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 but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Tom Mulder is an author on ‘ Constraints on percussive seismic signals in a noisy environment by European fiddler crabs, Afruca tangeri’, published in JEB. Tom is a postdoctoral researcher in the lab of Dr Beth Mortimer at the University of Oxford, investigating the role of seismic vibrations in wild animal behaviour.

Tom Mulder

How did you become interested in biology?

I grew up on a farm in the north of the Netherlands and consequently grew up very close to nature. Subsequently I had the good fortune to attend UWC Lester B. Pearson College of the Pacific on the south coast of Vancouver Island, BC, Canada. If you have ever been to Vancouver Island, you will understand that it is impossible not to fall in love with the natural world whilst living there. From giant Douglas fir forests full of old man's beard, bears and wolves, to the kelp forests teeming with fish, otters and sea lions – I could not have asked for a better source of inspiration to move into the field of biology.

Describe your scientific journey and your current research focus

I completed my undergraduate degree in zoology at the University of St Andrews, under Prof. Graeme Ruxton's supervision. There, I studied everything from marine mammals at the Sea Mammal Research Unit to bird nest predation for my thesis. Encouraged by the experience, I got in touch with Dr Beth Mortimer and Prof. Fritz Vollrath and worked for 1 year as a research assistant in the Oxford Silk Group exploring the effect of web disturbances on spider behaviour. I caught the bug, if you will, and ended up pursuing a PhD studying the role of seismic vibrations in the behaviour of wild African savanna elephants and European fiddler crabs as model species. This all was possible through the University of Oxford NERC Doctoral Training Partnership.

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

Fiddler crabs are incredibly numerous in terms of species and occur all around the world. Collectively, the males of these species are well known for their large claws and claw-waving displays to attract females – and this visual behaviour has been studied quite extensively. However, males of several fiddler crab species are also known to generate ground vibrations, which may be used to signal to other individuals. We studied these vibrations for a species in Southern Europe using geophones, which are essentially microphones for ground vibrations. Using a computing process called machine learning (ML), we subsequently tested whether the features of the vibrational signals could be clustered by behaviour type, to assess whether the vibrations conveyed information about the types of associated behaviours. In addition, we looked at whether the shape of the vibration-generating individual (for example, the size of its large claw) related to features of the vibration signals, and whether wind affects vibrational noise in the environment. In short, the ML process proved quite successful at categorising behaviours based on vibrations alone, but it is not yet sufficiently reliable to forego human verification. In addition, it appears that males with larger claws can produce stronger vibrations, and that wind does increase seismic noise in the intertidal zone. Overall, the seismic signals were all broadband in structure (meaning that they included a whole range of frequencies) – which may be advantageous when signaling seismically as a small animal.

Measuring morphological features of an Afruca tangeri male to correlate with seismic signals.

Measuring morphological features of an Afruca tangeri male to correlate with seismic signals.

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Why did you choose JEB to publish your paper?

Because we relied on a novel means to record fiddler crab behaviours in the wild, the work aligned nicely with the remit of JEB. Not to mention, the broad readership of the journal ensures that the work may be read by people across focal areas of research, and the methods used may prove useful for researchers studying animals in other contexts. Finally, but certainly not least, much of the work was generously funded by The Company of Biologists through the Travelling Grant and Travelling Fellowship.

What is the most important piece of equipment for your research, what does it do and what question did it help you address?

Geophones are ground vibration sensors and were the most important piece of equipment for this research. Although this tool is commonly used in the earth sciences, it remains underutilised in the field of biology. Interestingly, geophones are sufficiently sensitive to record seismic vibrations generated by tiny crabs, as well as elephants and other megafauna. In this case it allowed us to assess whether, from a recording perspective, distinct and behaviour-specific seismic signals are emitted by male fiddler crabs during courtship signalling. The seismic sense of these creatures is particularly interesting to me because it is a relatively unintuitive means of communication for us humans.

What's next for you?

As I am wrapping up my DPhil, I am looking to shift into the world of rewilding, conservation and nature credits in the private sector. I believe that seismic sensors may prove incredibly valuable supplementary tools to camera traps and acoustic sensors to assess the success of these undertakings and measure biodiversity. Crucially, with the rapid expansion of ML and AI techniques, it should become increasingly affordable to sweep through great volumes of acoustic and seismic data. Hopefully I can bring these components to the field and aid with the implementation of these methods in industry, and improve the verification processes that conservation and rewilding organisations rely on.

Tom Mulder's contact details: University of Oxford, Department of Biology, 11a Mansfield Road, Oxford OX1 3SZ, UK.

E-mail: [email protected]

Mulder
,
T.
,
Yang
,
Y.
,
Morley
,
E.
,
Miller
,
T. E.
,
Hending
,
D.
,
Taylor
,
G. K.
and
Mortimer
,
B.
(2025).
Constraints on percussive seismic signals in a noisy environment by European fiddler crabs, Afruca tangeri
.
J. Exp. Biol.
228
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jeb249323
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