Lect 4- Species and Speciation Flashcards
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
Sympatric hybridization
two spp exist in the same region and encounter each other
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?
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
When does it matter what species concept is used?
when orgs are about to split, currently split, or just split
Speciation
origin of two spp is from common ancestor and requires the evolution of biological barriers to gene flow
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
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
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
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
Hybrid Zone
region where genetically distinct pops meet and mate resulting in some offspring
- characteristics/loci are often clines (continual gradient)
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
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
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
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
Peripatric speciation
divergence of a small group due to dispersal from a widely distributed ancestral form
- earnst mayr
Parapatric speciation
neighboring pops with some gene flow diverge and become isolated
EX: flowers growing on heavy metal contaminated soil
Sympatric speciation
Evolution of reproductive barriers within single initially mixed pop
- disruptive selection
- fight against recombination
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
Recombination speciation
hybridization btwn two spp and chromos pair not forming a polyploid
instead pairs of chromos recombinate
