Evolution II - contents

• Macroevolution and Microevolution

• Phylogenetic trees and cladistics

• Examples of convergent evolution

• How to identify cases of convergent evolution

Definitions• Macroevolution: A term for the evolution of great

phenotypic changes, usually great enough to allocate the changed lineage and its descendants to a distinct genus or higher taxon (Futuyma). Examples: patterns of the divergence of lineages, families or classes; patterns of emergence of new lineages (e.g. mammals, dinosaurs) or their disappearance.

• Microevolution: A term for slight, short term evolutionary changes within species (Futuyma)

• Examples: changes of allele frequencies within a species over time, emergence of population differences.

Macro-and Micro-evolution

Patterns of macroevolutionPhyletic evolution (anagenesis) envisions gradual divergence of a lineage as the bell-shaped mean of successive populations changes, until a new species if formed. Punctuated equilibrium (cladogenesis) envisions long periods of more or less unchanging species persistence, suddenly interrupted by speciation, producing a new species.

Pace of macroevolution• For some biologists, each pattern implies a different rate of

new species appearance. Punctuated equilibrium produces new species relatively rapidly. Phyletic evolution produces new species more gradually and sometimes termed “Gradualism.”

Mode and tempo of evolution

• Gradual and rapid appearance of new species occurs in the fossil record.

Cladogenesis• Where sudden changes occur,

they can be represented with an angular, branching phylogenetic tree (cf. phyletic evolution, figure 12.7 or slide 4). Each independent lineage produced is a clade, shown here as Clade 1 and Clade 2. Vertical sections represent more or less unchanging persistence of a species; branch points represent the time of speciation where populations diverge and become two distinct species. Time runs upward; species divergence is indicated along the horizontal scale. The balloons show details of the phylogeny in a species before speciation (light shading), at a branching point of speciation wherein two species form (light and dark shading), and the subsequent fate of each species thereafter.

Definition cladistics

• Dividing (categorising) organisms based on quantitative analysis of biological traits.

• Building trees based on similarity between species: similar species on short branches in close proximity, distantly related ones on remote, long branches

• A clade is a lineage within a tree (or cladogram) and contains a group of species with a monophyletic origin

• A phylogenetic tree is a branched diagram that recaptures the history of a set of species

Taxonomic units above the species level

• Species: Apis mellifera• Genus: Apis• Family: Apidae• Order: Hymenoptera• Class: Insecta• Phylum: Arthropoda• note that these categories (except the species)

have no clear biological basis, except that they should be monophyletic.

A monophyletic group is one which contains a common ancestor and all its descendents

A paraphyletic group is one which contains a common ancestor and some, but not all of its descendents

A polyphyletic group is a group of taxa that are derived from two or more ancestral forms not common to all members

• Under a system of phylogenetic classification, we could name any clade on this tree. For example, the Testudines, Squamata, Archosauria, and Crocodylomorpha all form clades.

• However, the reptiles do not form a monophyletic clade, as shown in the cladogram. That means that "reptile" is not a valid phylogenetic grouping, or we would have to start thinking of birds as reptiles.

• Consider non-avian dinosaurs (which is what people mean by the informal term ``dinosaurs''). This is a paraphyletic group, because it can't be defined simply as ``this animal plus all its descendants'', but must be described as one clade minus another: in this case, Dinosauria minus Aves.

• Reminder: a paraphyletic group is one which contains a common ancestor and some, but not all of its descendents

Are warm blooded animals (birds and mammals) a monophyletic taxon?

• In other words, did warm-bloodedness evolve once in the common ancestor of birds and mammals? No – they

are polyphyletic: a totally unnatural assemblage of animals!

What came first, the chicken or the egg?

Convergent evolution

• Evolution of similar features independently in different evolutionary lineages, usually from different antedecent features or by different developmental pathways

Convergent evolution – Cacti and other prickly plants

• Different families of desert plants have evolved similar adaptations to the desert’s dry, hot conditions - namely, succulent shoots with spines. Two such plant species are shown from Africa. The third, from the New World, is the endemic member of the true cactus family (Cactaceae).

Convergent evolution - mammals• Australian marsupials

resemble placental mammals in the rest of the world. Within the relative isolation of Australia, the marsupials entered similar habitats as counterparts among the placentals elsewhere. Under similar selective pressures, similar features and ecological lifestyles evolved, but upon a marsupial theme.

Six legs in insects – have they evolved multiple times by

convergence?

Convergent evolution - wings

•

Are insects red-blind? Convergent evolution of red sensitivity in several lineages

From: Chittka 1996Naturwissenschaften

Lens eyes exist in vertebrates, many molluscs, some medusas,

some annelids, and some cephalopods

Development of vertebrate and Cephalopod eyes

Cephalopod Vertebrate (everse) (inverse)

Public lecture series on insect visionWednesdays 6pm Skeel Lecture theatre

• Thomas Döring Queen Mary, University of London: Tricks, traps, and treatments: insect vision in agriculture.

14th February 2007• Claire Rind University of Newcastle: Locust

motion detectors for collision avoidance in cars.21st February 2007

• Almut Kelber University of Lund, Sweden: How nocturnal insects see in dim light.28th February 2007

Practical this Thursday!!

• Walter Besant Building, 2nd floor 15/02/2007, at 2pm

Evolution II - contents

• Define Macroevolution and Microevolution

• What do phylogenetic trees represent

• Examples of convergent evolution

• How to identify cases of convergent evolution