Male orangutans exhibit bimaturism—two mature morphs—flanged and unflanged males. Flanged males are larger, have cheek pads (flanges) and large throat sacs, and produce long calls. Previous orangutan paternity studies found variation between the reproductive success of each morph and in the degrees of reproductive skew. However, these studies were limited by a lack of behavioral maternity data, the inclusion of ex-captive orangutans, and/or the presence of feeding stations. Here we present the first paternity data from completely wild orangutans with known mothers. We hypothesized that (1) flanged males would have higher reproductive success than unflanged males due to flanged male dominance and female preference and (2) a single male would not monopolize paternity due to the temporal and spatial distribution of fecund females. We used fecal samples collected in Gunung Palung National Park from 2008-2019 to genotype orangutans (13 offspring born 2002-2015, their 10 mothers, and 19 candidate sires) using 12 microsatellites. MICROCHECKER 2.2.3 and CERVUS 3.0 were used to confirm the suitability of the microsatellite panel, fidelity of individual identities, and genetic maternity. Paternity analysis was performed with both CERVUS 3.0 and COLONY 2.0.6.7. We were able to identify paternity for six offspring. Four flanged males sired five offspring, and one sire’s morph was unknown at the time of conception. We found that flanged males have higher reproductive success and that females are not monopolizable in this completely wild setting. We discuss the implications of all published orangutan paternity results for understanding bimaturism in orangutans.
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Reproductive success of Bornean orangutan males: scattered in time but clustered in space
The social and mating systems of orangutans, one of our closest relatives, remain poorly understood. Orangutans (
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.
- Award ID(s):
- 1719825
- NSF-PAR ID:
- 10478196
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Behavioral Ecology and Sociobiology
- Volume:
- 77
- Issue:
- 12
- ISSN:
- 0340-5443
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In many slowly developing mammal species, males reach sexual maturity well before they develop secondary sexual characteristics. Sexually mature male orangutans have exceptionally long periods of developmental arrest. The two male morphs have been associated with behavioral alternative reproductive tactics, but this interpretation is based on cross‐sectional analyses predominantly of Northwest Sumatran populations. Here we present the first longitudinal analyses of behavioral changes of 10 adult males that have been observed in both unflanged and flanged morph. We also analyzed long‐term behavioral data on an additional 143 individually identified males from two study sites, Suaq (Sumatra,
Pongo abelii ) and Tuanan (Borneo,Pongo pygmaeus wurmbii ), to assess male mating tactics cross‐sectionally in relation to population, male morph (unflanged and flanged), and other socio‐ecological factors. Both our longitudinal and cross‐sectional results confirm and refine previous cross‐sectional accounts of the differences in mating tactics between the unflanged and the flanged male morphs. In the unflanged morph, males exhibit higher sociability, particularly with females, and higher rates of both copulation and sexual coercion than in the flanged morph. Based on our results and those of previous studies showing that females prefer flanged males, and that flanged males have higher reproductive success, we conclude that unflanged males face a trade‐off between avoiding male‐male contest competition and gaining mating access to females, and thus follow a “best‐of‐a‐bad‐job” mating strategy. -
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Abstract Male mating strategies respond to female availability such that variation in resources that affect spatial distribution can also alter cost–benefit tradeoffs within a population. In arid‐adapted species, rainfall alters reproduction, behavior, morphology, and population density such that populations differing in resource availability may also differ in successful reproductive strategies. Here, we compare two populations of Cape ground squirrels (
Xerus inauris ), a sub‐Saharan species with year‐round breeding and intense mating competition. Unlike most mammals where males resort to aggressive interactions over females, maleX. inauris are tolerant of one another, relying instead on other nonaggressive pre‐ and postcopulatory strategies to determine reproductive success. Our findings suggest that differences in resource availability affect female distribution, which ultimately leads to intraspecific variation in male reproductive tactics and sexual morphology. Sperm competition, assessed by reproductive morphometrics, was more pronounced in our high resource site where females were distributed evenly across the landscape, whereas dominance seemed to be an important determinant of success in our low resource site where females were more aggregated. Both sites had similar mating intensities, and most males did not sire any offspring. However, our low resource site had a higher variance in fertilization success with fewer males siring multiple offspring compared with our high resource site where more individuals were successful. Our results lend support to resource models where variations in female spatial distribution attributed to environmental resources ultimately impact male reproductive behaviors and morphology. -
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Abstract The primate adolescent period is characterized by a series of changes in physiology, behavior, and social relationships. Orangutans have the slowest life history and the longest period of dependency of all primates. As members of a semisolitary species with high levels of sexual coercion, adolescent female orangutans face a unique combination of challenges when achieving independence from their mother. This study examined the mating behavior of adolescent female orangutans and compared it with that of adult females to assess whether mating behavior reflects distinct strategies at these different points in the life cycle. Data were collected in Gunung Palung National Park on the island of Borneo over 20 years. Mating events from adolescent (
n = 19) and adult females (n = 26) were scored and compared. Adolescent female mating events had significantly higher mating scores (indicating more proceptivity) than those of adult females (β = 1.948,p = .001). Adolescent females also engaged in elaborate sociosexual interactions with different flanged males, behaviors that were never observed during mating events of adult females. These interactions involved characteristic behavior on the part of both the adolescent females and the flanged males. Given these findings and the documentation of similar accounts of adolescent female–flanged male mating from the island of Sumatra, we propose that adolescent female orangutans display distinctive behavioral repertoires throughout the genusPongo which serves to overcome male ambivalence toward nulliparous females, establish familiarity, and evaluate coercive tendencies in flanged males. We suggest that these behavioral patterns are an integral part of female social development in a female philopatric, but highly dispersed species where consistent social support is absent after ranging independence is achieved.
