Date on Senior Honors Thesis
Senior Honors Thesis
College of Arts and Sciences
Tropical ants; sensory ecology; antennal lobe glomeruli; insect sensilla; insect antennae
Differential tissue allocation in animal sensory systems is common and varies with habitat. Worker ants perform a variety of complex tasks that depend on neural capacity, with chemical cues considered central to ant behavior. The antennal (olfactory) lobes of ant brains are often highly developed relative to other insects; however, arboreal ants that live in environments with higher light levels tend to rely more on visual cues than olfaction compared to terrestrial ants. The extent to which habitat-driven behavior affects neural investment in tropical rainforest ants is unknown. Here, I focused on three common tropical ant species (Pseudomyrmex boopis, P. oculatus, and P. gracilis) that nest and forage in different habitats from the ground to the canopy within neotropical rainforests. I tested the hypothesis that relative investment in olfactory neural structures varies interspecifically with habitat association. I predicted that: (1) Canopy-dwelling species have a lower density of sensilla on their antennae and fewer glomeruli associated with olfaction; (2) Canopy-dwelling species have a lower antennal lobe to glomeruli volume ratio; and (3) Antennal sensilla density is correlated with the number of glomeruli among individuals within species. The results did not support these predictions, with the canopy species P. oculatus having the greatest sensilla density relative to its body size and a higher average number of glomeruli. There were no differences in antennal lobe to glomeruli volume ratios among species. Despite a small sample size (n = 5) preliminary results suggest there is a positive relationship between the number of sensilla and the number of glomeruli in these ants. The findings of this study suggest that allometry is critical in determining the relative number of sensilla and glomeruli and that size differences do not restrict investment in necessary olfactory structures across the three species.
Short, Heather Evon, "Olfactory tissue investment in tropical rainforest ants scales with body size." (2020). College of Arts & Sciences Senior Honors Theses. Paper 231.
Retrieved from https://ir.library.louisville.edu/honors/231
Like many other animals, ants have brains with distinct lobes that manage different sensory inputs. Here, I explored patterns of neural investment in three closely related ant species that live in different habitat conditions within the rainforest. Specifically, I expected that the species that spends most of its time in the dark forest understory (Pseudomyrmex boopis) will show more investment in the brain regions associated with olfaction (antennal lobes) than with vision. By contrast, I expected that the species that spends most of its time in the brightly lit environment of the rainforest canopy (P. oculatus) to invest more in the visual portion of its brain. The third species, P. gracilis, is less habitat-specific, thus was expected to have more balanced olfactory and visual investment. Contrary to my expectations, two key sensory features of these ants—sensilla (hair-like receptors on the antenna) and glomeruli (globular structures within the brain antennal lobes)—did not follow these patterns. Pseudomyrmex oculatus showed a greater density of sensilla than the understory-nesting P. boopis, the opposite of what was expected. There were also no differences in antennal lobe to glomeruli ratios—a measure of how much of the antennal lobe was devoted to glomeruli—between all three species. The results of this study suggest that the differences observed in sensilla and glomeruli are best explained by scaling with changes in body size. More specifically, the necessity for retaining the same olfactory functionality across all three Pseudomyrmex species is more important than investing in other regions. Understanding the fit between organisms and their environment is critical to understanding how global change will affect biodiversity in vital ecosystems like tropical rainforests. The results suggest that the three species have the capacity for adequate functionality across their different habitats and are more likely to handle changes in their environment.