Transcript Biological Species

Fish History & Classification
Chapter 11
http://main.nbii.gov/portal/community/Communities/Geographic_
Perspectives/Mid-Atlantic/Featured_Projects/EKey__Electronic_Key_for_Identifying_Freshwater_Fishes/
Part I: Early Fishes
Ostracoderms and Placoderms
Refresher of geologic time scale
• Paleozoic Era 570 - 240 million years
before present (mybp)
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Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
570 - 505 mybp
505 - 438 mybp
438 - 408 mybp
408 - 360 mybp
360 - 290 mybp
290 - 240 mybp
Refresher of geologic time scale
• Mesozoic Era 240 - 63 mybp
– Triassic
– Jurassic
– Cretaceous
240 - 205 mybp
205 - 138 mybp
138 - 63 mybp
• Cenozoic Era 63 mybp - present
– Paleogene
– Neogene
63 - 24 mybp
24 mybp - present
What happened when?
• Notice where major
evolutionary events
occured.
• Ancestors of fish did
not happen spontaneously.
• Continuous development
was (is) working on each
taxonomic group all
the time.
Ostracoderms (shell-skins) - earliest
vertebrates in fossil record
• Originated in late Cambrian Period? (> 500
mybp) - first record is from Ordovician
• Were abundant and diverse through the
Ordovician and Silurian Periods (approx.
100 million years)
• Became extinct by the late Devonian Period
(approx. 380 - 400 mybp)
What group preceded
Ostracoderms?
• Earliest vertebrates probably like
modern Cephalochordates (Amphioxus)
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Bilateral symmetry
Free-swimming (perhaps neotonous larva)
with cephalic sensory structures
with branchial gill apparatus
without bone, jaws or paired fins
Traits of Ostracoderms*
• Boney armor - first record of bone in fossils protection from predators
• Internal skeleton - made of cartilage
• Heterocercal tail
• Lacked true jaws - were pump-filter feeders
• Lacked paired fins - weak swimmers
• Benthic habitat
• Small size - none longer than 15 cm
Ostracoderm classification
• Two classes:
– Class Pteraspidomorphi (sp. diplorhina = “two
nares”)
– they literally had two separate olfactory bulbs
in the brain.
– those with a different shell, i.e. dermal armor
Ostracoderm classification
– Class Cephalaspidomorphi (“single nostril”)
– jawless fish
Success of Ostracoderms
• First use of bone
– for protection, not support
– possibly used as auxiliary supply of Calcium?
• Use of filter feeding to exploit common and
abundant food source: plankton and
suspended organic matter
Limitations (failures) of Ostracoderms
• Habitat limitations
– restricted to benthos (no kiddin’!?!)
– weak swimmers due to heavy armor
• weight
• inflexibility
• Food limitations
– no jaws - restricted to plankton, suspended
organics - slow growth
Fate of Ostracoderms*
• Extinct within 100 million years - by late Devonian
• Lineage debated...
– possibly lampreys (Petromyzontiformes)
– possibly Chondrichthyes
– possibly Osteichthyes
How good were they?
• Ostracoderms were key to vertebrate evolution!
• Gave rise to jawed vertebrates!
• Jaw evoluation considered as the single "greatest
development in vertebrate evolution“
(Romer (1962)
I know I like mine....
Placoderms - earliest gnathostomes
(jawed vertebrates)
• Originated after the
Ostracoderms:
– Originated in Silurian
Period (440 mybp)
– Abundant and
Diverse in Devonian
Period
– Extinguished in
Carboniferous Period
(350 mybp)
Two key traits account for
Placoderm success:
• True jaws
– opened new realm of food sources - larger prey
items vs. filter-feeding - allowed faster growth
to larger sizes
• Paired fins
– coevolved with acquisition of jaws:
• greater control of movement
• more effective pursuit and capture of prey
Additional traits first appeared in
Placoderms
• Bony dermal plates (produced by dermal
cells) with three layers:
– enamel layer - outer surface - hard & shiny
– spongy layer - large vacuoles
– lamellar layer - layered strata with flat vacuoles
• Bony internal skeleton
Traits shared with Ostracoderms
• Negatively buoyant (due to heavy plates)
• Occupied benthic and near-benthic habitats
(epi-benthic)
• Dorsoventrally depressed (flat)--common
among benthic fishes
• Strictly marine
Differences from Ostracoderms
• Placoderms reached larger sizes
– up to 10 m (33 feet) in length
– why? - food source, mobility
• Placoderms had slightly
lighter and more flexible
(articulated) armor
Success of Placoderms
• Diversity:
– greater than any other group of fishes present in
Devonian
– seven orders within single class
• Duration:
– 440 - 350 mybp
Fate of Placoderms
• Probably evolutionary “dead-end”
• Plesiomorphies with Chondrichthyes &
Osteichthyes: jaws, paired fins, internal
skeleton - suggest common ancestor
• Apomorphies: armor, jaw structure,
depressed form - suggest they are NOT
ancestral to Chondrichthyes & Osteichthyes
Part II:
Classification Specifics
REM:
Taxonomy – The theory and practice of describing,
naming, and classifying organisms.
Systematics – The classification of living organisms
into hierarchical series of groups emphasizing their
phylogenetic interrelationships.
Nomenclature – The system of scientific names applied
to taxa.
Why is Classification Important?
• Communication- “Okay...I get that...”
• Prediction- “Don’t get that...”
Why is Classification Important?
• Communication
- apply consistent names to organisms
- Genus and species name for each organism is unique
- same name used everywhere
- important in keeping track of losses of biodiversity
- know which and how many species at certain time
to how severe the loss is in the present (management)
- Ex. Western United States = water habitats altered
Why is Classification Important?
Why is Classification Important?
• Prediction
- reflects evolutionary history
- members of a group will share a more common
ancestor with each other than with members of
other groups
- will have inherited similar traits
- use shared history to infer that closely related
species share similar traits
Suborder Anabantoidei
- Gouramies
- possess apparatus that allows extraction of O2
gulped air. (labyrinth organ)
- Betta
- systematically classified as gouramies
- possess apparatus?....yep!
- able to live in low O2 environments
Why is Classification Important?
• Prediction (cont.)
- environment
- can impose an adaptive regime on species that
live there
- results in shared features of unrelated species
-Gars and pikes
- similar body form due to ecological niche
Taxonomic Categories
Phylum -- Chordata
Subphylum Vertebrata
Superclass Gnathostomata
Grade Teleostomi
Class -- Osteichthyes
Subclass -- Actinopterygii
Infraclass -- Neopterygii
Division -- Teleostei
Order -- Perciformes
Family -- Centrarchidae
Genus -- Micropterus
Species -- salmoides
Taxonomic Categories
- Current system based exclusively on shared
common ancestry
- All categories that taxonomists apply to fish are
artificial (descriptive) except for one…species
-Species is a real entity (biological)…other
categories are artificial assemblages
- most biologists believe that species are
real entities that exist in nature.
What is a species?
Biological Species Concept (Mayr 1940)
Biological Species : A group of actually (or potentially)
interbreeding natural populations genetically isolated
from other such groups by one or more reproductive
isolating mechanisms.
- most commonly applied species concept
- Some associated problems
What is a species?
Problem:
- hybridization
--fish are notorious for this practice
--hybrids are often sterile (or thought to be! (HSB?)
--some are fertile and able to backcross with
either parent
Why are there so many species?
- random genetic changes
- differences in the selective environment
- Anagenesis: change in a species over time
-- species exist as a single population and whole species
will change over time and not branch off into
multiple discrete species.
Why are there so many species?
- formation of multiple species from a single
ancestral species is due to isolation of the population into
distinct populations or gene pools.
Why?
- each population undergoes anagenesis and
eventually individual populations are distinct
enough to be recognized as separate species.
Why are there so many species?
What causes isolation?
- vicariant event: a geological or climactic event
- Isthmus of Panama = the most studied
-- around 3.5 mya
-- tropical Atlantic separated from tropical Pacific
Allopatric speciation: single species diverge into two species
in separate geographic locations
(squirrels/mountains)
Why are there so many species?
- Sometimes populations of closely related species will
coexist in an environment.
- Genetic independence achieved through premating
and postmating reproductive isolating mechanisms
Why are there so many species?
- Postmating
- hybrid sterility
- inviability
Why is hybridization rampant among fish?
- external fertilization
- eggs and sperm drift in the proximity of gametes from
a different species
Avoidance:
- sexual selection: partners choose appropriate mates
- males are brightly colored to attract females
Why are there so many species?
- Premating
- sexual selection: partners choose appropriate mates
- males are brightly colored to attract females
- males especially colorful in genera that have a large
number of coexisting species
-Ecological differences
- limits degree of competition
- food preference, timing and location of spawning
African Cichlids
North American Darters
Linnaean Classification
Family
Genus 1
Species 1
Species 2
Genus 2
Species 3
Species 1
Species 2
Genus 3
Species 3
Species 1
Species 2
Linnaean Classification
-Rules of Nomenclature
- still named the same way as Linnaeus and Artedi did in 1758
- genus name is always capitalized
- species name is lower case
- oldest valid name sticks with the species
- genus names are unique among all biota
- species names are unique within a genus
- International Code of Zoological Nomenclature
- American Fisheries Society (US)
Phylogenetic Classification
Genus 1
Genus 3
Species 1
Species 2
Species 1
Genus 2
Species 2 Species 3 Species 1 Species 3
Species 2
Phylogenetic Classification
- Cladistics
- lumps together groups that are assumed to share a
common ancestor.
- Clade: group that contains an ancestor and all of its
descendents.
- Guidelines defining clade from Willi Hennig (bug man)
- shared derived characters
-derived character: is different from some primitive
common ancestor.
Character State: Gas Bladder
Physostomous
Physoclistous
Phylogenetic Classification
Terms
- homologous: characters that are alike in state due to
shared common ancestry
- homoplasy: characters that are alike in state for other
reasons
- independent origin: a trait can evolve
independently in two different lineages
e.g., countercurrent heat exchangers in
mako sharks and tuna.
Phylogenetic Classification
Terms
- homoplasy (cont.)
- reversion: a character may revert to a more
primitive state.
e.g., some eels lack scales and paired fins
like primitive agnathans. Ancestors
of eels possessed scales and paired fins,
but were lost, thus reverting to the
more primitive state.