Lecture 11 Origin of Species (speciation) Flashcards

1
Q

How do new species originate from existing species?

A

slide 3

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2
Q

How Do Species Attain and Maintain Separate Identities?

A

speciation, microevolution, macroevolution, reproductive isolation

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3
Q

Speciation

A

one of several processes by which
new species arise

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4
Q

microevolution

A

changes over time in allele
frequencies in a population

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5
Q

macroevolution

A

the broad pattern of evolution
above the species level

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6
Q

Reproductive isolation

A

– Absence of gene flow between populations
– Always part of speciation

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7
Q

The Biological Species Concept

A
  • Ernst Mayr defined species as …
  • “… groups of actually or potentially interbreeding natural
    populations which are reproductively isolated from other such groups”

Species composed of
– populations whose members mate with each other
– produce fertile offspring

  • Reproductive isolation – do not mate with each other or do not
    produce fertile offspring
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8
Q

Gene exchange

A

Focus on the ability to exchange genes
– Prezygotic isolating mechanisms
Mechanisms that prevent formation of a zygote

– Postzygotic isolating mechanisms
Mechanisms that prevent development into an adult

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9
Q

Prezygotic isolating mechanisms

A

Mechanisms that prevent formation of a zygote

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10
Q

Postzygotic isolating mechanisms

A

Mechanisms that prevent development into an adult

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11
Q

Reproductive isolation

A

Gene flow does not occur between populations
○ Different genetic changes accumulate
○ Reinforces differences between diverging
populations
○ If pollination or mating cannot occur, or if zygotescannot form, the isolation is prezygotic
○ If hybrids form but are unfit or infertile, the
isolation is postzygotic

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12
Q

Seven mechanisms of reproductive isolation

A

Temporal isolation

Mechanical isolation

Ecological isolation

Behavioral isolation

Gamete incompatibility

Hybrid inviability

Hybrid sterility

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13
Q

Temporal isolation

A

Some populations cannot interbreed because the timing of
their reproduction differs

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14
Q

Mechanical isolation

A

Size or shape of an individual’s reproductive parts prevent
it from mating with members of another population

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15
Q

Ecological isolation

A

Populations adapted to different microenvironments in the
same region may be physically separated

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16
Q

Behavioral isolation

A

In animals, behavioral differences can stop gene flow
between related species

17
Q

Gamete incompatibility

A
  • Even if gametes of different species meet, they often have molecular incompatibilities that prevent them from fusing
  • Primary speciation route of animals that release
    free-swimming sperm in water
18
Q

Hybrid inviability

A
  • If genetic incompatibilities disrupt development, a hybrid embryo may die, or hybrid offspring that
    survive may have reduced fitness (e.g., ligers)
19
Q

Hybrid sterility

A
  • Some interspecies crosses produce robust but sterile offspring (e.g., mules)
20
Q

B-Reproductive isolating mechanisms

A

Prezygotic isolating mechanisms
* Ecological isolation
* Behavioral isolation
* Temporal isolation
* Mechanical isolation
* Prevention of gamete fusion

Postzygotic isolating mechanisms
* Hybrid inviability or infertility

21
Q

Barriers to reproduction

A

slide 11-12

22
Q

Ecological isolation

A

– Different habitat
– Land iguana vs marine iguana

23
Q

Temporal isolation

A

– 2 species of wild lettuce grow along roadsides in the SE U.S.

– Hybrids can be made experimentally and are fertile

– Rare in nature because one flowers in early spring and the other in summer

slide 14

24
Q

Behavioral isolation

A

– Blue-footed boobies select mates after an elaborate
courtship display - Will not mate with other boobies

– Lacewings rely on auditory signals to attract mates
– Females are able to distinguish calls of different species

25
Mechanical isolation
– Structure of the male and female copulatory organs may be incompatible – Mating Bradybaena snails with shells that spiral in the same direction ) and unaligned genitals of snails with shells that spiral in opposite directions) slide 17
26
Gametic isolation
Prevention of gamete fusion in mechanical isolation – In animals that shed gametes directly into water, the eggs and sperm derived from different species may not attract or fuse with one another – In plants, the growth of pollen tubes may be impeded in hybrids between different species slide 18-19
27
Postzygotic isolating mechanisms
– Hybrids that do survive may be weaker – Hybrids may be sterile – mules * Abnormal sex organs * Failure to form gametes
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Limitations of the Biological Species Concept
* The number of species to which the biological species concept can be usefully applied is limited cannot be applied to fossils or asexual organisms (including all prokaryotes), because mating cannot be observed * emphasizes absence of gene flow, but gene flow occurs between many morphologically and ecologically distinct species For example, grizzly bears and polar bears are distinct species, but they can occasionally mate to produce “grolar bears” slide 22
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Other Definitions of Species
The morphological species concept distinguishes a species by its structural features The ecological species concept defines a species by its ecological niche, the sum of its interactions with the nonliving and living parts of the environment
30
The geography of speciation
Speciation can take place with or without geographic separation slide 24
31
Speciation Is Influenced by Geography
* Speciation is a 2-part process – Initially identical populations must diverge – Reproductive isolation must evolve to maintain these differences * Homogenizing effect of gene flow erases differences * Speciation more likely in geographically isolated populations Populations can become geographically isolated for a variety of reasons slide 25
32
Allopatric (“Other Country”) Speciation
* Geographically separated, or allopatric, populations appear much more likely to have evolved substantial differences leading to speciation * Ex. Little paradise kingfisher varies little throughout range – Isolated populations are strikingly different from each other and maintain slide 26
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Sympatric (“Same Country”) Speciation
* In sympatric speciation, speciation occurs in populations that live in the same geographic area * Sympatric speciation is less common than allopatric speciation * It occurs if gene flow is reduced by factors such as – Polyploidy – Sexual selection – Habitat differentiation slide 27
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Allopolyploidy
* Two species hybridize * Resulting offspring have one copy of the chromosomes of each species * Infertile: cannot reproduce with either species – can’t produce gametes * Can reproduce asexually * Can become fertile if chromosomes spontaneously doubled (polyploidy) slide 28
35
Autopolyploidy
* All the chromosomes arise from a single species * Error in cell division produces tetraploids * DNA is replicated, NO cytokinesis * Cannot produce fertile offspring with normal diploids slide 29
36
Sympatric speciation by disruptive selection
* Sympatric speciation may occur over the course of multiple generations through disruptive selection – Cause a population to contain individuals exhibiting two different phenotypes * Two phenotypes would have to evolve reproductive isolating mechanisms * Two phenotypes could be retained as polymorphism within a single population
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Sympatric
without geographical separation
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Allopatric
geographically isolated populations. * Polyploidy and disruptive selection are two ways by which a single species may undergo sympatric speciation.
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