Bio1B Evolution 10 - Integrative...
Transcript of Bio1B Evolution 10 - Integrative...
1
Bio1B Evolution 10Last lecture:Species & speciation• What is a species anyway? (Pp. 487-492) - e.g. hominids
– Interesting one - Ensatina salamanders• Speciation processes (Pp 492-504)• Geographic modes of speciation - allo/para/sym/peri- patry
TodaySpecies & speciation• Adaptive radiations• Hybridization - hybrid zones, reinforcement &
hybrid-speciation• Macroevolution:
– The fossil record, extinctions and major transitions
2
Geographic modes of speciation
Futuyma 2005
3
Adaptive radiations (pp. 524-5)
• Rapid speciation withecologically-drivendivergent selection
• Common on remoteislands or other novelenvironmentsfollowing colonization
• Promoted by isolation& ecologicalopportunity
e.g. Hawaiian silverswords(Fig. 25.18)
Other examples: African cichlids,Hawaiian arthropods, Andeanlupines, Carribean anole lizards etcetc
4
Speciation onislands:Losos &Rickleffs
2009
Adaptivedivergenceamong or
within islands
Adaptive divergenceof bill dimensions
leng
th
width & depth
5
Hybrid zones - alternative outcomesafter re-contact between lineages
Or, new “hybrid species”
Fig. 24.14
Or - lineages don’t hybridizeand eventually overlap ifecologically distinct
6
Hybrid zone - Bombina variegata-bombina (Fig. 24.13)
7
A stable hybridzone in
Ensatina
Alexandrino et al. 2005
20 yrslater
2nd contactwith samelineages
8
Recent (<8kya) expansion from long-isolated (>2 Myr)refugia in the NE Australian rainforest
Is there evidence forreproductive isolation?
Is there evidence forreinforcement =>prezygotic isolation?
Manyhybridzones
Skinks = narrow (<1km) hybridzones - selection against hybrids
Small marsupial - randommating, no evidence for RI
Frog - reinforcement =>Reproductive isolationMoritz et al.
2009 PRSL
refugia
9
Hybrid speciation
=> Formation of unique andisolated lineages from inter-lineage hybrids
• Allopolyploidy (see p. 496)• If same ploidy, requires eco-
geographic isolation fromparent lineages
• E.g. arid-adapted Helianthusanomalus = H.annuus X H.petiolaris
Fig 24.18, p. 503
10
Speciation wrap-up• Species are (largely) independent evolutionary
lineages• Divergent selection &/or genetic drift => increasing
divergence and RI with time. Opposed by gene flow• Speciation is inevitable if populations are isolated for
long enough - RI evolves faster and most reliably withdivergent selection in allopatry. Might also occurquickly in association with founder events andsubsequent selection (peripatry)
• If diverging populations are in close proximity(para/sympatry), disruptive selection must beaccompanied by non-random (like-like) mating toreduce gene flow
11
The fossil record:billions of years ofsedimentation =>
recoverable history
• E.g. Grand Canyon &environs - layeredsediments from recent topre-Cambrian
Fig. 22.3Fig. 25.5
12
Major transitionsin earth history
• Earliest prokaryotes - fossilstomatolites 3.5 Bya
• Increase O2 - 2.7 Mya• Fossil eukaryotes 2.1Bya;
multicell algae 1.2 Bya• Complex metazoa 0.55
Bya• Marine -> land 0.5 Bya• [Hominids only 0.005 Bya]
Fig 25.7
13
The Cambrian “explosion”- Burgess shale &
appearance of modernphyla
Fig. 25.10
Burgessshale
“Hallucigenia”
Weirdstuff…
14
The big 5mass
extinctions
• Evidence from analyses of extinction (red) and blues(diversity) or families of marine invertebrates
• Permian-Triassic - 96% species extinction, 8/27 orders ofinsects; Volcanism in Siberia?
• Cretaceous-Paleogene (“K/T”), 65 Myr - demise ofdinosaurs & large terrestrial animals => mammalianradiation