3, 4 & ...?
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
Biological Species Concept
Phylogenetic Species Concept
Sympatry vs. Allopatry
Traditionally- the BSC, as defined by Mayr in 1970 – “groups of
interbreeding natural populations reproductively isolated from other such
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?
Underlying paradigm is natural selection – species accumulate heritable
adaptations to their environment.
Populations are separated
Separate populations will be under different selective regimes
Genetic differences accumulate
Subsequent sympatry tests limits of reproductive isolation.
Hybridization zones – stable or not?
33% N.A. species have recognized subspecies
clines - balance between selection and gene flow
environmental influences on phenotype – transplant experiments
by Fran James
can be measured with new biochemical techniques
Gene flow determined by movement of young from nest to eventual breeding
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
Colonial species along coastlines
Nonmonogamous breeding systems (few males dominate
contribution to next generation – leks)
small populations on islands have founder effects –
evolve faster than larger continental pops.
Vicariant events likely to lead to slower speciation than
Island colonization – genetic founder effects, etc.
Secondary contact and hybridization
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”
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
Stable hybrid zones
Sinks constantly replenished by immigrants from parent populations,
“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
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
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
levels (species, genus, family) reflect accumulated changes through
First convincing avian classification by Hans Friederich Gadow - 1892-3
(based on 40 anatomical characters). Refined by many, including Alexander
shared through common ancestry
Passerines share structure of oil gland, sperm, and arrangement
of muscles and tendons in feet
conservative characters best –
not as likely to be convergent - how to tell? look at fine
important in bird systematics:
leg muscles and tendons of feet
arrangement of toes
scutes on tarsi
flight feathers on wing (remiges)
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
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
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 1st name and year of naming
v Type specimens
v 19th century plethora of exploration and collection led
to chaos with lots of people naming the same things. Rules – International
Code of Zoological Nomenclature
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
v Classifications include nested taxonomic levels and are usually
linear. More than 1 classification can accurately be applied to a given
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
v Good characters are often fine structure, not plastic ones like
feeding apparatus and plumage….