Reproduction week 6

Question 1

Intended learning outcomes

Answer 1

• Describe the diversity of reproductive strategies found in pinnipeds
• Describe the diversity of reproductive strategies and social systems found in cetaceans
• Discuss the effects of breeding habitat, resource availability and predators on reproductive strategy

Question 2

Why is it important?

Answer 2

• Reproduction is (obviously) essential to any species
• The key to successful reproduction:
  – Good body condition and fitness of females (and males)
  – Availability of food or energy stores (blubber)
  – Habitat to protect the females and their offspring
• A species reproductive strategy affects its ability to cope with human activities and climate change!!

Question 3

Standard reproductive cycle

Answer 3

1. Parturition (birth)
2. Lactation (days-years)
3. Weaning
4. Resting (days-years)
5. Mating (ovulation and mating)
6. Gestation (9-11 months)

Question 4

Male reproductive costs

Answer 4

Sperm production and mating
– Mating is costly
* Male-male competition (body size, sexual characters)
* Attracting females (body size, sexual characters)
– Sperm is cheap!
* Sperm competition (testis size)
* Few males successful – many are unsuccessful

Question 5

Male-male competition

Answer 5

• Sexual size dimorphism
  – Large males: sperm whales, beaked whales, larger dolphins, otarids, elephant seals, grey seals, hooded seals
  – Large females: porpoises, small dolphins
• Fighting and body scars
  – Beaked whales, Risso’s dolphin, humpbacks
• Ornaments
  – Narwhal tusks, male beaked whale teeth, killer whale fin, hooded seal nasal sack (red balloon), ribbon seal males
• Vocalisation/song
  – Fin whales, perhaps bowhead whales, many phocids (ringed, harbour, bearded and leopard seals)

Question 6

Male sperm competition

Answer 6

• Large testis size indicates sperm competition
• Mysticetes
  – Not larger than expected relative to body size, except for right and bowhead whales
• Odontocetes
  – Larger testis than expected relative to body size
  – Harbour porpoise (4% of body weight)
  – Dusky dolphin (8-9% of body weight)
  – Human testis (0.08% of body weight)

Question 7

Female reproductive costs

Answer 7

• Producing offspring and lactating is costly!
  – Egg production, mating, pregnancy, lactation and nursing
  – Birth mass, pup growth, lactation interval, milk composition
• Trade-offs
  – Pup/calf wants as much energy as possible
  – Mother wants to increase fitness of pup/calf, but also conserve energy for herself and future pups/calves
• Different lactation and nursing strategies
  – Fasting: mothers fasten during lactation
  – Foraging cycles: mothers forage during lactation
  – Nursing: mother and offspring stay together
• Many females are successful–few are unsuccessful

Question 8

Female lactation strategies

Answer 8

Fasting, foraging and nursing

Question 9

Fasting lactation strategy

Answer 9

Lactation duration: short (weeks)
Fasting duration: all of lactation
Milk fat content: high (60%)
Pup/calf growth: rapid
pup/calf foraging: no
Rules of thumb> Phocids and mysticetes

Question 10

Foraging lactation style

Answer 10

Lactation duration: intermediate (months
Fasting duration: variable (days)
Milk fat content: intermediate
Pup/calf growth: intermediate
pup/calf foraging: no
Rules of thumb> Phocids and Otariids

Question 11

Nursing lactation strategy

Answer 11

Lactation duration: long (years)
Fasting duration: short (hours-days)
Milk fat content: low (20%)
Pup/calf growth: slow
pup/calf foraging: yes
Rules of thumb: Odontocetes, walrus, Sirenia and polar bears

Question 12

Pinniped reproductive cycle

Answer 12

• Synchronous breeding (with exceptions)
• 1 year cycle (with exceptions)
• Stable habitat: Otariids
  – Long lactation
  – Slow pup growth
  – Forages while lactating
  – Large relative investment
• Unstable habitat: Phocids
  – Short lactation
  – Rapid pup growth
  – Fasts while lactating (with exceptions)
  – Low relative investment
• Oestrus and mating shortly after weaning
  – Phocids: mating at end of lactation or at weaning
  – Otarids: mating 1-2 weeks after birth
  – Walruses: mating 10 months after birth
• Delayed implantation of fertilized egg
  – Timing to fit the annual cycle
  – Time for resting, recovery and/or molting

Question 13

Pinniped breeding habitats

Answer 13

• Female behaviour affected by
  – Environment for protecting offspring from weather, climate and predators
  – Availability of food resources
• Male behaviour affected by
  – Distribution of females
  – Aggregated females => polygyny
  – Dispersed females => monogamy/mild polygyny
• Habitat and breeding system is closely linked!!

Question 14

Pinniped land breeders

Answer 14

• Otariids and some phocids (elephant seals+grey seals)
• Stable habitat; often limited space
• Females aggregated; males control access
• Long nursing period
• Polygyny, sexual size dimorphism

Question 15

Pack ice breeders (Pinnipeds)

Answer 15

• Many Arctic phocids (Hooded and bearded seal)
• Predators; unstable habitat; unlimited space
• Females dispersed; males cannot control access
• Short nursing period
• Mating in water (except hooded seal)
• Serial monogamy, or mild polygyny

Question 16

Fast ice breeders

Answer 16

• Mainly Antarctic phocids, and the Arctic harp seal
• Stable habitat
• Some female aggregation and male control
• Relatively short nursing period
• Mating often in water
• Mild polygyny

Question 17

Phocid lactation strategies

Answer 17

Mothers often forage a bit during lactation period

Lactation duration and milk production is related to habitat

Question 18

Example 1 of phocid lactation: hooded seal

Answer 18

• Unstable environment (pack-ice)
• Very short (3-4 days) lactation period
• Stored lipids converted to milk; fat content is 60%
• Pups drink 10 liters per day; increase from 25 to 50 kg
• No lanugo fur in pup; it rapidly builds an insulating blubber layer After weaning and mating, females go to sea to forage

Question 19

Example 2 of phoned lactation: Harp seal

Answer 19

• Breeds in somewhat stable environment (fast ice) in large groups
• Intermediate lactation (12 days)
• 10L milk/day; pup gains 2-3 kg/day
• Female fasten during lactation period
• Lanugo fur; insulation and camouflage
• Feeding migrations after breeding

Question 20

Example 3 of phoned lactation: Northern elephant seal

Answer 20

• Breeds in stable environment (land/beaches)
• Long (4 week) lactation period
• 60% of the mothers energy expenditure is for lactation
• Pups gain approx 4 kg per day; from 40 to 160 kg
• No lanugo fur; pup is born on land during summer
• After weaning, females (mothers) go to sea to forage for months
• Pups remain on site for 8-10 weeks after weaning

Question 21

Otarid lactation strategies

Answer 21

mother alternates between fasting while nursing during attendance periods and foraging at sea.

They wean the pups after a long lactation period.

Question 22

Example 4 of otarid strategies: Anarctic fur seal

Answer 22

• Stable environment; long lactation (4 months); low milk fat (40%)
• Mother only fast a week, then start foraging
• Females spend 4-9 days foraging + 2 days lactating
• Pup mass increase from 5 kg to 10-15 kg; weaning mass depends on how successful mother is at foraging
• After weaning, pups go to sea to forage

Question 23

Example 5 of Otarid strategy: Australian sea lion

Answer 23

• Exception to the rule; asynchronous breeding!
• Breeds every 17-18 months; 5-9 month breeding season
• The different populations’ breeding periods are out of sync with each other…
• Limits recovery from sealing!

Question 24

Walrus lactation strategies

Answer 24

• Mother and pup go to sea a few days after birth
• Pup learns to forage by mother
• 2 year lactation: 5 months milk, then milk and food
• Can lactate/suckle while at sea!
• Fat content is 15-30%

Question 25

Pinniped mating strategies

Answer 25

Territory/resource defence polygyny

Female defence polygyny

Maritory/resource defence polygyny

Mate guarding (triads)

Lek

Scramble competition (stalking)

Question 26

Territory/resource defence polygyny

Answer 26

• Males defend a geographical resource/territory
• Few male aggressions after establishment of hierarchy
• Male reproductive fitness determined by
  – Size and quality of territory/resource
  – Body size
  – Fasting ability
  – Fighting/defence ability

Question 27

Female defence polygyny

Answer 27

• Elephant seals
• Males defend group of females (harem); not a territory
• Males establish hierarchies among each other
• Less than 10% of males mate during their lifetime
• Male reproductive fitness determined by
  – Size of harem
  – Body size
  – Fasting ability
  – Fighting/defence ability
• Sneakymales/females?

Question 28

Maritory/resource defence polygyny

Answer 28

• Males defend access to water/air (maritory)
• Male reproductive fitness determined by
  – Size and quality of territory
  – Body size, visual displays, vocal displays
  – Fighting in ringed seals!

Question 29

Mate guarding (triads)

Answer 29

• Males defend one female (at a time)
• Mating once the pup is weaned
• Serial monogamy, or limited female defence polygyny
• Hooded seals, grey seals and crab eater seals

Question 30

Lek

Answer 30

• Males aggregate and display (without contact) to attract females
• Females visit site and selects male
• Walrus, leopard seal and harbour seals

Question 31

Scramble competition (stalking)

Answer 31

• Widely distributed females => limited resource!
• Multiple males stalk a single female, and compete with each other for mating opportunities
• Preventing recovery in Hawaiian monk seal??

Question 32

Pinniped sociobiology

Answer 32

• Pinnipeds often aggregate in groups on land/ice
  – Limited space
  – Protection of pups/young
  – Predator avoidance
  – Thermoregulation
  – Social interactions?
• Site fidelity (philopatry)
  – Females (and some males) return to same breeding site
  – Sheltered, stable environment, food, no predators, protection of young, etc => same sites used for millennia!
  – …and they were likely born there themselves
• Social structure/groups?
  – Not well-studied in pinnipeds, so many unknowns!!
  – Dominance hierarchies, pup “kindergardens” and indications of social networks in otarids, and perhaps harbour seals?
  – Mother-pup bonds and “learning” in walrus, and perhaps some phocis (harbour seals) and otarids?
  – Some species migrate in groups, but often solitary feeding, and no evidence of actual cooperation
• Otarid kindergarden; females take turn in watching pups when other females forage

Question 33

Female life-history and reproduction of cetaceans

Answer 33

• Large interspecific variation in female life-history events
• Correlation between female body size and age at sexual maturity

Question 34

Mysticete mating strategies: reproductive cycle

Answer 34

1.Parturition (calving)
2.Lactation
3.Weaning
4.Resting
5.Mating (and ovulation)
6.Gestation

Question 35

Mysticetes breeding

Answer 35

• Breeding generally occur individually, or in small groups
• Female produce a single calf; typically 1-3 years between births; big investment for females!
• Relatively short lactation period (months)
• Rapid growth of calf
• Mating system differences
  – Large testis; sperm competition (right whales) – Small testis; male-male competition (rorquals)
• Seasonal migrations between low latitude breeding grounds and high-latitude foraging grounds in several species…

Question 36

Seasonal migrations: mysticetes

Answer 36

• Most mysticetes (except Bryde’s whale)
• High latitude feeding; low latitude breeding
• Long migrations; long fasting period
• Advantage of breeding in warm waters
  – Thermoregulation easier; calf needs time to build blubber
  – Reduce risk of orca predation on calves

Seasonal migration between high-latitude (polar) foraging and low-latitude (tropic) breeding grounds

Frequency of seasonal migration depends on female body condition (and hence food availability)

Question 37

Frequency of seasonal migration depends on female body condition (and hence food availability) (Mysticetes)

Answer 37

• Good condition; 1-2 year cycle
  – Winter; low-latitude; give birth (and mate)
  – Summer; high-latitude; feeding
  – Fall; weaning of calf during migration
  – Winter; low-latitude; (give birth and) mate
• Poor condition; 3-? year cycle – Winter; low-latitude; give birth
  – Summer; high-latitude; feeding
  – Fall; weaning of calf
  – Winter; migrate or skip migration to stay at high-latitude feeding
  – Summer; high-latitude; feeding
  – Winter; low-latitude; mate

Question 38

Example: Humpback whales

Answer 38

• Breeding
  – Females give birth at low latitude breeding sites
• Mating
  – Females (with/without calf) become receptive
  – Male principal escort (PE)
  
  • Close to female, while chasing others away
  • Timing and level of aggression is key!
    – Male secondary escorts and challengers
  • Fight with PE and each other to establish hierarchy

Question 39

Odontocete mating strategies

Answer 39

• Large variation in life histories, social systems and mating
• Porpoises, river dolphins (“R species”)
  – Early sexual maturity; short nursing, birth interval and lifespan
  – Small pod size; large testis
  – Sperm competition
• Dolphins, sperm whales and beaked whales (“K species”)
  – Late sexual maturity; long nursing, birth interval and lifespan
  – Often social; small testis; some secondary sexual characters
  – Male-male competition
  – Strong social structure centred around females

Question 40

Example: orca social structure and mating

Answer 40

• North Pacific ecotypes
  – Transients: mobile; feed on marine mammals
  – Residents: stationary; feed on fish – Offshores: sharks, fish?
• Orca social structure and mating
  – Highly structured matrilineal social groups consisting of grandmothers, mothers and their offspring
  – Males stays with own group (mom), but mate in other groups

Question 41

(sociobiology) Group size and social structure of cetaceans determined by:

Answer 41

– Food availability vs. intraspecific competition
– Mating strategy
– Predator avoidance
– Inshore vs offshore habitat

Question 42

(sociobiology) What is the social structure and relationships of cetaceans, and how do we determine it?

Answer 42

• Large variation in social structure and networks
  – Non-modular (no structure); mysticetes and porpoises (??)
  – Fission-fusion; most dolphins, and perhaps beaked whales
  – Matrilineal; pilot whales, killer whales, monodontids
  – Clans; sperm whales
• Large variation in social structure!

Question 43

(sociobiology) Foraging cooperation in some cetaceans

Answer 43

– Humpback whales
– Killer whales, and many other dolphin species – Group size depends on amount/size of prey

Question 44

(sociobiology) Mysticetes social structure

Answer 44

– Unstructured (non-modular) social system
– Whales often solitary, except mother-calf pairs and when aggregating on feeding and breeding sites

Question 45

(sociobiology) Odontocete social structure

Answer 45

Large variation; correlate loosely with body size)

– Solitary, except mother-calf pairs (porpoises)
– Fission-fusion with loose bonds, and some long-term relationships (most dolphins, and perhaps beaked whales)
– Matrilineal societies with long-term bonds on multiple levels among relatives (pilot whales, killer whales, monodontids)
– Clans are smaller matrilineal societies (sperm whales)

Question 46

Female post-reproductive life-span

Answer 46

• Rarely seen in mammals (except humans)
  *Fitness benefit by grandmothers helping offspring and relatives finding food, predator protection and “teaching” calfs how to be whale…
• In humans, post-reproductive life-spans are a strong driver of evolution of culture…
• Beluga, narwhal, short- finned pilot whale (and orca) groups consist of high proportion of post- reproductive females
• Evolved multiple times!
• What about other social
  cetacean species…?