BIOEE 1780 Lecture Notes - Lecture 19: Fecundity, Nios Embedded Processor, Meiosis
7 May 2018
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Siblicide: siblings kill each other
• Example: blue-footed booby
o 2 eggs are produced, one chick is bigger than the other (senior chick vs. junior chick)
o The bigger chick usually pushes the smaller chick out of the nest, and then the parents stop
feeding the smaller chick.
• Causes the death of the smaller chick
When there are favorable conditions:
• No siblicide
• The inclusive fitness of the senior chick is higher if it has a surviving sibling
o When there are unfavorable conditions:
• The cost of food lost to the junior chick can outweigh its benefit to the senior chick.
• Siblicide is triggered when the senior chick is 20-25% lighter than average.
Cooperation should occur when it increases the inclusive fitness of an individual. This can happen
through:
1. Direct benefits (ex. group living)
2. Indirect fitness benefit (kin selection)
Asexual Reproduction: offspring derive from a single parent
Sexual Reproduction: two parents contribute genetic information to offspring
Hermaphrodites: individuals that produce both female and male gametes
• Self-fertilization occurs (still considered sexual reproduction, but lacks genetic variation)
Reproduction: the formation of offspring
Twofold Cost of Sex: the disadvantages of being a sexual organism rather than an asexual organism;
asexual lineages multiply faster because all progeny are capable of producing offspring
• In sexual lineages, half of the offspring are males who can't produce offspring.
o Halves the rate of replication of sexual species
Recombination: the formation of new allelic combinations in offspring
• Occurs during meiosis via the crossing over between homologous chromosomes in eukaryotes
• Other kinds of genetic exchange can function like sexual recombination (ex. Conjugation in bacteria)
Muller's Ratchet: the accumulation of deleterious mutations in asexual lineages
• In sexual lineages, recombination allows unfavorable mutations to be purged by natural selection.
Genetic Load: the burden imposed by the accumulation of deleterious mutations
With sexual reproduction, independent mutations can be brought together in recombinant
offspring. With asexual reproduction, mutations must arise sequentially in the same lineage.
Consequences of Sexual Reproduction
Disadvantages
Advantages
Twofold cost of sex
Combining beneficial/favorable mutations
• asexual lineages can grow more rapidly in each
generation because each individual can produce
offspring
• Combines alleles from 2 different
individuals
Search cost
• Males and females must locate each other in order
to mate
• Requires time, energy, and risk of predation
Generation of novel genotypes
• Recombination allows for crossing over,
creating gametes with unique combinations
of alleles
Reduced relatedness
• Sexually reproducing organisms pass only half of
their alleles to offspring (parents are less related to
their own offspring)
• Halves the relatedness between parents and
offspring
Faster evolution (Red Queen Effect)
• Offspring of sexual parents are more
genetically variable
• Increases evolutionary response to
selection
Risk of sexually transmitted diseases
• Allows for transmission of pathogens
Clearance of deleterious mutations (Muller's
Ratchet)
• Recombination excludes deleterious
mutations
• Asexual populations steadily and
irreversibly accumulate deleterious
mutations
Red Queen Effect: a phenomenon seen in coevolving populations
• To maintain relative fitness, each population must constantly adapt to the other
• Evolutionary arms race between parasites and their hosts.
• Sex allows for faster adaptation through reshuffling of genetic diversity.
Anisogamy: sexual reproduction involving the fusion of two dissimilar gametes
• Females = individuals producing the larger gamete (eggs)
• Males = individuals producing the smaller gamete (sperm)
• Leads to differences in the reproductive investment of males and females
Males and females differ in how they invest in each reproductive attempt. Females usually invest more.
• Sperm are cheap (small). Eggs are costly (large).
• Females have a higher certainty of parentage. Males can never be fully sure.
• Females often have specialized physiology for offspring care.
• Males and Females show different patterns of reproductive investment.
o Females
• Limited by their own energy and ability to produce eggs
• Often benefit if they invest extra parental care
• More eggs = higher fitness
• Common strategies
• Put energy into egg
• Wait to mate with the sexiest male
• Put time/care/energy into raising offspring
o Males
• Limited by access to females
Document Summary
When there are favorable conditions: no siblicide, when there are unfavorable conditions: The inclusive fitness of the senior chick is higher if it has a surviving sibling. The cost of food lost to the junior chick can outweigh its benefit to the senior chick. Siblicide is triggered when the senior chick is 20-25% lighter than average. Cooperation should occur when it increases the inclusive fitness of an individual. This can happen through: direct benefits (ex. group living) Asexual reproduction: offspring derive from a single parent. Sexual reproduction: two parents contribute genetic information to offspring. Hermaphrodites: individuals that produce both female and male gametes. Twofold cost of sex: the disadvantages of being a sexual organism rather than an asexual organism; asexual lineages multiply faster because all progeny are capable of producing offspring. Self-fertilization occurs (still considered sexual reproduction, but lacks genetic variation)
