Speciation and evolution Mechanisms Selection and genetic isolation

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Speciation and evolution § Mechanisms Selection and genetic isolation; founder effects; genetic drift; adaptive

Speciation and evolution § Mechanisms Selection and genetic isolation; founder effects; genetic drift; adaptive radiation; polyploidy; rates of speciation; centres-of-origin § Tools cladistic analysis

4 Ga of evolution = high organic diversity (1. 4 M species known) [5

4 Ga of evolution = high organic diversity (1. 4 M species known) [5 -100 M overall? ]

Number of known animal species “God, if he exists, shows an inordinate fondness for

Number of known animal species “God, if he exists, shows an inordinate fondness for beetles” J. B. S. Haldane (1951)

Number of known higher plant species

Number of known higher plant species

The Darwinian revolution Charles Darwin (1809 -82) §The species alive today evolved from a

The Darwinian revolution Charles Darwin (1809 -82) §The species alive today evolved from a single original life form as a result of progressive specialization; §Plants and animals evolve by natural selection (preservation of useful variation in a population); §Evolutionary change has been gradual, requiring thousands to millions of years

Selective pressures can reduce or increase the natural variation in a population e. g.

Selective pressures can reduce or increase the natural variation in a population e. g. body size

Disruptive selection may give rise to new species as a result of: • Geographic

Disruptive selection may give rise to new species as a result of: • Geographic segregation (e. g. islands), or • Habitat-niche segregation (e. g. savanna vs. forest), or • Behavioral segregation (e. g. seasonal or diurnal mating isolation), or • Sexual segregation (e. g. lack of female response to male colouration, smell, etc. ) of the divergent populations; or new species may be a product of • instantaneous mutation (polyploidy)

Genetic isolation Allopatric Peripatric Speciation Parapatric Sympatric Original Population Initial Step Evolution of genetic

Genetic isolation Allopatric Peripatric Speciation Parapatric Sympatric Original Population Initial Step Evolution of genetic isolation Barrier Formation In isolation New niche entered In isolated niche New niche entered In adjacent niche Increased genetic variation Within the population Based on Wikipedia graphic

Allopatric speciation Speciation may arise following the crossing or creation of barriers Barrier-crossing events

Allopatric speciation Speciation may arise following the crossing or creation of barriers Barrier-crossing events Barrier-creation events e. g. dispersal by storms e. g. continental drift

Vocabulary allo = “other” peri = “nearby” para = “around about” sym = “same”

Vocabulary allo = “other” peri = “nearby” para = “around about” sym = “same” patri = “of the country”

Allopatric speciation: barrier types Water island 1 island 2 Topographic grass land Habitat forest

Allopatric speciation: barrier types Water island 1 island 2 Topographic grass land Habitat forest Competition? grass land

Allopatric speciation Spotted owl subspecies living in different geographic locations show some genetic and

Allopatric speciation Spotted owl subspecies living in different geographic locations show some genetic and morphological differences. Will new species form through geographic isolation? http: //evolution. berkeley. edu/evosite/evo 101/

Paleo-allopatric speciation? More widely separated at 15 ka BP? http: //birds. cornell. edu/programs/All. About.

Paleo-allopatric speciation? More widely separated at 15 ka BP? http: //birds. cornell. edu/programs/All. About. Birds/Bird. Guide

Peripatric speciation (founder effects) Scarlet robin (Petroica boodang) Australia Pacific robin (Petroica multicolor) Norfolk

Peripatric speciation (founder effects) Scarlet robin (Petroica boodang) Australia Pacific robin (Petroica multicolor) Norfolk Island

Founder effects Colonizing populations are often very small, and therefore contain only a small

Founder effects Colonizing populations are often very small, and therefore contain only a small sample of the genetic diversity of the parent population. e. g. if a small flock of blueback grassquits was blown from the coast of Ecuador across >1000 km of ocean to the Galápagos, how much of the ancestral gene pool would it contain? Copyright of

Genetic drift Small populations are also subject to changes in their genetic constitution as

Genetic drift Small populations are also subject to changes in their genetic constitution as a result of chance; they can therefore diverge quickly from their ancestors. Changes in the species gene pool resulting from these stochastic effects are referred to as “genetic drift”.

“Darwin’s finches” 14 species. Primarily in the genus Geospiza, they are likely descended from

“Darwin’s finches” 14 species. Primarily in the genus Geospiza, they are likely descended from the blueback grassquit (Volatinia jacarina) of the South American mainland. Source: Lack, D. 1966. Darwin’s Finches. Harper, N. Y.

Darwin’s only comment on “his” finches “The most curious fact is the perfect gradation

Darwin’s only comment on “his” finches “The most curious fact is the perfect gradation in the size of the beaks of the different species of Geospiza - 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” my italics! Journal of Researches, 1842.

The Galápagos archipelago 1000 km Daphne major 100 km Galápagos Islands began to emerge

The Galápagos archipelago 1000 km Daphne major 100 km Galápagos Islands began to emerge over the hotspot beneath the Nazca plate ~5 Ma a

Evolutionary relationships: Galápagos finches

Evolutionary relationships: Galápagos finches

Adaptive radiation The evolution of a single species into many species that adopt diverse

Adaptive radiation The evolution of a single species into many species that adopt diverse habits, usually as a result of the invasion of a new area, (=allopatric speciation) followed by parapatric or sympatric speciation. Examples: Galápagos finches; Hawaiian honeycreepers and honeyswords

Adaptive radiation* in Galápagos finches • Seed eaters (like their S. American ancestors feed

Adaptive radiation* in Galápagos finches • Seed eaters (like their S. American ancestors feed on ground or in canopy) • Insect eaters (woodpecker-like and tool-using or warbler-like) • Nectar feeding (cactus finch) • Vampire-like (some finches suck blood of sleeping seabirds) * a. k. a. ecological release or niche segregation

Speciation by character displacement: beak size in three finches on four island groups G.

Speciation by character displacement: beak size in three finches on four island groups G. magnirostris colonized in 1982

Beak size and seedeating efficiency Large-beaked G. fortis (A) and G. magnirostris (B) can

Beak size and seedeating efficiency Large-beaked G. fortis (A) and G. magnirostris (B) can crack or tear the woody tissues of T. cistoides mericarps (D), whereas small -beaked G. fortis (C) cannot. Five mericarps constitute a single fruit. In (D), the left-hand mericarp is intact. The right-hand mericarp, viewed from the other (mesial) side, has been exploited by a finch, exposing five locules from which seeds have been extracted. Source: Grant, P. R. and Grant, B. R. 2006. Science 313, 224 - 226.

Squawk! Beak shape influences song, which controls mating behaviour, reinforcing differentiation Source: Podos, J.

Squawk! Beak shape influences song, which controls mating behaviour, reinforcing differentiation Source: Podos, J. 2001. Nature 409, 185 -188. Trill!

Competition and character displacement in drought years • Mean beak size of G. fortis

Competition and character displacement in drought years • Mean beak size of G. fortis on Daphne Major (19732005). G. magnirostris arrived on the island in 1982. • NB: Daphne Major is 0. 34 km 2 in area. • Population of G. fortis and G. magnirostris on Daphne Major (1996 -2005). There was no breeding in the drought years of 2003 and 2004. Source: Grant, P. R. and Grant, B. R. 2006. Science 313. 224 - 22

Many interisland transfers? e. g. Geospiza magnirostris on Daphne major on previous slide

Many interisland transfers? e. g. Geospiza magnirostris on Daphne major on previous slide

The salamander Ensatina: divergence resulting from repetitive colonization (founder effects) and genetic drift “ring

The salamander Ensatina: divergence resulting from repetitive colonization (founder effects) and genetic drift “ring speciation”

Ensatina semi-species X E. e. eschscholtzii = E. e. klauberi hybrid The salamanders in

Ensatina semi-species X E. e. eschscholtzii = E. e. klauberi hybrid The salamanders in the Ensatina eschschlotzii complex in California interbreed with their immediate neighbors, with one exception. In Southern California, E. e. klauberi and E. e. eschscholtzii can interbreed (see above), but rarely do so. Images courtesy of Chuck Brown, Santa Rosa Community College

Speciation may be slow, to moderate, …. e. g. Galápagos finches or Hawaiian silverswords:

Speciation may be slow, to moderate, …. e. g. Galápagos finches or Hawaiian silverswords: 28 silversword species in 3 genera derived from a tarweed ancestor in the last 5 million years Baldwin, B. G. , and Sanderson, M. J. 1998, PNAS, 95, 9402 -9406,

…. . or rapid: Cichlidae: ~700 species of freshwater fishes of tropics and subtropics

…. . or rapid: Cichlidae: ~700 species of freshwater fishes of tropics and subtropics • Common in lakes of East Africa • >300 species of cichlid fish in Lake Victoria • Varied feeding habits: predators [fish, molluscs] and grazers • Lake Victoria is shallow, and dried up in the late Pleistocene, so all cichlid species are a product of colonization and radiation in about the last 12 000 years • Is this an example of sympatric speciation?

Lake Victoria cichlids: genetic segregation by feeding habitat and colour signals Pundamilia pundamilia Neochromis

Lake Victoria cichlids: genetic segregation by feeding habitat and colour signals Pundamilia pundamilia Neochromis gigas http: //home. t-online. de/home/schraml. e/mbipi 2. htm

Lake Victoria: agricultural pollution -> loss of clarity -> hybridization 80% loss

Lake Victoria: agricultural pollution -> loss of clarity -> hybridization 80% loss

… or instantaneous: polyploidy • Polyploid organisms have a chromosome count that is a

… or instantaneous: polyploidy • Polyploid organisms have a chromosome count that is a multiple (2 x, 4 x, 6 x, 8 x, …) of that of some related form • All of these represent the spontaneous addition of extra (whole) sets of chromosomes in progeny • Polyploids are “instantaneous” species, only even-ploid hybrids are likely in nature

~50% of all plant species have a polyploid origin, e. g. Anemone Parent species

~50% of all plant species have a polyploid origin, e. g. Anemone Parent species Daughter

or Chrysanthemum species: many polyploid events and hybridization between members of polyploid complexes, e.

or Chrysanthemum species: many polyploid events and hybridization between members of polyploid complexes, e. g. (x[ base chromosome number] = 9) C. mankinoi (2 x, n=9) C. indicum C. mankinoi x C. japonese? (4 x, n=18) C. japonese (6 x, (hybrid of C. n=27)indicum and C. ornatum? ) C. ornatum (8 x, n=36) C. yezoensis and C. pacificum (10 x, n= 45)

Species diversity: pheasants centre-of-origin (area of maximal diversity)

Species diversity: pheasants centre-of-origin (area of maximal diversity)

Species diversity: crocodiles centre-of-origin?

Species diversity: crocodiles centre-of-origin?

Biodiversity: palms (number of genera) centre-of-origin?

Biodiversity: palms (number of genera) centre-of-origin?

Cladistics I • Attempts to answer the following question: “Given any group of taxa,

Cladistics I • Attempts to answer the following question: “Given any group of taxa, which ones are most closely related to each other? ” • Methods based on objective techniques based on the presence/absence of morphological characters (a. k. a. ‘numerical taxonomy’); or DNA sequences

Characters used to distinguish between species of Douglas-fir (Pseudotsuga) 1. Young cones purplish (not

Characters used to distinguish between species of Douglas-fir (Pseudotsuga) 1. Young cones purplish (not green). 2. Cones >10 cm long. 3. Leaves <1. 5 mm wide. 4. Bract scales >2. 5 cm long. 5. Bract scales reflexed (curved; not exserted) 6. Vegetative (leaf) buds > 7 mm long. 7. Seed scales have length-width ratio <1. 8. Mature trees have very thick bark with resin blisters.

Comparing characters Species menziesii macrocarpa sinensis japonica Range N. America Asia Characters 1 0

Comparing characters Species menziesii macrocarpa sinensis japonica Range N. America Asia Characters 1 0 0 + + 2 0 + 0 0 3 + 0 0 0 4 + + + 0 5 0 0 + + 6 + + 0 0 7 + 0 0 0 8 + 0 0 0 e. g. P. menziesii shares 4 of 8 characters (#1, 4, 5, 6) with its North American relative P. macrocarpa; their relative similarity therefore = 4/8 = 0. 5

Similarity matrix (Douglas-firs)

Similarity matrix (Douglas-firs)

A similarity linkage diagram for Douglas-fir japonica menziesii sinensis macrocarpa

A similarity linkage diagram for Douglas-fir japonica menziesii sinensis macrocarpa

Cladistics II • Cladistic analysis is based on the identification of distinctive morphological characters

Cladistics II • Cladistic analysis is based on the identification of distinctive morphological characters that can be placed in an evolutionary sequence. • Characters may be apomorphous (derived characters) or plesiomorphous (ancestral characters). • Once a taxon divides, an apomorphic character becomes plesiomorphic.

Constructing a cladogram • We will use some of the characters listed in the

Constructing a cladogram • We will use some of the characters listed in the similarity matrix for Douglas-fir to construct a hypothetical cladogram. • NB: this is for illustrative purposes only (the characters are not necessarily plesiomorphic/apomorphic).

The parsimony rule* Using characters 3, 4, 6, 7, 8 only; 3 steps to

The parsimony rule* Using characters 3, 4, 6, 7, 8 only; 3 steps to cladogram Using characters 3, 4, 6, 7, 8 only; 4 steps to cladogram menziesii macrocarpa japonica sinensis menziesii macrocarpa sinensis japonica 4 6 6 6 3, 7, 8 A 4 3, 7, 8 B By the parsimony rule cladogram ‘A’ is preferred [3 steps vs 4 steps]. (see Fig 8. 1 in text for a more complex example) *Alternatively known as “economy of hypothesis”; “Occam’s razor”, or the “KISS principle” ( as in, “Keep it simple, stupid!”).

Alternative cladograms menziesii macrocarpa japonica sinensis menziesii macrocarpa sinensis japonica 4 6 6 3,

Alternative cladograms menziesii macrocarpa japonica sinensis menziesii macrocarpa sinensis japonica 4 6 6 3, 7, 8 A 3, 7, 8 B Note that the information is in the branching sequence, and NOT in the proximity of the branches. A and B are identical in terms of information. 4