Isegoria

Flocking seems like a complex behavior that should require careful collaboration between all the birds involved, but Craig Reynolds demonstrated back in 1986 that simulated birds, or boids, would realistically flock if they just followed three basic steering behaviors:

• Separation: steer to avoid crowding local flockmates.
• Alignment: steer towards the average heading of local flockmates.
• Cohesion: steer to move toward the average position of local flockmates.

He went on to demonstrate all sorts of Steering Behaviors For Autonomous Characters, including pursuit and evasion — but not pack-hunting.

Now C. Muro et al. have demonstrated that the sophisticated teamwork of a wolf pack also stems from simple rules:

We have produced computational simulations of multi-agent systems in which wolf agents chase prey agents. We show that two simple decentralized rules controlling the movement of each wolf are enough to reproduce the main features of the wolf-pack hunting behavior: tracking the prey, carrying out the pursuit, and encircling the prey until it stops moving.

The rules are (1) move towards the prey until a minimum safe distance to the prey is reached, and (2) when close enough to the prey, move away from the other wolves that are close to the safe distance to the prey.

The hunting agents are autonomous, interchangeable and indistinguishable; the only information each agent needs is the position of the other agents. Our results suggest that wolf-pack hunting is an emergent collective behavior which does not necessarily rely on the presence of effective communication between the individuals participating in the hunt, and that no hierarchy is needed in the group to achieve the task properly.

I didn’t realize that killer whales — pardon, orcas — molt, which poses certain problems:

The problem for them and other polar mammals is that molting means losing a ton of body heat, which can be potentially dangerous in such frigid waters.

So they swim 3,000 miles to warmer waters:

Researchers from the US’s National Oceanic and Atmospheric Administration tracked the movements of five killer whales, all of which moved from the freezing Antarctic waters — average temperature 30 degrees Fahrenheit — to the relatively balmy subtropical waters off the coast of Brazil and Uruguay, where it’s 75 degrees. One whale managed the entire 6,000 mile round trip in just 42 days.

It appears these journeys are pretty much exclusively for regenerating their skin — at those speeds, they wouldn’t have enough time to go hunting or to take care of their young. It’s a trip that takes the whales far outside their natural comfort zone, as evidenced by the fact that the whales went slower and slower the further north they got.

A dolphin study seeks to start a two-way conversation:

Dolphins are known to make three types of sounds: whistles, clicks and burst pulses. Whistles are thought to be identification sounds, like names, while clicks are used to navigate and to find prey with echolocation.

Burst pulses, which can sound like quarreling cartoon chipmunks, are a muddy mixture of the two, and Dr. Herzing believes that much information may be encoded in these sounds, as well as in dolphins’ ultra-high frequencies, which humans cannot hear.

The two-way system she will test next year is being developed with artificial intelligence scientists at Georgia Tech. It consists of a wearable underwater computer that can make dolphin sounds, but also record and differentiate them in real time. It must also distinguish which dolphin is making the sound, a common challenge since dolphins rarely open their mouths.

In the new system, two human divers interact in front of dolphins: First they play a synthesized whistle sound, then one hands the other a scarf or a piece of seaweed. The idea is to establish an association between sound and object. Dolphins are excellent mimics, and the hope is that they will imitate the whistle to request an object or initiate play.

“I think if they pick up on it,” Dr. Herzing said, “they’re going to be excited and say, ‘Oh, my gosh, now I have the power to get what I want in real time.’ ”

Still, she is quick to play down expectations, noting that the system is still in development.

“We’re not talking to dolphins,” she said, adding, “We’ll keep it simple and then we can potentially expand it.”

And while other researchers praise her work, they point out that of dolphin-human communication has often fallen short of expectations.

“It depends on what you mean by communicate,” Dr. Kuczaj said. “I can communicate with my dog, too. But do I have conversations with my dog? Well, if I do they’re very one-sided.”

Matt Ridley discusses the polar bear problem — and how it has changed over a generation:

Today bears are now far more common in Spitsbergen and the other islands of Svalbard. They are more common all over the Arctic than 33 years ago. The US Fish and Wildlife Service estimated in 2008 that the polar bear population was at a historic high of 20,000-25,000 bears, up from as low as 5,000-10,000 bears in the 1960s. The International Union for the Conservation of Nature estimated in 1966 that there were 10,000 polar bears in the world; in 2006, the same source estimated 20,000-25,000 bears. Just last May the IUCN Polar BearSpecialist Group concluded there has probably been no drop in the numbers since then.

The reason for this boom is no mystery. When I travelled in Spitsbergen in the 1970s and 1980s you could still find old trap guns on remote headlands, dating from decades before: open-ended wooden boxes concealing rusty rifles with wires attached to the triggers so that a bear would shoot itself if it pulled the bait. The trapper would return later for the skin. Until 1973, bears were hunted for their fur and for sport; in that year, an international agreement banned unregulated hunting, shooting from aircraft and shooting from icebreakers. The species then thrived. Russia, Greenland and Canada all still allow some hunting, mainly by indigenous people, but at a much reduced level.

Not all populations are thriving. Some authorities think the numbers are declining in Hudson Bay and parts of the Canadian Arctic, while expanding elsewhere, but these are minor fluctuations compared with the impressive recovery of the species since the 1960s. Al Gore, in his film An Inconvenient Truth, made much of a report of four bears that drowned in open water off Alaska, implying this was a new and deadly fate awaiting polar bears as Arctic ice retreated. But polar bears often swim long distances — one was recorded swimming 400 miles — and nobody knows how unusual it was for four to get caught in a storm and drown.

The polar bear is a specialist seal-eating predator (so it is little wonder that it goes for other elongated six-foot mammals when hungry). It occupies a specific niche: the ice edge. It cannot thrive on unbroken Arctic sea ice, because seals are not found there. Nor can it survive on ice-free sea because it cannot kill seals in open water. In parts of the Arctic, notably Hudson Bay and Wrangel Island, it takes refuge on land for several late summer months when the ice vanishes, fasting — or scavenging ineffectually for young walrus, birds and fish — till the ice re-forms. This is when it is hungriest and most dangerous.

If the ice-free season lengthens in these places because of climate change, the bears might die out. After all, the most southerly polar bear dens in the world, in James Bay in Canada, are on the same latitude as Nottingham: they are at the extreme southerly end of their range. But by the same token, areas further north, currently too solidly frozen for seals, will become more hospitable to bears.

There is now good evidence that this sort of ice retreat has happened in the past. For example Svend Funder of the University of Copenhagen recently published a paper with two colleagues, based on a study of driftwood and beach ridges in north-eastern Greenland, where today year-round ice fastened to the shore prevents waves that can form beach ridges. They concluded that for thousands of years when the Arctic was known to be 2-4°C warmer, beach ridges formed and driftwood failed to make it to Greenland, indicating open water on this coast (driftwood needs multi-year ice to be transported from Siberia without sinking).

In Funder’s words: ‘Our studies show that there have been large fluctuations in the amount of summer sea ice during the last 10,000 years. During the so-called Holocene Climate Optimum, from approximately 8,000 to 5,000 years ago, when the temperatures were somewhat warmer than today, there was significantly less sea ice in the Arctic Ocean, probably less than 50 per cent of the summer 2007 coverage, which was absolutely the lowest on record.’

Much has been made of the 2007 summer ice retreat being the ‘greatest on record’, but records began only in 1979. In the 1920s and 1930s, there were probably still more open seasons; likewise in the medieval, Roman and other warm periods all the way back to the Holocene Optimum. Polar bears certainly survived such warmer spells, presumably by ranging somewhat further north. Indeed, fossils suggest that polar bears already existed in their current form during the last interglacial period, 120,000 years ago, when the Arctic was almost certainly wholly free of ice in late summer.

A total disappearance of sea ice at all seasons would undoubtedly doom thepolar bear’s lifestyle. But no scientist in his wildest exaggerations is suggesting the disappearance of Arctic sea ice in winter. As long as there is pack ice for much of the year with an ice edge, plenty of seals and controls on hunting, thepolar bear is going to thrive — and tent-based tourism to the Arctic is going to be dangerous.

Snakes evolved venom as part of their eternal war with opossums — which eat snakes:

[American Museum of Natural History] Department of Mammalology curator Robert Voss explains:

Snake venom toxins evolve incredibly rapidly. Most herpetologists interpret this as evidence that venom in snakes evolves because of interactions with their prey, but if that were true you would see equally rapid evolution in toxin-targeted molecules of prey species, which has not yet been seen. What we’ve found is that a venom-targeted protein is evolving rapidly in mammals that eat snakes. That suggests that venom has a defensive as well as a trophic role.

There’s at least a hundred different opossum species, most of which are found throughout Central and South America. Recent genetic studies into these marsupial species revealed rapid evolution in von Willebrand’s factor, a blood-clotting protein that is targeted by the snake toxins.

Sharon Jansaof the University of Minnesota explains further:

This finding took us by surprise. We sequenced several genes — including the one that codes for von Willebrand Factor (vWF) — to use in a study of opossum phylogeny. Once we started to analyze the data, vWF was a real outlier. It was evolving much more rapidly than expected in a group of opossums that also, as it turns out, are resistant to pitviper venom. Most nucleotide substitutions have little or no effect on protein function, but that doesn’t seem to be the case with vWF in these venom-resistant opossums. The specific amino acids in vWF that interact with toxin proteins show unexpectedly high rates of replacement substitutions. These substitutions undoubtedly affect protein function, suggesting that the vWF protein can no longer be attacked by these snake toxins.

Voss explains what this all means for vipers and possums:

It is so uncommon to find genes under strong positive selection, that the exceptions are really interesting and often conform to one evolutionary circumstance when two organisms are coevolving with each other. We’ve known for years that venom genes evolve rapidly in snakes, but the partner in this arms race was unknown until now. Opossums eat snakes because they can.”

Researchers are sequencing the naked mole rat’s genome to uncover how it lives over 30 years, when similarly sized rats live just four, and how it remains immune to cancer:

Unique physical traits allow naked mole rats to survive in these harsh, underground environments for so many years. And the genetic secrets of those traits are contained in the mole rats’ DNA.

Previous research has shown that the small wrinkled rodents have very little or no pain sensation in their skin and a low metabolic rate that allows them to live with limited oxygen.

Charla Nash, the woman who was mauled last year by her friend’s 200-pound chimpanzee, Travis, has received a full face transplant, the third such surgery performed in the US, at Boston’s Brigham and Women’s Hospital:

Nash’s face was rebuilt last month by a medical team of more than 30 physicians, nurses, anesthesiologists and residents, the hospital announced on Friday.

Working for more than 20 hours, the team replaced Nash’s nose, lips, facial skin, muscles of facial animation and nerves.

It’s not all good news:

The hospital said a double hand transplant was also attempted, but the hands did not thrive and were removed.

Female mosquitoes follow a trail of carbon dioxide to their human prey, so researchers are exploring smelly chemicals to confuse them:

Scientists at the University of California, Riverside, tested smelly chemicals on three species of mosquito: Anopheles gambiae, which spreads malaria; Culex quinquefasciatus, which spreads filariasis and West Nile virus; and Aedes aegypti which spreads dengue and yellow fever.

The researchers say that these insects combined infect half a billion people each year, some in at risk countries will be infected multiple times in their lifetime, and cause millions of deaths.

The researchers identified three groups of chemicals, which disrupt a mosquito’s carbon dioxide receptors.

One mimicked carbon dioxide and could be used as bait in insect traps, another prevented the mosquito from detecting carbon dioxide and the last group tricked the mosquito’s brain into thinking it was surrounded by huge quantities of the gas — so it could not pick which way to go.

Oribatid mites thrive in llama dung, which means you can trace the rise of domesticated llamas — and thus the Inca empire — by counting mite remains in sedimentary layers:

Tracking social and economic change in Andean societies prior to the invasion of the Spanish has always been a difficult task, especially given that these cultures failed to develop any form of written record. Here we present a new method of reconstructing socio-economic shifts in a rural setting from the analysis of the frequency of oribatid mite remains present in a sedimentary lake sequence.

Oribatid mites are soil-dwelling microarthropod detritivores, some of which inhabit areas of grassland pasture. One of the primary controls governing their abundance in such habitats is the level of animal dung present. We propose that past fluctuations in mite remains can be related to the density of domestic animals using the area of pasture and, by extension, may provide a proxy for broad-scale social and economic change through time. To test this hypothesis, we analysed a high-resolution (6 years) mite record from a sequence of well-dated sediments from Marcacocha, a climatically sensitive lake site located close to an important Inca trading route across the Andes.

The timing and magnitude of mite fluctuations at Marcacocha since the 1530s show remarkable correspondence with a series of major, well-documented socio-economic shifts in the region relating to political and climatic pressures. This provided the confidence to extend the record back a further 700 years and reconstruct changes in domestic herbivore densities for a period of time that lacks historical documentation and thereby infer changes in human occupation of the basin. In particular, high mite abundances appear to correspond clearly with the rapid rise and fall of the Inca Empire (c. AD 1400–1532). We argue that small lake basins such as Marcacocha may be particularly suitable for obtaining continuous oribatid mite records and providing the possibility of reconstructing large herbivore abundances in the Andes and elsewhere.

(Hat tip to io9.)