Author Archives: Adam Hasik

It’s Who and Where You Are

A role for the local environment in driving species-specific parasitism in a multi-host parasite system (2022) Hasik & Siepielski, Freshwater Biology,

Image credit: Adam Hasik, image cropped

The Crux

Parasites are an ever-present part of every ecological community on Earth, yet there are some species that harbor more parasites than others. In systems where parasitism is density-dependent, meaning parasitism increases with host density, the most common/numerous species will harbor the greatest amount of parasites. Yet there are also cases of species-specificity, whereby parasites specifically target a single host species. In other host-parasite systems, local-adaption plays a role in parasitism dynamics, whereby parasites are better at attacking their local hosts than they are attacking foreign hosts and/or hosts are better at defending themselves from local parasites than foreign parasites.

With all of these different factors affecting how host-parasite systems operate, it is important to identify when and if each one is operating within specific ecological communities. This is especially necessary when ecological communities are comprised of multiple host species and multiple parasite species, all of which can/do interact with one another.

To investigate the above factors, we first conducted a survey of parasitism in damselflies (Enallagma spp.) and their water mite parasites (Arrenurus spp.). From there, we then carried out to field experiments to understand why parasitism operates the way it does within this system.

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My Enemy is Not the Enemy of My Other Enemy

Do predators keep prey healthy or make them sicker? A meta- analysis (2022) Richards et al., Ecology Letters,

Image credit: Angah hfz, CC BY-SA 4.0, via Wikimedia Commons

The Crux

Ecology is all about understanding how the various parts of the natural world interact with one another. While we tend to think about things like predators, competitors, and parasites as separate entities that have their own effects, it is important to remember that these species interactions can interact with one another. Such interactions will have implications for the dynamics of natural populations.

Of interest is how predators and parasites interact with one another through their shared resources, prey/host species. Specifically, the Healthy Herds Hypothesis (HHH, see Did You Know?) predicts that predators reduce parasitism within the populations of their prey. While the HHH was based on a mathematical model, other theoretical models predict a range of effects, from predators decreasing parasitism to actually increasing parasitism. Because the empirical results from experimental studies show similar variation in their results, today’s authors wanted to determine if there is indeed a consistent, overall effect of predators on the parasitism of their prey.

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Hunting and Evolution

Hunting alters viral transmission and evolution in a large carnivore (2022) Fountain-Jones et al., Nature Ecology & Evolution,

Image credit: Joachim S. Müller, CC BY-NC-SA 2.0

The Crux

It’s no secret than humans have had an enormous impact on the native wildlife of our planet, and we have looked into many of these complicated relationships and effects before on Ecology for the Masses. One common interaction is that of hunting, whereby humans hunt and kill an animal for recreation and/or food. Regardless of your feelings on hunting, such removal of animals can be an issue in systems where there is density-dependent transmission, meaning the more animals there are, the more likely there is to be parasite transmission within the populations of these animals. Reducing animal populations via hunting can either decrease, have no effect on, or even increase density-dependent transmission.

These changes in transmission dynamics (and subsequent changes in infection patterns) will have effects on the evolution of the parasites infecting these animals, making it easier for researchers to detect if (and how much) transmission is occuring. To investigate these patterns, today’s authors studied data on feline immunodeficiency virus (FIV) and its puma (Puma concolor) hosts. FIV is mostly benign and infects its hosts for life, though puma hosts can become infected with different strains of FIV. The goal of today’s study was to understand how hunting affects transmission dynamics of FIV within populations of puma that are hunted.

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Your Immune Defenses Are What You Eat

Condition‐dependent immune function in a freshwater snail revealed by stable isotopes (2022) Seppälä et al., Freshwater Biology, link to article

Image credit: Bj.schoenmakers, CC0, via Wikimedia Commons

The Crux

There are myriad factors at play when it comes to parasitic infections, but the primary physiological barrier for the parasite is the immune function of host organisms. Despite its importance and usefulness, the immune function is costly to maintain. Building and effectively using immune defenses relies on the host being able to secure enough food to properly fuel its defenses. As a result, individuals in poor condition are more susceptible to parasites. Building off of that, if the conditions in a given area are poor/worsening, then an entire population of organisms may be vulnerable to disease outbreak.

Many studies have investigated the dependence of immune function, including one of my own, but many of those studies take place in lab settings where the food given to a host is carefully controlled. While there are obvious benefits to controlling experimental conditions, it can be hard to generalize the findings of a lab study to the natural settings that organisms actually live in. Today’s authors utilized an observational study of a freshwater snail (Lymnaea stagnalis) to better relate host condition in nature to immune function.

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Can You Afford to be Picky?

The better, the choosier: A meta-analysis on interindividual variation of male mate choice (2022) Pollo et al. , Ecology Letters,

Image credit: barloventomagico, CC BY-NC-ND 2.0

The Crux

Choosing who to reproduce with (mate choice – see Did You Know?) is a major player when it comes to the evolution of a species, yet it can be tough to know when individuals (and which individuals) should be choosy in their partners. A general trend is that when there are a plethora of potential mates available, too many for a given animal to mate with, they must make decisions on who to mate with. For many species, females tend to be the choosy sex, given the limited number of reproductive resources that are available to them (i.e., eggs) and how many males are usually available to mate.

Despite this commonality of female mate choice, male mate choice is also widespread in the animal kingdom. It is therefore important to know how different factors affect how a male chooses his mates. One factor that may play a key role is male quality, or the ability of a male to acquire mates. It could be that males that vary in their quality also vary in how picky they are. Today’s authors used a meta-analysis, or a “study of studies”, to understand how males make their decisions.

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Getting Hot Hot Hot

How melanism affects the sensitivity of lizards to climate change (2022) Mader et al. , Functional Ecology,

Image credit: Tony Rebelo, CC BY-SA 4.0, via Wikimedia Commons

The Crux

Climate change is a fact of life. Every day we uncover more of the negative effects it will have on the various animals, plants, and fungi in the natural world. Species range contractions are one such effect, and they occur when the area that a given species normally occupies shrinks. They are directly linked to a species’ risk of extinction, with this risk growing as a species inability to adapt to new environments grows. Though the theory sounds logical, many of the exact mechanisms behind range contractions are still unknown.

Ectotherms are organisms that depend on the surrounding environment to regulate their own body temperature, making them particularly vulnerable to climate change. Many different biological mechanisms are involved in regulating temperature, but the ability to reflect solar radiation is a key player. Indeed, the ability of organisms to reflect solar radiation (aka energy from sunlight) is part of the thermal melanism hypothesis (see Did You Know?). Melanistic (darker) organisms may be favored under climate change, due to the protection against UV radiation provided by melanin. However, melanistic individuals are more prone to increased heating, which can be bad. Today’s authors sought to understand how climate change would affect melanistic organisms.

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Why Are There So Many Species?

The causes and ecological context of rapid morphological evolution in birds (2022) Crouch & Tobias, Ecology Letters,

Image credit: Andrej Chudý , CC BY-NC-SA 2.0

The Crux

One of the biggest questions facing evolutionary ecologists is why some groups of organisms contain SO MANY species, while others are relatively sparse in comparison. We’ve discussed adaptive radiations on Ecology for the Masses before, which is when a burst of speciation occurs within a group, with new species adapting to fill new ecological niches. It could be that the reason for such uneven groups is that some clades, or related groups of organisms, are more prone to such adaptive radiations than others. If this is true, it would mean that such clades experience not only an increase in the number of lineages (species) that they contain, but also the number of traits they exhibit.

Increases in the speciation rate and trait evolution are the hallmarks of adaptive radiations, but they may not occur at the same time, which can lead to some different outcomes. Clades may diversify rapidly, without really evolving new traits, and this is known as a “non-adaptive radiation“. In contrast, a lineage may quickly evolve new traits without speciating, which is known as an “adaptive non-radiation“. To understand the causes and context of such evolutionary scenarios, today’s authors studied the history of bird evolution.

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The Lazy Bird Gets the Worm

A fine-scale analysis reveals microgeographic hotspots maximizing infection rate between a parasite and its fish host (2021) Mathieu-Bégné et al., Functional Ecology,

Image credit: Viridiflavus via Wikimedia Commons, CC BY-SA 3.0

The Crux

Interactions between hosts and parasites can be broken down into two broad stages: the encounter filter and the compatibility filter. The encounter filter determines whether a parasite actually comes in contact with a host, through either a spatial or temporal overlap. After the encounter filter comes the compatibility filter, the stage at which a parasite either successfully infects a host and takes the resources needed, or is successfully repelled by the host. Though the encounter filter must come before the compatibility filter, most studies tend to focus on the compatibility filter. Yet for a parasite to successfully encounter a host, many obstacles must first be overcome.

Parasites tend to be very small, and hosts tend to be rare. Furthermore, many hosts move around the environment and/or are only available to a parasite at specific times of the year. Finally, in many cases the environment that a single host can occupy is huge. With all of these difficulties facing parasites, it is not surprising that they have evolved many different strategies to effectively find hosts.

However, some species don’t appear to display these strategies. For them to succeed, it is possible that they distribute themselves in a non-random (see Did You Know?) fashion in the environment, clumping together to form “hot-spots” of infection. Other studies have investigated this “hot-spot” phenomenon before, but tended to focus on larger spatial scales, anywhere from hundreds to thousands of meters. Today’s authors wanted to understand if investigations at much smaller spatial scales (i.e., ~10 meters or less) could provide further insight into the spatial aggregation of parasites.

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Inbreeding is Depressing

Sex-specific inbreeding depression: A meta-analysis (2021) Vega-Trejo et al., Ecology Letters,

Image credit: Monica R., CC BY 2.0, Image Cropped

The Crux

One very basic rule in nature is that it is bad to produce offspring with a close relative. The loss of fitness associated with this sort of breeding is called the inbreeding depression, and it happens because inbreeding leads to a greater chance that recessive or deleterious (i.e., bad) alleles will be expressed. Though inbreeding affects both male and female offspring, it is unknown as to whether or not there is a general rule of it affecting one sex more than another. Today’s authors sought to answer that question by using one of my favorite statistical techniques: the meta-analysis (see Did You Know?).

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Mussel Mass

Facilitation alters climate change risk on rocky shores (2022) Jurgens et al. 2022, Ecology,

Image credit: Paul Asman and Jill Lenoble, CC BY 2.0, Image Cropped

The Crux

Climate change has a marked effect on the environment, and in most cases will be (and already is) devastating to natural systems. However, some areas (and the organisms within them) are less vulnerable to harm than others. Biogenic habitats, or habitats created by a given species which reduce physical stress for other species that live in them (more in Did You Know?), are predicted to reduce the harmful effects of climate change. In particular, they can reduce heat and desiccation.

There have been an abundance of studies on the positive effects of biogenic habitats, but little has been done to explore if these habitats can provide protection against climate change. Today’s authors utilized a marine system to understand how biogenic habitats respond to climate change, allowing for predictions of what will happen to these systems.

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