Featured Research

from universities, journals, and other organizations

Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo

Date:
March 5, 2013
Source:
Swiss National Science Foundation
Summary:
The sexual development, mating habits and social hierarchy of the orangutans are more heavily dependent on their environment than had previously been assumed: where the rain forest supplies more food, the influence of the dominant male increases. In order to escape his attention, many other males remain "small."

Left -- a male orangutan with cheek pads. Right -- without secondary sexual characteristics.
Credit: © Lynda Dunkel, AIM Zurich

The sexual development, mating habits and social hierarchy of the orangutans are more heavily dependent on their environment than had previously been assumed: where the rain forest supplies more food, the influence of the dominant male increases. In order to escape his attention, many other males remain "small."

This is the conclusion of a study supported by the Swiss National Science Foundation (SNSF).

In Malay, the word "orangutan" means man of the woods. In fact, however, these rain forest dwellers clad in a reddish-brown coat are our most distant relatives within the great ape family. The orangutan differs from all of the others because the male can go through two different phases of development. It is for this reason that there are two types of sexually mature males, the smaller appearing externally like the female and the larger developing secondary sexual characteristics such as cheek pads and throat pouches.

Arrested development

Certain small males may remain at an arrested stage of development for years or even throughout their lives without the final spurt of growth ever arriving. As Lynda Dunkel, holder of a Marie Heim-Vφgtlin scholarship of the SNSF, and her colleagues at the Anthropological Institute and Museum of Zurich University have now shown, this developmental arrest occurs more frequently on Sumatra than on Borneo, the other south-east Asian island which is home to the orangutans.

On Sumatra, the researchers observed twice as many small males as adults with cheek pads. During a five-year period of observation in the rain forest, only a single male was seen to develop secondary sexual characteristics. By way of contrast, on the island of Borneo, there are twice as many males with cheek pads as without.

Forced copulation

These males engage in disputes for the favour of fertile females much more often than those on Sumatra where, within the area under observation, a single dominant male monopolises sexual relations with the females. As there is more food available in the jungle on Sumatra than in the forests of Borneo, the dominant male has sufficient time to keep a close watch over the females in his environment and he drives out any other males with cheek pads before they can mate with a female.

However, smaller males without secondary sexual characteristics are less conspicuous. On Sumatra, this makes it easier for them to copulate with a female, even though the females put up resistance in 60% of the cases observed. Forced copulation also takes place on Borneo. There, however, as the males are constantly engaged in fighting in which the smaller ones never prevail, the advantages of developmental arrest disappear.

The fact that food supply in the forest has such a strong impact on the mating behaviour of the orangutan came as a surprise to Dunkel. "It goes to show," she says, "that the organisation of these great apes -- and perhaps that of our ancestors as well -- is more variable than we had hitherto assumed. Apparently, natural selection not only moulds appearance but also adapts social behaviour to the conditions of the local environment."


Story Source:

The above story is based on materials provided by Swiss National Science Foundation. Note: Materials may be edited for content and length.


Cite This Page:

Swiss National Science Foundation. "Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo." ScienceDaily. ScienceDaily, 5 March 2013. <www.sciencedaily.com/releases/2013/03/130305080648.htm>.
Swiss National Science Foundation. (2013, March 5). Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2013/03/130305080648.htm
Swiss National Science Foundation. "Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo." ScienceDaily. www.sciencedaily.com/releases/2013/03/130305080648.htm (accessed July 28, 2014).

Share This




More Plants & Animals News

Monday, July 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Traditional African Dishes Teach Healthy Eating

Traditional African Dishes Teach Healthy Eating

AP (July 28, 2014) — Classes are being offered nationwide to encourage African Americans to learn about cooking fresh foods based on traditional African cuisine. The program is trying to combat obesity, heart disease and other ailments often linked to diet. (July 28) Video provided by AP
Powered by NewsLook.com
Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Newsy (July 28, 2014) — The asteroid that killed the dinosaurs struck at the worst time for them. A new study says that if it hit earlier or later, they might've survived. Video provided by Newsy
Powered by NewsLook.com
Raw: Sea Turtle Hatchlings Emerge from Nest

Raw: Sea Turtle Hatchlings Emerge from Nest

AP (July 27, 2014) — A live-streaming webcam catches loggerhead sea turtle hatchlings emerging from a nest in the Florida Keys. (July 27) Video provided by AP
Powered by NewsLook.com
Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) — The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins