Phylogeny and Systematics

Ch. 25

Phylogeny

• Evolutionary history of a species or group of related species

• Reconstructing phylogeny is part of the scope of systematics– Systematics—the study of biological diversity

in an evolutionary context

Phylogenetic Trees

• Diagrams that trace evolutionary relationships as best as they can be determined

• Systematist use evidence from:– Fossil record

• Phenotypic appearances

– Molecular biology• Comparison of nucleic acid sequences/amino acid sequences

• DNA sequence analysis—identifying & comparing homologous sequences

• Species diverge as changes (genetic mutations) occur

Taxonomy

• Branch of biology concerned with naming and classifying the diverse forms of life

• Scientific name of an organism = binomial system

• Genus / species

Phylogenetic trees reflect the hierarchical classification

Cladistic Analysis

• Synonymous with phylogenetic systematics

• Clade=evolutionary branch

• Classifying organisms according to the order in time that branches arose along a dichotomous tree

Cladogram

• Analyzing the taxonomic distribution of homologies enables us to identify the sequence in which derived characters evolved during vertebrate phylogeny.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 25.11

Kingdom: PlantaePlant Diversity

Ch. 29 & 30

Land plants evolved from green algae

• Green algae called charophyceans are the closest relatives of land plants

• Four key traits in common:– Rose-shaped complexes for

cellulose synthesis– Peroxisome enzymes– Structure of flagellated sperm– Formation of a phragmoplast

• Supported by genetic similarites in both their nuclear and chloroplast genes

10 mm

40 µm

Chara,a pondorganism(LM).

Coleochaete orbicularis, a disk-shaped charophycean (LM).

Adaptations Enabling the Move to Land

• In charophyceans a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out

• The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants

Land plants possess a set of derived terrestrial adaptations

• Many adaptations emerged after land plants diverged from their charophycean relatives

• Five key traits appear in nearly all land plants but are absent in the charophyceans:– Apical meristems– Alternation of generations– Walled spores produced in sporangia– Multicellular gametangia– Multicellular dependent embryos

Plant Characteristics

• Multicellular eukaryotes• Photosynthetic autotrophs• Chloroplasts with photosynthetic pigments

– chlorophyll, carotenoids• Cell walls contain cellulose• Excess glucose stored as starch in plastids

Life Cycles of Plants: Alternation of Generations

• Gametophyte—multicellular individual with haploid cells– Produce haploid cells

that fuse to form zygotes

• Sporophyte—multicellular individual with diploid cells– Develop from the

zygotes that are formed

Dark round structures are antheridia or archegonia of the fern gametophyte (x12)

Gametophyte Phase

The fern sporophyte grows from a fertilized egg in an archegonium

on the gametophyte. (x12)

Fern Fiddleheads

Fern Leaf with Sori

Sporophyte Phase

Sori on Fern Leaf

Plant Phylogeny

1. Origin of plants from aquatic ancestors— Ordovician period (475mya)

– Cuticle formation and jacketed gametangia– Vascular tissue with conducting cells

2. Diversification of seedless vascular plants—Devonian period (400mya)

Plant Phylogeny

3. Origin of the seed—Devonian period (360mya)

– Seed = plant embryo packaged with food store and protective coat

– Gymnosperms—early seed plants—naked seeds

4. Emergence of flowering plants—Cretaceous period (130mya)

– Angiosperms—plants bear seeds inside flower’s protective ovaries

Ancestralgreen alga

Origin of land plants(about 475 mya)

Origin of vascular plants(about 420 mya)

Origin of seed plants(about 360 mya)

Land plants

Vascular plants

Seed plantsSeedless vascular plantsBryophytes

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Classification of Plants I•Nonvascular Plants (Bryophytes)

•Division Bryophyta (mosses)•Division Hepatophyta (liverwarts)•Division Anthocerophyta (hornwarts)

Characteristics:•Small herbaceous plants (nonwoody)•No vascular tissue, so relies on diffusion and capillary action to get water

•Need water to reproduce•Gametophytes—larger and longer-living than sporophytes•Sporophytes—typically present only part of the time•Gametangia protect developing gametes

•antheridium—produce flagellated sperm•archegonium—produce single egg

Division Bryophyta (mosses)

•Spongy mat—can absorb and retain water•Grips substratum with rhizoids (cellular filaments)

http://www.dkimages.com/discover/previews/998/35002390.JPG

http://gallery.criticalmoss.net/cache/moss_Moss.png_400.jpg

http://www2.una.edu/pdavis/images/liverworts/rhizoidUlbasechipol10CM.jpg

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• The green leafy structures are gametophytes. • The brown structures are sporophyte stalks and

spore capsules.

http://www.davidlnelson.md/Cazadero/CazImages/Moss_sporangium2.jpg

Malegametophyte

“Bud”Spores develop intothreadlike protonemata.

Protonemata“Bud”

The haploid protonemataproduce “buds”that grow into gametophytes.

Raindrop

Sperm

Antheridia

Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively.

Egg

Haploid (n)

Diploid (2n)

Key

A sperm swims through a film of moisture to an archegonium and fertilizes the egg.

Archegonia

Rhizoid

Femalegametophyte

GametophoreSpores

Sporangium

Peristome

MEIOSIS

Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores.

The sporophyte grows a long stalk, or seta, that emerges from the archegonium.

FERTILIZATION

(within archegonium)

Archegonium

Zygote

Embryo

Calyptra

Youngsporophyte

Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte.

The diploid zygote develops into a sporophyte embryo within the archegonium.

Capsule(sporangium)

Seta

Foot

Maturesporophytes

Capsule withperistome (SEM)

Femalegametophytes

Life Cycle of Moss

Division Hepatophyta (liverworts)

•Sporangia have coil-shaped cells that spring out and disperse spores LIVERWORT

SPOROPHYTE

http://www.kingsnake.com/westindian/hepaticopsida5.JPG

hornwort Phaeoceros

Division Anthocerophyta (hornworts)

•Sporophytes are horn-shaped, elongated capsules that grow from the mat like gametophyte

•Photosynthetic cells have only one large chloroplast

www.botany.hawaii.edu/.../Cyanobacteria.htm

http://taggart.glg.msu.edu/bot335/Hornw.jpg

sporophyte

gametophyte

Classification of Plants•Vascular Plants Seedless Vascular Plants

•Division Lycophyta (lycophytes)•Division Sphenophyta (horsetails)•Division Pterophyta (ferns)

•Characteristics:•Sporophytes are the larger generation•Gametophytes are tiny plants that grow on or below the soil surface

•Terrestrial Adaptations:•Roots-transport water•Cellulose (structure support) •Vascular tissue-xylem (water) and phloem (food)•Pollen-eliminates need for water in reproduction•Increased dominance of diploid sporophyte

Lycopodium annotinum

Order IsoetalesQuillworts

Division Lycophyta (lycophytes)

•Low-growing plants with rhizomes and true leaves•Some are epiphytes (use another organism as a substratum

Rhizome: stem like part of the plant from which the leaves grow

Sphenophytes consist of only one genus, Equisetum, with about thirty living species known worldwideHomosporous-bisexual gametophyte produces egg and sperm

Division Sphenophyta (horsetails)

http://hcs.osu.edu/hcs300/svp1.htm

sporangia

http://hcs.osu.edu/hcs300/svp1.htm

Division Pterophyta (ferns)

• Most diverse seedless vascular plants

• Fronds-compound leaves• Homosporous• Sporangia borne on

underside of specialized sporophylls

• Water necessary for fertilization

• Sporophyte develops within archegonium

http://en.wikipedia.org/wiki/Fernhttp://en.wikipedia.org/wiki/Fern

http://en.wikipedia.org/wiki/Image:Sa-fern.jpg

3 Variations on Alternation of Generations in Plants

Evolution of Roots

• Roots are organs that anchor vascular plants

• They enable vascular plants to absorb water and nutrients from the soil

• Roots may have evolved from subterranean stems

Evolution of Leaves

• Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

• Leaves are categorized by two types:– Microphylls, leaves with a single vein– Megaphylls, leaves with a highly branched

vascular system• According to one model of evolution, microphylls

evolved first, as outgrowths of stems

Classification of Plants II

• Vascular Plants• Seed Plants• Gymnosperms

– Division Coniferophyta (conifers)

– Division Cycadophyta (cycads)

– Division Ginkgophyta (ginkgo)

– Division Gnetophyta (Gnetae)

Seeds Replace Spores

• Relatively harsh terrestrial environment led to development of resistant structures for the dispersal of offspring

• Seeds more hardy because of multicellular nature• Seed = sporophyte embryo + food supply

surrounded by protective coat• Seed plants are heterosporous

– Megasporangia produce megaspores female gametophyte

– Microsporangia produce microspores male gametophyte

Heterospory: The Rule Among Seed Plants

• Seed plants evolved from plants with megasporangia, which produce megaspores that give rise to female gametophytes

• Seed plants evolved from plants with microsporangia, which produce microspores that give rise to male gametophytes

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Ovules and Production of Eggs

• An ovule consists of a megasporangium, megaspore, and one or more protective integuments

• Gymnosperm megaspores have one integument

• Angiosperm megaspores usually have two integuments

Integument

Megasporangium(2n)

Megaspore (n)

Unfertilized ovule Fertilized ovule

Spore wall

Male gametophyte(within germinatingpollen grain) (n)

Micropyle

Femalegametophyte (n)

Egg nucleus (n)

Dischargedsperm nucleus (n)

Pollen grain (n)

Seed coat(derived fromintegument)

Embryo (2n)(new sporophyte)

Gymnosperm seed

Food supply(femalegametophytetissue) (n)

Pollen and Production of Sperm

• Microspores develop into pollen grains, which contain the male gametophytes

• Pollination—transfer of pollen to the part of a seed plant containing the ovules

• Dispersal by air or animals• If a pollen grain germinates, it

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The Evolutionary Advantage of Seeds

• A seed develops from the whole ovule• A seed is a sporophyte embryo, along with its

food supply, packaged in a protective coat

commons.wikimedia.org/wiki/Image:Avocado_seed...

Araucaria cunninghamii. The hoop pine. Lake Tinaroo Falls Dam, Queensland, Australia.

Division Coniferophyta (conifers)

•Largest division of Gymnosperms -most are evergreens: pines, spruces, firs, larches, yews, junipers,

cedars, cypresses, and redwoods

Sequioadendron giganteum. The Giant Sequoia. Yosemite National Park, Mariposa County, California.

Division Coniferophyta (conifers)

Needle-shaped conifer leaves are adapted to dry conditions•thick cuticle covers the leaf•stomata are in pits, reducing water loss

Division Coniferophyta (conifers)

Mature ovulate cones and seeds

Heterosporous- both male and female gametophytes develop from different types of spores on separate cones

http://www.esu.edu/~milewski/intro_biol_two/lab_3_seed_plts/images/Male_stroboli.jpg

http://www.seinan-gu.ac.jp/~djohnson/natural/campusplants/023pine.cone3.JPG

Cedrus deodora. Near Placerville

Division Coniferophyta (conifers)

Division Cycadophyta (cycads)

• Living fossils—Jurassic Period is sometimes called the "Age of Cycads"

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http://a.abcnews.com/images/Technology/nc_cycads_071004_ms.jpg

http://www.hort.wisc.edu/mastergardener/Features/botgardens/lotusland/Lotusland-cycads.jpg

Division Cycadophyta (cycads)

Cycas revoluta

Division Ginkgophyta

(ginkgo)

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Division Gnetophyta (Gnetae)

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Classification of Plants II

•Vascular PlantsSeed Plants Angiosperms

Division Anthophyta (flowering plants)

Reproductive adaptations of angiosperms include flowers and fruits

• Angiosperms are flowering plants

• These seed plants have reproductive structures called flowers and fruits

• They are the most widespread and diverse of all plants

California Poppy

Sunflower

Indian Paintbrush in Grand Canyon.

Division Anthophyta (flowering plants)

Stamen

Filament

Anther

StigmaCarpel

Style

Ovary

Petal

Receptacle

Ovule

Sepal

Fruit develop from the ovary

http://www-plb.ucdavis.edu/labs/rost/Tomato/Reproductive/stages2aa.gif

Fruits• A fruit typically

consists of a mature ovary but can also include other flower parts

• Fruits protect seeds and aid in their dispersal

• Mature fruits can be either fleshy or dry

Tomato, a fleshy fruit with softouter and inner layers of pericarp

Ruby grapefruit, a fleshy fruitwith a hard outer layer and softinner layer of pericarp

Milkweed, a dry fruit that splitsopen at maturity

Walnut, a dry fruit that remainsclosed at maturity

Nectarine, a fleshyfruit with a soft outerlayer and hard innerlayer (pit) of pericarp

Fruits

• Various fruit adaptations help disperse seeds

• Seeds can be carried by wind, water, or animals to new locations

Wings enable maplefruits to be easilycarried by the wind.

Seeds within berries and other edible fruits are often dispersed in animal feces.

The barbs of cockleburs facilitate seed dispersal by allowing these fruits to hitchhike on animals.

The Angiosperm Life Cycle• In the angiosperm life cycle, double fertilization

occurs when a pollen tube discharges two sperm into the female gametophyte within an ovule

• One sperm fertilizes the egg, while the other combines with two nuclei in the central cell of the female gametophyte and initiates development of food-storing endosperm

• The endosperm nourishes the developing embryo

The Angiosperm Life Cycle

Anther

Mature flower onsporophyte plant(2n)

Key

Haploid (n)

Diploid (2n)

Microsporangium

Microsporocytes (2n)

MEIOSIS

Microspore (n)

MEIOSIS

Ovule withmegasporangium (2n) Male

gametophyte(in pollengrain)

Ovary

Generative cell

Tube cell

Megasporangium(n)

Survivingmegaspore(n)

Female gametophyte(embryo sac)

Antipodal cellsPolar nucleiSynergidsEggs (n)

Pollentube

Sperm(n)

Pollengrains

Pollentube

Style

Stigma

Pollentube

Sperm

Eggs nucleus (n)

Discharged sperm nuclei (n)

Germinatingseed

Zygote (2n)

FERTILIZATION

Nucleus ofdevelopingendosperm

(3n)

Embryo (2n)

Endosperm(foodsupply) (3n)

Seed coat (2n)

Seed