A major issue in modern ecology, evolution and behavior for all organisms, including humans, is to understand factors that explain why some individuals have higher mating and reproductive success than others. What traits (e.g., behaviors or morphological characters) make some individuals more successful than others, and how might these key traits differ depending on the social situation? This project provides a new framework for quantifying how differences among individuals in behavioral type (or personality; e.g. boldness, aggressiveness, social flexibility) interacts with variations in social situation (e.g., group size, sex ratio, mix of personalities and patterns of social interaction within the group) to determine individual behaviors, group social dynamics and mating patterns. To exemplify and refine the new framework a model system that is ideal for studies of mating patterns is used, namely the stream water strider, Aquarius remigis. These animals mate frequently and are unusually easy to observe. The experimental approach involves repeated observations of the behavior of male and female water striders in semi-natural streams in a range of experimentally determined social situations. Based on preliminary work, the results are expected to show that individual variation in 'social skill' (the ability to choose good social situations, appropriate mating partners and the ability to respond effectively to those partners) will have major impacts on mating success. Although anecdotes suggest that social skill is crucial for success in humans and other animals, this project will provide a new, statistically sophisticated, quantitative framework to scientifically study this hypothesis in animals in general, including humans. Previous work conducted by the investigator on this basic topic has been widely cited in scientific journals, and widely covered by popular and scientific media (newspapers, magazines, radio). The project will train several Ph. D. students and undergraduates (including women and minorities) in modern behavioral, experimental and statistical methods.
This project examined how individual differences in behavior (aggressiveness, activity level) and the mix of behavioral types in a social group interact to influence social and mating patterns – overall behavior of males and females, how many times individuals mate, how long they stay with each partner, and the degree to which differences in mating success can be explained by the individual’s behavioral type (BT) interacting with the social environment. While these questions are of high interest and importance for all social species (including humans), this project focused on stream water striders that have been a model system in behavioral ecology for about 3 decades. The usual mating system for this genus features males harassing females continually (attempting to mate) with a result that: a) many males are active on the water searching for females; b) most single females are inactive, hiding along the water’s edge; and c) males guard females by riding on their back for 2-10 hours thus keeping that female from mating with other males during that period. We first found that at the group level, behavior (activity and aggressiveness) and mating success (number of matings) depended critically on the presence (or not) of a hyperaggressive male (HAM). The presence of HAMs substantially reduced everyone else’s activity. At a group level, mating activity depended on the group’s average BT and on the presence of HAMs. The manuscript reporting these results was published in Behavioral Ecology. Further analyses showed that at the individual level, variation in male mating success depended on the individual male’s BT, on his hyper-aggressiveness, and on his social environment, in particular, time spent with a HAM. More active/aggressive males tended to have higher mating success, but not if they became hyper-aggressive. Hyper-aggressive males wasted time harassing others and thus had low mating success. Finally, co-occuring with a HAM substantially reduced any given male’s mating success. The paper reporting these results is in press in Animal Behaviour. An additional paper (in review) examined the exclusivity of a male’s matings. A male can have higher fitness either by mating with more females or by mating more exclusively with those females (e.g., by being the only male to mate with a female as opposed to sharing the female with several other males). We found that the exclusivity of a male’s matings depended on the male’s BT, on the presence of HAMs, and on the BT of his female partners. Our most recent experiments revealed surprising flexibility in the overall social/mating system. We confirmed the usual, basic mating system in larger pools, but found that in smaller pools (with only 3 males and 3 females), in most cases, an ‘alpha-male’ system emerged where 1 male drove the other 2 males off the water, but left the females unharassed. That is, a low proportion of males were on the water, but a high proportion of females were on the water – the opposite of the classic water strider mating system. Also, instead of having 2-10 hr mating durations, the alpha male typically had very short mating durations, often < 30 min. Apparently, if an alpha male can keep other males off the water, he does not need to exhibit contact mate guarding, and if he did engage in contact mate guarding, he would not be able to keep other males off the water. Notably, we found that when we moved striders from small to larger pools (at the same density), they switched back to the usual water strider mating system within hours. Moved back again to smaller pools, they again switched back to the alpha male system, but it took on average 3-4 days. Also, while all larger pools exhibited the usual water strider mating system, smaller pools developed a diversity of mating systems. While most of the smaller pools developed an alpha-male system, three other mating systems also emerged: a) in a few pools, a hyper-aggressive male drove everyone else (male and female) off the water; b) in a few pools, the usual water strider mating system emerged; and c) in a few pools, all males and females stayed on the water with little or no aggression. With regard to training, this project involved 2 PhD students (one an Asian-American woman), 4 postdocs (one an Asian-American woman), a sabbatical visitor, and numerous undergraduate researchers (about half of whom were women). Broader impacts were enhanced by the PI giving, during the period of this grant, over 30 invited presentations at international conferences and major research universities that included this project’s results, as well as several talks for undergraduates, teachers and high school students, and a public talk for a non-profit group. Results from this work was also featured in a radio interview, a segment of a documentary on animal behavior, and several magazine articles.
