Category Archives: Paper of the Week

Do As I Do

Predators like these Great tits (Parus major) eat a wide variety of insects, but some of those insects are so unpleasant to eat that birds tend to avoid them. How does this trait evolve in prey animals when its maintenance and origin depend on the predators learning by eating them? (Image Credit: Shirley Clarke, CC BY-SA 3.0).

Social information use about novel aposematic prey is not influenced by a predator’s previous experience with toxins (2019) Hämäläinen et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13395

The Crux

Many animals in nature have evolved a defense strategy known as aposematism, meaning that they display warning colors or patterns that tells predators that they are not worth eating due to their toxicity. Predators can learn to avoid aposematic prey by either sampling different prey animals and learning for themselves, or they can watch other predators eat different prey species and, depending on the reaction of that predator, learn what may or may not be good to eat.

The paradox of the evolution of this aposematic trait is that toxic prey species are not only highly visible and easily noticed by predators, but they must be attacked in order for predators to learn that they shouldn’t eat them, meaning that these prey species may not even survive long enough for them to enjoy the benefits of predator avoidance. The question then becomes are aposematic prey able to persist in nature because predator learn to avoid them? The authors of today’s paper wanted to investigate how predators that have learned to avoid toxic prey will watch and learn from other predators eating new, possibly toxic prey.  Read more

It’s What and Where You Eat

Animals depend on consumable energy to live, and that energy can come from a variety of places. If the energy that animals get from their food varies in quality depending on where the animals get their food, what does this mean for birds like the Eastern Phoebe (Sayornis phoebe) that consumes both terrestrial and aquatic food? (Image Credit: Andrew Cannizzaro, CC BY 2.0).

Aquatic and terrestrial resources are not nutritionally reciprocal for consumers (2019) Twining et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13401

The Crux

In the natural world, ecological subsidies, or the influx of sustenance from one habitat type to another, connect a variety of environments. While research has been conducted on this topic in the past, most of it has dealt with the quantity of energy moving between habitats, but not the quality of the resource itself.

When one habitat (such as an aquatic habitat) is rich in a specific resource that is hard to find in other habitats, subsidies of these resources play a unique role by providing animals and plants with food or energy that they could otherwise not get. The authors of today’s paper wanted to investigate if subsidies from aquatic habitats and terrestrial habitats contain the same amount of that hard to find, valuable resource: highly unsaturated omega-3 fatty acids (HUFAs). Read more

Using eDNA to Monitor Fish Dispersal

Environmental DNA is a hot topic in biomonitoring. But what is it exactly, and how can it be used to monitor the dispersal of a reintroduced fish species? (Image credit: Gunnar Jacobs, CC BY-SA 2.0, Image Cropped).

Guest post by Christopher Hempel

Using environmental DNA to monitor the reintroduction success of the Rhine sculpin (Cottus rhenanus) in a restored stream (2019) Hempel et al., PeerJ, https://peerj.com/preprints/27574/

The Crux

The term “environmental DNA (eDNA)” is currently booming in molecular ecology. But what exactly is this technological marvel? Essentially, eDNA comprises all DNA released by organisms into their environment, and originates from mucus, scales, faeces, epidermal cells, saliva, urine, hair, feathers – basically anything an organism might get rid of during its life. The eDNA can be collected from the environment, extracted, and analyzed to detect species using molecular approaches. As this is a very sensitive and non-invasive approach, it is a very hot topic for biomonitoring.

eDNA can be collected from any animal (in theory), but aquatic organisms in particular have been shown to be good target individuals (as eDNA is easiest to handle in water samples). Consequently, there are many studies using eDNA to monitor the activity of fish, reaching from the presence of invasive species to the effects of aquaculture. Here, we applied eDNA analysis to monitor a reintroduced fish species, the Rhine sculpin. The sculpin’s poor swimming ability make it useful as a bioindicator of the passability of streams and rivers. We wanted to investigate the potential of using eDNA to monitor the dispersal of the species in a remediated stream on a fine spatial and temporal scale.

Read more

Fading Into the Background

Mostly limited to ocean animals, transparency is thought to help escape predators by blending the animal in with its environment, but is this what actually happens? (Image Credit: Wikicommons, CC BY 3.0).

Transparency reduces predator detection in mimetic clearwing butterflies (2019) Arias et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13315

The Crux

Predators are one of the strongest forces of selection in the natural world, and as a result it can be quite costly to stand out and be more easily noticed. This means that in order to survive, animals must adapt to avoid predators. Besides running away from what is trying to eat you, your best bet is to evolve body coloration that helps you avoid being seen by a predator.

Animals that rely on blending in will match the color or even the texture of their backgrounds, but when prey species live in areas where they cannot easily blend in (like plankton in the water column) they often evolve to be transparent. Unlike their marine counterparts, transparency is normally rare in terrestrial animals. The clearwing butterfly is one notable exception to this rule, and the authors of today’s paper wanted to test whether or not these clear wings actually reduce predation.
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Monitoring Freshwater Populations in the Chernobyl Exclusion Zone

Radiation can have extremely negative effects on an individual. But is it as easy to measure its effects on an entire population? (Image Credit: Hnapel, CC BY-SA 4.0, Image Cropped)

Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone (2019) Goodman et al., Ecology and Evolution, DOI: 10.1002/ece3.4931

The Crux

As anyone who has recently watched HBO’s Chernobyl can tell you, large doses of radiation are capable of doing some pretty serious damage to an organism. But whilst examining the effect of radiation on an individual might be simple, monitoring those effects on a population can be difficult. Whilst radiation negatively effects fitness, it can also help individuals with higher radiation tolerance to reproduce and dominate within the population of a single species, making it difficult to monitor the exact effects of radiation on that population. If a population is filled with only those who were strong enough to survive, you don’t get an idea of the variation in the radiation’s effects.

This week’s researchers tried to break through that problem by looking at different populations of a water flea in Chernobyl’s Exclusion Zone (CEZ) – the area still barred from entry in eastern Europe.

What They Did

The researchers sampled populations of the water flea Daphnia pulex (see below) from 8 lakes within the CEZ, all of which had experienced different doses of radiation since the Chernobyl disaster. Information on how much radiation those lakes were subject to was taken from Ukraine’s radiation databases and water samples collected at the site. The 38 types of Daphnia from the 8 lakes were then transported back to a laboratory and bred for three generations. The survival and reproductive success of this third generation was then modelled against radiation dose.

Did You Know: Daphnia as Study Organisms

Some species are frequently used across different ecological disciplines as model organisms. One example is the genus Daphnia, a genus of water fleas. They have a short life cycle, and can reproduce asexually. This means that scientists have the opportunity to disentangle environmental effects on populations of genetically similar individuals, as well as between populations of different genetic backgrounds.

What They Found

Whilst reproductive success and survival varied between the populations of Daphnia at different lakes, this did not seem to occur as a result of radiation dose. Radiation did not have a pronounced effect on any fitness variable.

Problems?

Daphnia_pulex

The water flea Daphnia, here used to test the effects of radiation on populations (Image Credit: Paul Hebert, CC BY 2.5)

Sample size is of course an issue here. Only having 8 lakes to compare the effects of radiation on populations was always going to make an effect of radiation dose hard to find. It was made more difficult by the fact that the effects of one lake were significantly different to the others, skewing results considerably. This is of course no fault of the authors, and hopefully technology in the future will allow us to expand the data used in these projects.

So What?

It’s important to note here that these results do not necessarily mean that radiation has no effect on Daphnia populations. Radiation is known to have negative effects on individual fitness, so what this study could tell us is that we need to view radiation as an environmental process which acts in concert with a variety of other biotic factors. Perhaps a study which takes into account further environmental variables and more lake populations would be able to further advance the work done in this paper.

The Roles of Aquatic Predators

Image Credit: Neil Hammerschlag, Oregon State University, Image Cropped, CC BY-SA 2.0

Ecosystem Function and Services of Aquatic Predators in the Anthropocene (2019) Hammerschalg et al., Trends in Ecology and Evolution, https://doi.org/10.106/j.tree.2019.01.001

The Crux

Aquatic predators play an important role in many ecosystems, and are often among the more charismatic species in the ecosystem. Because of this, they are often the target of conservation for ocean management bodies worldwide. This paper aims to provide a synthesis of the ecosystem services that aquatic predators provide in marine and freshwater ecosystems worldwide. Below, we’ve chosen 4 of the more interesting and important roles to go into.

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To Blend in or Stand Out?

Body coloration of an animal can be useful for not only attracting prey, but also avoiding being eaten. One important question is whether or not this coloration can simultaneously serve both purposes? (Image Credit: Chen-Pan Liao, CC BY-SA 3.0).

Multifunctionality of an arthropod predator’s body coloration (2019) Liao et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13326

The Crux

One topic that has interested ecologists for decades is that of animal body coloration, and what function that coloration can serve for the animal. Despite this fascination and the work that has been done to study this aspect of animal biology, the actual mechanisms driving the evolution and maintenance of body color are not well understood. Many different aspects of an organism’s life can shape and affect body color, such as avoiding predators, attracting mates, and whatever resources an organism has available to create specific colors. In addition, many of these aspects often compete with one another, such that a color that is good for attracting mates may also make you more easily-spotted by a predator.

Spiders provide an excellent system in which to study the evolutionary significance of body colors, as previous work has shown that body color affects mate attraction, predator avoidance, and prey attraction. The authors of today’s study wanted to know if these complex color patterns could serve more than one function in the spider’s life.
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