Male mammals typically die sooner than females. Why is that? Researchers in Madagascar are asking this very question. Recently published in the Journal of Behavioral Ecology a team of researchers studying Milne Edwards sifaka may have discovered why males of this species die so much younger than females.
Milne-Edwards’ sifaka are a large dark lemur that lives in the tropical wet forests of eastern Madagascar. This large lemur spends much of its day consuming leaves and resting. However, they are no slouch when it comes to moving. These species employ a fantastic form of locomotion called vertical clinging and leaping. To move through the forest they spring off a large tree with powerful and especially long legs. As they fly through the air they turn to land on the next tree. As the make contact their body compresses and they shoot off that tree to the next - like a pinball they bounce through the forest. Some sifaka species can breach horizontal gaps between trees as large as 8m (26 feet)!
There are many hypothesis as to why males tend to die off quicker than females. Tecot et al. (2013) describe a few which include the "high risk, high gain" hypothesis which states that males engage in more risky behaviours such as competition for mates or dispersal which increase mortality than females. Imagine lemurs in a bar fight! There is the "fragile male" hypothesis which suggests that males and females have different developmental strategies with males having for example faster growth rates leading to higher mortality as juveniles - especially in times of resource scarcity. This evokes images of male teenagers growing like sky scrapers all while trying to keep up through incredible consumption of food. While females may employ their own strategies like the "live slow, die old" hypothesis which predicts that females actually slow down development in response to increase resource unpredictability and in some cases females may not even reproduce during times of resource scarcity.
Male and female Milne-Edwards' sifaka are roughly the same size and weight, which is particularly unusual for group living primates - but not so for lemurs as many lemur species show little to no sexual dimorphism (differences in size between sexes). Like many lemur species females are dominant. Both sexes leave their natal group (disperse). However, males in this species continue to secondarily disperse long after maturity. Growth rates between the sexes of this species are very similar as are levels of testosterone. Based on their life history one might expect that males and females have the same mortality based on the above hypotheses.
Tecot et al. (2013), determined that male and female mortality were virtually the same until 18 years of age. At this point males became very likely to die while females of this age were more likely to live into their 30's. They suggest that because males engage in "risky" behaviour through adulthood by continuing to disperse while females remained within their group resulted in higher males mortality. It seems that for this species the most likely reason for increased mortality is that males perform more risky behaviour through adulthood than females.
Research like this is fundamental to our understanding of many fascinating aspects of evolution and opens doors to more questions such as why do males disperse more during adulthood than females?
To find out more check out the original article referenced below and stay tuned for more interesting reads.
Tecot, Stacey R., et al. "Risky business: sex differences in mortality and dispersal in a polygynous, monomorphic lemur." Behavioral Ecology (2013).
Reposted from: http://www.planetmadagascar.com/blog/2013/3/7/can-lemurs-tells-us-why-males-die-younger
Ankarafantsika National Park, Madagascar -- "With their white hair and their black faces, they look like little old men wearing masks," says primate-researcher Keriann McGoogan. "When they're clinging to a tree and staring back at you, they are so cute! But then you see them move . . . and wow!"
She gestures towards a group of lemurs leaping, twisting and bounding across an open space in Madagascar's largest national park. About ten sifaka lemurs, an animal that can be found nowhere else in the world, are bouncing around an area that serves as a parking lot, looking for a place to rest or feed. "They look like kangaroos practicing kung fu," says McGoogan, a PhD researcher from the University of Toronto. "But if they want, they will be gone in a flash. And just try to follow them in the forest. There, they can really move."
Welcome to northwestern Madagascar, home to some of the most extraordinary creatures in the world. Here you can find colour-changing chameleons, spiky tenrecs, birds sporting Mohawk haircuts, and eight species of lemurs, among them the Coquerel’s sifaka that McGoogan is studying.
She is spending a year in the park, which is essentially a tropical dry forest extending over 1300 square kilometres. Most visitors come for two or three days -- just enough time to see dozens of birds, most of the lemur species, and the always entertaining chameleons.
The typical tour begins near the parking lot at reception, where visitors can find Malagasy guides, whom speak French and English. They lead the way past the leaping lemurs and birds that will put you in mind of 1985. The Madagascar hoopoe, for example, has a colour scheme similar to that of a Bengal tiger and shows off a massive Mohawk of feathers that would make any punk rocker proud; while the crested drongo, a robin-sized black bird with a forked tail, has bangs that would embarrass Cindy Lauper.
An encounter with a chameleon might evoke a scene in a pub back home in Canada. Picture this: a large male panther chameleon, entirely black, walks with a robot-like gait -- and rather quickly, for a chameleon -- toward a much smaller female. Normally, males are brownish in colour, but when on the prowl for a female they put on their black suit.
If interested, the female will show off some bright, come-hither colours – or else, as in this situation, change colour rapidly from a bright green to a more subdued green with huge white splotches, indicating her lack of interest in this male's intentions.
Like many guys at a bar, the male chameleon is undeterred and keeps coming, probably thinking that if he is able to reach her and buy her a drink, she will change her mind. As the male approaches, the female leaves – and so begins the slowest high-speed chase in the world. In this instance, the male realizes that he has been snubbed and gives up, turning elsewhere in search of another potential mate.
From the parking lot, the guide will take you into the forest, where you will probably be greeted by another group of sifakas. These lemurs are named after the sound they utter when excitement is at hand – something like "shee fawk!" If you hear this call, look around, because maybe a group of common brown lemurs is near. These are easily found as they make a lot of noise barking and screaming, and they wag their tails to warn their fellows that you are nearby. Probably they will come down from the canopy to look you over, and leave you wondering wonder who is watching whom.
Another bizarre creature found in the forest is the common tenrec, a spiny creature that resembles a fat hedgehog. During the wet season (December to March), literally hundreds of these tenrecs rustle around in the forest, with many moms taking thirty-odd kids out for a snort through the leaf-litter in search of tasty insects. Fortunately for those keen on observing them, tenrecs have poor eyesight and, well, a certain lack of wit. If you stay quiet and still, a tenrec may walk right into you. According to McGoogan, "they sometimes run into my boot when I am trying to watch the lemurs."
A stroll through the park at night is a must. The sounds of the forest will make you feel like a kid going out for your first Halloween. This is when you will understand why lemurs are named after Roman "spirits of the dead," as their haunting yells fill the air.
There is a boat tour on the sacred Lake Ravelobe which allows visitors to see even more birds and numerous crocodiles, and then there is a stroll to some beautiful baobab trees, or to a beautiful canyon. Not to be missed.
HOW AND WHEN TO GO:
Ankarafantsika National Park protects one of the last remaining patches of tropical dry forest in Madagascar. It is situated on a main highway (Rue de National 4) that allows easy access from either the capital city, Antananarivo, or nearby Mahajunga, which also has an airport.
The park is open year round for ecotourism. Within the park, there are well-constructed cabins, tent platforms, a restaurant, washroom facilities, and a fantastic network of trails.
Permits and guides are required to visit the park, but these can be purchased and hired on location. If you are interested in spotting birds, the best time to visit is October to December, when bird life is at its most active. The heaviest rains come from December through March. After March there are fewer visitors, the forest is much greener, and you may have the park largely to yourself. From Toronto, return airfare to Madagascar (usually via Paris) starts at around $2,200.
Travis Steffens leads active-travel tours for Backroads Inc. through Belize, Costa Rica, South Africa and Botswana, as well as in the Canadian Rockies and with Civilized Adventures in Madagascar. Travis is married to Keriann McGoogan.
Originally published in the Nashwaak Review Vol. 22-23; Reposted from http://www.planetmadagascar.com/blog/2013/2/5/a-trip-to-ankarafantsika-national-park-madagascar