lecture 18- speciation

Question 1

speciation

Answer 1

single ancestral species becomes two or more descendant species

Question 2

what is a species

Answer 2

most resolved level of organization for how we classify the organisms in the world around us

Question 3

evidence about species: species identification does not differ between cultures/peoples

Answer 3

Question 4

evidence about species: animals can recognize different species

Answer 4

Question 4

evidence about species: identification of statistical clusters

Answer 4

Question 5

how many species exist on earth?

Answer 5

1.2 million now

Question 6

biological species concept

Answer 6

reproductively isolated

Question 7

reproductive barriers: prezygotic isolation

Answer 7

before the formation of the zygote

act to prevent or limit mating from even occurring (before a hybrid is produced)

Question 8

reproductive barriers

Answer 8

features of organisms (or their ecology) that prevent or limit their ability to produce viable and fertile offspring with another species

Question 9

reproductive barriers: postzygotic isolation

Answer 9

after the formation of the zygote

reduce the likelihood that a hybrid offspring will survive or itself reproduce after mating has occurred

Question 10

5 examples of the reproductive barriers in prezygotic isolation

Answer 10

ecological: separated in space
temporal: separated in time
sexual/behavioral: separated by preference
mechanical: mating cannot physically occur (snails left vs right curl)
gametic incompatibility: eggs and sperm cannot combine (marine animals)

Question 11

5 examples of prezygotic reproductive barriers: behavioral isolation

Answer 11

usually involves variation in male mating rituals or signals, and female recognition and preference for species-specific displays

caused by differences in behavioral
preferences, and most often these include mating rituals or signals.
These barriers may be substantial – as in the case of humans and
chimpanzees, our closest relatives – or subtle – as in the case of song
differences between closely related crickets

Question 12

5 examples of prezygotic reproductive barriers: gametic incompatibility

Answer 12

corals and urchins

occurs when the egg and sperm themselves
are not compatible. This is common in broadcast spawners, that is
organisms that eject gametes into the water column, with the hope
that they will encounter each other (but do not fertilize if they meet a
gamete from another species)

Question 13

postzygotic isolation: hybrid inviability

Answer 13

the offspring does not survive or is impaired in some way

Question 14

postzygotic isolation: hybrid sterility

Answer 14

the offspring may be perfectly viable (horse plus donkey equal mule) but is infertile. often this is the case when there are chromosomal differences between the parents (so meiosis cant work properly)

Question 15

speciation

Answer 15

the process where a lineage splits during evolution: a single ancestral species becomes 2 or more descendant species (darwin finch)

Question 16

allopatric speciation

Answer 16

speciation in the absence of gene flow (geographically isolated populations)

Question 17

allopatric speciation: vicariance

Answer 17

population split by extrinsic event

Question 18

allopatric speciation: dispersal

Answer 18

some individuals disperse to a new isolated location

Question 19

sympatry

Answer 19

populations in the same place

Question 20

sympatric speciation

Answer 20

the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region

Question 21

sympatric speciation: chromosomal rearrangement

Answer 21

plant evolution; new polyploid can sometimes self-fertilize

Question 22

sympatric speciation: gradual divergence

Answer 22

for non chromosomal sympatric speciation to occur, there must be strong disruptive selection

Question 23

disruptive selection

Answer 23

selection that favors different parts of the spectrum of variation in the population (counteracts the homogenizing influence of gene flow)

Question 24

dobzhansky-muller model: speciation through epistasis

Answer 24

The Dobzhansky–Muller model describes the negative epistatic interactions that occur between different alleles (versions) of different genes with a different evolutionary history. These genetic incompatibilities can occur when populations are hybridising (decreased fitness of hybrids)

Question 25

epistasis

Answer 25

interaction between genes

Question 26

mapping the genetic incompatibilities between closely related species

Answer 26

Question 27

limitations of bsc: fossils (reproductive isolation makes a species)

Answer 27

Fossils. In general (but not always), species are morphologically distinct from each other, so we can categorize individuals according to their morphological affinities. This provides us with a way, for example, of classifying different fossils, or classifying extinct versus living organisms. If they are morphologically similar enough (i.e., they cluster in morphospace), we assign them to the same species; if they’re not, we classify them as different species.

Question 28

limitations of bsc: asexual species (reproductive isolation makes a species)

Answer 28

Most microbes reproduce asexually, therefore, generally we define microbial species based on genetic similarity (i.e., by comparing their genome sequences). However, even normally asexual species occasionally undergo a form of genetic exchange, corresponding roughly to sexual exchange of genetic material. For example, some microbes conjugate – exchange genetic material – via sex pili. Thus, many microbial species show the same clustering in morphospace as we see in sexual ones

Question 29

limitations of bsc: hybridization (reproductive isolation makes a species)

Answer 29

Some species – e.g., the tiger and the lion – that do not normally encounter each other in nature can still produce viable and fertile offspring (i.e., tigons and ligers) in captivity. Yet, I don’t think any of us would question that tigers and lions are distinct species. While hybridization can occasionally occur between closely related species, if it’s not frequent enough to compromise the identity of the species (i.e., cause them to merge into one), we are comfortable considering both species to be “good biological species”

Question 30

5 examples of prezygotic reproductive barriers: mechanical isolation

Answer 30

occurs when the male and female reproductive equipment is incompatible, thus mating cannot occur effectively for physical reasons

Question 31

5 examples of prezygotic reproductive barriers: temporal isolation

Answer 31

occurs when two species are separated in time. For example, two species of plants may flower at different times and therefore are unable to cross pollinate.

Question 32

5 examples of prezygotic reproductive barriers: ecological isolation

Answer 32

occurs when two species are separated in space. For example, while lions and tigers can mate and produce hybrid offspring (e.g., the liger), they never meet in nature

Question 33

genetic divergence

Answer 33

once two populations have diverged beyond a certain point, individuals in the two populations will no longer be reproductively compatible. In some cases, incompatibility may arise relatively rapidly. In other cases, the process can be gradual. There is no set rule for the rate at which speciation occurs, though it appears in general to occur slowly and gradually

Question 34

Sympatric speciation: chromosomal rearrangement

Answer 34

Chromosomal rearrangements are the result of large-scale changes in one or more chromosomes, or in the number of chromosomes, that in effect instantaneously isolate individuals from other members of the population. Specifically, individuals (or populations) with different chromosome content (or arrangements of chromosomes) have a hard time pairing properly, resulting in offspring with non-viable combinations of chromosomes. This seems to have been an important mode of speciation in plants.

Question 35

Sympatric speciation: disruptive selection

Answer 35

disruptive selection is the result of selection favoring different extremes of a trait distribution and acting against intermediate phenotypes (i.e., hybrids) disruptive selection can counteract the effect of gene flow, preventing the diverging populations from becoming genetically homogeneous because the hybrid offspring are at a disadvantage. While it is uncertain how common this mechanism is in natural populations, what is clear is that very powerful disruptive selection is required to counteract the homogenizing effect of gene flow