Rhodamine B – a non-toxic biomarker for assessing the distance travelled by rats in urban slums

Post provided by Awoniyi Michael Adedayo

Each year Methods in Ecology and Evolution awards the Robert May Prize to the best paper published in the journal by an author at the start of their career. Ten Early Career Researchers made the shortlist for this year’s prize, including Awoniyi Michael Adedayo, who recently defended his PhD from the Federal University of Bahia (UFBA) Brazil. In this interview, Awoniyi shares insights on his paper ‘Using Rhodamine B to assess the movement of small mammals in an urban slum’.

Tell us your career stage, what you work on, your hobbies and interests

I would say I am in the early stage of my career, as I recently defended my PhD thesis a few days ago and hoping to join a new institution soon. I am interested in the management of zoonotic diseases transmission, via the development of a lasting rodent population management plan in urban low-income environments. Considering that the populations of those living in these areas will likely experience a geometric increase by 2030, it would likely lead to high human-rodent contact and probable disease transmission.  My hobbies include but are not limited to football, chess, adventure and music.

How would you pitch your article to someone if you had just 30 seconds in an elevator?

This article sought to in part, expose the misery behind the unsatisfactory results from the previous rodent control initiatives. Rats are difficult to control, as the surviving population could rapidly recover through reproduction/immigration from a nearby community following population decline/intervention, probably due to the lack of sufficient information about their movement ecology. Also, the current methods (i.e. capture-mark-recapture, passive integrated transponders & telemetry) that are available for tracking rat movement come with ethical concerns in urban settings. Besides, these methods are capital intensive and risky as infected animals could be introduced into the environment without the assurance of being recaptured. Considering the economic and medical importance of rodents, this study illustrates the movement of rats in a difficult urban environment using a unique method “Rhodamine B (RB)” that is effective, easy to use, and capable of producing fast and precise results that are devoid of GPS-signal difficulties, and the ethical uncertainty that is synonymous with the previous methods. Therefore, this method should be useful in the development of future rodent control protocols.

Where did the idea to develop this method come from?

This idea emanated from my experience in Nigeria and Brazil. Generally, there is no holistic government approach that is targeted at rodent population management in Nigeria. Individuals usually employ rodenticide application to their infested apartments which have been largely ineffective. Contrarily in Brazil, there is a body called “Centro de Controle de Zoonoses – CCZ” that is tasked with keeping household rodent propagation at bay. However, whenever the body is called to attend to a building that is infested with rodent population, what it does is basically apply rodenticide to such building and maybe a few others around the infested building which has similarly not been effective just like the case of Nigeria. 

Considering these, I felt the management of rodent populations, will greatly benefit from a genuine understanding of their travel distance within or around households. Therefore, I carried out a literature review to see what has been done about rodent movement ecology, especially in urban settings. Upon discovering that not much has been done in this field, I came up with different methods that at the time I thought could be useful in investigating the movement of rodents in urban slums. However, upon the presentation of these ideas to my senior colleagues and supervisor, it was agreed that we should explore the option of Rhodamine-B “RB”, and as they say, today the rest is history.

What were the major challenges in developing this method? How did you overcome this?

The major challenges experienced during the development of this method were

1. The fear of the rats not accepting/eating the RB baiting
2. Rats getting utterly dispersed after RB bait consumption
3. Residents not allowing the snap traps to be activated in their buildings as experienced in Marechal Rondon (another of our study site “favela” that is also located in the outskirt of Salvador) due to the presence of chicks in the same environment
4. Residents not able or willing to put up with dead rats overnight and thereby throwing captured rats away before the team’s arrival the following day after activation.

These challenges were overcome by:

1. Carrying out at least two nights pre-baiting, to acclimatize the animals to the bait type
2. Against the initial proposal to capture rats in just a direction, we ended up capturing rats in four directions in order to increase our trapping success
3. We adequately engaged and explained the purpose of the experiment to the residents to get their buy-in. Also, we placed snap traps in areas that are mostly accessible to rodents and not non-target species
4. We urged the residents to keep any captured animal in a black polythene bag until the arrival of the team       

How do you plan to apply the method you published/what have you been working on since its publication?

I am working on disseminating the results via presentations in conferences/seminars to as many audiences as possible, to get the results to the policymakers and government representatives. Likewise, there are plans to incorporate the same method into another future research plan.   

Who will benefit from your method?

Researchers and community groups, especially those that are interested in rodent control programs should greatly benefit from this method.

If you could travel back in time, would you add to or change anything about your method?

Although, this might be difficult considering the terrain where the samples were collected, however, if it is possible, I would probably increase the distance to which the rats were trapped to at least 200m and see if it yields a different result. Also, I would conduct rat trapping twice a year, to evaluate the probable variations in rat movement across seasons (dry and rainy) .

You can read Awoniyi’s full paper here.

Learn more about the Robert May Prize 2022 shortlist here.