*Know which groups fall into each strategy and the trade-offs with each strategy

• Maternal care strategies (3 categories)

  • 1) Fasting (phocids and mysticetes)

    • Can provide constant care to offspring, but there is a limit to how long she can do this

    • Not really a risky strategy but body condition for mom dwindles.

  • 2) Foraging cycle (otariids and some phocids)

    • Fasts when nursing, but then goes back to forage leaving offspring alone, and returns. 

  • 3) Aquatic nursing (Odontocetes, sirenians and odobenids)

    • Mom and calf can eat when hungry

• See handout

  • Table 1 

    • Fasting: Short-term, high investment strategy (in terms of milk fat content)

      • Pup must learn how to hunt on its own

        • Breeding grounds and foraging grounds are distant. Weaning is very abrupt, and no knowledge of foraging is transferred from mother to pup.

    • Foraging Cycle: Intermediate, intermediate investment strategy (in terms of milk fat content)

      • In gaps when mom is out foraging, offspring spend time learning for themselves how to forage.

    • Aquatic nursing: Long-term, low investment strategy (in terms of milk fat content)

      • If milk content was high, it would deplete mother’s reserves very quickly. Since she’s nursing over a long period of time, she can afford to have a lower fat content and just feed her offspring longer.

      • Calf learns by watching mom (particularly during foraging). Will supplement diet with smaller prey items. (Gradual transition from milk to solid  foods)

    • Milk fat content in marine mammals is very high in comparison to terrestrial mammals.

  • Table 2

    • When you compare maternal investment strategies, you want to compare within taxonomic group since the variation between taxa is large (example, phocids vs mysticetes)

    • Longer lactation → Lower fat content

• Foraging constraints on aquatic nursers

  • Problems for odontocetes

    • Foraging requires fast accelerations and deep dives

      • Not a problem for manatees because they can just graze while their calves nurse

  • Solutions

    • Temporary separations

      • Calf is left vulnerable

    • Shift in maternal prey preferences

      • Example: Pan-tropical spotted dolphins feed on flying fish when they have a nursing calf, and otherwise catch deep diving squid.

    • Matrilineal groups with communal care

      • With female relatives who take turns to provide care for the offspring while mothers are foraging

        • Well studied in sperm whales (adult females stay at surface with calves while other females forage at depth)

      • Allomaternal care: Someone other than the mother provides care for the offspring. Benefits the offspring and the mother. 

        • Limited to species that have social relationships among individuals

        • Who provides care? (Typically females)

          • Juvenile females 

            • Learning to parent hypothesis

              • Low risk way to develop care-giving skills

              • Overall, better to leave calf with somebody than by themselves

            • Young females have an affinity to babies

          • Adult females (often moms themselves, more experience than juveniles)

            • Inclusive fitness hypothesis

              • Direct fitness: Personal reproduction (offspring you produce)

              • Indirect fitness: Family’s reproduction (offspring close relatives produce)

              • Inclusive fitness = Direct + Indirect fitness

            • If animals live in matrilineal groups, all females in the group are relatives. 

Mating system theory

• Individuals behave to maximize RS (reproductive success) over their lifetime

  • Sex differences - Limitations on fitness:

    • Females typically focus on gaining resources (only need to mate once for a baby), males typically focus on gaining mates (mating multiple times will produce more babies)

    • Paternal care unlikely

      • If female mates with more than one male, fathers do not know which offspring is his

  • Polygyny predominates (1 male mating with many females)

    • Successful competitors mate and fertilize more than 1 female

  • Competition for mates

    • Contest competition

      • Males directly compete physically (ie. elephant seals)

    • Scramble competition

      • Moving through habitat, trying to find a fertile female that is not already taken. Low aggression.

    • Mate choice competition

      • Males actively try to convince the female that she should choose him as a mating partner (classic example is humpback whales singing)

    • Sperm competition

      • Low rates of aggression. Stronger sperm will fertilize egg. (ex. Right whales)

• Types of mating systems

  • Resource defense

    • Some resource that is valuable to females is defended by a male so that the females come to his territory and he can mate with them.

  • Leks

    • Males set up little territories, but there is nothing valuable within the territory other than the male himself. Males will advertise themselves to convince females to mate with them

    • Allows female a small area to go to compare and assess mates

  • Female defense (Mate-guarding)

    • Males follow females around

  • Scramble competition

    • A race to fertile females (no guarding, no combat, just trying to mate with as many females as possible). Success often comes down to sperm competition