lecture 6

Question 1

species are fundamental units in…

Answer 1

comparative studies in ecology, evolution, and biodiversity.

Question 2

species concept

Answer 2

the primary theoretical defining property of a species category

Question 3

species delimitation

Answer 3

the process of determining the boundaries and numbers of species from data

Question 4

specitation

Answer 4

the outcome of isolation and divergence

Question 5

divergence can occur…

Answer 5

from genetic drift, selection, and mutation (NOT GENE FLOW – MAKES MORE SIMILAR)

Question 6

when distinct species?

Answer 6

when allele frequencies change sufficiently over time, populations are considered distinct species. but what is sufficient?

Question 7

agreement on species concept?

Answer 7

biologists generally disagree on species concepts, over 24 different ones.

Question 8

biological species concept

Answer 8

• reproductively isolated groups;
• pops are evolutionary independent if they are reproductively isolated from each (do not interbreed or if they do, they fail to produce fertile, viable offspring)
• disadvantages: how do you evaluate in fossils or asexual species or in pops that don’t overlap?

Question 9

ecological species concept

Answer 9

• different niche or adaptive zone;

Question 10

morphological species concept

Answer 10

• phenotypically distinct;
• species are identified by differences in morphological features.
• disadvantages: the features used to distinguish species are subjective. cannot identify cryptic species, which are distinct species that are erroneously classified (and hidden) under one species name.
• similar species are often differentiated by very small differences in the frustule such as shape, period, and band stria.

Question 11

phylogenetic species concept

Answer 11

• monphyletic gene trees;
• equates species with monphyletic groups
• disadvantages: deciding how many clades to name is subjective and genealogies (phylogeny of genes) often disagree with one another (coalescent theory can help)
• what is the limit to the number of monophyletic groups that we should call species?

Question 12

species concept

Answer 12

• most people respect and value diversity within species
• likewise, biologists should embrace the diversity of ways in which new species form.
• all formation of biological diversity deserve ‘equal rights’; each of the 3 concept provide unique and irreplaceable evidence for describing the process of speciation.
• don’t buy into speciation prejudice by favoring one concept.

Question 13

unifying species concept

Answer 13

• general lineage concept: species are separately evolving lineages, an all-inclusive species concept.
• deliminating species is the tricky part; how do we determine the boundary and number of species using real data

Question 14

species delimitation

Answer 14

• integrative taxonomy - combine multiple sources of evidence for delimiting species such as DNA, geography, ecology, morphology, behavior, reproductive isolation
• integrative taxonomy solution: consider the evolution of the traits on the phylogenetic tree

Question 15

Coalescent theory

Answer 15

• coalescence - the merging of alleles as they are traced back in time to their common ancestor. it’s a link between pop. genetics and phylogenetics
• random mating and constant size (equal to or greater than n=2)
• each gene copy is drawn from a random one in the previous generation
• probability of coalescence depends on effective population size

Question 16

TMRCA

Answer 16

time to the most recent common ancestor

Question 17

probability of common parent

Answer 17

P1 = 1/2N

Question 18

probability of distinct parents

Answer 18

P2 = 1 - P1 = 1 - 1/2N

Question 19

large population means

Answer 19

slower time to coalescence to a single lineage

Question 20

small population means

Answer 20

faster time to coalescence to a single lineage

Question 21

if all samples coalescence before reaching their ancestral pops…

Answer 21

then the gene tree will match the true pop. history (gene tree)

Question 22

if samples fail to coalescence

Answer 22

then genealogy may not match the true pop. lineage. incomplete lineage sorting.

Question 23

if delta t is twice the pop size of the human-ancestral branch…

Answer 23

incomplete lineage sorting will occurring 24% of the time.

• about 50% of the human genome coalescence with chimps
• remaining 50% has a huge impact on our ability to accurately infer phylogenetic trees and delimit species