ANTH 204 - Exam 2

What morphological traits are common to primates?

Grasping hands and feet with opposable thumbs (and big toes in most), flat nails instead of claws, and sensitive tactile pads. Forward-facing eyes with stereoscopic vision, color vision in many species, a reduced snout and sense of smell, a postorbital bar or closure, a large brain for body size, generalized teeth, and hindlimb-dominated locomotion.

What behavioral and life history traits are common to primates?

Long gestation, usually one infant at a time, heavy maternal investment, slow growth, long juvenile periods, late maturity and long lives. Most are highly social, live in stable groups with complex relationships, and rely heavily on learning.

What kind of teeth do primates have? What is the dental formula of the old world monkeys and apes?

Primates have generalized, heterodont teeth (incisors, canines, premolars, molars) suited to a varied diet. OWMs and apes have the formula 2.1.2.3: 2 incisors, 1 canine, 2 premolars and 3 molars per quadrant.

What is the geographic distribution of primates (currently)?

Mostly tropical and subtropical forests of Central and South America, mainland Africa, Madagascar, and South and Southeast Asia. A few live in temperate areas (Japanese macaques; Barbary macaques in North Africa and Gibraltar). There are no native primates in Australia or North America, besides humans.

When did the primate lineage emerge? What was the first major phylogenetic split (into two large suborders)?

Primates emerged around the end of the Cretaceous to the early Paleocene, roughly 65 mya; molecular estimates go older, and the first true primates (euprimates) appear around 55 mya. The first major split was into the Strepsirrhini (lemurs, lorises, galagos) and the Haplorrhini (tarsiers, monkeys, apes).

What are the two Strepsirrhine infra-orders?

Lemuriformes (the lemurs of Madagascar) and Lorisiformes (lorises and galagos of Africa and Asia).

Tarsiers are nocturnal insect-eaters. Why are they classified as Haplorrhines?

Although they look and live like strepsirrhines, tarsiers share derived traits with anthropoids: a dry nose with no rhinarium, a free upper lip, partial postorbital closure, no tapetum lucidum, a haplorhine-type placenta, and an inability to make their own vitamin C. Genetic evidence also puts them closer to monkeys and apes.

Where are OWMs and apes found?

Africa and Asia. OWMs live across Africa and South and Southeast Asia (plus Gibraltar). Gibbons and orangutans are in Southeast Asia; gorillas, chimpanzees and bonobos are in equatorial Africa.

Know examples of at least 2 Strepsirrhines, Haplorrhines, OWMs, NWMs. Know their social organization and dietary niche.

Strepsirrhines: ring-tailed lemur (multi-male, multi-female groups with female dominance; fruit and leaves) and slow loris (solitary, nocturnal; insects, gum and fruit). Haplorrhines: tarsier (small pairs or family groups; insectivore) and chimpanzee (multi-male, multi-female fission-fusion; frugivore-omnivore). OWMs: savanna baboon (multi-male, multi-female troops; omnivore) and black-and-white colobus (one-male groups; folivore). NWMs: howler monkey (one-male or small multi-male groups; folivore) and common marmoset (cooperative-breeding family groups; gum and insects).

What are hominoids? How do they locomote? What are some morphological characteristics common to hominoids?

Hominoids are the apes and humans (superfamily Hominoidea): gibbons, siamangs, orangutans, gorillas, chimpanzees, bonobos and humans. They move by suspensory locomotion: brachiation in gibbons, quadrumanous climbing in orangutans, knuckle-walking in African apes, and bipedalism in humans. Shared traits: no tail, a broad flat chest, shoulder blades on the back, long arms, very mobile shoulders and wrists, a short stiff lower back, Y-5 molars and large brains.

What are the lesser apes? How do they locomote? What is their social organization?

The lesser apes are the gibbons and siamangs (Hylobatidae) of Southeast Asia. They brachiate, swinging arm-over-arm through the canopy. They live in pair-bonded, territorial family groups and defend territories with duet songs.

What are the great apes (list)?

Orangutans (Bornean, Sumatran, Tapanuli), gorillas (eastern and western), chimpanzees and bonobos. Humans are also great apes (hominids) in modern classification.

Know the social organization, mating system, locomotion method, and dietary niche of each of the great apes.

Orangutan: semi-solitary; polygynous (flanged males attract females, unflanged males often force copulations); arboreal quadrumanous climbing; mainly fruit. Gorilla: one-male, multi-female groups led by a silverback (sometimes multi-male); polygynous; terrestrial knuckle-walker; folivore, with western lowland gorillas eating more fruit. Chimpanzee: multi-male, multi-female fission-fusion communities with male philopatry; promiscuous (polygynandrous); knuckle-walking plus climbing; frugivore-omnivore that hunts monkeys. Bonobo: multi-male, multi-female fission-fusion with high female status and strong female bonds; promiscuous, with frequent sociosexual behavior; knuckle-walking and more arboreal than chimps; mostly fruit, little meat.

Which ape is arboreal? A knuckle walker? A vegetarian? Solitary?

Arboreal: the orangutan (gibbons too). Knuckle-walkers: gorillas, chimpanzees and bonobos. Vegetarian: the gorilla, which eats mostly leaves and stems. Solitary: the orangutan.

Which ape(s) live in one-male, multi-female groups? Multi-male, multi-female groups?

One-male, multi-female: gorillas. Multi-male, multi-female: chimpanzees and bonobos.

In which ape species is strong female bonding observed (2)? Strong male-bonding? Which are pair-bonded?

Strong male-bonding? Which are pair-bonded?#Strong female bonding: bonobos and Old World monkeys (cercopithecoids), many of which have female bonding with male dispersal. Strong male bonding: chimpanzees. Pair-bonded: gibbons and siamangs (the lesser apes).

Understand what an activity budget is.

An activity budget is how an animal divides its day among activities such as feeding/foraging, traveling, resting and socializing (grooming, play), usually given as a percentage of time.

Most NWMs spend half their day engaged in what kind of activity?

Foraging and feeding: searching for, processing and eating food.

What other activities do wild primates engage in?

Resting, traveling, socializing (grooming, playing), watching for predators, mating, fighting and sleeping.

What dictates the amount of time primates spend foraging?

Their nutritional and energy needs, set by body size, metabolism, reproductive state and activity. Also the quality, abundance and distribution of their food: poor-quality or scattered food takes longer to collect.

List the four factors that determine how much food primates require, be able to briefly describe each.

(1) Body size: bigger animals need more total energy but less per kg. (2) Basal metabolic rate: the energy needed just to stay alive at rest. (3) Activity level: travel, foraging and social activity burn extra energy. (4) Reproductive status: pregnancy and especially lactation sharply raise females' needs, and growing juveniles need extra energy too.

From what food sources do primates obtain protein, carbohydrates and fats and oils?

Protein: insects, young leaves, seeds and meat. Carbohydrates: ripe fruit, gum, sap, nectar, flowers and underground storage organs. Fats and oils: seeds, nuts, insects and some oily fruits.

Provide an example of an insectivore, a frugivore, a folivores and a gumnivore.

Insectivore: tarsier. Frugivore: spider monkey (or chimpanzee). Folivore: colobus monkey (or howler monkey). Gumnivore: marmoset.

Why are very large gorillas able to sustain themselves on leaves, while very small primates must consume energy-dense foods?

Metabolic rate rises more slowly than body mass (Kleiber's law, about mass^0.75), so large animals need more total energy but less per kg. Gorillas can meet their needs with abundant, low-quality leaves, using a big gut to ferment them slowly. Small primates burn energy fast per kg and have small guts, so they need high-energy, easily digested foods like insects, gum and fruit, eaten often.

Which has the simplest digestive system: an insectivore, a frugivore, a folivores and a gumnivore. Which has the most complex digestive system and why?

Insectivores have the simplest gut: a simple stomach and short intestines, because insects are easy to digest. Folivores have the most complex: sacculated stomachs (colobines) or an enlarged caecum and colon (howlers) where bacteria ferment cellulose and break down plant toxins over a long time.

Provide 2 reasons that primates may be territorial.

(1) To keep exclusive access to food resources that are worth defending. (2) To defend mates and protect infants from outside males (and keep other groups away from sleeping sites).

Under what circumstances are primates less likely to be territorial?

When the home range is too large to patrol relative to how far they travel each day (low defensibility), when food is too scattered, unpredictable or abundant to be worth defending, or when the costs of defense outweigh the benefits.

Provide two examples of a territorial primate, and two examples of a non-territorial primate.

Territorial: gibbons and titi monkeys (chimpanzees and vervets also defend territories). Non-territorial: savanna baboons and gorillas (orangutans too).

What are the costs and benefits of territoriality?

Costs: time and energy spent patrolling, calling and displaying, risk of injury or death in fights, and possible exposure to predators. Benefits: exclusive access to food, mates and sleeping sites, and protection of infants from outsiders.

How can primates defend themselves against predation?

Living in larger groups, staying vigilant, giving alarm calls (vervets have predator-specific calls), mobbing or counterattacking, fleeing, choosing safe sleeping sites, crypsis and nocturnality, large body size, and associating with other species.

How does increasing group size protect primates from predation (3 ways)

(1) Detection: more eyes spot predators sooner. (2) Dilution: each individual's odds of being the one caught are lower. (3) Deterrence/defense: groups can mob, confuse or fight off predators.

What are the costs and benefits of sociality for primates?

Costs: competition for food (scramble and contest), easier disease and parasite spread, being more conspicuous, longer daily travel, and aggression including infanticide. Benefits: protection from predators, group defense of food against other groups, access to mates, help from allies and kin, and shared information about food.

Social groups are organized based on mating system. What 4 main types of social groups form?

Solitary, pair-bonded (monogamous), one-male multi-female (polygynous), and multi-male multi-female (polygynandrous).

What percent of primate species are threatened with extinction?

About 60% of primate species are threatened with extinction, and about 75% have declining populations.

Why are primates at risk? Provide 3 reasons.

(1) Habitat loss from deforestation, agriculture (e.g., oil palm), logging and mining. (2) Hunting for bushmeat and traditional medicine. (3) The live pet trade, plus disease and climate change. Slow reproduction makes it hard for populations to recover.

Define “mating system.”

The pattern of mating relationships in a species: how many partners each sex has, who mates with whom, how long the relationships last, and often who cares for the young.

List three characteristics of mammals that constrain primate mating systems.

(1) Internal fertilization, so males can't be sure of paternity. (2) Internal gestation by females. (3) Lactation, so only females can nurse. Together these make females invest far more than males.

Define “strategy” (in terms of natural selection) and provide one example of a mating strategy.

A strategy is a genetically influenced set of behaviors, shaped by natural selection, that tends to maximize reproductive success in a given situation; it is not conscious planning. Example: male mate guarding during the female's fertile period (another: females mating with several males to confuse paternity).

Under what circumstances will male primates invest their energy in finding new mates?

When additional fertile females are available to compete for, when paternity is uncertain, and when male care adds little to infant survival. Then more matings give a greater fitness payoff than caring for offspring.

Under what circumstances will primate males invest in offspring?

When paternity certainty is high (pair bonds), when male care substantially improves offspring survival, and when chances to get other mates are limited. Examples: titi monkeys, owl monkeys and marmosets, where males carry infants.

How do gestation and lactation constrain female reproductive success?

Both are long and energetically costly, and nursing suppresses ovulation (lactational amenorrhea). This creates long interbirth intervals, so a female can produce only a limited number of offspring in her lifetime, and her success depends on her access to food and energy.

What happened in a Japanese study when semi-wild female macaques were provisioned?

With extra food, females grew faster, matured and started reproducing earlier, and had shorter interbirth intervals and higher birth rates, so the population grew quickly. This shows food and energy limit female reproduction.

Why might very young and very old mothers have compromised offspring survival?

Young mothers are still growing, so they split energy between their own growth and the infant, and they lack experience. Old mothers are senescing, in poorer condition, and may die before the infant is independent.

What five factors influence female reproductive success? Why?

Resources: food means babies, so provisioned macaques and food-enhanced Amboseli baboons matured earlier and had shorter interbirth intervals.

Longevity: a longer life means more years to reproduce.

Rank: dominant females get better access to food, safer spots, more grooming and coalition partners and less stress.

Sociality: baboon females with strong social bonds have more offspring survive and live longer, independent of rank.

Adversity: harsh early-life conditions (drought, maternal loss, low maternal rank, orphaning) shorten lifespan and lower fitness. Group size is also listed, and age has its own slide: young mothers have about 50% higher infant mortality and old mothers are senescing.

Which explains the majority of the variance in female reproductive success?

Longevity: how long a female lives, and so how many years she has to reproduce.

How does sociality affect reproductive success in female baboons?

Females with strong, stable social bonds (frequent grooming partners, often close kin) have higher infant survival, lower stress and longer lives, regardless of rank.

What is the quality-quantity tradeoff in reproduction? Provide an example.

Energy put into one offspring can't go to another, so producing more offspring means investing less in each and lowering their survival or quality. Example: a female who weans early to conceive sooner raises the risk that her current infant dies. Likewise, primates have single, intensively cared-for infants rather than large litters.

What main factor limits Reproductive success in female primates? Males?

Females: access to food and energy for gestation and lactation. Males: access to fertile females (mates).

What is sexual dimorphism? What three types were discussed in class?

Sexual dimorphism is a difference between males and females in traits such as size, color, weaponry, ornamentation and behavior, which evolves through sexual selection.

Main types:

• body size (from intrasexual male-male competition, e.g., orangutans),

• weaponry such as canines (also from male-male competition),

• color/ornamentation (from intersexual selection or female choice, the “primate peacock’s tail,” e.g., mandrill faces, proboscis monkey noses, orangutan cheek pads).

Why does sexual selection usually act more strongly on males in mammalian systems?

Females invest much more in each offspring (gestation, lactation), so fertile females are the limiting resource. Male reproductive success varies far more and depends on how many mates a male gets, so males compete intensely for females.

Know the difference between inter-sexual and intra-sexual competition, provide examples for sexually selected traits associated with each.

Intrasexual selection is competition within one sex (usually males fighting males) for access to mates; it selects for large bodies, large canines and, through sperm competition, large testes. Intersexual selection is mate choice by one sex (usually females) among members of the other; it selects for ornaments, bright coloration (mandrill faces), displays and calls.

Is sexual dimorphism most pronounced in: pair-bonded, one-male multi-female, or multi-male multi-female groups? Why?

One-male, multi-female groups. A single male can monopolize many females, so winning fights pays off hugely and male-male competition favors large size and canines (e.g., gorillas). Dimorphism is lowest in pair-bonded species.

Is sperm competition most pronounced in: pair-bonded, one-male multi-female, or multi-male multi-female (polygynandrous) groups? Why?

Multi-male, multi-female groups. Females mate with several males during one cycle, so sperm from different males compete to fertilize the egg, selecting for large testes relative to body size (chimpanzees and bonobos, versus small-testes gorillas).

Be able to categorize the apes by mating system: solitary, pair-bonded, one-male multi-female, or multi-male multi-female groups.

Solitary: orangutans. Pair-bonded: gibbons and siamangs. One-male multi-female: gorillas. Multi-male multi-female: chimpanzees and bonobos.

Know three examples of pair-bonded primates.

Gibbons (and siamangs), titi monkeys and owl monkeys.

What is mate guarding? Provide 2 examples.

Mate guarding is when a male stays close to a fertile female and keeps other males from mating with her. Examples: savanna baboon consortships, and hamadryas baboon males herding their females with neck bites (chimpanzee consortships also count).

Define “cooperative breeding.” What primates are cooperative breeders (list 2)?

Cooperative breeding is a system in which individuals other than the parents (helpers, often older offspring or other group members) help raise young by carrying them and sharing food. Examples: marmosets and tamarins (humans are also often counted).

Is rank associated with enhanced reproductive success in males?

Generally yes: high-ranking males get more matings and sire more offspring, as paternity studies of baboons, macaques and chimps show. The link is imperfect, though: an alpha can't monopolize all females when several cycle at once, and low-ranking males use coalitions, sneaky matings or female choice.

What is infanticide, and why might it evolve as a sexually selected strategy?

Infanticide is the killing of infants by members of their own species, typically by males who have just taken over a group (e.g., Hanuman langurs, gorillas). Killing an unweaned infant ends the mother's lactation, so she cycles again sooner and the new male can sire his own offspring during his often short tenure. Males target infants they did not father.

What female counter-strategies can deter infanticide?

Mating with multiple males to confuse paternity (aided by concealed or ambiguous ovulation and sexual swellings), forming friendships with protective males (baboons), forming female coalitions against males, transferring to a strong protective male (gorillas), pseudo-estrus (langurs), and aborting after a takeover (the Bruce effect, as in geladas).

Define altruism

Altruism is a behavior that is costly to the actor (lowers its fitness) and benefits the recipient (raises its fitness).

What is the difference between altruism and mutualism?

In altruism the actor pays a cost so another can benefit. In mutualism both the actor and the partner benefit immediately, so it needs no special evolutionary explanation.

Provide an example of mutualism in non-human primates.

Group mobbing of a predator, or chimpanzee males patrolling and defending their shared territory, where every participant benefits. Cooperative hunting of colobus monkeys by chimps is another example.

Do we expect a gene for altruism to evolve in a random assortment of individuals? Why or why not?

No. With random interaction, altruists help non-altruists as often as other altruists, so non-altruists get the benefits without paying the costs and out-reproduce altruists. Altruism can spread only if altruists interact preferentially with other altruists, such as kin.

What is kin selection?

Kin selection is natural selection for behaviors that help genetic relatives, who share genes identical by descent. It favors altruism when rB > C (Hamilton's rule): relatedness times the benefit to the recipient exceeds the cost to the actor.

How do non-human primates recognize their kin?

Mainly through familiarity and close association, especially with their mother and the relatives she spends time with (maternal kin). Some may use phenotypic matching (appearance, smell) or age-similarity cues, which can let them recognize paternal half-siblings.

In polygynous species, do juveniles interact more with maternal or paternal kin? Why?

Maternal kin. Maternal relatives are easy to identify through constant association with the mother, while paternity is uncertain and fathers often provide little care.

What are three types of cooperative behaviors observed in primates?

Grooming, coalitions (alliances), and cooperative breeding/infant care. Food sharing and alarm calling are also cooperative.

What are the costs and benefits of grooming another?

Costs: time and energy taken from foraging, and reduced vigilance against predators. Benefits: the recipient gets parasites removed, hygiene and stress relief. The groomer builds social bonds, gets reciprocated grooming, coalition support, tolerance and access to infants or mates, and helps relatives (kin selection).

What are the costs and benefits of participating in coalitions?

Costs: risk of injury, energy spent, and retaliation from the targets. Benefits: gaining or keeping rank, access to mates and food (e.g., male baboon coalitions taking over consortships), defending kin, and support returned by allies later.

How do males and females establish rank in baboon and macaque troops?

Females inherit rank through their matriline: mothers and relatives back daughters in disputes, so daughters rank just below their mothers (in macaques, the youngest sister often ranks just below the mother). Males establish rank by fighting and competition after moving into a new group, so their rank depends on size, age, strength and sometimes coalitions, and changes over their lives.

Which three primates practice cooperative breeding? Why are marmosets so cooperative?

Marmosets, tamarins and humans. Marmosets often have twins, so a mother can raise more young, and reproduce again sooner, when helpers carry and feed them. Helpers are favored by kin selection, and marmosets are genetic “chimeras,” which raises relatedness between fraternal twins and strengthens kin selection.

What is inclusive fitness?

An individual's total genetic contribution to future generations: its own reproductive success (direct fitness) plus its effect on relatives' reproductive success, weighted by how closely related they are (indirect fitness).

Define reciprocal altruism. Is it really altruism?

Reciprocal altruism means helping another individual at a cost now, with the help returned later ("you scratch my back, I'll scratch yours"). It is not truly altruism in the long run, because both partners come out ahead over repeated exchanges; it is really delayed mutual benefit.

What are two criteria needed for reciprocal altruism to occur?

(1) Individuals must interact repeatedly over long periods (stable groups). (2) They must recognize each other and remember past interactions, so they can stop helping cheaters who don't reciprocate. The benefit to the recipient should also exceed the cost to the helper.

Provide 4 lines of evidence suggesting that primates are intelligent.

(1) Large brains, especially the neocortex, relative to body size. (2) Making and using tools (chimp termite fishing and nut cracking, capuchin stone tools). (3) Complex social knowledge, such as knowing third-party kinship and rank relationships (baboon playback experiments) and tactical deception. (4) Problem solving, learning and cultural traditions, mirror self-recognition in great apes, and referential alarm calls (vervets).

According to life history theory, what are the two main tradeoffs in reproduction?

(1) Current versus future reproduction. (2) Quantity versus quality of offspring.

According to life history theory, what are the three main energy allocation trade-offs?

Energy is limited, so it must be divided among growth, maintenance (survival and repair) and reproduction. The trade-offs are growth vs. reproduction, maintenance vs. reproduction, and growth vs. maintenance.

Why hasn’t natural selection designed organisms to live and reproduce forever?

Energy is limited and extrinsic mortality (predators, disease, accidents) eventually kills everyone anyway. It pays more to put energy into reproducing early than into perfect body repair (the disposable soma idea). Selection weakens at older ages, so genes that help early in life but harm later are favored (antagonistic pleiotropy), and harmful late-acting mutations build up.

How does testosterone affect senescence?

Testosterone boosts male mating effort (muscle, aggression, competition, risk taking) but diverts energy from body maintenance and suppresses immune function. This speeds senescence and shortens male lifespans; castrated males tend to live longer.

Know the general characteristics of a fast life history versus a slow life history, and provide 2 examples for each.

Fast: small body, early maturity, short gestation, many offspring per litter, short interbirth intervals, little investment per offspring, short life and high mortality; examples are mice and mouse lemurs. Slow: large body, late maturity, long gestation, single offspring, long interbirth intervals, heavy parental investment and long life; examples are elephants and orangutans (great apes and humans).

What extrinsic factor drives the evolution of life history strategies?

The extrinsic (unavoidable) mortality rate from predation, disease and accidents. High mortality favors fast life histories; low mortality favors slow ones.

How do strepsirrhine, monkey, and ape life history strategies compare?

Strepsirrhines are the fastest: smaller bodies, shorter gestation, earlier maturity, sometimes twins or litters, and shorter lives. Monkeys are intermediate. Apes are the slowest: longest gestation, juvenile periods and interbirth intervals (about 6–8 years in orangutans), and the longest lives.

Primates have large brains. What are three hypotheses to explain this energetically life history trait? Be able to describe each one.

(1) Ecological/foraging (mental maps): frugivores must remember where and when patchy, short-lived fruit is available across large ranges. (2) Extractive foraging (technical): getting at hidden or protected foods (nuts, insects in wood, termites) requires skill, planning and tools. (3) Social intelligence: life in large, complex groups demands tracking relationships, alliances, competition and deception. Some lectures instead use a cultural intelligence hypothesis (big brains for social learning) as the third.

What evidence supports the social intelligence hypothesis? What evidence does not support the social intelligence hypothesis?

Support: across primates, neocortex ratio correlates with group size, and also with grooming clique size, coalition use, tactical deception and social play; primates also track third-party relationships. Against: orangutans are semi-solitary yet very intelligent and large-brained; newer comparative studies find diet (frugivory) predicts brain size better than group size; and the correlation doesn't prove causation.

What evidence supports the ecological challenge hypothesis?

Frugivores have larger brains for their body size than folivores (spider monkeys vs. similar-sized howler monkeys). Brain size correlates with home range size and with diet. Extractive foragers such as capuchins, chimps and aye-ayes have large brains and complex foraging and tool use.

What is the neocortex ratio? Why is this a better measure of brain size than absolute size?

The neocortex ratio is the volume of the neocortex divided by the volume of the rest of the brain. Absolute brain size mostly scales with body size (bigger bodies need bigger brains to run them), while the ratio removes that effect and focuses on the neocortex, the region behind complex thinking and social cognition.

Why does a tarsier have to consume energy dense foods frequently, while a large gorilla can survive on a diet of plant material?

Metabolic rate scales at about mass^0.75 (Kleiber's law), so the tiny tarsier burns much more energy per kg and has a small gut that can't hold or ferment bulky leaves; it must eat high-energy prey like insects often. The gorilla needs more total energy but far less per kg, and its large gut can slowly ferment abundant, low-quality, fibrous plants, so it can live on leaves.