Peter Nonacs

(310) 206-7332
310G Botany
lab website

Recent Courses

EE BIOL 132 - Field Behavioral Ecology
EE BIOL 250 - Professional Skills for Biological Research
EE BIOL C126 | EE BIOL C242 - Behavioral Ecology

Research Areas

Behavior, Evolutionary Biology, Theory

Research Interests

My overall research program intersects Evolutionary and Behavioral Ecology. I explore both evolutionary why questions and behavioral how questions. For the past three years we have produced several high quality and interesting pieces of work. It is also important to take into account my research ethos. Much of my work is conceptual and theoretical; done alone or in collaboration with individual students to develop theory for their thesis projects. I have 7 ongoing areas of research.
1. Skew
In 1992 Kern Reeve and I published an experimental paper that laid out and provided a test of Reproductive Skew Theory (RST). The basic premise was that cooperative breeding between two or more individuals could enhance the evolutionary fitness of all participants as long as they agreed on a mutually satisfactory apportionment of reproduction (i.e., the skew). The key variable in this transactional framework was genetic relatedness, such that skew could always be greater between closely related dominants and subordinates. Our 1992 paper and subsequent theoretical and experimental papers created great excitement within the behavioral and molecular ecology communities as ?skew? could be a Rosetta Stone for understanding the evolution of stable cooperation.
For the time period of 2006-11, an average of almost 15 papers a year were published on RST (as found in a Web-of-Science search for RST as a topic). However, as RST was reaching its zenith of popularity, I was having grave problems with the idea. In 2006, I published two papers that I believe showed convincingly that our original work suffered from a serious methodological flaw and that relatedness appeared to play no significant role in determining cooperation. In 2007 and 2010, I published papers showing that mathematical models expanding on original work were also fundamentally flawed. Finally, in 2011 I published, with Reinmar Hager, the definite review of RST experiments and models that clearly showed RST to not be the hoped-for general solution to how cooperation as a phenomenon evolves.
Although my conclusions were strenuously opposed in print by some of my former co-authors, I believe my arguments have carried the day. From the same search as above, over the last three years only 4 papers come up as hits for RST, on average. The number of citations of yearly citations of RST are declined rapidly from its peak of 682 in 2014 (citation number always lags publication numbers!).
The paradox is that my later papers are more substantive and will stand the test of time far better than my early papers, but will be cited less (e.g., early pro-RST papers cited 80+ times; better anti-RST papers, less than 40). Their greatest value is to dissuade young researchers from going down a rabbit hole. Nevertheless, the rise and fall of RST has served a valuable purpose in sharpening thinking about cooperation, even though ultimately having failed. Reproductive skew exists as a significant phenomenon across cooperatively-breeding groups. We can now move on to more productive avenues for explaining its occurrence (e.g., my work on social heterosis).
2. Parental Investment
The connection of reproductive success to foraging strategies is the one of the dominant themes of decades of work with ants. Building on my past collaboration with Jay Rosenheim and Marc Mangel and my field work (e.g., Gilboa & Nonacs 2006), led to testing several models of parental investment theory in ants, through collection and measurement of 10,000+ individuals. This NSF-supported work is the final stages of being prepared for submission (see Enzmann and Nonacs manuscript).
3. Foraging strategies
Over the past three years, my focus has been on how ant colonies organize themselves in response to the fundamental necessity of finding food. With Amelia Yates, we found an interesting phenomenon in Argentine ants (Linepithema humile) for a foraging ?rule?. When given several paths of equal distance to a food item, the ants significantly organized to use the one with the fewest number of turns (Yates & Nonacs, 2016). The value of having such a rule is not immediately obvious and has led to subsequent work with Kaleda Denton on much more ambitious project. Here we observe ants foraging in our ?grid-world?, where different areas in which food might be found, vary in complexity and predictability. Interestingly in a more predictable world, ants become fixated on certain spots and often miss food. In fact, they are more efficient in encountering food when it is randomly and unpredictably distributed. We also found that ant foraging strategies appear to maximize rapid exploitation rather than maximization of encounters. Both Amelia and Kaleda did their work as part of their Honor?s theses.
With my incoming PhD student, Amanda Robin, we are beginning projects on how animals (squirrels in this case) decide between two food items: one which can be eaten when found or stored for later, and an alternative which must be eaten when found and cannot be cached. This will test between present and future food value in animal?s foraging behaviors.
4. Genetic Diversity
With Karen Kapheim, I have developed a new model for how genetic diversity is maintained in populations through across-genome epistasis and multilevel selection. The concepts and models we are developing have implications to understanding a wide range of infectious diseases and for the evolution of social behavior through genetically diverse groups rather than groups of closely-related kin. Most recently, I have extended this work in Frontiers in Ecology and Evolution reconciling how kin nepotism and the benefits of genetic diversity can both be incorporated in the simple framework of Hamilton?s Rule for cooperation (rb ? c > 0). The paper shows that societies of low relatedness can readily evolve as long as genetic diversity enhances group success. This framework then explaining a commonly observed phenomenon in social insect colonies: Worker drifting, where workers will abandon their natal nest and enter an unrelated one. This was assumed to be either a mistake of recognition or a selfish strategy where the worker sought to reproduce and therefore parasitize non-kin. However, drifting has been observed across many species at high frequencies that the pure mistake explanation is difficult to rationalize. Also, drifters rarely act selfishly and mostly are indistinguishable from natal workers in how they contribute to nest welfare. My models show that drifting, far from being negative, can operate as a positive indirect reciprocity for the good of all nests in a population. Exchanging sterile and hard-working offspring generates positive genetic diversity with all the attendant benefits and little to no down sides from conflict or selfish behavior.
5. General Issues about Sociality
Working with a recent graduate, Dr. Kenny Chapin, has opened up a new avenue of social evolution concerning the first steps of sociality in whip spiders (Amblypigids). Populations of whip spiders that live in caves appear to exhibit the incipient stages of a social life history when compared to solitary populations living in forests. We are currently collaborating on experimental work on how cave evolution may or may not be affected by gene flow from surface populations.
6. Intraindividual interactions.
With Dr. Chapin, we are modeling how territorial and other conflicts are resolved between pairs of animals (with the eventual application of the models to experiments with Kenny?s whip spiders). The interesting experimental result that matches our models is that animals often appear to use only assessment of their own condition, rather than appearing to assess both themselves and their opponent. Mutual assessment would appear to give superior information and therefore always be preferable to only assessing one?s self. However, our models show that the possibility that a mutual-assessor makes two errors that can sum (i.e., mis-assess both self and the opponent) can lead to dire errors. Hence, our model makes the novel prediction that species ought to have a variety of assessing strategies and not just be self or mutual-assessors. Mutual assess when small; relay primarily on self-assessing when large. When we have presented this work at conferences and seminars it has generated an excited response and we will soon be submitting it to peer-review.
7. Endosymbiont-host coevolution.
Endosymbiotic bacteria such as Wolbachia spend their entire life histories within other organisms? cells. This close proximity of endosymbiont and host genomes allows for transfers of DNA between them. Such events are observed to be strongly biased, however, with DNA migrating in the direction from cytoplasmic elements to host nuclei. Sarah Tolley and I showed, via simulations, that the dynamics of cell division can produce such a bias. Nuclear DNA is predictably distributed to offspring, but random chance plays a large role in vertical transmission of cytoplasmic elements. Thus, even if DNA initially transfers equally across genomes, transfers into host nuclei are retained more often than ones into endosymbionts. Bias in retention may also explain the extensive DNA migration from organelles like mitochondria and chloroplasts into nuclei. Consequently, biased migration has potentially interesting consequences for life history evolution, whereby genes that exchange locations also switch ?sides? for intergenomic conflict. Thus, biased migration of genes is a long-term evolutionary process favoring host interests.

Selected Publications

Chapin, K. J., Nonacs, P. and Hayes, L. D., "Evaluating an open-exam approach to engaging students in evolutionary paradoxes: Cheating to Learn", American Biology Teacher, 79 : 144-148 (2017) .

Kapheim, K. M., Chan, T. -Y., Smith, A. R., Wcislo, W. T. and Nonacs, P., "Ontogeny of division of labor in a facultatively eusocial sweat bee Megalopta genalis", Insectes Sociaux, 63 : 185-191 (2016) .

Yates, A. A. and Nonacs, P., "Preference for straight-line paths in recruitment trail formation of the Argentine ant, Linepithema humile", Insectes Sociaux, 63 : 501-505 (2016) .

Nonacs, P. and Tolley, S. J., "Certainty versus stochasticity: Cell replication biases DNA movement from endosymbionts and organelles into nuclei", Evolutionary Ecology Research, 16 : 195-202 (2014) .

Nonacs, P. and Kapheim, K. M., "Cultural evolution and emergent group-level traits through social heterosis", Behavioral and Brain Sciences, 37 : 266-267 (2014) .

Nonacs, P., "Resolving the evolution of sterile worker castes: a window on the advantages and disadvantages of monogamy", Biology Letters, 10 : 20140089- (2014) .

Kapheim, K. M. Smith, A. R. Nonacs, P., Wcislo, W. T. and Wayne, R. K., "Foundress polyphenism and the origins of eusociality in a facultatively eusocial sweat bee, Megalopta genalis (Halictidae)", Behavioral Ecology and Sociobiology, 67 : 331-340 (2013) .

Nonacs, P., "Reciprocity, reputation and nepotism", American Scientist, 99 : 422-424 (2011) .

Nonacs, P., "Kinship, greenbeards, and runaway social selection in the evolution of social insect cooperation", Proceedings National Academy of Sciences, USA, 108 (Supp. 2): 10808-10815 (2011) .

Nonacs, P. and R. Hager, "The past, present and future of reproductive skew theory and experiments", Biological Reviews, 86 : 271-298 (2011) .