Tropes

ScienceDaily_2013 15857.txt

#Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneothe 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 developmentcertain 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-VÃ gtlin scholarship of the SNSF and her colleagues at the Anthropological Institute and Museum of Zurich University have shown now this developmental arrest occurs more frequently on Sumatra than on Borneo the other southeast 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 copulationthese 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 engaged constantly 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 assumed hitherto. 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 provided based on materials by Swiss National Science Foundation. Note: Materials may be edited for content and length g

< Back - Next >