Pinniped Reproduction Life History PDF

Pinniped reproduction Life histories and reproductive strategies reed.edu MARI 3090 – Marine Mammalogy Dalhousie University Dr. Amanda Babin Fall 2023 Life History • How natural selection has shaped all events that happen from birth to death • Explains the allocation of resources for survival, g...

Pinniped reproduction Life histories and reproductive strategies reed.edu MARI 3090 – Marine Mammalogy Dalhousie University Dr. Amanda Babin Fall 2023 Life History • How natural selection has shaped all events that happen from birth to death • Explains the allocation of resources for survival, growth, and reproduction to maximize fitness • Parameters include body size, age, sexual maturity, pregnancy rates, breeding season, calving interval, longevity • Best studied using longitudinal studies – following known individuals through their lifetime • Cross-sectional studies make up most of our knowledge – often from dead animals (whaling, strandings) • Studying multiple groups lets you see the influence of natural selection General Life History Characteristics • Three main features: • High annual survival • Average age of sexual maturity ranges from 3-7 years • Each female gives birth to 1 pup per cycle • Phocids and otariids have interbirth intervals of 1 year, odobenids every 2 years • Lifespan of 20-40 years • • • • Precocial Must meet thermal demands for a semi-aquatic lifestyle Must be vigilant of predators Forage independently days to weeks after birth frierworks.com • Offspring are: Life History Studies • Colonial (rookeries), synchronized, annual breeders • Except the Australian sea lion which breeds year round (14 month gestation) • Longitudinal studies • Long-term mark-recapture • Species/populations that we have relatively easy access to, hard to do • Weddell Seals, Northern Elephant Seals, Grey seals (Sable Island) • Cross-sectional studies • One-off or sequential culls (mostly commercial harvest) • Limited information, easy to misinterpret • Information gathered is mostly on females, especially when attending to offspring on land • Variation between populations of the same species can sometimes be as large as the variation between species Life History Strategies • Capital Breeder • No food intake, uses endogenous reserves (blubber) to produce milk during lactation period Weight of At birth (lbs) After weaning* • Ex. Elephant seals mother 500 290 *4 months post-partum pup 40 140 • Income Breeder • Offset some of the costs by foraging • Ex. Antarctic Fur seals maintain steady weight with several foraging trips, trade-off is a longer lactation period (40 days) • Not mutually exclusive, part of a continuum of adaptive strategies Cost vs. Benefit of Breeding • Individuals have the option of reproducing annually, but do not always breed every year (~0-10 pups/female lifetime) • In years that they do breed, they adjust how much energy is invested to maximize fitness: grida.no • Benefit: propagate genetic material • Cost: risk to survival of parent if they exhaust their energy reserves! • ex. Antarctic Fur seals have a 40% greater chance of dying the year after breeding Polygyny • Attributes: Large body size Sexual dimorphism – males 3-6x larger than females (most extreme among mammals) Internal fertilization/gestation and lactation Strong canines (weapons) Seasonal fasting Gregarious breeding Few males breed (marginal males) • Breeding grounds: • Resource defence – most species, males arrive first • Female defence – arrive 1-2 days before giving birth • Mate choice (lek system) animal.memozee.com • • • • • • • Female clustering (harem) • Possible causes: Selfish herd hypothesis (safety in numbers) Male aggression Marginal males Thermoregulation celebrating200years.noaa.gov • • • • Female Reproductive System • Similar to terrestrial carnivores • Entrance to vagina and urinary meatus are withdrawn into the body • Bicornate (two-horned) uterus • Phocids have two nipples (except bearded and monk seals have four), otariids and odobenids have four nipples • Sexual maturity at 3 years (/20s) • Sexually receptive 5-10 days after giving birth • Similar to terrestrial carnivores, including a baculum • Phocid and odobenid testes retained within body contour embedded in groin • Otariid testes in conventional scrotum to keep sperm at optimal temperature • Sexual maturity at 5-7 years (/10s), but don’t breed until they reach social maturity of size and dominance (hold territory) • Ex. Steller sea lion 9+ years • No paternal care polarbearscience.com Male Reproductive System Gestation and Birth (whelping) • Embryonic diapause – zygote is dormant • Synchronized birth pulse – births occur within a 2-3 week period • 5 months (Crabeater seal) to 15 months (Walrus) • Phocid neonates are larger than otariids • Lanugo (long white fur) • Thermoregulation (greenhouse effect) • Camouflage on ice • Shed in uterus in short lactation species Lactation in Phocids • Milk with fat builds-up blubber • Lactation period depends on stability of habitat and vulnerability to predation • Weaning is sudden for phocids, gradual for otariids • Weaned at 25-30% of mother’s mass • Ice-breeding phocids • 8 species on pack ice (4-30 days), 4 species on land-fast ice (up to 57 days) • Shortest of any mammal = Hooded seals, 3-5 days (22 to 42 kg bluecoat, 60+% fat) • Ringed seals use a birth lair for protection, longer period of 42 days Lactation in Phocids • Land-breeding phocids • 5 species (average 32 days) • Grey seal takes 16-21 days, 17,000 kcal per day • Elephant seal takes 23-28 days, and pups lose 30% of body mass from fasting after weaning • Harbour seals take 4-6 weeks, extended care may have survival value Wikimedia Commons • Grey seals give birth Dec-Feb • Harbour seals May-July • Same prey, but offset whelping seasons to avoid competition Richard Croft Lactation in Otariids • Land-breeding otariids • Several months to one year • 2-3 years for Galapagos Fur seals • Foraging trips cheesemans.com • Fur seals take longer trips than sea lions – 250 km from colony, 5-9 days at sea • Sea lions – 30-100 km from colony, 1-3 days at sea Mother-pup relationship • • • • Species Maternal investment level Climate effects (ex. El Niño) Disease bloomberg.com • Colonial species often have complex individual vocal signatures • Mom recognizes vocal signature of the pup within 2 days • Pup recognizes vocal signature of its mom within 2 months, and for 2 years after weaning • Olfactory signatures are also important • Pup survival depends on: • Polygynous • Can breed year-round • Sexual maturity • Manatee 2-5 years • Dugong 6-17 years (disputed) • Gestate for 1 year • Wean at 1-2 years • Nipples in armpits • Dugong tusks used for lekking (competition, female choice) Burgess et al. 2013 Sirenian reproduction Sea otter and Polar bear reproduction • Territory defence and mate choice • Breed and give birth in water • Nurse for one year • Not territorial, males pursue females Suzi Eszterhas • Sexual maturity 3 y females, 6 y males • Give birth on ice to 2 cubs • Weaned at 2.5 years • Both are polygynous, use embryonic diapause, and have altrical young Getty Images • Sexual maturity 4 y females, 6 y males Take Home Messages • Life history explains the allocation of resources for survival, growth, and reproduction to maximize fitness • Pinniped breeding is colonial • Strategies of capital vs. income breeding/feeding, breeding that year vs. survival risk • Duration of lactation dependent on stability of habitat and vulnerability to predation • Ice vs. land • Pinnipeds, sea otters, and polar bears (Carnivora) use embryonic diapause • Pinniped and sirenian young are precocial, sea otter and polar bear young are altrical elephantseal.org Thank you!