In this insight, we discussed with Rony Izhar and Chen Gilboa the background behind their paper “Disentangling the steps of the infection process responsible for juvenile disease susceptibility”.

Dr. Rony Izhar is currently a research assistant in the School of Zoology in Tel Aviv University. She completed her PhD under the supervision of Dr. Frida Ben-Ami, studying the effects of host age on parasite evolution. She is interested in ecology, evolutionary biology and behavioral sciences.

Chen Gilboa currently works at a Global Contract Research Organization (CRO) as an Administrative Trial Assistant, focusing on drug development and management for oncological patients. Prior to this role, Chen served as a data and help desk support manager at a local CRO. Chen completed her MSc in the School of Zoology in Tel Aviv University, under the supervision of Dr. Frida Ben-Ami. Her thesis focused on the influence of host age on disease spread.

About the paper

What’s your paper about?

Our paper examines how different steps of the infection process of a water flea by a bacterium are influenced by the age at which the water flea host was exposed. In doing so, we are trying to explain why juvenile water fleas are more likely to become infected than older ones.

What is the background behind your paper?

Daphnia magna is a tiny water flea that is found in many fresh waterbodies – in rain pools, ponds, springs and lakes, among others. Pasteuria ramosa is a bacterium that infects several species of Daphnia, causing castration and premature death. The Daphnia–Pasteuria system is one of the most well-studied host-parasite model systems worldwide. It is used for tackling “pure science” questions in evolution, ecology and epidemiology, as well as in applied fields such as ecotoxicology and environmental safety. Here we try to uncover the mechanism responsible for high juvenile susceptibility to parasites in Daphnia.

How did you come up with the idea for it?

During Rony’s PhD thesis, she discovered differences in parasite success among young, recently-matured, and adult D. magna infected by P. ramosa (Izhar & Ben-Ami 2015; Izhar et al. 2015). We wanted to figure out the source of these differences.

What are the key messages of your article?

“The devil lies in the details of the infection process”.

How is your paper new or different from other work in this area?

This is the first paper to delve deep into the step-wise infection process of an invertebrate host, in order to uncover why juveniles are more susceptible to infection than adults, and which steps in the infection process are responsible for these differences. Childhood diseases in humans and other vertebrates are well-documented. So are phenomenological observations in many invertebrates that juveniles are more susceptible to infection than adults. But never before has an attempt been made to strip down the infection process into steps, in order to understand which step is age-dependent and which step isn’t. By disentangling a few infection steps and observing the infection dynamics in different age groups, we were able to infer general infection symptoms and point out more than one defense mechanism in Daphnia.

Does this article raise any new research questions?

The main research questions that rise from our study relate to the need to better understand invertebrate immunity, its improved ability to cope with parasitic infections with age, and in particular with chronic diseases.

Who should read your paper?

People interested in epidemiology, evolutionary biology and ecology, as well as those interested in understanding the eco-evo dynamics of parasite virulence.

About the research

What is the broader impact of your paper?

That host age at exposure, which is often considered an intrinsic property of the population and thus overlooked in infection assays and experimental evolution studies involving invertebrates, actually matters for understanding host-parasite interactions.

Did you have any problems setting up the experiment/gathering your data?

The logistics involved in preparing three separate experiments were extremely challenging. In one experiment, we had to observe the animals for 48 hours, in 4-hour shifts around the clock. Chen spent the first night in the lab in a sleeping bag. It’s definitely a night to remember!

Where you surprised by anything when working on it?

We were very much surprised to find evidence of clearance in late infection steps, a previously undocumented phenomenon in invertebrates, where late infections are often considered chronic, lasting until host death. Another cool insight was finding a relationship between disease symptoms and the progression of parasite development.

What are the big questions still to answer?

Our study explains how individual-level responses to infection contribute to susceptibility. However, we still lack knowledge on how individual-level age effects influence the ecology of within-host competition among parasite strains/species as well as parasite transmission. It is time to move beyond individual-level studies of age effects into studies of eco-evo dynamics in age-structured populations.

What is the next step in this field going to be?

The next step includes finding the immunological factors and mechanisms responsible for parasite inhibition, the regulation on their genes expression and how they change with age.

About The Authors

How did you get involved in ecology?

Rony still recalls going to water ponds as a kid, swiping a net, and collecting all the little creatures in the pond. Some became fish food, while others became pets, but it was always fascinating to find all this richness and to observe the interactions between them.

What’s your current position?

Both of us are research assistants, Rony at Tel Aviv University and Chen in a biotech firm.

What is the best thing about being an ecologist?

The added value of being an ecologist is being out in nature. It is so nice that your daily work takes you to beautiful places and by doing so, you can contribute to nature conservation. Water ponds are becoming a rare scenery in Israel; studying them and the animals inhabiting them may help in conservation.

What is the worst thing about being an ecologist?

Watching the decrease in natural habitats as well as the change in the species composition of water ponds as a result of anthropogenic actions, such as when the local municipality introduces Gambusia fish that prey on everything in the water pond.

What do you do in your spare time?

Yoga, traveling, swimming, going out with friends and during Corona, we watched a lot of Netflix.

One piece of advice for someone in your field…

Although there are lots of challenges, nature is fascinating, the interactions are endless, and it’s totally worth it!

• Izhar, R, Gilboa, C, Ben‐Ami, F. Disentangling the steps of the infection process responsible for juvenile disease susceptibility. Funct Ecol. 2020; 00: 1– 13. https://doi.org/10.1111/1365-2435.13580