chpt24_bio115_baird

8/2/2019 chpt24_bio115_baird

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Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPointLecture Presentations for

BiologyEighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 24

The Origin of Species


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What, if anything, is a species.

Morphological species definitionbased on appearance/similarities

Phylogenetic species definition

based on inferred evolutionary history

Biological species definition

based on reproduction isolation

No species definition

species are artificial constructs of humans


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Other Definitions of Species

Other species concepts emphasize the unitywithin a species rather than the separatenessof different species

The morphological species concept definesa species by structural features

It applies to sexual and asexual species but

relies on subjective criteria


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The ecological species concept views aspecies in terms of its ecological niche

It applies to sexual and asexual species and

emphasizes the role of disruptive selection

The phylogenetic species concept: defines aspecies as the smallest group of individuals on

a phylogenetic tree It applies to sexual and asexual species, but it

can be difficult to determine the degree of

difference required for separate species


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Fig. 26-3

Species:Pantherapardus

Genus: Panthera

Family: Felidae

Order: Carnivora

Class: Mammalia

Phylum: Chordata

Kingdom: Animalia

ArchaeaDomain: EukaryaBacteria


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Bacteria

Archaea

Eukarya

Unikonta

Archaeplastida(incl. plants)

Rhizaria

Chromalveolata

Excavata

Fungi

Animals

Sponges

Metazoa

Silicea

Calcera

Ctenophora

Cnidaria

Aceola

Nematoda

Arthropoda

Echinodermata

Chordata

Platyhelminthes

Rotifera

EctoproctaBrachiopoda

Mollusca

Annelida

Domain Kingdom Phylum


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Jovelin et al., 2003

Caenorhabditis


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Caenorhabditis


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Caenorhabditis


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Caenorhabditis


12/50Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Biological Species Concept

The biological species concept states that aspecies is a group of populations whosemembers have the potential to interbreed innature and produce viable, fertile offspring;

they do not breed successfully with otherpopulations

Gene flow between populations holds the

phenotype of a population together



Reproductive Isolation

Reproductive isolation is the existence ofbiological factors (barriers) that impede twospecies from producing viable, fertile offspring

Hybrids are the offspring of crosses betweendifferent species

Reproductive isolation can be classified by

whether factors act before or after fertilization


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X

donkey horse

mule

(sterile)


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Prezygotic barriers

Habitat Isolation

Individualsof

differentspecies

Temporal Isolation Behavioral Isolation

Matingattempt

Mechanical Isolation Gametic Isolation

Fertilization

Reduced Hybrid Viability Reduced Hybrid Fertility

Postzygotic barriers

Hybrid Breakdown

Viable,fertile

offspring

(a)

(b)

(d)

(c) (e) (f) (g) (h) (i)

(j)

(l)

(k)

Prezygotic Isolation: no fertilization no mating gametes incompatible

Postzygotic Isolation: F1 hybrids inviable F1 hybrids sterile F2 (etc) hybrids inviable/sterile



Prezygotic barriers block fertilization fromoccurring by:

Impeding different species from attempting to

mate Preventing the successful completion of

mating

Hindering fertilization if mating is successful



Habitat isolation: Two species encountereach other rarely, or not at all, because theyoccupy different habitats, even though notisolated by physical barriers



Temporal isolation: Species that breed atdifferent times of the day, different seasons, ordifferent years cannot mix their gametes



Gametic isolation: Sperm of one species maynot be able to fertilize eggs of another species



Postzygotic barriers prevent the hybridzygote from developing into a viable, fertileadult:

Reduced hybrid viability Reduced hybrid fertility

Hybrid breakdown



Reduced hybrid viability: Genes of thedifferent parent species may interact andimpair the hybrids development



Reduced hybrid fertility: Even if hybrids arevigorous, they may be sterile


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Hybrid breakdown: Some first-generationhybrids are fertile, but when they mate withanother species or with either parent species,offspring of the next generation are feeble or

sterile

i i i f h i l i l S i C


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Limitations of the Biological Species Concept

The biological species concept cannot beapplied to fossils or asexual organisms(including all prokaryotes)

C 24 2 S i i k l i h


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Concept 24.2: Speciation can take place with orwithout geographic separation

Speciation can occur in two ways:

Allopatric speciation Sympatric speciation

All i (O h C ) S i i


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Allopatric (Other Country) Speciation

In allopatric speciation, gene flow isinterrupted or reduced when a population isdivided into geographically isolatedsubpopulations

Fig. 24-6


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g

A. harrisi A. leucurus

Th P f All t i S i ti


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The Process of Allopatric Speciation

The definition of barrierdepends on the abilityof a population to disperse

Separate populations may evolve

independently through mutation, naturalselection, and genetic drift


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ancestral population

geographic isolationmutation

fixation


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ancestral population

geographic isolationmutation

fixation

hybridization,novel (dygenic)

allele combination

E id f All t i S i ti


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Evidence of Allopatric Speciation

Regions with many geographic barrierstypically have more species than do regionswith fewer barriers

Fig. 24-7


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Mantellinae(Madagascar only):100 species

Rhacophorinae(India/SoutheastAsia): 310 species

Other Indian/Southeast Asian

frogs

Millions of years ago (mya)

1 2 3

1 2 3

100 80 60 40 20 0

88 mya 65 mya 56 mya

India

Madagascar


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Reproductive isolation between populationsgenerally increases as the distance betweenthem increases


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Barriers to reproduction are intrinsic;separation itself is not a biological barrier

Sympatric (Same Country) Speciation


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Sympatric (Same Country) Speciation

In sympatric speciation, speciation takesplace in geographically overlapping populations

Fig. 24-4h


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(f)

Bradybaenawith shellsspiraling in opposite

directions

Polyploidy


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Polyploidy

Polyploidy is the presence of extra sets ofchromosomes due to accidents during celldivision

An autopolyploid is an individual with morethan two chromosome sets, derived from onespecies

Fig. 24-10-1


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2n= 6 4n= 12

Failure of celldivision afterchromosomeduplication givesrise to tetraploid

tissue.

Fig. 24-10-2


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2n= 6 4n= 12


tissue.

2n

Gametesproducedare diploid..

Fig. 24-10-3


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2n= 6 4n= 12


tissue.

2n

Gametesproducedare diploid..

4n

Offspring withtetraploidkaryotypes maybe viable andfertile.


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x

fertilization (2n x 4n)

hybrid (3n)

meiosisgametes (1.5n ???)


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An allopolyploid is a species with multiplesets of chromosomes derived from differentspecies

Xenopus laevis Xenopus tropicalis


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Polyploidy is much more common in plantsthan in animals

Many important crops (oats, cotton, potatoes,

tobacco, and wheat) are polyploids

Habitat Differentiation


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Habitat Differentiation

Sympatric speciation can also result from the appearance

of new ecological niches

For example, the North American maggot fly can live onnative hawthorn trees as well as more recently introducedapple trees

Sexual Selection


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Sexual Selection

Sexual selection can drive sympatric speciation

Sexual selection for mates of different colorshas likely contributed to the speciation in cichlid

fish in Lake Victoria

Fig. 24-12


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EXPERIMENT

Normal lightMonochromatic

orange light

P. pundamilia

P. nyererei

Allopatric and Sympatric Speciation: A Review


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Allopatric and Sympatric Speciation:A Review

In allopatric speciation, geographic isolation restricts gene

flow between populations

Reproductive isolation may then arise by natural selection,genetic drift, or sexual selection in the isolated populations

Even if contact is restored between populations,interbreeding is prevented

In sympatric speciation, a reproductive barrier isolates asubset of a population without geographic separation fromthe parent species

Sympatric speciation can result from polyploidy, naturalselection, or sexual selection


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