Tag Archives: Research Blogging

With or without you? Species interactions and responses to climate change

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ResearchBlogging.orgReading a pair of papers recently published in PLoS ONE, you might be forgiven for thinking that ecologists don’t know whether or not interactions between species matter. Both examine the effects of climate change on ecological communities — but where one assumes that species in a community are as interchangeable as bricks in a wall, the other concludes that the presence of competitors is pretty important.

First, Stralberg et al. attempt to predict what will happen to the birds of California under projected climate change. They constructed individual models of each bird species’ environmental requirements, and then figured out where those requirements would be met under a range of possible climate change scenarios. They find, not surprisingly, that this produces a lot of never-before-seen bird communities:

Our analysis suggests that, by 2070, individualistic shifts in species’ distributions may lead to dramatic changes in the composition of California’s avian communities, such that as much as 57% of the state … may be occupied by novel species assemblages.

But do species really move across the landscape as independent agents? It’s hard to believe that the do. Every species interacts with others — competitors, predators, prey, parasites — and presumably these interactions have some impact on where that species can survive.


How far can this common crossbill move its range if its favorite food tree doesn’t come along? Photo by omarrun.

That’s certainly what the other paper suggests. Adler et al. tested the effects of altered water availability (as a proxy for climate change: normal, supplemental, or drought conditions) and competition (normal or with competitors removed) on experimental plantings of three different prairie grass species. They found significant effects of both competition and rainfall on the plantings’ growth — although there wasn’t a meaningful interaction between the two factors. (That is, competition conditions didn’t alter the effect of water availability.)

There are actually a lot of studies suggesting that species interactions will be important in determining how communities cope with changing climates:

All of which is to say, we may not know how the species interactions within a particular community will shape its response to climate change, but there’s good reason to think that they will.

References

Adler, P., Leiker, J., & Levine, J. (2009). Direct and indirect effects of climate change on a prairie plant community PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0006887

Pelini, S., Dzurisin, J., Prior, K., Williams, C., Marsico, T., Sinclair, B., & Hellmann, J. (2009). Translocation experiments with butterflies reveal limits to enhancement of poleward populations under climate change Proc. Nat. Acad. Sci. USA, 106 (27), 11160-5 DOI: 10.1073/pnas.0900284106

Post, E., & Pedersen, C. (2008). Opposing plant community responses to warming with and without herbivores Proc. Nat. Acad. Sci. USA, 105 (34), 12353-8 DOI: 10.1073/pnas.0802421105

Stralberg, D., Jongsomjit, D., Howell, C., Snyder, M., Alexander, J., Wiens, J., & Root, T. (2009). Re-shuffling of species with climate disruption: A no-analog future for California birds? PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0006825

Visser, M., Holleman, L., & Gienapp, P. (2005). Shifts in caterpillar biomass phenology due to climate change and its impact on the breeding biology of an insectivorous bird Oecologia, 147 (1), 164-72 DOI: 10.1007/s00442-005-0299-6

Bat-eating tits!

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ResearchBlogging.orgLike pretty much anyone else writing about this, I’m in it for the headline. Well, maybe 30% for the headline — this is also just freaky natural history. A paper in Biology Letters reports that great tits (Parus major — basically big chickadees) will hunt and eat hibernating bats [$-a] if they can’t find other food sources.

The paper reports on ten years of recorded bat-eating by a population of great tits in Hungary, capped by two years of systematic observations and a couple simple experiments. Are the tits hunting bats because other food is scarce? The authors put out birdseed and bacon near the bat cave, and observed that the birds killed many fewer bats. Do the tits use audio cues to find their prey? The authors played a tape recording of bats calling, and watched as the birds oriented to the sound and approached the speaker. There are also a number of grisly photos of tit-killed bats.

This is really the kind of work that attracts most field biologists to science in the first place — a wild, interesting observation that provides an excuse to do some really unusual (and thorough) birdwatching. More complicated science will follow, I hope, like an estimate of the selective advantage this new food source provides to the birds. But it all starts with an incredible story.


You might want to count your fingers after hand-feeding a great tit. Photo by joyrex.

Reference

Estok, P., Zsebok, S., & Siemers, B. (2009). Great tits search for, capture, kill and eat hibernating bats Biology Letters DOI: 10.1098/rsbl.2009.0611

The omnivores’ solution: Tadpoles independently solve a common problem the same way

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ResearchBlogging.orgOne of the key observations in support of evolutionary theory is that similar lifestyles can lead distantly-related living things to evolve strikingly similar traits. Compare an echidna and a hedgehog, distantly related mammals with very similar lifestyles. This kind of convergence can occur on much smaller scales of time and space, too, as a new paper just released online by Proceedings of the Royal Society shows. Its authors demonstrate that populations of spadefoot toads have independently evolved the same response to competition from another toad species [$-a].


Spea multiplicata, the New Mexico spadefoot toad. Photo by J.N. Stuart.

As tadpoles, spadefoot toads (Spea multiplicata) have two feeding strategies: they can be omnivores, feeding on organic debris in the water around them; or carnivores, feeding on aquatic crustaceans and sometimes other tadpoles. The two strategies are linked to a developmental switch — tadpoles that start eating crustaceans develop larger heads, the better to eat their fellows, presumably. This switch is handy in minimizing competition for food with another, related toad species, S. bombifrons. In ponds where S. multiplicata and S. bombifrons occur together, S. multiplicata tadpoles are much more likely to become omnivores, and S. bombibfrons are more likely to become carnivores, than is the case for either species when they’re the only ones in the pond.

This solution to competition might have evolved two ways: it may have turned up once, in a single population of S. multiplicata, which was then able to colonize other ponds containing the competitor; or it may have emerged independently in multiple populations experiencing similar natural selection from competition. The new study’s authors show that the second scenario is more likely by comparing the genetic similarity of multiple S. multiplicata populations to the frequency of their competitors, and showing that competition strength, not genetic relatedness, is the better predictor of how likely S. multiplicata tadpoles are to become omnivores.

References

Pfennig, D., & Frankino, W. (1997). Kin-mediated morphogenesis in facultatively cannibalistic tadpoles Evolution, 51 (6) DOI: 10.2307/2411019

Rice, A., Leichty, A., & Pfennig, D. (2009). Parallel evolution and ecological selection: replicated character displacement in spadefoot toads Proc. R. Soc. B DOI: 10.1098/rspb.2009.1337

That possum you just ran over? It might have saved you from Lyme disease

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ResearchBlogging.orgGrowing up in suburban Pennsylvania, where the most hazardous wildlife not extirpated from our woods is the occasional crazed whitetail deer, there was really only one danger I associated with the outdoors — ticks. Specifically, ticks carrying Lyme disease, a not-very-pleasant bacterial infection that attacks the joints, heart, and nervous system if left untreated. According to a paper released online early in Proceedings of the Royal Society B, my risk of picking up Lyme disease on an excursion into the woods behind my parents’ house may have depended on the diversity of bird and mammal species in those woods [$-a].



Sure, it looks like a giant rat, but that opossum is a walking death trap for disease-carrying ticks. Photos by ricmcarthur and jkirkhart35.

In a way, the ticks that carry Lyme disease are a threat to humans precisely because they don’t rely on us as a regular source for blood. Instead, they feed on a variety of mammals and birds, which allows them to maintain population densities high enough that a human wondering into a woodlot stands a good chance of picking up one or two of the little buggers.

But it turns out that not all of these non-human hosts are equally hospitable for ticks. The new paper’s authors, Keesey et al., caught a range of tick hosts — white-footed mice, eastern chipmunks, gray squirrels, opossums, veeries, and catbirds — and experimentally infested them with ticks. They found a huge range of tick success across the six host species: almost half of all ticks introduced onto mice were able to feed, while only 3.5% of ticks introduced onto opossums were. Most ticks that failed to feed disappeared — they were probably eaten when the host groomed itself.

The authors’ field surveys of ticks carried by these animals in the wild make the difference even more pronounced. Wild-caught opossums carried an average of almost 200 ticks — if that’s 3.5% of the ticks that try to feed on a opossum, then that means each opossum had attracted, and eaten, up to 5,500 ticks!

But the real impact of this result comes into focus in a mathematical model the authors develop to determine the effects of removing each of the six hosts from a woodland ecosystem. Removing intermediately-useful hosts like veeries or catbirds doesn’t have much effect on tick density. On the other hand, if you remove very tick-friendly hosts like the white-footed mice, tick populations plummet. And if you remove opossums, they increase dramatically. This is important because, the authors say, larger mammal species are the first to leave as patches of woodland are reduced to make way for human development — so an early effect of woodland fragmentation may be to reduce or eliminate opossums in that woodland, and boost the density of disease-bearing ticks.

This result goes a long way to fulfilling a proposal the authors made in a 2006 review article, that the diversity of alternative hosts for disease vectors like mosquitoes and ticks may shape the risk they pose to human populations [$-a]. It shows that, even in the relatively tame landscapes of suburbia, the way we humans manage what wildlife remains may have real consequences for our own well-being.

References

Keesing, F., Holt, R., & Ostfeld, R. (2006). Effects of species diversity on disease risk Ecology Letters, 9 (4), 485-98 DOI: 10.1111/j.1461-0248.2006.00885.x

Keesing, F., Brunner, J., Duerr, S., Killilea, M., LoGiudice, K., Schmidt, K., Vuong, H., & Ostfeld, R. (2009). Hosts as ecological traps for the vector of Lyme disease Proc. R. Soc. B, (online early) DOI: 10.1098/rspb.2009.1159

A helpful invasive species?

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This post was chosen as an Editor's Selection for ResearchBlogging.orgIntroduced species can wreak havoc on the ecosystems they invade. But what happens after they’ve been established for centuries? A new study in the latest Proceedings of the Royal Society suggests that, in one case, an introduced species has actually become an important part of the native ecosystem — and helps protect native species from another invader [$-a].



Dingoes (above) control red
foxes, which is good for native
critters. Photos by ogwen and
HyperViper.

The introduced species in question is the Australian dingo, the wild descendant of domestic dogs [$-a] that moved Down Under with the first humans to settle the continent. Today, 5,000 years after their introduction, dingoes are the largest predator in much of Australia, and they were a prominent part of the ecosystem encountered by European settlers. Europeans, like previous waves of human arrivals, brought their own domestic and semi-domestic animals — including red foxes, which prey on small native mammals.

The new study’s authors hypothesized that because dingoes reduce red fox activity both through direct predation and through competition for larger prey species, dingoes should reduce fox predation on the smallest native mammals. At the same time, dingoes prey on kangaroos, the largest herbivore in the Australian bush — and reducing kangaroo populations should increase grass cover, providing more habitat for small native mammals. When the authors compared study sites with dingoes present to sites where dingoes had been excluded to protect livestock, this is what they found: increased grass cover, and greater diversity of small native mammals where dingoes were present.

Recently a news article in Nature discussed ragamuffin earth [$-a] — the idea that human interference in nature has so dramatically changed natural systems that it may often be impossible to restore “pristine” ecological communities. In these cases, some ecologists say, conservation efforts might be better focused on how to maintain and improve the diversity and productivity of the novel ecosystems we’ve inadvertently created. It looks as though the dingo could be a poster child for exactly this approach.

References

Letnic, M., Koch, F., Gordon, C., Crowther, M., & Dickman, C. (2009). Keystone effects of an alien top-predator stem extinctions of native mammals Proc. R. Soc. B, 276 (1671), 3249-3256 DOI: 10.1098/rspb.2009.0574

Marris, E. (2009). Ecology: Ragamuffin Earth Nature, 460 (7254), 450-3 DOI: 10.1038/460450a

Savolainen, P. (2004). A detailed picture of the origin of the Australian dingo, obtained from the study of mitochondrial DNA Proc. Nat. Acad. Sci. USA, 101 (33), 12387-90 DOI: 10.1073/pnas.0401814101

Munger on Milk

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ResearchBlogging.org editor Dave Munger inaugurates his new column on the Seed Magazine website by drawing together RB-aggregated posts about milk — and giving very kind attention to my own recent post about a new study of lactation lactase persistence in European and African populations. (Thanks, Dave!) It looks like the new column will shape up to be another good way to keep abreast of the ever-expanding science blogosphere.

How it does a body good: The selective advantage of drinking milk depends where you drink it

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ResearchBlogging.orgI am a super-powered mutant. For a given value of “super-powered” and “mutant,” anyway: I am an adult human who can drink milk. This is unusual among mammals, but as those (in retrospect, somewhat creepy) PSAs that used to run during my Saturday morning cartoons said, milk has a variety of nutritional benefits, if you can digest it. Which of these is behind the evolution of adult milk digestion in humans? According to a new paper in this week’s PLoS ONE, the benefit you get from drinking milk depends on where you live.

Originally, every human on Earth was lactose intolerant, like most mammals. That is, they lost the ability to digest lactose, the major sugar in milk, when their bodies stopped producing the necessary enzyme lactase after weaning. Then, some populations of humans domesticated milk-producing animals, and this seems to have generated strong natural selection [PDF] for a form of the lactase gene that remains active in adults.


Photo by bensonkua.

In fact, milk-drinking populations in Europe and Africa have evolved “lactase persistence” independently [$-a]. This parallel evolution of a single trait motivates the new study by Gerbault et al. — drinking milk might have different advantages for African pastoralists and Northern European farmers. Milk has two major dietary benefits:

  • It’s generally nutritious as a source of protein and calories, and
  • Lactose can aid in calcium uptake in lieu of Vitamin D.

The main source of Vitamin D, for humans, is sun exposure — the UVB rays in natural sunlight stimulate production of the vitamin. In Africa, close to the equator, it’s easy to get plenty of direct sunlight; but in northern Europe, sunlight is less direct — so it’s harder to produce enough Vitamin D. (This is actually thought to be one reason for geographic differences in human skin color [$-a]: under lots of direct sunlight, dark skin is favored to minimize cancer risk; but under indirect sunlight, light skin is favored to allow more Vitamin D production.)

If the benefit of milk is calcium, not protein, then we would expect adult-active forms of the lactase-producing gene to be common in northern populations, and to decrease in frequency with decreasing latitude. This has been observed in a survey across Europe [$-a] — but while the north-south pattern supports the calcium-benefit hypothesis, it is not conclusive evidence. This is because the same pattern could arise without any natural selection acting on the gene — populations generally tend to be less genetically similar if they’re farther away from each other, a phenomenon called isolation by distance, or IBD [PDF]. In fact, Gerbault et al. find that the north-south pattern of genetic similarity is replicated in genes that probably aren’t under selection arising from life at high latitudes, suggesting that IBD, not selection, is responsible for the pattern in the lactase gene.


Photo by tricky.

For a more conclusive test, Gerbault et al. developed computer simulations of the evolution of early European communities. By simulating populations’ evolution with different strengths of selection acting on the lactase gene, they could estimate how probable a particular value of selection was given the present-day frequency of lactase persistence in the real population — but also take into account the population genetic forces that create IBD. They found that in southern Europe, no natural selection was necessary to explain the present frequency of lactase persistence — but in the north, selection coefficients as high as 1.8% were needed. That is, in northern Europe, lactase persistence is so common that the simulations only produced the observed frequency when people who could not drink milk as adults had, on average, 1.8% fewer children than those who could.

In contrast to Europe, African communities don’t show the same gradual transition from frequent to rare lactase persistence, so IBD is less likely to explain the observed patterns. To explain the frequency of lactase persistence in African populations, the authors compared it to the frequency of pastoralism — and, finding a strong positive correlation, they concluded that lactase persistence evolved in Africa because it allowed shepherds to derive more nutrition from the animals they kept.

In short, widespread lactase persistence evolved in Africa because milk is a good source of protein; but it seems to have evolved in Europe because milk is a good source of bone-building calcium. Human populations on separate continents arrived at the same evolutionary solution, but for slightly different reasons.

Update, 18 October 2009: I’ve submitted this post to the NESCent competition for a travel award for the ScienceOnline 2010 conference in Durham, NC, January 14‐17th, 2010.

Update, 15 December 2009: Ye gads. I won!

References

Diamond, J. (2005). Evolutionary biology: Geography and skin colour Nature, 435 (7040), 283-4 DOI: 10.1038/435283a

Gerbault, P., Moret, C., Currat, M., & Sanchez-Mazas, A. (2009). Impact of selection and demography on the diffusion of lactase persistence PLoS ONE, 4 (7) DOI: 10.1371/journal.pone.0006369

Ingram, C., Mulcare, C., Itan, Y., Thomas, M., & Swallow, D. (2008). Lactose digestion and the evolutionary genetics of lactase persistence Human Genetics, 124 (6), 579-91 DOI: 10.1007/s00439-008-0593-6

Swallow, D. (2003). Genetics of lactase persistence and lactose intolerance Annual Review of Genetics, 37 (1), 197-219 DOI: 10.1146/annurev.genet.37.110801.143820

Tishkoff, S., Reed, F., Ranciaro, A., Voight, B., Babbitt, C., Silverman, J., Powell, K., Mortensen, H., Hirbo, J., Osman, M., Ibrahim, M., Omar, S., Lema, G., Nyambo, T., Ghori, J., Bumpstead, S., Pritchard, J., Wray, G., & Deloukas, P. (2006). Convergent adaptation of human lactase persistence in Africa and Europe Nature Genetics, 39 (1), 31-40 DOI: 10.1038/ng1946

Wright, S (1943). Isolation by distance Genetics, 28, 114-38 Other: http://www.genetics.org/cgi/reprint/28/2/114

Here you see it, there you don’t: What determines species distributions?

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ResearchBlogging.orgFor a year between undergrad and graduate school, I interned with the ecologists at the Western Pennsylvania Conservancy. A fair bit of the work revolved around documenting the locations of rare plants or animals. But “rare” can be relative: common ravens (for instance) were hard to find in Pennsylvania, but much more abundant just over the border in New York. In Pennsylvania, striped maples are so abundant that they can interfere with the regrowth of logged woodland, but in Ohio they’re rare enough to be considered endangered.


Striped maple: rare in Ohio, a pest in
Pennsylvania.
Photo by homeredwardprice.

This, of course, is because Pennsylvania’s human-drawn political boundaries straddle important ecological boundaries, like the transition from raven-friendly Circumboreal forests of New England to the raven-free forests to the south. And you might imagine that, even if there weren’t major topographic features within a particular set of human-created boundaries, there would still be enough climatic changes from one side to the other so that the species present at the southernmost edge of a flat, boring state like Kansas wouldn’t be entirely the same species present at the northernmost edge. That is, if you travel south to north across Kansas, you’ll probably pass a point where the lowest winter temperature becomes too low for some species.

Still, there are probably fewer species whose ranges end within the borders of Kansas than within Pennsylvania. As a paper in the latest Proceedings of the Royal Society attempts to show, this is for the intuitive reason I’ve tried to describe above: while Kansas is comparatively uniform, Pennsylvania is located at a transition between ecological regions. At such transitions, landscapes get complicated — and that complication, the paper’s authors say, is what helps create the boundaries of species distributions [$-a].

To make their point McInnes et al. examine the distribution of bird species across Africa. The broke the continent up into a grid, and scored each grid cell by the proportion of birds present in the square whose ranges had an edge within the cell, a measure they call “impermeability.” The impermeability of a given cell was strongly related to the number of habitat types represented in the cell — and these heterogeneous cells tended to be distributed along the boundaries of major ecological regions, like the Sahara Desert.

That is, species ranges tend to end in areas where desert is shading into grassland, or savanna into forest. Or, to put it another way, one group of species (birds) tend to have range edges that coincide with the boundaries of whole ecological communities. That’s an important observation — but it’s not exactly new. The entire concept of ecological communities arose because it’s obvious there are groups of living things that tend to occur together. McInnes et al. have quantified that observation, but they haven’t really explained it.

References

McInnes, L., Purvis, A., & Orme, C. (2009). Where do species’ geographic ranges stop and why? Landscape impermeability and the Afrotropical avifauna Proceedings of the Royal Society B: Biological Sciences, 276 (1670), 3063-70 DOI: 10.1098/rspb.2009.0656

Finding Joshua tree’s niche

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ResearchBlogging.orgA new Joshua tree study is just out in the current issue of New Phytologist, presenting an analysis of the environments occupied by the two different types of Joshua tree. The results demonstrate that the two tree types mostly grow in similar climatic conditions [PDF], which suggests that coevolution with its pollinators, not natural selection from differing environments, is responsible for the evolution of the two different tree types.

The Pellmyr Lab has been studying the two types of Joshua tree, which are pollinated by two separate, highly specialized moths, for several years now. Previous papers have shown that the two types of Joshua tree, first described in the 1970s based only on their vegetative features, are most strongly differentiated by the shape of their flowers [$-a]; and that, although the two moths are separate species, the two tree types are not fully genetically differentiated [PDF].


Hey, those Joshua trees look kinda
different.
Photo by jby.

The latest paper is a chapter from the dissertation of Will Godsoe, who just received his doctorate last week. It presents an analysis that sidesteps a fundamental problem with studying long-lived, specialized organisms — they’re hard use in fully controlled experiments. To determine whether the two types of Joshua tree really evolved as a result of coevolution with their pollinators, we’d like to be able to eliminate the alternative hypothesis that the two types evolved in response to different environmental conditions. Except for a small contact zone in central Nevada, each tree type occurs in a different part of the Mojave desert, and the two regions do have some broad-scale differences in when they receive precipitation.

Ideally, to determine whether two plants have different environmental needs, you just perform an experimental transplant, growing each plant in the other’s environment to see whether it fares as well as it does at home. This isn’t really possible with Joshua trees, which are pretty tricky to sprout from seeds (I’ve tried), and which, in any event, take something like twenty years to mature. So Will proposed to use niche modeling methods instead. Niche models are statistical descriptions of environments where an organism is known to live, often used to predict where it could live. To build niche models for each type of Joshua tree, Will assembled location data we’d collected over several field seasons in the Mojave, then spent another field trip driving around the desert some more to fill in the gaps — he wanted locations where Joshua trees were definitely growing and where they definitely weren’t, to fully “inform” the models.

Using the location data, it was possible to determine what kinds of climates each Joshua tree type tended to occupy by cross-referencing with existing climate databases, then fitting statistical models to the results. The models produced for each tree type could then be compared — and, for the most part, they’re similar. That is, if you collected seeds from one tree type, planted them where the other type grows, and waited around for a few decades to check the result, you’d probably find that it grew as well as it did in its home range.

So, if differing climates don’t explain the origin of the two types of Joshua tree, does that leave no other possibility but the pollinating moths? Not exactly — there are lots of environmental variables that weren’t available for Will’s niche models, for instance, or there could be a third, completely unknown factor. But this does make coevolution with the moths a more plausible explanation. In light of some of our very latest results — which should be going to press fairly soon — coevolution is looking like a better and better possibility.

Reference

Godsoe, W., Strand, E., Smith, C.I., Yoder, J.B., Esque, T., & Pellmyr, O. (2009). Divergence in an obligate mutualism is not explained by divergent climatic factors New Phytologist, 183 (3), 589-99 DOI: 10.1111/j.1469-8137.2009.02942.x

Godsoe, W., Yoder, J.B., Smith, C.I., & Pellmyr, O. (2008). Coevolution and divergence in the Joshua tree/yucca moth mutualism The American Naturalist, 171 (6), 816-23 DOI: 10.1086/587757

Smith, C.I., Godsoe, W., Tank, S., Yoder, J.B., & Pellmyr, O. (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: Asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x

Sonar gives whales the bends

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ResearchBlogging.orgThe New York Times Magazine has a cover article on human-whale interactions, with special attention to whales’ cognitive, communicative, and social abilities. It’s pretty neat stuff, and I started reading it with the intention of posting something about it with a title along the lines of “So long, and thanks for all the fish.” But, rather than all the whales-as-fellow-sentients stuff, this early aside about the effects of navigational sonar on whales is what actually caught my attention:

The results of the examinations performed on the [beached] Canary Islands whales, however, added a whole other, darker dimension to the whale-stranding mystery. In addition to bleeding around the whales’ brains and ears, scientists found lesions in their livers, lungs and kidneys, as well as nitrogen bubbles in their organs and tissue, all classic symptoms of a sickness that scientists had naturally assumed whales would be immune to: the bends.

That’s right — the bends. As in the harmful effects of a rapid decrease in atmospheric pressure associated with rising too rapidly from deep water to the surface, which can cause gasses dissolved in the bloodstream to come out of solution and form bubbles. Human divers take precautions to avoid “decompression sickness,” but it’s surprising to find that mammals who spend their lives underwater should run the same risk. The idea is that navigational sonar is so irritating or disorienting that it drives whales to the surface faster than is safe, and often kills them.

Naturally, I went to Google Scholar: although the original report of “gas-bubble lesions” in beached whales [$-a] generated some controversy [PDF] at first, the most recent review I could find seems to accept the diagnosis [PDF]:

Although no potential mechanisms can be eliminated at this stage, we highlight gas bubble formation mediated through a behavioural response as plausible and in need of intensive study.

The review cites a number of documented whale strandings closely associated with offshore naval maneuvers, and calls for, among other things, re-evaluating past records of strandings with an eye to whether sonar use may have been involved.

This, of course, is what prompted conservation groups to sue the U.S. Navy for investigation of the environmental impact of navigational sonar; the Supreme Court eventually ruled, regrettably, that the Navy’s need for sonar use in training exercises trumps the requirements of federal environmental law. I’d followed the story when it originally unfolded, but never really understood exactly how whales were hurt by sonar — I think I assumed they were just sort of driven onto beaches. So, my totally non-marine biologist, non-mammalogist reaction: wow. And, ugh.

References

Cox, T.M., T.J. Ragen, A.J. Read, E. Vos, R.W. Baird, K. Balcomb, J. Barlow, J. Caldwell, T. Cranford, & L. Crum (2005). Understanding the impacts of anthropogenic sound on beaked whales. J. Cetacean Res., 7 (3), 177-87

Jepson, P., Arbelo, M., Deaville, R., Patterson, I., Castro, P., Baker, J., Degollada, E., Ross, H., Herráez, P., Pocknell, A., Rodríguez, F., Howie, F., Espinosa, A., Reid, R., Jaber, J., Martin, V., Cunningham, A., & Fernández, A. (2003). Gas-bubble lesions in stranded cetaceans Nature, 425 (6958), 575-576 DOI: 10.1038/425575a

Piantadosi, C., & Thalmann, E. (2004). Pathology: Whales, sonar and decompression sickness Nature, 428 (6984) DOI: 10.1038/nature02527a