Horace Zeng

I joined the lab of Dr. Kenneth Ross as a Ph.D. student at the University of Georgia in 2016 to study the red imported fire ant (Solenopsis invicta), a problematic pest but also a great study organism for the evolution and behavior of ants.

One advantage of researching invasive ants is their ubiquity. I could observe natural colonies just outside our lab, gaining in-depth knowledge of their natural history. I cultivated and studied hundreds of colonies in the lab, including mature colonies, experimental fragments, and new queen-founded colonies. This hands-on experience is crucial for designing effective experiments.

The polygyne, or multiple-queen, colony in fire ant is a complex social syndrome governed by a inversion-based supergene termed Sb. So far, the proximate mechanisms, including the chemical signals and worker preferences influencing queen acceptance, remain poorly understood. My Ph.D. work helped construct the genotype-to-phenotype map of the polygyny syndrome in S. invicta, with an emphasis on the phenotypic (behavioral) end.

For my future research, I wish to continue working with ants or other social insects.

To me, social insect behavior represents the most remarkable phenotype to analyze scientifically. I would like to focus on the evolution of complex “extended phenotypes” exhibited in ant colonies, such as social form polymorphism, nest building and migration, and the formation of dynamic bodily structures. I wish to study them with an emphasis on the proximate level: how the genetic, chemical signaling, and behavioral pre-adaptations permit the emergence of these complex behaviors.

@ UNIVERSITY OF GEORGIA

Project: Investigate key signals on the polygyne queen of Solenopsis invicta (red imported fire ant) that mediate worker supergene discrimination

Zeng H, Millar JG, Chen L, Keller L, & Ross KG. (2022). Characterization of Queen Supergene Pheromone in the Red Imported Fire Ant Using Worker Discrimination Assays. Journal of Chemical Ecology, 48(2), 109-120.

Project: Investigate how Sb workers influence the collective queen preference of the whole colony

Zeng H, Ross KG, Sasaki T. (2023) Conversion of Social Organization in an Ant Induced by a Minority of Colony Members. In prep.

Abstract: The multiple-queen (polygyne) social form of the red imported fire ant (Solenopsis invicta) is associated with the Sb supergene, a Mendelian genetic element formed by chromosomal inversions. When workers carry this Sb supergene, the colony accepts multiple reproductive queens, given the queens also carry the supergene. In contrast, when a colony’s workers lack the Sb supergene, as is the case in monogyne colonies, the colony tolerates only a single reproductive queen. Colonies previously were shown to display polygyne behavior with as few as 10% to 20% of workers carrying the Sb supergene. However, it remains unknown how such a low proportion of Sb workers affects the collective social phenotype of the whole colony. To identify essential factors in the collective acceptance of Sb queens, we conducted a series of behavioral assays using mixed polygyne-monogyne worker units with the proportion of Sb workers around the threshold level of 20%. We changed the type and amount of interaction between the two worker types in the assays to see which conditions favor the acceptance of multiple polygyne queens. Our results showed that Sb-carrying (polygyne) workers directly reduce aggression by monogyne workers towards the queen when polygyne workers roam freely, potentially an effect of volatile pheromones. As well, Sb workers indirectly influence the queen preference behavior of monogyne workers without contacting the queens. As the duration or intensity of direct interactions between worker types increased, acceptance of polygyne queens also increased, suggesting that specific cuticular compounds from Sb workers play a critical role in the process.

Review Paper: Functions of queen pheromones in ants

As part of my thesis, I wrote a review to summarize our current knowledge of queen pheromones from experimental studies that expressly demonstrate the functional properties in ants.

Zeng H. (2023) Functional properties of ant queen pheromones as revealed by behavioral experiments. Behavioral Ecology and Sociobiology.

Figure: Summary of generalized functional properties of queen pheromones in ants, as represented in a polygyne Solenopsis invicta colony. These functions include: 1) attracting workers; 2) inducing colony maintenance (such as brood care); 3) inducing nestmate discrimination; 4) inhibiting larval sexual development; 5) inhibiting adult reproductive development; 6) inducing worker policing; 7) inducing execution of supernumerary queens in monogyne colonies; and 8) mediating the regulation of queen acceptance in polygyne colonies. White numbers in dark circles indicate that a chemical basis has not yet been demonstrated for this functional category.

Project: Self-assembly of fire ant pontoon bridge

paper in prep, in collaboration with Dr. Dan Goldman’s group in Georgia Tech.

Abstract draft: In social insects, the formation of joint bodily functional structures is often triggered by environmental heterogeneity, such as gaps along the foraging path prompting ants to assemble into bridges across the gap. We show that fire ants (Solenopsis invicta) can self-assemble into functional structures in a homogeneous environment. In laboratory experiments of 8000-ant subcolonies, when ants detect food at the center of a water-filled bowl, they adeptly self-assembled into a floating pontoon bridge of around 500 ants to reach the food. Despite multiple proto-bridges usually initiated around the dish, eventually, a single bridge is formed while other proto-bridges dissipate. The round petri dish provides a radially symmetric set of possible bridge seed points, thus there is no environmental heterogeneity to facilitate the construction of a single bridge. Our mechanistic, agent-based model of the system suggests that this coordinated behavior at the scale of the colony can emerge from individual ants acting (under the uniform and simple behavioral rules??) based on information available locally, including the strength of the local food scent. This lack of centralized control suggests ants’ ability to build a single bridge should be sensitive to environmental conditions. When the environment is made heterogeneous by creating a dish with nonuniform distance between the food and rim, our model prediction that ants form multiple bridges rather than continuing to coordinate across the bowl is verified in experiments. Our study thus gives insights into how self-assemblages can form without the aid of environmental heterogeneity that break environmental symmetry using only local information.

(links to my presentation abstract at >>>> SICB 2022 & >>>> APS 2022 meeting)

@ University of ILLINOIS (undergraduate)

Sep 2015 – April 2016 With Dr. Heath, University of Illinois, Searching for selection for higher wind dispersal ability in western redcedar in the Pacific Northwest. (Poster)

Sep 2014 – Jan 2015 With Dr. Dietrich and Dr. Zaya, University of Illinois, The relationships between Auchenorrhyncha insect diversity and vegetation community composition in Illinois 

Summer research 2014: with Dr. Molano-Flores & Dr. David Zaya, The relationship between reproduction, photosynthetic traits, and genome size for a rare Illinois plant species along the Mississippi River” (Poster)