Survival of the laziest: does evolution permit naps?
Introducing our blog
Yes, evolution does permit naps, if you ask either of us, or if you could observe the rabbit that parks itself every afternoon under Bruce’s ornamental maple tree. But wait, we're getting ahead of ourselves. We're two scientists that have been inspired by many people, places, and things: Charles Darwin and Miles Davis; fossil grounds in upstate New York and beaches in the Galapagos; Martin Scorsese's "Goodfellas" and George Simpson's "Tempo and Mode in Evolution.” We study the pattern of macroevolution to make inferences about the processes that have produced that pattern. We love biodiversity and working in natural history museums. We're glad to be here, and we're hoping you are too and that you'll stick around as we have open-ended musings and at times back and forth conversations about science, especially paleontology and macroevolution, and its intersection with society and culture. For our first blog post, we're going to focus on some recent scientific research one of us (BSL) was involved with, that connects to our longstanding interests in the history of life and the causal factors that influence evolution and extinction.
As we mentioned, we are inspired by fossil grounds in upstate New York, and both of us, especially Niles, has spent much time collecting fossils there.
but there are many other places to collect fossils.
Introducing our first blog post
One especially prolific set of fossil sites can be found along the southeastern coast of the US. There, one can find an exceptional record of marine invertebrate organisms, especially mollusks, the group including clams and snails, from the last 10-15 million years or so.
Some of the fossilized shells are so beautifully preserved that they look as if the mushy, mucousy denizens that once occupied them just died last month. We turn our attention to such sites and especially those from the state of Florida and nearby environs containing fossils deposited over the last 3.5 million years.
One of the things that has always intrigued paleontologists and evolutionary biologists is understanding why certain species survive and others go extinct. In research conducted by Luke Strotz, BSL, and Julien Kimmig from the University of Kansas, and Erin Saupe from Oxford University http://rspb.royalsocietypublishing.org/content/285/1885/20181292 (hence forth Strotz et al. 2018) we tried to get insight into just this by focusing on how the metabolism or physiology of organisms effects the long term survival of the species they are contained in. There are all kinds of highfalutin definitions of metabolism, e.g.,
that invoke hardcore physico-chemical principles, and if you want to think of it that way, that’s fine. We, however, are just as happy if you think of it like your “get up and go” which sadly sometimes may “have got up and left”. (Thank you Steven Tyler of Aerosmith.)
To survive, sometimes being a sluggard is the best strategy #survivalofthesluggish
What Strotz et al. (2018) found is that the mollusk species that were most likely to survive over the long term contained organisms with statistically lower metabolisms, relative to the ones that went extinct. Note, in general we don’t tend to think of mollusks as having inherently high metabolisms. After all, a synonym for snail is “sluggard” or “dilly-dallyer”, yet some snails (and clams) are more “sluggish” and perhaps really do “dally” more than others. In turn, there is reason to believe from ecological studies of modern organisms that those with lower metabolisms tend to live longer than their high metabolism kin. In short, Strotz et al. (2018) found a direct link from enhanced survival of organisms to enhanced survival of species. This result shows how microevolution can sometimes translate or extrapolate directly to macroevolution (stay tuned for other blog posts where we will discuss how such extrapolation is not always possible). Note, the pattern Strotz et al. discovered his has been termed “survival of the laziest” in some circles, e.g., https://www.usatoday.com/videos/tech/science/2018/08/22/survival-laziest-may-key-avoiding-extinction/37567419/ , LOL!
Now at this point you might be wondering, “how the heck did Strotz et al. calculate metabolic rate values for mollusks that lived 3.5 million years ago?”. It is not as if a long dead, antediluvian snail can be asked to run on a treadmill, but thankfully nothing of the sort is required (further, recall that some of the species that Strotz et al. analyzed are still alive). It turns out that metabolic rates have been calculated for many groups of still living mollusks by other scientists. If you know the taxonomic group a long deceased snail or clam specimen belongs to, its body size, and the temperature it experienced, you can calculate its metabolic rate. Just as metabolic rates have been calculated for various mollusk groups, past ocean temperatures (the mollusks being studied were marine organisms) have been determined by climate scientists such as Harry Dowsett and colleagues at the United States Geological Survey and Stephen Hunter and colleagues at the University of Leeds and are thus also available. In short, the work performed by Strotz et al. builds on and utilizes earlier studies conducted by previous generations of scientists. Also important in this regard are earlier generations of avocational and professional scientists that collected fossil and modern specimens of mollusks housed today in museums. In any event, if you want to learn more about how Strotz et al. calculated metabolic rates please check out their paper: http://rspb.royalsocietypublishing.org/content/285/1885/20181292 .
Hierarchies and evolution
Another way of framing this result is as part of a discussion of hierarchies. As a short, apposite digression, there are “things” (“entities” is the more technical term) in biology that all scientists recognize like cells, organisms, populations, and species. These exist at different levels of organization, in this case listed from lower to higher levels, and lower levels are nested (or contained) within higher levels. For instance, cells are parts of organisms, organisms are subsumed within species, etc. Why do we need to think hierarchically to understand evolution? Here we provide only a brief précis as an answer, but we will return to this topic again in future blog posts. Notice for now that generations of scientists have asserted the importance of approaching scientific (and other) problems hierarchically., e.g:
Each of us has written extensively as to how evolution is the result of interactions between the environment and entities such as organisms, populations, and species. For more on the connections between hierarchies and evolution see this recent book:
and also the following video:
Sometimes evolutionary processes operating at the level of species determines what happens to the organisms contained within them. Other times it is processes acting at the level of organisms that determines the properties of the species they belong to: Strotz et al. (2018) found this was the case in their study system. Further, physiology seemed to be a paramount process. Metabolism and physiology are about energy use and ultimately energy consumption (think especially food and nutrients). Intuitively, having a lower metabolism and using less energy could be seen as a favorable evolutionary strategy, especially during times of environmental change and disruption: at these times less resources and food might be available. Those organisms that need less resources and less food are more likely to survive during such times, and thus the species they belong to are more likely to survive over the long term.
There’s no excuse for being a wastrel
Note, this in no way constitutes an evolutionary (or any other type of) justification for human lassitude. In fact it may be the case that some of those “lazy humans” consume the most resources, foment the greatest climate change, and favor the ever increasing suburban sprawl and clearing of lands to make way for more domesticated animals and plants, that is causing the present day biodiversity crisis: the gravest threat to the existence of so many species, including our own. But, if you’re a lassitudinous mollusk, or a conservation minded human, your future may be bright, and we thank you for doing your part to conserve resources and help make for a better tomorrow.
Ecology and evolution: sometimes separate, often not equal
Another result from Strotz et al. (2018) worth mentioning regarding hierarchies is the pattern they found when they focused on groups of organisms occurring together in ecological assemblages. As already mentioned, the basal metabolic rate of your average mollusk species alive today is lower than that of the average mollusk living 3.5 million years ago. It might perhaps be reasonable to posit a concomitant decline in the energy usage of ecological assemblages of mollusks over the same time interval. But as with so many things that seem reasonable, things don’t always pan out that way. Instead, Strotz et al. found that the total metabolic expenditure of molluskan organisms through time in this region was constant. How can that be, given the demise of more species containing high energy organisms? One possibility is that the total number of organisms increased, even as the number of species fell. If that is the explanation it is as if there is some fairly constant available stream of resources or energy “out there” in the ecological realm. Like there’s a pie of constant size, and one way or another all of that energy is going to get “eaten up” or consumed. One way that “pie” of energy gets totally consumed is by many species that each contain few organisms; another way is if there are few species but each contains a plethora of organisms.
A related phenomenon was uncovered by Elisabeth Vrba in 1987 (Vrba, E.S., 1987. Ecology in relation to speciation rates: some case histories of Miocene-Recent mammal clades. Evolutionary Ecology 1:283-300). She showed, in a comparison of the closely related African antelope and impala clades, that there were many species of antelope, yet each antelope species had relatively few organisms. By contrast, impalas are of low diversity yet are far more abundant. In short, the total number of organisms in each clade was roughly coeval, they were just broken up into different numbers of species.
It just goes to show that ecological patterns and evolutionary patterns are each fascinating yet not necessarily equivalent. Life seems to be broken up into genealogic and economic (or ecologic) actors. The former comprise genes, cells, organisms, populations, species, and clades; the latter cells, organisms, populations, communities, and regional biotas. Sometimes the twain will meet, consider cells, organisms, and perhaps populations. But sometimes they branch apart, like Robert Frost’s roads in a wood, https://www.poetryfoundation.org/poems/44272/the-road-not-taken . One of the obfuscatory aspects of 20th century evolutionary biology was it often assumed that ecology and evolution were like two lanes of the same highway, running in parallel, and leading to the same place. We suspect that’s not the case. And we’ll consider this issue a lot more in subsequent blog posts. But recognize for now that Strotz et al. and Vrba each showed that ecology and evolution are more like two roads in a network, ultimately connected, but leading to different places.
Until next time, take good care, thanks for reading, and try to avoid the blues, unless they’re this kind of blues … https://youtu.be/0fC1qSxpmKo
This blog was written by Bruce S. Lieberman and Niles Eldredge. The current manager of the website is named below.