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.