Lethal coalitionary attacks of chimpanzees on gorillas in the wild

Lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on gorillas (Gorilla gorilla gorilla) in the wild. Lara M. Southern, Tobias Deschner & Simone Pika. Scientific Reports, July 19 2021. DOI: 10.1038/s41598-021-93829-x

[Popular version: https://www.mpg.de/17223684/0719-evan-lethal-attacks-by-chimpanzees-on-gorillas-observed-150495-x. Here, climate change shows up three times (also appears there as a keyword), while in the paper there is no occurence of climat*, warm*, or temperat*. Also, in the paper's 90+ references, the titles do not make mention of those three word stems.]

Abstract: Intraspecies violence, including lethal interactions, is a relatively common phenomenon in mammals. Contrarily, interspecies violence has mainly been investigated in the context of predation and received most research attention in carnivores. Here, we provide the first information of two lethal coalitionary attacks of chimpanzees (Pan troglodytes troglodytes) on another hominid species, western lowland gorillas (Gorilla gorilla gorilla), that occur sympatrically in the Loango National Park in Gabon. In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas. We discuss these observations in light of the two most widely accepted theoretical explanations for interspecific lethal violence, predation and competition, and combinations of the two-intraguild predation and interspecific killing. Given these events meet conditions proposed to trigger coalitional killing of neighbours in chimpanzees, we also discuss them in light of chimpanzees’ intraspecific interactions and territorial nature. Our findings may spur further research into the complexity of interspecies interactions. In addition, they may aid in combining field data from extant models with the Pliocene hominid fossil record to better understand behavioural adaptations and interspecific killing in the hominin lineage.

Discussion

Here, we report the first observations of two lethal coalitionary attacks of chimpanzees on another hominid species, gorillas. In both events, the chimpanzees considerably outnumbered the gorillas, however in the second event, the lethal attack started when the silverback had abandoned his group. In both events, the victims were gorilla infants, but the consumption of the victim was observed in one event only.

Recent studies59 were able to distinguish genetically distinct gorilla groups within the study area; when overlaid against the Rekambo chimpanzee community home range there was clear overlap with seven distinct gorilla groups (see Supplementary Fig. S1 in the Supplementary information). However, further data are needed to clarify whether our rare observations are due to lack of data or indeed mirror true frequencies of interspecies interactions in the study area.

In the following paragraphs, we will present and discuss several possible explanations that may account for the two lethal coalitionary encounters observed.

One explanation may be that the observed events represent cases of predation with the chimpanzees hunting and opportunistically targeting the smaller-bodied gorilla infants as prey. Although differences in behaviours accompanying hunting and hunting patrol patterns have been observed across sites, the behaviors observed at Loango were similar to the patterns reported for Taï41,60 and Ngogo38. For instance, the chimpanzees showed conspicuous behaviours prior to hunting such as being extremely attentive to any arboreal movements, scanning, changing directions several times without vocalizing, and performing specific call types—hunting calls38,45. Post-hunting behaviour is characterized by the prevalence of high-ranking males as the primary prey possessors and consumers, high levels of attention, arousal and excitement of party members, as well as begging and food sharing13,40,41,41,61. However, the behaviours observed during the two events were very different to those reported during hunting: The chimpanzees were noisy, emitted alarm barks and screams and performed displays long before the infants were killed. The excitement levels dropped immediately following the death of the infant gorillas. In addition, the observed feeding behaviours during the two events also differed from patterns expected during conventional hunting for the purpose of gaining nutritional benefits through the consumption of prey27. In the first encounter no feeding behaviour was observed, and in the second event the gorilla infant was almost entirely consumed by a single adult female. In contrast to species-typical hunts, in the second event the majority of individuals present, including adult males, showed almost no interest in the carcass, and only small amounts of meat were exchanged between low ranking individuals.

Another explanation may be that the two cases are the product of interspecific competition such as IGP and IK. So far, studies investigating interspecific competition in gorillas and chimpanzees have provided evidence for dietary niche differentiation and mutual avoidance to limit competition e.g.,62,63,64,65,66,67. All previous accounts of interspecies interactions as well as co-feeding events have been reported as peaceful despite a relatively high potential for feeding competition concerning key resources or during certain periods e.g.,68,69,70. Thus far, aggressive interference competition, including infanticide, has been observed between monkey species (e.g., Cercopithecus nicitans stampflii, Cercopithecus diana diana71; Ateles hybridus, Alouatta seniculus72) but not between chimpanzees and gorillas. Such interactions are however frequent in carnivore species and have been suggested as key determinants of their abundance and distribution33,73 (but see for an overview of other taxa31). As in the lethal interactions discussed here, carnivores tend to attack their closest dietary competitors31, most agonistic encounters occur in seasonal environments when food is scarce27, and killings decrease abruptly when dietary overlap is reduced73. Gorillas and chimpanzees show considerable dietary overlap and have a relatively high potential for dietary competition45,74. Across study communities, the degree of dietary overlap ranges between: 50% Kahuzi-Biega; Gorilla beringei graueri, Pan troglodytes schweinfurthii75 and 60–80% Loango, Lopé, and Ndoki; Gorilla g. gorilla, Pan t. troglodytes66,74,76. The two lethal encounters we observed occurred at times characterized by food scarcity and a period of high dietary overlap (for fruit resources)45,74—February and December 2019. In contrast, the two previously observed peaceful co-feeding events took place in April, a month characterized by relatively low dietary overlap between the two species45,74.

Furthermore, age, size and patterns of grouping seem to play a significant role in the outcome of IGP’s and IK’s (see e.g.,27). While relative body size of the opponents is the primary determinant of lethal interactions and results in favour of the larger species, in interactions involving adults, smaller species frequently kill the young of larger species27,73. There are cases where smaller species were able to kill or deter larger species such as wolves (Canis lupus) killing adult black bears (Ursus americanus)77 and hyenas (Crocuta Crocuta) killing lions (Panthera leo)27, however, these outcomes were only possible when individuals of the smaller species formed coalitions27,77. The grouping style of a species was found to strongly influence the outcome of IGP’s resulting largely in favour of species that form groups78. This is in line with our current observations, where the chimpanzees were at an advantage even against the larger gorilla species, given their ability to cooperate. Additionally, specific adaptations to prey-capture also influence the outcome of IGP’s, resulting in favour of species more adapted for vertebrate predation73 where the successful species, here, the chimpanzee, has adaptations to vertebrate predation13,39,41. Hence, as in IGP food webs (with specific emphasis of species classification) portrayed by Arim and Marquet79, the two reported killings may represent cases of IGP and IK between an intermediate omnivorous species (i.e. broad diets comprising both animal and plant foods80), the chimpanzee, and a herbivorous species (feeding mainly on plant foods81), the gorilla.

Lastly, both of the lethal encounters reported here also showed similarities to behaviours observed during chimpanzee intercommunity encounters. For instance, similar to territorial patrols, where chimpanzees move to the periphery and beyond their territorial boundaries to search for neighbours e.g.,11,13,82,83, the observed events took place in the peripheries of the territory before and during territorial patrols. In both events, infants were targeted and adult males were the main attackers and played the most active roles. Similarly, in lethal chimpanzee intercommunity encounters, infanticide is common and adult males are the main participants11,83,84,,83,84 (but see for female roles51). It has been proposed that in chimpanzees, adult males may kill infants of other communities to reduce competition for food by inducing foreign females to avoid contested regions84. The observed interspecies killings of gorilla infants by chimpanzees could have similar motivations85. We also observed behaviours before and during the encounters characteristic to coalitionary intercommunity encounters such as aggression (e.g., charges, chases, threatening displays, contact aggression), high levels of arousal and the use of loud vocalizations13,14,15,51. The imbalance-of-power hypothesis postulates that the function of unprovoked intercommunity aggression (such as deep incursions into other chimpanzee communities’ territory and coalitionary attacks) is a drive for dominance over neighbours resulting in fitness benefits for the attackers through improved access to resources such as food, females, or safety6,13. Two conditions are proposed to be required to trigger coalitional killing of neighbours: (i) a state of intergroup hostility, and (ii) sufficient imbalances of power between interacting parties resulting in impunity from aggressors. Thus, it may be possible that at Loango, which is characterized by relatively high dietary food overlap in specific months45,74, gorillas are perceived as competitors, for both space and resource use, similar to members of other chimpanzee communities. Lastly, we cannot rule out that the presence of human observers, in both events, may have had an effect on the unhabituated silverback’s departure and may have tilted the imbalance of power in favour of the habituated chimpanzees.

In sum, the observed events show similarities to patterns reported in IGP’s, IK’s and intraspecies agonistic encounters. Ultimately, additional observations in combination with isochronous assessments of fruit availability and dietary overlap are needed to differentiate whether coalitionary attacks are indeed the output of interspecific predation spurred by opportunistic hunting, interspecies competition for food resources or whether these interactions are merely a non-adaptive by-product of the “xenophobic nature” of chimpanzees. Finally, analyses of long-term phenological data could aid in investigating if potential high levels of feeding competition may be a more recent phenomenon caused by a collapse in fruit availability as observed in other tropical forests in Gabon86.

Women rated stronger men as more attractive than weaker men irrespective of the ecological condition, & had a relatively stronger preference for stronger men for short-term relationships in a resource scarce ecological condition

Women’s Preferences for Strong Men Under Perceived Harsh Versus Safe Ecological Conditions. Ray Garza, Farid Pazhoohi, Jennifer Byrd-Craven. Evolutionary Psychology, July 23, 2021. https://doi.org/10.1177/14747049211032351

Abstract: Ecological conditions provide information about available resources for one’s environment. In humans, this has been shown to influence reproductive behavior, as individuals may engage in trade-offs between partner quality and investment. For instance, many women may trade-off preferences for men with physical features indicative of social dominance and health over physical features indicative of commitment and investment. The current study explored women’s preferences for formidable men under safe vs. harsh ecological conditions. Across three studies, U.S. university women (N = 1,098) were randomly assigned to a perceived harsh or safe ecological condition. They were asked to rate the attractiveness of men’s body types (i.e., muscular vs. less muscular). Findings revealed that in general, women rated stronger men as more attractive than weaker men irrespective of the ecological condition. Evidence for preference as a function of ecology appeared only when a two-alternative forced-choice task was used (Study 3), but not in rating tasks (Studies 1 and 2). Study 3 showed that women had a relatively stronger preference for stronger men for short-term relationships in a resource scarce ecological condition. This research provides some evidence that perceived ecological conditions can drive women’s preferences for men with enhanced secondary sex characteristics as a function of mating context. These findings are consistent with previous research indicating the importance of physical characteristics in men’s attractiveness, and it adds to the existing literature on ecological factors and mating preferences.

Keywords: formidability, short-term mating, attractiveness, evolutionary psychology, ecology

General Discussion

Results of the current investigation provides evidence for women’s overall preferences for strong men. Across three studies, women were more likely to find stronger men more attractive than weaker men. However, manipulating mating context and ecological conditions were only effective when participants viewed men in pairs using an alternative forced-choice task (2afc) in Study 3, as opposed to viewing men sequentially, in Studies 1 and 2. This discrepancy provides empirical evidence supporting the argument that the judgements of attractiveness might differ according to study task (Jones & Jaeger, 2019), as Likert-type scale responses may be measuring something different compared to forced-choice measures (Bartlett et al., 1960). Accordingly, results of this research suggest that women consider differences in men’s attractiveness under a short and long-term mating contexts and perceived harsh ecology (i.e., resource scarcity), only when making comparisons to other men. This might imply that the priming effect to harsh ecology is small and imaginative resource scarcity do not induce prolonged effects influencing mate preference in women. Such effects might be more meaningful and conspicuous while measuring mate preferences as the result of exposure to an actual ongoing environmental harshness.

Women’s preferences for strong men has been supported by previous research (Braun & Bryan, 2006; Buunk & Dijkstra, 2005; Pazhoohi et al., 2019; Provost et al., 2006, 2008; Sell et al., 2017). Men with strong body types are more likely to be successful in intrasexual competitions (Puts, 2010), secure access to resources (Buss & Schmitt, 1993; Sell et al., 2017), and establish relationships with higher social status individuals (Lukaszewski et al., 2015). Additionally, strong body types are reflective of overcoming energetic demands to maintain strength and muscularity, and this may reflect putative good genes to women in mate choice (Sell et al., 2017).

Ecological conditions have been shown to be influential in women’s mate preferences, as women may trade-off indicators of investment for good genetics when in a safe versus harsh environments (Brooks et al., 2011; Dixson et al., 2017; Little et al., 2013; Reeve et al., 2019; Sacco et al., 2015). Overall, the effects of ecological conditions on ratings of attractiveness to men across mating conditions were only significant in Study 3 when an alternative forced-choice task was used. Women were more likely to select stronger men for a short-term relationship under a resource scarce environment. Preferences for masculine men have been shown to be related to ecological harshness (Little et al., 2007, 2013). Others have demonstrated that preferences for good-dad traits (i.e., parental investment, commitment) and not good-genes are associated with resource scarce environments (Lee & Zietsch, 2011). We did not find that women preferred stronger men under a violent ecological condition, as women preferred stronger men in a safe and violent ecology more than in a resource scarce ecology. Research has suggested that women can significantly gain from indirect and direct benefits in violent ecologies through protection and resource acquisition (Puts, 2010). Traits associated with masculinity are beneficial in male hierarchies, particularly in environments with income inequality (Brooks et al., 2011).

The current studies suggest that female mate choice favored strength in males, as women considered strong men more attractive than weak men (Study 1 and 2), and more so when they were presented in pairs (Study 3). These findings are in line with sexual strategies (Buss & Schmitt, 1993) and strategic pluralism theory (Gangestad & Simpson, 2000). Mating strategies are highly context dependent, and women may evaluate potential partners for short- or long-term relationships. Additionally, when provided with different ecological scenarios and presented with men in pairs, women may make trade-offs in the evaluation of potential mates. According to this view, women’s mate preferences are contingent upon prevailing environments, such as environments with increased pathogen prevalence or resource scarcity that would have been recurrent in ancestral conditions. This suggests that women may trade off indicators of parental investment and good genetics contingent upon environmental conditions. For instance, in a resource scarce environment, women may prefer stronger men for long-term relationships due to their ability to acquire resources. In Study 3, we found that women preferred the opposite (i.e., masculine over good-dad traits) when considering men under a resource scarce ecology. Were resource scarcity to affect preferences, we would expect this to primarily apply to preferences for long-term, not short-term partners, therefore this finding may not prove robust to replication. It is possible that the current economic outlook (i.e., lockdowns, slow economic growth) during the pandemic may have made resource scarcity more salient in considering stronger men under different mating conditions. Indeed, the resource scarce condition was rated higher on emotional arousal, which warrants further investigation. Our findings are inconsistent with previous research where women considering masculine men in a safe ecology for short-term mating were rated as more attractive (Little et al., 2007, Marcinkowska et al., 2019), and depictions of violence influenced women’s preferences for masculine men (Little et al., 2013). Furthermore, our findings are in direct contrast to Lee and Zietsch (2011) who found that women preferred good-dad traits for a resource scarce environment. Moreover, in line with Snyder et al. (2011), violent manipulations did not affect women’s preferences for stronger men.

The discrepancy between our results and the previous research on facial preference may reflect differences in the way that women rate men’s facial compared to bodily traits. We suggest further research investigate the effect of women’s choice for men’s body form (in combination with and separate from faces) as a function of ecological environments. In our study, ecological vignettes and slides depicting safe and harsh ecologies were used. Although these methods have been effective in demonstrating ecological contingent responses in laboratory settings (Griskevicius et al., 2011; Hill et al., 2013; Little et al., 2007), they did not generate an effect when target stimuli were presented in a sequential format for attractiveness ratings (Studies 1 and 2). Our study also relied on a between-subjects design for mating strategy across ecological conditions. Previous studies (Al-Shawaf et al., 2019; Thomas & Stewart-Williams, 2018) have shown that ecological conditions can affect mating at the strategy level, such as using short- and long-term mating preferences as a within-subjects condition as opposed to a between-subjects condition. Future work may want to consider if women adjust their mating strategy preferences (short-term vs. long-term) when facing a harsh ecology. Furthermore, the reliance of a college-aged sample limits the generalizability of the findings. All women participants were in the age range of 18–20 attending a public state university and were mostly White, with the exception of Study 3 where the inclusion of a larger Hispanic population was used compared to Studies 1 and 2. Although participants did indicate that the ecological manipulations were considered violent, arousing, and influenced their likelihood of being a victim of a crime, they may not captured actual ecological harshness compared to populations living in harsh environments. In Study 2 & 3, the inclusion of an SES measure to capture childhood and adulthood resources availability was used to account for actual ecological harshness. Further, the lack of a control group could limit the interpretability of women in the safe condition. Safeness could have served as a prime to influence women’s mating psychology, and it was shown in Study 3 that women’s preferences for stronger men in a safe ecology was similar to a violent ecology. It is important to use a control group in future work to make more definitive conclusions on the comparison across ecological conditions. The study relied on women only, and the effects of perceived ecology may not reflect women’s mating psychology but human psychology in general. Future work would benefit from making comparisons to both men and women’s perceptions of men’s body types in order to make stronger conclusions on the role of perceived ecology on mate preferences. Finally, it is important to note that the ratings of attractiveness (Study 1 and 2) were at the low end of the spectrum (i.e., closer to unattractive). The results for these studies should be interpreted as differences in relative attractiveness and not an indication of the highest rating of attractiveness. Therefore, we suggest future research look at these effects using a control group examining difference in both men and women’s preferences for men’s body types across perceived ecology.

Conclusion

Men’s physical features connoting strength provides information relating to indirect (i.e., genetic) and direct (i.e., resource acquisition) benefits in mate preferences. Given these cues, women should be sensitive to these physical features and indicate preferences for them, and they should be influenced by their mating strategies and ecological cues. Consistent with the importance of physical cues in mate choice, women preferred strong over weak men, and their preferences for strong men were associated with ecological cues when using an alternative forced-choice task.

COVID-19 Lockdowns/shelter-in-place policies in 43 countries: These authors think that, following the implementation of SIP policies, excess mortality increased

The Impact of the COVID-19 Pandemic and Policy Responses on Excess Mortality. Virat Agrawal, Jonathan H. Cantor, Neeraj Sood & Christopher M. Whaley. NBER Working Paper 28930, June 2021. DOI 10.3386/w28930

Abstract: As a way of slowing COVID-19 transmission, many countries and U.S. states implemented shelter-in-place (SIP) policies. However, the effects of SIP policies on public health are a priori ambiguous as they might have unintended adverse effects on health. The effect of SIP policies on COVID-19 transmission and physical mobility is mixed. To understand the net effects of SIP policies, we measure the change in excess deaths following the implementation of SIP policies in 43 countries and all U.S. states. We use an event study framework to quantify changes in the number of excess deaths after the implementation of a SIP policy. We find that following the implementation of SIP policies, excess mortality increases. The increase in excess mortality is statistically significant in the immediate weeks following SIP implementation for the international comparison only and occurs despite the fact that there was a decline in the number of excess deaths prior to the implementation of the policy. At the U.S. state-level, excess mortality increases in the immediate weeks following SIP introduction and then trends below zero following 20 weeks of SIP implementation. We failed to find that countries or U.S. states that implemented SIP policies earlier, and in which SIP policies had longer to operate, had lower excess deaths than countries/U.S. states that were slower to implement SIP policies. We also failed to observe differences in excess death trends before and after the implementation of SIP policies based on pre-SIP COVID-19 death rates.

Rolf Degen summarizing... There is a tragic tendency for romantic relationships to run out of steam in the long term, and psychological interventions have proved incapable of reversing the "loss of positives"

When the Loss of Positives feels Negative: Exploring the Loss of Positive Experiences in Committed Couples. Danielle M. Weber, Donald H. Baucom. Current Opinion in Psychology, July 22 2021. https://doi.org/10.1016/j.copsyc.2021.07.015

Highlights

• Positive experiences in committed couples can decrease over time.

• Positives can decrease for various reasons, including increased external demands.

• Interventions from Cognitive-Behavioral Couple Therapy can enhance positives.

Abstract: Despite romantic relationships being characterized by high positives (e.g., enjoyable activities, positive feelings) early in commitment, many couples experience a loss of positives over time. However, interventions are typically not as effective at enhancing positives as they are at reducing negatives (e.g., hostile conflict). Thus, it is important to understand why positives decrease and how to use interventions to enhance positives optimally. In this article, we present how the field has evolved to (a) heighten focus on positives independent of negatives, (b) identify trajectories of positives over time, and (c) clarify major factors which predict loss of positives. From a Cognitive-Behavioral Couple Therapy perspective, we offer therapeutic strategies that may hold promise for enhancing positives in relationships.

Keywords: positives in relationshipscouplescouple interventionscognitive behavior therapy

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Against this optimistic abstract, I prefer Rolf Degen's take: There is a tragic tendency for romantic relationships to run out of steam in the long term, and psychological interventions have proved incapable of reversing the "loss of positives"

Princess culture is criticized for contributing to gender stereotypes & poor body esteem; but (at least) modern princess engagement was associated with lower adherence to norms of hegemonic masculinity & higher body esteem

Princess Power: Longitudinal Associations Between Engagement With Princess Culture in Preschool and Gender Stereotypical Behavior, Body Esteem, and Hegemonic Masculinity in Early Adolescence. Sarah M. Coyne, Jennifer Ruh Linder, McCall Booth, Savannah Keenan-Kroff, Jane E. Shawcroft, Chongming Yang. Child Development, July 20 2021. https://doi.org/10.1111/cdev.13633

Abstract: Princess culture is criticized for contributing to gender stereotypes and poor body esteem, however, there is little longitudinal research examining these claims. This study examines associations between engagement with princess culture during early childhood and gender stereotypes, body esteem, and adherence to hegemonic masculinity in early adolescence. Participants included 307 children (51% female, Mage = 4.83 years, 87% White) who completed questionnaires at two time points, 5 years apart. The results indicated that early engagement with princess culture was not associated with later adherence to female gender stereotypes. However, princess engagement was associated with lower adherence to norms of hegemonic masculinity and higher body esteem. Socioeconomic status and gender moderated the results. Effect sizes were small to moderate. The changing nature of Disney princesses is discussed in the context of gender development across childhood.

Orgasms from clitoral stimulation seem to have a second-class quality for some women, although there is no evidence that these orgasms feel like less pleasureable

The Influence of Types of Stimulation and Attitudes to Clitoral Self-stimulation on Female Sexual and Orgasm Satisfaction: a Cross-sectional Study. Madita Hoy, Katharina van Stein, Bernhard Strauss & Katja Brenk-Franz. Sexuality Research and Social Policy, Jul 21 2021. https://rd.springer.com/article/10.1007/s13178-021-00618-2

Abstract

Introduction: Societal assumptions and individual myths that define vaginal penetration as normal sexuality can affect the sexual pleasure of varied sexual activities. Although women orgasm much more easily through direct clitoral stimulation than through vaginal intercourse, many couples desire the latter. The purpose of this study is to investigate how orgasms from different types of stimulation with a partner affect sexual satisfaction and orgasm satisfaction in cisgender women. Also, the attitude of women to stimulate their clitoris themselves to reach orgasm during sex with their partner will be included.

Methods: Two independent surveys (N = 388 and N = 555) were conducted online in 2016 and 2020.

Results: Regression analyses showed that orgasm consistency through sexual intercourse had a stronger influence on orgasm satisfaction and sexual satisfaction than orgasm consistency through oral sex, stimulation by the partner’s hand, or self-stimulation. Positive thoughts and feelings about self-stimulation of the clitoris during sex with the partner showed only little effect, but in some cases, they were even negatively related to the reported satisfaction.

Conclusions: The results indicate that the common misconception about sexuality, that it is normal for women to experience orgasms during penile-vaginal intercourse, influences the subjective evaluation of one’s own sexuality. Orgasms from clitoral stimulation seem to have a second-class quality for some women, although there is no evidence that these orgasms feel like less pleasureable.

Policy Implication: Rigid assumptions about what normal sexuality should look like should be publicly addressed and discussed in sex education classes.