Peter                          Nonacs

Peter Nonacs


phone:  (310) 206-7332
fax:  (310) 206-3987
office:  LS 3125
lab:  LS 3125

Recent Courses

EE BIOL 132 - Field Behavioral Ecology
EE BIOL 250 - Professional Skills for Biological Research
EE BIOL 98T - Science and Animal Behavior in Media

Research Interests

My overall research program is at the intersection of Evolutionary and Behavioral Ecology. I explore both evolutionary why questions and behavioral how questions. My students and I use a wide range of methods, which range from the development of theory through mathematical modeling, to controlled experiments in the lab and semi-natural field situations, to field work at various sites in California and Panama. This has made the overall research program of my lab unique within Behavioral and Evolutionary Ecology by the range of issues we address. There are five areas in which I have been active over the last decade: (1) Reproductive skew theory; (2) Parental investment strategies; (3) Biocontrol of invasive pest ants; (4) The maintenance and evolutionary consequences of genetic diversity; and (5) General questions of social evolution.
The past three years have been to a degree contemplative as several research threads are winding down, while I set up new ones to explore. Since much of my work is conceptual and theoretical, it is also work that I tend do alone, or in collaboration with a single graduate student. Thus, I do not have the luxury of being part of large publishing consortium that churns on even as I am just ?thinking?. My immediate interests are to more intensely pursue areas 4 and 5, plus I have started a new direction (#6!) on the coevolution of endosymbionts and their hosts.

1. Skew
Most of my experimental work on skew is on task allocation and group benefits in Polistes paper wasps. Social behavior is considered facultative in Polistes, because wasps can always initiate colonies alone. Even supposedly sterile workers, retain all reproductive options. Thus, cooperation between dominants and subordinates can result from mutual benefits, although these can also be skewed in distribution. With Kern Reeve, I played a large role in the development of ?Transactional Skew? (TS) models for the study of cooperative breeding in many taxonomic groups from insects to birds and primates. To measure such skews I derived an index that allows statistical tests to reject assumptions of random distributions (free software is available on my website). This index continues to be the most widely used for distributional questions. Nevertheless, although I feel skew models have served a valuable purpose in sharpening thinking about cooperation, I have come to believe that they do not explain significant aspects of the evolution and maintenance of social behavior (see the 2011 Biological Reviews paper).

2. Parental Investment
The connection of reproductive success to foraging strategies is the one of the dominant themes of my work with ants. In the past, I have shown that ant colonies will trade off between foraging gain and forager mortality in a manner that maximizes colony growth and that the perceptions ant colonies have about foraging risks and resource variability directly affects colony growth strategies. These interests led to collaboration with Jay Rosenheim and Marc Mangel in which we explored how varying ecological and reproductive constraints can affect parental investment strategies in Hymenoptera. The resulting paper showed that instead of a single, optimal size of offspring, there may be a range of investment strategies depending on patterns of foraging success. We have demonstrated considerable variation in offspring size in three species of ants in patterns as predicted by Rosenheim et al. (Gilboa & Nonacs 2006). These ideas formed the basis of a successful NSF proposal on the effects of food availability in Pogonomyrmex salinus. We have finished our field collections and are currently analyzing size distributions of 10,000+ ants. This grant also supported Brittany Enzmann in her related work on the costs and benefits of size for several Pogonomyrmex species in their colony initiation and how this might predict their ecological distribution (e.g., 2010 Insectes Sociaux paper and the paper currently in press at J. Insect Physiol.).

3. Biocontrol of Invasive Species
A quite different aspect of the connection between social behavior and foraging success underlies my work with Argentine ants, Linepithema humile. Argentine ants are a widely introduced pest species that often causes considerable economic and ecological damage. In the Los Angeles area the Argentine ant has practically eliminated all the native ant species. The key to its competitive success is a social structure known as unicoloniality where individual Argentine colonies are not aggressive to each other. Thus Argentine ants truly appear to behave as a superorganism that is immune to the forces of kin selection for nepotism. However, research in my lab found that aggression exists between non-neighboring nests. The results suggest that colony-level identity in the Argentine ant come from environmental cues due to living in different substrates or feeding on different food items (i.e., previously aggressive colonies loss their aggression towards each other if maintained in the lab on identical diets). Since then, we have mapped the infestation patterns of Argentine ants on the UCLA campus in relation to landscaping patterns. Our work shows that infestations appear to follow from water-searching behavior. Two papers have been published on this topic (see Psyche 2012 and J. Appl. Entomol. 2012). The general question of how Argentine ants search their environment continues to be of interest.

4. Genetic Diversity
With Karen Kapheim, I have developed a new model (published in 2 papers in J. Evol. Biol. In 2007 and 2008) for how genetic diversity is maintained in populations through across-genome epistasis and multilevel selection. We have applied the ideas of social heterosis to the evolution of HIV and how the virus progresses within patients from an asymptomatic state to AIDS (the 2012 paper in the J. Evol. Medicine). We also extended the idea of social heterosis to cultural evolution (see the 2014 BBS commentary). This is a very exciting new dimension to my overall research program. 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. I currently have a paper in review at The American Naturalist that attempts to reconcile 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).

5. General Issues about Sociality
Much of my earlier work looked at kin-selective conflicts within social insect colonies, with a particular emphasis on sex ratios and genetic parentage. My student, Claire Narraway, is extending this work to look at how worker policing occurs in honey bee (Apis mellifera) colonies. Her thesis involves multiple levels of analysis from inter-genomic conflicts between maternal and paternal DNA, to individual-level fitness of egg-laying worker bees, to colony-level benefits of preventing reproduction by worker bees.
Kenny Chapin?s thesis work 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 a theoretical model that examines whether encounters between whip spiders are better suited to using self or mutual assessment of fighting ability. Kenny?s experimental work is very exciting on how cave evolution may or may not be affected by gene flow from surface populations. We have an NSF grant proposal currently in review (i.e., invited for a full proposal after an initial preproposal was evaluated) for studying this problem.
Finally, I have published two papers showing that high relatedness may not be as predisposing for social evolution as a commonly accepted paradigm claims (2011 in BMC Evol. Biol. and 2014 in Biol. Letters). These papers have contributed to the heated ongoing discussion as regards the centrality of kin selection in terms of explaining the evolution of cooperative breeding.

6. 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. This work is now in press at Evolution Ecology Research. Sarah is the early stages of her thesis that will build on this model and examine ants as taxonomic group where we might expect to find conflict resolution through the movement of Wolbachia genes into host genomes. This work is currently funded by a $5000 Academic Senate Grant, and formed the basis of Sarah Tolley?s successful NSF-GFRP award.

Selected Publications

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) .

Nonacs, P., "Monogamy and high relatedness do not preferentially favor the evolution of cooperation", BMC Evolutionary Biology, 11 (58): 1-9 (2011) .

Kapheim, K. M., Bernal, S. P., Smith, A. R., Nonacs, P. and Wcislo, W. T., "Support for maternal manipulation of developmental nutrition in a facultatively eusocial bee, Megalopta genalis (Halictidae)", Behavioral Ecology and Sociobiology, 65 : 1179-1190 (2011) .

Nonacs, P., "Ground truth is the test that counts", Nature, 467 : 655- (2010) .

Nonacs, P., "Bordered tug-of-war models are neither general nor predictive of reproductive skew", Journal Theoretical Biology, 266 : 739-741 (2010) .