Viral zoonotic risk is homogenous among taxonomic orders of mammalian and avian reservoir hosts (2020) Mollentze & Streicker, PNAS. https://doi.org/10.1073/pnas.1919176117
Image Credit: Tom Spinker, CC BY-NC-ND 2.0
Diseases that jump from other animals to humans, or zoonotic diseases (see Did You Know?) have become something that all of us are now very familiar with. COVID-19 is one such disease, and the impact it has had on the world as a whole is all the evidence that anyone could ever need for understanding why it is important to know where these diseases come from. Classically, specific groups of animals have been thought to act as reservoirs for the viruses that cause these diseases. Take rabies, for example. This is the disease that results in rabid animals, but you may not know that bats act as a reservoir for rabies, meaning that the rabies virus survives within bat populations and can be spread by them.
This is known as the “special reservoir hypothesis”, and it posits that there are certain traits associated with these reservoir species and/or their ecology that make them more likely to act as reservoirs for these viruses. In contrast, it could be that all animal species are equally likely to act as a reservoir for zoonotic viruses, and the risk of virus transmission is instead due to how many host species are within a given group of animal hosts. All this means is that you expect to find more diverse groups of animals hosting a more diverse group of viruses. This is known as the “reservoir richness hypothesis”.
In order to better manage zoonotic disease emergence and even predict where it is likely to occur in the future, it is important to understand if there are indeed special reservoirs among animal hosts, or if disease emergence is instead a consequence of host species richness. Today’s authors utilized data on zoonotic viruses and host species to understand this relationship.
High parasite diversity accelerates host adaptation and diversification (2018) Betts et al., Science. https://doi:10.1126/science.aam9974
Image Credit: Dr. Graham Beards, CC BY-SA 3.0
Host-parasite relationships are often thought of or depicted in a pairwise structure. That is, one host is attacked by one parasite, without an acknowledgement or consideration of how complex the relationship can be. For example, hosts are often attacked by more than one type of parasite, and the parasites themselves have to compete with one another for resources from the host. Because parasites are costly for a host, the hosts benefit from evolving resistance to the parasites. It follows that the more parasites a host is attacked by, the higher the benefit of evolving resistance, so we’d expect to see more resistance in hosts that are attacked more often. This should then result in differential evolutionary rates among hosts, which would then result in greater evolutionary divergence (see Did You Know?)
To test this idea, the authors of today’s study used a bacterium (Pseudomonas aeruginosa) and five lytic viral parasites (hereafter bacteriophages). These bacteriophages reproduce within host cells until they eventually cause the host to burst, killing the host (think of the chestburster in Alien, but a LOT of them). Because their reproduction results in the death of the host, lytic parasites impose a very strong selection pressure on hosts, making this a perfect host-parasite system to test the above prediction.
The cost of travel: how dispersal ability limits local adaptation in host–parasite interactions (2020) Johnson et al., Journal of Evolutionary Biology. https://doi:10.1111/jeb.13754
Image Credit: Francis Eartherington, CC BY-NC 2.0, Image Cropped
There are countless parasites in nature, and many of them tend to have relatively short life-cycles. For example, ticks live for about two years, while may of their hosts (us included) live for much longer. Because there is such a disparity in lifespan, parasites are predicted to have a greater evolutionary potential than their hosts. In other words, parasites should evolve faster than their hosts, which theoretically means that parasites should be more fit on local hosts than they would be on non-local hosts, as they would have had more time to adapt (i.e., local adaption, see Did You Know?).
Despite these predictions, the evidence from experimental studies of parasite local adaptation is mixed at best. Some studies show the adaptation to local hosts we’d expect, but some studies don’t. One reason for the lack of consistent evidence is that parasite dispersal between habitats can limit the ability of parasites to adapt. To help explain that I’ll use a comparison to cooking. If you are cooking a dish and you want to make it spicier you add in more spice. But imagine that when you add in that spice, you are also adding a lot of cream. The dish could be spicy, because you are adding spice, but the cream is diluting the spice and masking any potential heat. That is what parasite dispersal does to local adaptation: parasites within a given habitat (the dish) may have the ability to adapt to their hosts (become spicier), but because parasites from other habitats (the cream) are coming into their habitat and diluting those adaptations it masks any overall adaptation to the host (never gets spicy). Today’s authors therefore wanted to test how parasite dispersal affected local adaptation to hosts.
Environmental controls on African herbivore responses to landscapes of fear (2021) Davies et al., Oikos. https://doi: 10.1111/oik.07559
Image Credit: Olga Ernst, CC BY-SA 4.0, Image Cropped
Despite the incredible variation seen in nature when it comes to flora and fauna, it always seems like the two types that most people know are predators and prey. Prey animals being those that eat plants (or other animals), and the predators being those that eat those prey animals. Because prey animals must not only eat food, but try to avoid becoming food for something else, they must always be on the lookout. This watchfulness and awareness is what creates a “landscape of fear” (See Did You Know?), but variation is inherent to the natural world, and there are likely many things that prey animals consider when they pick where they decide to forage. Today’s authors wanted to investigate what factors influence the prey animals choice of foraging areas, and if that selection varies with the environment during the dry season when there isn’t much food available.
Infection of filamentous phytoplankton by fungal parasites enhances herbivory in pelagic food webs (2020) Frenken et al., Limnology and Oceanography. https://doi.org/10.1002/lno.11474
Image Credit: MarekMiś, CC BY 4.0, Image Cropped
Pelagic ecosystems (see Did You Know) make up more than 70% of the Earth’s surface, and the base of the food web is composed of primary producers like phytoplankton. Primary producers produce their own energy and provide an important service to the rest of the food web (and planet!). Not only do they provide a resource for the upper levels of the food web, but they also contribute to the global climate by making carbon available to other organisms. Because of these large-scale ramifications for any changes in phytoplankton primary production, many studies have investigated how things like nutrients, light, and temperature are able to affect phytoplankton.
A key aspect of certain phytoplankton is that they have morphological characteristics that make them more resistant to consumption by grazers further up the food web, like zooplankton. However, chytrid parasites (the same fungus that is ravaging amphibian populations the world over) are able to get around these defenses and reconnect phytoplankton to their zooplankton consumers. Chytrid infects phytoplankton, it then releases a free-living infectious stage, the zoospore, which is eaten by zooplankton. This indirect connection between inedible phytoplankton (like cyanobacteria) and zooplankton is called the mycoloop, and it can provide zooplankton with up to 40% of their food. Interestingly, studies have shown that zooplankton populations do better when their food, the inedible cyanobacteria, is infected by chytrid. Today’s study investigated how exactly chytrid is able to reduce the cyanobacteria defenses and provide zooplankton with more food.
Honey bees (Apis cerana) use animal feces as a tool to defend colonies against group attack by giant hornets (Vespa soror) (2020) Mattila et al., PLoS One. https://doi.org/10.1371/journal.pone.0242668
Image Credit: Rushen, CC BY-SA 2.0, Image Cropped
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.
Evolution and maintenance of microbe-mediated protection under occasional pathogen infection (2020) Kloock et al., Ecology and Evolution, https://doi.org/10.1002/ece3.6555
Image Credit: Zeynep F. Altun, CC BY-SA 2.5, Image Cropped
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.
Phenological asynchrony: a ticking time-bomb for seemingly stable populations? (2020) Simmonds et al., Ecology Letters, https://doi.org/110.1111/ele.13603
Image Credit: Ian Kirk from Broadstone, CC BY 2.0, Image Cropped
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.
An empirical attack tolerance test alters the structure and species richness of plant–pollinator networks (2020) Biella et al., Functional Ecology, https://doi.org/10.1111/1365-2435.13642
Image Credit: Adamantios, CC BY-SA 3.0, Image Cropped
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.
Interspecific competition slows range expansion and shapes range boundaries (2020) Legault et al., Proceedings of the National Academy of Sciences, https://doi.org/10.1073/pnas.2009701117
Image Credit: CISRO, CC BY 3.0
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.