1. Processes that Drive Evolution
Coevolution
Sexual selection
Genetic drift

2. Coevolution: Evolutionary arms race between species
Predator prey relationships are an excellent example
The bat has evolved to catch moths but the moths fight back as will be shown in the video that follows. The leopard/antelope is a classic of coevolution where the slower antelope is caught by the faster leopard whith the average leopard speed being lower than the average antelope speed. If this were not the case all of the antelope would be eaten and disappear.
Leopard and Antelope
Bat and Moth

3. Video: Coevolution YouTube copy
Video on coevolution where bats and moths are an example along with other examples.
YouTube copy

4. Coevolution is:
A. a special type of evolution that differs from Darwinian evolution.
B. a type of evolutionary change that occurs between a population and the physical environment in which that population lives.
C. the evolution of individuals within a population in response to selection pressure from other individuals in the population.
D. the evolution of two populations of different species in response to selection pressures that individuals from the two populations place on each other.
correct answer is D.

5. Sexual Selection Why such big antlers? Why such fancy tails?
The Descent of Man, and Selection in Relation to Sex is a book on evolutionary theory by English naturalist Charles Darwin, first published in It was Darwin's second great book on evolutionary theory, following his 1859 work, On The Origin of Species. In The Descent of Man, Darwin applies evolutionary theory to human evolution, and details his theory of sexual selection. The book discusses many related issues, including evolutionary psychology, evolutionary ethics, differences between human races, differences between sexes, the superiority of men to women, and the relevance of the evolutionary theory to society. From Winkipedia
Why such a colorful nose? 5

6. Video: Sexual Selection
youtube copy 6

7. Questions:
If there are costs associated with these exaggerated traits, why did they evolve?
Why do females choose males with exaggerated traits?
Questions for class discussion:
Are there costs associated with these exaggerated traits? Answer: Yes. Males must invest large amounts of energy to produce and maintain their extravagant plumage, and their huge tails interfere with their ability to fly and escape predators.
Then why did these traits evolve? Answer: Due to sexual selection, generations of females chose males who had larger, showier tails or antlers.
But why do females choose males with exaggerated traits? Answer: A hint is given in the next slide. 7

8. The Peacock’s Tail
Data showing selective advantage of peacock’s tail. Pea hens that mate with peacocks who have many eye spots in their tails have more surviving chicks (tail size and eye spot-number are positively correlated). An experiment was done where spots were cut off a previously successful male and he was not chosen nearly as a much during the next breeding season. 8

9. Ornaments Signal Good Alleles
‘Eyespot’ number and tail length in peacocks positively correlate with progeny weight and survival. Figure modified from M. Petrie, 1994: Improved growth and survival of offspring of peacocks with more elaborate trains. Nature 371, Another test of the better alleles hypothesis for the evolution of exaggerated male ornaments was conducted by Marion Petrie with peacocks. In a population inhabiting a large, forested park in Britain, she found that the sons and daughters of fathers with more elaborate tails (greater number and area of ‘eyespots’) weighed more and had a significantly higher probability of surviving for two years after birth. 9

10. Ornaments Signal Good Alleles
Length of male barn swallow tail positively correlates with fewer mite parasites on offspring. Figure modified from A.P. Moller, 1990: Effects of a haematophagous mite on the barn swallow Hirundo rustica: a test of the Hamilton and Zuk hypothesis. Evolution 44, Moller sought to determine if male swallows with longer tails passed on parasite resistant genes to their offspring. He found that fathers with longer tail lengths had offspring with fewer blood sucking mites. He cross-fostered the offspring by putting them in another pair’s nest. Thus the genetic origin of the nestlings was the important variable, not the site of rearing or whether or not they were reared by their own parents. The data suggest that female preference for long tailed males evolved because this male ornament was an honest signal of better alleles. 10

11. Females Select Indicators of Good Genes
Tragopans are a species of bird commonly called horned pheasants.
In tragopans, brightness and symmetry of display are honest indicators of male health.
In stalk-eyed flies, females have more offspring when they choose mates with long eye stalks.

12. Video: Male Seahorse Gives Birth
Video: Seahorse Reproduction
Video: Male Seahorse Gives Birth
Question Slide: “Based on the video, which sex would you predict to be choosier when it comes to mating?” Since seahorse males make the greater investment in reproduction, one might predict that they would be the choosier sex. This is the case for most polygamous seahorse species. For monogamous seahorse species, both parents invest considerable time and effort rearing the young. And females and males are similar in their choosiness when mating.
Local copy 12

13. Seahorse Mating Behavior
Based on the video, which sex would you predict to be choosier when it comes to mating?
Male
Female
Both
Neither
Question Slide: “Based on the video, which sex would you predict to be choosier when it comes to mating?” Since seahorse males make the greater investment in reproduction, one might predict that they would be the choosier sex. This is the case for most polygamous seahorse species. For monogamous seahorse species, both parents invest considerable time and effort rearing the young. And females and males are similar in their choosiness when mating.

14. The sex lives of voles Male Montane Vole Polygamous Male Prairie Vole-
Monogamous
Choose female, mate 24 hours, remain with mate and become a good father helping in rearing of offspring, social but possessive
Never settles down with one partner, lives more in isolation, gets around

15. Behavioral differences
Studied trios of each type of vole in the field- 1 male and 2 females.
Marked difference in social displays seen in the graphs to the right.

16. Slowing down the montane vole
The monogamy genes- encode a particular type of vasopressin receptor protein where the receptor is present in the brain. Montane voles have a different version of the controlling genes and if they are dosed with vasopressin and oxytocin, they become pair bonded and good fathers.
Vasopressin is a peptide hormone made in the hypothalamus, stored in the pituitary. Most common use is homeostasis- regulation of salts in blood and kidneys. A variant called AVP (arginine vasopressin) goes to the brain where it is believed to have a role in social behavior. The montane vole can make the hormone but is lacking the receptors to detect the hormone in brain cells. Oxytocin is a known neuropeptide regulating social interaction, bonding, etc.

17. The human signal of good alleles
It’s the length of your gene that matters….
In voles, the length of the gene matters with the longer version of the gene indicating monogamy and parenting.
The human gene comes in at least 17 different lengths….

20. Genetic Drift in Small Populations
Cheetahs in Africa
H* =
H = for other large cats
Lowest of any felid
* H = % of loci that are heterozygous

21. Genetic Drift in Small Populations
70% of sperm abnormal
Sperm count < 10% of other felids
Very difficult to breed

22. Genetic Drift in Small Populations
Cheetah population was 10-20,000
Now 1000
One or more historical “bottlenecks”
i.e. periods in past 10,000 years when population < 100
Bottlenecks occur when few members of the species survive. This causes a change in the frequency of certain alleles from the previous population with higher numbers. After a bottleneck, genetic drift can affect significantly the population making it have less genetic diversity and lesser ability to survive.

23. Consequences of Reduced Variation
Desert Pupfish
Mandarte Sparrow
Deleterious alleles become ___________?
Cheetah
fixed
Black footed ferret

24. Consequences of Reduced Variation
Deleterious alleles become homozygous.
Similar to “inbreeding depression”
Cheetah ~100
Occurs when close relatives mate
Fewer, less viable offspring
Mandarte Sparrow ~ 7 pairs
Lower survivorship
Increased chance of extinction
Inbreeding depression is what happens when two closely related individuals are mated. The populations ability to reproduce and survive may be lowered.
Desert Pupfish ~30
Black footed ferret ~5

25. Unpredictable genetic shifts occurring after a few individuals establish a new population are known as:
Founder effects.
When small numbers of a larger population move to a new location (island), the genetic diversity is likely lower than in the original population. Genetic drift can cause fixation of alleles and some of these may be deleterious which impacts overall fitness and survival.
Darwin’s famous finches migrated from Ecuador and not likely in large numbers. If genes were fixed, some were advantageous.

26. Hidden Assumptions of Natural Selection:
Natural Selection operates on individual variation within a population by selecting for favorable individual variations and eliminating unfavorable ones – i.e. it does not act on the whole population all at once.
Nor does selection act at the species level, i.e. traits are not selected for the “good of the species” – they are selected only if they allow individuals within a population to survive and reproduce better.
The environmental context determines whether or not a trait is beneficial and adaptive. What is beneficial in one setting may be a liability & un-adaptive in another.
Natural selection acts on phenotypic variation, not directly on genes or genotypes. As a result of selection, both phenotypes and genotypes change since genes are the ultimate, underlying cause of phenotypic variation.
Natural Selection can act on both acquired and inheritable traits. But evolution will occur only from selection on heritable traits that are passed on to future generations.