When cold is not cold enough.

Winter can be tough on invertebrates. Even endotherms can find winters a bit grim if it’s extremely cold. Harsh freezing conditions are unforgiving, especially to those who cannot regulate their own body temperature. Parasites that have life stages involving intermediate hosts fare somewhat better than those free-living in the environment. But  there is still risk to their survival, especially if the intermediate host is an invertebrate. In this way, the cold winter temperatures regulate the populations of parasites by increasing their mortality.

Muskox (via Wikimedia commons)

The effects of warmer winters on parasite abundance, and as a consequence, host health, have been known for some time. A neat example of this comes from the Canadian arctic, in the relationship between the nematode Umingmakstrongylus pallikuukensis and its definitive host is the muskox (Ovibos moschatus). The nematode has an intermediate host, usually a slug, where larvae develop to infective stages. When the infective stage nematodes are consumed by a muskox, they take up residence in its lungs. Heavy infections can accumulate as the host gets older, causing serious pathology and can even kill muskox (Kutz et al. 2009). The accumulation was key, because under ‘normal’ (i.e., cold) winter conditions, it takes two years for the nematodes to reach maturity in their intermediate hosts. But if it warms up, they can be ready to infect muskox in only one year, without having their development arrested during a winter (Kutz, et al. 2002). This is bad news for the muskox, because it means that far more nematodes will be around at any one time.

It’s a tick-infested ghost moose. If this makes you a bit sad, please don’t google ‘ghost moose’ images.

Another effect of warmer winters is increased survival of ticks. While not yet present in the Arctic, the winter tick, Dermacentor albipictus, feeds on moose (Alces alces) in parts of southern Canada and the northern United States. Cold winters play a large part in regulating the populations of the ticks, as many larvae perish during winter as they wait for a moose to walk past. The time it takes for females to reach maturity is also thought to be regulated by a combination of time and temperature (Hueffer et al. 2011), meaning that warmer weather will go some way to speeding up the development of the ticks. The ticks stay on their moose hosts for their whole life, feeding and moulting. This means that moose can be subject to thousands of ticks feeding on them continuously from winter to the start of summer. Moose that suffer heavy infestations are called ‘ghost moose’. With up to 400,000 individual ticks feeding on a single individual (Kutz, et al. 2009), the ghost moose suffer hair loss, anemia, emaciation and secondary infections, and can die. Increased mortality of moose populations in northern US have been linked to increased abundance of ticks (ref Washington Post), which will affect trophic cascades in the boreal forests the moose live.

These are just two examples of how parasites interact with their hosts. By adding environmental perturbation (be it climate, urbanisation, habitat loss etc.), the dynamics of these interactions will change. Distribution changes, host switches, alteration to phenology and emerging pathogens are all on the cards as we hurtle through the 21st century.


Hueffer et al. (2011) Acta Veterinaria Scandinavica 53, doi: 10.1186/1751-0147-53-17

Kutz et al. (2002) Canadian Journal of Zoology 80, 1977-1985.

Kutz et al. (2009) Veterinary Parasitology 163, 217-228.

Scarily accurate climate warming projections

Something interesting spotted on the website RealClimate, via Crikey.

Over 30 years ago, a neat paper by Hansen et al. on climate predictions was published in Science. Climate change, as an impending disaster, was not a big research drawcard, but the authors did graph predictions for warming trends for 2000 – 2100. Recently (as in, a couple of weeks ago), Geert Jan van Oldenborgh and Rein Haarsma revisited the data and presented their results on the RealClimate blog.

image from RealClimate

Given that we now have an additional 30 years’ observations from the dataset published in 1981, van Oldenborgh and Haarsma overlaid the new observations on the original predictive graph. You can see in the picture above: the fat pink line is the observations, versus the black line of the original prediction. They found a lovely congruence to the observations against the predictions – scarily accurate. As they say at the end of their analysis:

To conclude, a projection from 1981 for rising temperatures in a major science journal, at a time that the temperature rise was not yet obvious in the observations, has been found to agree well with the observations since then, underestimating the observed trend by about 30%, and easily beating naive predictions of no-change or a linear continuation of trends. It is also a nice example of a statement based on theory that could be falsified and up to now has withstood the test. The “global warming hypothesis” has been developed according to the principles of sound science.

I really like the last line. This research was done at a time when ‘climate change’ was not a buzzword. Now, it seems that we have a somewhat uncomfortable situation where researchers are hell-bent on adding ‘climate’, ‘climate change’, ‘climate impacts’ etc etc to research proposals in the hope of getting things funded. This usually results in projects being funded that have only a very tenuous link (if any at all) to actual climate change, and IMO potentially damages the climate change ‘brand’ (for want of a better word) when dodgy links to climate are made. Meanwhile, the politicians and the people with actual power to change the way humans go about their CO2-emitting business are more preoccupied with not actually doing anything, lest they get it wrong and climate change turns out to not be a big deal after all. Well, here’s some evidence that suggests that it is a big deal, and it’s coming our way.

Thanks to John, who brought my attention to this by posting the Crikey version on FB.

Philosophising about sustainability

Last night, I watched a documentary about life on Earth with 7 billion people, (called How Many People Can Live on Planet Earth, link) narrated by David Attenborough. It gave a matter-of-fact depiction of the challenges faced by a growing global population in the quintessential Attenborough style. It was interesting to see that many countries such as Japan and some in the eastern European bloc will see population levels fall over the next 50 years, many countries are likely to double, Continue reading

Too much data? Never!

(graph from Berkley Earth Surface Temperature, http://www.BerkeleyEarth.org/)

Climate and climate change have been talking points lately – especially in a political sense, with the whole ‘carbon tax’ thing going on. Something that comes up time and time again, and that I recently waffled on about myself, is that good science on climate and climate change is either not communicated effectively, or drowned out by noisier but less well-informed people. So, the Berkeley Team has put together a very nice and very comprehensive data set and one of the things they’ve found is that climate change is happening (see graph above). Cue shocked gasp. Continue reading