Tag / invertebrates

by Roslyn

Innovative, naturally

bluegill sunfish field work

Chandra Rodgers sampling bluegill sunfish on Lake Opinicon.

This spring I had the opportunity to write a feature article on the Queen’s University Biological Station, a site just north of Kingston where researchers have a long history of major scientific breakthroughs involving modest Ontario wildlife. Several of these discoveries have proved to be as useful as they are compelling. The story was published in the Kingston Whig Standard, and on the web through the Queen’s Alumni Review and InnovationCanada.ca. Funding for photography was provided by the CFI’s 2011 Emerging Science Journalists Award.

Talking to scientists about their research was by far the best part of this project – much more fun than I expected! And even the toughest interviews were a gold mine of ideas. Thanks to everyone who participated. The full story is posted below…

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by Roslyn

Cuttlefish strike a pose for 3D camouflage

In the game of hide and seek, cuttlefish have the upper hand. These chameleons of the sea are astonishingly good at disappearing: they can instantaneously change the colour of their skin to blend in with the background, matching even the finicky details like the pattern of coloured rocks on the ocean floor.

Divers have long known that cuttlefish are masters of the 3D camouflage game, too, and new research from the Wood’s Hole Oceanographic Institute has revealed how they do it.

Alexandra Barbosa, a graduate student, and Dr. Roger Hanlon were interested in the way cuttlefish strike a pose when trying to hide. After encountering a predator, these octopus-like animals will flee among the corals, rocks and algae, and freeze with their arms contorted into shapes that mimic nearby objects – a feat made all the more impressive by the fact that cuttlefish arms can bend in any direction. Some birds and insects are also known to camouflage themselves with body posture, but few come close to cuttlefish in shape-shifting flexibility (see photos of cephalopod camouflage in the wild here).

To understand just how they do it, Barbosa and her colleagues in Dr. Hanlon’s lab presented captive cuttlefish with some highly unusual surroundings: jailbird stripes, in black and white. In response, the cuttlefish got theatrical, raising their arms roughly parallel to the angle of the stripes. And when the researchers shifted the angle of the background image, the cuttlefish stretched their arms into a new position in an attempt to stay hidden.

Cuttlefish posing on artificial backgrounds

Cuttlefish posing against different backgrounds. Modified from Barbosa et al. 2011 (see Figure 1).

Intriguingly, not all of the ten individuals tested were able to match the angle perfectly all of the time – but these quirks may not be surprising given that cuttlefish camouflage is so complex. After all, in nature cephalopods get to choose their own hiding places, a decision that might involve several different factors. According to the researchers, camouflaged cuttlefish are even known to gently wave their arms to match the movement of the underwater plants they are trying to mimic.

These results are a clear demonstration that cuttlefish use vision to guide their 3D camouflage, since the study animals matched a flat background image. Moreover, Barbosa and Hanlon have shown that shape-shifting cephalopods can easily handle scenarios that would never occur in the environment where these behaviours evolved, and adjust just as flexibly to this artificial environment as they do in their natural habitats.

Captive experiments like this are just the first step in understanding how cuttlefish use visual cues to hide, and some big questions remain. For instance, little is known about how cuttlefish can detect and match colours so well despite the fact that they are, in effect, colourblind – Hanlon has found that giant Australian cuttlefish can take on the colouration of rocks on the ocean floor even in the middle of the night.

These remarkable split-second decisions about where, and how, to hide might also help us understand something bigger. Strategic camouflage is just one aspect of the surprising intelligence of cuttlefish, which have the largest brains for a given body size of any invertebrate – these animals are also able to learn and communicate with one another at a level that rivals many land-based animals. It will be intriguing to see where hide and seek fits in to the history of cephalopod brain evolution.

Further Reading

Barbosa, A. et al. 2011. Proceedings of the Royal Society B. In press.

by Roslyn

The ancient mariner

I drove a tractor for the first time a few weeks ago, when we were furiously collecting the last of the sap run for maple syrup. A small triumph for me since it seemed so terrifying at first. Trying to hide my confusion, I waited until the last moment to ask, “Which pedal is the brake, again?” Both of them? Right. No chance for a screw up, so I charged ahead. It only took until my second trip – with shouts of “Slow down!” from the trailer behind – for me to figure out why those two brakes weren’t working so well. Turns out that the hand throttle was the missing part of my pedal equation.

Locomotion does not come naturally to me. It does, however, for a huge variety of other living things. Powered flight evolved several times in the history of life: at least once in the ancestors of birds, and separately in insects, pterosaurs and bats. Human inventors have had a much harder time with it: unlike animals, we haven’t progressed much beyond our earliest working designs. Orgel’s second rule applies:

“Evolution is cleverer than you are.”

Thinking about this made me realize that the situation today, where most of us are more familiar with human-engineered forms of locomotion than we are with the natural examples, is kind of strange. For most of our history, the inspiration to look for new ways to get around probably came from seeing it done in nature.

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by Roslyn

A case of mistaken celebrity

They all look the same to us. Celebrities, that is. And by us, I mean academics.

The proof starts with peacocks. Last fall, I was working on some measurements I took of the crest ornament in these birds. Peafowl have this funky little fan of feathers on top of their heads, and though it’s not that small in the grand scheme of fancy bird plumage ornaments, the peacock’s five centimetre crest looks a bit ridiculous next to the metre-and-a-half long train.

Why bother having a crest when you also have a big train? And why do females wear crests too? In this species, the crest appears to be the only plumage ornament shared by both sexes. Here are some of my pictures from the field, taken on the cusp of the breeding season:

Crest ornaments of male and female peafowl

Crests of (a) male and (b-c) female peafowl. Scale bars are 10 cm. Photos by Roslyn Dakin.

Over the years, I’ve measured the crests of close to 150 birds. These data lend some support to the idea that the crest is a signal of health in both males and females, although it might work in slightly different ways for the two sexes1. As you can see from the picture above, there is a lot of variation in how the crests look – and it’s mostly on the female side of the equation. Almost all adult males have tidy looking crests like the one shown in (a), but females often have crests with a lot of new feathers growing in (c). It turns out that males in better condition tend to have fuller, wider crests. The healthiest females, on the other hand, have crests that look most like those of males, with all feathers grown out to the top level (b).

The extreme variability among females leads to an additional hypothesis, and it’s one that I can’t rule out at this time. Perhaps the crest is a signal of individual identity that the birds use to sort out who’s who in their social groups – just as faces do for us. A clue that this could potentially work for peahens is that my field assistants and I can do it. Once you spend enough time hanging around with these birds, you find yourself recognizing certain females that haven’t been captured yet (and that therefore lack identifying leg bands). Your first clue? Usually a unique pattern of crest feathers.

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by Roslyn

How to raise a science major

The newspapers have been abuzz lately about a controversial book: Battle Hymn of the Tiger Mother, by Amy Chua, is a memoir on the rewards and perils of stereotypically strict Asian-American parenting. This week I asked students in my 4th-year biology class to tell me about their earliest memory of being fascinated with something biological, information that could be useful for parents hoping to form their children into university science majors.

And so, some lessons learned:

1. Worms work. Let your kids get close to the ground, outside. At least two students listed earthworms appearing after the rain as their most important early memory. A large portion of the class described similar encounters with tadpoles, snails, caterpillars, ants, spiders and their webs, and other minutiae found on the lawn. Larger examples of charismatic megafauna barely got a mention. Perhaps opportunity plays a role. For instance, one student remembers being particularly enamoured with deer in the backyard.

2. Pain. A wise teacher once told me that “learning hurts”. The converse might also be true: harmful organisms can be educational. An encounter with razor-sharp zebra mussels was particularly salient for one student. Another recounted a family vacation in the New Mexico desert, where a first-hand experience with cacti led to an early lesson in adaptation.

Well-armed cacti

Hidden Valley, Joshua Tree National Park, California.

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by Roslyn

Beware of the blob

It creeps, and it might be more like us than we care to admit. That was a lesson I learned last fall when trying to choose between pigeons and slime moulds for our lab journal club. The birds, it seems, are on a different level.

It started with the Monty Hall problem and a new study that asks, “Are birds smarter than mathematicians?”1. For those not familiar, the Monty Hall problem is a puzzle made famous by columnist Marilyn vos Savant, based on the popular 1960s game show Let’s Make a Deal (which was, incidentally, hosted by Winnipeg-born Monty Hall). Here it is:

Suppose you’re on a game show, and you’re given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what’s behind the doors, opens another door, say No. 3, which has a goat. He then says to you, “Do you want to pick door No. 2?” Is it to your advantage to switch your choice?2

If you were on Let’s Make a Deal, would you take Hall’s offer to switch doors? Or would you stand by your original choice?

Let's Make a Deal

Does it make any difference?

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by Roslyn

Reaching the other side, in synchrony

It’s a familiar site on campus here during the first week of class: packs of jaywalkers moving in tight co-ordination, in sync with the flow of oncoming cars. From traffic lights and power grids to stereo sound and cinema, synchrony is so common in our environment that we usually only notice it when it fails. Not so with nature: the examples of synchrony in living things tend to be much more surprising to people studying animal behaviour.

Group courtship displays are a classic example. Think of chorusing songbirds in the morning or calling frogs gathered around a pool of water at night. Readers of my blog on peacock field work might be familiar with lek-mating birds gathered around a clearing to wait for females. Peacock train displays also tend to happen in sync. One traditional explanation for these co-ordinated displays is that, by synchronizing their most conspicuous behaviour, animals might gain some protection from predation1. Another possibility is constructive interference: co-ordinated timing might allow a pair of animals to spread the message farther than either one could on its own2. Two innovative new studies on animal courtship have added to this list. The first, on firefly displays, shows that synchrony might help insects recognize members of their own species by getting rid of visual clutter.

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by Roslyn

Honed

We brought home a new kitchen knife from my parents last month. The knife block was full, but Charlie exchanged the new one for what was previously our smallest and dullest. He wasted no time wrapping the old one up in plastic and hiding it from me. My hand naturally gravitates towards whichever tool will fit nicely inside it, even when I’m cutting a monster squash. We have a good arrangement: Charlie keeps the knives sharp, I keep my fingers, and I toss him the odd carrot slice in return.

But could he eventually be replaced by a sea urchin? A new study in the journal Advanced Functional Materials explains how sea urchin teeth never dull or break. In fact, they get sharper with use1.

Most people are probably familiar with sea urchins as the spiny little balls one occasionally encounters on the beach. Evil looking, but mostly harmless, so long as you avoid stepping on them. Sea urchins live in shallow tidal pools, eating algae and other plant material. So why do they need such sharp teeth? Much like their spines, the teeth probably serve a protective function. The urchins use them to chew burrows, often in solid rock, where they can take shelter from predators and waves.

In the current study, a group of physicists and biologists used an arsenal of sophisticated imaging, chemical and nano-scale stress test procedures to investigate the teeth of the California purple sea urchin (Strongylocentrotus purpuratus). Like starfish and sea cucumbers, urchins are members of a group of animals known for their penta-radial, or five-fold, symmetry. They have five teeth arranged in what is known as Aristotle’s lantern.

Aristotle's lantern

Aristotle’s lantern, as viewed from below with teeth closed. From Killian et al. 20111.

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by Roslyn

Deep archives: Iridescence: From insect crystals to nature’s transformers

Iridescent cuttlefishNow that I’ve given my talk at the iridescence conference, I feel like I can relax and reflect on the last few days.

The biggest success of this trip so far was undoubtedly making it across the border. When I arrived at the airport, I was informed by a rather sour US customs lady that because I didn’t already have a return ticket, she didn’t have to let me into the country. This was news to me, but in retrospect my story that I was a grad student attending a conference and then traveling indefinitely in California probably wasn’t the best choice. Customs lady expressed her disbelief, handed my passport back to me in a bright yellow folder and directed me to take my warning-beacon folder into a special room for suspicious types. I was terrified that she would would somehow find and confiscate the stuffed peahen or any of the other bizarre (but critical) items in my suitcase full of field equipment. Somehow, however, I was able to get by without having to provide any more details about my plans. As for the peahen, I waited until I was settled into my Arizona hotel room before anxiously opening the suitcase to survey the damage. I’m relieved to report that she survived the trip without confiscation or serious injury. Although she does look a little worse for wear I’m confident that the males will still find her an acceptable target.

The conference has been amazing – I’ve heard talks from the world’s experts on the physics, development, evolution, and behavioural display of nanostructural colours in animals. The very first talk was on ways to manufacture macro-scale versions of the colour-producing nanostructues found in butterflies, and then use microwaves to measure optical properties of these models in a scaled-up way. The advantage of this technique is that it lets you get around the problems of performing accurate optical experiments with very small things (such as single butterfly scales).

I’ve also heard about how to model the optical properties of animal nanostructures, how to improve my goniometer for feather colour measurements, how insects build crystal-like cuticular nanostructures with exquisite control at the cellular level, and how some butterflies are similar to peacocks in terms of orienting themselves for optimal reflectance of their iridescent wing colours during display flights. We’ve had serious discussions about the developmental differences between “squishies” (vertebrates) and “crunchies” (arthropods), the meaning of the word “crystal”, and the use of dark framing around bright colours in both art and animals.

By far the most interesting talks, however, were about work from the Hanlon lab on the cuttlefish colours. Cephalopods have evolved an incredible ability to control the hue, patterning and texture of their skin – including what one speaker referred to as “changeable iridescence” – for use in predation and camouflage as well as in conspicuous signaling. Cuttlefish skin contains a base layer of bright blue-green iridophores covered by a layer of pigment sacs called chromatophores. All of these structures are laced together in a network of muscle cells allowing the cephalopods to actively control their appearance by essentially expanding or contracting the sacs of colour. Amazingly, the iridophores can reflect polarized signals that cuttlefish can perceive but that predators cannot. By producing this polarized iridescence from beneath the layer of pigmented chromatophores these animals can accomplish camouflage and signalling simultaneously. For those interested in camouflage, I’ve also learned that a number of sea creatures produce a countershading effect by producing iridescence or even bioluminescence on the undersides of their bodies.

Apart from the mystery font-size changes and video problems on the conference laptop, my talk went tremendously well. I managed to draw a crowd of questioners afterwards and received a great deal of feedback (and encouragement) – sweet. Time to start worrying about how to draw a crowd of peacocks instead.

by Roslyn

Language Instincts: A bug’s life

From September 30, 2006

The colony of the leafcutter ant is a strange parallel to human civilization. These ants can often be seen in tropical America parading down trails they create in the forest carrying small leaf clippings. When they return to their nest mound, the ants use these clippings as a substrate for growing fungus; the fungus is used to feed leafcutter larvae. Amazingly, ants are the only group besides humans to have developed agriculture. And leafcutter agriculture is more advanced than you might think – the ants use feces as fertilizer and they even secrete antibiotics to protect their crop from mould.

Leafcutter ants at work in Costa Rica

Leafcutters hit the trail in Costa Rica

Biologists and naturalists have often wondered how relatively simple insects like this can maintain complex social systems; systems that have been around longer than any human civilization and will probably still be here long after we’re gone.

On one level, these systems work because social insects have evolved caste-specific division of labour. Within a colony, individuals are morphologically and behaviourally specialized to carry out specific jobs. A leafcutter ant colony will include a reproductive queen and various sub-castes of workers. Workers are content to give their lives to the colony without any hope of reproduction because of a quirk of genetics that makes them more closely related to the queen’s offspring than their own.

But that still leaves open the question of how simple animals can organize themselves without any obvious authority to command them. How are the activities of various castes coordinated? To address this, scientists in the 1980s began to apply self-organization theory to the behaviour of social insects. This is the idea that a group of simple individuals following basic rules can produce a complex pattern. Self-organization theory has been successfully applied to explain everything from spiraling patterns formed by molecules to the movement of schools of fish and cars in traffic (see here for more). All insects would need is some simple built-in rules to govern their behaviour and the capacity for sharing information with others; if so, the adaptive complexity of the insect colony could be explained by the theory. Indeed, as early as 1989 researchers were able to demonstrate that self-organization explains how a group of foraging ants are able to pick the best path to a food source. They performed an experiment where ants were given the choice of two available routes to their food. Eventually the ants converged on the shorter of the two paths. And this happened without any individuals having knowledge or prior experience of either path!

How could the ants in the experiment accomplish this? The answer is chemical communication. Research into chemical communication in insects took of in the 1960s when E.O. Wilson showed that foraging trails used by ants can be maintained by a positive feedback system of pheromones deposited on the substrate. Trails are reinforced by the deposition of positive pheromones. The more the trail is used by successful foraging individuals, the more the attractant pheromone is deposited and the more additional foragers will be encouraged to try that trail. In the experiment described above, ants traveling on the shorter of the two paths took less time, so pheromones accumulated faster on that route. This set up a positive feedback cycle, resulting in all ants making the right choice for the shorter path regardless of past experience – just as self-organization theory predicts.

More recently, research has revealed chemical communication in social insects to be more detailed than was first imagined. For example, ants generally possess an arsenal of different trail pheromones for different purposes – repellent signals to mark unprofitable branch points that should be avoided, alarm pheromones to signal predators or other dangers, and often different short-lived and long-lived versions of their pheromones. Thus, foragers can communicate a surprising amount of detail just by excretion.

And chemical communication isn’t the end of the story. Insects can also share a great deal of information through tactile and vibrational means. The classic example of this kind of communication is the waggle dance of the honey bee forager, which was shown in the 1940s by Karl von Frisch to convey information regarding both the distance and direction to a food source. Scientists have shown that ants use vibrational communication as well. For example, leafcutter ants that find a good leaf will rub their appendages together (called stridulation) in order to attract tiny hitchhiking workers. These hitchhikers ride on the leaf fragment on the way back to the colony and defend the forager from parasitic flies.

Social insects are remarkably adapted for communication and one can imagine how the combination of various signals and modes of transmission allows insects to share the range of information necessary to run a colony (or farm, as it were). Indeed, the capacity for advanced communication is what sets animals apart from the simple units in other self-organizing systems (like molecules in a beaker or cars in traffic). Understanding communication in social insects is critical to helping us understand how these insect microcosms evolved in the first place, and may even teach us something about our own societies.

More on communication in social insects can be found in articles here, and here.