Category Archives: Paper of the Week

Measuring Immunity With Transparent Hosts

Host controls of within-host dynamics: insight from an invertebrate system (2021) Stewart Merrill et al., The American Naturalist. https://doi.org/10.1086/715355

This is a guest post by Dr. Tara Stewart Merrill

Image Credit: Per Harald Olsen, NTNU, CC BY 2.0, Image Cropped

The Crux

When it comes to understanding how parasites and pathogens spread, immune defenses may be an especially important factor. The immune system is the gatekeeper for parasites and pathogens (I’ll just use the term “pathogen” from here on out). Whether you are exposed to influenza, a parasitic worm, or a tick-borne bacterium, your immune response will determine the outcome of infection — either you will become infected (which benefits the pathogen’s reproduction) or you will not (which is a barrier to the pathogen’s reproduction). So now, picture a whole population of individuals. A room full of individuals with poor immune responses should result in more infections (and more transmission) than a room full of individuals with strong and robust immune defenses. By shaping the fate of pathogens, host immune defenses can shape transmission.

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Some (Don’t) Like it Hot

Do latitudinal and bioclimatic gradients drive parasitism in Odonata? (2021) da Silva et al., International Journal for Parasitology. https://doi.org/10.1016/j.ijpara.2020.11.008

Image Credit: Adam Hasik, image cropped

The Crux

If there is one thing that people know about me and my research it’s that I love parasites. They’re everywhere, and more than half of all animals are parasites. They also make ecosystems more stable and link organisms within food webs to one another. For example, some parasites connect prey animals and their predators by making it easier for the predator to find and/or eat the prey. Though they can be found all over the world, there are a variety of environmental factors that make it more likely for a parasite to be found in a given environment. Today’s study focuses on one particular hypothesis related to the effects of the environment, the latitudinal diversity gradient (LDG, see Did You Know).

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Not Giving Into the (Selection) Pressure

A common measure of prey immune function is not constrained by the cascading effects of predators (2021) Hasik et al., Evolutionary Ecology. https://doi.org/10.1007/s10682-021-10124-x

Image Credit: Adam Hasik, Image Cropped

The Crux

The immune function is a critical component of an organism’s ability to defend itself from parasites and disease. Without it, we would be in much worse shape when we got sick. Despite this usefulness, the immune function is costly to use as organisms have to consume enough food to have the energy needed to mount an immune response. This is easier said than done, however, and there are often many factors that come into play when it comes to acquiring energy.

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The Importance of Green Spaces in a Locked Down World

Image Credit: Mariia Honcharova, CC BY 2.0, Image Cropped

Back to nature: Norwegians sustain increased recreational use of urban green space months after the COVID-19 outbreak (2021) Venter et al., Landscape and Urban Planning, https://doi.org/10.1016/j.landurbplan.2021.104175

The Crux

Getting out and spending time in green spaces can have a number of benefits for people, which have been recently shown to include benefits for mental health. It can also foster a connection with nature, which can improve our relationship with the natural world going forward.

When the COVID pandemic hit last year, people all across the world were forced into lockdown. Yet in many places, getting out and spending time in nature was still an option. So did people in these areas increase their use of green spaces during the pandemic? And was this maintained after lockdown?

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Is the Enemy of My Enemy My Friend?

Natural enemies have inconsistent impacts on the coexistence of competing species (2021) Terry et al., Journal of Animal Ecology. http://doi.org/10.1111/1365-2656.135434

Image Credit: Alandmanson, CC BY 4.0

The Crux

In nature, organisms are often competing with other organisms for food, mates, or even just for a place to call home. This competition comes in two forms: interspecific competition (meaning competition between two different species) and intraspecific competion (meaning competition within the same species). These two forms of competition play into the phenomenon known as mutual invasibility (see Did You Know), which is a necessary component of coexistence. If two organisms coexist, one species will not outcompete the other and drive it extinct, and thus the two species will coexist over time.

Because competition plays such a strong role in species coexistence, any factor that affects competition between two species has the potential to also affect coexistence. Today’s authors wanted to ask how an antagonistic species interaction (specifically, interactions with a parasitoid) affected coexistence in rainforest flies.

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Analysing The Impact of Blackfish on SeaWorld’s Orca Program

Nature documentaries as catalysts for change: Mapping out the ‘Blackfish Effect’ (2021) Boissot et al., People and Nature, https://doi.org/10.1002/pan3.10221

The Crux

Wildlife documentaries generally have the best of intentions, but our ability to determine their actual impact is limited at best. There have been attempts to analyse a documentary’s content or impact before, but they’re few and far between (outside of financial success).

Blackfish is a 2013 documentary which brought to light the poor treatment of orcas at SeaWorld, in particular the whale Tilikum, who killed three people while in captivity. Blackfish received widespread publicity, and in the years following its release, SeaWorld saw an enormous drop in attendance. They also saw a huge drop in stock price, redesigned their orca show to focus on conservation, and ceased their orca breeding program.

Today’s researchers wanted to investigate how closely the release of Blackfish was linked to the negative impacts and subsequent revamp that SeaWorld’s orca program underwent.

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Better Means Faster

Species interactions have predictable impacts on diversification (2021) Zeng and Wiens, Ecology Letters. https://doi.org/10.1111/ele.13635

Image Credit: MacNeil Lyons/NPS, CC BY 2.0

The Crux

No organism on the planet lives in complete isolation from other organisms. Many organisms serve as a food source for others, and even apex predators have to compete for their food. Species interactions like predation, competition, and parasitism directly impact organisms in their daily lives, but there is also a possibility that these same species interactions have had an impact on much longer timescales. That is, species interactions may have had a direct effect on the diversity of life on our planet.

Species interactions have been previously shown to affect diversification rates (see Did You Know?), so the question that today’s authors asked was whether there is a general trend to the effects of species interactions on diversification rates? Specifically, do species interactions with negative fitness (such as being killed by a predator) impacts decrease diversification rates, and do species interactions with positive fitness (such as successfully parasitizing a host) impacts increase diversification rates?

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Light My Fire: How Birds Respond to Extreme Climate in the Wake of Bushfire

Fire, drought and flooding rains: The effect of climatic extremes on bird species’ responses to time since fire (2021) Connell et al., Diversity and Distributions, https://doi.org/10.1111/ddi.13287

The Crux

Both bushfires and extreme climate events are capable of shaping not only habitats, but also the number of different species that inhabit them. Yet the interaction between these phenomena can be equally important. For instance, an extreme flood or drought could have a very different impacts on a forest depending on how recently that forest was burned by fire. If a fire tore through recently, an extended period of drought may finish off species already under stress, yet if there has been a longer period of time since the last fire, the ecosystem may be able to tolerate a drought.

Given that climate change is increasing the occurrence of both extreme climate events and bushfires, it’s better to start investigating the effects of these interactions sooner rather than later. This week’s authors looked at the interaction between the two phenomena in south-eastern Australia, an area whose wildlife has come under a lot of pressure recently.

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Cause and Effect

Temporally consistent species differences in parasite infection but no evidence for rapid parasite-mediated speciation in Lake Victoria cichlid fish (2020) Gobbin et al., Journal of Evolutionary Biology. https://doi.org/10.1111/jeb.13615

Image Credit: Kevin Bauman, CC BY 1.0

The Crux

Ecological speciation (see Did You Know?) can be driven by both abiotic (non-living) and biotic (living) factors. The biotic factors that tend to be studied in regards to ecological speciation are antagonistic in nature, such as competition for resources or interactions with predators. However, parasitism is another antagonistic species interaction that is ubiquitous in nature, and therefore might be expected to contribute to ecological speciation via its effects on host-parasite coevolutionary dynamics.

Though a number of studies have investigated the effects of parasites on ecological speciation, little is known about the role of parasites in adaptive radiations, which are bursts of speciation from a single ancestor to many descendent species that then adapt to fill new ecological niches. In other words, an ancestor will be adapted to a specific environment/food types, but its descendants adapt to live in different environments/eat different food. One of the best examples of an adaptive radiation are the Africa lake cichlids, which are the focus of today’s study. The authors wanted to understand if parasites may have contributed to/caused the adaptive radiation seen in African lake cichlids.

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Do Disturbances Promote Biodiversity in the Presence of an Invasive Species?

Image Credit: Paresh Poriya, CC BY 4.0, Image Cropped (also not featuring tunicates)

Testing ecological theories in the Anthropocene: alteration of succession by an invasive marine species (2021) Christianson et al., Ecosphere, https://doi.org/10.1002/ecs2.3471

The Crux

Ecological disturbances, such as fire, floods, or storms, might seem like a catastrophe at first glance, but often they open up space for new species to take the place of dominant ones, creating a more diverse ecosystem. When a disturbance occurs matters as well – if a storm hits right before a particular species starts to reproduce, that species could take advantage of the extra space and become dominant in a short time.

In the 1970s, John Sutherland and Ronald Karlson tested this theory, looking at the invertebrate community of a coastal dock in North Carolina, USA. They found that which species dominated depended on when the community began to grow (a proxy for when disturbance opened up new space).

The area has since seen the introduction of an invasive species of tunicate, Clavelina oblonga. This week’s authors wanted to test whether the original patterns seen in the 1970s still showed up in the presence of the invader.

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