Sociality and Mating Patterns
Lemurs (Prosimians / Strepirhini)
The tropical forest of
Madagascar, with its forest and woodlands, is the only home to all Lemurs. Madagascar
broke away from Africa some 160 million years ago and has a dry climate. Limurs had no other primates as competitors for resources. They are considered the
most endangered vertebrates in the world and their species has a size range
from 3 inches to 3 feet. Lemurs are arboreal as well as terrestrial, an adaptation to their environment of Madagascar, following the food sources. The Lemur, as
well as the Loris, are considered the most non-derived or primitive primate. They
are the only primates that, while having nails on most digits, also maintained
a claw.
Their social behavior depends
on the species. In general the larger lemurs live larger groups of 25 – 30. The
Ringtail Lemur for example has a matriarch hierarchy in which the mother/daughter
or sister/sister unit is very strong. They are aggressive towards non group
females. The males have a hierarchy within their ranks as well, however, are
still below the female.
Another species, the Indris
Lemurs are living in social units with their mate and offspring. And yet the small nocturnal ones live in
solitude.
Their matting patterns are
diverse as well. In groups the dominant male will mate with the dominant female. This way
they can fend of predators, guarantee the best access to resources such as food
and water and thus increase their reproduction success. Lemurs greatly depend on their environment
and have adapted their gestation times to the times of a draught for example. The
females are only receptive for mating 1 or two days a year and only mate when
they are ready. They may approach a male when they are ready for courtship.
Their trait of sociality and
matting patterns has adapted to the environment, as their mating season is only
3 weeks out of the year, with the female being in estrus only a few days per
year. The time of year the mating takes places is depending on the environment
and the availability of food. It is interesting that the smaller lemurs give
birth to multiples, a trait that ensures the survival of their species, as they
have many predators and all Lemur babies are very vulnerable at birth.
Spider Monkey (New World
Monkey / Platyrrhini)
There are about 70 species of
Spider Monkeys. They are arboreal and live in the forested South Mexico as well
as in the evergreen forests of Central and South America. Living high up in the
top of the trees, they have little competition for the food of their choice
such as fruits. They are considered as frugivorous rather than omnivorous.
Their social behavior is shown
in their need of living in medium size groups. Even if an individual wants to
be on its own, it stays close to the group. All offspring has a very close
relation to its mother. Their trait to be able to breed all year round is due
to the fact that supplies of resources determine the size of the group. The group is not able to expand, if there are
not going to be enough food for all, therefore they keep the group size at an
optimum that allows for offspring.
In regards to the gender
roles, the females play a larger role in the group and are leading in the food
foraging sector. However, should the group encounter enemies the males are taking
over the dominant role of protector.
In most primate groups
grooming is an important social aspect, which is not observed with Spider
Monkeys due to the lack of opposable thumbs. Only mothers and offspring are
seen interacting socially like this.
Due to the access to resources
Spider Monkeys breed year round. The male is sexually mature at around 5 years
and the female at around 4 years. The majority of Spider Monkeys is preferring
polygamy and a female mates with many mates.
They produce 1 offspring at a
time, which is being cared for by both parents, which is rare for all primates.
As in any primate species,
there are differences here as well. Some species of Spider Monkeys, such as the
Marmosets or Tamarins live in mated pairings with their offspring.
Baboon (Old World Monkey / Hylobatidae)
Baboons
All five species of Baboons
live in either Africa or Arabia. They prefer living in the savanna, while only
a few live in tropical forests. They have been considered a pest by African
farmers as Baboons like to eat their crops. In regards to food they eat
anything they can get really from crops to fruit, bark and seeds to meat such
as rodents or even sheep and antelopes.
Socially Baboons live in what
is called ‘troops’ of 15-150 members. It is a blended group with both adult
males and females and offspring. Hierarchy within the troop enables the
dominant male and female to access resources and thus increase the changes for
a successful reproduction. Baboons almost constantly groom each other and have
a very close relationship especially once they mated with each other.
The female baboon is a very
good example for the ischial callosities, which turns her genital skin a bright
red. This trait serves as a “visual clue” for the male and has evolved to show that
she is ready for mating. At the time of the swelling the reproductive success
is the highest and females that mature early have a greater chance of
continuous healthy offspring. It appears that the size of the swelling is an
attraction for the male and they prefer the female to not mate with others.
Mates might cause infanticide and the female, in order to protect her young,
mates with many males so that paternity is not certain for any male.
The males of the group mate
with one or more females while males without a group have a harder time mating,
as they try to start their own group. He has to do so carefully, as he needs one
or more females from a group to follow him to do so. The male leader of a group
does not treat such attempts to steal a female or a female that tries to
deflect with kindness.
Baboons express sexual
dimorphism seen here during mating
Gibbons (Lesser Apes / Hylobatidae)
Gibbons are the smallest apes
around. They are the best brachiations of all primates and live in the trees of
south-east Asia. They have adapted to
living in trees and barely ever touch the ground. While their environment, like
that of many primates is being destroyed, they live off the fruits from trees
and leaves. Both males and females are
territorial and they have a whoop or a siren sound to protect their home. They
are also called the “singing apes of Asia’.
Gibbons live in small groups
with their mating partner and are monogamous for life. They may cheat on their
mating partner though.
Like Baboons the female expresses a swollen backside,
to indicate that she is ready for mating. This happens about once a month,
however, conception usually takes place during the dry season (March) and birth
is given 7 month later (in October) during the rainy season, ensuring that
enough food is around for the offspring and the mother come birthing time. They give birth to
one offspring, which is going to live with them until they are about 7 years
old and then go off to find their own mating partner.
Chimpanzee (Great Ape / Hominidae)
There are 3 subspecies of Chimpanzee. They live
primarily in East Africa. Chimpanzee are omnivorous and eat anything and even
hunt smaller mammals including other primates. They are known to use a tool to
go “termite fishing” an adaptation for the need to find food in any place
possible. Their environment is
endangered as well due to forests being taken down and human expansion. There
is also a ‘bush meat’ market, that increases hunting of primates. An
international demand for African bush meat endangers the species.
Chimpanzees live in social groups of 10-100, also
called ‘troops’ and some of them wonder of but always return to the group, so
that not all of them are all together all the time. The do not live in nuclear
families and are close to each other with great aggressions towards outsiders.
They have a hierarchy and their leader can break up fights between males with
just a gesture.
Often times the fights are about a female and they can end up
with fatalities. The females usually stay with their natal group and if their
offspring stays, they are very close. Due to the large size of the ‘troops’
they are living in, they have access to many males and their reproduction rate
is very high. The most shocking behavior that has been observed is infanticide,
where a male Chimpanzee kills the offspring of another male. The female, unable to nurse, stops lactating and
is able to conceive again. DNA tests have shown that the male Chimpanzee has
not killed his own offspring and that the following birth by the female is his.
His reproductive success is ensured by his killing and his genes are going to
go on.
Chimpanzees, along with Gorillas, are the only non-human primates
that mate facing each other. Primates generally face the same direction during
mating.
My findings are that all primates have greatly depended on the access to resources, such as food when it comes to social matters and mating patterns. They either keep a small group size to ensure that all are able to eat and time the mating to create healthy offspring, added items to their food chain when competition was high or retreated to the top of the trees to access food that others can't reach. Their social behavior is primal, meaning that they are often times in a hierachy with a 'leader' of the troop. The leader is the one that keeps peace and again, a group that can live together can procreate together. I even go a step further and suspect that without a leader there would be a lot more infanticide and violence than is reported now. The mating habits are also in accordance with their environment to a point where certain species are only breading at a time that will ensure a birth during a season that provides food to the offspring. The non-human primates are interested in having their genes passed on, as they kill other males offspring and use the female to create offspring. Overall my findings are that the social as well as the mating habits have evolved to ensure a successful mating season.
Sources:
Overall, great coverage of the details on each primate and you made very good connections on how the environment has shaped these traits.
ReplyDeleteA couple of comments:
"It is interesting that the smaller lemurs give birth to multiples, a trait that ensures the survival of their species"
In evolutionary biology, you have committed the "group selection" error. :-) Organisms don't do anything that ensures the survival of their species. Traits do not evolve that help the "group" survive. Traits evolve that benefit the individual and their reproductive success. Introduce two traits into a population, one that benefits the group's survival and one that benefits one individual's survival and guess which one persists and which one gets eliminated from the gene pool? The trait that benefits the group disappears and the one that benefits the individual spreads. Every time.
Baboons are the only primate that travels in those large troop sizes. Why is that? How does it benefit baboons to do so? (I notice you mention this for chimpanzees but not baboons.)
Other than these two points, well done.
Dear Professor Rodriguez,
ReplyDeleteThanks for the clarification. I associate giving birth to many offspring with the survival of the species as they face predators, malnutrition and other diseases and natural disasters.
You are absolutely right, I did mention that Baboons live in troops, but not why. I believe they travel in troops as this is their social conditioning. They are social creatures by nature and depend on the physical contact and support of the group. They defend the troop against other baboon families as well as predators together. The leader in the hierachy is in charge of finding food and moving the troop along peacefully. In return he receives the first pick at food and has the dominance over the female. Hope that provides the missing link.
Best,
Andrea
Giving birth to many offspring ensures that the genes of the *parents* are more likely to survive and reproduce in the next generation. That this usually benefits the species as well is an incidental result, not a *cause* of the behavior. This is an important difference.
DeleteGood answer on the baboons. Thank you for the response.
Got it, thanks.
ReplyDelete