Comparative Primate Blog: Comparing Primates through the defining trait of body size and Sexual Dimorphism

1-3. Comparing Primates through the defining trait of body size and Sexual Dimorphism

a.       Lemurs (Prosimians/Strepsirhini): Lemurs live on the island of Madagascar and the nearby Comoro Islands.  The island is located in the Indian Ocean of the eastern coast of Africa. The location of the island allows for tropical climate along the coast as well as inland, yet arid in the southern part of the island. The climate allows for two seasons: hot, rainy about half the year and cool, dry the other part. The geography includes many rivers and lakes, coastal beaches and central highlands. Madagascar has a unique and rare variety of species. Since the island separated from Africa about 65 mya, it does not have many of the large mammals or poisonous snakes found on the continent, making it a hotspot for new species to evolve. Lemurs have evolved to become fit for living on the island. Their body and behavior is different from other monkeys throughout the world.

“A World Apart”

b.      Lemurs vary greatly in size, they can be anywhere from 1.1 ounce to 15-20 pounds and seem to the smallest of all living primates. However an extinct Lemurs species, the Archaeoindris fontoynonti, could range from 350-440 pounds. The ring-tailed lemur has a black and white striped tail on both males and females. Male ring tailed lemurs have dark colored scent glands located inside their wrist, chest, and armpits. Females and males both have anogenital scent glands. Male and females are the same in size growing to around 1.39 feet and weighing around 4.87-4.89 pounds. Other variations of lemurs have more noticeable Sexual Dimorphism in the color of their fur. The male black lemur is completely black while the females display a white collar around their face and have white on their chest. The rest of her body is a reddish color. Another lemur that has this white marking on the female is the mongoose lemur. Other than this, Lemurs seem to have developed traits allowing for Sexual Monomorphism.

c.       Since Lemurs where secluded from other primates on the island of Madagascar, they evolved differently due to the seasonal changes on the island, which create a larger diversity within the clade of Lemurs. Isolated, there was not much in the way of competition and the Lemurs used their intelligence over other species on the island which lead to their successful diversity. Before humans learned of Madagascar about 2000 years ago, some Lemurs grew to the size of gorillas, but today those larger Lemur primates are extinct and there remains about 100 species of Lemurs. The harsh weather of Madagascar accounts for the fur that Lemurs have developed. Also they have a trait for seasonal fat storage. Resource limitation and seasonal breeding also account for the Sexual Monomorphism, creating little to no differences between male and female phenotype. The diet accounts for their stature too in that they live on mostly fruit and leaves. Most Lemurs are arboreal which accounts for their small sizes, but the Ring-tail Lemurs are terrestrial which explains why these Lemurs are so much larger in size.

d.      “Lemurs: Spirits of Madagascar”

Ring-Tailed Lemur

Mongoose Lemur

a.       Spider Monkey (New World Monkey/ Platyrrhini): Spider Monkeys live in tropical rainforest of the central and Southern parts of America and can be found as far north as Mexico. Spider Monkeys tend to stay high in the tree-tops and eat the variety of fruit and leaves found in the rainforest. Central America is prone to earthquakes as well as volcanoes. It also has large mountain rangers and fertile valleys lying in between them. The climate is generally associated with tropical to sub-tropical allowing for a rich landscape with a variety of flora. The rainforest provides homes for a large variety of species as well, including dangerous predators such as large cats like Jaguars and Pumas. With its dense forest and Amazon River, the rainforest is home to about 30% of the world’s species. Unfortunately, deforestation is threatening the biodiversity of the worlds Eden because of the cultivation of soybeans and cattle. Every year the Amazon loses an area of forest the size of New Jersey!

“The Last Eden”

b.      Spider Monkeys are relatively small for primates. The largest Spider Monkey is the Black Spider Monkey with males weighing about 23.8 pounds and females around 21.3 on average. The height for the male is around 1.83 feet and females average 1.81 ft. There is not really a noticeable Sexual Dimorphism in Spider Monkeys size. Male and females seem to be relatively the same; females are only slightly smaller than their male counter-parts.

c.       Spider Monkeys tend to be small to accommodate their arboreal lifestyle. The size allows them to move in the forest tree-top. They have long arms and prehensile tails that allow them to grip tree, which allows them to move freely. Their weight is taken into consideration here for their ease of movement. Also, spider monkeys have a high caloric which encompasses their dependency on fruit. They must be able to travel freely and widely to accommodate their demanding diet because of the scarcity and wide-spread resources to eat in their habitat.

d.      “New World Spider Monkeys”

Black Spider Monkey

a.       Baboon (Old World Monkey/ Cercopithecidae): Baboons are found in the sub-Sahara in Africa as well as some Arabic regions. The sub-Sahara has harsh climates and is separated from Sudan by the Nile River. Baboons prefer the savanna and other somewhat humid atmospheres. The savanna is a grass land area with trees that are too small to create an enclosed canopy, but in some places has some pretty dense forest. There is a seasonal water supply so availability is small. The area comprises about 20% of the earth’s surface and the land transitions from forest to desert.  The savannas are threatened by wildfires, human clearing for cultivation, and human induced climate changes through greenhouse gases.

“Land which is without trees but with much grass”

b.      Baboons vary in size. The Guinea baboon is 20 inches long and weighs about 28-57 pounds, while the larger chacma baboon can be 47 inches tall and weigh up to 90 pounds.  Baboons are marked with sexual dimorphism.  The males tend to be larger than the females and the females and young baboons are dependent on males for protection. Males are often twice the size of females and are more aggressive. Females have pink rumps and males have a mane of fur around their heads. Male baboons have long canines used to fend off predators and to compete with other males. Females have sex skins around their private parts and are developed during ovulation time to let males know she is ready. The forelimbs and hind legs on a baboon are equal in length, making it hard to climb.

c.       Baboons are terrestrial which accounts for the large size and relatively equal length forelimbs and hind limbs. They are omnivores and can eat just about anything including fruit, roots, and grass seeds and leaves. They also can eat small mammals and invertebrates. Their environment is not one needed for high tree living so Baboons evolved into larger mammal and they have more resources of food. Large Male baboons have evolved the canines to hunt other monkeys , gazelle, or flamingos for food.

d.      “Old World Baboons”

Female Baboon with swollen sex skin 

Male Baboon showing canines and strength. Also notice equal size forelimbs and hind limbs

a.       Gibbon (Lesser ape/ Hylobatidae): Gibbons inhabit parts of China, Southeast Asia, and islands, like the Philippines and Singapore. Southeast Asia has two regions, Mainland and Maritime. The climate is mainly tropical-hot and humid all year round; however, in the higher mountain ranges the weather is dry and desert like. There is also plenty of rainfall with accounts for the diversity of species because the area is vulnerable to monsoons. The rainforest is the second largest on earth, second to the Amazon. Loaded with predators and prey, Southeast Asia is home to tigers, rhinoceros, elephants, Gibbons, Eagles, six subspecies of Binturong, Komodo Dragons, and more. The biodiversity in Southeast Asia is amazing. The forest floor is immersed in nutrients which allow thick forest growth. Unfortunately, the rainforest of Southeast Asia is a victim of the “slash and burn” cultivation and is facing extinction, along with its many species. Some have predicted that 40% of the region and species will be wiped out in the 21^st century.

“The land of Plenty (Monsoons)”

b.      Gibbons are known as the lesser ape because they only reach about 3 feet in height and 12-20 pounds, which is small for an ape. Gibbons do not have too much sexual dimorphism in the way of size other than the siamangs, whose males get to about 30 pounds.

c.       They are arboreal and are the fastest of tree dwelling creatures. Their small, compared to most apes, stature allows for them to move bipedal at times and swing with great ease through trees. Gibbons have evolved a ball and socket joint with allows for biaxial movement. This allows the Gibbons to swing while reducing stress on the upper body and arms. Some of these evolutionary traits can be tied to the environments monsoons and the predators around the floor, posing threats to the Gibbon which keeps them high in the trees.

d.      “Gibbon: The Lesser Ape”

a.       Chimpanzee (Great ape/ Hominidae): Live in the middle region of Africa. Typically Chimpanzees prefer tropical environments like the rainforest, but you can find Chimps in the savanna forest and the montane rainforest. The montane rainforest generally has cooler temperatures in higher mountain regions. The common chimpanzee however lives in the lowland rainforest south of the Congo River. The great rainforest basin from the Congo River is found throughout middle Africa. The large forest of the region allows for plant diversity with well over 10,000 species. The biodiversity of plant life provides home and shelter for many species, including four from the great ape family, elephants, buffalo, bongo, hogs, etc. Unfortunately these animals fall victim to bush meat hunters which is posing a large threat to the biodiversity of Africa’s middle region.  In addition, because of the rich soil this area is good for cultivating cocoa, coffer, and rubber. There are environmental concerns about the deforestation occurring through the lumber business and farming.

“Cloud forest and Congo Basin”

b.      Chimpanzees can reach to about 5.6 feet in height. Chimpanzees are sexual dimorphic in that the males weigh around 150 pounds and female tend to be around 100 pounds and are less muscular. Males are more aggressive than females and tend to eat more meat than females. Females’ behavior is different in that they leave and find new mates while males generally stay with their natal community to help protect their territory.  

c.       Chimpanzees are both arboreal and terrestrial. Chimpanzees have the ability to climb trees and walk on the ground either by “knuckle-dragging” or bipedal. Since they dwell on both the ground and in the trees their body size accounts for predators on the ground while giving them ease of maneuvering through trees. The difference in the behavior of staying and leaving the natal community is evolutionary in that the female goes off in search of a mate, to procreate, while the males stay to protect their food sources and territory. This is a strategy used to sustain their species and is a great example of sexual dimorphism created out of necessary evolution to the species survival.  

d.      “Common Chimpanzees”

Female Chimpanzee with infant

Male Chimpanzee with toddler

4. The research and comparative traits of the five primates through body size and sexual dimorphism has shown that there is a definite link between how a species evolves in their respective environment. The primates that tend to be smaller, Lemurs and Spider Monkeys, are arboreal and live on a mostly fruit diet. Their habitats are tropical, with thick forest growth. The larger primates, Baboons, Gibbons, and Chimpanzees tend to be arboreal and terrestrial which allows us to see why they grow to be much larger in size. They also seem to be more omnivorous than the smaller primates which accounts for why they are larger, not only through nutrition, but also because of the necessary strength needed in obtaining prey. While the Gibbon and Chimpanzees inhabit tropical forest regions like the smaller primates, they are adapted for ground living and tree living. Baboons live in an area that is not so dense populated by forest which accounts for their canine teeth and their hindering ability to climb trees. After the extensive research for this post it is interesting to look at the common environments of each primate and the differences to compare and contrast why those primates have evolved so differently with respects to their needs in their own ecological niches of the world. The primate I found to be the most interesting is the Lemurs of Madagascar because they, being separated from all other primates, found their own way to evolve through natural selection.