Tag Archives: adaptation

Climate Change Not Good For Red Knots

You’ve heard the phrase, “Nothing in biology makes sense except in the light of evolution,” an insightful phrase penned in 1972 by Theodosius Dobzhansky. I would like to add a second part to that phrase, and it goes like this: “… and, nothing in evolution makes sense except in the light of co-evolution.” This would hardly be an exaggeration, and it can hardly be better exemplified than with examples from migratory birds. Migratory birds have to be adapted to at least three different ecological settings. They breed in one area, migrate (and often spend considerable time) through another area, and winter in a third area. In each area they must feed and avoid predators, and in the nesting area, they must have make and protect nests, and the feeding is even more critical because they are growing their chicks.

Changes in one or more of these zones can change the viability of a bird species’ strategy, and even influence the bird’s survival chances in other areas. In the case of one subspecies of the Red Knot, a migratory bird, changes in the breeding ground caused by anthropogenic global warming have caused changes in the morphology of the bird, which in turn have caused changes in the birds’ ability to survive in the migratory zone.

The Red Knot (Calidris canutus) is a shorebird, a kind of sandpiper, with a global distribution. The subspecies C. c. canutus breeds in the Taymyr Penninsula and migrates to Western Europe then western and southern Africa.

The birds arrive in Arctic in the spring, where the adults, and later, their chicks, feed on insects. The insects are abundant after the snow melt. So, the birds arrive, ideally, just in time to take advantage of the abundant insects. The young then grow, and migrate south where they stay an entire year before doing their own migratory thing. While in Europe, these birds feed on bivalves that hide in mud, and on plants. The long beak of this bird facilitates their foraging on the bivalves. Having a long beak is good, because the shallower and more readily accessible bivalves are smaller, less abundant, and slightly toxic, especially to young birds (adults may have somehow adjusted to the toxin), but deeper bivalves are less toxic and more abundant.

Climate change has caused the timing of the snowmelt in the Arctic to change, with the snow melting off on average a half a day per year earlier over the last three or do decades.

This has caused the insects to emerge earlier. Also, the earlier snowmelt has affected the insects so they are less abundant, and their body sizes are smaller.

However, the Red Knots continue to arrive at about the same time every year, so the abundance and quality of the insect food source is measurably reduced. This, in turn, has stunted the growth of the young. The smaller young have smaller beaks. So, when they arrive in Europe, they have access mainly to the shallower, somewhat toxic bivalves, and plant material, and can’t get as easily at the deeper, more abundant, and non toxic bivalves down deeper in the mud. This, in turn, causes a lower survival rate for these young birds.

The population of these Red Knots has been declining, and this may be the reason.

Meanwhile, the adults that have lived for a few years are seen to have longer (normal length) beaks. It is likely that some Red Knots either grow more quickly or have some other way of addressing the problem of food supply. It is possible that natural selection is changing this bird population to manage these changes in climate.

This may be a good thing long term, but it is hard to say. The Arctic has indeed been warming more than the rest of the planet, and this is likely to continue. It is not easy to predict how Arctic insect populations will change under these changing conditions. If insects end up emerging over a more prolonged period of time, or if some other aspect of the ecology changes that causes the insects to be exploited more efficiently by a competitor of the Red Knot — or less efficiently — or if some other change in ecology happens in the wintering grounds or the flyways, then this could get even more complicated.

Climate change has happened in the past, and it is certainly true that many populations of birds and other critters have adapted, in an evolutionary sense, to these changes. Just as likely, species or subspecies have gone extinct. Every population of migratory bird probably has a very interesting (and often harrowing) story behind how they arrived at their current co-evolutionary relationship to the world around them. The problem with the currently changing climate, changing because of the human release of copious amounts of greenhouse gasses into the atmosphere, is that this change is happening at a rate that has rarely, if ever, been seen since birds evolved to begin with.

This is not entirely unexpected. JP Myers and Robert Lester predicted, in the 1992 book Global Warming and Biological Diversity that asynchrony of insect emergence and shorebird migration would cause population declines in shorebirds like the red knot.

Caption to the figure at the top of the post:

Fig. 3. Prey choice and prey availability at the Mauritanian wintering grounds. (A) Analysis of stable isotopes of blood samples shows that juvenile red knots (n = 676 birds) largely ignored the most abundant but mildly toxic prey, Loripes. However, with an increase in age, adult red knots (n = 1664) added substantial amounts of Loripes to their diet, but only if they had long bills. Plotted are means ± SE. (B) This bill length–dependent diet shift may be explained by the depth distribution of Loripes. The majority of these bivalves live between 30 and 40 mm below the seafloor, which is precisely the range of the bill lengths. The other two food sources, Dosinia bivalves and Zostera rhizomes, are found at shallower depths and are accessible to all red knots. Bars indicate medians, boxes indicate 25th to 75th percentiles, and whiskers indicate ranges.

The research is reported in this paper:

SCIENCE13 MAY 2016 : 819-821


Reductions in body size are increasingly being identified as a response to climate warming. Here we present evidence for a case of such body shrinkage, potentially due to malnutrition in early life. We show that an avian long-distance migrant (red knot, Calidris canutus canutus), which is experiencing globally unrivaled warming rates at its high-Arctic breeding grounds, produces smaller offspring with shorter bills during summers with early snowmelt. This has consequences half a world away at their tropical wintering grounds, where shorter-billed individuals have reduced survival rates. This is associated with these molluscivores eating fewer deeply buried bivalve prey and more shallowly buried seagrass rhizomes. We suggest that seasonal migrants can experience reduced fitness at one end of their range as a result of a changing climate at the other end.

Micro-Evolution In Greenland: Inuit Diet, Weight, and Stature

There is a new paper in Science linking genetic variation in people living in Greenland with long term selection for managing a marine-oriented diet, affecting stature, weight, and probably, physiological processing of omega-3 polyunsaturated fatty acids (PUFAs).

The vast majority of the variation we seen in stature (height) among humans is not genetic. That is a fact hard to swallow by so many of us who were told in biology class that “height is a complex genetic trait with many genes affecting it.” It also seems wrong because the classic examples of variation in stature, the Pygmies of Central Africa (short) and the Maasai of East Africa (tall) are assumed to be populations under selection that caused them to be outliers. Of course, the Maasai are really not that tall by modern Western standards, but the story about them being tall, first told by relatively short European travelers who met them in the 19th century, persists, despite the fact that those travelers’ offspring, such as Modern Americans and Brits, are in many cases significantly taller than their own ancestors without natural selection being the cause.

But there are some genetic factors that control height and weight and account for some percentage of variation in those phenotypes. Pygmies taken from their homeland and raised among people with unlimited food supply do not grow tall. They may become obese, but not tall, because one of the main genes that regulates growth in almost all humans simply does not function in Pygmies. (One individual Efe Pygmy I’ve met who was raised among Italian nuns, in Italy, was short but rather wide.) There may be other short statured populations with a similar genetically determined stature. But as far as we can tell, something like 20% (and that is probably an overestimate) of variation in stature in living humans over the last century or so can be accounted for by genetic variation. The rest is a combination of diet and, I suspect, an epigenetic effect linked to maternal size and diet. When a population of relatively short people get unlimited food the next generation is taller. But then, the next generation is taller still. It is as though mothers won’t give birth to maximally sized offspring, just somewhat larger offspring, who then give birth to somewhat larger offspring, so the part of the demographic transition where everyone gets taller happens over a few generations. This is a well documented but not very well explained phenomenon, and the explanation I suggest here is merely a hypothesis.

A new study in Science looks at the Inuit people, and some Europeans living in the same place they live, in this case Greenland, and finds a genetic component to Inuit stature and weight. There are also other differences having to do with processing elements of their relatively unusual diet.

The key result with respect to weight and height is shown in the graph at the top of the post. The letters (GG, GT, TT) are the alleles (T is the derived allele). Homozygotes for the derived allele are quite a bit less massive, and a small amount shorter, than those without the allele, and heterozygotes are in between.

Here is the abstract from the paper:

The indigenous people of Greenland, the Inuit, have lived for a long time in the extreme conditions of the Arctic, including low annual temperatures, and with a specialized diet rich in protein and fatty acids, particularly omega-3 polyunsaturated fatty acids (PUFAs). A scan of Inuit genomes for signatures of adaptation revealed signals at several loci, with the strongest signal located in a cluster of fatty acid desaturases that determine PUFA levels. The selected alleles are associated with multiple metabolic and anthropometric phenotypes and have large effect sizes for weight and height, with the effect on height replicated in Europeans. By analyzing membrane lipids, we found that the selected alleles modulate fatty acid composition, which may affect the regulation of growth hormones. Thus, the Inuit have genetic and physiological adaptations to a diet rich in PUFAs.

How long have the Inuit been living this lifeway, in this environment? Actually, not that long. The researchers, in their supplemental information, suggest that it could be as long as 30,000 years, but this is unlikely, or at least, the story is more complicated.

There are several complications to understanding the history of the selective environment of the Inuit, the environment that would have shaped this genetic adaptation. First, the environment has changed. Not only have we gone from an ice age to no ice age during this 30,000 year time period, but with sea level rise during the Holocene, the ecology of the arctic has changed considerably. Large areas of the continent have been inundated by the sea. Prior to that, most of the ocean adjoining land was immediately deep. With the inundation of the continent, vast relatively shallow areas of ocean would exist. Nutrients well up along the continental shelf, but shallow areas are also potentially nutrient rich because of sediments coming off shore. During glacial melt periods, there may have been frequent large scale fresh water incursions which would have had occasional disastrous effects on the local ecology. The position of estuarine settings, which can be very productive, would change. As sea level rise slowed, near shore sediments may have had a chance to build up, causing regional increases in productivity.

The migratory patterns, overall distribution, and abundance of marine mammals and common shoaling fish would have changed dramatically, and multiple times, during the last several thousand years. It would not have been until about five thousand years ago that things would have settled down allowing long term regional foraging adaptations to emerge. Prior to that there may have been periods when the marine environment was significantly more, or significantly less, productive.

Meanwhile, the ancestors of the Inuit themselves moved a great deal during this period. They were not in Greenland, or anywhere in North America, 30,000 years ago, but rather, in an unknown location in Asia. The Inuit ancestors were part of a later migration into the New World. The association (population wise) of true Arctic people and others living farther south is not known.

A second factor is cultural adaptation. When we look at the traditional Inuit foraging patterns and associated technology, together with the preceding prehistoric Thule adaptations, we can’t help but to be impressed with the highly specialized effective approaches, both strategically and technologically, to acquiring marine resources. Boats, lamps, harpoons, and processing tools are highly refined and efficient. That material culture and strategic approach, however, is only a few thousand years old. Before that, in the region, were the Dorset, who simply lacked many of these tools. It is possible that the Thule and Inuit had sled and sled dogs, but earlier people in the Arctic did not. And so on. The ancestors of the Inuit, just a few thousand years ago, could not have had as specialized a diet as the traditional (modern ethnohistoric) Inuit. Cultural adaptations changing over time is as important as, if not more important than, the afore mentioned likely changes in environment.

So, I’m not going to argue that these adaptations are not 30,000 years in the making. Rather, I’ll argue that strong selection for these alleles could be as recent a few thousand years or even less, and that prior selective environments (the combination of the natural environment and human cultural adaptations to it) may have different and the situation may have been rather complicated for many years. In other words, the new, and very interesting, results looking at the Inuit genome need to be integrated with a better understanding of Inuit history, which is probably going to require a lot more research in the region.

There is a second point I want to make about this paper. We see research suggesting a genetic explanation for a lot of things, but often, in the past, that has involved finding a correlation between this or that genetic variation and a presumed phenotypic feature. Often, the next key step to establish the link isn’t, perhaps sometimes can’t be, taken. This is the link between the observed genetic variation and a good physiological story. The present research finds genetic variation associated with physiological features that seem to be associated with a marine-oriented diet in an Arctic or Sub Arctic setting. That makes this research really valuable.

Greenlandic Inuit show genetic signatures of diet and climate adaptation
Matteo Fumagalli, Ida Moltke, Niels Grarup, Fernando Racimo, Peter Bjerregaard, Marit E. Jørgensen, Thorfinn S. Korneliussen, Pascale Gerbault, Line Skotte, Allan Linneberg, Cramer Christensen, Ivan Brandslund, Torben Jørgensen, Emilia Huerta-Sánchez, Erik B. Schmidt, Oluf Pedersen, Torben Hansen, Anders Albrechtsen, and Rasmus Nielsen
Science 18 September 2015: 349 (6254), 1343-1347. [DOI:10.1126/science.aab2319]

What is your comfort zone?

Today, I took out the trash. I may or may not have taken the trash out last week, but I can tell you that the last time I did take it out, whenever it was, I had to drag the trash barrel across ice. Yesterday I went to the gym without a coat or jacket. That made me have to decide if I wanted to go to the locker room to stow the contents of my pockets (car keys, etc.) or just keep those things in my pocket. The grass outside is green. We expect snow on Friday.
Continue reading What is your comfort zone?