Hermit crabs as an animal model for social interaction and resource inequality

Hermit crabs as a model for resource distribution and acquisition in social groups

Emily Yang

Includes a link and file of my full research paper, as well as a full list of references.

Hermit crabs as a model for resource distribution and acquisition in social groups

Emily Yang

Mentor: Amy Sheck

North Carolina School of Science and Mathematics (NCSSM)

Durham, NC

Rationale/Introduction

The land hermit crab: Not a hermit, and not a crab

They are social animals!

Shell resources: scarce (not many to go around), quantifiable (can be counted), and discrete (in distinct pieces)

Hermit crabs exhibit some very interesting social structures regarding resources: vacancy chains

Chase et al. 2020 sampled wild hermit crabs and found that the resource distribution did not resemble theoretical models based on purely ecological factors — in fact, they more closely resembled human wealth distributions.

The distribution of shell resources in terrestrial hermit crabs may be affected by factors analogous to those affecting wealth distributions in humans.

What if we studied the social aspects affecting resource distributions in hermit crabs, but in a controlled, experimental environment? And could that tell us something about resource inequality in humans?

Experimental Design

THE QUESTION: What is the effect of exposure to varying levels of social interaction, as represented by group size and line of sight, on the overall distribution of resources in social groups of hermit crabs?

Two measures of social interaction:

Group size Sight

Individual: 1 Restricted: wood walls

Dyad: 2 Unrestricted: clear plastic walls

Group: 6

Methods

30 Coenobita clypeatus hermit crabs from Carolina Biological

I placed groups of hermit crabs into the study arena and gave them a choice test to switch into random shells provided (or not switch at all)

Hermit crab behavior was observed and video recorded

Trials were conducted simultaneously, with dividers (sight restricted or unrestricted) between compartments

Results

To investigate the effect of varying levels of social interaction on the resource distribution of hermit crabs, I approached my results from several angles. I also approached my results from a shell behavior-focused view to broaden my scope of behavior and inform further discussion.

Comparison of initial and final average (using weight and opening size as measures of value)

Difference in Gini coefficient between the initial and final state

Line of sight and crab behavior: Compared crab-shell interactions (antennation) and shell changes between sight restricted and unrestricted for individual trials

Shell change frequency per crab: Plotted indication of change in shell and crab identification number

Discussion

Interpretations

Crabs that change their shells tended to switch into larger shells (in weight and/or opening size)

In almost all cases, the Gini coefficient increased from initial to final state, with a larger positive change in individual groups compared to dyads

Changing shells was a rare event, potentially due to risk inherent of switching

Presence of other crabs may play a factor in crab behavior

Implications

No synchronous vacancy chains were observed; however, the Gini coefficient changed anyway

This suggests that there may be other factors and social behaviors that may also impact distribution of resources beyond synchronous vacancy chains

Limitations

This study was limited by scale, size, and time; I was working with a very small sample size of hermit crabs in a very limited period of time

A universal measure of “value” for crab shells remains undefined, and not all shells “fit” all crabs

Recommendations

Get to know your study organism! Does it have specific behaviors regarding shells and other hermit crabs? What type of shell is preferred? How do they sense each other, shells, and the world?

This is an area that has a lot of potential for further exploration, especially with larger sample sizes and longer periods of time

Resource inequality in human societies is much more complex, but studying hermit crab resource distributions in a controlled study environment could offer insight into one aspect of a multifaceted issue.

Selected References

Brent, L. J. N. (2015). Friends of friends: Are indirect connections in social networks important to animal behaviour? Animal Behaviour, 103, 211–222. https://doi.org/10.1016/j.anbehav.2015.01.020.

Chase, I. D., Douady, R., & Padilla, D. K. (2020). A comparison of wealth inequality in humans and non-humans. Physica A: Statistical Mechanics and Its Applications, 538, 122962. https://doi.org/10.1016/j.physa.2019.122962.

Davidson, R. (2010). Innis Lecture: Inference on income distributions. The Canadian Journal of Economics, 43(4), 1122–1148. https://www.jstor.org/stable/40925271.

Rotjan, R. D., Chabot, J. R., & Lewis, S. M. (2010). Social context of shell acquisition in Coenobita clypeatus hermit crabs. Behavioral Ecology, 21(3), 639–646. https://doi.org/10.1093/beheco/arq027.

Sokolowski, M. B. (2010). Social interactions in “simple” model systems. Neuron, 65(6), 780–794. https://doi.org/10.1016/j.neuron.2010.03.007.

A full list of references can be found at the end of my research paper.

Acknowledgments

This presentation covers a research journey I started a little over two years ago — I owe much to those around me, who have believed in me and my work, and provided invaluable support to me, in and out of the lab.

Many thanks my research mentor, Dr. Amy Sheck, for her guidance in research methodology and design as well as her editorial and statistical advice; the Glaxo Research Endowment for supporting my research financially; Dr. Kimberly Monahan, for her support during the Glaxo Summer Research in Biology Program; Dr. Floyd Bullard for his statistical advice during my data analysis phase; the NCSSM Research in Biology Class of 2020 for their research mentorship in the early stages of this project; and the NCSSM Research in Biology Class of 2021 – Melissa Du, Benet Ge, Viha Patel, Nick Sortisio, and Jamie Wenzel – for their editorial comments and support throughout the undertaking of this project. Finally, thank you to my parents, for their boundless support of me, my ideas, and this project throughout its many stages; and thank you to the friends, faculty, and community members who have shaped me into the scientist and person I was when I embarked on this project, and who I am today.

It started with a story.

Junior year me was sitting at my computer with the New York Times Science section open for a weekly assignment in her Research in Biology class. Typical Thursday. She clicked on an article that caught her eye, read it, thought oh, that’s cool, and chose another article for her assignment. That article, Even Hermit Crabs Have Wealth Inequality (or rather, the paper that article had covered) would become the basis of the research project she would spend the next year working on. But she didn’t know that then. It was just an interesting story.

Before that, it started with another story. As a child, I used to devour book after book about natural science. My favorite word was “why?” — the answers that science gave to each “why” and the further “whys” revealed with each answer thrilled me. Maybe it has to do with my parents, both scientists by trade; maybe it has to do with a lifetime of seeking. Either way, science has always been a part of my life, and as I’ve grown, so too has my relationship with science.

In my sophomore year of high school, I applied to and was accepted to the North Carolina School of Science and Mathematics (NCSSM), and in junior year, I was one of twelve students who applied and was accepted to my school’s Research in Biology program, a year-long course teaching research methodology through practice and culminating in an independent biology research project. I was excited and apprehensive to conduct my own independent research. I loved biology, but there was a seed of insecurity inside of me, always whispering that I wasn’t good enough, or smart enough, or experienced enough for this. I carried on anyway, unsure of the future — of myself or my research.

It was not an overnight discovery that led to my project. I didn’t know it would be hermit crabs, and I didn’t know it would be resources. But reading that article opened a door that opened more doors until I was stumbling into new worlds of behavioral science, ecology, and, well, hermit crabs, that I didn’t even know where there.

Several long nights of writing literature reviews and grant proposals later, I was looking forward to spending three weeks in the summer conducting research at NCSSM’s biology lab — we all are. However, due to COVID-19 restrictions, I had to shift to conducting my experiments at home. Rooms became converted to at-home labs, as tanks filled with sand and then, hermit crabs. In this research, I was both the principal investigator — formulating the research topic, hypothesis, and experimental concepts and design — and the lab technician — carrying out the study, setting up hermit crab habitats and testing arena at my home with my parents’ help.

Fall 2021. I finished my data collection. Started analyzing, interpreting, and writing about the data. Struggled through the process of writing a paper. Made a poster. Made another poster.

Winter 2022. I hear that I’m an AJAS Fellow, and my heart skips a beat. The old adage of good enough? rings through my head. But I did it, and it’s done, for now, and I learned a lot from it — now, I hope someone else can learn something from it, too.

Doing independent research in high school was a transformative experience for me. In many ways, the work was tough and monotonous, and I found myself scared time and time again of failure. Embracing the ever-questioning nature of science as directed toward myself is something I’m still learning, even now. But it also taught me an invaluable lesson about the nature of science: that it is tedious, that it is work — that every drop of knowledge gained throughout the centuries has been the result of so much effort poured in by scientists across the ages. And, that throughout the tedium that research so often can become, holding onto the wonder that made you first start is important. Making connections is important; collaborating is important; learning just for the sake of learning is important.

Science is a story, and I’m honored to write a line in it.