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email:  pnonacs@biology.ucla.edu
phone:  (310) 206-7332
fax:  (310) 206-3987
office:  LS 3125
lab:  LS 3125
homepage:  http://www.eeb.ucla.edu/Faculty/Nonacs

research interests:  Behavioral ecology and social evolution, using both theoretical and experimental approaches.

Research Interests

In their 1978 book, George Oster and Edward O. Wilson likened a social insect colony to a factory/fortress. The fitness of the colony in terms of lifetime production of sexuals is dependent on the efficiency at which the sterile workers collect resources and defend the colony. This, of course, entails a trade off: the more workers that are produced, the more secure the fortress, but at a cost of lowered factory production. This simple metaphor attracted me as a graduate student because of the potential with social insects to directly connect foraging behavior to reproductive consequences. In the ensuing years, I have come to realize how much more complicated the functioning of the factory/fortress truly is. Fortunately, these complications almost always produced new avenues of research in social evolution and foraging behavior and made my overall research program unique within Behavioral Ecology by the range of issues it addresses. Along with the factory/fortress analogy, Oster and Wilson presented the colony as a superorganism where commonality of interests overwhelm individual goals. Although common interests are certainly strong selective factors, my research has shown that individual interests are far from suppressed. Conflicts can and do arise within colonies over sex ratios of offspring, parentage of males, the number of reproductives and the role of the queen in organizing colony activity, the developmental future of larvae, the colony initiation process and the formation of stable partnerships between colony-founding Polistes paper wasps. My present work with Polistes deals with skew in task allocation and group benefits. Social behavior is considered facultative in Polistes, because wasps can always initiate colonies alone. Even individuals thought to be constrained to be sterile workers, can retain all reproductive options. Thus, cooperation between all dominants and subordinates must result from mutual benefits, although these can be skewed in distribution. Collaborating with Kern Reeve, we have modelled 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’. We have found that: (i) Subordinates are particularly sensitive to manipulations of sexually-destined offspring and reproductive skew can change markedly with the season; and (ii) A significant fraction of wasps neither begin their own nests or engage in cooperative behavior. Instead they are floaters, waiting for opportunities to usurp weak foundresses or adopt orphaned nests. I have also recently published papers on more accurate methods of measuring skew in both reproductive and non-reproductive contexts . The idea that group stability can be predicted by skew models is certainly not restricted to reproductive contexts. Understanding the dynamics of group foraging and the stability of dominance hierarchies can also be increased by using skew-based transactional models. 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 growt and that the perceptions ant colonies have about foraging risks and resource variability directly affects colony growth strategies. These interests led to a collaboration with Jay Rosenheim and Marc Mangel in which we explored how varying ecological and reproductive constraints can affect parental investment strategies in Hymenoptera. This paper shows that instead of a single, optimal size of offspring, there may be a range of investment strategies depending on patterns of foraging success. I have shown such a correlation between sex ratio strategies and foraging success and I am now collecting an extensive data set of individual colony reproduction across several species of ants. With my postdoc, Dr. Smadar Gilboa, we will use this data set to test for investment patterns predicted by Rosenheim et al. Although the analyses are not yet complete, the preliminary data support our predictions of a considerable variation in offspring size, with a non-normal distribution. 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 ‘super’ superorganism that is immune to the forces of kin selection for nepotism. However, recent research in my lab (with my Masters student, J. S. C. Chen) 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). Further research with Argentine ants will try to elucidate the mechanisms by which aggression does or does not develop between colonies. Besides the conceptual interest of how selfish interests are repressed in unicolonial species, this work may have significant applied benefit. If we can identify ways of disrupting unicolonial behavior in field populations of Argentine ants, this would make the species considerably less effective in competition with native species and thus aid in much needed biocontrol. I am also interested in generally 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. However, because ants routinely exchange food with each other, workers are not necessarily restricted to having only as much food as leaves with them from the colony. Food can be diffused out throughout the foraging range of the colony. Experiments with Formica planipilis and Pogonomyrmex salinus show that this results in a pattern of well-stocked ants near the colony entrance, with energy reserves declining with distance from the colony. There also appears to be a size class of worker that acts as ‘refueling’ stations in that they carry more food further away from the colony than closer to it. 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. Finally, although my main interests are with social insects, I certainly do not view myself as taxonomically restricted. In one of my postdocs I applied foraging models to predicting schooling behavior and population growth of anchovies (Engraulis mordax). Recent papers on measuring skew and the Marginal Value Theorem address broad phenomena in Behavioral Ecology. Further, in my lab students and postdocs are working on non-insect problems such as: seed dispersal and territory acquisition in scrub jays; sampling behavior in prey selection by jays; and song function and variability in wrentits. I enjoy the multidisciplinary nature of my lab and plan to continue to have it reflect the full diversity of Behavioral Ecology.

Selected Publications

Nonacs, P. and K.M. Kapheim. 2008. Social heterosis and the maintenance of genetic diversity at the genome level Journal of Evolutionary Biology 21: 631-635 .

Liebert, A.E., J. Hui, P. Nonacs and P.T. Starks. 2008. Extreme polygyny: Multi-seasonal “hypergynous” nesting in the introduced paper wasp Polistes dominulus Journal of Insect Behavior 21: 72-81 .

Nonacs, P. 2008.. 2008. Nature Revealed: Selected Writings 1946-2006, by E.O. Wilson Quarterly Review of Biology 83: 198 .

Nonacs, P.. 2007. Tug-of-war has no borders: it is the missing model in reproductive skew theory Evolution 61: 1244-1250 .

Nonacs, P. and K.M. Kapheim. 2007. Social heterosis and the maintenance of genetic diversity Journal of Evolutionary Biology 20: 2253-2265 .

Nonacs, P.. 2006. The ecology and evolution of hybridization in ants Ecology 87: 2141-2142 .

Nonacs, P.. 2006. Interspecific hybridization in ants: at the intersection of ecology, evolution, and behavior Ecology 87: 2143-2147 .

Nonacs, P.. 2006. Nepotism and brood reliability in the suppression of worker reproduction in the eusocial Hymenoptera Biology Letters 2: 577-579 .

Liebert, A.E., P. Nonacs and R.K. Wayne. 2005. Solitary nesting and reproductive success in the paper wasp Polistes aurifer Behavioral Ecology and Sociobiology 57: 445-456 .

Nonacs, P. and Reeve, H. K.. 2004. Optimal reproductive skew models fail to predict aggression in wasps Proceedings of the Royal Society of London, B 271: 811-817 .