Honey bees are one of the most familiar sights in the natural world. Even for those who know nothing about insects, many will be well acquainted with those small, black and yellow striped bugs that fly from flower to flower. Most people also know that bees live in hives, but what you may not know is that these hives make honey bees the target for many predators and opportunistic parasites. A large group of animals living together in one spot is like an all you can eat buffet for a wide variety of species that have evolved to exploit just such a collection of resources. One of the bee’s most notorious enemies is the giant hornet, an insect that has become rather famous in my home country due to its recent invasion. These large, well-armored predators not only pick off bees one-by-one, but groups of them can slaughter an entire hive of bees within a matter of hours.
The fun thing about evolution though is that when you have enemies evolve to exploit a hive, the hive has to evolve its own defenses against the enemies, otherwise they go extinct. Honey bees are known to gather into a “heat ball” (see Did You Know), but they have also been seen smearing plant matter around their nest entrances, possibly as a way of confusing the chemical-sensing ability of the giant hornets. Though researchers have seen unknown material smeared on the entrance of hives, beekeepers have reported that this material was in fact animal feces that the bees had collected. Today’s authors wanted to study if these honey bee (Apis cerana) were in fact using animal feces as one of their defenses against a formidable, but under-studied giant hornet predator, Vespa soror.
Microbes are everywhere in nature, and I don’t just mean out in the wild. They live inside of every plant and animal, including humans. These microbes can be harmful, beneficial, or do nothing to their hosts. When they help us, microbes take part in what’s called “defensive mutualism”, which is where they help their hosts fight off parasites. Benefiting from this mutualistic relationship depends on whether or not there are parasites around to defend against, as microbial defense mechanisms can harm not only the parasite but also the host itself.
For this symbiotic relationship to continue and not be selected against over time, the benefits of hosting the microbe must outweigh the costs. This is all well and good when there are always a lot of parasites to defend against, but that is not always the case. Today’s authors wanted to test how changes in parasite pressure over time affected the relationship between a defensive microbe and its host.
When we think of climate change we tend to think about extreme weather events and melting ice caps, but the way in which our environment is changing is giving the planet more than just unseasonal weather. Phenology (the timing of biological events in nature) dictates when an organism begins a given part of its life cycle, and changes in phenology are one of the most frequent responses to climate change. Take bees and flowers; bees feed on the flowers of certain plant species, and in turn spread the plants’ pollen for them. They both depend on the other being around at the same time, and if flowers bloomed too early, or if the bees came around before the flowers were “ready” for them, both parties would suffer.
Such a mismatch is known as an asynchrony, and it is hypothesized to cause population declines due to the harmful impacts on one or more of the interacting species involved (see another recent post to understand how the loss of one or more interactions can lead to cascading effects throughout a local community). While many theoretical models have investigated these processes, today’s authors wanted to combine such models with long-term data on the phenology and population size of great tits (Parus major). Great tits rely on a small period of insect abundance to feed their young, and as such the more closely they can match the needs of their young to the abundance of insect populations the more they will increase their fitness.
Put simply, ecosystem function is the process that control how nutrients, energy, and organic matter move through an environment. Think about a forest. You have small plants that are eaten by small animals, small animals that are eaten by larger animals, and those larger animals are eaten by even larger animals. When those animals die, they are broken down and consumed by scavengers, fungi, and bacteria. These processes result in a continuous flow of nutrients and energy through the ecosystem. However, if one link (organism) in this chain breaks (goes extinct), the ecosystem could lose its function, and other species that depend on this cycle could go extinct as well.
The way in which a given ecosystem reacts to or recovers from any negative impact that it sustains is key to understanding how ecosystems function. Classically, this is tested with attack tolerance tests, in which all species on a given trophic level are removed and the ecosystem is then monitored to see how/if it maintains its function. In studies of plant-pollinator networks, this is usually modeled with computers, but studies which use natural systems are lacking. Today’s authors wanted to use a natural plant-pollinator system to see what happens.
Climate change has resulted in multifarious changes in the natural world, not the least of which being where one can find a given species. Because areas are growing warmer, some species are shifting their habitats to stay within the type of environment that they like. The thing about shifting habitats though is that a species that shifts is likely to run into/need to compete with another species that is already there. Competition affects the growth and dispersal of organisms, so it follows that this should have an effect on the ability of a given species to shift or expand its range. However, most studies do not take competition into account when predicting range expansion.
A classic example in the scientific literature that did take competition into account was that of the gray squirrel invasion of Britain. Gray squirrels invaded and subsequently displaced the native red squirrels, but competition appeared to have no influence. Instead, a pathogen appeared to be the likely cause of the contraction of the red squirrel range. This example, however, comes from an observational study of a single replicate. Today’s authors instead conducted a manipulative lab experiment to test for the effects of competition on range expansion.
Working together to achieve a common goal is nothing new to us. We as humans are famously social organisms that not only crave interactions with others, but quite often succeed due to the way that we work together. Interestingly, we tend to work well when we have some form of organizations or leadership, but there are other animals that do not require such leadership. This so-called “collective behavior” is the behavior of a group that emerges without a form of central control. Think of a large school of fish avoiding a predator at the same time, or birds flocking together and flying through the sky. All of this happens as a result of those animals interacting with one another, not because there is some boss animal telling them to do it.
Not surprisingly, groups of animals will vary in their exact method of collective behavior. It’s assumed that this variation is largely dependent on natural selection, but there isn’t actually much that is known about it. For this variation in behavior to have been the result of natural selection, the variation itself has to be advantageous and heritable, meaning that it is better to have the variation and you can then pass it on to your offspring. Today’s authors wanted to measure just that.
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.
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.
QUICK NOTE: Harvestmen (aka Daddy Long Legs in North America) are NOT spiders! Despite the false myth that they can’t bite you due to short fangs, harvestmen aren’t even venomous. They can’t hurt you! There, now that I got that off my chest…
Sexual dimorphism is a common phenomenon in nature whereby male and female members of a given species differ from one another physically. Think of the large bull moose or elk with its antlers, peacocks and their colorful tails, or the larger horns of male stag beetles. Because of these differences, natural selection is able to act on both their behavioral and functional differences. That is to say, differences in performance and morphology mean that males and females of the same species may experience differential selection pressures. As a result, males and females could be expected to react differently to the same challenge, such as a predator.
Harvestmen (known in North America as Daddy-Long-Legs) are a group of arachnids that, although bearing a resemblance to and being commonly mistaken for spiders, are not actually spiders. They belong to a group called Opiliones. Some males of this group have thicker legs with pronounced spines, used in male-to-male competition and anti-predator defenses. In addition to using these spines against predators, these arachnids also engage in thanatosis (“playing dead”, see Did You Know?) and use chemical defenses. Due to these morphological differences, the authors hypothesized that males and females would differ in their response to predators.
Quantitative analysis of selected plastics in high-commercial-value Australian seafood by pyrolysis gas chromatography mass spectrometry (2020) Ribeiro et al., Environmental Science & Technology, https://doi.org/10.1021/acs.est.0c02337
Plastic is one of those things that we hear about all the time these days. More specifically, we hear about how there is an absolute ton of it in the environment thanks to human negligence and the lack of concern that a large amount of people have for where their plastic goes when they are finished with it. Plastic isn’t like paper or metal, it takes a long, LONG time for it to break down. Plastic bags take anywhere from 10-20 years, but the normal time it takes for most plastic waste to decompose is about 1000 years. To put that into perspective, Leif Erikson led an expedition from Greenland to the coast of what is now North America in the year 1002. If his crew had some plastic with them and left it in the places they visited (typical tourists) there’s a good chance that it would STILL be there today.
I hope I’ve convinced you why plastic is bad, but another danger that plastics pose are microplastics, small bits of plastic that have come from a larger piece, all of which are less than 5mm in size. Our environment is full of them, and the ocean in particular has been saturated with microplastics. In 2014 a research expedition sailed from Bermuda to Iceland (a trip of 2500 miles/4023 km) and found microplastics in every single sample they took. And that was just plastic in the environmental samples they took, the real threat to marine life comes from what happens to all of that microplastic.