Good evening all,
I read a lot of science each week. More accurately, I scan a lot of science journal Tables of Contents, and science news headlines, and I select articles to read from them. Throughout the term, I will occasionally send you links to articles, along with a short 'blog' about why I think the article is worth sharing.
The article whose link I am forwarding below describes a recent study, whose primary finding may seem, at face value, insignificant. In this study, scientists monitored multiple (several thousand) neurons in the brains of fish, which they had trained to left, or right, in response to a sensory cue. Then, analyzing the neural recordings they had obtained, they could predict (from the neural data they collected) which direction the fish would turn, up to 10 seconds before the turn.
Wow, right? They can predict whether a fish turns one way, or the other. It doesn't sound like much. But, it is a useful result, for a number of reasons.
Experiments like this are designed to assess decision-making, something that our brains have to do an incomprehensible number of times each day. Sure, we make many 'big' decisions, conscious ones, including many with life-altering consequences (like staying in our lane on the freeway). But, we make untold more smaller decisions, many unconsciously, steadily throughout the day. Think of something like typing, or writing - each letter requires a series of motor actions, in order, that have to planned and executed, against a background of many alternative movements that are possible. That's a lot of decision-making, even just to write or type a single word. How do our brains accomplish it? What can go wrong to impair decision-making? What can we do when that happens? Each of these 'big questions' must be addressed in tiny pieces, like in the study described here.
In the neuroscience research community, there are lots of different experimental models for decision-making. Larval zebrafish do not seem like an obvious choice, but they offer several specific advantages. They are small, easy to breed and house. They are relatively low on the 'scale' of vertebrate animals, such that their use raises relatively little ethical concern. Importantly here, they (1) readily learn this simply task, (2) reliably report their decision, and, (here's the big one) have brains that are small and nearly transparent. This allows researchers to monitor essentially every neuron at once, which is quite remarkable. (Remember - these are free-swimming animals, less than a cm in length, with *tiny* brains.)
Most studies of decision-making in mammals focus on the frontal cortex. Neurons there are engaged in decisional tasks, and damage to this cortex impairs decision-making (causing slower, and often faulty, performance). This new study suggests that decision-making activates neurons across the entire brain, including in areas thought to be primary reflexive, or involved in motor coordination (like the cerebellum). It's an interesting result, and one that will cause those who focus narrowly on one region or another to take a step back, and evaluate their scope of investigation.
The second primary advantage of a model system such as this is that a system of only 5,000 neurons is one that can be computer-modeled in its entirety. We may not have all of the information about how these neurons are connected, or their individual biophysical characteristics, but we definitely have the computing power to incorporate all of them into a single model. They are multiple, ambitious projects to map and model the human brain, but they remain limited both by data as well as by computing power. The more we learn about the brain, the more we realize that neurons across the brain seem to be involved in collective networks. That's a much harder nut to crack than a group of neurons in one location being solely responsible for some singular function.
So, the next time you see even the simplest of organisms behave, such as a fly taking-off or landing, recognize that its nervous system is performing functions very analogous to our own!
I will occasionally pass along articles of this type during the semester. My purpose in doing so is to help you to become more aware of current neuroscience topics, and also to help you assess how you obtain your science and health news.
Those of us working in science obtain our scientific news, quite often, directly from the original sources: the people conducting the studies and reporting the results. They publish their findings in science journals, or present them at conferences.
Most people do not obtain their science news directly, but hear news via secondary sources, such as news releases from scientific organizations, or as science news stories from the major news outlets. These secondary reports often are then carried by tertiary outlets (smaller/other reporting sources). I'd encourage you to think a little about the translation of news from source to consumer, and the reputability of the news outlets that you use.
Along the way from source to audience, science news is normally distilled (a lot) - much of the detail is excluded or simplified, and the reports often are boiled-down to singular take-home messages, which may, or may not, be good representations of the original work. When you browse the links that I will forward, or when you access science and health news on your own, I'd encourage you to delve a little bit deeper into them, to read more than just the summaries, and to follow links back to original sources when possible (like this one: https://www.cell.com/cell/fulltext/S0092-8674(19)31380-7). Some of these ultimate sources will be behind paywalls, but others will be accessible, especially if accessed via an IUP campus computer. If you ever really want to chase down one of the source articles and cannot, let me know and I can help you get to it.
Some of the science and news sources whose links I will forward allow only a handful of free articles each month; I will try to use them sparingly. I also will generally send reports only from sources (professional societies and reputable science and news outlets) that I trust.
The material that I send you as science news will not specifically be represented on our course exams, but I do hope that the material in them makes its way into our conversations.
Have a great rest of the weekend -
Good evening all,
We've made it a point several times during class this term to highlight how behavioral knowledge could be applied to conservation efforts. Here's a link to a recent (and lengthy) discussion of how captive breeding in cheetahs has been enhanced by applying more-naturalistic methods than simply pairing together single males and females. It's quite striking the lengths to which breeders have gone in order to improve the success rate of their breeding programs!
Good morning all,
Hot off of the presses - new information on the genetic basis of avian migratory behavior, a topic we have considered in class. Here, researchers believe that they have identified a single gene on one of the avian sex chromosomes that is linked to specific migratory targeting in warbler species of conservation concern. Interestingly, this avian gene is related to a human gene thought to be associated with movement.
This is a good example of the current state of much of the study between genetics and behavior. Through large-scale genomic analyses, it is possible to identify associations (correlations) between individual gene variants and particular aspects of behavior, but there is much to be learned "in the middle" - how does any one gene, and its gene product, mechanistically contribute to behavior? Or is the association identified in first-order analyses spurious, or non-causal? There is plenty of room for further work, as these researchers note.
Good luck with all of your remaining exams -
As part of our discussions of sociality for Thursday, we'll need this short reading. It suggests that passenger pigeons, which once numbered in the billions, were driven to extinction over the course of a few decades in part because their large population size made them more at risk from extinction than if they had existed in smaller populations. This argument is directly counter to what we normally think of, in terms of how population size relates to extinction risk.
The article references a piece of original scientific literature, linked here:
Good morning all,
As I noted on Tuesday, we will not meet for lecture today. We have only one textbook chapter remaining, which we will save for our first meeting after the Thanksgiving break.
Instead of lecture today, I'll offer you a reading instead, one that encompasses several of our recent topics. In recent classes, we have considered the degree of cooperation and conflict between reproductive partners, as well as the signaling that occurs to influence each other. When sexual investment is strongly different between the sexes, we expect that sexual selection can drive exaggerated displays, enhance female 'choosiness' of mates, and promote unequal reproductive tactics. But, curiously, sexual displays also are common within pair-bonded species, in which males and females have equal (or nearly equal) roles and should be in cooperative agreement over parental investment, rather than in conflict. An explanation for this paradox has been lacking.
A very recent paper sheds some light on this problem, and present a mathematical model which supports the idea that inter-sexual signaling displays which originate to exploit a sensory bias in the signal receiver can evolve into a cooperative exchange, suggesting that sexual conflict can morph into sexual cooperation. This has significant implications for parental investment and care, as we've noted that the degree of sexual conflict is one of the primary drivers of sexual dimorphism in parental investment.
This paper was published in the Proceedings of the National Academy of Science (PNAS), our national body of 'science experts'. Election to the Academy is reserved for the top thinkers in one's field, and is a prestigious badge of honor. Their Proceedings journal publishes papers submitted by Academy members, as well as those that Academy members recommend for publication.
If you access this link from an IUP campus computer, you can obtain access to the full article and its associated material, through IUP library subscription. If you try to access the article from off-campus, you will be blocked. I've attached the PDF of the article, just in case.
The math of the authors' model is well beyond us. If we accept their model as being sound, it suggests that, instead of females being 'lured' into over-investment in their offspring by male displays, females instead evolve to require (or at least benefit from) the male display in terms of stimulating female condition/motivation to a level of investment which is optimal for the female (but less than that which is maximally optimal for the male). This causes males to remain invested in the pair-bond and their role in parental investment, and reinforces the pair-bond between mating partners. In a sense, the females are now requiring the males to remain present, remain attentive, and to offer displays, in order to ensure that their female partner is providing enough investment of her own.
As do many science journal, PNAS occasionally offers peer commentary on papers which are especially important, or especially difficult (this one is perhaps both). The associated commentary on this paper (link below, PDF attached), describes this result in the context of dove mating pairs, for which male stimulation of female reproductive condition is a well-understood and very necessary component to the reproductive cycle. Interestingly, as the commentary notes, the capitulation of this male-female exchange may ultimately be female self-stimulation of reproductive condition, a result which has been suggested to occur in doves. That may be the current evolutionary end-point to this exchange, but it also has the potential to serve as a type of an "escape clause", which males may now be selected to exploit. It would be interesting to see how much variation exists in this end-point, and whether males can benefit from females which perform more of their own reproductive stimulation.
I hope that you find this article interesting - it represent a nice, theoretical treatment of a difficult (= interesting) problem, and should set the stage for experimental work to come.
I hope that you all have an excellent Thanksgiving break - please be safe, rest, relax, eat, and enjoy. See you early in December for our last chapter.
As I mentioned in lecture on Tuesday, we are caught-up with our lecture material and will not meet for lecture on Thursday. Instead, I am offering a reading (attached) that I had described earlier, along with some explanation of one of the more important points described in this study.
Last weekend, I sent to our class description (below) of a recent publication examining behavioral-genetic associations in domestic dogs. I hadn't yet seen the original research when I wrote to you last weekend, but forwarded a news report about it that came from the home institution of the senior author on the study. I described in my message to you that some of the behavioral-genetic associations the authors reported were as high as 0.7, near to the limit of those ever reported for narrow-sense heritabilities of behavior.
Over the weekend, I requested a copy of the actual research paper from its senior author, and, upon seeing it, wanted to offer some interpretation.
Early in the term, in chapter 03, we discussed trait variation within species, and we noted (using the canine example) that artificial selection has created an abnormally high amount of trait variation within the single species of domestic dog Canis lupus familiaris.
In our next lecture (Chapter 04), we discussed behavioral genetics and narrow-sense estimates of heritability, describing the upper limit of such associations as around 0.7. We saw in that same chapter (as well as in later chapters, including Chapter 10) some estimates of narrow-sense behavioral-genetic heritability estimates that all were < 0.3, which is typical.
In this new report, the authors report behavioral-genetic associations that are much higher than those typically reported. How can this be? It stems from the artificial (and unusually large) degree of trait variation within this domestic species.
Typically, when one examines associations between traits within a natural (e.g., not artificially-selected) species, we expect some small, defined range of trait values, with correlation (association) between traits of some relatively low magnitude. Here in my Figure 1, I show the trait values and the within-species bivariate trait association for two (hypothetical) different species, such as a fox and a wolf. Within either species, there is some defined range of values for trait X (such as body length) and some defined range of values for trait Y (such as body mass). In my hypothetical example, these traits are correlated somewhat weakly within species A, and uncorrelated within species B. Notice that the two species do not overlap in trait values - a small wolf is always larger than than a large fox.
If domestic dogs were a natural species, chances are good that their trait values would fall somewhere in between these two species, perhaps closer to the 'wolf' end of the spectrum. Nonetheless, they would be expected to occupy only a small potion of the overall trait ranges.
Now, consider what the authors have done in their analysis. They have considered all domestic dog breeds to be of the same species, a fact that is technically true but which ignores the other fact that their range of trait values is anything but normal. They have analyzed behavioral-genetic associations across breeds within this single species, but here the individual breeds represent much more trait variation than natural species might, as size variation across domestic dog breeds is much greater than size variation across canine species in the wild. When associations are evaluated across multiple species (such as in my hypothetical Figure 2), the associations are often of higher magnitude. In the current study, analysis across the very artificially-distributed dog breeds behaves in the same way, resulting in behavioral-genetic associations much higher that those reported within single, natural species. 13/14 of their within-breed estimates (their Figure 1) are <0.3, just as one would expect.
This study is quite interesting, and represent the application of some very modern techniques (canine SNP chip, anyone?) to this interesting question of the heritability of behaviors. It also serves as a very useful reminder of
- the power of artificial selection - modern dog breeds are estimated to have been developed only over the last 300-500 years. For a natural species to evolve as much trait variation in this short time is unheard of.
- the danger of reliance upon secondary news sources - the original news story that I sent to you accurately describes the gist of this research study, and highlights the very strong associations found. But, it also leaves out enough detail that it is not possible to immediately assess why the associations are of such magnitude.
- the importance of proper modeling of evolutionary constraint - as shown in my hypothetical example Figure 2, trait associations across species can be artificially inflated if simple, linear techniques are used instead of methods that account for shared evolutionary history, such as independent contrasts analysis or nested ANOVA. The authors do have a phylogenetic model for their dog breeds; I am not schooled well-enough in the jargon of their analytical models to know if they have fully controlled for relatedness. Whether they have, or have not, these types of broad comparisons should always be examined with an eye for that type of concern.
- the imperfection of any one study - this is a research report describing one body of work on this topic, and I'm certain we could find other, similar/related studies. Is this study perfect? Certainly not. Is it still interesting, and useful? Absolutely. Any one research study can only advance our understanding incrementally. It's too easy, and too common, to dismiss work outright for containing flaws - it's more important to ask, given such flaws, is there anything that we can learn? The latter approach is more fruitful, and provides a much better return on one's investment of time and effort. Here, the traits with the highest across-breed heritabilities are trainability, aggression, and attachment - exactly those traits we might expect to have been key in the artificial selection/shaping of the human-dog relationship. It's a nice confirmation that these are strongly heritable, in ways that have translated into very powerful differences among breeds.
I've spent perhaps too much time dissecting some of these points, but I do so because they put some of our lecture material into sharp relief. Textbook examples are often too carefully culled to represent cutting-edge investigation; it's both fun as well as useful to see where current researchers in these areas actually are working.
Have a great rest of the week - see you on Tuesday for Chapter 11.
Good morning all,
At several points this term, we have discussed the genetics of behavior, including both the ability of single genes to influence behavior, as well as the heritability of individual behaviors and how traits can potentially be mapped onto phylogenetic histories. In the recent behavioral news is a report of a study that used large databases on dog behavior and genetics to look for behavioral traits that were associated with consistent genetic features. The researchers found >100 potential sites in the genome that were strongly associated with dog breed characteristics, including train-ability, aggression, excitability, and others.
One of the strengths of the method used here was that the researchers restricted themselves to a subset of the data pertaining to purebred dogs. This has the advantage of eliminating cross-breed variation which could dilute the strength of the genetic signals they were trying to detect. Dogs also are an advantageous species for a study like this, because they are popular, have long been bred in relatively pure lines, and have been artificially selected for a range of behavioral characteristics.
Some of the associations reported are quite strong, with heritability estimates as high as 60-70%. Those are very high values, near the limit reported for animal behavior-genetic comparisons. It's also surprising, in that, while this study has several strengths in its design, it also has one specific weakness: the researchers did not have genetic and behavioral information from the same individual animals, but instead were relying on databases (and breed averages) assessed across different individuals. That suggests that some of the associations, if tested within individual subjects, could be even stronger.
The human-dog relationship is a long one, and our artificial selection of dogs has been enormously powerful - when you think about all of the different dog breeds in the world, from Danes to dachshunds, Newfoundlands to chihuahuas, they all are the same species. That is testament to an enormous phenotypic plasticity (reaction norm) within their development. I'm going to request a copy of the original research article that this news report references, if anyone would like to see it - I'll bet it is interesting reading. Perhaps it will shed some light on my dog's (a rescue Rottweiler) behavior...
Have a great rest of the weekend - see you on Tuesday.
We've considered recently the concept of aposematism, the display of warning coloration to indicate to potential predators that one is unpalatable or otherwise unsuitable as a prey item. As we have seen, there are many implications to this type of signaling, including the costs involved, the degree to which it is effective, and its potential to be mimicked (and thus rendered potentially less effective) by palatable species.
The issue of aposematic costs is one that has been considered for some time, particularly the metabolic costs of producing warning coloration as well as the predation cost of being conspicuous. In addition to these are the metabolic costs of actually being unpalatable, and in no system has this been better explored than in monarch butterflies, conspicuous in both larval and adult forms, as well as highly unpalatable in each for the glycosidic compounds they acquire and sequester from milkweed plants (their near-exclusive forage). These compounds are highly toxic disruptors of Na+ channels, and being able to ingest and store them has required some evolutionary tinkering.
In the recent science news is consideration of this phenomenon, with some genetic work that explains the evolution of caterpillar resistance to these glycosides. The plant defenses have evolved to deter caterpillar feeding, but the caterpillars were able to evolve resistance with as few as three genetic mutations. These researchers were able to induce these same mutations in fruit flies, rendering them resistant to the glycosides as well - a very powerful experimental demonstration. The researchers also demonstrate some of the costs associated with the evolution of resistance to glycosides, including reduced ability to withstand physical shock. No evolutionary benefit is free, and beneficial changes to genes often are paired with deleterious side-effects. Here, the benefit (unpalatability) appears to outweigh the costs (reduced ability to withstand physical rotation).
Many of the plants and animals around us are conspicuous, while many others are cryptic. Those that are colorful and eye-catching may be silently playing potentially-deadly games of chemical warfare. Nature has been described as 'red in tooth and claw' (William Congreve); we might expand that to '... tooth, and claw, and toxin', for many toxins (including these glycosides) are quite deadly. What is remarkable to me is the role of simple sugars in glycosides, forming one side of the glycosidic bond. This is why some dangerous chemicals (such as automotive antifreeze, ethylene glycol) taste sweet and thus are dangerously attractive to the uninitiated. It makes me wonder whether glycosides have ever been used in nature as deadly bait, to lure, and then poison, potential prey. I'm willing to bet that it has...
Have a great weekend-
Good morning everyone,
In the recent science news are articles related to several of the topics we have considered recently - this is a nice confirmation that our course topics are 'up-to-date'!
Early in the term we considered the behavior of parasitic wasps, that stun prey and then oviposit eggs within them so that their larvae have a ready food supply during early growth. In the news this week is description of a different kind of parasitic wasp, one which parasitizes other wasps.
Here, the form of parasitism is less direct, in that the parasite deposits its eggs into the same plant gall that its host occupies. The parasite larvae then can attack the host, and in doing so, they accomplish a form of behavioral and physiological 'hypermanipulation'. Not only do they use the host tissues for their own nourishment, but they actually trigger a malformed version of the hosts normal escape behavior, which ensures that the host itself doesn't escape the gall but which provides the parasite an escape route.
The degree to which parasites manipulate their hosts can be extraordinary. We are used to thinking that parasites can make use of host tissues, but examples like this reveal more complicated interactions, with some parasites hijacking host behavior as well. There are plenty of examples, such as these:
All are good reminders that host behavior, as well as host tissues, can be exploited by parasites.
Even more recently, I sent you some information about humans who have developed some ability to perform echolocation. Just this week came a report on this topic, suggesting real, functional remapping of the brain's visual cortex to support this new capability:
At some level, neural plasticity is responsible for all that we can learn, but to have whole-scale re-functioning of a part of the brain from one sense to another is very impressive.
Have a good weekend -
Our next chapter (for Thursday) covers learning and cognition in animals, and I wanted to offer a couple of supplemental readings to accompany the material in our text. Our textbook describes a bit about the extent to which our closest relatives (the other members of the "great ape" lineage) may possess mental faculties approaching our own, and these two readings expand upon that idea, with the caveat that we may not also know how to best test, or interpret, animal behaviors.
The first reading describes some of the work done by researchers at Kyoto University, which houses a rich group of researchers in primate cognition. This report describes an attempt to interpret the mental states of chimpanzees, based upon their reaction to stimuli. If animals possess the capacity for thoughts and behaviors related to traits like empathy, jealousy, or disbelief, we can predict that they may respond in specific ways to certain kinds of stimuli. It's a challenging argument, to be sure, but many in the primate community believe that our closest primate relatives share more of our "higher" cognitive abilities than many would care to admit.
The second reading is from a prominent primate behaviorist (Frans de Waal), who has long argued that we approach animal behavior too simplistically, and often erroneously. Taken to an extreme, he suggests that, at least at times, we are testing the wrong things and making interpretations that are illogical. I do not believe that his interpretations are widely held by members of the behavioral community, but they do serve as a useful reminder that we often make too many assumptions in our design and interpretation of behavioral experiments.
When we delve into Chapter 07 on Thursday, it will be useful to keep these viewpoints in mind.
See you this afternoon for collection of exam corrections. We'll have time to review and discuss any material we wish to cover today.