Systematics

2. Advanced Ornithology
by
Maryam Riasat
SYSTEMATICS

3. Systematics
 The challenge of reconstructing the history of
life belongs to a field of scholarly endeavor
called systematics
 Systematics are scientists who evaluate
evolutionary relationships among organisms
through comparisons of fossils, preserved
specimens, behavior, and increasingly the
genetic code of life itself, DNA

4. Species and Speciation
The diversity of life is a result of three
evolutionary processes
o Phyletic Evolution:
The gradual change of a single lineage
o Speciation:
The splitting of one phyletic lineage into two
or more
o Extinction:
The termination of a lineage

5. Species
 Species are the fundamental units of
biological classification
 Species are groups of interbreeding natural
populations that are reproductively isolated
from other such groups
 Birds species have characteristics sizes,
shapes, songs, colors, ecological niches, and
geographical ranges

6. Speciation
 Speciation is the formation of new and distinct
species in course of evolution
 The evolutionary legacy of the earliest birds
includes roughly 100,000 species of which only 1
in 10 is now with us
 Behind this legacy lies the process of speciation:
The multiplication of species through the division of
one species into two or more as a result of genetic
divergence of isolated population

7.  Geographical separation of populations
reduces the exchange of genes, thereby
allowing independent divergence and enable
speciation
 Most species of birds evolve as geographical
isolates
 Reproductive isolation may sometimes play a
role

8.  Birds populations become geographically
isolated in two principal ways
o Pioneering individual birds may colonize an
oceanic island and thus are separated from
their main population
o Fragmentation of habitats can also isolate the
bird populations
 Remnant populations

9. Classification and phylogeny
 Classification is the arrangement of organisms
in taxonomic groups in accordance with the
observed similarities
 Ornithologiae by Francis and John, published
in 1676 was the first formal classification of
birds
 Nearly a century later, Linnaeus used this
elementary classification as the model for
subsequent classifications

10.  These early efforts, however, classified birds
according to superficial adaptations to
aquatic versus terrestrial habitats rather than
according to evolutionary relationship
 Charles Darwin’s theory of evolution by
natural selection transformed the basis of
systematics into one based on common
ancestries

11. Taxonomic characters
 Reconstruction of the evolutionary history of birds
requires the analysis of specific traits, called as
characters
 In common ancestry these characters are called as
shared characters
 Conservative characters – that do not easily
change in the course of ecological adaptation
 These are of greatest value because they retain
clues to ancestors
 A constant challenge to accurate reconstruction is
the possibility of convergence between unrelated
species

12.  Thomas H. Huxley helped to
lay the foundation of
modern systematics in birds
with his study of the
arrangement of the bones
of the avian bony palate
 Skeletal partition between
the nasal cavities and the
mouth
 Succeeding generations of
the ornithologists added
new characters to the
taxonomic tool kit

13.  Form of the nostrils
 Structure of the leg muscles
 Tendons of the feet
 Arrangement of toes
 Morphology of vocal apparatus
 Behavior
 Vocalization
 Protein yielded clues
 Plumage patterns

14. Unique characters
Unique characters define related groups of species
with common ancestors
Song Birds
Order Passeriformes have several unique characters
i.e.
Preen gland with a unique nipple
Unique sperms
Specialized perching foot with a large hallux
Uniquely arranged deep tendons
Simplified foot muscles

15. These features indicate that members of the order
Passeriformes evolved from a common ancestor i.e.
they are monophyletic

16. Cladistics
 Categorized in groups (clades) based on
hypothesis of most recent common ancestry
 Cladistics analysis enables ornithologists to
separate primitive characters from common
derived characters and to sort them rigorously
across taxa
 Phylogenetic studies require homologous
characters which can be traced to the same
feature in the immediate common ancestor of
both organisms
 Exist in both their original and their changed
states

17. Flipper like wings of penguins evolved from the
wings of their petrel ancestors
o Wings of petrels represent ancestral/primitive
character state
o Flipper like wings of penguins represent
advanced/derived state

18. If two species have a character state in common,
we can hypothesize that they have a common
ancestor with the same character state
Example:
o The flipper like wings common to all penguin
species correspond to their common ancestry
(Hypothetical ancestor)
o We assume that the cladogram with the fewest
evolutionary changes is the most likely or most
plausible phylogeny