This new review explains why soft sweeps are the bane — and the baseline — of ecological genetics

(Flickr: andrew)

If you’ve done ecological genetics research in the last decade, you’ve almost certainly cited a series of papers by Pleuni Pennings and Joachim Hermisson, which broke down the problem of soft selective sweeps. Pennings and Hermisson have revisited soft sweeps in a big, detailed new review article for Methods in Ecology and Evolution, which pulls together more than a decade of research following the original studies, and makes a good case that everyone’s favorite excuse for a less-than-dramatic genome scan result is not going away any time soon.

First, what exactly is a soft sweep? Well, it’s a selective sweep that is … not hard. The original papers addressed a couple different ways that natural selection might fail to produce the classic signature of a “hard” selective sweep — in which a single advantageous genetic variant spreads through a population over a few generations, eventually becoming the only variant present — but didn’t quite line them up for comparison. In the new review, Hermisson and Pennings do this very explicitly.

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No, I don’t write for the Genetic Literacy Project (and I never will)

So yesterday I got a notification on Twitter that the Genetic Literacy Project had posted about my pushback on an account of scientific racism published by NPR. Well, nifty, I guess. I’d encountered the GLP before — it’s a news site covering “the intersection of DNA research and real world applications of genetics with the media and policy worlds in order to disentangle science from ideology”. So, great, they wrote something about my post? When I clicked through, though, it turned out to be a ham-fisted edit of my post extracting the gist … annoying, but bog-standard blog-aggregation, no value added. But something about the layout of page caught my attention.

Screenshot from the GLP page. (Google cached version)

That’s my name under the GLP post title, where any respectable news site puts a byline. There’s no other authorial or editorial name on the GLP post page. The date, July 11, is the date of the GLP post, not my original. It does say “Molecular Ecologist”, but there’s no explanation what that indicates from the page layout. If you click on my name, you get an “author” page explaining that GLP posts may be original writing for the GLP, or aggregation-posts. And at the end of the GLP post, there’s a disclaimer to the effect that GLP aggregated the post from The Molecular Ecologist, with a link to the original — but it still doesn’t clarify who did the aggregation. There is no indication, on the post page or elsewhere, as to what human being or algorithm is responsible for the bowdlerized “excerpt” of my TME post … except me.

Call me crazy, but I happen to think my byline has some value, and that it means something — specifically, that when it appears on a post on a website, I had some authorial or editorial role in the creation of that post. (For a post about scientific racism, in particular, I want to be in control of what’s attached to my name!) GLP’s site design obscures that — and after an extended e-mail exchange with the site’s editor, I’m inclined to think that’s deliberate. GLP appears to be quite happy to make it look as though writers all over the web are contributing material for them, without any prior consultation with those writers or the sites where their work is posted.

I’ve lodged my complaints on Twitter and on the comments on the GLP post and in that e-mail back-and-forth, and I will not go on at further length. There’s not a lot more I can do, anyway. A DMCA takedown notice is not really appropriate because, as I noted above, the excerpting of my post itself is pretty standard practice, and probably not a violation of fair use — and some sort of injunction against the use of my name in connection with material I didn’t create seems like overkill, and is beyond both my legal ken and budget. So I’ll simply close out by saying: The Genetic Literacy Project doesn’t understand how authorship and web design works, and any post you see there with my name on it was created without my authorization and against my express wishes.

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#Evol2017 catch-up — or remember that time when someone stole your field gear?

To borrow from our lead in paragraph for post-Evol2017 wrap-ups:

Two weeks after the closing day of the 2017 Evolution Meetings, the Molecular Ecologists have all dispersed from Portland, though items from the Krueger-Hadfield lab didn’t make the return journey! Still, the conference was so big that there’s a lot we missed the first time around — many great talks were scheduled against each other. Fortunately, hundreds of talks were recorded on video and posted online, so it’s possible to go back and catch up with them all. Be sure to check out the great videos on the conference’s well-organized YouTube channel, but, here, I’ll tell a tale of woe …

In the month leading up to #Evol2017, my lab had embarked on some ambitious field sampling down the Pacific coast of North America. It was mostly a reccy to facilitate new lines of inquiry based on natural history. Maybe a few small natural history papers could even come out of it.

If you caught Stephanie Meirmans’ talk (Doing research in the wild: Why does it matter?) on the final day of #Evol2017, she highlighted exactly what this trip was about:

We went out, hoping to stumble over something cool (we did, more about that in the future).

We went to almost 70 sites over 15 days of low tides. That sounds like a ton, but in reality, many sites had nothing for which we were searching or they were very close to one another making it possible to hit several sites in the space of a few hours.

It was amazing, good fun and facilitated by my longest-serving seaweed roadies (my mom and dad), and during the second leg, a grad student at UAB (Sabrina Heiser wrote a post for TME as a #SciComm student).

As I hadn’t planned on attending #Evol2017 this year due to prior commitments to other conferences, I returned to Birmingham for two days before venturing out west again for another few sites of algal adventuring. Field + jet lag can make you sick …

Nevertheless, whither we went, so did the dissecting microscope with which to identify reproductive structures, boots, Falcon tubes, and an herbarium press!

At many other stops along the first legs before the serendipitous #Evol2017 sampling, we’d left the Pelican case (complete with stickers attesting to the scope’s first, of what I’d assumed to be many, outings) and other suitcases in the back of our rental minivan. So, we did the same thing in Portland in what we assumed was a secure hotel parking lot.

Well, you know what happens when you assume …

The Friday night, or technically early Saturday morning, blissfully unaware, we got a good night’s rest before the first full day of #Evol2017. Simultaneously, someone was relieving us of our duffle bag filled with all the goodies, including precious herbarium specimens, and the Pelican case complete with microscope

The next morning, unaware, I went to see some talks. Then, I headed over to the train station to hang out with a colleague who happened to be transiting through Portland.

Then, I found out …

Burglarized …

Microscope, gone.

Pelican case, gone.

Herbarium press, gone.

Boots, gone.

Brand new waders, gone.

Cool drawstring backpack from the Tour of California with pre-labeled Falcon tubes, gone.

Sense of security and opinion of humanity … severely dented.

It was all caught on video … the thief brazenly walked along “casing” cars. Popped the window (it turns out some minivans are dead easy to break into …), climbed in, took our things and went off into the night.

I imagine when he popped the Pelican case open and saw a Leica scope, he was bitterly disappointed to have committed a felony for a scope and some boots and some stinky seaweed drying on paper.

Honestly, I was most upset about the Pelican case. I’d begun to populate the case with stickers of places we’d been. Like, the most amazing fish and chips in Oregon that incidentally has the most amazing stickers. Tangible memories that are not replaceable …

As I thought of the sticker loss (silly as it was), I immediately thought of the herbarium samples. Luckily, I’d had the genetic samples in silica gel in my other luggage. All wasn’t completely lost.

However, those herbarium specimens were destined for my lab’s herbarium, along with the University Herbarium at Berkeley and the Natural History Museum in London once we’d completed some genetic and morphological analyses completed. There were quite a few talks on using herbarium specimens at #Evol2017, such as the talks by Lua Lopez or Kathryn Turner, so the loss of these for future reference was saddening. And, it was such a waste!

It was only a few sites lost in the end, but I’m still angry that someone had the audacity to brazenly take things that weren’t theirs!

The microscope can be replaced.

New stickers will decorate my new Pelican case.

But, the herbarium samples cannot be replaced. They are forever lost in presumably a Portland dumpster somewhere … or maybe now a landfill.

So, if you see these items:

Get in touch … I’ve replaced the scope, but I’d quite like the herbarium samples back!

At least, I’ve progressed to acceptance. I can even find humor in the situation.

And, we’ve learned a lesson … never leave anything in a car, or at the very least as a friend told me today, chain it to the seats.

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#Evol2017 catch-up — Effects of range expansions on mating system

Two weeks (more about that in a post I’ve written for Wednesday!) after the closing day of the 2017 Evolution Meetings, the Molecular Ecologists have all dispersed from Portland, though some may have left things behind! Still, the conference was so big that there’s a lot we missed the first time around — many great talks were scheduled against each other. Fortunately, hundreds of talks were recorded on video and posted online, so it’s possible to go back and catch up with them all. Over the next few days, we’ll highlight some recommendations from the conference’s well-organized YouTube channel

Matthew Koski’s talk on mating system evolution (The effects of historic range expansion on drift load, inbreeding depression, and autonomous selfing) is one I somehow missed.

Patterns of historical migration can influence geographic structuring of the magnitude of inbreeding depression and genetic drift, both of which are correlated with the evolution of mating systems. For example, low costs of inbreeding can facilitate the evolution of selfing, and small populations that experience strong drift are more likely to evolve elevated self-fertilization. Here, we identify clinal patterns of autonomous self-fertilization across 24 populations of the short-lived herb, Campanula americana. Specifically, autonomous fruit set is elevated at the leading range edges, but is low in populations near glacial refugia. We predict that the populations further from glacial refugia that display elevated autonomy also express higher drift load, and have reduced inbreeding depression. In each population we estimated the amount of inbreeding depression and heterosis (drift load) by conducting controlled hand-pollinations, and evaluating the fitness of progeny. We explore geographic patterns of inbreeding depression and drift load, and associate each parameter with the observed spatial variation in autonomous selfing. Our study highlights how genetic structuring following range expansion can affect the evolution of mating systems.

Koski presented work done with Jeremiah Busch and Laura Galloway on when we might expect selfing to evolve. The benefits include the automatic transmission of genes, but the costs include inbreeding depression.

By studying migration from glacial refugia, we can explore how migration may structure genetic loads and mating system variation. At the leading edges, we should expect increased selfing as a form of reproductive assurance (aka Baker’s Law). Thus, we may expect a cline in mating system patterns. As we get further away from the refugium, we should expect to see increasing frequency of selfing.

They studied 24 populations of Campanula americana, the American bellflower, across the North American range.

This species spread from the southeastern part of the continent following the last glacial maximum.

Screen grab of migration schematic for C. americana      © Matthew Koski

They posited three hypotheses:

  1. The leading edge should have an increased capability of selfing
  • They found the northwestern populations exhibited more autonomous fruit set in a common garden with no pollinators. There was, therefore, latitudinal and longitudinal clines in selfing, occurring farther away from the glacial refugium.
  1. The leading edge should have increased drift load
  • Looking at the variation in flower production, the northwestern populations showed evidence of increased drift load, consistent with migration route and selfing capability. However, when they looked at the cumulative drift load and not focused solely on germination, bolting or flower production, the longitudinal pattern dissolved. So, for this hypothesis, Koski gave it a “luke warm” check mark!
  1. The leading edge should have decreased inbreeding depression
  • There was no evidence for inbreeding depression for those leading edge populations.

Thus, the genetic underpinnings of inbreeding depression and drift load may differ. Importantly, the evolution of mating systems will depend on the magnitude of selection for reproductive assurance and inbreeding depression. We can forget to asses the historical processes and their effects on mating system evolution.

Here’s the video with some pretty cool heat maps of selfing!

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NPR’s muddled take on scientific racism and direct-to-consumer genetics

NPR’s science blog Cosmos & Culture has a post up about a new book on scientific racism and population genetics, particularly in connection with personal genetic ancestry reconstruction like that offered by 23andMe and other “direct-to-consumer” (DTC) genetic testing outfits. Now, these are important and complex issues, and we have some interest in them right here at TME, so it was only sensible to take a look. But the post, in which biological anthropologist Barbara King reviews the new book Is Science Racist by anthropologist Jonathan Marks, starts off with a premise that took me aback:

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#Evol2017 catch-up — Wing shape evolution in non-migrating monarch butterflies

A week after the closing day of the 2017 Evolution Meetings, the Molecular Ecologists have all dispersed from Portland. Still, the conference was so big that there’s a lot we missed the first time around — many great talks were scheduled against each other. Fortunately, hundreds of talks were recorded on video and posted online, so it’s possible to go back and catch up with them all. Over the next few days, we’ll highlight some recommendations from the conference’s well-organized YouTube channel.

Micah Freedman’s “Contemporary evolution of monarch butterflies in their introduced range” is a good example of a talk I’d have been excited to see if I weren’t double-booked elsewhere — monarchs have some fascinating natural history, including cool tripartite interactions with their hosts plants and damaging microbial parasites, and recent rapid evolution is a topic that’s been on my radar for a while. Here’s the abstract, with the video following:

Monarch butterflies are best known from their North American range, where they migrate extremely long distances–up to 4,000 km over the lifetime of an individual–to track seasonally available milkweed host plants. Over the past 200 years, monarch butterflies have achieved a nearly global distribution, and can now be found on every major Pacific island group. These introduced island populations are almost all residents (i.e. they breed year-round and do not migrate seasonally). Because each Pacific island population is derived from the ancestrally migratory North American population, these isolated island populations can be treated as replicate exeriments for investigating phenotypic evolution associated with the loss of migration. Here, I present evidence suggesting that Pacific island monarch butterflies are undergoing contemporary evolution associated with the loss of migration. Using a combination of contemporary wild-caught individuals and museum specimens dating back to 1871, I show that monarch forewing morphology is changing predictably across multiple island groups. Specifically, time series data indicate that Pacific island monarch forewings have become both signifcantly smaller and signficantly more round through time. These findings are consistent with (1) relaxation of selection previously imposed by the demands of long-distance migration and/or (2) directional selection for smaller, rounder wings to promote maneuverability. Results are discussed in the context of functional tradeoffs associated with divergent wing morphologies and recently published genomic data that compares migratory and resident populations of monarch butterflies.

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#Evol2017 catch-up: Biome turnover and body size evolution in Australian vertebrates

A week after the closing day of the 2017 Evolution Meetings, the Molecular Ecologists have all dispersed from Portland. Still, the conference was so big that there’s a lot we missed the first time around — many great talks were scheduled against each other. Fortunately, hundreds of talks were recorded on video and posted online, so it’s possible to go back and catch up with them all. Over the next few days, we’ll highlight some recommendations from the conference’s well-organized YouTube channel.

I didn’t see Ian Brennan’s “Late Miocene biome turnover constrained body size evolution across Australian vertebrates” at the meeting, but I really liked the video (clear and beautiful). It’s totally not my field, but I found it super cool. Here’s the abstract from the online program, and then the video.

Climatic trends may influence macroevolutionary trajectories via abiotic and biotic paths. Evidence from mass extinction events suggest rapid climatic oscillations can influence ecological diversification by opening niche space and precipitating adaptive radiation. However, dramatic climatic events represent infrequent deviations from extended periods of protracted climate change and biome turnover. Our understanding of the macroevolutionary impacts of the intervening periods of gradual change remain limited. In contrast to rapid perturbations, gradual climatic change may constrain ecological diversification by making conditions favorable for allopatric and nonadaptive speciation. The degree to which this response is congruent among ecologically different groups also remains unknown. I tested these concepts using a series of fossil-calibrated, species-level phylogenies, and continuous morphological and discrete ecological data for six diverse Australian vertebrate radiations encompassing mammals, birds, and reptiles. To observe temporal trends in the frequency and timing of cladogenetic dispersal events among biomes, and investigate a Late Miocene shift in dispersal patterns, I used a likelihood method for reconstructing ancestral states and modelling cladogenetic dispersal event types (sympatry, allopatry, vicariance). I then compiled body size data for each group, and using maximum likelihood, modelled the temporal trend in body size evolution by comparing standard evolutionary models against novel models which account for a shift in the mode of size evolution in the Miocene. I compared the results of biogeographic and body size modelling, principally temporal shifts in trends, and suggest that coincident timing of changes indicate that Miocene cooling and aridification restricted niche diversification of these diverse radiations. Bounded morphological divergence during the late Miocene coincided with elevated rates of allopatric, particularly vicariant, speciation, characterizing a shift from adaptive to nonadaptive processes during a period of considerable biome transition. These findings suggest that niche evolution can be constrained not only by biotic interactions, but also by gradual abiotic change.

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