Avian Evlution

Natural Selection

Differential survival and reproduction of individuals due to differences in phenotype

Four necessary conditions of natural selection:

1. Variation in a population

2. That variation is heritable

3. Differences in reproductive success

4. That reproductive success depends on that heritable variation

Crypsis

Crypsis: patterning or coloration that allows a bird to remain concealed by blending into its environment.

Many adaptations are under strong natural selection

• Bill shape

• Wing shape

• Foot shape (think talons, swimming feet)

• Plumage (for camouflage)

• Skeleton (for flight)

• Lungs (more efficient)

Fitness

The relative success of an individual, compared with other individuals of the same population, in passing along their own genes to later generations

Sexual Selection

Differential survival and reproduction of individuals due to differences in phenotype, due to preferences by one sex for characteristics in the other sex

Inter-sexual selection:

individuals selecting for traits in members of the opposite sex

Intra-sexual selection:

competition among members of the same sex for a mate

Why be “choosy” about a mate?

Honest signal (choosing a high-quality mate) • Direct benefits for the other sex • Better genes passed on to offspring

Runaway sexual selection

Sexual preference in at least one of the sexes (usually in females) • A corresponding reproductive advantage to the preference

Extended Phenotype

When an organism’s genes affect structures and behaviors expressed outside the physical body. (birds who build elaborate mating displays).

Artificial Selection

• Selection imposed by humans, when we choose which phenotype will breed • Often used to select for better food production or for ‘fancier’ / ‘friendlier’ phenotypes

Speciation

• The evolutionary process by which one lineage splits into multiple descendant lineages

• Usually in allopatric populations (allopatric speciation)

• Allopatry can be due to vicariance or dispersal/colonization

Allopatric Speciation

Populations in different places diverge

What about Sympatric Speciation?

• Extremely rare, at least in birds • Standards for evidence are very high, and rarely met

(EX. Brood parasites, target mated with same vocalizations)

Classification

How do we define what a species is?

Taxonomy

The practice of applying names to organisms

Species

• a fundamental category of biological organization

Species Complex

Complex species is defined as a group of organisms that were initially classified as a single species but are later revealed to be a species complex,

Species Concepts

Different philosophies for deciding at what point along this continuum we can call the two lineages different species

Application of a species concept to real data is Species Delimitation

Biological Species Concept (BSC):

Members of populations that actually or potentially interbreed in nature. Emphasis is on reproductive isolation

Phylogenetic Species Concept (PSC):

An irreducible group whose members are descended from a common ancestor and who all possess a combination of certain defining, or derived, traits

Unified Species Concept:

Separately evolving metapopulation lineages

Taxonomy

• The practice of applying names to organisms

• Established by Carolus Linnaeus (Carl von Linné)

• Stability is key (for ease of communication)

• The Principle of Priority – the first name applied to a taxon is the valid one. All subsequent names are synonyms

The Type Concept

A specimen to which a name is tied • e.g. holotype, paratype, syntype, neotype, lectotype

The principle of priority

The Principle of Priority – the first name applied to a taxon is the valid one. All subsequent names are synonyms.

Nominate

The oldest names subspecies within a species