Transcript BIOLOGY 2210 Biology of the Vertebrates 7 March

Evolution and Systematics
Meganosed fly carrying pollinaria
to Pelargonium suburbanum
Evolutionary trends; extinctions (Chapt. 15)
SUDDEN CHANGES?
• Richard Goldschmidt (1940) suggested that
large (“systemic”) mutations could produce
rare “hopeful monsters” that could endure
• Casarea, Bolyeria (Serpentes: Boidae) on
small island near Mauritius
2-part maxilla: unique among amniotes
ADAPTIVE RADIATIONS
Diversification of large number of descendant
species from ancestral species:
• Galapagos finches, African cichlid fishes,
Hawaiian swilverswords, etc.
(Text Fig. 15.14)
KEY INNOVATIONS
• “Novel morphological or behavioural traits that open
up new ‘adaptive zone’ or facilitate rapid speciation”
(e.g., after environmental or colonization event)
• Traits involved in reproductive isolation may 
increased speciation rates
• Invoked to explain large radiations in some clades
• Key innovation in jaw morphology: pharyngeal jaws
in cichlid fishes (Liem, Syst. Zool. 22:425; 1974)
AFRICAN RIFT-LAKE CICHLIDS
• Cichlids advanced teleost; include angelfish
• ~2,000/~30,000 species
• Lake Malawi: 500 species in last 2 my
• Lake Tanganyika: 150 species in last 2 my
• Lake Victoria: 250 species in last 750,000 yr
• Much rapid evolution: e.g., 300 species in Lake
Victoria derived from single founding population with
last 12,000 years
Corematodus shiranus (upper):
scale-eating mimic
L. Victoria
L. Tanganyika
L. Malawi
Caprichromis orthognathus:
Head-ramming paedophage
Melanochromis labrosus:
Seals openings w/lips, sucks
Cichlid fishes of East Africa’s rift lakes:
>1500 species in last 10 million years
Tangle-veined fly (Prosoeca ganglbaueri) visits
mountain drumstick (Zaluzianskya microsiphon)
FLORAL SPURS
• Floral spur: long outgrowths of
floral parts, increase distance
between floral reward and
reproductive parts of flower
• Associated with reproduction so
may diverge rapidly and
 rapid reproductive isolation
Between closely related lineages
Malagasy orchid (Angraecum sesquipedale):
• Nectar pool of nectar ~30 cm from flower opening
• Darwin received flower from Kew Gardens,
predicted existence of moth with long proboscis:
discovered, described 1903!
• Geographic variation: in Aquilegia caerulea, spur
length and colour vary in association with
different types of pollinators
• Spur differences prevent hybridization between
Aquilegia species that can hybridize
• Spur morphology varies with morphological
variation in bee pollinators of Diascia
• Aquilegia: little DNA sequence divergence, many
species: suggest recent radiation
• Floral spurs arose independently several times;
other groups like Aquilegia
Taxon with
floral spurs
Aquilegia
No. species:
TFS
Sister groups
70
1, 14
Delphinium, Aconitum
350
37
Fumariaceae
450
15
Tropaeolaceae
88
2
Lentibulariaceae
245
2
Pelargonium
280
399
STASIS
Major pattern: New morphospecies appear in fossil
record, then change little over long periods of time
Amborella trichopoda:
sister group to all extant angiosperms
(LCA ~140-210 Ma)
“LIVING FOSSILS”
• Gingko (Permian; maximal diversity and
geographic range in Cretaceous; 1 species
left in Paleocene): phylogenetic and
geographic (distributional) relict
• Horseshoe crabs (Early Triassic, ~230Ma)
• Snapping turtles (Late Paleocene, ~57 Ma)
THE THEORY OF
PUNCTUATED EQUILIBRIUM
Eldredge & Gould (1972):
• Stasis real, not artifact
• Stasis normal: relatively rapid change (saltation)
occurs periodically
• Patterns viewed over different temporal scales
lead to different interpretations (What does
“gradual” mean?)
STASIS vs. GRADUALISM
(Text Fig. 15.16)
Darwin:
• Evolution and extinctions gradual
• Sudden extinctions are artifacts
• Extinctions result from competition
between species
• Extinctions tied to natural selection
and trend to “progressive” evolution
George Gaylord Simpson:
• Extinctions rarely result from
competition
• Dominant groups die out and
are then replaced
• Successor group often present
during decline of other group
DEMONSTRATING STASIS
• Distinguish stasis from gradual change: fine
temporal scale best
• Is change independent of or coincident with
speciation events?
• Is rapid change followed by stasis or by gradual
change?
Test for stasis:
• Phylogeny of clade must be known
• Ancestral species must overlap with descendants
CHEILOSTOME BRYOZOANS:
Morphological and genetic concordance
(text p. 407)
Bracebridgia
Buskea
DEMONSTRATING STASIS:
BRYOZOANS OVER ~16 x 106 YEARS
• Stylopoma: 12 fossil, 7 extant species
• Morphologically established phylogeny
• Phylogeny scaled: branch points at first appearance
in fossil record, tips at last appearance
• Similar analysis for Metrarabdotos
1) No intermediates
2) Species stable through time
(Text Fig. 15.17a)
1) No intermediates
2) Species stable through time
(Text Fig. 15.17b)
PUNCTUATED EQULIBRIA NOT UNIVERSAL
• Varied patterns across taxa
• Gradualism common in microscopic marine forms
CAUSES OF STASIS
• Lack of genetic variation?
• Compare horseshoe
crabs with other
arthropod clade
(Text Fig. 15.19)
DYNAMIC STASIS
AND ZIGZAG EVOLUTION
• Averaging over long periods can blur trends
(Text Fig. 15.20)
QUANTIFYING RATE OF EVOLUTION
J.B.S. Haldane (1949) defined darwin:
• “change by factor of e per 106 years”:
• Simpson’s Tertiary horse data: 0.04 d
• Domestic animals: thousands of d
• Kurtén: post-glacial Holocene mammals, 13 d;
Pleistocene mammals, 0.5 d; Tertiary mammals,
0.02 d
RECORD OF EXTINCTION
• Known fossils ~ 250 000 species (~ 1% of
species that have ever lived)
• Bias: marine animals with hard skeletons
• Incomplete sampling biases extinction rates (few
short-lived localized fossils)
• Distribution of recorded lifespans of genera
highly skewed
BACKGROUND EXTINCTION
• Within radiation, likelihood of extinction is
constant, not affected by how long clades have
been in existence
• Select random samples within clade
• Plot proportion of surviving clades vs. time
• Analogy: survivorship curves in ecology
EPISODES OF EVOLUTION
• “Mass extinction” often defined as extinctions of
75-95% in brief period
• Dramatic but combined effect ~ 4%
• Implies 2 extinction modes: but this is not clear cut
CLUSTERING OF EXTINCTIONS
• Due to removal of key taxa? Ecosystem loss?
• Major extinction events cannot be explained by
species interactions
• Long aftermath following mass extinctions
• Post-mass-extinction biota very different
SELECTIVITY OF EXTINCTIONS
• Sometimes taxonomic selectivity
• Species with planktonic larvae survive background
extinction better than species with direct development
• Widespread species survive mass extinctions better
MASS EXTINCTIONS
Five commonly recognized:
• End-Cambrian (~ 500 Ma)
First vertebrates in Cambrian
Trilobites and conodonts reduced; many invertebrate
groups disappeared
• Terminal-Ordovician (~ 440 Ma)
• Late-Devonian (~ 365 Ma)
~75% of fish families died out: most agnathans,
placoderms & several families of acanthodians,
bony fishes
• End-Permian (~250 Ma)
Amniotes diversified, large terrestrial nonamniotes
declined
Large “therapsids” became dominant
Pangaea formed; reduced epicontinental shallow seas
Large land area, fewer geographic barriers
Widespread marine extinctions (88-96% of all species);
also many large land animals
• End-Triassic (~215 Ma)
• Cretaceous-Tertiary (K-T) boundary (65 Ma) (text
pp. 403-405)
EVIDENCE OF K-T IMPACT
Iridium layer at K-T
boundary; rare in
earth’s crust, common
in meteorites
Shocked-quartz crystals
Microtektites
Magnetic and gravitational anomalies;
crater confirmed 1990s
EFFECTS OF IMPACT
• Huge influx of [SO2 + water vapour]  H2SO4
(therefore acid rain)
• SO2 also scatters solar radiation
• Cooling enhanced by dust
• Extensive forest fires  soot
• Thus Earth became cold and dark
• Massive earthquakes triggered  volcanoes
• Huge magma deposits (Indian Decca Traps)
contemporaneous; connected?
• Vulcanism  release of SO2, CO2, ash
• Tsunami (4 km high?)
• Oceanic primary productivity reduced
• Disruption of ecological processes
Stack of ~ 20 Columbia River Basalt lava flows
(Grande Ronde River, Washington State)
EFFECTS OF MAGMA DEPOSITS
• Environmental impact from released gases
• Climatic cooling from H2SO4 aerosols?
• Greenhouse warming from
CO2 and SO2 gases, acid rain?
• Indirect effects: changes in ocean chemistry,
circulation, and oxygenation?
K-T VERTEBRATE EXTINCTIONS
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100% of dinosaurs, pterosaurs, plesiosaurs
75% of marsupial families
75% of bird families
36% of squamate families
27% of turtle families
23% of mammal families
18% of chondrichthyian families
12% of bony fish families
Overall (families): 30% of vertebrates, 48% of
amniotes, 43% of tetrapods, 15% of fishes