Polar sea ice sets two records

On August 26th this year, Arctic sea ice extent fell to its lowest ever since records began in 1979. Sea ice continued to melt into September reaching a minimum of 3.41 million square kilometers on the 16th of September. Which is 790 thousand square kilometers less than the previous record minimum (2007) and roughly half the average minimum from 1979 to 2000 (7.04 million square kilometers).

At the other end of the planet Antarctic sea ice was setting a new winter maximum of 19.44 million square kilometers on the 26th of September. Which is 740 thousand square kilometers more than the 1979 to 2000 average maximum (18.7 million square kilometers). So the gain in the south is far lower than the loss in the north. And the gain in the Antarctic is no cause for celebration.

Antarctic sea ice extent on the 26th of September when the record maximum was set (image NSIDC)

The gain in sea ice in the Antarctic is likely to be due to two effects. The hole in the ozone layer has a cooling effect on the continent because ozone is a greenhouse gas. Warming in the Southern Ocean, which is well documented, has also lead to an increase in the strength of westerly winds. This has pushed more sea ice away from shore expanding its extent in most places except the Antarctic peninsula where it has decreased.

Playing Russian Roulette with Gaia

The addition of iron to the oceans has been suggested as a mechanism to reduce the amount of carbon dioxide in the atmosphere. In several parts of the ocean, plankton abundance in much lower than expected given the availability of nutrients and sunlight. But, these areas are also low in iron, leading many people to suggest that it's the availability of iron that limits plankton numbers. A while ago I wrote about an experiment in the Southern Ocean that investigated this hypothesis. 

Permission to conduct these experiments was hard to get because the UN has agreed to a moratorium on iron fertilisation until more is known about the effects on other marine life. But, in contravention of the moratorium a rogue businessman has conducted an iron fertilisation 'experiment' in the northeastern Pacific, off the coast of Canada. Russ George has been trying to sell his iron fertilisation scheme to the world as part of the lucrative market for carbon credits.

He convinced the Haida Nation to provide one million dollars funding, apparently by telling them that the dumping of iron would increase salmon numbers in the area. With that money he dumped 100 tons of iron sulfate into the ocean 200 nautical miles west of the islands of Haida Gwaii in July this year. The plankton bloom this created reached 10,000 square kilometers in size. In comparison, the experiment in the Southern Ocean dumped just seven tons of iron sulfate and the bloom peaked at 800 square kilometers.

In conducting this 'experiment' Russ George may have broken international and Canadian laws. It violates the UN moratorium on iron fertilisation and he may have committed fraud in obtaining the funds from the Haida Nation. In any case, there is no evidence that plankton blooms will improve salmon number and only limited evidence that iron fertilisation is an effective mechanism for reducing carbon dioxide. And we know next to nothing about the potential negative impacts of such large blooms.

For more information, including Russ George's history in trying to sell iron fertilisation as a carbon credit scheme, try The Guardian and Deepsea News.

It's Yoda, but not as you know him

A new species of acorn worm has been named after Jedi Master Yoda, the best character in the Star Wars trilogy*. Acorn worms are not true worms. They are more closely related to echinoderms (starfish, sea urchins, sea cucumbers, etc.) than they are to worms. They were once placed as a subphylum of the chordata (i.e. our own phylum), but are now placed within their own phylum, the hemichordata.

Yoda purpurata, the newly described species of acorn worm

The paper described three new species of deep-sea acorn worms in the family Torquaratoridae. Two of which, Allapasus isidis and Tergivelum cinnabarinum, were from previously known genera. But, Yoda purpurata is a new genus and species. It's named after Yoda because the appendages at the head end of the animal are reminiscent of Yoda's ears. All three species were found at about 2.5 kilometers deep on the mid-Atlantic ridge.

*To count as a true Star Wars film, it can't just carry the name. You also have to be able to sit through it without wanting to punch George Lucas. This caveat leaves just three films that can be considered part of the Star Wars canon. And these three films are the originals, not the remakes. 

Priede, I G, Osborn, K J, Gebruk, A V, Jones, D, Shale, D, Rogacheva, A, & Holland, N D (2012). Observations on torquaratorid acorn worms (Hemichordata, Enteropneusta) from the North Atlantic with descriptions of a new genus and three new species Invertebrate Biology, 131 (3), 244-257 DOI: 10.1111/j.1744-7410.2012.00266.x

Human-induced evolution

Human activities have influenced that evolution of many species and not just through artificial selection. Our impacts on ecosystems, use of drugs and pesticides and our harvesting of wild populations is all having an effect on the rate and direction of evolution in many organisms. In fact, many of the frequently cited examples of 'evolution in action' are also examples of human-induced evolution, such as mosquito resistance to DDT and drug resistant bacteria.

The detailed studies on the peppered moth, Biston betularia, provide a classic illustration of evolution in action. The peppered moth is nocturnal, resting during the day on light coloured trees, where it is reasonably well camouflaged. However, during the industrial revolution, trees in forests between London and Manchester became covered in soot and dark coloured morphs increased in frequency from 0.01% of the population to 98% due to increased bird predation on the less camouflaged light coloured morph.

The light (top) and dark (bottom) coloured morphs of the peppered moth, Biston betularia (images Wikipedia)

Although we don't often think of ourselves as predators, hunting and fishing are essentially the same thing. Like predation on peppered moths by birds, they can produce evolutionary change in the target populations. For instance, trophy hunting of bighorn sheep, Ovis canadensis, results in sheep with smaller horns and lighter body weight over time. A couple of recent studies show that behavioural traits are selected too.

Bighorn sheep in Montana (image Wikipedia)

Using GPS devices, Ciuti et al. tracked 122 (77 females and 45 males) elk, Cervus elaphas, to monitor their movements over the course of a year. The males that were the most likely to fall victim to hunters were those that moved more often, traveled the furthest and made greater use of open areas. The pattern was similar, but less pronounced, in females. Older females tended to move less and use of open areas less than younger females, suggesting that they may learn to avoid hunters. They could not assess learning with age in males as all the tracked males were of the same age.

A male elk (image Wikipedia)

Ciuti et al. suggest that the bolder behaviour of the elk that were harvested may provide them with protection from other predators, like wolves and bears. Moving long distances and using open areas may make it easier for elk to avoid natural predators, but it favours harvesting by humans with high-powered rifles. It's a neat hypothesis and they say that they intend to test it in future experiments.

A second study in rainbow trout, Oncorhynchus mykiss, looked at growth rate, a trait closely correlated with activity rate. To fuel a fast growth rate, it's thought that fish must spend more time actively searching for food, which is supported in the literature. Biro stocked four fishless lakes in Canada with trout that were slow-growing, intermediately-growing and fast-growing. By stocking the lakes, Biro knew the numbers of fish present in each lake and in each experimental group. He then randomly sampled the four lakes using a sampling method that wasn't size-selective.

Rainbow trout (image US Fisheries and Wildlife Service)

There was substantial variation in the proportion of each of the experimental groups that was caught in each lake. However, faster growing trout were consistently more likely to be caught than intermediate or slow-growing trout. Overall, fast-growing trout were nearly twice as likely to be caught than the two groups with slower growth rates. Importantly, size did not matter; small, slow-growing fish were still less likely to be caught than small, fast-growing fish.

Biro's study has the issue that it did not directly assess behaviour, but relied on growth rate as a proxy measure. However, it is consistent with other studies that show fish personalities influence the probability that they are caught by different collection techniques. Bluegill sunfish, for instance, are more likely to be caught in the wild by angling when they're less active. Intriguingly, there is also an interaction between habitat and capture method as less active bluegill sunfish are also less likely to be caught by angling in the open areas of artificial ponds.  

I'm troubled by the correlation between growth rate and supposed personality traits. It suggests that what is being measured as personality might actually be a by-product of physiology and not a separate trait. But, other studies I looked at showed that in some situations less active fish grow faster than more active fish, which suggests that they are independent traits.

In any case, the Cuiti et al. and Biro studies show quite nicely that humans are probably influencing the direction of evolution in the populations that we harvest by hunting and fishing. Their work adds to a growing body of research that humans are influencing the evolution of many species. Indeed, Stephen Palumbi has argued that humans are currently the World's greatest evolutionary force.

Biro PA (2012). Are most samples of animals systematically biased? Consistent individual trait differences bias samples despite random sampling. Oecologia PMID: 22885993  

Ciuti, S, Muhly, T B, Paton, D G, McDevitt, A D, Musiani, M, & Boyce, M S (2012). Human selection of elk behavioural traits in a landscape of fear Proceedings of the Royal Society: B, 279 (1746), 4407-4416 DOI: 10.1098/rspb.2012.1483  

Palumbi, S R (2001). Humans as the World's greatest evolutionary force Science, 293 (5536), 1786-1790 DOI: 10.1126/science.293.5536.1786  

Wilson, A D M, Binder, T R, McGrath, K P, Cooke, S J, & Godin, J J (2011). Capture technique and fish personality: angling targets timid bluegill sunfish, Lepomis macrochirus Canadian Journal of Fisheries and Aquatic Sciences, 68 (5), 749-757 DOI: 10.1139/f2011-019

Evolution, the most fascinating science

There are many amazing evolutionary adaptations. Here is a short video documenting just one.

Carnival of Evolution #52

The Carnival of Evolution #52 is now up at the Genealogical World of Phylogenetic Networks. There are some interesting posts there from some excellent science writers.

ENCODE continues to fester

Many expert bloggers are still annoyed with the science communication failure that was the ENCODE project's coverage in the popular science press. Larry Moran has another post about it regarding the profile of lead coordinator of ENCODE, Ewan Birney. And I have just run across a great collection of links to stories that more critically examine the ENCODE claims on Ryan Gregory's blog.

Vampire squid

Ed Yong is a science writer who's work I often enjoy reading. He has an interesting piece about vampire squid, Vampyroteuthis infernalis, that he has written for his blog "Not Exactly Rocket Science". Vampire squid are not actually squid, although they are related to squid and octopus. They are classified in their own order of cephalopods, the Vampyromorphida, in which they are the only known extant species.

A little fish makes big sand sculptures

In the ocean off Japan an industrious pufferfish has been crafting elaborate sand sculptures. And they're spectacular!

The sculptures created by the pufferfish (photos Yoji Ookata)

The sculptures appear to be sexually selected. Only the males make them and females prefer to mate with males who make sculptures with more ridges. During mating the eggs are laid into the center of the sculpture where they may receive some protection from the currents preventing them from being dispersed far and wide.

A male pufferfish creating a sculpture (photo Yoji Ookata)

These pufferfish (I can't work out the species) are not the only fish to make sand sculptures. Many species of African cichlids make structures, known as bowers (after the bowerbird), that function in sexual selection too. But, for many species the bowers, although they appear nest-like, do not hold the eggs. The female broods them in her mouth until they hatch and often longer.

A male cichlid patrols his volcano shaped sandcastle in Lake Malawi (photo Justin Marshall)

Unflappable albatrosses

Wandering albatrosses, Diomedea exulans, are among the largest flying birds in the world and are renowned for soaring flights of thousands of kilometers to feed. Several adaptations allow their flight to be extremely energy-efficient. For instance, their extremely long wings allow them to glide remarkably long distances and a modified tendon allows them to hold their wings open without the use of their muscles.

A wandering albatross showing its fight position (photo Wikipedia)

For a long time, it's been clear that albatrosses are using wind energy to power their flight. Indeed, Lord Rayleigh proposed that albatrosses were using wind shear to soar in 1883. Although other mechanisms have been proposed, dynamic soaring in wind shear has since been cited as the principle mechanism that they are able to gain energy from the wind. 

At the ocean surface the wind travels more slowly because of friction, but as you move away from the surface wind speeds get higher. Albatrosses can gain airspeed by rising away from the sea into the faster winds and then dropping back into the slower winds at the surface. They first turn into the wind and rise followed by a turn with the wind as they descend, gaining energy in both directions while losing some to drag.

The dynamic soaring cycle of an albatross. It starts with a turn into the wind, then a climb in altitude, then a turn with the wind and a descent back to the sea surface. The length of yellow arrows to the left of the figure indicate the strength of the wind at different altitudes (Image taken from Sachs 2005).

Penncuick argued that albatrosses couldn't get enough energy from the wind-gradient and must be deriving a large amount of energy from moving in and out of the pockets of almost still air in the lee of wave crests, which he termed 'gust soaring'. Other authors have suggested that they slope-soar off the windward side of wave crests. But, the debate over how albatrosses are gaining enough energy for their long distance flights has played out in the theoretical literature, sometimes accompanied by anecdotal observations of flight behaviour.

The gust soaring cycle of an albatross. As the albatross moves through the 'separated boundary layer' (blue line) from the leeward side of a wave crest it gets a kick of energy from the wind allowing it to gain altitude and potential energy to power its soaring flight (Image taken from Richardson 2011)

With their paper published recently in PLOS One, Sachs et al. have added some empirical data to help resolve the issue. They attached small GPS devices to the backs of 16 albatrosses, which measured the position and altitude of each individual once every second and the velocity 10 times a second. This allowed them to look at the small scale of the flight cycle and draw inferences about the physics of the manoeuver.

A plot of a recorded dynamic soaring cycle. The numbers indicate each stages from the ascent [1], to the turn at peak altitude [2], to the descent [3] and the turn to restart the cycle [4] (Image taken from Sachs et al. 2012).

They used the data to calculate the total energy over the entire dynamic soaring cycle by summing the potential and kinetic energy. Contrary to the expectations of gust soaring and slope soaring, the maximum energy in the cycle was reached on the descent. And the energy accumulation was gradual, without any large spikes that would result from a big kick in energy close to the surface.

A two-dimensional plot of the soaring cycle showing the point at which maximum and minimum energy are reached. The track shown here is the same as the one above (Image taken from Sachs et al. 2012).

Sachs et al. also calculated the energy gain that the albatrosses could achieve throughout the cycle. The maximum energy in the cycle was ~360% of the minimum energy and provided enough surplus to overcome drag forces. Indeed, the energy gain was so large that it far exceeded what the albatrosses could achieve by flapping their wings.

The efficiency that the albatrosses converted the wind into usable energy for flight allowed them to achieve ground speeds higher than the wind speed. On average the 16 birds that they followed traveled at ~60 kilometers per hour, but one bird was clocked traveling at an average of 76 kilometers per hour. If that's not amazing enough, an earlier study that Sachs et al. cite, clocked a grey-headed albatross (Thalassarche chrysostoma) traveling at an average ground speed of 110 kilometers per hour for 9 hours in high winds! 

My only concern about the paper, which isn't a very big one, is that all of the energy calculations are based on a single dynamic soaring cycle (the one in the two figures above). The authors do present three others in their supplementary material, which all look essentially the same. But, I wonder why they don't use them for the calculations. And they tracked 16 birds for at least 176 kilometers, did they really only get four cycles which occur in the space of ~150 meters? They don't say.

References:

Sachs G, Traugott J, Nesterova AP, Dell'omo G, Kümmeth F, Heidrich W, Vyssotski AL, & Bonadonna F (2012). Flying at no mechanical energy cost: disclosing the secret of wandering albatrosses. PloS one, 7 (9) PMID: 22957014  

Richardson PL (2011). How do albatrosses fly around the world without flapping their wings? Progress in Oceanography, 88 (1 - 4), 46-58 DOI: 10.1016/j.pocean.2010.08.001  

Pennycuick CJ (2002). Gust soaring as a basis for the flight of petrels and albatrosses (Procellariiformes) Avian Science, 2 (1), 1-12