Macrobrachium ohione, by Clinton and Charles Robertson, via Flickr.
The Mississippi River that we know today is a creation of the army corps of engineers. Before they got to levying, dredging and damming it into submission, it was a wild and meandering thing that harbored great concentrations of wildlife. One component of that was a massively abundant shrimp with an amazing life cycle:
It turned out that in pre-colonial times the shrimp traveled all the way north into the upper reaches of the Mississippi’s main eastern tributary, the Ohio River, and back again – a 2,000-mile round trip. It was a journey more amazing than similarly epic migrators like salmon. For whereas adult salmon may have an equally long journey to their upstream spawning sites, it is the quarter-inch juvenile shrimp that swim and crawl 1,000 miles upstream against the strong currents of the Mississippi.
What happened to these shrimp? Go read the story to find out.
Environments can vary substantially in habitat quality, local population abundance, or carrying capacity. Under some climate change scenarios, new, higher quality habitats become available along the margin of a species’ range (e.g. higher latitudes or altitudes) (Thomas et al 2001). These new habitats may be able to support larger population sizes. Factors of demography, evolution, and qualities of the abiotic and biotic communities all interact to determine where a species is found and may influence the ability of a species to expand its range. New research is building genetically explicit models in order to understand how the interplay of these different factors influence evolutionary changes,
The authors of a recent study focus on how the interaction of the demographic process of range expansion changes the way that natural selection favors beneficial and deleterious mutations (Peischl et al 2013). Using both computer simulations as well as mathematical approximations, the authors find that at the range margins, individuals carry a substantial load of deleterious mutations.
I, until very recently, believed that there were two types of people in this world – those who accept the theory of evolution and those who do not understand the theory of evolution. In my mind, it was impossible to be presented with the overwhelming evidence for and beautiful simplicity of The Theory and not be convinced. Yet, a small, informal survey of sophomore-ish biology majors here at LSU revealed only 35% responded with “Evolution” to the question: What are your feelings/beliefs about how we, as humans, came to exist on Earth? To be fair, the highest category was “Some mix of evolution, creationism and intelligent design”, which really means only 23% of respondents did not include evolution. These numbers are much better than our national average: Miller et al. (2006) conducted a multinational survey that showed nearly 40% of Americans deem evolution “false”. This makes us second from the bottom (out of 34 countries!) in acceptance of evolution – right below Cyprus and above Turkey.
Small informal survey of undergraduate science majors.
As it turns out, I have overlooked a third type of person: a person who can be exposed to a well-supported argument for an uncontroversial scientific consensus and reject it. These people are a major source of science denial. Rosenau (2012) published an amazing and concise review this week in Trends in Microbiology that discusses science denialism and how it’s more about identity and social groups than scientific facts.
It’s already the third day of concurrent sessions a Evolution 2012, and I’m starting to get science overload. And I still have to present my own science tomorrow! But here are some more cool results I saw Sunday and Monday:
Vera Domingues presented a study of beach mice, which have evolved lighter fur after colonizing the sandy dunes of barrier islands off the Gulf Coast. As in many other animal species, a mutation at the pigment-related locus MC1R explains a lot of the color change; Domingues showed that in the population of barrier island mice, every copy of the mutant, “light color” form of MC1R is descended from the same ancestor, and that DNA sequence near the mutation resembles sequence from the ancestral population on the mainland—which suggests that the original mutant predates the move to the barrier islands.
Richard Lankau showed how garlic mustard, an invasive weed in the United States, uses chemical warfare to out-compete native plants. Garlic mustard secretes chemicals into the soil that suppress the growth of other plants, and alters the environment for beneficial mycorrhizal fungi—and plants grown with competitors produce more chemicals. But native plants can adapt; samples of a native competitor collected from sites invaded by garlic mustard were better able to survive near the invader than plants from non-invaded sites, and were less able to benefit from mycorrhizal fungi in soil that hadn’t been exposed to garlic mustard chemistry.
Some highlights from the first day of concurrent sessions in the Ottawa Convention Centre, on Saturday the 7th:
Mohamed Noor described the importance of chromosomal inversions—literally, chunks of DNA code that have been flipped end-to-end within the chromosome—in reproductive isolation between two species of Drosophila fruit flies. Inversions have the interesting effect of preventing recombination from breaking up groups of genes within the inversion; but some recombination is still possible, if very rare, and it should create predictable patterns of genetic divergence across the inverted region.
Most of the major phenotypic differences between Drosophila pseudoobscura and D. persimilis map to three regions that are inverted in one species relative to the other—Noor presented work from his lab that finds very fine-scale differences in genetic differentiation across the inversions, consistent with predicted variation in recombination. In a much-retweeted line, Noor pointed out that it’s possible to think of species as “groups of alleles in long-term association.” Chromosomal inversions being one way to help maintain those associations, plainly.
This post is a guest contribution by Kathryn Turner, a PhD student at the University of British Columbia, who studies the evolution of invasive thistles. Kathryn writes about her scientific interests at the slyly named site Alien Plantation and tweets under the handle @KTInvasion.
Invasive species are a big problem. A real big problem. In the US alone, invasive species cost nearly $120 billion in damages per year (Pimentel 2005). 42% of species on the Threatened and Endangered list are there primarily because of invasive species.
Which leaves us with two questions. First, most obviously, how is it that a species is able to come into a new environment that it is not adapted to, surrounded by new environmental conditions and foreign biological interactions, and thrive? Thrive so exaggeratedly, that it can out-compete and displace species which have been there for millennia, adapting precisely to those environmental conditions and biological interactions? How can an individual survive to propagate a population? How can any species accomplish this? Second, less obviously: why can’t more species do it? Humans transport animals and seeds (and spores and larvae, etc, etc) around all the time, but only 10% establish self-sustaining populations, and only 1% spread to new habitats, becoming potentially invasive; this is known as the ‘tens rule’ (Williamson 1993) – a funny ‘rule of thumb’ for which I could never quite figure out the math.
For those of you who don’t dabble* in genetics, we’re in the midst of a major revolution. New technologies have literally transformed the questions we can ask and the data we can gather. It is currently possible (although not always advisable) to collect hundreds of gigabases (that’s 10^11) of data in a single run of a “high-throughput sequencer” (HTS). As a reference, I think there were 10^5 bases in my entire master’s thesis which, let me do the math, means one run on a HTS is equivalent to 1,000,000 of my theses?!?! Although that makes me a little queasy, it’s obvious and amazing progress.
Anyway – what can we do with these awesome new technologies? Coghlan et al. have found novel use, published in a recent PLoS Genetics.
"Bear Bile Crystals". One of the samples genetically audited for illegal and harmful components. From Figure 1 of Coghlan et al. (2012).
Traditional Chinese medicines (TCMs) have been used to remedy maladies for thousands of years. The popularity of TCM as a primary, secondary or supplementary medical practice has grown to the point where it is a multi-million dollar industry. TCMs rely heavily on plant and animal components – some of which can come from highly endangered (and thus illegally acquired) species or be harmful to the user. However, determining exactly what’s in a pill or powder isn’t as easy as reading the label.
HTS to the rescue!
- Bighorn sheep (Ovis canadensis) at Glacier National Park in Montana. Photo by Noah Reid.
As humanity spreads out over the globe, finding ever more clever ways to domesticate wild landscapes and harness natural processes to its will, many species of wildlife find their natural distributions becoming fragmented. Iconic North American species such as grizzly bears, red-cockaded woodpeckers, and the American burying beetle today inhabit only small fractions of the ranges they occupied only 100 years ago. A result of this fragmentation is that many individuals exist in small, isolated populations. In these populations, a curious phenomenon often emerges, one that can only be understood in light of some basic evolutionary theory. That phenomenon is known as inbreeding depression, and it refers to the decline in average fitness of individuals in a shrinking population.
Inbreeding depression is essentially a result of individuals in small, isolated populations being more likely to mate with close relatives. It’s well known that mating with close relatives produces less fit offspring, and the aggregate effect in natural populations is seen as low average fitness and an ensuing low population growth rate. This can be a serious problem in populations subject to conservation efforts because even after protective measures have been taken (removing threats, restoring habitat) recovery can be hindered by inbreeding depression. Inbreeding depression is slightly more complicated than this, however, because it is not consistently seen in all small populations. In some island populations with very small population sizes (such as the Chatham Robin, Petroica traversi) inbreeding depression has not been observed (Jamieson et al. 2006).