frequent presence of harasser males (in a laboratory setting) during copulation [Duvoisin et al. 1999], though they note that none of them successfully displaced the first male during mating in their observations. At any rate, this is a behaviour that has been documented previously, so it's very unlikely that I witnessed a one-off event.

Some previous work suggests that (2) is a contributing factor to the observed phenomenon of bee threesomes: male bumble bees very rarely get a chance to reproduce. This alone wouldn't explain the behaviour, though, since the harassing male has to hang around harassing this mating pair, which, if he's got no chance of siring any of the queen's eggs, is a complete waste of time that might be better spent looking for another queen to mate with. When I moved this mating threesome off the sidewalk--I was worried they would get trampled--I did notice that the harassing male seemed to be trying to displace the first male, but he didn't succeed. He may have waited until the pair were done mating and then tried his luck with the queen afterward, but if so there has to have been a good reason to do so. I did get some footage of his attempt to disrupt the first male:

(3) and (4) are related issues. If the mating plug is imperfect as a mechanical blockage, then a subsequent male partner still has some chance of siring her offspring; similarly, if the mating plug serves a different purpose, then subsequent males' sperm might still have a chance as well. One indirect but very telling question to examine (3) would be to ask whether all the offspring produced by one queen are half- or full-siblings. If they're all full siblings, then she must only have a single successful mate, who gets to sire all of her offspring. If they can be half siblings, then that means that multiple males can sire her offspring (i.e., that subsequent males definitely have a chance). Multiple patrilines (groups of offspring with the same father) have been documented in some bees, notably honeybees, but very little is currently known about how closely related individuals in bumble bee hives are. Certainly it is theoretically possible to find multiple patrilines within a bumblebee colony, and Lierch and Schmid-Hempel (1998) created colonies with multiple patrilines and showed that Bombus terrestris colonies with multiple patrilines are more resistant to parasites; a related study by Shykoff and Schmid-Hempel (1991) showed that pathogen transmission between bumble bee workers is lower in hives with more patrilines; consequently, multiple mating could be beneficial for queens, whose likelihood of producing a strong enough hive to reach end of season and produce new queens and males is higher if their resistance to parasitism is greater, e.g., through the presence of multiple patrilines. So, from the female perspective it may be better to have more mates and thus a more genetically diverse group of workers in the hive. However, the relationship between colony success and number of patrilines is not linear: Baer and Schmid-Hempel (2001) found that colonies with either just one, or more than four, patrilines did better than those with 2 or 3, and they speculate that this may be due to problems with worker social structure (i.e., conflicts between workers of different patrilines) with 2-3 patrilines present in the colony. Some older research has shown that more related honeybee workers are more likely to undertake the same kinds of colony work (i.e., that the tasks that individual workers end up doing within the colony structure are partly determined by genetics and/or relatedness) (Robinson and Page 1989), which raises the possibility that more patrilines can result in improved division of labour within the colony, but I don't think any such pattern has been shown in bumble bees.

The Duvoisin et al. (1999) paper mentioned above for discusses possible alternative functions of the mating plug, though they reject many of them and do not make any firm commitment to any particular function. It may be a form of nuptial gift (nourishment to improve the female's reproductive success), as is found in some organisms (e.g., a male bringing a female food), but this is unlikely as they found no useful nutrients in the mating plugs in their study. Another possibility is that the mating plug might actually serve more to prevent backflow of sperm, and thereby its loss, than to prevent subsequent males from transferring sperm. These researchers did note that the duration of copulation, which greatly exceeds the time needed to transfer sperm into the female's genital tract, may be related to the time needed for the sperm to get to the sperm storing organ inside the queen; if so, then this might be a secondary function of the mating plug (it wouldn't be the primary function, as you don't need a mating plug to stay attached to the queen for a longer period so if this were the main important thing, we would expect no mating plug but long mating duration). Fortunately, there's a very interesting analysis that suggests a possible function of the mating plug that is not mechanical interference with subsequent males: chemical behaviour modification! Baer et al. (2001) found a chemical in the mating plugs of one bumble bee species that reduced queens' willingness to accept other mates afterward. In other words, the mating plug may make the queen more likely to refuse other males and so allow a male to monopolize opportunities to fertilize her eggs through behavioural modification rather than through mechanical interference.

There are so many more amazing things to talk about in bumble bee mating, but I'm going to leave off here in the interest of not overwhelming everybody (including myself). I would just like to end by saying that there are so many questions left to answer in biology. It's a fascinating field, and every day I am confronted with the vastness of scientific knowledge, and the even greater vastness of things we have yet to understand. It's a wonderful time to be a scientist!

Wednesday, September 27, 2017

Cheating in mutualisms? Nectar-robbing and nectar-thieving

As a pollination ecologist, I study the mutualistic relationship between plants and their pollinators. Mutualism is roughly defined as an interaction between organisms in which both partners benefit in some way. Pollination is often treated as a classic case: the pollinator gets nectar (i.e., food), and the plant gets pollination (i.e., reproduction).

However, it's worth remembering that neither participant is engaging in the interaction for the benefit of the other: in broad terms, the plant doesn't offer nectar to help out the pollinators, it does it because offering nectar improves the plant's success; the pollinator doesn't pollinate in order to help out the plants, it does it because foraging for food in flowers improves the pollinator's success. I've talked about plants that are jerks a few times before (1, 2, 3); today I'm going to talk about the flip-side of that, the 'pollinators' who are jerks. In this case, when I say that a plant or a pollinator is a "jerk", I mean that it has developed an adaptation that allows it to gain the benefits of the plant-insect interaction without offering the interaction partner any benefit -- in other words, it's a cheater. Deceptive plants fall under this umbrella, because they deceive pollinators by seeming to offer a reward, but without actually doing so and thus without incurring the cost of making the reward (usually nectar). There's some really cool research that has been done on the evolution of cheating in mutualistic relationships, which I may talk about another time. For today, I'm going to focus more narrowly on floral larceny.

So what is floral larceny? The general idea is that the putative pollinator is obtaining the reward without offering the service. So a floral visitor gets nectar without moving any pollen. Nectar-robbing is a frequently-studied form of floral larceny: the visitor, rather than trying to get in through the regular opening of the flower, just cuts a hole near the nectary and sucks up the nectar, avoiding contact with the reproductive parts of the flower and consequently providing no pollination service. In principle, certain floral shapes are adaptations that exclude bad pollinators and improve the fit of good ones by orienting them in particular ways in the flowers, but at least some of these flowers, particularly with long, tubular flowers, and especially the more rewarding ones, are more likely to be the targets of nectar robbers (Rojas-Nossa et al. 2016), so the extent to which they're actually excluding bad pollinators, as opposed to converting them into nectar robbers (which might be worse? Or not, see below), is unknown. Actual measured consequences of floral larceny on floral fitness actually range from negative to positive, which further complicates interpretation of nectar-robbing behaviour (see Irwin et al. 2010 Annual Reviews of Ecology, Evolution, and Systematics).

I managed to get some footage of a nectar robber on Impatiens capensis (jewel-weed). You can see that the robber bites a hole in the flower to get at the nectar; it's quite clear that the nectar-robbing wasp is bypassing the reproductive parts of this flower, but I witnessed several wasps engage both in nectar-robbing, and then in the more standard foraging that involved entering the flower and possibly transporting pollen. 

Similarly, if you look at the Xylocopa virginica (carpenter bee, notably one of the largest insect pollinators in this region; there are several shown in the videos below) on the hostas in the video below, first you can really clearly see in the slow-motion video as she pushes her tongue through the flower into the nectary, but in the next video in real-time, you can see that in some instances she may be brushing her very large abdomen over the reproductive parts of the plants anyway, and you can actually see some pollen grains on her shiny abdomen as she engages in this nectar-robbing behaviour, so it's not really clear whether she's truly failing to provide pollination services here, even while she engages in fairly classic nectar-robbing.

Another form of floral larceny is nectar thievery: the visitor enters through the normal floral opening, but does not make contact with the reproductive parts of the flower and consequently transfers no pollen. 

I have some footage of visitors engaging in nectar thievery on the hostas in my back yard. The video shows a relatively classical case, where the nectar thievery arises because of a morphological mismatch (i.e., the shape of the insect and flower don't match up correctly);this nectar thief is just too small to contact the reproductive parts of the flower, but of course that doesn't prevent it from foraging for nectar on the flowers.

There are also forms of floral larceny relating to pollen-robbing (which causes damage in the course of pollen removal, and in which the pollen isn't transmitted elsewhere), and pollen-thieving (no damage, but pollen is not transferred). There is very little information on these phenomena, probably because they would probably be extremely hard to confirm. Unfortunately, I don't have any footage of these. Pollen-thieving in particular might actually be quite common, depending on how we define it: here's some footage of X. virginica (carpenter bee) grooming pollen off herself; grooming is a common bee behaviour. Bees collect pollen to stock their nest cells with it (i.e., it's food for developing larvae), so a large quantity of the pollen they collect ends up not on other flowers but instead in the bees' nests. This might be considered a form of pollen theft, depending on how you want to define it. Pollen thieving is a rather understudied area, but there's an interesting review for those interested (Hargreaves et al. 2009).

Bonus, partial answer to one of the questions I raised in my first post about I. capensis (why are they shaped like this), here's Apis mellifera (honeybee) grooming herself after visiting I. capensis. Notice that the big patch of pollen between her wings isn't getting removed. Possibly, then, the shape of I. capensis helps to ensure that pollen is deposited on a part of the pollinator where it's less likely to get groomed off and therefore lost as food for bee larvae. The shape could also be at least partially driven by improved accuracy of pollen deposition onto stigmas; if the pollen ends up just anywhere on the pollinator, it might not be very accurately transmitted onto the stigmas of other flowers.

For fun, here's some footage of a Bombus sp. (bumblebee) worker who is definitely picking up pollen as she goes, though it's less obvious whether she's successfully depositing it on stigmas. Look at all that pollen on her abdomen! Pretty much whenever she enters and leaves the flower, she's brushing right up against the reproductive parts of the hosta:

Sunday, September 24, 2017

Pop! goes the seed pod

Earlier this week, I posted about the profusely blooming Impatiens capensis (jewel-weed), particularly a few visitors I managed to film visiting the flowers.

Today, I want to share something rather different. It's not as much in my area, but it is a rather awesome feature of this and some other plants: explosive seed dispersal. Yes, that's a thing.

The biological purpose of a flower, of course, is reproduction. Remember from the last post that I. capensis individual plants make male flowers, which donate pollen to fertilise ovules, and they also make female flowers, which produce ovules that, when fertilised with pollen, will develop into seeds.

Impatiens capensis male flower (middle) and female flower (right).

Impatiens capensis is an annual, so any given individual won't grow back in the spring; consequently, it won't compete directly with its offspring for suitable growing space. The seeds are all at least half-siblings, however, so it's in the interest of the genes not to have (half-)siblings too close together.

Basically, there's good reason to suppose that a strategy that disperses seeds within a few meters of the plant (i.e., close to where suitable conditions for growth and reproduction were found, since the parent grew and successfully reproduced there, and because the plant is an annual there's no major incentive to disperse offspring further from the parent plant to avoid parent-offspring competition), but not all too close to one another (since they're at least half-siblings and share genes, so the genes would spread better through a population if they don't spend too much energy directly competing with each other), would be advantageous for this species.

There are all sorts of seed dispersal mechanisms. Explosive seed dispersal (a.k.a. projectile dispersal) is one of my favourite, however, because it's very dramatic. Here's what a seed pod looks like in I. capensis:

Impatiens capensis seed pod

Inside this elongated structure, there are a bunch of seeds (somewhere around 8-10, if I remember correctly). Each plant can produce quite a lot of these. So the explosive seed dispersal may be how I. capensis got one of its common names, "touch-me-not", but I think that's a misnomer because it's so fun to pop them that I highly recommend that anybody who gets a chance should definitely touch them.

They pop quite audibly:

So how does this even work? I tried to slow my videos down so that it's a bit easier to see what's happening, but it's so rapid that I have limited success. Watch for the seeds and pod flesh flying off:

In order for the seed pod to explode like this when touched, it has to be storing energy. Fortunately for me, I don't have to speculate too much in explaining what's happening here, because New Phytologist just published an article by Hugo Hofhuis and Angela Hay on the topic of explosive seed dispersal in Cardamine hirsuta, a species with extremely similarly shaped seed pods to I. capensis (though the two species are not closely related). I'm going to presume that the broad strokes, at least, are pretty similar in I. capensis. The article is really neat and I highly recommend that you read it, but here's my very brief summary of the findings from the article that may apply to I. capensis explosive seed dispersal.

The TL;DR is that these seed pods (likely) have specially shaped cells and extra lignin in places; essentially they're shaped so that they're always just on the very edge of curling up together, and touching them disturbs the delicate balance that is holding the seed pod's shape. Notice what happens to the fleshy parts of the pods afterwards:

Impatiens capensis seed pod after explosion is triggered
Neat, eh?

Tuesday, September 19, 2017

Impatiens capensis pollination (Bonus: even bees can be clumsy)

I know I haven't blogged in quite a while. Life got very hectic for a while. In the months my last post, I have finished my M.Sc., gotten published, and moved to the University of Toronto to start my Ph.D.!

Over the weekend I got a chance to take a long walk with my patient and long-suffering husband, who indulged my snagging his new blackberry to take a ton of footage of bees visiting the tens of thousands (at least!) of Impatiens capensis (common name jewel-weed) in the ravine park near our new home. I made all sorts of exciting videos, but today I'm going to share just a few simple ones, as the others will take quite a bit of research and time to write up. I will post these throughout the fall because they're very exciting.

NOTE: I have been informed that my videos don't work on mobile. I'm working on it, but in the meantime they do run on desktop.
UPDATE: try clicking the title of the video instead (treat as link) on mobile. Opens in youtube app. If you don't have youtube app, please report back telling me what it does when you click the video link!

To start, here's a picture of the plant itself:

Impatiens capensis whole plant view

Let's take a quick look at some general reproductive biology of I. capensis. The plant is monoecious, meaning that each plant reproduces through both male and female function; however, each individual flower is unisexual (i.e., any given flower is either male or female but not both). In the photo below, I show three flowers on the same individual. If you look at the top of the "mouth" of each of the lower two flowers in the picture, you will see that each has a different structure; the middle flower has a large, bulbous, whitish structure, while the rightmost flower has a slender green structure.

Impatiens capensis male (middle) and female (right) flower
The middle flower is a male flower; the whitish deposit on it is pollen, ready to be deposited on the back of a pollinator that climbs into the flower looking for nectar (the nectar is in the nectar spur, the little narrow tube curling off the back of the flower, visible on the middle flower). The rightmost flower is a female flower, with a stigma ready to pick up pollen from the back of a visiting insect.

The flower has some rather complex floral anatomy I won't get into right now. There's a pretty good explanation of which parts are sepals and which parts are petals here for those interested. The important thing to note is the lower lip, made of two structures wrapping around the front of the flower, one on each side, that form a sort of landing area of pollinators. They also restrict the width of the flower opening (see photos below).

Impatiens capensis male flower front view. Note that the two sides of the "landing" petals on the front are not fused, just overlapping, and that their shape, because they come down from above around the opening of the cone, reduces the size of the entrance into the flower

Impatiens capensis male flower side view. Notice that the lower "landing" petals are not attached to the conical structure behind.

So I'm going to skip over all sorts of exciting stuff about this plant (why does it have unisexual flowers? Why place pollen on a visitor's back? What's up with that super-complex floral shape?) in order to move straight to some awesome video of assorted Hymenopterans (bees, wasps, ants) visiting this awesome flower!

So I noted above that the '"landing" petals form not just a place for a pollinator to land on the flower, but also a constriction around the opening of the conical part; remember that the nectar is all the way at the back of that cone, in the little nectar spur curling down under the flower. There are several strategies to get past the opening to access this nectar (and then leave again after): one is to simply be small enough to fit through the constriction made by the landing petals; that's how Apis mellifera (honeybee) is doing it (note at 10:00 that you can really see the pollen on this honey bee's back!):

Backing out of the flower can be quite tricky. I managed to get some footage of a visiting wasp finding an alternate method of exiting, which capitalises on the fact that the landing platform and the conical structure behind are not attached to each other:

The Bombus sp. (bumblebee) workers I saw visiting the plants, however, were too big to fit through the opening. But, have no fear! They worked it out anyway. Here's one worker diligently visiting lots of flowers. She's making more room for herself by using her strong back legs (2 pairs) to push the landing petals apart a bit, so that she can shove her head and thorax into the flower and get at the nectar. You'll notice that she doesn't have much difficulty leaving, either, since she's well placed with four legs outside the flower. As far as I can tell, she's just dropping right out of the flower and then flying away.

Here's a longer video of the same bee, diligently visiting a lot of flowers in a row. There's also a little bonus at the end of this video. If you've been clumsy and felt ridiculous for it recently, I have something to comfort you: even bees can be clumsy. If you watch closely at the end, you'll see her climb into a flower, and then she and the flower both fall off the plant to the ground!

Monday, May 29, 2017

It takes a special kind of obsession to do fieldwork

I wrote a few weeks ago about the start of the field season. I have been back up to the field site a couple of times since then mostly for basic surveying and laying out the plots that will stay in place for the next few years.

This week things got serious, though. Our orchids of interest, Cypripedium arietinum (ram's head orchid, fr: Cypripède tête-de-bélier), are finally blooming! This year they're blooming rather later than usual, as I have informal records going back several years showing the orchid flowering by May 17th -- they didn't start this year until May 22nd.

Here's what these little beauties look like:

C. arietinum
These little guys are gorgeous up close, but actually not very showy (at least to the human eye) -- they are very small, generally somewhere between 10 and 25cm tall at the flower (around a handspan off the ground) and the labellum (white and purple-veined petal-looking portion of the flower) is only about 1-1.5cm tall from lip to point, around 1cm wide, and only 1-1.5cm from front to back -- similar in size to the tip of an index finger. Moreover, their sepals (the brownish-red petal-like things sticking up, or out to the sides) are brownish and earlier in flowering development they lean down over the labellum, disguising it from view from above. This position of the sepal over the labellum can be seen in a photo in one of my previous blog posts, here. These factors come together to make C. arietinum a subtle, hard-to-spot little orchid.

C. arietinum flower
One rather interesting aspect of orchid pollination biology is the production of pollinia. Basically, instead of presenting pollen in loose grains that are removed and delivered in small numbers by pollinators, orchids (and a few other plants, e.g. milkweeds) produce their pollen in two big sticky masses called pollinia (singular pollinium) -- a pollinator either leaves with a big blob of sticky pollen, or without any pollen at all. Similarly, a flower receives pollen in big sticky masses. There are a couple of advantages to this kind of system: paternal success per pollinator visit is improved, because if a flower gets an opportunity to sire seed (i.e. its pollinium is transported to another flower), it gets to sire a lot of seed all at once because there are enough pollen grains in the pollinium to fertilize most/all of the available ovules; maternal success per pollinator visit is also improved, for similar reasons to the above. Of course, there's a loss of genetic diversity in offspring, as under these conditions all seeds from the same flower are full-siblings (same paternal and maternal parent), whereas if pollen grains were carried individually or in small numbers many of the resulting seeds would be half-siblings (same maternal parent, but different male parents).

I actually took some photos that show the pollinia of C. arietinum, so let's take a look:

C. arietinum pollinium -- look at the top of the labellum, where we have a fleshy structure below the dorsal (top) sepal -- if you look closely, under that structure (which is composed of filaments and pistil, fused), we see a round yellow blob -- that's the pollinum!
So why would it be better to increase reproductive success per pollinator visit at the expense of genetic diversity of the offspring? Current thought is that it's related to the plant being deceptive (or rather, to the plant receiving very few floral visitors because it's deceptive). I've talked about floral deception before, but in a nutshell the flower lures pollinators in by signalling that it offers a reward (nectar), but once the pollinator arrives it discovers that it's been had, that there's no nectar reward at all. Being food deceptive allows a flower to reduce its investment of energy in pollinator attraction (it doesn't have to make nectar, which is costly), but being food deceptive also means that the flower gets a lot fewer visits, because the pollinators learn that this flower is a liar and not worth visiting.

It's a pretty liar, though, eh? C. arietinum looking into the labellum

Regardless of the delay in their flowering time this year, now that the orchids are blooming the intensive fieldwork starts. We set out several days this week to tag all of the flowering individuals (we're already up over 200 individual orchids), measure a suite of their characteristics, measure soil pH and moisture for each of them, take down canopy closure and other plot characteristics, and note the size of the flowering community around each individual. This is an enormous amount of work, as you might have guessed. And there are still at least 100 orchids left to go!

One of the best things about fieldwork, which I touched on briefly in my last post, is that making close observations out in the field can lead to new questions and new discoveries. For example, yesterday during my fieldwork I noticed something very odd and cool. It won't come as a complete surprise to my blog readers, as I have talked about mutations twice before. This time, no fasciation, but instead I found five two-flowered individuals in this species that generally only has one flower per stalk. Individuals producing more than one flower on the same stalk naturally have been documented in quite a few orchids, especially Cypripedium spp.; however, there are a number of possible reasons for the multiple flowers: stress-related growth malfunction? soil contamination growth malfunction? natural genetic mutation? natural morphological variation? When it comes right down to it, we don't currently know the cause.

Of these two-flowered individuals, there seemed to be two broad 'types'. The first is a two-flowered individual wherein the upper flower is right-side-up and the lower flower is upside-down. There were three of this type in one of our study plots. Here are some pictures:

C. arietinum two-flowered individual. The upper flower is on the right, and the lower on the left.
One visible consequence of the orientation of the second (lower) flower is that the bottoms of the labellums of the two flowers press together and result in some distortion of the shape of the labellum -- for all three of this type of two-flowered individual in the plot, the lower flower's labellum was compressed such that the point at the bottom (oriented upward in this flower) was folded back instead of deployed (flower on the left in the above photo), while the upper flower's labellum had its point deployed (flower on the left in the photo below).

C. arietinum two-flowered individual, from the other side -- the upper flower is on the left and the lower on the right
 As you may have guessed, the second type of two-flowered individual I saw yesterday during my fieldwork was on in which both the first and second flowers were oriented correctly.

C. arietinum 2-flowered individual with both flowers correctly oriented
Though there's no interference between the two flowers in their growth like with the two-flowered individual above, I did notice that this individual also had some weird sepals on the upper flower -- notably, the dorsal sepal is oddly tilted off to the side (you can't really see it in the photo below, for example), and on that side where the dorsal sepal is the lateral sepals are actually entirely missing, so it's short a pair of lateral sepals and the dorsal sepal is positioned oddly. Because of my low sample size (only two flowers), I have no idea if this weird sepal situation is related at all to the double flowers. The lower flower, though smaller than the upper, appears well-formed.

C. arietinum two-flowered individual showing the flowers up close
I am still mulling over what kind of work we might be able to do with these unusual individuals. We will be limited by our very low sample size, but I live in hope -- maybe there will be more that we haven't spotted yet, as there are quite a few plots left to go! In the meantime, they're a curiosity worth documenting. Maybe this natural history find will turn into an ecological one in future!

I suppose I've had a good ramble through the orchid patch now and will get back to the title of this post, which is ostensibly the main point here. These lovely pictures don't convey one aspect of the season: blackflies! It is peak blackfly season, so it's absolutely brutal out there. We are all wearing bug hats and tucking our pants into our socks, our shirts into our pants, binding our cuffs with rubber bands, wearing gloves, and just about bathing in DEET because the blackflies are ravenous and exceptionally numerous. It takes a special sort of obsession to put up with them for ten hours a day!

I shared this video last year, but it's particularly apropos at the moment. Here's some delightful Canadiana about blackflies, sung by Wade Hemsworth and the McGarrigle Sisters and with animation by the national film board:

Wednesday, May 24, 2017

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.