國立交通大學生物科技學院 助理教授 林勇欣 一、參選類別（請勾選）： ■「學士班必修課程與全校性共同課程」候選人 □「其他 ( 學士班選修及研究所 ) 課程」候選人 四、近二年任教之學士班必修課程與全校性共同課程

The “mystery of mysteries” that captivated Darwin is speciation, the process by which one species splits into two or more species Speciation fascinated Darwin (and many biologists since) because it is responsible for the tremendous diversity of life, repeatedly yielding new species that differ from existing ones Speciation explains not only differences between species, but also similarities between them (the unity of life)

Speciation also forms a conceptual bridge between microevolution, changes over time in allele frequencies in a population, and macroevolution, the broad pattern of evolution over long time spans Chapter 23 – microevolution Chapter 25 – macroevolution In this chapter, we will explore the “bridge” – the mechanisms by which new species originate from existing ones First, we need to establish what we actually mean when we talk about “species”

The tephritid fly has distinctive dark bands on its wings. When disturbed, the fly holds its wings perpendicular to its body and waves them up and down. Entomologists had noticed that this display seems to mimic the leg-waving, territorial threat display of jumping spiders.

The first step in any evolutionary analysis is to phrase the question as precisely as possible In this case: Do the wing markings and the wing waving of the fly mimic the threat displays that jumping spiders use on each other, and thereby allow the flies to escape predation?

When the researchers tested treatments A, C, and E against other predators, all of the test flies were captured and eaten There was not even an appreciable difference in time-to- capture among the three treatment groups

The initial allele frequencies are 0.01 for B 1 and 0.99 for B 2

A general treatment of selection If there are two alleles, B 1 and B 2, with frequencies p and q We incorporate selection by imagining that B 1 B 1 zygotes survive to adulthood at rate w 11 ; B 1 B 2 zygotes survive at rate w 12 ; and B 2 B 2 zygotes survive at rate w 22 All individuals that survive produce the same number of offspring We can therefore refer to the survival rates as fitnesses The average fitness for the whole population, w, is given by the expression:w = p 2 w pqw 12 + q 2 w 22 ≦ 1

A general treatment of selection The average fitness for the whole population, w, is given by the expression:w = p 2 w pqw 12 + q 2 w 22 ≦ 1 The new frequencies of the genotypes are: B 1 B 1 B 1 B 2 B 2 B 2 p 2 w 11 2pqw 12 q 2 w 22 w w w The new frequency of B 1 is The new frequency of B 2 is

A general treatment of selection It is instructive to calculate the change in the frequency of allele B 1 from one generation to the next This value, ∆p, is the new frequency of allele B 1 minus the old frequency of B 1 : The change in the frequency of allele B 2 from one generation to the next is

An algebraic treatment of selection on recessive and dominant alleles AA Aa aa frequencies p 2 2pq q 2 fitness w AA = 1 w Aa = 1 w aa = 1 + s Where s called selection coefficient If a is a lethal recessive, then s is equal to -1

An algebraic treatment of selection on recessive and dominant alleles AA Aa aa frequencies p 2 2pq q 2 fitness w AA = 1 + sw Aa = 1 + s w aa = 1 If A is a lethal dominant, then s is equal to -1 A lethal dominant is eliminated from a population in a single generation

An algebraic treatment of selection on recessive and dominant alleles