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1. Reproductive success of Bornean orangutan males: scattered in time but clustered in space

   https://doi.org/10.1007/s00265-023-03407-6  

   van Noordwijk, Maria A. ; LaBarge, Laura R. ; Kunz, Julia A. ; Marzec, Anna M. ; Spillmann, Brigitte ; Ackermann, Corinne ; Rianti, Puji ; Vogel, Erin R. ; Atmoko, S. Suci Utami ; Kruetzen, Michael ; et al ( December 2023 , Behavioral Ecology and Sociobiology)

   The social and mating systems of orangutans, one of our closest relatives, remain poorly understood. Orangutans (Pongospp.) are highly sexually dimorphic and females are philopatric and maintain individual, but overlapping home ranges, whereas males disperse, are non-territorial and wide-ranging, and show bimaturism, with many years between reaching sexual maturity and attaining full secondary sexual characteristics (including cheek pads (flanges) and emitting long calls). We report on 21 assigned paternities, among 35 flanged and 15 unflanged, genotyped male Bornean orangutans (Pongo pygmaeus wurmbii), studied from 2003 to 2018 in Tuanan (Central Kalimantan, Indonesia). All 10 infants born since mid-2003 with an already identified sire were sired by flanged males. All adult males ranged well beyond the study area (c. 1000 ha), and their dominance relations fluctuated even within short periods. However, 5 of the 10 identified sires had multiple offspring within the monitored area. Several sired over a period of c. 10 years, which overlapped with siring periods of other males. The long-calling behavior of sires indicated they were not consistently dominant over other males in the area around the time of known conceptions. Instead, when they were seen in the area, the known sires spent most of their time within the home ranges of the females whose offspring they sired. Overall, successful sires were older and more often resident than others.

   It is difficult to assess reproductive success for individuals of long-lived species, especially for dispersing males, who cannot be monitored throughout their lives. Due to extremely long interbirth intervals, orangutans have highly male-skewed operational sex ratios and thus intensive male-male competition for every conception. Paternity analyses matched 21 immature Bornean orangutans with their most likely sire (only 10 of 50 genotyped males) in a natural population. Half of these identified sires had multiple offspring in the study area spread over periods of at least 10 years, despite frequently ranging outside this area. Dominance was a poor predictor of success, but, consistent with female mating tactics to reduce the risk of infanticide, known “sires” tended to have relatively high local presence, which seems to contribute to the males’ siring success. The results highlight the importance of large protected areas to enable a natural pattern of dispersal and ranging.

    

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2. Experience matters: genetic variation affects male reproductive success across sequential mating events in Drosophila melanogaster

   https://doi.org/10.1093/jeb/voae038  

   Fiumera, Anthony C. ( March 2024 , Journal of Evolutionary Biology)

   The cost of reproduction is well studied in females but only recently have the costs of mating been investigated in males. Research suggests that males allocate resources between subsequent mating events, resulting in differential success across mating bouts. Selection should favor allocation strategies that match the likelihood of successive matings. The complexity of the system, however, suggests that one fixed strategy is unlikely to be universally favored and thus I predict that genetic variation for different allocation strategies will be segregating in natural populations. To test this, I measured several components of reproductive performance in eight inbred genotypes of Drosophila melanogaster across three sequential mating events. As predicted, there was genetic variation for how previous experience affected a male’s reproductive performance for both the proportion of matings that produced offspring and the proportion of offspring sired (P1). Some genotypes had the highest success in their first matings and declined in successive matings while other genotypes did best in later matings. Mating experience had consistent effects across genotypes on fertility and induced refractoriness to remating. On average, virgin matings produced the highest fertility and third matings most effectively induced refractoriness. Genotype also had a significant effect on fertility. These results have important implications for understanding how selection may be acting on males when there is variation in the likelihood of multiple mating events and could affect the evolution of male allocation strategies in the face of perceived competitors.

    

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3. Multilevel selection on social network traits differs between sexes in experimental populations of forked fungus beetles

   https://doi.org/10.1093/evolut/qpac012  

   Costello, Robin A. ; Cook, Phoebe A. ; Brodie, III, Edmund D. ; Formica, Vincent A. ( December 2022 , Evolution)

   Both individual and group behavior can influence individual fitness, but multilevel selection is rarely quantified on social behaviors. Social networks provide a unique opportunity to study multilevel selection on social behaviors, as they describe complex social traits and patterns of interaction at both the individual and group levels. In this study, we used contextual analysis to measure the consequences of both individual network position and group network structure on individual fitness in experimental populations of forked fungus beetles (Bolitotherus cornutus) with two different resource distributions. We found that males with high individual connectivity (strength) and centrality (betweenness) had higher mating success. However, group network structure did not influence their mating success. Conversely, we found that individual network position had no effect on female reproductive success but that females in populations with many social interactions experienced lower reproductive success. The strength of individual-level selection in males and group-level selection in females intensified when resources were clumped together, showing that habitat structure influences multilevel selection. Individual and emergent group social behavior both influence variation in components of individual fitness, but impact the male mating success and female reproductive success differently, setting up intersexual conflicts over patterns of social interactions at multiple levels.

    

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4. Variation in Female Leverage: The Influence of Kinship and Market Effects on the Extent of Female Power Over Males in Verreaux’s Sifaka

   https://doi.org/10.3389/fevo.2022.851880  

   Lewis, Rebecca J. ; Bueno, Gabrielle L. ; Di Fiore, Anthony ( May 2022 , Frontiers in Ecology and Evolution)

   Female mammals employ reproductive strategies (e.g., internal gestation) that result in power asymmetries specific to intersexual dyads. Because the number of eggs available for fertilization at any given time for most mammals is quite limited, having a fertilizable egg is potentially an important source of economic power for females. Control over mating opportunities is a source of intersexual leverage for female Verreaux’s sifaka ( Propithecus verreauxi ). We examined economic factors thought to influence the value of mating opportunities, and, thus, the extent of female leverage: kinship and market effects. Using a longitudinal dataset of agonistic interactions collected during focal animal sampling of all adult individuals in 10 social groups from 2008 to 2019, we tested the effects of relatedness, female parity, reproductive season, and adult sex ratio (population and group) on (1) the direction of submissive signaling and (2) which sex won a contested resource. While 96% of the acts of submission were directed from males toward females, females only won a third of their conflicts with males. Thus, our study has implications for evolutionary explanations of female-biased power. If female power evolved due to their greater need for food and other resources, then intersexual conflicts would be expected to result in males more consistently relinquishing control of resources. As expected, males were more likely to chatter submissively toward successful mothers, during the mating season, and when the sex ratio was male-biased. Although females generally had less power to win a conflict when their fertilizable egg was less valuable (when they were nulliparous or unsuccessful mothers or when interacting with male kin) and with an increasing female-bias in the sex ratio, this ability to win additionally was influenced by which sex initiated the conflict. Our study demonstrates that female leverage can be influenced by the supply and demand for mating opportunities, but evoking submission does not translate into winning a resource. Indeed, intersexual power is dynamic, contextual, and dependent on the individuals in the dyad. 

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5. Multiple paternity in a lek mating system: Females mate multiply when they choose inexperienced sires

   https://doi.org/10.1111/1365-2656.13158  

   Rivers, Pearl R. ; DuVal, Emily H. ; Sheldon, ed., Ben ( December 2019 , Journal of Animal Ecology)

   Multiple mating by females is common and often driven by social constraints on female mate choice. However, females mate with multiple males even in systems without these social constraints and rates of multiple mating tend to be highly variable within and between populations. In lek mating systems, females are able to assess multiple males and their choice is unrestricted by pair bonds or the need for biparental care, yet some females mate with multiple males.

   To better understand the factors affecting variation in multiple mating, we investigated the occurrence of multiple paternity within clutches in a highly polygynous lek mating system.

   Using long‐term data on genetic paternity, survival, social status and individual age from a population of lance‐tailed manakinsChiroxiphia lanceolata, a species where males lek in cooperative alpha‐beta pairs, we tested five non‐exclusive hypotheses about the causes of variation in multiple mating and its benefits in females.

   We found that inexperienced males, including new alphas and rare beta sires, were disproportionately likely to share paternity when they sired any chicks. In contrast, female age (experience) was unrelated to multiple paternity. Multiple mating did not result in higher reproductive success or reduced variance in success for females, and there were neither consistently promiscuous females nor males that consistently shared paternity.

   The occurrence of multiple paternity in this lek mating system was best explained by female choice related to male characteristics that change with male experience. Our results support the hypothesis that there is a developmental component to the occurrence of multiple mating, and suggest females choose to mate multiply when their choices are not optimal.

    

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