Marine Mammal Reproductive Structures, Strategies, & Patterns

MARE 390 Dr. Turner

Testes, One, Two

Phocid – testes inguinalOtariids – testes scrotalWalrus – inguinal; scrotal during matingPinnipeds – bacculum (penis bone)

Cetaceans & Sirenians – fibroelastic penis

“We're talking about S-E-X in front of the C-H-I-L-D-R-E-N." – Maude Flanders

"What?!?! Sex cauldron? I thought they closed that place down“ – Krusty the Clown

Sex Your Seal Ma’am?Teats & position of genital opening

I’m Too Sexy for my DolphinDistance between Anal & Genital slit♀ both within common groove♂ separation between; testes internal cavity

Is that a manatee in your pocket..?Distance between Anal & Genital slit♀ short distance♂ separation between; testes internal cavity

Reproduction↑ Fitness of female = ↑ Fitness offspring

Females: cost of egg, pregnancy, lactation, postnatal care

Males: invest energy in competition with other males (physical & sperm)

ReproductionPinniped, Ursid, mustellid mating typically on land; some phocids shallow water

ReproductionCetaceans – belly-to-belly

ReproductionSirenians – belly-to-belly

GestationPlacental mammals – 18 days to 22-24 months

Marine mammals: sea otter (6-7mo) to Sperm whale (16.5mo)

↑ Gestation time = ↑ Fetus size

Gestation Mass (kg) Gest.(mo) Int.(Y)

Harbor seal 11 9-12 1N. Elephant 40 11 1N. fur seal 6 12 1Walrus 50 14-16 2-4Porpoises 8 8-11 n/aBottlenose 20 12 n/aSperm Whale 1050 14-16 3Blue Whale 2500 11-12 2-3

GestationMass (kg) Gest.(mo) Int.(Y)

Manatee 30 12-13 2-5Dugong n/a 14 3-7Sea Otter 2 6-7 1Polar Bear 0.7 8 2-4

Delayed ImplantationDelayed implantation – development of the blastocyst is slow or negligible

Is obligate in pinnipeds, ursids, and mustelids

Period of delayed implantation allows flexibility of timing of parturition, and is controlled by photoperiod

Delayed ImplantationDev.Gest(mo) Delay Impl.(mo)

Harbor seal 8-9.5 1.5-3N. Elephant 7 4N. fur seal 8 4Walrus 10-11 4-5Sea Otter 4 2-3Polar Bear 4 4

Pinniped Reproduction

Pinniped Reproductive Cycle

Cetacean Reproductive Cycle

Change in latitude in grey whales

Migration

Mating SystemsHigh degree of variability in reproductive systems

2 major groups: polygyny & promiscuity

Polygyny – successful male mating with several females

Promiscuity – males associate with several females during a variable amount of time

Evolution of Polygyny

Mating SystemsDriven by sexual selection – competition

1. Contest comp. – Direct comp. over ♀2. Endurance comp. – ♂ Endure longer3. Scramble comp. – Search/locate ♀4. Mate choice comp. – Entice/attract ♀5. Sperm comp. - ↑ Quality/Quantity of sperm

Pinniped Mating SystemsMale otariids typically utilize Resource Defense PolygynyCharacteristics:1. Males arrive before females2. Females receptive close to place of birth3. Rookery substrate stable but discontinous4. Few aggressive interactions once dominance is established

Otariid Mating Systems

Most males defend Territories – not females

Pinniped Mating SystemsMale phocids typically utilize Female (Harem) Defense PolygynyCharacteristics:

Most dominant male (Alpha) defends females from other subordinate males

Phocid Mating Systems

Most males defendFemales – not Territories

Phocid Mating SystemsElephant Seals – High level polygyny – alpha controls large harems

Phocid Mating SystemsMonk Seals – Low level polygyny – alpha controls individual females

Odobenid Mating SystemsWalrus – either display a Female-Defense Polygyny (like Phocids) or a Lek-like behavior (similar to Otarriids)

Odobenid Mating SystemsLek - gathering of males, of certain animal species, for the purposes of competitive mating display

Cetacean Mating Systems

Mysticetes – little social behavior beyond mother-calf pair

Many utilize sperm competition – attempt to dilute out other males sperm

Odontocetes – exist in groups of variable size for persist longer than any member’s life span

Odontocete Social Groups

Arranged as schools, pods, or units

Size varies by species & geographic location

Mating structure a mixture of promiscuous & polygynous

Male-male competition – sexual dimorphism

Spinner Social Groups

Aggregate in schools of up to 100 individualssubgroups – up to 12

Subgroups travel in echelon formation

Orca Social Groups

Sperm Whale Social Groups

Similar to orca groups

Males leave pods and form juvenile groups

Solitary adult males rove among female groups

Sirenian Mating Systems

Similar to mysticetes- little social structure past mother-calf pairs

Animals congregate into herds during summer months to breed

Dugongs found in larger associations than manatees

Lactation Strategies

Most energetically expensive aspect of reproduction

Best interest to pass as much energy as possibly even at expense of future offspring

3 strategies: Fasting, Foraging Cycle, Aquatic Nursing

Fasting Lactation StrategyExample: Northern elephant seal

Duration of fasting: All of lactation

Duration of lactation: Short (4-weeks)

Fat content of milk: High (55%)

Pups forage during lactation: No

Foraging Cycle Lactation Strategy

Example: Antarctic fur seal

Duration of fasting: Variable (few days)

Duration of lactation: Intermediate (4-months)

Fat content of milk: Intermediate (40%)

Pups forage during lactation: No

Aquatic Nursing Lactation Strategy

Example: Walrus

Duration of fasting: Short (hours-days)

Duration of lactation: Long (2-3 years)

Fat content of milk: Low (2-3%)

Pups forage during lactation: Yes

LactationLength(w) Fat% Prot.%

Harbor seal 3.4 50 9N. Elephant 4 54 5-12N. fur seal 18 42 14Walrus 100 14-32 5-11Porpoise 32 46 11Bottlenose 76 14 12-18Sperm Whale 100 15-35 8-10Blue Whale 24-28 35-50 11-14

Length(w) Fat% Prot.%Manatee 52 n/a n/aDugong 78 n/a n/aSea Otter 20-30 21-26 9-12Polar Bear 130 17-36 9-13

Lactation

Got Milk!