SCIENCE MATTERS: EVOLUTION OF EYESPOTS

Lepidopteran with eyespots in Costa Rica

By David Dannecker
Senior Editor

Readers of Prospect Journal’s Week of Photo Journals last week may have noticed a striking example of defensive eyespots in one of the photos in the Central America article. These visual patterns are a particular type of mimicry that can be found in many species of butterflies and caterpillars, and a diverse array of other kinds of animals. They can be a handy disguise, allowing an animal to appear bigger or more dangerous than they really are, or letting a predator blend in with its prey. Sometimes the level of detail achieved in eyespots is astounding. Particularly convincing eyespots, like the pair in the cover photo, can have extra levels of details – notice how each eyespot has a small white pattern within it, which mimics light shining off of a cornea, making it look even more like a genuine eye. How and why might such a trait evolve? And why might they resemble eyes in the first place?

In order for a trait to be selected, it must be hereditary (able to be passed on to offspring), and it must confer some competitive benefit to the individual. In general, that benefit could be the ability to more easily find a mate, or have greater numbers of offspring, or find food or other resources more easily. In this particular case, eyespots often promote easier survival by repelling predators, which we will discuss in more detail later. For a trait like this to develop in the first place, there must have been some variable patterns of pigmentation to begin with. Random pattern variations are fairly common throughout nature, but why do these patterns look like eyes? Spots, speckles, rosettes, and other circular shapes are generally pretty common throughout the animal kingdom. Think about cheetahs, leopards, many kinds of fish, salamanders, seals, hyenas, deer, etc. Spotted patterns crop up all over the place, and while they don’t typically resemble eyes all that closely, it is possible to see how they might evolve gradually from generic spot to eyespot.

Zebra long-wing caterpillar

Let’s consider a few different species of caterpillar to illustrate different calibers of eye-mimicry in naturally occurring spots. Pictured here is the caterpillar of the zebra longwing butterfly (Heliconius charithonia). As you can see by its numerous spines, it has gone for an entirely different type of defensive strategy, but underneath that prickly shield is a smattering of spots that don’t look like eyes much at all. However, spots similar to these must have been the original foundation, the starting point of many of the detailed eyespots that eventually evolved.

Elephant hawk-moth caterpillar

Pictured above is the caterpillar of the elephant hawk-moth (Deilephila elpenor). This is a pretty good example of a caterpillar with spots that are much closer to eyespots in size and position, but still rather unconvincing. The spots are certainly there, but they don’t really look very much like eyes, and they are probably less likely to scare off a predator. However, if genetic variation caused some of the individuals in the population to have spots that were even closer to the right shape, or size, or color or position to start resembling eyes, thus causing the whole animal to look more like a snake, then it would start to be effective at repelling predators.

Lepidopteran with eyespots in Costa Rica

Like this guy, the caterpillar of the spicebush swallowtail butterfly (Papilio troilus). This species’ eyespots are very lifelike, and definitely give the impression that the caterpillar is both larger and more potentially dangerous than it actually is.

The selective pressure acting on the eyespotted animal here relies less on how the individual utilizes the trait, and more on how the predator interacts with the potential prey. Typically, eyespots are exclusively visual traits. Although some kinds of butterflies and moths do flash them to momentarily surprise predators, it is unlikely that they know except by instinct that a predator might react to them the way they do. Nevertheless, the action of displaying eyespots has been shown to startle predators and give the would-be prey an opportunity to potentially escape.

The notion of eyespots repelling predators has been theorized to be based on risk assessment on the part of the predator. Consider a scenario where you are walking along a trail and see something coiled up on the side of the path. It might be a snake, or it might be a pile of rope. You can’t see it well enough to tell what it is. If there is a small possibility that it is a snake and not a rope, it would generally be a bad idea to go and pick it up. Sure it might be a harmless rope, but it also *might* be a deadly snake, and you have a lot more to lose than to gain if that’s the case. It’s a similar phenomenon at work with eyespots. With the caterpillar example, if you are a predator, such as a mantis, and you are looking for a meal, when you see an eyespotted caterpillar, there is a chance that it is a harmless tasty caterpillar, but also a chance that it is a well-defended snake that might do you harm. Really the only way to determine what it is would be attempting to attack it, but if there are other prey options available, why on earth would you take that risk?

With eyespotted butterflies, the disparity is even greater. If it is a butterfly, it would make a good meal, but if the eyespots are instead the face of a larger animal, you’d be walking or flying right into a trap. If the eyespots are flashed suddenly, the benefit of surprise would be conferred as well, forcing the predator to pause and process the new stimulus, allowing the butterfly an extra moment to escape. A predator would be smart not to take the risk at all, especially if there are other, more clearly vulnerable prey options out there. The risk avoidance behavior in predators discussed here is one of the selective forces that would allow eyespots that passively resembled eyes to become more common in the population. Individuals without eyespots would lack that defense and hence become more accessible prey options for predators, while individuals with eyespots would benefit from the risk avoidance behavior. By further random variation, and selective predation, the eyespots that are most effective would become more common over time. Since individuals without any protective eyespots are gradually weeded out of the population, some species have evolved to have eyespots as a universal characteristic.

There are species of flies that utilize a similar strategy of disguise. Many species of hoverfly in the family Syrphidae passively resemble bees for the same reason – why should a bird try to eat a fly that might be a stinging bee? It’s just not really worth the risk.

Lepidopteran with eyespots in Costa Rica

Conversely, there are some species of spiders that mimic ants for the opposite reason; they want to look benign and blend in until the last possible moment when they reveal they are actually dangerous. More of a “wolf-in-sheep’s-clothing” example. Amazingly, the organism pictured below is a spider, not an ant. Another spider disguises itself abdomen-first as an ant, complete with abdominal eyespots, which are intended here to make it look harmless rather than dangerous. This species of crab spider’s resemblance to its weaver ant prey is pretty incredible.

Lepidopteran with eyespots in Costa Rica

Among moths and butterflies, there are a few other examples of patterns besides eyes. Any pattern could theoretically work as a defense as long as it is perceived as scary by a predator. The main reason eye patterns are so commonly evolved is that circles are a comparatively common shape in nature. More complicated shapes are less likely to appear in random variation, but they still can happen. As is the case with this recently-discovered moth, whose wing patterns strongly resemble a spider, complete with hairy body and eight spindly legs.

Cover photo by David Dannecker, Prospect Senior Editor

Authors of additional images linked here, in order of appearance: First caterpillar by DeadEyeArrow; Second caterpillar by Richerman; Third caterpillar by Michael Hodge; Bee-mimicking fly by Bruce Marlin; First spider by Sean Hoyland; Link to photo gallery by Alexander Wild.

New to Prospect Journal’s Science Matters blog? Check out our introductory post to see what we’re about!

CENTRAL AMERICA: TREKKING CLOUD FORESTS AND CANYONS

By David Dannecker
Senior Editor

This is the third article in our 2015 Week of Photo Journals: Changing Perspectives. Check back each day this week to see more beautiful photography and travel accounts from UC San Diego students. Click on the images in the article to view the photos up close.

In my third year as an undergrad, I had the amazing experience of studying abroad in Costa Rica. I spent two and a half months living in Costa Rica, followed up by a month of exploring Nicaragua and Belize. The nations of Central America host a range of stunning environments, from crystalline coastlines and boggy mangrove forests, to humid lowland forests and river valleys, to otherworldly cloud forests threaded through the many mountain ranges. Amid all of these beautiful ecosystems, Central America also hosts a mind-boggling amount of native biodiversity, much like their Amazonian neighbors. Costa Rica alone has five percent of the world’s biodiversity, including thousands of species of insects and plants, and hundreds of species of birds, mammals and reptiles.

Costa Rica Cloud Forest

In Costa Rica, I had the chance to venture into the Monteverde Cloud Forests on horseback. Cloud forests are tropical forests that tend to occur at higher elevations around the world. Besides Central America, cloud forests can also be found in the mountains of South America, the highlands of tropical Africa, and the islands of Southeast Asia and the Caribbean. As you can see in the photo above, these forests are aptly named for the ever-present cloud banks which permeate the forest canopy. In fact, some of the cloud forest’s native plant species have adapted to utilize the moisture held in the mist, absorbing water from the so-called ‘horizontal precipitation’ in order to better withstand the tropical dry season.

Purple-throated Mountain-gem

Violet Sabrewing

Monteverde is known for its access to one of Costa Rica’s best-preserved cloud forests, and the incredible diversity of birds and insects that call it home. Particularly notable are the hummingbirds – 14 different species of brightly-colored and energetic hummingbirds can be found in the town of Monteverde alone. Compare that to the 54 species found in Costa Rica as a whole, and it’s clear why Monteverde is a prime destination for tropical birders. The photos show two of the 14 species that can be found in Monteverde, tending to artificial feeders at a local butterfly garden: a female Purple-throated Mountain-gem (Lampornis calolaemus) [top] and a male Violet Sabrewing (Campylopterus hemileucurus) [bottom].

Orange and Black Froghopper

Caterpillar

Butterfly with eyespots

The size of Costa Rica’s insect community is staggering. You can hardly walk through the rain forest without encountering a species of insect that you haven’t seen before. The sizes range from walking sticks several inches long and moths the size of a human hand, down to plentiful minuscule species that you’d scarcely notice. Costa Rica has over 300,000 species of insects, comprising the vast majority of the species that have been described in the country. Pictured are an orange and black species of planthopper (Auchenorrhyncha) [top], a well-defended caterpillar [middle], and a sizable Lepidopteran showcasing prominent eyespots for defense as it rests on the underside of a fern [bottom].

Fer-de-lance

Eyelash Viper

Snakes are another category of species that are especially diverse in Costa Rica. Over 160 species of snakes can be found in the country, and 22 of them are venomous. Pictured here are two of the more venomous species: the Fer-de-lance (Bothrops asper) [top] and the Eyelash Viper (Bothriechis schlegelii) [bottom]. Fer-de-lances are generally considered the most dangerous of Costa Rica’s venomous snakes, and bites can often be critical, especially if you are not near an emergency medical center or hospital. The arboreal eyelash vipers are also quite venomous, but are smaller, and less prone to biting humans unless directly provoked or disturbed. Eyelash vipers also occur in a broad range of color variations, from mossy camouflaged patterns like this one, to bright yellows, greens and blues.

Somoto region panorama

Somoto Canyon

Somoto Canyon Walls

After my study program ended, I spent a couple of weeks exploring Nicaragua, devoting much of that time to the mountainous northern region. Nicaragua has quite a few amazing natural sites to offer, especially if you are willing to venture slightly off the beaten path. Near the small town of Somoto, guides are available to lead you on a tour of Somoto Canyon, which is an incredible geologic feature that was actually fairly unexplored until just over 10 years ago. The steep walls rise up on either side of the often narrow canyon as you hike, swim and float your way from one end to the other. It makes for some spectacular views.

Miraflor waterfall

Arbol Historico

Another attraction well worth a look in Nicaragua is the Miraflor Natural Reserve. Home to plenty of biodiversity, engaging hiking trails, friendly guides, and picturesque waterfalls, Miraflor is really an unmissable diversion if you find yourself in the city of Estelí. One truly unique sight in the reserve was a 600-year-old tree (Ceiba pentandra) that stands between two open fields. At that age, the tree has been standing since before Europeans ever visited Nicaragua.

Tapir

Jaguar

After my time in Nicaragua, I flew northward to Belize for the final leg of my journey. Lying on the eastern coast of Central America, Belize had a far more Caribbean atmosphere, both in terms of environment and culture, than the largely Pacific areas of Nicaragua and Costa Rica I’d seen so far. Belize is sparsely populated, and so much of its natural land is untrammeled by human development. One of the easiest ways to witness some of Belize’s most impressive native wildlife is to pay a visit to the Belize Zoo. Founded as a sanctuary for tame native species that had been filmed for a documentary in the 1980s, the Belize Zoo now houses an impressive collection of some of Central America’s most iconic wildlife, including the Tapir (Tapirus bairdii), which is the national animal of Belize and the largest terrestrial animal in Central America, and the Jaguar (Panthera onca), the largest species of feline in the Western Hemisphere. While Belize has plenty of natural spaces where it is possible to view these species in situ, visiting the Belize Zoo is a nice way to guarantee a view of some of Belize’s rarer species.

Howler Monkey

Central America is home to fewer than 10 species of monkey. That figure pales in comparison to the dozens of primate species that can be found in the Amazon rain forest. Nevertheless, monkeys in Central America play several crucial roles in the ecosystem, having spread out to fill different niches. Squirrel monkeys are omnivorous; spider monkeys are active, mobile herbivores; and capuchins are voracious generalists, eating insects and fruits, but even going so far as preying on lizards and birds. Howler monkeys [pictured] are much more lethargic and eat the most foliage of the various species. They spend the vast majority of their time sleeping.

Bats indoors

Bats outdoors

Bats comprise about one fifth to one quarter of all mammal species worldwide. In the tropics, the proportion is even greater. Bats make up over half of the mammal species in Costa Rica, and nearly 60 percent of mammal species in Belize. Bats perform many vital services, from pollinating flowers, to dispersing fruit seeds, to keeping the insect population under control. While many tropical bats are under threat from disease and habitat destruction, some bats have been able to find ways to coexist with human communities. Pictured [top] is a small colony of bats sleeping in the rafters of a visitor center in Bermudian Landing, Belize. The second picture shows a roost of well-hidden bats, camouflaging against the bark of a tree on the banks of a river in northern Belize.

Black-collared Hawk

Vermillion Flycatcher

One of my final stops in Belize was the Crooked Tree Wildlife Sanctuary. This sanctuary sits on a lagoon and is best known as a birdwatching hotspot. I saw over 50 different species of birds on a two-hour boat tour, and it wasn’t even peak season. Belize has a singularly impressive 543 species of birds, including perennial species and migrants. To put that diversity in perspective, Belize is slightly smaller than the State of Massachusetts, but Massachusetts is only home to roughly 200 species of birds. Pictured here are a striking Black-collared Hawk (Busarellus nigricollis) moments before taking flight, and an equally stunning Vermillion Flycatcher (Pyrocephalus rubinus) perched on a fence, both observed at the Crooked Tree Sanctuary.

All images by David Dannecker, Prospect Senior Editor

MIND GAMES: HOW VIRTUAL REALITY CAN HELP SAVE THE OCEANS

Rendering of an Underwater Scene

By Annam Raza
Contributing Writer

How many of us have actually dived in the Great Barrier Reef? Or explored the waters off the coast of Costa Rica? I haven’t; despite growing up near the Persian Gulf, and going to university right next to the Pacific Ocean, I never got around to getting a scuba license. My interest in seeing the ocean was whetted by pictures or documentaries, a vicarious exploration of a foreign world, guided by a photographer or cameraman. A glimpse of an intriguing fish flitting away into the distance would often make me wish I could turn to follow it, but that was a privilege reserved for the actual diver, not the viewer safe in the comfort of her own home.

What if that wasn’t the case? What if you could explore a shipwreck, searching for fish and coral at Chuuk Lagoon, the site of a pivotal World War II battle, since transformed into a glorious reef, without leaving your own home? This is exactly what players do in the initial levels of ‘Infinite Scuba’, a next generation simulation game launched in March 2013 by Seattle game designers Cascade Game Foundry, partnering with many diving industry groups, including Professional Association of Diving Instructors (PADI), Diving Equipment and Marketing Association, Mission Blue (an ocean conservation group), various scuba equipment manufacturers such as Scubapro, Body Glove, Oceanic and BARE, among others. The game hopes to “raise public awareness about the importance of ocean health” by painstakingly recreating famous dive sites from around the world in order to spread information about important environmental issues through entertainment.

This is an incredibly unique response to Dr. Earle’s 2009 TED prize wish (which inspired the creation of Mission Blue itself, as described on their website): “to use all means at your disposal — films, expeditions, the web, new submarines — to create a campaign to ignite public support for a global network of marine protected areas.”

Although video games may seem like an unusual medium to employ to educate the public about conservation, research suggests that they can be used effectively for education. As Professor Resnick of MIT states, “many of [sic] people’s best learning experiences come when they are engaged in activities that they enjoy and care about…[one is] likely to learn the most, and enjoy the most, if [one is] engaged as an active participant, not a passive recipient.”

The Internet has a particularly remarkable number of active participants – you included. You are reading this blog post online, alongside (probably) several other tabs: email inboxes, Facebook, and a myriad of other websites. According to Jane McGonigal, a video game designer and inventor at Institute of the Future, more than half a billion people use a computer or play a video game for at least an hour a day- with over 183 million of those in the US. She says, “The average young person racks up 10,000 hours of gaming by the age of 21 – or 24 hours less than they spend in a classroom for all of middle and high school if they have perfect attendance. It’s a remarkable amount of time we’re investing in games. Five million gamers in the U.S., in fact, are spending more than 40 hours a week playing games – the equivalent of a full time job!”

So why not reappropriate this time to serve the purpose of marine conservation?

That is what the organization Games for Change aims to do. Their mission statement is “Catalyzing Social Impact Through Digital Games”. Founded in 2004, it consists of a group of people that create and distribute games that aim to create a social impact by engaging contemporary issues in a meaningful way. Clicking through the “play” section of their site makes it obvious they haven’t restricted themselves to merely the marine realm: categories also include poverty and economics, and they even have a “Games for Change” festival, which unites people interested in accessing the positive social aspect of games.

On an individual level, games can be used to teach children and young adults about the threats facing endangered wildlife. ‘Predator Protector’, an online game on PBS’s website that is meant to accompany the channel’s documentary ‘Ocean Adventures’ with Jean Jacques Costeau, has players “swim with sharks and experience the threats they face,” striving to stay alive and thus inadvertently learning about the vital role sharks play in the delicate balance of a marine ecosystem. It makes one reevaluate the label of ‘mindless predator’ that sharks have been burdened with by a misinformed media.

“Sea Turtles and the Quest to Nest,” launched by National Oceanic and Atmospheric Administration and the Fisheries Service, is similarly structured. It is the second educational game in the WaterLife series, centering on loggerhead sea turtles, listed as threatened under the Endangered Species Act, and involving six stakeholders critical to the turtle’s protection. Players must work through a series of mini-games, which encompass activities such as beach cleanups to assist turtle nesting, improving the likelihood of the turtle’s survival. Without understanding how human actions affect turtles and how to improve the chance of survival for the species, players cannot succeed.

As players experience firsthand the harmful effects of human activities on marine animals, they are forced to think about the importance of conservation and the role we, as humans, play in the loss of biodiversity. These games require players to use their minds, combining “difficult challenges, possibilities, and use of information” in a way that can be used to establish “real pedagogical constructivism”. Constructivism is the learning theory that refers to the idea that “learners construct knowledge for themselves”, and is the most powerful argument for the use of video games in education: as players work their way through levels, they absorb information and store it away, subconsciously learning facts about conservation that may have bored them had they been presented to them in a traditional classroom environment. This can evoke powerful emotional responses in players – delight if they win, and sadness if they lose. More than knowledge, it is that awareness and emotion that is necessary. I firmly believe that although the most important part of conservation as a science is research, it is one’s passion for conservation, and his or her motivation to embrace it in all realms of their life, that can make it truly successful.

Image by Ian Burt