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1.  The deterrent effect of bird song in territory defense 
Behavioral Ecology  2008;20(1):200-206.
Using the responses of territory owners to playback to infer the territorial function of acoustic signals is common practice. However, difficulties with interpreting the results of such experiments have obscured our understanding of territorial signalling. For instance, a stronger response to playback is often interpreted as more aggressive, but there is no consensus as to whether this should be in response to the least or most threatening simulated intruder. Rather than following a gradual increase or decrease, the relationship between signal intensity and response strength may instead describe a peaked curve. We manipulated banded wren (Thryophilus pleurostictus) songs to simulate low-, median-, and high-performance singers and used these songs as stimuli in playback experiments. Banded wrens were less likely to approach the high-performance stimulus compared with the low- and median-performance stimuli. However, the birds that did approach the high-performance stimulus sang more than those that approached the low-performance stimulus. In addition, birds were more likely to match the songs when exposed to the median- and high-performance stimuli compared with the low-performance stimuli, and song matching predicted approach behavior. These results are in accordance with theoretical models of aggressive encounters in which low-performance opponents are challenged without further assessment. Median- and high-performance opponents, however, may require further assessment, and the latter may be perceived as too intimidating for approach.
doi:10.1093/beheco/arn135
PMCID: PMC2662740  PMID: 19337589
assessment; playback; sexual selection; song; territory defense
2.  Courtship attention in sagebrush lizards varies with male identity and female reproductive state 
Behavioral Ecology  2008;19(6):1326-1332.
Previous experiments suggest that males spend more time with the more receptive of 2 novel females or the one with the higher fitness potential. However, males often court individual females repeatedly over a season; for example, male lizards sequentially visit familiar females as they patrol territorial boundaries. It may benefit males to vary display intensity as they move between multiple females. In this study, we explored the factors influencing amount of male courtship to familiar females in the sagebrush lizard, Sceloporus graciosus. We tested whether males vary the amount of courtship exhibited due to individual differences among males, female reproductive state, or female fitness potential. Each male was allowed to interact separately, but repeatedly, with 2 females until both females laid eggs. Male courtship behavior with each of the 2 females was assayed at an intermediate point, after 3 weeks of interaction. We found that individual differences among males were considerable. The number of male courtship displays was also positively correlated with female latency to lay eggs, with males displaying more often toward females with eggs that had not yet been fertilized. Courtship behavior was not well predicted by the number of eggs laid or by female width, both measures of female quality. Thus, male S. graciosus appear to alter courtship intensity more in response to signals of female reproductive state than in response to variation in potential female fitness.
doi:10.1093/beheco/arn072
PMCID: PMC2583109  PMID: 19458780
courtship; male choice; mate choice; reproductive state; Sceloporus graciosus; sexual selection
3.  Courtship attention in sagebrush lizards varies with male identity and female reproductive state 
Previous experiments suggest that males spend more time with the more receptive of two novel females or the one with the higher fitness potential. However, males often court individual females repeatedly over a season; for example, male lizards sequentially visit familiar females as they patrol territorial boundaries. It may benefit males to vary display intensity as they move between multiple females. In this study, we explored the factors influencing amount of male courtship to familiar females in the Sagebrush lizard, Sceloporus graciosus. We tested whether males vary the amount of courtship exhibited due to individual differences among males, female reproductive state, or female fitness potential. Each male was allowed to interact separately, but repeatedly, with two females until both females laid eggs. Male courtship behavior with each of the two females was assayed at an intermediate point, after three weeks of interaction. We found that individual differences among males were considerable. The number of male courtship displays was also positively correlated with female latency to lay eggs, with males displaying more often towards females with eggs that had not yet been fertilized. Courtship behavior was not well predicted by the number of eggs laid or by female width, both measures of female quality. Thus, male S. graciosus appear to alter courtship intensity more in response to signals of female reproductive state than in response to variation in potential female fitness.
doi:10.1093/beheco/arn072
PMCID: PMC2583109  PMID: 19458780
Sceloporus graciosus; male choice; mate choice; sexual selection; reproductive state; courtship
4.  Conclusions beyond support: overconfident estimates in mixed models 
Behavioral Ecology  2008;20(2):416-420.
Mixed-effect models are frequently used to control for the nonindependence of data points, for example, when repeated measures from the same individuals are available. The aim of these models is often to estimate fixed effects and to test their significance. This is usually done by including random intercepts, that is, intercepts that are allowed to vary between individuals. The widespread belief is that this controls for all types of pseudoreplication within individuals. Here we show that this is not the case, if the aim is to estimate effects that vary within individuals and individuals differ in their response to these effects. In these cases, random intercept models give overconfident estimates leading to conclusions that are not supported by the data. By allowing individuals to differ in the slopes of their responses, it is possible to account for the nonindependence of data points that pseudoreplicate slope information. Such random slope models give appropriate standard errors and are easily implemented in standard statistical software. Because random slope models are not always used where they are essential, we suspect that many published findings have too narrow confidence intervals and a substantially inflated type I error rate. Besides reducing type I errors, random slope models have the potential to reduce residual variance by accounting for between-individual variation in slopes, which makes it easier to detect treatment effects that are applied between individuals, hence reducing type II errors as well.
doi:10.1093/beheco/arn145
PMCID: PMC2657178  PMID: 19461866
experimental design; maternal effects; mixed-effect models; random regression; repeated measures; type I error
5.  Size and heterozygosity influence partner selection in the Formosan subterranean termite 
Behavioral Ecology  2008;19(4):764-773.
In monogamous species that exhibit extensive biparental investment, such as termites, both sexes are predicted to be selective when choosing a mate. Size-related traits are expected to be important in partner selection because the fat reserves of the colony founders sustain the incipient colony. Partner relatedness and heterozygosity determine the degree of inbreeding and genetic diversity within the colony and may thus also influence partner selection. To test these predictions, we investigated whether phenotypic and genetic traits influence mate choice and/or competitive advantage during pair formation of Formosan subterranean termites, Coptotermes formosanus (Isoptera: Rhinotermitidae). Pair formation in termites normally occurs within a short period after swarming when alates form tandem pairs on the ground. Alates were collected from 5 light trap samples in the French Quarter of New Orleans, LA. From each sample, both tandem pairs and single individuals were collected and their sex, body weights, and head widths were recorded. Pairwise relatedness and individual levels of heterozygosity were determined by microsatellite genotyping. Males in tandem pairs with females had a significantly larger head width than males that did not form tandem pairs. Weights as well as head widths of tandem running partners were positively correlated. For the majority of the samples, relatedness between tandem partners did not differ from the relatedness to members of the other tandem pairs. Thus, no kin discrimination occurred during tandem running. However, females engaged in tandem running had a higher degree of heterozygosity than females that remained single. These findings suggest partner selection and/or competitive advantage based on size-related phenotypic parameters and genetic diversity. The pairing advantage of heterozygous females might explain previous findings of sex-biased alate production depending on the degree of inbreeding in colonies of several species of the genus Coptotermes.
doi:10.1093/beheco/arn041
PMCID: PMC2474661  PMID: 19461839
Isoptera; mate choice; microsatellite genotyping; morphometry; relatedness; Rhinotermitidae; sexual selection

Results 1-5 (5)