In Insights we discover the story behind a recent publication in Functional Ecology: what inspired the authors to do the research, how did the project develop and what wider impact might the work have?

This week, Bjorn talks with Wilco Verberk about his recent paper, Thermal limits in native and alien freshwater peracarid Crustacea: The role of habitat use and oxygen limitation. Wilco is affiliated with the Radboud University in the Netherlands, where he works in the Department of Animal Ecology and Ecophysiology. With his Dutch-German research team, Wilco’s paper is the result of an impressive laboratory experiment that aimed to study the heat tolerance of four native and four alien crustaceans under different levels of oxygenation. Wilco’s work was the result of a Marie-Curie Fellowship, funded though the European Research Council.

In your research, you aim to understand the effects of warming on the physiology – respiration physiology to be precise – of aquatic ectothermic species. On your website, you state that you’re trying to solve the question of why species grow faster in warm water, but stay smaller. How does this relate to the work you published in Functional Ecology?

The FE paper illustrates how oxygen can modify aquatic ectotherms’ (in this case, crustaceans) sensitivity to warming by looking at their survival. While lethal effects are manifested at quite extreme temperatures, sublethal effects, including those on growth and the resulting size, are manifested at less extreme temperatures. In my research of the conundrum you mentioned (i.e. the Temperature-Size Rule), I am taking a similarly oxygen-based perspective to investigate how temperature affects size at age.

You collected the individuals for the species used in your experiment from very specific locations. Habitat use was one of the drivers that best explained differences in heat tolerance, irrespective of species. I immediately think of a potential role of adaptation and plasticity. Would plasticity be of importance to the successful spread of a species?

Differences in habitat use across our studied species were indeed instrumental in explaining patterns in heat tolerance, much more so than geographical origin (alien vs native species). So it appears that you can’t judge species on their origins. Instead, what seems to matter are the underlying traits, and these could be well captured by habitat mode (and likely relate to differences in respiratory physiology between standing and running waters). Clearly not only the absolute level of tolerance, but also the ability to change tolerance levels with acclimation and adaptation will be a key factor governing the successful spread of exotic species. This aspect was not part of our study, but we did show that the role of water oxygenation was more important in species that were sensitive to heat tolerance. This suggests that different mechanisms may underpin heat tolerance across species. These different mechanisms could be more or less malleable by acclimation and adaptation, thus also having consequences for interspecific differences in the role of adaptation and plasticity.

Your research suggests that the physiological mechanisms that underlie heat tolerance are species specific, but that in general poor oxygenation of water reduced heat tolerance. The invasive species Dikerogammarus villosus is rather susceptible to hypoxia and heat stress. In your plain language summary, you conclude that improving oxygenation of water can offset the negative effect of global warming. Maybe I’m thinking along the wrong lines, but would D. villosus not also profit from waters richer in oxygen?

The conclusion was about how to alleviate the looming threat of global warming for species in general, but you are correct in saying that Dikerogammarus villosus will be one of these species that will profit from improving the oxygenation of water. Incidentally, this high susceptibility to hypoxia likely goes a long way in explaining its the current habitat use: D. villosus occurs mainly underneath large stones that protect the shoreline of the river. The transport ships cause a lot of water movement and this keeps their microhabitats well-oxygenated.

In this paper, one of the results shows that the influence of oxygen on heat tolerance is very much context dependent. What do these results mean for conservation strategies aimed at preventing invasions?

For both native and alien species, we found species that were tolerant and species that were susceptible to interactive effects of heat and hypoxia. Hence, you cannot manage sites in one specific way to prevent invasions (though you may control which alien is more likely to invade). Although this was not investigated in our study, it helps to have a healthy, biodiverse assemblage of native residents. These can limit opportunities for alien invaders, and as such confer biotic resistance to the ecosystem. Managing sites to restore and conserve biodiversity appears to be the best course of action in general, but I would be cautious in advising a one-size-fits all strategy. Usually tailor-made approaches based on local circumstances work best.

Your personal website suggests your children to be heavily involved in your research. Are these helping hands the key to being incredibly productive as you are? More seriously, how do you balance work and home life?

Sometimes my children accompany me in the field or in the lab. I try to involve them to some extent so they have some understanding of why I like my work so much. At the same time, my family also provides perspective on what is really important in life, which is not always research.

Would you have any advice for early career researchers, pursuing a similar career pathway as you took? What to do, what to avoid?

I have really learned a lot from collaborating with many different people. They invariably perceive the issue at hand slightly differently to myself, and discussing and reconciling these different viewpoints is fun, can build friendships and will make for better science.

Read the paper here.