1. Lecture 11 Reproduction and Life Histories
An organism’s life history is its lifetime pattern of growth, development, and reproduction
Maximal reproductive success or fitness is constrained by limited resources and an organism must balance trade-offs
Modes of reproduction
Age at reproduction
Allocation to reproduction
Time of reproduction
Number and size of eggs, young, or seeds produced
Parental care

2. Sexual reproduction is the fusion of haploid egg and sperm to form a diploid zygote
A major source of genetic variation due to the recombination of chromosomes during egg and sperm production
Asexual reproduction produces offspring without the involvement of egg and sperm
Individuals are genetically identical to the parent

4. Asexual vs. Sexual Reproduction Asexual reproduction
Benefits
Offspring are well adapted to current conditions
Potential for high population growth
Costs
Low genetic variability in the population
May be unable to adapt to a change in environmental conditions
Sexual
High genetic variability in the population
Increased probability that some individuals will survive environmental changes
Parents only contribute one half of its genes
Specialized reproductive organs required
Expense of reproduction not equally shared between parents

6. Hermaphroditic organisms possess both male and female organs
Sexual Expression:
Dioecious (‘two houses’) plants have respective male and female organs
Monoecious (‘One house’) plants have separate male and female flowers on the same plant
Hermaphroditic organisms possess both male and female organs
Plants with flowers with both male and female parts are termed perfect
Animals which possess both male and female reproductive structures

7. In simultaneous hermaphrodites, the male organ of one individual is mated with the female organ of the other individual, and vice versa
These populations have the potential to produce twice as many offspring as a unisexual one
In sequential hermaphrodites, a sex change takes place as an individual matures, grows larger, or the population ratio changes
Coral reef fish, gastropods, bivalves, and jack-in-the-pulpit

8. The mating system is the pattern of mating between males and females in a population
Influenced by resource availability and distribution
If the habitat is diverse in productivity, competition for mates may be intense
Forms:
Promiscuity
Polygamy
Monogamy

9. Parents cooperate to raise young
Monogamy involves the formation of a lasting bond between one male and one female
Common in birds and rare in mammals
Parents cooperate to raise young
Increased survival of young and the parents’ genes
But…one of the parents may “cheat.” Why?
To increase fitness by producing more offspring

10. In polygyny, an individual male pairs with two or more females
Polygamy is the acquisition by an individual of two or more mates (pair bonds do exist)
The individual having multiple mates is generally not involved in caring for the young
In polygyny, an individual male pairs with two or more females
In polyandry, an individual female pairs with two or more males
Relatively rare

14. Sexual selection: includes two aspects:
How are mates chosen?
Sexual selection: includes two aspects:
Intrasexual: males compete - selection leads to evolution of structures used in combat with other males
Deer’s antlers or ram’s horns, bright colors, etc.
selective pressure is for ability to compete successfully with members of same sex
Intersexual selection- Females select amongst winners
agents of selection
Selection based on various cues – appearance and behavior
goal (evolutionary sense) select mate with best fitness

15. Female peahens prefer to mate with males with greater number of eyespots in their tail feathers

16. Knobs that look like eggs

17. The benefits of mate choice for the female
1. The male that provides the best offspring care
2. The male that provides the best territory
Superior nesting cover
Abundance of food
3. The male that provides the best genes
Handicap hypothesis: burden of bright plumage or other characteristics to attract mate counter to survival – those surviving such a handicap are genetically superior
4. Evidence of reproductive success (Fantail darter)

18. What do we mean by sexual selection?
How is it a part of natural selection?
How does it contribute to genetic fitness –
For females?
Females produce larger, more energetically costly gametes.
Female reproduction thought to be limited by resource access.
For males?
Males produce smaller, less energetically costly gametes.
Male reproduction limited by mate access.
How is it important in terms of shaping and survival of the species?

19. The answer is more complicated among polygamous species
Does the female select the male (and his territory) or the territory (and the male in it)?
The answer is more complicated among polygamous species
Female choice is apparent for those species that aggregate into groups on communal courtship grounds called leks

20. Figure 8.10

21. How many young are produced?
Limited access to energy/resources results in trade-off between number and size of offspring
ie.- species producing a larger # if offspring means offspring are smaller, and vice-versa
Parent provides extended care for young  fewer young produced but greater survival rate
The amount of energy invested in reproduction varies for different individuals
Investment in reproduction includes production, care, and nourishment of offspring
An individual’s fitness is determined by the number of offspring that survive to reproduce

22. Common Murre

23. Three Survivorship Patterns Type I = K selected
Mortality rises in post-reproductive years
Type II
Mortality constant throughout life
Type III = r selected
Many offspring with high juvenile mortality

24. K selected species
Low number of young produced
Offspring size tends to be large
Low mortality of young
Extended parental care
High rate of survival past reproductive age
Long time to maturity
Relativly long life span
Live near carrying capacity

25. High number of young produced
r selected Species
High number of young produced
Low parental input to each individual young
Short maturation time
Breed at young age
Produce many offspring quickly
High mortality of young
Nonexistant parental care
Opportunists – populations quickly develop but may crash
Examples:
Waterfleas, insects, bacteria

26. Life History Classification
MacArthur and Wilson
r selection (per capita rate of increase)
Characteristic high population growth rate.
K selection (carrying capacity)
Characteristic efficient resource use.
Pianka : r and K are ends of a continuum, while most organisms are in-between.
r selection: Unpredictable environments.
K selection: Predictable environments.

27. Life Histories – Age Structure and Survivorship in Populations
Cohort populations
Birthrate and survival of young
Competitive ability vs population size – survivorship patterns
Principle of allocation and reproduction
Dispersal and seed size
Ecological succession

28. Cohort – a group of individuals of the same age within a population (individuals born at same time) - see p
Study of cohort provides information about:
Mortality and survival vs. age
Used to construct a cohort life table
Static life table
Pattern of survival  survivorship curve

29. Static life table – ‘snapshot’ of population at a given time
Data corrected to 1000 – actual number sampled 608
Dall sheep – Murie study 1944
Collect skulls
Evaluate age of animal at time of death
Allows evaluation of survivorship: percentage of an original population that survives to a given age

30. Plant Succession and Life History Patterns JPGrime (pages 286-288)
Ruderals (highly disturbed habitats)
Grow rapidly and produce seeds quickly.
Stress-Tolerant (high stress - no disturbance)
Grow slowly - conserve resources.
Competitive (low disturbance low stress)
Grow well, but eventually compete with others for resources.
Stress: environmental extremes or competition that limits (or provides excess) light, temperature, nutrients

31. Plant Life Histories

32. Old Field Succession: Dwight Billings
Early species to invade: ‘weedy’ or r-selected species
Do not compete well for resources, high reproductive rate
Shift to k-selected species
Changes in nature of habitat favor species which reproduce successfully at or near carrying capacity