Lectures 3, 4 & ...?

21-?? January 2003

Species and Speciation--Where Did All those Birds Come From?

Lecture 4 - 21 January 2003

Species and Speciation – What are species and how do they arise?

Chapter 22 in Gill

Key terms

Biological Species Concept

Phylogenetic Species Concept

Sympatry vs. Allopatry

Vicariance

“diagnosable”

leks

polytypy/polytypic

assortative mating

heritability

sister species

Species definitions

Traditionally- the BSC, as defined by Mayr in 1970 – “groups of interbreeding natural populations reproductively isolated from other such groups.”

1. Guesswork involved

Challenged by the Phylogenetic Species Concept, which recognizes any isolated, diagnosable population as a species.

9,600 species goes to 20,000+

recognizes separate evolutionary tracks of isolated populations

important for conservation?

The process

Underlying paradigm is natural selection – species accumulate heritable adaptations to their environment.

Populations are separated

Island colonization

Vicariant event

mountains

rivers

glaciers

Separate populations will be under different selective regimes

Genetic differences accumulate

Subsequent sympatry tests limits of reproductive isolation.

Ecological

Social/behavioral

Hybridization zones – stable or not?

Geographical variation

33% N.A. species have recognized subspecies

complicated by

clines - balance between selection and gene flow

environmental influences on phenotype – transplant experiments by Fran James

can be measured with new biochemical techniques

allozymes

mtDNA

Population structure

Gene flow determined by movement of young from nest to eventual breeding territory

Philopatric species stick close to home

Some species females return to natal territories, in others it’s the males that move

High dispersal rates mean large effective population sizes (demes)

low effective population size increases chances of random events fixing genes.

Colonial species along coastlines

Nonmonogamous breeding systems (few males dominate contribution to next generation – leks)

small populations on islands have founder effects –

sampling

inbreeding

evolve faster than larger continental pops.

Geographical Isolation

Vicariant events likely to lead to slower speciation than

Island colonization – genetic founder effects, etc.

Secondary contact and hybridization

Genetic introgression

Audubon vs. Myrtle warblers

secondary contact 7500 ybp at end of Wisconsin glaciation

contact in narrow mt. passes so exchange of genes slow, but now 150 km wide

lead ornithologists to lump the two forms into “yellow-rumped” warbler

11 of 14 pairs of species that meet in the great plains hybridize

where stable hybridization zones exist, the BSC is applied and the species lumped

where limited hybridization occurs with most individuals distinct (e.g. Lazuli and Indigo Buntings) species are recognized as distinct.

Stable hybrid zones

Sinks constantly replenished by immigrants from parent populations, or

“bounded superiority” where ecological conditions are intermediate so intermediate individuals formed by interbreeding are superior to either parental form.

Problems with hybrids

Infertility – often the heterogametic sex (females in birds)

Blended characters lead to “diluted sex appeal”

Taxonomy - naming vs. systematics - scientific study of evolutionary relationships

Morphology

behavior

ecology

Tree of genealogical relationships – phylogeny

Review our concept of species –

biological - Review def of species: Groups of interbreeding natural populations that are reproductively isolated from other such groups (Mayr)

# spp 19,000 at turn of century,

down to 8,600 by 1940s

now ca. 9,600

phylogenetic - Cracraft, McKitrick, Zink

Classification

provides a systematic scheme for communication

is based on hypotheses of sequences of evolutionary relationships - note that Darwin provided the theoretical basis for systematics (vs. just taxonomy)

levels (species, genus, family) reflect accumulated changes through natural selection

First convincing avian classification by Hans Friederich Gadow - 1892-3 (based on 40 anatomical characters). Refined by many, including Alexander Wetmore.

Taxonomic characters

shared through common ancestry

Passerines share structure of oil gland, sperm, and arrangement of muscles and tendons in feet

conservative characters best –

reflect ancestors

not as likely to be convergent - how to tell? look at fine structure

important in bird systematics:

bony palate

nostrils

leg muscles and tendons of feet

arrangement of toes

scutes on tarsi

flight feathers on wing (remiges)

more recently

behavior

plumage of young

calls and morphology of syrinx

proteins and genes

rapidly evolving characters worst

feather color, ornamentation - sexual selection, bill shape

why? the rules of the game keep changing

it always takes the same thing to fly

it often takes something different (novelty?) to attract a mate

bill shape changes with food--Grant’s work on Galapagos

¨ must be homologous - not analogous

v Taxonomy vs. systematics (See chapter 3 in Gill for more on systematics)

Ø Taxonomy is naming

Ø Systematics is the formulation and testing of hypotheses about evolutionary histories—family trees

v 4 parts to a scientific name

Ø Parus major Linnaeus 1758

§ Genus is a noun and unique in the zoological world. Species is an adjective and often repeated-but never within a genus.

§ Names needn’t be descriptive or accurate! Examples abound

Ø Author of 1^st name and year of naming

v Type specimens

v 19^th century plethora of exploration and collection led to chaos with lots of people naming the same things. Rules – International Code of Zoological Nomenclature

v Systematics

Ø Introduce concept of clades

Ø Standard sequence vs. phylogenies

Ø Every group has a unique phylogeny, but this is impossible to know with certainty because of the inadequacies of the fossil record

v Phyletic change (along one branch in a clade vs. phylogenetic branching

v Classifications include nested taxonomic levels and are usually linear. More than 1 classification can accurately be applied to a given phylogeny.

v Standard sequences are heuristic—they aid in learning, information retrieval, etc.

Ø Currently most use the system began by Gadow in 1892, modified by Stresemann, , Wetmore, and Peters (Checklist of Birds of the World).

Ø But now Sibley and Ahlquist have challenged much of the phylogenies of the prior group.

v Shared derived characters

v Have to be homologous, not analogous – convergent evolution can confuse!

v Parsimony

v Good characters are often fine structure, not plastic ones like feeding apparatus and plumage….