Una barriera ecologica si
trasforma in una barriera
riproduttiva
Le specie ad anello
LA STASI EVOLUTIVA
Cause della stabilità
(intervallo di variazione
stabile per lunghi
periodi):
- Selezione stabilizzante
- Plasticità ecologica e dello
sviluppo
- Costrizioni dello sviluppo
- Habitat tracking
Sopravvivenza dell’antenato (verificabile)
1835
2006
Calmodulin: regolazione genica
della morfogenesi dei becchi
Nature, agosto 2006
IL MITO DELL’ILLUMINAZIONE…
Cinque
settimane
Avvistamento
15 sept. 1835
Un puzzle
morfologico
Seeing this
gradation and
diversity of structure
in one small,
intimately related
group of birds, one
might really fancy
that from an original
paucity of birds in
this archipelago, one
species had been
taken and modified
for different ends.
(1845, Viaggio di un
naturalista attorno al
mondo)
Un esperimento privilegiato di evoluzione
- recente
formazione
(4 Mil. – oggi)
- ecosistema
unico (sistema
delle correnti)
- arcipelago
vulcanico isolato
- disabitate fino
al 1535
Radiazione
adattativa
LO SPAZIO (selezione naturale, adattamento, speciazione)
14 specie strettamente
imparentate
Nessuna estinta finora
Antenato comune sicuro:
2-3 M di anni fa
Cambiamenti adattativi
rapidi (anche 1 anno)
Rosemary e Peter Grant
Studi sistematici continuativi
(1973 – 2007): la selezione
naturale vista all’opera!
Modi di speciazione
(Coyne, Orr, 2004)
- Sp. allopatrica normale (max frequenza)
- Sp. parapatrica e simpatrica (flusso genico interrotto e non;
ibridazioni intermedie)
- Sp. con selezione di rinforzo (simpatrica; dopo ibridazione
disadattativa)
- Sp. simpatrica per selezione sessuale (isolamento
comportamentale, West-Eberhard 1983)
- Sp. per ibridazione (cromosomica o genica) (*solo nelle piante)
Nei fringuelli (Grant):
Interazioni competitive fra
specie simpatriche
Effetto del fondatore
Speciazione come effetto
collaterale dell’adattamento
Ibridazioni
Differenti barriere di isolamento riproduttivo
(Coyne, Orr, 2004)
Basi genetiche dell’isolamento riproduttivo + ecologia
Prima della fertilizzazione:
Dopo la fertilizzazione:
- Ecologiche (habitat
isolation; differential
adaptations; allochronic
isolation; pollinator isolation)
- Intrinseche (hybrid
inviability; hybrid physiological
or behavioral sterility)
- Comportamentali
(ethological or sexual
isolation)
- Estrinseche (ecological
inviability of hybrids)
- Meccaniche (incompatibility
of reproductive structures)
Nei fringuelli (Grant): alimentazione (becchi) e canto
(Processi continui che producono entità discrete!)
IL TEMPO (discendenza comune, diversificazione)
Filogenesi dei fringuelli di Darwin (mtDNA, PNAS 1999)
Albero di
discendenza
<>
(almeno quattro generi)
Morfologia e
adattamenti
alimentari
Split or lump…
Sei generi!
Ground Finches
Small Ground Finch
Geospiza
fuliginosa
Medium Ground Finch
"
fortis
Large Ground Finch
"
magnirostris
Sharp-beaked ground Finch
"
difficilis
Cactus Ground Finch
"
scandens
Large Cactus Ground Finch
"
conirostris
Tree Finches
Small Tree Finch
Camarhynchus
parvulus
Medium Tree Finch
"
pauper
Large Tree Finch
"
psittacula
Woodpecker Finch
Cactospiza
Mangrove Finch
Vegetarian Finch
Warbler Finch
Cocos Island Finch
pallidus
"
heliobates
Platyspiza
crassirostris
Certhidea
olivacea
Pinaroloxias
inornata
UN LABORATORIO DI SPECIALIZZAZIONI ADATTATIVE
Specie terricole, 3 si cibano di
semi, una vive sui fichi d’India,
due integrano con cactus
Geospiza difficilis
septentrionalis (isola di Wolf),
fringuello vampiro (evoluzione
culturale: dai parassiti delle
sule al loro sangue)
Camarhynchus heliobates e
pallidus (arboricoli), uso di
spine o bastoncini per estrarre
insetti
Specie arboricole, 4 insettivore,
una germogli e frutti
Fringuello cantore (insettivoro)
Fringuello vegetariano
(Platyspiza crassirostris)
Fringuello dell’isola di Cocos
(Pinaroloxias inornata) (piante e insetti)
FOUNDER EFFECT
BOTTLENECK
EFFECT
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
(courtesy, Kenneth Kidd, Yale University)
HOMO SAPIENS GLOBALIZATION
Tutti parenti, tutti differenti
DINOSAURI CON LE PENNE
1996-2006:
AMNH di NY
Transizione
dinosauri-uccelli
(corsa-volo)
Exaptation di
penne e piume
Velociraptor mongoliensis con Mononykus olecranus
MASS EXTINCTIONS
- Frequenza
- Intensità
- Rapidità
- Selettività
Michael Benton
Dimensione cosmologica dell’evoluzione
ESTINZIONI ANTROPICHE
RADIAZIONI ADATTATIVE
PESCI CICLIDI DEL LAGO VITTORIA
- Effetti specie-area
- Turnover pulses
- Adaptive radiations
IRRIDUCIBILITA’ DELLA MACROEVOLUZIONE
Un nocciolo esplicativo comune:
IL QUADRIMOTORE DELL’EVOLUZIONE
MUTAZIONE
(sorgenti di variazione)
DERIVA GENETICA
(processi neutralistici)
SELEZIONE NATURALE
(processi selettivi)
MACROEVOLUZIONE
(migrazione, radiazione
adattativa, estinzione di
massa)
Niles Eldredge (2008) , “Hierarchies and the Sloshing Bucket: Toward the Unification of Evolutionary Biology”, I
n Evo Edu Outreach 1 pp. 10–15.
Niles Eldredge (2008) , “Hierarchies and the Sloshing Bucket: Toward the Unification of Evolutionary Biology”, in
Evo Edu Outreach 1 pp. 10–15.
Niles Eldredge (2008) , “Hierarchies and the Sloshing Bucket: Toward the Unification of Evolutionary Biology”, in
Evo Edu Outreach 1 pp. 10–15.
Niles Eldredge (2008) , “Hierarchies and the Sloshing Bucket: Toward the Unification of Evolutionary Biology”, in
Evo Edu Outreach 1 pp. 10–15.
NO PARADIGM SHIFT:
1 – “Paradigm” is too strong a concept (normal
science; language; world-view)
2 – There are no growing, irrecoverable anomalies
3 - Exceptions are no confutations (but, the need for
pluralistic patterns of explanation)
4 – Anomalies find explanation with integrative
hypotheses, consistent with the core of the
“research programme”
5 – A no longer debated core is surrounded by a
“protective belt” of auxiliary assumptions in progress
What is happening is a progressive transition of RP (I. Lakatos)
What is under falsification is not a single theory, but
a
RESEARCH PROGRAMME
Protective belt in
progress
Auxiliary assumptions
Observative theories
RP Core
Open problems
Domains
of relevance
Initial conditions
- No longer debated explanations
and concepts (corroborated;
method. infalsific.)
- Positive and negative heuristics
Assumptions
of marginality
Controversial issues
The core evolves through
integrations
A confutation in the belt is not a
refutation of the core
ERP1 - MODERN SYNTHESIS
(not a monolith, but an open yard)
Auxiliar assumptions
Philetic Gradualism
Extrapolationism
DW Core
Common Descent –
Genetic Theory of Nat.
Selection
Strong or methodological
Adaptationism
(Macroevolution from
microevolution)
Universal Darwinian
“algorythm”
Ronald A. Fisher
Great explanatory capacity
Coherent theoretical framework
A “regressive” RP
(less empirical contents, between crisis and transition)
Accumulation
of anomalies
Auxiliar assumptions
Philetic Gradualism
Phenotypic
plasticity
Extrapolationism
(Macroevolution from microevolution)
Punctuated
equilibria
Epigenetics
DW Core
Ecology
Common Descent – Genetic Theory
of Nat. Selection
Evo-Devo
Genetic Drift
Neutralism
Accumulation
of ad hoc hypotheses
Strong or methodological
Adaptationism
Exaptation
Niche
construction
Incompleteness
Progressive inclusions, integrations and revisions
ERP2: A DARWINIAN
EXTENDED CORE
MUTATION
(sources of variation)
GENETIC DRIFT
(neutralistic processes)
NATURAL SELECTION
(selective processes)
MACROEVOLUTION
(migrations, adaptive
radiations, mass
extinctions…)
ERP2: A more PLURALISTIC
“PROTECTIVE BELT”
Auxiliar assumptions
New views on
inheritance
(epigenetic
inherit., niche
inherit.)
Understanding the phenotype
(phenotypic plasticity,
macroevolution, origins of form)
Extended DW
Core
Evo-Devo
(innovation,
modularity,
evolvability)
Selection and adaptation reformed
(neutralism, multilevel selection,
niche construction, exaptation,
symbiosis)
The evolving structure of Darwinian Research Program
EXTENDED DARWINIAN SYNTHESIS
(more empirical contents and predictions of “new facts”)
Understanding the phenotype
(phenotypic plasticity,
macroevolution, origins of form)
New views on
inheritance
(epigenetic
inherit., niche
inherit.)
Advances of Darwinism
(population genetics,
drift, speciations)
Evo-Devo
(innovation,
modularity,
evolvability)
Selection and adaptation reformed
(neutralism, multilevel selection,
niche construction, exaptation,
symbiosis)
The evolving structure of Darwinian Research Program
TRANSITION ERP1 – ERP2:
1 – CONTINUITY (LAK: scientific is not only the theory
itself, but the dynamic of succession of theories, the process
of growth of knowledge)
2 – A RATIONAL DYNAMIC OF REVISION AND
EXTENSION of the RP (compatibility with previous RP)
3 – Neither A PARADIGM SHIFT nor, at the opposite, A
SUPERFICIAL RESTYLING (updating internal problems):
an evolution of the structure of evolutionary theory
WHAT A CHALLENGING “ALTERNATIVE THEORY OF
EVOLUTION” (or ERP) SHOULD DO:
1 – DESCRIBE AND EXPLAIN ALL THE EMPIRICAL
CORROBORATED BASIS OF THE PREVIOUS RP
(incorporation; not single controversial cases)
2 – DESCRIBE AND EXPLAIN SOMETHING MORE (new
facts, predictions: additional empirical contents)
3 – PERFORM POINT 1 AND 2 USING PRINCIPLES AND
CONCEPTS NOT REDUCIBLE TO THOSE OF THE
PREVIOUS RP
There is nothing like that in the field