Lect 4- Species and Speciation Flashcards Preview

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Flashcards in Lect 4- Species and Speciation Deck (20):
1

Existentialist View

individual members of sp if they conform to the ideal "type"
often phenotypes and morphology are used to distinguish spp

probs:
1. sp highly varied
EX: color of red tail hawk, humans -genotyping is
necessary
2. sp cryptic (morph identical)
EX: microbes, lacewing calls, mosquito/malaria
3. hybridization
EX carrion and hood crow = intermediary colors
EX gambel's oak and grey oak = hybrids may look like either spp

2

Sympatric hybridization

two spp exist in the same region and encounter each other

3

Biological species concept

spp are defined as group of actual or potential interbreeding pops with are reproductively isolated from other groups.
reproductive isolation need not be perfect if biological diff btwn pops greatly reduce gene flow
PROBS:
asexual spp
what is lowest threshold of gene flow?
how assess potential gene flow?

4

Phylogenic species concept

spp are irreducable clusters of orgs that share common ancestor and are different from other such clusters
PROBS:
minor nucleotide diffs could count as diff spp TF spp cut offs 2-5% DNA divergence

5

When does it matter what species concept is used?

when orgs are about to split, currently split, or just split

6

Speciation

origin of two spp is from common ancestor and requires the evolution of biological barriers to gene flow

7

Pre-mating barriers

barriers that restrict transfer of gametes to other pops/spp

ECOLOGICAL- EX breed diff times of year, prefer diff habitat (insects breed on diff types of flowers)
BEHAVIORAL- differences in mate recognition systems EX lacewing calls

8

Post-mating barriers

Reduce/prevent formation of viable hybrids after mating has occurred

PRE-ZYGOTIC- prevent zygotes from forming
EX: lock and key genetailia; sperm missing proteins to reach egg; pollen out-competed by other mates

POST-ZYGOTIC- reduce/prevent survival/reproduction of hybrids
EX: incompatible chromosomes
incompatible genes- epistasis
population level cause- hybrid with higher fitness out performs parent population

9

Holadane's Rule

Hybrid sterility limited to the sex that results from different sex chromosomes (hetrogameic sex)
XY fruit flies and humans; -- birds and butterflies

10

Examples of reproductive barriers often associated with divergence among spp

ECOLOGICAL- temp tolerace, habitat use
SELECTION- females of 2 spp have diff pref for voice sound, looks, etc.
NEUTRAL DIFF DUE TO MUTATION AND GENETIC DRIFT

11

Hybrid Zone

region where genetically distinct pops meet and mate resulting in some offspring
- characteristics/loci are often clines (continual gradient)

12

Primary Hybrid Zone

original divergence taking place btwn adjacent pops of previous homogeneous spp.
- one pop may spread to new more drastic env TF adaptation

13

Secondary Hybrid Zone

two formerly separated pops (allopatric) expand TF meet and interbreed
- can be a tension/transition zone
- most hybrid zones are prob secondary but hard to rule out due to proving speciation in the past

14

What is the fate of hybrids?

- presist due to NS
- NS favors reinforcement of pre-zygotic isolation
- alleles increase hybrid fitness leading to spp merge
- hybrids become reproductive isolated and make third spp

15

Allopatric speciation

occurs when members of one sp become isolated from one another enough to interfere with gene exchange bc of geography (mountains, etc.).
- gene flow effectively zero

16

Peripatric speciation

divergence of a small group due to dispersal from a widely distributed ancestral form
- earnst mayr

17

Parapatric speciation

neighboring pops with some gene flow diverge and become isolated
EX: flowers growing on heavy metal contaminated soil

18

Sympatric speciation

Evolution of reproductive barriers within single initially mixed pop
-disruptive selection
-fight against recombination

19

Polyploid speciation

join two foreign genomes or double genome for new sp - have more than just pairs of chromos
how to not ploid again
- self fertilize
- diff sizes to enter diff space

20

Recombination speciation

hybridization btwn two spp and chromos pair not forming a polyploid
instead pairs of chromos recombinate