Life Histories Flashcards
Reproduction
What is life history theory?
Describes how animals should allocate time and energy in order to maximize fitness
Energy is finite spending too much energy on one thing (ex: reproduction) means you have less energy for other things (ex: growth / maintenance)
What are some principle life history traits?
- Size at birth
- Patterns of growth
- Age at sexual maturity
- Size at maturity
- Reproductive schedule
- Number and sex of offspring
- Lifespan
What are some life history constraints for marine mammals?
- Single offspring per pregnancy (twins = very rare)
- Long juvenile period of physical and social development
- Terrestrial childbirth (pinnipeds)
How are life histories typically studied in cetaceans?
Through necropsies
Not much information is known
What are some methods of studying life histories?
- Cross-Sectional Approach
- Longitudinal Approach
- Combined Approach
Describe a cross-sectional approach to studying life history in marine mammals
- Specimen collections
- Carcass salvages through fisheries bycatch, strandings etc.
Describe a longitudinal approach to studying life history in marine mammals
- Following the lives of individual animals
- Photo ID, tagging, mark recaptures etc.
Describe a combined approach to studying life history in marine mammals
Utilizes methods from both cross-sectional and longitudinal approach
Do larger animals have higher or lower birth rates?
Lower!
Describe the duration of gestation in marine mammals in relation to body size?
As body size increases, gestation period also increases
Based on body size, how long should the gestation periods of mysticetes and pinnipeds be?
- Mysticetes: gestation > 12 months
- Pinnipeds: gestation < 12 months
Is this the case?
What are some selective advantages to a 12-month reproductive cycle in mysticetes and pinnipeds?
- Mysticetes: annual migrations provide ideal conditions for birthing / raising a calf
- Pinnipeds: Minimize the number of trips to shore
How are pinnipeds able to have a gestation period of 12 moths despite their small body size?
Embryonic diapause lengthens the duration of gestation
Describe embryonic diapause
- Mating takes place in late March
- Embryo free floats for several months before implantation
- Implantation takes place in July
- Birth occurs at the beginning of March (same time as mating)
Why does birth take place at the same time as mating in pinnipeds?
To limit the amount of trips to land
How is the duration of gestation shortened in baleen whales?
By elevated fetal growth rates
What are some life history characteristics of pinnipeds?
- Terrestrial childbirth
- Post-partum estrus: mating occurs directly after birth
- Embryonic diapause
Post-partum, estrus and embryonic diapause work in unison to limit trips to land
What are some life history characteristics of Phocids?
- Give birth on pack or fast ice
- Short periods of intensive lactation
- Monomorphic or slightly dimorphic
What are some life history characteristics of Otariids?
- Give birth on land
- Long periods of intermittent lactation
- Highly dimorphic
What are some life history characteristics of Mysticetes?
- Extensive seasonal migration
- Seasonal reproduction
- Large body size
- Short period of parental care
Why do baleen whales migrate?
Benefits to adults:
1. Thermoregulation in warm water during winter
2. Evolutionary tradition
3. Tracking resources
Benefits to calves:
1. Thermoregulation is easier in warmer waters
2. Calm water after birth
3. Reduced risk of predation from killer whales (found less often in tropical waters)
Describe the reproductive cycle of baleen whales
- Breeding takes place in low latitude (cold) waters
- Pregnant female migrates to warmer waters to feed
- Pregnant female migrates back to colder waters to give birth and mate
- Female with calf travels back to warmer waters to feed (while pregnant)
What are some life history characteristics of Odontocetes?
- Weakly migratory
- Seasonal reproduction in high latitude species
- Great variation in size and dimorphism
Some species
- Long periods of maternal investment
- Extended life spans
- Reproductive senescence
Compare the life histories of dolphins and porpoises
Dolphins:
- Slow
- Larger size
- Long birth interval
- High age of first reproduction
- Long reproductive life
Porpoises:
- Fast
- Smaller size
- Annual birth interval
- Early age at first reproduction
- Short reproductive life
What is reproductive senescence?
The equivalent of menopause in humans
What are the two hypotheses for reproductive senescence in marine mammals?
- Stop early
- Grandmother effect (most likely)
Describe the grandmother effect
For animals that require large investments in juveniles, grandmothers are beneficial as they can help raise their grandchildren. This directly contributes to the fitness of the individual by producing viable offspring.
What are the energetic costs of reproduction in marine mammals?
Females:
- Gestation (less demanding)
- Lactation (very demanding)
Males:
- Gaining and maintaining access to females
Describe income breeders
- Energy is converted directly from diet
- Otariids
Describe capital breeders
- Energy is obtained from stored supplies
- Ex: Phocids and Mysticetes
Requires a large body size
What is a benefit of the capital breeding strategy?
Feeding is separated from lactation
what are some advantages of the capital breeding strategy?
Allows feeding in environments that are unsuitable for giving birth
Describe the foraging strategy of otariids
- Income breeders
- Moderate maternal energy stores prior to birth
- Alternating nursing and feeding trips
- Long lactation period
- Low milk fat
- Slow pup growth
- Small adult body size
Describe the foraging strategy of phocids
- Capital breeders
- Large maternal energy stores prior to birth
- Fast during lactation
- Short lactation period (4-50 days)
- High milk fat
- Rapid pup growth
- Large adult body size
You must have a big enough body size to hold sufficient energetic stores
Describe the fasting lactation strategy of elephant seals
Elephant seals fast for the entire duration of lactation resulting in rapid weight loss for the mom and rapid weight gain for the pup
Describe the lactation strategy of odontocetes
- Income breeders
- Nurse while feeding
- Energy from food = directly transferred into milk
- Long lactation period
How can changes in maternal and calf body volume be measured?
Drones
