Weird-cool bubble-headed Barreleyes like only evolution can come up with

Now here's a wonderful, bizarre discovery from scientists at our neighboring Monterey Bay Aquarium Research Institute:

Researchers at the Monterey Bay Aquarium Research Institute recently solved the half-century-old mystery of a fish with tubular eyes and a transparent head. Ever since the "barreleye" fish Macropinna microstoma was first described in 1939, marine biologists have known that its tubular eyes are very good at collecting light. However, the eyes were believed to be fixed in place and seemed to provide only a "tunnel-vision" view of whatever was directly above the fish's head. A new paper by Bruce Robison and Kim Reisenbichler shows that these unusual eyes can rotate within a transparent shield that covers the fish's head. This allows the barreleye to peer up at potential prey or focus forward to see what it is eating.

The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head. The fish's tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead. They point forward when the fish is feeding. The two spots above the fish's mouth are are olfactory organs called nares, which are analogous to human nostrils. Image: © 2004 MBARI

Deep-sea fish have adapted to their pitch-black environment in a variety of amazing ways. Several species of deep-water fishes in the family Opisthoproctidae are called "barreleyes" because their eyes are tubular in shape. Barreleyes typically live near the depth where sunlight from the surface fades to complete blackness. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.

Although such tubular eyes are very good at collecting light, they have a very narrow field of view. Furthermore, until now, most marine biologists believed that barreleye's eyes were fixed in their heads, which would allow them to only look upward. This would make it impossible for the fishes to see what was directly in front of them, and very difficult for them to capture prey with their small, pointed mouths.

And what's more, the researchers got them on video too - look below the fold:

Robison and Reisenbichler used video from MBARI's remotely operated vehicles (ROVs) to study barreleyes in the deep waters just offshore of Central California. At depths of 600 to 800 meters (2,000 to 2,600 feet) below the surface, the ROV cameras typically showed these fish hanging motionless in the water, their eyes glowing a vivid green in the ROV's bright lights. The ROV video also revealed a previously undescribed feature of these fish--its eyes are surrounded by a transparent, fluid-filled shield that covers the top of the fish's head.

Most existing descriptions and illustrations of this fish do not show its fluid-filled shield, probably because this fragile structure was destroyed when the fish were brought up from the deep in nets. However, Robison and Reisenbichler were extremely fortunate--they were able to bring a net-caught barreleye to the surface alive, where it survived for several hours in a ship-board aquarium. Within this controlled environment, the researchers were able to confirm what they had seen in the ROV video--the fish rotated its tubular eyes as it turned its body from a horizontal to a vertical position.

In addition to their amazing "headgear," barreleyes have a variety of other interesting adaptations to deep-sea life. Their large, flat fins allow them to remain nearly motionless in the water, and to maneuver very precisely (much like MBARI's ROVs). Their small mouths suggest that they can be very precise and selective in capturing small prey. On the other hand, their digestive systems are very large, which suggests that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two net-caught fish contained fragments of jellies.

After documenting and studying the barreleye's unique adaptations, Robison and Reisenbichler developed a working hypothesis about how this animal makes a living. Most of the time, the fish hangs motionless in the water, with its body in a horizontal position and its eyes looking upward. The green pigments in its eyes may filter out sunlight coming directly from the sea surface, helping the barreleye spot the bioluminescent glow of jellies or other animals directly overhead. When it spots prey (such as a drifting jelly), the fish rotates its eyes forward and swims upward, in feeding mode.

Barreleyes share their deep-sea environment with many different types of jellies. Some of the most common are siphonophores (colonial jellies) in the genus Apolemia. These siphonophores grow to over 10 meters (33 feet) long. Like living drift nets, they trail thousands of stinging tentacles, which capture copepods and other small animals. The researchers speculate that barreleyes may maneuver carefully among the siphonophore's tentacles, picking off the captured organisms. The fish's eyes would rotate to help the fish keep its "eyes on the prize," while its transparent shield would protect the fish's eyes from the siphonophore's stinging cells.

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The Evolution Will Be Televised

And may be viewed by those of you fortunate to be subscribed to the National Geographic TV channel via cable/satellite. The above is the tagline NatGeoTV is using to promote their celebration of Darwin's 200th birthday. Click on the image here for the program, which kicks off this Sunday, Feb 8th with a new 3-part series "Morphed".

They will also run a live-blog starting an hour before Morphed, and are already inviting questions in their Evolution forum. Then on the 10th, they're showing Darwin's Secret Notebooks, and Explorer: Monster Fish of the Congo. All of this looks pretty exciting, and I will try to post previews/reviews as time permits over the next couple of weeks. I may even try a bit of live-blogging here if enough of the students are interested (so let me know!). And if you don't have access to NatGeoTV, find someone who does and might tolerate you on their couch for a few hours! Meanwhile, the complete announcement I received in my email, with links to video clips, is below the fold:

Below are brief descriptions of each of our five Darwin-related programs, and attached is the full press release for your information.

MORPHED

Sunday, February 8, 2009 at 8PM – 11PM ET/PT, with Live Blogging Event at 7PM ET/PT

http://natgeotv.com/morphed

Using advanced CGI, forensic examination of the latest fossil evidence and 3-D, biomechanic animation, Morphed brings ancient creatures back to life and recreates the most dramatic forces impacting their evolution — from natural disasters to competitors and brushes with extinction.  Also, during the first hour of Morphed, join a panel of experts in the fields of biology, molecular science, and theology for a Live Blogging Event to discuss the topic of evolution and its significance in today's science community, education, and its relationship to religion and theology. Be sure to submit your questions in advance at http://ngccommunity.nationalgeographic.com/ngcforums/evolution/ and log in on Sunday, February 8 at 7 PM ET/PT! The three back-to-back episode premieres include:

MORPHED: FROM DINOSAUR TO TURKEY digs 230 million years back into the fossil record to witness the emergence of the first dinosaur and follows different dinosaur species as they respond to changes in the earth's environment.

Video "Dinosaur Descendents" – Next Year at Thanksgiving dinner, imagine you're eating a dinosaur. You won't be far from the truth:http://channel.nationalgeographic.com/channel/videos/feeds/cv-seo/Animals--Nature/All-Videos/Prehistoric-Turkeys.html

MORPHED: WHEN WHALES HAD LEGS examines the environmental pressures that turned a wolflike creature that hunted in shallow waters into a leviathan of the seas.

Video "Ancient Whale Bones" – In the plains of Pakistan, archaeologists discover clues to help solve the mystery of how land mammals became whales:http://channel.nationalgeographic.com/channel/videos/feeds/cv-seo/Animals--Nature/All-Videos/Archaeologists-Find-the-Missing-Whale-Link.html

MORPHED: BEFORE THEY WERE BEARS travels back 30 million years to watch the bear's doglike ancestor climb down from the trees of central Europe and set out on a journey that spanned the planet.

Video "Giant Historic Bear" – In the struggle for survival, the giant short-faced bear evolved into a towering kiling machine:http://channel.nationalgeographic.com/channel/videos/feeds/cv-seo/Nat-Geo-Wild/All-Videos/Ancient-Predators-in-Beringia.html

DARWIN'S SECRET NOTEBOOKS

Tuesday, February 10, 2009 at 9 PM ET/PT

http://natgeotv.com/darwin

Using Darwin's own diary and field notes as a travel guide, National Geographic Channel retrace Darwin's expedition beyond the Galapagos to uncover the forgotten evidence that inspired his revolutionary work. We see how fossils in Argentina, seashells in the Andes and fish in the South Pacific helped him cultivate his radical theory of evolution.

Video "Inside Darwin's Mind" – The oddity of flightless birds leads Darwin to question the intentions of the Creator:http://channel.nationalgeographic.com/channel/videos/feeds/cv-seo/Animals--Nature/All-Videos/Darwin-Ponders-Flightless-Birds.html

EXPLORER: MONSTER FISH OF THE CONGO

Tuesday, February 10, 2009 at 10 PM ET/PT

http://channel.nationalgeographic.com/series/explorer/3826/Overview

Join a team of adventurers and scientists and travel deep into the heart of Africa's Congo River Basin in search of an elusive man-sized predator known as the tiger fish.  While locals believe this ravenous relative of the piranha is cursed, scientists believe the fearsome fish may hold the key to understanding the evolution of an extraordinary array of bizarre creatures found throughout the Congo.

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Convergence of the Death Adder with Viperidae

Submitted by Brandon Williams for the Birds & Reptiles class.

In a study of the Australian death adder (Acanthophis antarcticus), a member of the Elapidae, Richard Shine observes the convergence of the snake with the Viperidae (Shine 1980). There are no vipers that live in Australia, yet the death adder resembles vipers much more so than other members of the elapids. Shine hypothesizes that the sit-and-wait ambush hunting techniques select for similar adaptations in vipers and death adders. Most elapids are more active searching foragers.

In many ways Shine shows how death adders are adapted in similar ways to vipers rather than their elapid cousins. Death adders feed mostly on ectotherms as juveniles and switch to endotherms as adults. Death adders have a shorter stouter body than most elapids and a pronounced head. A. antarcticus have a delayed sexual maturation and a corresponding slow growth rate. The delayed maturation probably evolved after the ambush hunting strategy, which tends to allow for high survivorship because that leaves less opportunity for predation on the snakes. A. antarcticus has a unique adaptation for ambush hunting which is completely absent in all other elapids, yet is found in nine different vipers. This adaptation is caudal luring; using the thin, yellow wriggling tip of their tail as bait for prey. All of these adaptations point to convergence of the death adder with vipers. The reason for this is the ambush hunting technique.

Shine also posits that because just over half of mature females were found not to be reproductive that female death adders reproduce every other year. He was probably correct, however there could be some genetic or another unseen reason why many of the females were non-reproductive. Testing his hypothesis could be done. He could collect live female specimens of mature size during the breeding season, tag them with a number, noting whether they were reproductive or not, and let them go. Then over the next few breeding seasons he could collect female death adders that had been tagged and note whether the ones that were specifically reproductive last season were non-reproductive the following season. Over a few seasons he could see how consistent the data was with his every other year hypothesis.

Reference:

Shine, R. 1980. Ecology of the Australian Death Adder Acanthophis antarcticus (Elapidae). Pp. 281-289. Evidence for Convergence with the Viperidae. Herpetologists' League.

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A Bite of Beta-Carotene for Better Twitterpation

Submitted by Pedro Garcia for Evolution

Birds, birds, and more birds, with over 10,000 species of birds well known and classified, one can get an array of different colors which would make even the most non-bird lover’s staring in awe. With some species having such intricate combinations of reds, yellows, greens, and blues, (such as the scarlet macaw of South America) one might ask, “Why do they have such vibrant and magnificent plumage?” (or something along those lines). It’s a well known fact that skin and feather color (yellows and reds) is linked with carotenoids in the body. One well known example is the Caribbean flamingo, known for its brightly reddish/pink color. This species of bird gets its color from the high intake of beta-carotenes obtained from its diet of crustaceans and algae. But why? What good is it to be so brightly colored? One might even think that such bright colors would be a sort of bull’s eye for predators as if saying “Hey, you…the one with the sharp teeth…I’m over here!” Well, in short, it can all be explained by loosely quoting the hip hop song… “it’s all about sex, baby!”

That’s right, ongoing research has been linking brightly colored plumage in birds to…well, sex! This is the not-so-PG stuff that Darwin didn’t really talk about in his book (at least not directly), however it is merely the process of evolution at work. Researchers Negro, et al, (2002), have gone even more in depth concerning the correlation of plasma carotenoid-dependent skin color in relation to sexual selection. Their work consisted of analysis of brightness of color, not in the feathers, but, in the cere, lores, and tarsi of the small falcon the American Kestrel (Falco sparverius) along the time scale of mating season to hatching of offspring. As stated in the article, research has shown that color of plumage in birds does have an effect on sexual selection in brightly colored birds (Negro, 2002). As stated earlier, the brightness of plumage (specifically reds and yellows) is dependent on the amount of carotenoids found in the body; and beta-carotene is taken in directly from food source. Simply put, female birds choose the male with the brightest plumage because he is the one that can successfully obtain the most food, thus passing on the “better” genes to the offspring. As said before, it’s the process of natural selection at work.

Although there has been much research on sexual selection and plumage color, this article delves in even further and tries to find a correlation with skin color in birds as a function of sexual selection. It seems that, as hypothesized before, there is a brighter skin hue during the mating season. However, what came next seemed to be of even greater interest. It seems that, at least among American Kestrels, the “brightness” of the skin color began to fade as soon as the mating season ended. This was directly linked with a reduction in plasma-carotenoid levels (Negro, 2002). It is believed that the reduction occurs as a trade-off between sexual selection (during mating season) and maintaining better health (post-mating season). Since the bright coloration is no longer needed after mating, it would seem that a reduction in plasma-carotenoids would allow for the carotenoids to assist in other health-related body functions (such as anti-oxidants aiding in the reduction of oxidative damage by free radicals).

One concern I have with research is the methodology used for the experiments. All subjects were captive Kestrels from the “Avian Science and Conservation Center of McGill University, Canada…” which were fed a consistent diet of “…day-old cockerels” which were carotenoid-rich (Negro, 2002). This brings up my concern that the Kestrels were not mimicking natural processes, thus adding, in my eyes, a great amount of tolerance and bias to the results. It should be noted that the author does state that they have “previously shown that variation in plasma carotenoids during the mating period (April) was not attributable to diet, parasites or androgen levels” (Negro, 2002). Ideal settings that would eliminate this tolerance would include plasma collection of marked Kestrels in the wild throughout a series of mating and fledging seasons.

References

J. J. Negro, G. R. Bortolotti, J. L. Tella, K. J. Fernie, D. M. Bird (1998). Regulation of integumentary colour and plasma carotenoids in American Kestrels consistent with sexual selection theory Functional Ecology, 12 (2), 307-312 DOI: 10.1046/j.1365-2435.1998.00176.x

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Lizards Showing Some “Leg”

Submitted by Cindy Hua for Evolution

Most of us think that evolution in species take several generations to thousands of years to occur. However, how about if I say in one generation’s time there is a significant change in morphology? Jonathan Losos and his team of researchers from Washington University, St. Louis has found a peculiar lizard that is evolving in a tremendous rate. The brown anole, a Caribbean native lizard, spends most of its day hunting on the ground. One of its main predators is the curly-tailed lizard.

As we all know from our evolution class, a chain of islands sets up a great opportunity for parent species to change significantly. Since the Bahamas are home to the brown anole, natural selection will most likely to occur if there is a change in predator population. Losos has tested his hypothesis that with the introduction of more curly-tailed lizards into the main island, the brown anoles are under the influence of selection pressure change (Losos, et. al, 2006). When brown anoles sense danger of increasing populations of curly-tailed lizards, it flees towards trees and stay away from the ground activities for a few generations.

After a year’s experiment, Losos discovered that the brown anoles are experiencing a change in leg morphology. In the first six months of his study, the anoles originally had long legs, which enable them to outrun the predators. However, six months later, the survivors had drastically shorter legs, which permit them to hide in narrow crevices and climb in trees. Losos noticed that within a single generation, the anoles went to quick reversals in selection pressure (Losos, et. al). The behavior of the lizards changed, as they prefer treetops than the ground. Here we see natural selection at its finest.

Over several generations down, the continuing threat of curly-tailed lizards will force the anoles population to evolve shorter and shorter legs. However, I find it hard to believe that brown anoles can evolve in one generation at such a fast pace. Perhaps through time the longer legged anoles died off and Losos found mostly shorter legged since it was able to survive and reproduce.

The quick reversal of evolution by means of selection pressure is quite interesting. The brown anoles started with long legs to outrun its predators but discovered it to be a hindrance as it cannot bend its legs to hide in crevices. It preferred to have shorter legs to save energy and it is easier to live in trees away from the main predator. The anoles do not have a use of long legs anymore so it does not have to evolve back. For example, ostriches, emus, and kiwis all are flightless birds yet they have small wings. Their ancestors were flying species, but, through time, with fewer predators to run away from, they probably foraged on the ground more. Over generations, they most likely could adapt better on land and did not need developed wings for flight. That is why they evolved long, strong legs for running and scratching for food. I believe this is similar to what is occurring to the brown anoles. Their ancestors must have evolved longer legs to run away from predators. however, current species reverted to shorter legs when selection pressure changed. Although I believe the leg lengths did change because of pressure, I find it hard to believe this had all occurred in one generation.

Reference:

J. B. Losos, T. W. Schoener, R. B. Langerhans, D. A. Spiller (2006). Rapid Temporal Reversal in Predator-Driven Natural Selection Science, 314 (5802), 1111-1111 DOI: 10.1126/science.1133584

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Development and Divergence of Canid Morphology, A Critical Review

Submitted by Tara Clever for the Evolution class.

When considering the comparison, it is astonishing that toy poodles belong to the same family as wolves: Canidae. Even more interesting is the observation of the divergence of domestic dogs from wolves. Robert K. Wayne approaches this topic with his paper “Limb Mophology of Domestic and Wild Canids: The influence of Development on Morphologic Change.” His primary objective was to determine whether allometry as an index of development and function is the same in domestic and wild canids. (Wayne 1986)

Bivariate Analysis

Domestic dog breeds have wider long bones than their wild counterparts of the same femur length. When comparing relative long bone width, there was little difference between domestic dogs and wild canids. Metapodial, scapula, and olecranon length difference were ovbious between dogs and wild canids. Long bone width and development reflect that fact domestic dogs do not need to hunt or escape predation.

Discriminate Analysis

General size of all canidae family members, domestic and wild, was analyzed to determine similarity of morphologic patterns. Despite diversity in limb size and proportion, domestic dogs are highly distinguished from all except wolf-like canids. Morphologic separation of wild canids among each other and of domestic dogs and wild species depends on difference in metatarsal and olecranon morphology. This suggested that morphologic evolution abides by phylogenetic boundaries (Wayne 1986).

Ontogenetic Analysis

Similarity of dog-intraspecific and dog-ontogenetic analysis showed that small dog breeds are paedomorphic whereas large dog breeds are hypermorphic. This assumes that diversity of limb diversity is predetermined and reflected in the development of an individual as breeders artificially select domestic dogs for favorable traits.

Conclusion

Wayne’s study indicated that allometry can be utilized as an index of devlelopment and function in both domestic dogs and wild canids. Morphological and bone differences were apparent amongst all members of the canidae family. However, some differences were not as distinguishable between domestic dogs and closely related wolves. As domestic dogs are bred for entertainment value, these differences will become more apparent.

Literature cited

Wayne, R. K. (1986). "Limb Morphology of Domestic and Wild Canids: The influence of Development on Morphologic Change." Journal of Morphology 187: 301-319.

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