ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year, but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Marco Graziano is first author on ‘ Frequency-dependent viscosity of salmon ovarian fluid has biophysical implications for sperm–egg interactions’, published in JEB. Marco conducted the research described in this article while a PhD candidate in Matthew Gage's lab at University of East Anglia, UK. He is now a senior postdoctoral associate in the lab of Simone Immler at University of East Anglia, investigating how sexual and natural selection shape eco-evolutionary processes at the gametic level: before, during and after the reproductive event.

Marco Graziano

Describe your scientific journey and your current research focus

I studied biological sciences and marine biology at the Università Politecnica delle Marche, in Ancona, Italy (my home country). There, I also eventually achieved my Master's degree in marine biology and oceanography. During those years I tried to absorb everything and got involved in as many practical research experiences as possible. This period gave me amazing opportunities: to take part in several research trips abroad, for example, in the Philippines and Indonesia. Subsequently, I embarked on a series of postgraduate research projects which solidified my knowledge of fish reproductive biology and evolution and granted me crucial experience in molecular and physiological techniques. I then spent a year at the Memorial University of Newfoundland (MUN), where I investigated the differences in reproductive performance between repeat and virgin spawner fish, and the reproductive isolating mechanisms that are expected to evolve between closely related species such as Atlantic salmon (Salmo salar) and brown trout (Salmo trutta).

As a PhD candidate at University of East Anglia (UEA), under the supervision of the late Matthew Gage, I investigated sexual selective mechanisms at the gamete level in Atlantic salmon. My work, done in collaboration with the population genomics lab at the Institute of Marine Research (IMR) in Bergen, Norway, focused on investigating inbreeding avoidance mechanisms in salmon and farmed salmon introgression into wild populations. We also determined reproductive competitiveness between farmed and wild salmon and tested the presence of evolutionary adaptive responses of gametes to improve offspring fitness.

My goal now as a postdoc in Simone Immler's Lab at the UEA is to make the most of the powerful genomic approaches available to gain further insights into the mechanisms driving the inheritance and preservation of specific traits from the haploid to the diploid stage and vice versa, through natural and sexual selection processes, using zebrafish as a model.

How would you explain the main finding of your paper to a member of the public?

You may be familiar with the video in which a guy is able to run on the water of a swimming pool filled with water and corn starch. That is possible because the solution that fills the pool is a non-Newtonian fluid, and can behave as a solid, giving a strong elastic response underneath the runner's feet, if hit strongly enough. The same fluid behaves instead as a liquid when the force impressed is not strong enough – if you walk on it, you sink!

Well, we discovered that the ovarian fluid of salmon, a substance released with eggs that is pivotal for fertilisation success, mate choice and offspring fitness, is also a non-Newtonian fluid. However, in contrast to the corn starch, the ovarian fluid gets thinner and thinner under increasing shear stress, and this happens in ranges that are comparable to those acting on the fluid by sperm that are trying to reach the egg. This could mean that faster sperm will swim through a looser molecular structure in their path toward the egg, gaining an advantage in their chances to fertilise it. Slower and poor-quality sperm will instead be disadvantaged from reaching it, because they will encounter a more solid-like structure hindering the passage. This shows the co-evolution of male and female gametes and could be a way by which females are able to control and bias fertilisation, within and among partners (with different sperm speeds and qualities), even when this process occurs outside of their bodies.

Which part of this research project was the most rewarding?

Seeing a wild salmon at the peak of its reproductive beauty is incredible. The brilliant display of patterning, colours and the ‘hooks’ tells us quite a lot about how much these guys invest in reproduction. These characteristics are striking, especially when you are adapted to seeing salmon just in their farmed, marine and/or filleted form.

Why did you choose JEB to publish your paper?

The other co-authors and I believe that JEB has a history of diverse and influential fish biology articles at the interface between biophysics, biochemistry, evolution and reproduction. It is a well cited and multidisciplinary journal, and its impact factor is growing steadily. Moreover, some of the pivotal papers in reproductive and evolutionary ecology which guided our work were also published in JEB.

Are there any important historical papers from your field that have been published in JEB?

Yes, there are quite a few indeed. ‘The Propulsion of Sea-Urchin Spermatozoa’ by Gray and Hancock (1955; doi:10.1242/jeb.32.4.802), as well as several pioneering works on sperm bioenergetics and guidance published by Charles Brokaw between 1965 and the early 1970s.

A large adult male Atlantic salmon (Salmo salar) displaying reproductive colour patterning and ‘hook’. Photo credit: Monica Solberg, Havforskningsinstituttet.

A large adult male Atlantic salmon (Salmo salar) displaying reproductive colour patterning and ‘hook’. Photo credit: Monica Solberg, Havforskningsinstituttet.

What do you think experimental biology will look like 50 years from now?

I can imagine a wider usage of computational models and synthetic biology approaches. I see the experimental biology of the future being the result of solid scientific exchanges between very different fields, with a better knowledge and higher attention to the welfare of model organisms, and with students and trainees learning techniques in the metaverse.

I would like to study sexual selection and reproduction in deep sea species, where neither light nor temperature change can trigger reproductive seasonality and where visual precopulatory cues are scarce or absent. That is fertile land for new-post copulatory mechanisms of sexual selection. I bet that in these environments we could have the chance to unveil new and curious reproductive strategies, adaptations that can tell us a lot about our evolution, and at the same time pave the road for new discoveries to be applied in the biomedical and biotechnological fields.

What's next for you?

In the short term, I will still be working on sexual selection, but I would like to broaden my technical skill set and master a few more molecular techniques and computational tools, to be a more independent researcher. I would like to use diverse animal models (although fish will still be my favourite) to answer more efficiently specific evolutionary questions with the organisms that better allow me to do so. I also want to take this opportunity to write some grants to secure fundings for my future lines of research and keep associating a teaching component to my research activities.

I like to think that I will stay in an academic environment and eventually make my way to be a principal investigator. I have been lucky because my family supported my choices and supported me economically during my studies, but this is not always the case. I left my home country long ago, and this was a good decision for me; however, I would like to go back in the future, to share what I have learned over the years to hopefully contribute to the cultural and scientific development of the place that gave me a lot.

Marco Graziano’s contact details: Department of Biology, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.


M. J. G.
C. F.
Frequency-dependent viscosity of salmon ovarian fluid has biophysical implications for sperm–egg interactions
J. Exp. Biol.