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1. Experimental manipulation of chest spotting alters territorial aggression in urban and rural song sparrows

   https://doi.org/10.1007/s00265-023-03396-6  

   Beck, Michelle L. ; Sewall, Kendra B. ; Akҫay, Ҫağlar ( December 2023 , Behavioral Ecology and Sociobiology)

   In many taxa, melanin-based coloration is a signal of dominance or fighting ability and is associated with concentrations of hormones that may mediate aggressive behavior. Previous studies found that experimental manipulation of melanin-based signals can result in manipulated individuals receiving more social challenges in some but not all species. These differences could arise from mismatches between the signal, behavior, and hormone concentrations. In the present study, we experimentally manipulated the chest spotting of urban and rural male song sparrows (Melospiza melodia) following an assessment of their territorial aggression and initial concentrations of corticosterone and testosterone and then assessed their behavior and hormone concentrations 2 weeks later. We found that males generally displayed less territorial aggression in the second trial, consistent with our previous findings. Males in the enlarged treatment decreased aggression to a greater degree than those in the reduced treatment. The effect of the plumage manipulation was similar across the rural and urban habitats. Despite the changes in behavior we detected, we found no effects of the manipulation on concentrations of testosterone or corticosterone. Our results show that melanin-based spotting in male song sparrows is a signal of territorial aggression but the physiological mechanisms that mediate the relationships between chest spotting and behavior remain to be identified.

   Many bird species use their plumage to signal their dominance status, fighting ability, or motivation during interactions with other individuals to resolve conflicts without a fight. Here, we asked whether chest spotting is a signal in territorial interactions among male song sparrows. We experimentally increased or reduced the extent of spotting in males and measured the change in their aggression. We found that reduced-spotting males showed a more moderate seasonal decrease of aggression compared to males with enlarged spotting reduced aggression, possibly because the former experienced more intrusions later on in the breeding season while the latter experienced fewer intrusions. These results are consistent with chest spotting size in song sparrows functioning as a signal of territory holding potential of the bearer.

    

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2. Weaponry, size, and sex ratio affect spatial distribution within small and large groups of the maritime earwig ( Anisolabis maritima )

   https://doi.org/10.1111/eth.12855  

   Dodgen, Rose E. ; Iyengar, Vikram K. ; Ebensperger, ed., L. ( February 2019 , Ethology)

   Dispersion patterns within a group can reveal important aspects about social interactions and sexual selection within a species. We examined the distribution patterns of the maritime earwig (Anisolabis maritima), an insect well suited for studies of aggression, sociality, and sexual selection since both sexes live in close proximity and possess weaponry in the form of sexually dimorphic pincers. To examine intra‐ and intersexual interactions within small groups, we conducted trials with three earwigs with limited access to shelters. In single‐sex trios, we found that both males and females exhibited strong size‐based intrasexual aggression, as larger individuals were less likely to be excluded from shelters; however, males were more likely to cohabitate than females. In mixed‐sex trios, we found that both males and females preferred smaller opposite‐sex partners, and cohabitation patterns indicate that both sex‐ and size‐based differences in aggression can influence overall spatial distribution. We also examined larger single‐sex and mixed‐sex groups of 18 earwigs to determine whether they had random, uniform, or clumped distributions. Similar to previous field observations, males tended to form aggregations, whereas females were distributed uniformly, a pattern indicative of territoriality. Mixed‐sex groups, on the other hand, were uniform during nocturnal periods of high activity but then become clumped after settling into more stable daytime positions. Overall, our results suggest that females have high levels of aggression regardless of the social context, whereas males alter their aggressive behavior in the presence of females.

    

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3. “Can You Take the Heat?” Heat-Induced Health Symptoms Are Associated with Protective Behaviors

   https://doi.org/10.1175/WCAS-D-18-0035.1  

   Esplin, Emily D. ; Marlon, Jennifer R. ; Leiserowitz, Anthony ; Howe, Peter D. ( April 2019 , Weather, Climate, and Society)

   Abstract The risks associated with extreme heat are increasing as heat waves become more frequent and severe across larger areas. As people begin to experience heat waves more often and in more places, how will individuals respond? Measuring experience with heat simply as exposure to extreme temperatures may not fully capture how people subjectively experience those temperatures or their varied impacts on human health. These impacts may also influence an individual’s response to heat and motivate risk-reduction behaviors. If subjectively experiencing negative health effects from extreme heat promotes protective actions, these effects could be used alongside temperature exposure to more accurately measure extreme heat experience and inform risk prevention and communication strategies according to local community needs. Using a multilevel regression model, this study analyzes georeferenced national survey data to assess whether Americans’ exposure to extreme heat and experience with its health effects are associated with self-reported protective behaviors. Subjective experience with heat-related health symptoms strongly predicted all reported protective behaviors while measured heat exposure had a much weaker influence. Risk perception was strongly associated with some behaviors. This study focuses particularly on the practice of checking on family, friends, and neighbors during a heat wave, which can be carried out by many people. For this behavior, age, race/ethnicity, gender, and income, along with subjective experience and risk perception, were important predictors. Results suggest that the subjective experience of extreme heat influences health-related behavioral responses and should therefore be considered when designing or improving local heat protection plans. 

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4. Behavioral and physiological responses to fruit availability of spider monkeys ranging in a small forest fragment

   https://doi.org/10.1002/ajp.22292  

   Rimbach, Rebecca ; Link, Andrés ; Montes‐Rojas, Andrés ; Di Fiore, Anthony ; Heistermann, Michael ; Heymann, Eckhard W. ( May 2014 , American Journal of Primatology)

   Numerous animal species currently experience habitat loss and fragmentation. This might result in behavioral and dietary adjustments, especially because fruit availability is frequently reduced in fragments. Food scarcity can result in elevated physiological stress levels, and chronic stress often has detrimental effects on individuals. Some animal species exhibit a high degree of fission–fusion dynamics, and theory predicts that these species reduce intragroup feeding competition by modifying their subgroup size according to resource availability. Until now, however, there have been few studies on how species with such fission–fission dynamics adjust their grouping patterns and social behavior in small fragments or on how food availability influences their stress levels. We collected data on fruit availability, feeding behavior, stress hormone levels (measured through fecal glucocorticoid metabolites (FGCM)), subgroup size, and aggression for two groups of brown spider monkeys (Ateles hybridus) in a small forest fragment in Colombia and examined whether fruit availability influences these variables. Contrary to our predictions, spider monkeys ranged in smaller subgroups, had higher FGCM levels and higher aggression rates when fruit availability was high compared to when it was low. The atypical grouping pattern of the study groups seems to be less effective at mitigating contest competition over food resources than more typical fission–fusion patterns. Overall, our findings illustrate that the relationship between resource availability, grouping patterns, aggression rates, and stress levels can be more complex than assumed thus far. Additional studies are needed to investigate the long‐term consequences on the health and persistence of spider monkeys in fragmented habitats. Am. J. Primatol. 76:1049–1061, 2014. © 2014 The Authors.American Journal of PrimatologyPublished by Wiley Periodicals, Inc.

    

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5. How does the timing of weapon loss influence reproductive traits and trade-offs in the insect Narnia femorata ?

   https://doi.org/10.1093/evolut/qpad046  

   Greenway, E. V ; Angelis, Emily ; Miller, Christine W. ( March 2023 , Evolution)

   A longstanding goal of evolutionary biology is to understand among-individual variation in resource allocation decisions and the timing of these decisions. Recent studies have shown that investment in elaborate and costly weapons can result in trade-offs with investment in testes. In this study, we ask the following questions: At what point plasticity in resource allocation to these different structures ceases during development, if at all? Furthermore, can individuals tailor their reproductive behavior to accompany structural changes? We experimentally addressed these questions in the insect Narnia femorata, quantifying resource reallocation across development for the first time, using a phenotypic engineering approach. To investigate whether allocation plasticity diminishes throughout ontogeny, we induced weapon loss at a range of different developmental stages and examined subsequent testes mass and reproductive behavior. We found that relative testes mass increased as weapon investment decreased, implying a direct trade-off between testes and weapon investment. However, autotomy postadulthood ceased to induce larger testes mass. Intriguingly, losing a weapon while young was associated with extended adult mating duration, potentially enabling compensation for reduced fighting ability. Our results highlight the importance of examining the ontogeny of trade-offs between reproductive traits and the flexibility of the relationship between reproductive morphology and behavior.

    

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