Ma.Luisa V. CuaresmaBiological Sciences

Department

Chapter 3Evolution, Systematics and Phylogeny

Organic evolution•A change in the genetics of a population over time (generations).• Population-all individuals of the same species living in a defined area at the same time.

• 2 levels:– Microevolution –

small genetic changes within population.

– Occurs through several mechanisms.

– The best known is natural selection.– Natural selection is

evolution that occurs because individuals with some traits survive and reproduce better than do individuals with other traits

• Fitness – refers to degree to which individuals with certain traits are expected, on average, to survive & reproduce.

• Adaptation- refers either to the process of natural selection, or to a trait that has evolved through natural selection.

Natural selection is simply the logical result of four features of living systems:1. variation - individuals in a population vary from one another 2. inheritance - parents pass on their traits to their offspring genetically 3.selection - some variants reproduce more than others 4.time - successful variations accumulate over many generations

Darwin’s Four Postulates

• More young are produced each generation that can survive to reproduce.

• Individuals in a population vary in their characteristics.

• Differences among individuals are based on genetic differences.

• Individuals with few strong characteristics survive & reproduce better.

There are four properties of the population, called Darwin’s Four Postulates that together result in Natural selection…………….

If these four postulates are all true of a population, they result in natural selection…….

• Those individuals with higher fitness end up being the ones who survive each generation, and as a result, reproduce more

• Since the traits are genetic, they passed on to the next generation, and therefore become more common than they were in the previous generation.

Macroevolution• Evolution within population• Series of microevolution• Speciation – the formation

of new species when one ancestral species evolves more than 1 typical descendant.

• Since speciation occurs when one species evolves into more than 1 new species, it increases the number of species that exist.

Figure 1. The hierarchical relations between Macroevolution (Ma) and Microevolution (Mi), and the Environment (E). Mi consists of Organisms (O) and their Interactions (I) together with factors from the Environment. Examples A-G illustrate the levels of environmental influence:

A. Mutation caused by chemical, thermal or radioactive interference.

B.Heat shock on developing zygotes. C.Local adaptation to a niche. D. Climatological change causing

migration. E. Geographical isolation. F. Environmental changes that cannot

be adapted to for historical or developmental reasons (causing extinction).

G. Changes that affect speciation rates and type.

Systematics

• Study of phylogenetic relationships• Active area of evolutionary biology• CLADISTICS – special area of systematics that

studies phylogenetic relationships based on shared or derived traits.

• Applications:– Provides in-depth knowledge about evolution

of traits within groups.– Traces the origin & spread of diseases

especially zoonotic diseases (animalhuman).

– Relation of species helps in formulation of advocacy programs for conservation of species.

2 Approaches in studying relationships of species…

1. Fossils – provide a preserved record of the history of life forms; portrays the phylogeny of life.

2.Hierarchical pattern of homology – different species that share the same structures depicts that they may have evolved from the same ancestor. (common features / traits shared close relationship of species; less traits shared distant relationships)

• CLADISTICS – answers those gaps in systematics that do not rely in the number of shared characteristics.

Phylogeny

• Shows the pattern of evolutionary relationships or history of speciation.

• Represented by a TREE that shows where points of ancestors speciated into 2 new species.• Refers to the evolutionary relationship

among species or to the family tree of all life, indicating how all living things are related, typically diagrammed as a tree.

Phylogenies can be drawn in several different ways…..

A B C D E F G H I J K

Phylogenetic Tree

BA

C

D

E

Sala

man

der

Frog

Mou

se

Bird

Liza

rd

Snak

e

HORIZONTAL FORMAT

Legend:

A – ancestor to all modern species

B – ancestor to salamander & frog

C – ancestor to mouse & D (bird, lizard, snake)

D – ancestor to bird & E (lizard, snake)

E – ancestor to lizard & snake

SALA

MAN

DER

FRO

G

MO

USE

BIRD

LIZA

RD

SNAK

E

A

B C

D

E

SLANT FORMAT

Legend:

Every line that branches into species above the branch (descendants) arised from species below the branch point (ancestor).

Ex: Trees on the right shows the relationship between mouse, bird, lizard, snake.

Trees on the left shows relationship between salamander and frogs.

Primitive and Derived Traits

• 1. Primitive Traits (plesiomorphic characters) are characters of organisms that were present in the ancestor of a certain group of related organisms– Ex: Ancestor of lizard, bird,

alligator = scaly skin; 3-chambered heart; (+) teeth; (-) wings

• 2. Derived Traits (apomorphic characters) are characters of organisms that have evolved within the group or related organisms that were not present in the ancestor.– Ex: birds, lizard, alligator =

(+)gizzard; 4-chambered heart, feathers, (-) teeth; wings

BIRD

LIZA

RD ALLI

GAT

OR

SYNAPOMORPHY

• Character/s is present in immediate ancestor only but not in the earliest ancestor.

• Derivative traits

SYMPLESIOMORPHY

• Character/s is present in immediate ancestor and earlier ancestor.

• Primitive traits

Ex: Birds developed wings but lost the primitive 4 legs that have been present with the birds’ ancestor.

OUTGROUP COMPARISON

• Method in determining primitive vs. derived traits.

• Determine 1 or more species that are relatives of the group of interest (ingroup), and the species equally related to all members of the group of interest (outgroup).

• Character/s of comparison found common in both groups is considered Primitive trait, while, character/s found common only in one group but absent to other is considered as Derived trait.

Outgroup comparison

A

B

Amphioxus•(+)Cartilage skeleton•(-) jaws•(-) fur

Shark•(+)Cartilage skeleton•(+) jaws•(-) fur

Trout•(+)bone skeleton•(+) jaws•(-) fur

Frog•(+)bone skeleton•(+) jaws•(-) fur

Mouse•(+)bone skeleton•(+) jaws•(+) fur

•Bony skeleton(+) trout, frog, mouse; (-) sharkTherefore, ancestor B had evolved a bony skeleton.•In general, provides evidence of ancestry that bony skeleton as a phylogenetic trait traced from ancestor B to trout, frog, mouse.

Analyze the figure below and answer the following questions.

A

B

Amphioxus•(+)Cartilage skeleton•(-) jaws•(-) fur

Shark•(+)Cartilage skeleton•(+) jaws•(-) fur

Trout•(+)bone skeleton•(+) jaws•(-) fur

Frog•(+)bone skeleton•(+) jaws•(-) fur

Mouse•(+)bone skeleton•(+) jaws•(+) fur

QUESTIONS……….

1. Which is/are the ingroup/s?2. Which is/are the outgroup/s?3. What characteristic is present both

in the ingroup and outgroup?4. Which is considered a primitive

characteristic?5. How would you account on the

presence of fur in mouse species only?

ANSWER…….

1. shark, trout,frog, and mouse.2. Amphioxus3. Cartilage skeleton4. Cartilage skeleton5. The fur evolved in the ancestor to

just this species