Biology with a Side of Engineering

      If the HMC Bee Lab were a restaurant which served only academic disciplines, its specialty dish would be an exquisite concoction of social insect ecology. Its most popular side dish would undoubtedly be engineering design. As an engineering student with a strong interest in biology, this menu excites me! What could be better than designing something for a biological application? (Hint: Designing something that works!) 

     One of the main things I’ve worked on this summer is a platform which will serve as the playground for our turtle ant nesting choice experiment. The purpose of our experiment is to understand whether and how the connectivity between nests can affect which nests a colony chooses to inhabit. To do this, we need a platform that mimics the natural habitat of the ants as much as possible in a lab setting. The ants will be placed onto it and allowed to choose among 8 possible nests, half of which are connected via a bridge. Halfway through the experiment, the bridge is moved to connect the other half. Video recordings of the ants’ movement are made throughout the week-long experiment and saved for later analysis. 

      During our field collection trip to the Florida keys, we observed that the trees colonized by the ants had (1) multiple hollow twigs, some of which the ants used as nests, (2) nests separated by at least one branching node, and (3) nests that were spatially separated from food sources. The platform would, therefore, have to incorporate the field observations plus the following functionality set by experimental needs: 

1. Ability to easily create and break bridges/connection points between two areas, as a way to manipulate relative distances between nests;  
2. Fit in a 26x13x10” box;
3. Have ant paths that are at least 0.5 cm wide;
4. Be structurally sound; and 
5. Facilitate automatic tracking of ants along pathways.

      Armed with the platforms from previous experiments (see them here and here), Nora’s preliminary version of the platform, and my toolkit from E4: Introduction to Engineering Design and Manufacturing, I began the iterative design process outlined below.  

Step 1:  Use AutoCAD software to create the pieces for the platform. [1]  

Step 2: Laser cut sheets of acrylic to transform the digital design into a physical one. [2]

Step 3: Glue the pieces together to create a structure. 

The last step is my absolute favorite part of the process because there is a rush of emotion either from knowing that all calculations, hard work, and patience paid off, or from realizing that it’s time to go back to step 1.

Top: [1] Screenshot of the file used to laser cut some of the platform pieces. Bottom: [2] Laser cut parts for the inner pentagon piece. This particular part of the platform took about five trips to the laser cutter, lots of glue, and multiple failed prototypes.

                                     

Left: [3] Bridges visible on the left side of the platform. Right: [4] Fully constructed platform in experimental set up.

  The end result is a 5 spoke platform [3] with holes almost everywhere as a way to increase perceived distance under the limitations of the box dimensions. As the ants walk around the platform, they are forced to make decisions about which path to choose, making the overall trip seem longer. The platform’s pentagon shape helps with stability and increases the number of nests from 6 in past experiments to 10. 

       

                         

Left: [5] The notches on the top leg are visible from this angle. Middle: [6] Semi-transparent red acrylic tube nests in T-shaped base. Right: [7] Top leg with red rectangles.

      The top leg [5] is designed to hold two acrylic tube nests in a T-shaped base [6] and has small notches on the sides where removable bridges can be placed and relocated depending on the needs of the experiment. Areas of interest are marked with a red polygon [7] so that computer algorithms can more easily track how many and where ants go.

                                                               

[8] Bottom leg with food platforms but no food.

      The bottom legs [8] have slots where two rectangular pieces can slide through. These rectangular pieces serve as platforms where food is placed so that ants have to travel a bit further between their cozy homes and their yummy food.

                                                                 

[9] Pentagon tower with central decision point marked in red. 

      Another element of the platform is the inner pentagon tower [9]. It is designed to increase the distance travelled by the ant by forcing them to climb over it if they want to get to a nest on another leg. Some areas of the tower are covered with fluon to keep ants from walking in places where they aren’t supposed to. The walls on the top of the tower guide the ants further toward the center of the pentagon, where they are forced to choose a side to exit through, kind of like being presented with a menu and having to choose just one out of the many delicious options. 

      Now that we’re halfway through the experiment, I’m excited to see what parts of the platform worked the intended way and which ones not so much. For example, when the ants choose to explore the platform, they walk exactly in the areas I hoped they would. However, the ants sometimes (frustratingly!) choose to explore the floor of the box they are in. Because these ants live in trees, it would be more realistic if they spent their time exploring their fake tree (a.k.a. the platform). I hope that at the end of the experiment, we will not only learn something about the way these seemingly simple creatures choose to create their networks, but also about how to design a better platform for future experiments. As for me, I’ve thoroughly enjoyed rolling up my sleeves, bringing a little spice to the HMC Bee Lab with what I’ve learned in my engineering classes, and getting a further taste of biology with a side of engineering. 

Further Reading:

Ben-Alon, Lola, et al. “Similarities and Differences between Humans' and Social Insects' Building Processes and Building Behaviors.” Construction Research Congress 2014, 2014, doi:10.1061/9780784413517.006.

Dym, Clive L., et al. “Engineering Design at Harvey Mudd College: Innovation Institutionalized, Lessons Learned.” Journal of Mechanical Design, vol. 134, no. 8, 2012, p. 080202., doi:10.1115/1.4006890.

Powell, Scott. “Ecological Specialization and the Evolution of a Specialized Caste In Cephalotes ants.” Functional Ecology, vol. 22, no. 5, 2008, pp. 902–911., doi:10.1111/j.1365-2435.2008.01436.x 

Media Credits: 

All figures created by author.