Tag Archives: Research Blogging

Arrested development, and reproductive incompatibility, from duplicate genes

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ResearchBlogging.orgSpeciation isn’t something that evolution sets out to do – it just sort of happens. One day, a species colonizes two sides of a river, say, migration across the river drops off, and then a few million years of genetic drift later, there are two species where once there was one. The question is, what’s the final genetic change that makes the accident of speciation irrevocable?

A paper in this week’s Science pinpoints exactly that change. Bikard and coauthors report that, in the little flowering plant Arabidopsis thaliana (the plant world’s answer to white lab mice and Drosophila fruit flies), it only takes one duplicated gene to finalize speciation [$-a]. It’s a clear-cut case of a classic speciation scenario, Bateson–Dobzhansky–Muller incompatibility.


Arabidopsis thaliana
Photo by tico bassie.

It all comes down to gene duplication, which I’ve discussed before in the context of the trouble it gives to genetic analysis. Making copies of an entire genome is an error-prone process, and sometimes a whole gene gets duplicated twice. If that extra copy is inherited, it means that the carrier has redundant coding for whatever the original gene does – so now one copy can mutate without affecting its carrier’s fitness. Often this just results in loss of function for the mutating copy – sometimes it leads to new gene functions. In Arabidopsis, it’s lead to reproductive incompatibility between two strains of the plant that took different evolutionary paths.

Bikard et al. noticed that, when they crossed two strains of Arabidopsis, the resulting seeds didn’t include every possible combination of the parental strains’ genes – and a few seeds grew short, not-quite-healthy looking roots when germinated. Some of the hybrid seeds just died in mid-development. With a lot more controlled crosses, the authors narrowed the candidate genes down to a pair that normally work together in synthesizing the essential amino acid histidine. Each of the two parental strains had working copies of the two genes – but when you crossed them, sometimes the seeds couldn’t produce histidine, and so they snuffed it.

This looked like the above-mentioned (and awkwardly named) Bateson-Dobzhansky-Muller incompatibility [$-a], which is an old idea about how populations evolve reproductive incompatibilities to become separate species. Under B-D-M incompatibility, a new gene evolves in one population that doesn’t work if it interacts with genes from the other. Imagine if Windows users didn’t have to share documents with Mac users: as the two operating systems went through multiple redesigns and their respective versions of Microsoft Office(TM) were revised to keep up, it might no longer be possible to read a Mac-written Word document on a Windows machine.

Here, as Bikard et al. showed, one of the histidine-producing genes in Arabidopsis was accidentally duplicated – and one copy mutated into non-functionality. The catch is that, in the two partially incompatible strains, different copies went nonfunctional. So now, when the two lines are crossed, a small fraction of the seeds produced get nonfunctional copies of the duplicated gene. They die. And where once there were two strains of Arabidopsis thaliana, there’s something a little more like two separate species, all because of what boils down to the flip of a coin.

References

D. Bikard, D. Patel, C. Le Mette, V. Giorgi, C. Camilleri, M.J. Bennett, O. Loudet (2009). Divergent evolution of duplicate genes leads to genetic incompatibilities within A. thaliana Science, 323 (5914), 623-6 DOI: 10.1126/science.1165917

K. Bomblies, D Weigel (2007). Arabidopsis — a model genus for speciation Current Op. Genet. & Dev., 17 (6), 500-4 DOI: 10.1016/j.gde.2007.09.006

Morality and empiricism

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Jerry Coyne reviews two new books, Kenneth Miller’s Only a Theory and Karl Giberson’s Saving Darwin that vivisect the Intelligent Design movement, and seek to explain how Christianity (or indeed, any faith) is not only compatible with but complimentary to the scientific worldview. Coyne is effusive in praise of Miller and Giberson’s science, but he doesn’t buy their theology:

True, there are religious scientists and Darwinian churchgoers. But this does not mean that faith and science are compatible, except in the trivial sense that both attitudes can be simultaneously embraced by a single human mind. (It is like saying that marriage and adultery are compatible because some married people are adulterers.) It is also true that some of the tensions disappear when the literal reading of the Bible is renounced, as it is by all but the most primitive of JudeoChristian sensibilities. But tension remains.

Miller and Giberson make the same fundamental mistake that creationists do, says Coyne, when they look for God in the empirical world.

[To Miller], God is a Mover of Electrons, deliberately keeping his incursions into nature so subtle that they’re invisible. It is baffling that Miller, who comes up with the most technically astute arguments against irreducible complexity, can in the end wind up touting God’s micro-editing of DNA. This argument is in fact identical to that of Michael Behe, the ID advocate against whom Miller testified in the Harrisburg trial. It is another God-of-the-gaps argument, except that this time the gaps are tiny.

I haven’t read either of the books in question (I’m putting them in my queue after Dreams from My Father), but this does sound like a complaint I’ve previously had with prominent scientists who try to reconcile faith and science by direct, causal connections. It seems plain enough to me that a Christian who accepts science must also accept that God is the ultimate in untestable hypotheses, and no amount of speculation about the Anthropic Principle can change this. Furthermore, I think we need to reconcile ourselves to the idea that Homo sapiens might not be the only thing on God’s mind, as it were.

This line of thought draws mockery from fundamentalists on both sides of the religion-science schism. A six-day creationist I met with a few months ago condescended to tell me that, if I wouldn’t join him in rejecting the very laws of physics (which is what you have to do if you want to believe that Earth is six thousand years old), my faith was nothing but “warm fuzzies.” And in his own response to Coyne’s essay, the atheist PZ Myers jeers that Christianity without biblical literalism is “weak tea.” (Got the Christians coming and going on that one, don’t you, PZ?) But what all of these people are missing is that Christianity, and all religions, are not (or should not be) primarily interested in empirical claims about the physical universe. They’re about how humans can best live with each other.

The essence of Christianity, the absolute core of what it means to follow Christ, is a few revolutionary teachings, and one extraordinary act. “Love your enemies,” Jesus taught his disciples, calling them to a moral standard above and beyond the bonds of family, tribe, or nation. And when the Roman government and its local collaborators got nervous about his popularity and executed him as a common criminal, Jesus embodied that moral standard at the cost of his life. You can quibble with every factual claim in the Bible, you can cut out everything in the Gospels that smells of the supernatural as Thomas Jefferson famously did, and that’s what’s left: an innocent teacher accepting death at the hands of civil and religious authorities, and thereby revealing them for the fallible, human things that they are. Vicit agnus noster.

Science can (conceivably, at least) account for the entire history of the universe, from the Big Bang to the invention of digital watches by the ape-descended inhabitants of one small, blue-green planet. But in the end, this is just data. Data can’t tell me whether I should tip the barista at my local coffee shop, or stay late to answer a student’s questions on a lab, or give to NPR, or donate blood. But Christ crucified (Mohamed at prayer, Buddha under the Bo tree, Hume at his books) has something to say about it. The human struggle with the moral universe, the core of all religious thought, is the challenge of a lifetime – every lifetime – and the example of Christ is powerful no matter how many days it took to make the Earth.

The cost – and benefits – of hostility to strangers

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ResearchBlogging.orgBruce Schneier points to an interesting post by Stephen Dubner, who asks why we humans are so prone to fear strangers, given that strangeness is such a poor predictor of dangerousness. Dubner proposes, and Schneier agrees, that it has something to do with our tendency to focus on rare, shocking dangers:

Why do we fear the unknown more than the known? That’s a larger question than I can answer here (not that I’m capable anyway), but it probably has to do with the heuristics — the shortcut guesses — our brains use to solve problems, and the fact that these heuristics rely on the information already stored in our memories.

And what gets stored away? Anomalies — the big, rare, “black swan” events that are so dramatic, so unpredictable, and perhaps world-changing, that they imprint themselves on our memories and con us into thinking of them as typical, or at least likely, whereas in fact they are extraordinarily rare.

That’s probably right. But when I read Dubner’s post, I immediately thought of another factor: hostility toward outsiders is instinctive because it can help communities bond.

This idea actually grew out of an attempt to understand altruism. Altruism is something of a puzzle to evolutionary biologists – the easiest thing to assume, under a “survival of the fittest” framework, is that selfishness is always the winning strategy. Yet again and again in human and nonhuman societies, we see examples of altruism, in which individuals help each other without immediate repayment. Societies in which everyone is altruistic should be able to out-compete societies in which everyone is selfish – but a single selfish person in a mostly altruistic society can out-compete her neighbors, make more selfish babies, and eventually drive altruism to extinction. So, if you can come up with a way to make altruism stable in the long term, you’ve got a good shot at publishing in Science or Nature.


Photo by Lawrence OP.

One such paper was published back in 2007. Co-authors Jung-Kyoo Choi and Samuel Bowles noted that tribal human societies spend a lot of time and blood in inter-tribal wars, and wondered if what they called parochialism – hostility to outsiders – helped stabilize within-tribe altruism [$-a]. They built a mathematical model of competing tribes, in which individuals within those tribes had one of four inheritable personality types: parochial altruists, tolerant altruists, parochial nonaltruists, and tolerant nonaltruists. Parochial altruists were something like the medieval ideal of a knight, willing to fight outsiders and die for the benefit of others in their tribe. Parochial nonaltruists weren’t willing to risk their lives for others; and the two tolerant types were, well, tolerant of others.

As I described above, nonaltruists were favored by within-tribe competition: altruists all contributed toward a common resource pool, which was shared among the whole tribe. So nonaltruists got a share, but didn’t contribute, which benefits them but is ultimately bad for the tribe. Tribes that fought other tribes and won could expand their territories and take the losers’ resources. On the other hand, if tribes interact peacefully, the tolerant individuals – and only the tolerant individuals – received a resource reward. (Is this putting anyone else in mind of certain new-school German board games?)

Choi and Bowles found that their model led to two alternative stable kinds of tribe dominated by either tolerant nonaltruists or parochial altruists. This is almost too tidy, because it looks like a dichotomy between peaceful-but-selfish “moderns” and mutually-aiding, warlike “primitives.” Yet tribal societies really do seem to be more prone to a certain kind of war (more like feuding, really), as Jared Diamond discusses in a 2008 essay for the New Yorker [$-a]. And, even in our modern, globalized society, we are immediately and instinctively suspicious of – hostile to – those different from us. Commenting on Choi and Bowles’s paper in the same issue of Science, Holly Arrow called this the “sharp end of altruism,” [$-a] and wondered how to tease apart the apparent association between altruism to neighbors and hostility to outsiders.

The most obvious option may be to expand our definition of “neighbor.” In a world where an Internet user in Malaysia can see (selected portions of) my ramblings on this ‘blog, maybe I’m less of a stranger than I would be otherwise. That’s not much, really, but it’s a start. The wonderful thing about being human is that, understanding our own tendencies, we can seek to overcome them.

References

H. Arrow (2007). EVOLUTION: The sharp end of altruism Science, 318 (5850), 581-2 DOI: 10.1126/science.1150316

J.-K. Choi, S. Bowles (2007). The coevolution of parochial altruism and war Science, 318 (5850), 636-40 DOI: 10.1126/science.1144237

Stick insects not so excited about sex, apparently

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ResearchBlogging.orgStick insects in the genus Timema have evolved asexual reproduction on five different occasions in their evolutionary history, according to a new study in this month’s Evolution [$-a]. Why? Well, it turns out that from an evolutionary perspective, sex isn’t always a good thing.


A Timema walking stick.
Photo by WallMic.

The problem comes down to the mathematics of evolutionary fitness. Natural selection favors individuals who make more copies of their genes in the next generation – that’s the most basic definition of the “fittest” who survive. In most sexually reproducing organisms, each parent contributes half of the genes necessary to build each offspring. So for every two babies a parent makes with someone else, her genome is replicated once – half for each baby. Consider the possibilities if this parent can instead make a baby all by herself: for each baby, her entire genome is reproduced. That means that, all else being equal, an asexual critter has twice the fitness of a sexual one.

So it makes sense that asexual reproduction might pop up pretty frequently in the evolution of any group, let alone Timema – a mutant who gains the ability to reproduce asexually should be able to overrun a population of sexual competitors with ease. The question turns out to be not, why are some critters asexual? but why are any critters sexual?

One hypothesis is that sex helps in arms races against parasites, by shuffling genes to generate new combinations of defensive traits. This is called the Red Queen hypothesis because the parasite-host arms race recalls the Red Queen’s advice to Alice in Through the Looking Glass, that in looking-glass land, “It takes all the running you can do, to keep in the same place.” Population genetic studies have shown evidence of Red Queen dynamics in some species [$-a], but it’s not clear how widespread they are. Currently, more biologists favor the alternative hypothesis that sex is important in counteracting the Hill-Robertson effect, which prevents useful genes from spreading through a population if they are associated with damaging genes [$-a].

Under either hypothesis, sex is in some sense more useful in the long term than in the short term. That is, an asexual mutant can overrun a population faster than its offspring are killed by parasites or disadvantaged by the Hill-Robertson effect. This conflict should lead to a specific pattern: evolutionary lineages switch to asexuality rapidly if an asexual mutant arises, then die off when parasites or other hazards of natural selection catch up with them. This is what we see in Timema – several species have given up on sex, but all of them have recent sexual ancestors. Not only does giving up sex make life less exciting – it’s probably an evolutionary dead end.

References

M. Dybdahl, A. Storfer (2003). Parasite local adaptation: Red Queen versus Suicide King Trends in Ecology & Evolution, 18 (10), 523-30 DOI: 10.1016/S0169-5347(03)00223-4

P.D. Keightley, S.P. Otto (2006). Interference among deleterious mutations favours sex and recombination in finite populations Nature, 443 (7107), 89-92 DOI: 10.1038/nature05049

T. Schwander, B.J. Crespi (2009). Multiple direct transitions from sexual reproduction to apomictic parthenogenesis in Timema stick insects. Evolution, 63 (1), 84-103 DOI: 10.1111/j.1558-5646.2008.00524.x

Climate change and the food supply

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ResearchBlogging.orgOne of the most-cited effects of global warming is that of rising temperatures on crops – hotter average conditions should lead to warmer, drier conditions, reducing yields in the best growing areas and maybe eliminating them where conditions today are marginal. In this week’s Science, a new study puts some numbers behind that speculation [$-a], and the news is not good.


Photo by Josh Sommmers.

Assembling the results of 23 climate models, authors Battisti and Naylor compare projected temperature ranges for the coming century with the ranges observed in the previous one. By the final decade of the twenty-first century, they say, summertime high temperatures in most of the continental U.S. have a 70% probability of exceeding the hottest summer temperatures ever recorded; in Saharan Africa, much of the Middle East and central Asia, the probability is 90-100%.

To put these numbers into perspective, Battisti and Naylor go to the history books, citing an array of cases in which local high temperatures have disrupted food production, creating regional shortages that eventually impacted worldwide food markets:

By comparison, extremely high summer-averaged temperature in the former Soviet Union (USSR) in 1972 contributed to disruptions in world cereal markets and food security that remain a legacy in the minds of food policy analysts to this day. … Nominal prices for wheat — the crop most affected by the USSR weather shock — rose from $60 to $208 per metric ton in international markets between the first quarters of 1972 and 1974.

Battisti and Naylor end by calling for substantial investment in adaptation measures to prevent “a perpetual food crisis.” Increasingly, this looks like the only practical course of action – although reducing and eliminating man-made greenhouse gas emissions is critical, turning global climate around is going to be like steering an aircraft carrier, and it’s going to get pretty warm before we turn the corner.

Reference

D.S. Battisti, R.L. Naylor (2009). Historical warnings of future food insecurity with unprecedented seasonal heat Science, 323 (5911), 240-4 DOI: 10.1126/science.1164363

Evolution applied: Biological warfare against mosquito-borne disease

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ResearchBlogging.orgThis week’s issue of Science starts the new year with an exciting application of evolutionary dynamics: a sort of biological warfare agent to control disease-bearing mosquitoes.

Even in the twenty-first century, mosquito-borne diseases like malaria and Dengue fever remain major public health challenges, particularly in the developing world. When vaccines are not available, the only way to prevent these diseases is to control the mosquitoes that spread them. Yet mosquito populations have evolved resistance to commonly-used pesticides, and others, like DDT, have dangerous environmental side effects.


Aedes aegypti, a disease-bearing
mosquito species
Photo by dincordero.

It’s no wonder, then, that biologists are interested in ways to harness evolutionary population dynamics to reduce mosquito populations. McMeniman et al. take a big step toward this goal using the parasitic bacterium Wolbachia [$-a]. Wolbachia, which infects many other insect species, behaves like a “selfish gene” within its hosts. The bacterium is transmitted from females to their offspring, but not from males; so it induces infected females to lay more female eggs, and it kills the offspring of matings between infected males and uninfected females. This lets Wolbachia spread rapidly through populations, even if being infected is bad for the host.

Using Wolbachia against mosquitoes is not new; previously, people have discussed using genetically engineered forms of the bacterium to deliver agents that fight the diseases inside their carriers. But as McMeniman et al. describe, infection of the Dengue-bearing mosquito Aedes aegyptes actually already cuts the lifespan of the host in half. The Dengue pathogen needs time to incubate inside the mosquito host before it can be passed on to a human – longer, it turns out, than Wolbachia-infected mosquitoes typically live.

With this discovery, controlling Dengue or malaria could be as simple as introducing Wolbachia-infected female mosquitoes into at-risk areas, and monitoring the infection’s spread. Together with common-sense public health measures like distributing mosquito nets and reducing standing water sources, Wolbachia has the potential to save and improve millions of lives.

References

C.J. McMeniman, R.V. Lane, B.N. Cass, A.W.C. Fong, M. Sidhu, Y.-F. Wang, S.L. O’Neill (2009). Stable introduction of a life-shortening Wolbachia infection into the mosquito Aedes aegypti. Science, 323 (5910), 141-4 DOI: 10.1126/science.1165326

A.F. Read, M.B. Thomas (2009). MICROBIOLOGY: Mosquitoes cut short Science, 323 (5910), 51-2 DOI: 10.1126/science.1168659

Shrikes take their cues from the competition

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ResearchBlogging.orgOver evolutionary time, the easiest way to deal with a competitor is to do something different – if your competitor eats big seeds, say, it may be easier to start eating small seeds than to fight for the big ones. This idea goes all back to the Origin, wherein Darwin proposed that competition drives evolutionary diversification, with living things dividing up available resources into ever-finer slices as they scramble for shares:

Lighten any check, mitigate the destruction [of offspring] ever so little, and the number of the species will almost instantaneously increase to any amount. The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force.

But what if competition can sometimes make competitors more like each other? A new study, published through PLoS ONE this week, shows that red-backed shrikes prefer to set up hunting territories in places where their competitors have already been hunting.


Photo by phenolog.

Shrikes are cute but vicious predators – they capture small prey and spear them on thorns or twigs for storage, or to indicate to a prospective mate what great hunters they are. Red-backed shrikes migrate from Africa to Eastern Europe for the summer mating season. When they arrive, male red-backed shrikes must establish a hunting territory with a nesting site, but they have to contend with the established territories of great gray shrikes, which live in the same area year-round, and eat the same kind of prey.

You might expect, then, that red-backed shrikes would establish nest sites well away from the impaled victims of great gray shrikes. In fact, as the paper’s authors show, red-backed shrikes are more likely to nest near great gray shrike caches. They don’t raid the competitors’ larders, but, the authors argue, understand the presence of a great gray shrike’s cache to mean there is plenty of prey nearby.

This could mean a number of things: perhaps great gray shrikes and red-backed shrikes prey on critters that are so abundant, it’s arguable that they’re not really competing. If that’s the case, it makes plenty of sense for red-backed shrikes to use great gray shrike caches as cues to find particularly good hunting grounds. Alternatively, red-backed shrikes settling near great gray shrike caches might shift their prey preferences to avoid competition – the presence of one type of prey may very well correlate with the abundance of many other types, so that the great gray shrike caches are only indirect indicators of prey abundance. Unfortunately, the current paper has no data comparing prey preferences of red-backed shrikes nesting nearby and away from great gray shrike caches, so there’s no way to test this hypothesis.

Still, this observation has significant implications for the way we think about species interactions across evolutionary time. If competitors can be drawn together as well as driven apart, maybe competition doesn’t contribute to diversification as much as we think it does.

Reference

M. Hromada, M. Antczak, T.J. Valone, P. Tryjanowski (2008). Settling decisions and heterospecific social information use in shrikes PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003930

Vikings brought violence, destruction – and mice

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ResearchBlogging.orgTraveling groups of humans are really mobile ecosystems, as we bring with us a whole collection of species we find useful, and not-so-useful: domestic animals, crop plants, pests, diseases, and parasites. Even if we fumigated our clothes and our vehicles, we’d still bring with us a whole collection of intestinal microbes. If you knew nothing more about humans than this, you could reconstruct our historical movement from the changes we’ve made to the living communities around us.


Photo by Pehpsii.

This is one thesis of a new paper in Proceedings of the Royal Society, which shows that the population genetics of house mice in the British Isles still bear the mark of medieval Viking raids. It’s an extremely simple result: in sites especially subject to regular Viking depredations, the northwestern coasts of Scotland and Ireland, the house mice are more closely related to house mice in Norway than they are to mice from other parts of Britain. It’s not clear whether this is because the Vikings brought the first house mice to these areas, or whether stowaway mice from Norway interbred with an already-established population. House mice were in Britain well before the Vikings came along, but human settlements along the northwestern coasts apparently weren’t established much before the Vikings started raiding them.

The authors propose expanding a survey of mouse genetics in Europe to better document the extent of Viking travel. It’s one more biological tool for archaeologists, reconstructing the past based on what we leave behind.

Reference

J.B. Searle, C.S. Jones, İ. Gündüz, M. Scascitelli, E.P. Jones, J.S. Herman, R.V. Rambau, L.R. Noble, R.J. Berry, M.D. Giménez, F. Jóhannesdóttir (2009). Of mice and (Viking?) men: phylogeography of British and Irish house mice. Proc. R. Soc. B, 276 (1655), 201-7 DOI: 10.1098/rspb.2008.0958

Snail trails lead toward speciation

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ResearchBlogging.orgFinding a mate is at the top of just about every to-do list in the animal kingdom. This might involve following the smell of pheromones or triangulating the source of a mating call; in the snail Littorina saxatilis, it turns out to require tracking your beloved by the trail of her slime [$-a].

That’s according to a paper in the latest issue of Evolution, in which Kerstin Johannesson and coauthors took video of male and female snails to catch slime trail-following in action. And it occurred to them that slime-following could be a component of speciation in L. saxatilis. This particular snail comes in two forms, or “ecotypes”: a small one that lives in the crevices of exposed rock faces and a larger one that lives in quieter, sheltered pools. When Johannesson et al. presented male snails with slime trails from each ecotype, the males preferred to follow trails made by females of their own ecotype.

This is what’s called assortative mating – preferentially mating with similar individuals – and it’s usually thought of as a first step towards speciation. Whether L. saxatilis ever eventually evolves into two species is another question, though. The world is full of experiments in speciation, where adaptation to local conditions or difficulty moving between populations can cause a species to begin diverging. But it’s just as likely that the forces pushing a species apart will change or disappear, and diverging groups re-merge into a single interbreeding population. Part of the fun of studying the natural world is finding things like snail’s slime trail discrimination, and trying to figure out what will happen next.

Reference

K. Johannesson, J.N. Havenhand, P.R. Jonsson, M. Lindegarth, A. Sundin, J. Hollander (2008). Male discrimintation of female mucous trails permits assortative mating in a marine snail species Evolution, 62 (12), 3178-84 DOI: 10.1111/j.1558-5646.2008.00510.x

Acorn shortage? Maybe …

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ResearchBlogging.orgThe Washington Post reports that this fall’s acorn crop is apparently very poor, at least in parts of the Eastern Seaboard. There are lots of interviews with naturalists concerned about starving squirrels:

For 2 1/2 miles, Simmons and other naturalists hiked through Northern Virginia oak and hickory forests. They sifted through leaves on the ground, dug in the dirt and peered into the tree canopies. Nothing.

“I’m used to seeing so many acorns around and out in the field, it’s something I just didn’t believe,” he said. “But this is not just not a good year for oaks. It’s a zero year. There’s zero production. I’ve never seen anything like this before.”


Photo by Martin LaBar.

Accompanying the article is a photo of a northern flying squirrel, a species so cute that Disney is probably trying to copyright their genome. There is, however, no reference to a systematic survey of acorn production in any of the areas affected. As the saying goes, the plural of anecdote is not data.

That might sound like a picky thing to ask for, but without hard numbers we have no way of knowing whether this really is an unusually bad year for acorns. Oaks are masting species, meaning that their seed production varies a lot from year to year. It’s been suggested that this is actually a defense against seed predators [$-a], such as squirrels. In “mast” years, trees produce a huge seed crop, and seed predators cache more seeds than they will eventually eat, so that some seeds survive to sprout. Masting works for long-lived trees because an oak that lives for decades can afford to take a year off from reproduction every so often, if it means that when it masts a larger fraction of its seeds survive to adulthood.

So it’s hard to say whether this acorn shortage is unusual. If it continues two years in a row in the same regions, that would be surprising. Of course, by that time, populations of cute seed predators may have already declined precipitously. Common squirrel species are probably in no real danger, but critters like flying squirrels and anything else that can’t make a living on suburban bird feeders could be in trouble.

Reference

D.H. Janzen (1971). Seed predation by animals. Annual Review of Ecology and Systematics, 2 (1), 465-92 DOI: 10.1146/annurev.es.02.110171.002341