Alternative reproductive tactics of unflanged and flanged male orangutans revisited

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.

Maternal behavior in Sumatran orangutans (Pongo abelii) is modulated by mother-offspring characteristics and socioecological factors

“…Males disperse from their natal area and do not provide paternal care (Arora et al, 2012; Morrogh-Bernard et al, 2011; Nietlisbach et al, 2012; van Noordwijk et al, 2023). This, along with a prolonged period of lactation relative to gestation length (van Schaik, 2000), sexual size dimorphism (Utami Atmoko et al, 2009), and potential for contest competition between males for mating opportunities (Kunz et al, 2023; Spillmann et al, 2017; van Schaik & van Hooff, 1996), puts orangutans at a high risk of infanticide by males, even though there are no confirmed cases (Beaudrot et al, 2009; Knott et al, 2019; van Schaik & Janson, 2000).…”