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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

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Geographic modes of speciation

Futuyma 2005

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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

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Speciation onislands:Losos &Rickleffs

2009

Adaptivedivergenceamong or

within islands

Adaptive divergenceof bill dimensions

leng

th

width & depth

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Hybrid zones - alternative outcomesafter re-contact between lineages

Or, new “hybrid species”

Fig. 24.14

Or - lineages don’t hybridizeand eventually overlap ifecologically distinct

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Hybrid zone - Bombina variegata-bombina (Fig. 24.13)

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A stable hybridzone in

Ensatina

Alexandrino et al. 2005

20 yrslater

2nd contactwith samelineages

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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

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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

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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

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The fossil record:billions of years ofsedimentation =>

recoverable history

• E.g. Grand Canyon &environs - layeredsediments from recent topre-Cambrian

Fig. 22.3Fig. 25.5

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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

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The Cambrian “explosion”- Burgess shale &

appearance of modernphyla

Fig. 25.10

Burgessshale

“Hallucigenia”

Weirdstuff…

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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