A katydid, proudly displaying the front legs in which it houses its ears (Image Credit: Charlie Woodrow, CC BY 2.0)
Tag Archives: evolution
The evolution of crocodilian nesting ecology and behavior (2020) Murray et al., Ecology and Evolution, https://doi.org/10.1002/ece3.5859
One goal of evolutionary ecology is to understand the links between microevolution and macroevolution, meaning evolution in the short term (multiple generations) and how that scales up to the long term (millions of years). In macroevolution, a group of organisms is thought to be successful if it not only exists for a long period of time, but if it also boasts a large number of species. With those criteria in mind, crocodilians (alligators, crocodiles, gharials, and caimans) are one of the most successful lineages to have ever existed on the planet. Though they may not be the most diverse group of organisms with only 25 species, they have been around for about 100 million years. To put that into perspective, dinosaurs went extinct about 65 million years ago, meaning that the crocodilians not only lived with dinosaurs, but they survived the mass extinction that the dinosaurs didn’t.
This longevity as a lineage raises some questions as to what it is about the crocodilians that made them so successful, when their cousins the dinosaurs died out. An interesting aspect of crocodilians is that there is very little variation among these organisms, as they are all generalist carnivores, live aquatic lives, exhibit mating vocalizations, their sex is determined by the temperature of their eggs (see Did You Know?), and they care for their eggs and young. Despite these similarities, there are some notable differences in the reproductive ecology and behavior of the different species, specifically how they build and care for their nests. Because of these differences, the authors of today’s study asked if variation in how crocodilians reproduce may have been the cause of their success.Read more
The silver lining of extreme events (2018) Coleman & Wernberg, Trends in Ecology and Evolution, https://doi.org/10.1016/j.tree.2020.08.013
We here at Ecology for the Masses recognize the harm of climate change and the danger that it poses to countless species the world over. Part of climate change involves extreme climate events such as floods, droughts, unusual cold spells, or cyclones, all of which can be devastating to natural systems. By and large these events are seen as negative, and rightfully so! But today’s paper offers another perspective on extreme climate events: their potential for driving evolution towards increased resilience.
Now, I’m not saying that these extreme climate events are good. I dislike them just as much as the next person with a shred of concern about the natural world. That being said, the authors raise some interesting points about the evidence that exists for these events being a positive force for evolution and adaptation. As such, I want to touch on a few of those points, address some issues with this ‘silver lining’, and talk about what it means going forward.
What Evidence Exists
Extreme climate events result in massive losses of organic life, local extinctions, and can drive range shifts. This is quite costly from not only an ecological point of view, but also a social and and an economic one. Due to these costs, a significant amount of effort and money has been dedicated to working on issues associated with these events. Interestingly enough, despite the negative connotations and costs associated with extreme climate events, there is emerging empirical evidence for a “benefit” in that they can cause non-random mortality (see Did You Know?), driving rapid evolution and adaptation.
Scientific theory has predicted that when extreme climate events occur in such a way that they select against weak individuals, but aren’t so extreme that “tougher” individuals cannot live, then these more tolerant and stronger individuals can persist in populations/areas undergoing extreme events. If these tougher individuals can pass on their genes, then a population can rapidly adapt to these extreme conditions. For example, a study showed that a severe cold snap selected for cold tolerance in green anoles (Anolis carolinensis), and similar work has shown that heatwaves selected for thermal tolerance in kelp. While plenty of the lizards/kelp didn’t have the proper traits to survive these extreme temperatures, some of them did. And because they passed on those genes to the next generation, the population is better-suited to survive future extreme temperatures.
Did You Know: Non-Random Mortality
Evolution is a fact of life, and the driving force behind the persistence of life on our planet. However, what you may not know is how evolution actually results in changes in a population/species over time. Individual organisms don’t evolve, species do. So how does that work? Well, it all has to do with how often certain individuals pass on their genes. “Survival of the fittest” refers to the biological concept of “fitness”, which is how good a given organism is at passing on its genes. So in order to be the most fit, you have to pass on the most genetic material, relative to other members of the population. This is where non-random mortality comes into play. Non-random mortality means that there is a pattern behind the death rates. Put into other words, the individuals that survived had something that the ones that died did not. This is how evolution works slowly over time, non-random mortality means that individuals with a given trait tend to die less often than those that don’t have that trait, which means that that trait gets passed on more often than others. Eventually, that trait will become the new normal for that population/species, and evolution has occurred.
What This Means
The potential for extreme events to select for resilience and drive rapid adaptation means that groups dedicated to conservation and preservation of species and ecosystems may be able to proactively anticipate future events. The authors highlight the difficulty inherent in studying non-model organisms for traits/genes that may promote persistence to future climate events, as it involves a LOT of background research to understand the mechanisms behind such persistence. However, to use the anoles from earlier as an example, there are better ways. If one was to go to an area that recently suffered a cold snap like those anoles did and collect the survivors, chances are that most of those survivors have the cold-tolerance trait. By selectively breeding/relocating those survivors conservation workers could prevent future die-offs due to cold snaps.
Problems With These Approaches
This all sounds great, right? No issue? Well, not quite. Just because a given trait may promote persistence to one stressor (the environment) does not mean that it promotes persistence to all others (like disease). Another issue with this silver-lining of adaptation and rapid evolution is the bottleneck effect: extreme events cause mass die-offs. Though the survivors may have a trait that allows them to persist in extreme events, the reduced population size of the survivors may result in such a marked decrease in genetic diversity that the population fails eventually anyway due to the issues associated with inbreeding.
Extreme climate events are an unfortunate reality, and they are only predicted to get worse and become more frequent. Today’s paper offers a pleasant silver lining to that very grim reality, as it highlights the potential for these events to drive evolution and selection to extreme conditions. It may not be as good as not having these events in the first place, but the authors bring up an important point by drawing attention to the evidence that exists for populations adapting to these extreme conditions, many of which seem to be driven by human-induced climate change. I’ve recently re-read Michael Crichton’s Jurassic Park, and I can’t help but think of a quote from the character Dr. Ian Malcolm’s as I was reading this paper: “The planet has survived everything, in its time. It will certainly survive us”.
Adam Hasik is an evolutionary ecologist interested in the ecological and evolutionary dynamics of host-parasite interactions. You can read more about his research and his work for Ecology for the Masses here, see his personal website here, or follow him on Twitter here.
Of poisons and parasites—the defensive role of tetrodotoxin against infections in newts (2018) Johnson et al., Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.12816
Many organisms in nature produce powerful (and sometimes deadly) toxic substances, often taken as evidence that prey evolved chemical defenses against predators. Interestingly, these chemical defenses are deadly not only to predators, but also to parasites. This complementary defense, in addition to the ubiquity of parasites themselves, indicate that parasites may have had a hand in the evolution of host toxicity.
One particularly potent toxin found in the animal kingdom is tetrodotoxin (TTX). It can cause paralysis, difficulty with breathing, and even death in some cases. Newts in the genus Taricha are notorious for having high concentrations of TTX in their skin and eggs, and this has long been thought to have evolved as a defense against predators. In particular, Taricha newts and garter snakes (Thamnopholis spp.) are a classic example of arms-race dynamics (see Did You Know). Despite this relationship, newt toxicity and snake resistance to the toxin don’t always match up perfectly in nature, suggesting that other factors may influence newt toxicitiy. The goal of today’s study was to study parasitic infection and compare it to variation in toxicity among two newt species, the rough-skinned newt (T. granulosa) and the California newt (T. torosa).
Local Adaptation to Biotic Interactions: A Meta-analysis across Latitudes (2020) Hargreaves et al., The American Naturalist, https://doi.org/10.1086/707323
Local adaptation is a process whereby individuals native to a given area are better-suited to live in that environment than foreign individuals, and those local individuals will out-compete foreign individuals. This adaptation to local conditions can range from a predator that is better at finding and catching prey, to a plant that is more efficient than another at taking nutrients from the soil, or to a host that has evolved defenses against a local parasite. Despite a wealth of literature and science that has been dedicated to the study of local adaptation, it is not clear what it is about the environment that commonly drives it.
Early studies of local adaptation measured abiotic (non-living) factors like temperature and the amount of light, but this ignores the fact that all environments include biotic factors like other species and any interactions with them. A small amount of studies have shown that biotic interactions (i.e. interactions with other species) can drive local adaptation, but there isn’t a consensus on how common of a pattern that is. Today’s authors used a meta-analysis of previous studies to test how these biotic interactions affect local adaptation. Read more
Macroevolutionary convergence connects morphological form to ecological function in birds (2020) Pigot et al, Nature Ecology & Evolution, https://doi.org/10.1038/s41559-019-1070-4
There are an astounding amount of different forms that the animals on our planet take. Likewise, there are a multitude of diverse functions that animals serve in the environment, such as that of a herbivore, a predator, or scavenger. In some cases it’s a clear link between the form of a given animal and its function in the environment, like that of the beak of a hummingbird that allows it to feed on nectar and their role as a pollinator. But whether or not there is a reliable way to predict the function of an animal based off of its form is has been the subject of considerable controversy.
Deciding on how many morphological traits to use to predict ecological function is a difficult prospect. One could argue that it’s impossible to pick a finite number of traits, as there are infinite possible niches that organisms can fill so there’s no way that a set of traits could fill those infinite possible niches. Mapping animal form to function has major implications for quantifying and and conserving biodiversity, and the authors of today’s paper wanted to to determine just how many traits are needed to do that.
City life alters the gut microbiome and stable isotope profiling of the eastern water dragon (Intellagama lesueuriii) (2019) Littleford-Colquhoun, Weyrich, Kent & Frere, Molecular Ecology, https://doi.org/10.1111/mec.15240
It’s a pretty fair call to assume that if you build a city on a species’ habitat, it might be a little miffed. Yet as human settlements expand worldwide, many species are showing that they’re able to make rapid changes to their biology to adapt to living around humans.
This includes their diet, of course. As diets shift, many other aspects of a species’ biology follows, including the microbes that live in a species’ gut. And gut microbes influence a huge range of factors, including immunology, development, and general health. The response of a gut microbe community (the gut microbiome) to a new diet can in turn affect an animal’s ability to adapt to that environment.
Phenotypic plasticity or evolutionary change? An examination of the phenological response of an arctic seabird to climate change (2019) Sauve et al., Functional Ecology, https://doi.org/10.1111/1365-2435.13406
If you’re here on Ecology for the Masses, then you know that climate change is not only real but is causing all kinds of problems for organisms the world over. One of the things that climate change is doing is altering seasonality, the time of year in which a given season will take place. For example, where I live in the US, it is normally cold at this time of year, but as I write this it is 60F/16C, much warmer than it should be despite it almost being winter. These changes can affect when organisms start their seasonal breeding, but how these breeding events change is not always the same.
Some changes are due to evolution, or the change in a population’s gene frequencies over time. As mutations and selection take place, a given population may have some traits or behaviors selected for over others. Another way that these changes can happen is via plasticity, which is a change induced by the environment, but without changing the gene frequencies (See Did You Know? for more information). The authors of today’s paper wanted to know if the change in breeding dates of a colony of seabirds (Mandt’s black guillemont, Cepphus grylle mandtii) was due to evolution or plasticity.
You would think that after researching how a species will react to climate change, which individuals are more likely to avoid predators, and what its DNA says about its evolutionary history, simply classifying what species an animal is would be pretty simple. Unfortunately that’s not the case. I distinctly recall being given the runaround by my primary school teacher when asked to define what a mammal was (according to the internet a coconut qualifies, so maybe that debate’s not over yet).
Image Credit: Friends, 1995