Mountains, mice and the impacts of infection

In this Insight, Luke Wilde talks about his new paper, varying costs of infection, extreme environments and taking a metabolic lab in to the field.

Specifically, we showed that the effects of an infection can be greatly heightened if the host exists in a consistently stressful environment, and if the investigators use current, relevant metrics of performance and fitness.

About the research

What’s your paper about?

The article (Botfly infections impair the aerobic performance and survival of montane populations of deer mice, Peromyscus maniculatus rufinus) is about the interaction of biotic and abiotic stresses as a context-dependent happening. Specifically, we showed that the effects of an infection can be greatly heightened if the host exists in a consistently stressful environment, and if the investigators use current, relevant metrics of performance and fitness. For lowland mice, the costs of infection are usually minimal to their survival and fitness; however, as we have shown these costs can be greatly heightened when the host is already under physiological stress. In our system, the mice experiencing the hypoxic and cold conditions of higher altitudes show such an increased cost to their survival and fitness. These mice likely experience selection for certain values of flexible traits that when taxed by such an infection, cannot stand up to these harsh conditions

Infected deer mouse.pngBot flies (Cuterebridae) are a large parasitic fly. The female bot deposits her eggs on the ceilings to mouse burrows, which hatch when they feel the warmth of a passing mouse. Once hatched, they enter the nostrils and settle into a warble for development, eventually weighing up to 5% of their host’s body mass. While in the warble, the bots injest the interstitial fluids and cellular debris before exiting  ~25 days later. Despite this, for more than 120 years, small mammal ecologists have viewed the bot fly as a highly co-evolved parasite that imparts little detriment to its host, even increasing female fitness post infection (Burns et al., 2005). Any investigation we came across showed that botflies did not change survival, did not greatly alter fitness, and barely affected resting metabolic rate. We then, wanted to investigate how this relationship could be context-dependent at higher altitudes in Colorado.

On a mountain
On a mountain

What makes your paper different from previous work?

One of the big differences is our study region. We are among the first studies to investigate the impacts of botfly infections on highland and montane populations of Peromyscous since the 70’s (2350 m a.s.l., Capelle et al., 1970).

What’s more, we are only the second known paper (after Careau et al. 2007 with T. striatus) to investigate the effects of bot fly infection on small mammal performance. By using respirometry and cold-induced VO2,max, we could detect a drastically depressed metabolic scope in infected mice. What’s more, because our study took place over a 3-year span, we show that bot fly mice has a 19 – 34% lower over-winter survival than those without infection!

Deer mouse eating
Deer mouse eating

Were there any problems setting up the experiment and gathering your data?

Capturing mice is always difficult, especially at higher elevations in complex terrain. But the most challenging part was operating a metabolic lab in the field- that meant transporting massive tanks of helium and mini-fridge style containers to reestablish the lab every time we moved between sites.

Were you surprised by anything when working on it?

I was surprised by how clearly we could see the trends during our data collection. We would capture a botfly- infected mouse and as we read its hemoglobin levels everyone in the crew would give a resounding ‘woah’ at just how depleted some of them were. Before this, I hadn’t seen such strong effects with my own eyes.

Now that this paper has been published, what’s the next step?

 The next step is to dive into thinking about pathogen expansion to novel elevations. The Cheviron Lab is collaborating with an entomologist to investigate the distribution of bot flies, establish more sites at the lower ends of our current transects, and to develop further hypotheses. Most notably, we’re trying to investigate how the adaptive landscape – the differential fitness of a trait across all possible values – of lowland populations may be affected such that individuals with trait values similar to those of highland populations because botflies and hypoxia/cold seem to induce a lower achievable summit metabolic rate and truncated metabolic scope.

Who should read your paper (and why)?

Anyone interested in exploring the possible changes in biotic interactions as a result of global climate change. Also, anyone who is interested in animal physiology, as we use some really cool techniques to assess aerobic performance! This paper provides more knowledge to build from when considering the way natural communities may be affected.Parasites and pathogens are an area of research that will only grow if current trends persist.

Luke WildeAbout The Author

How did you get involved in ecology?

I have always been enthralled by the natural world, and while growing up, I spent every moment I could in the woods or on the rocks of Montana, but I discovered my great inspiration for ecology during a biodiversity-focused study abroad in Ecuador during my time at Gonzaga University (2017) as an undergrad,. That experience, and the thrill of analyzing data, cemented my passion for my career.

What’s your current position?

I am a master’s student in the Senner Lab at the University of South Carolina. For my thesis, I am studying the adaptive, predator avoidance behaviors of nesting waterbirds (specifically Hudsonian Godwits) in the sub-Arctic and the ways that small-bodied predators (Red Fox) respond to the spatiotemporal distribution of prey.

What’s the worst thing about being an ecologist?

Sunburn and uncooperative study species.

What is the best thing about being an ecologist?

I get to see the world through another being’s perspective everyday! Ecology allows me a brief glimpse into the logic and elegance of an animal’s life-experience.

What do you do in your spare time?

In my spare time, I like to mountain bike, rock climb, and go birding. I am also a sucker for southern rock, jazz, and beer gardens.


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