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. Here, I outline six current areas of ongoing research in the topics of: (1) Reproductive skew theory; (2) Parental investment strategies; (3) Biocontrol of invasive pest ants; (4) The maintenance and evolutionary consequences of genetic diversity; (5) General questions of social evolution; and (6) Sexual selection, sexual conflict and alternative reproductive strategies. Although most of my work and that of my students is with social Hymenoptera (ants, bees and wasps), my lab is open to any model system or species depending on how well suited they are to answering exciting evolutionary questions.

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 modeled such cooperation in a transactional framework that predicts: the level of benefits needed to retain subordinates; and the reactions of wasps to perceived changes in their ‚??social contract‚??. Our early positive results 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). 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 2011 Biological Reviews paper).
For example, one of our first major findings within Polistes was that subordinates increased their aggression when sexual eggs were removed. Even though this result appeared supportive of reproductive skew models, I was unhappy with this conclusion for a number of reasons. When we reanalyzed a replication of our 1992 experiments, we found a fundamental error in our previous method of behavioral analyses. When the data were properly analyzed, it became clear that aggression in wasps has no connection to reproduction. A second significant failure of TS models relates to predicting the dynamics of reproduction in groups of distantly-related or unrelated wasps. All variants of TS models predict that reproduction should be significantly split across such group members. However, the data across several species almost universally show that reproduction is highly monopolized by the dominant wasp, regardless of relatedness (see 2006 American Naturalist paper). Finally, I showed why TS models may not predict behavior. TS models predict optimal behavior, but ‚??TS-type‚?? wasps have minimal selective advantages over wasps using simpler conventions for group association. Thus, any evolutionary cost will prevent transactional behavior from arising in populations (see 2006 paper in Annales Zoologici Fennici).
Although TS models fail to explain the evolution of cooperative behavior, high skew in reproduction is a defining feature of cooperative groups in many species. Our continuing work is on how skew in non-reproductive behaviors (e.g., foraging, vigilance, etc.) is established and the degree to which it improves group success. This work is being actively pursued by my Ph.D. student, Thea Wang. Also I published with Dr. Reinmar Hager a review that simplifies the various reproductive skew mathematical models, summarizes tests of skew models, and suggests exciting new directions for research on reproductive sharing (e.g., examining the quantitative genetics of skew and the importance of indirect genetic effects created by the social environment).

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).

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 are in submission on this topic.

4. Genetic Diversity
With Karen Kapheim, I have developed a new model (published in 2 papers in J. Evol. Biol.) 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. 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.

5. General Issues about Sociality
I am interested in how ants explore and sample their environment. In the past, I have shown that: (i) Foragers can communicate both the food quality and associated mortality risks of patches; (ii) Foragers leave ‚??footprints‚?? even when they are not actively recruiting nestmates; and (iii) Sampling behavior of novel territory is based on expectations generated through previous experience. Currently I am working on projects that look how colonies distribute and fuel their foragers. Foraging for most species is a dangerous activity. If the forager is lost, then also all the valuable food reserves it is carrying are lost too. Thus colonies face yet another trade off: well-fed foragers can range far and have little chance of starving, but are costly to lose. It seems that most species solve this trade off by having their foragers carry very little food so they are always close to starvation. This work may also have some interesting implications in artificial life and robotics as one of the problems with miniaturizing robot explorers is providing them with suitable energy supplies. How ant colonies deal with very similar problems may suggest novel solutions.
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.

6. Sexual selection, sexual conflict and alternative reproductive strategies
My graduate student, Gilene Young, is studying the effects of sexual selection and sexual conflict on male and female alternative reproductive strategies in sand wasps (Steniola nigripes).

Selected Publications

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) .

Wang, T. B., A. Patel, F. Vu and P. Nonacs, "Natural history observations on the velvety tree ant (Liometopum occidentale): unicoloniality and mating flights", Sociobiology, 55 : 787-794 (2010) .

Rossi, B. H., P. Nonacs and T. L. Pitts-Singer, "Sexual harassment by males reduces female fecundity in the alfalfa leafcutting bee, Megachile rotundata", Animal Behaviour, 79 : 165-171 (2010) .

Enzmann, B. L. and P. Nonacs, "Digging beneath the surface: incipient nest characteristics across three species of harvester ant that differ in colony founding strategy", Insectes Sociaux, 57 : 115-123 (2010) .

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