Chapter 5 Flashcards
Evolution and biodiversity
Heritable characteristics
characteristics that an organism possesses due to its genetic make-up
Evolution
the change in heritable characteristics of a species over time
Fossil record
provides a record of the order of the changes in certain species over time
- hence, fossil record provides evidence for evolution
How was the fossil record determined?
- geologists interpreted different rock strata in which fossils were found
- dating of those strata allowed chronological ordering and deduction of which organism came first
- later, came radioisotope-dating
- use of radio isotopes, more accurate dating methods became available, supporting chronology of fossils
Selective breeding
- a form of artificial selection
- where humans select animal or plant with the best characteristics to create a breed or plant line that retains these desired characteristics
- it accelerates the evolutionary process, as evolutionary changes become visible in a much shorter time interval than might have occurred through natural selection
NB/ artificial selection can only happen through human intervention
Domestication of animals and evolution
- selective breeding of domesticated animals shows how artificial selection can cause evolution
- all breeds of household dogs today are the products of selective breeding
- original bloodline is from wolf-like animals that were tamed and bred for more docile traits
- when inheritable physical features of domesticated dogs are compared w/ wolves, it’s clear evolution has occurred
- following several generations of selective breeding, domesticated breeds can differ a lot from their wild ancestor
Homologous
refers to something that is similar in position, structure and evolutionary origin, but not necessarily in function
Homologous structures
structures that share the same origin and ancestral form, but not function
- suggests that the species must have had a common ancestor, but they diverged over time to be better adapted to their respective environments
Divergent evolution
- where there’s an accumulation of differences between groups which led to the formation of new species
- there is a shared ancestor, but the end points are two different lines with two structures that have different functions
Divergent evolution of homologous structures
divergent evolution of homologous structures explains the similarities in limb structure of mammals, birds, amphibians and reptiles, even if each of them has a different method of locomotion
Analogous structure
the function may be similar, but there is no similarity in bone structure or common ancestor
Convergent evolution
when organisms that are not closely related evolve similar structures that are used for similar purposes
- structures develop to resemble each other and have the same function
Speciation
process by which new species form
How do species form?
- Physical separation
2. Adaptive radiation
Physical separation and speciation
- separated populations adapt to environment they inhabit
- if they remained isolated over a long period of time, they would become genetically different
- if, by chance, they met with members from original population, they could no longer interbreed to produce fertile offspring
NB/ a group can be said to be of a different species when they can no longer interbreed to produce fertile offspring
Adaptive radiation
a process in which organisms rapidly diverge from the form of the original species into several new forms specialised to make use of different environmental niches
Darwin’s finches
- shows how related populations, isolated from each other due to geographical barriers, change over time to be better adapted to their environment
- Galapagos finches show continuous variation across their geographical range
- Beak sizes gradually get bigger, there is no sudden change from small beaks to large beaks, w/ no intermediate sizes present
- this supports idea of gradual divergence; organisms change through a slow process and may ultimately form new species
- Thus, when all members of related species are compared, they show continuous variation across geographical range
Industrial melanism
- example of how a change in environment can precipitate an evolutionary adaptation - moth, Biston betularia is active at night and roosts during the day
- It rests on trees and uses tree bark covered w/ lichen as camouflage to remain undetected so birds won’t prey on it
In the 19th century, industrial revolution led to widespread burning of fossil fuels to power machinery
- produced large amounts of sulphur dioxide- killed many plants and lichen
- also produced vast quantities of soot which changed colour of the tree bark- result was darker coloured trees
Populations of Biston betularia consist of two main morphs: a darker and a lighter coloured moth
- melanistic morph was better camouflaged in the most industrial areas
- lighter coloured moth was better adapted to non-polluted areas, because trees were still covered in lichen and had little or no soot - making it less visible to predators
- hence, in industrial areas, no. of darker moth increased, and no. of lighter moth declined
- can be explained as lighter peppered moths were easily spotted and eaten while resting on dark and sooty tree barks
- darker peppered moths were well camouflaged in polluted areas and many survived to reproduce
- hence, pollution brought about by industrial revolution acted as a selection pressure that favoured darker moth over lighter moth
Principle of evolution
- evolution concerns interaction of environment and fitness of a population
- If a change in the environment occurs, only best able to adapt individuals will survive
Gene pool
refers to the sum of all genes found in an interbreeding population
- hence, each species has its own gene pool
Bigger gene poole
- means that if conditions change, a species has a better chance of survival
- It also helps to have a large population
- If there is only a small population left, gene pool will also be small
- species will be endangered
Variation
- phenotype of a species is one way to observe certain characteristics, but a lot of variation is invisible
- range of alleles present in a species accounts for variation in the population
- is a good measure of a healthy gene pool
Causes of variation
- Mutation: any change to DNA sequence is classified as a mutation
- It can range from a single base change to removal of one segment of a chromosome - Meiosis: produces gametes w/ unique combinations of alleles, thus increasing genetic variation of individuals within the species.
- Sexual reproduction: combination of gametes results in a zygote that has genes from both of its parents
Asexual reproduction and variation
- Not all species reproduce sexually
- most prokaryotes and some eukaryotes reproduce asexually
- a species reproduces asexually, it produces a clone that is an identical genetic copy of itself
- only way asexual species can increase variation is through mutation
How does the gene pool change over time?
- according to natural selection, organisms better adapted to their environment tend to survive and produce more offspring
- successive cycles of selection of the ‘fittest’ or best adapted from varying members of a population bring about evolution
- no. of individuals possessing that adaptation, and genes that code for it, increases in frequency
- characteristics, and their genes, that don’t confer an advantage are gradually lost from population
Adaptations
characteristics that make an individual suited to its environment and way of life
Overproduction of offspring
- Species tend to produce more offspring than their environment can support
- But, overpopulation in nature is rare
- consequence of overproduction is that not all of the offspring survive- ensures a power struggle within population
- indirectly ensures that best adapted to the environment will survive
- those surviving long enough to reproduce will contribute to next generation
Well adapted individuals
- individuals that are better adapted tend to survive and produce more offspring, while less well adapted tend to die or produce fewer offspring
- Survival to an age where an organism can reproduce means individual was well adapted
- Its offspring will inherit genes for these characteristics
- hence, better adapted individuals reproduce to pass on characteristics to their offspring, contributing to their survival
- organisms that aren’t as well adapted are more likely to die before they reach reproductive age
- hence, their genes (or specific alleles) will be eliminated from the population- alternatively, they may survive but produce fewer offspring
Adaptation of characteristics
- characteristics that are favoured make a species better adapted to its environment
- if that environment changes, those w/ genes that confer characteristics that are well adapted to new environment will survive and pass on these genes to their offspring
- hence, natural selection increases frequency of characteristics that make individuals better adapted
- decreases frequency of other characteristics
- leads to change within the species
- thus, the whole species become better adapted to their changed environment w/ time
Galapagos finches
- finches have evolved to adapt to particular food sources available on the islands
- this change is visible in their beaks
- some beaks can crack larger beaks seeds
- some smaller beaks cope better w/ smaller seeds
- this adaptive radiation has allowed various finch populations to survive side by side, even on smaller islands, because of food specialisation
Geospiza fortis
- lived off smaller and larger seeds because of a variation in beak size in the G. fortis population
- 1977, a drought caused a shortage of smaller seeds
- G. fortis population collapsed
- birds w/ slightly longer and narrower beaks survived because they could feed on larger seeds as well
- El nino 1982/1983 caused massive rainfall
- so, Geospiza population increased due to higher small seed availability
- w/ return of drought conditions in Geospiza population, only a small no. of birds were still breeding
- the average beak size of these birds was longer and narrower than those of the earliest populations
- their beaks were better suited to eating larger seeds
Reason for antibiotic resistance- why has antibiotic resistance spread so widely and rapidly?
- Bacterial generation times are short, 20 mins - several hours
- means that evolution can progress rapidly - Widespread use of antibiotics in general population and in animal feed
- people often don’t finish a course of antibiotics, leaving residual populations of bacteria in their system that have been exposed and are likely to have developed partial or full resistance - Antibiotic resistance is often coded for by a gene (or genes) located on plasmid
- plasmids are easily exchanged between bacteria, even if they aren’t of same species or strain - Hospitals are breeding grounds for antibiotic resistance
- is where patients w/ severe infections are treated w/ high doses of antibiotics, creating enormous selective pressure on bacteria
Genus
a group of species that share characteristics
- species name is specific to that organism
- may refer to a specific trait of that particular organism
Hierarchy of taxa
Domain Kingdom Phylum Class Order Family Genus Species
3 Domains
- bacteria
- archaea
- eukaryote
Characteristics of bacteria
- no histones
- no introns
- cell membrane made of glycero-esters of lipids
- cell wall made of peptidoglycan
Characteristics of archaea
- histones are present in some species
- introns are present in some genes
- cell membrane made of glycerol-ether lipids
- cell wall is not made of peptidoglycan
Characteristics of eukaryotes
- histones are present
- introns are present
- cell membrane made of glycerol ester lipids
- cell wall not made of peptidoglycan, sometimes absent
What are the three domains?
Archaea:
- usually unicellular organisms
- live in extreme habitats eg. hot water springs, deep earth sediments and lakes or pools w/ extremely high salt conc.
Bacteria: remaining prokaryotic organisms
Eukaryotes: includes remainder of all living organisms
NB/ viruses aren’t included in this taxonomy
- they don’t have enough features to be considered living organisms
- taxonomy is concerned w/ living organisms
Phylogenetic tree
a tree showing evolutionary relationships and ancestry
Classification of eukaryotes
- Kingdom Animalia
- Kingdom Plantae
- Kingdom Fungi
- Kingdom Protoctista
Classification of one animal
HUMAN Kingdom: Animalia Phylum: Chordata Class: Mammlia Order: Primates Family: Hominidae Genus: Homo Species: sapiens
Classification of one plant
Buttercup Kingdom: Plantae Phylum: Angiospermophyta Class: Eudicotidae Order: Ranunculuses Family: Ranunculacae Genus: Ranunculus Species: acris
Natural classification
where a genus and its accompanying higher taxa consist of all the species that have evolved from one common ancestral species
Reclassificaiton
- ancestry can also be confirmed by DNA and protein analysis
- this makes the grouping of certain organisms much more reliable
- new findings, eg. DNA sequence analyses, reveal that previous classification is wrong eg. taxon may contain species that have evolved from different ancestors
- in this cases, taxonomists reclassify groups of species according to new evidence
Natural classification
- shared features between organisms and their ancestors are used to classify a newly discovered organism
- allows prediction of characteristics shared by species within a group
Dichotomous keys
- a series of paired statements that guides the user to the identity of/ allows classification of an item or organism
- helps to quickly identify organisms
- rely on visible features to classify organisms
Plant phyla
- Phylum Bryophyta
- Phylum Filicinophyta
- Phylum Coniferophyta
- Phylum Angiospermophyta
Phylum Bryophyta
- mosses, liverworts and hornworts
- a group of non-flowering plants (1-10cm)
- don’t have vascular tissue for water transport
- produce spore capsules, they’re held above the plant on thin stalks
- don’t have proper roots, have rhizoids
- leaves contain chlorophyll and carry out photosynthesis
Phylum Filicinophyta
- ferns and horsetails
- have shallow roots
- leaves are fronds
- have a primitive vascular system
- don’t have woody stems
- spores are produced in clusters on the underside of their fronds
Phylum Coniferophyta
- conifers eg. cedars, cypresses, redwoods
- are gymnosperms, their seeds aren’t enclosed in an ovary
- cone-bearing seed trees w/ vascular tissue
- trees are made of wood and have narrow leaves w/ a thick, waxy cuticle
- conifers are monoecious plants
- reproduce sexually by releasing pollen from male cones, carried by the wind to the female cones where ovules are fertilised to form seeds
Monoecious plants
produce both male and female reproductive structures or cones on the same plant
Phylum Angiospermophyta
- flowering plants w/ vascular tissue
- stem may be woody
- can by classified as monocotyledons or dicotyledons
- reproduction involves transfer of pollen grains from anthers to stigma of carpels, followed by fertilisation of ovules found in the ovary
- once fertilised, ovules form seeds, while ovary develops into a fruit
Animal phyla
- Phylum Porifera
- Phylum Cnidaria
- Phylum Platylhelmintha
- Phylum Annelida
- Phylum Mollusca
- Phylum Arthropoda
- Phylum Chordata
Phylum Porifera
- sponges
- multicellular organisms w/ bodies full of spores and channels allowing water to circulate
- no mouth or anus
- no nervous, digestive or circulatory system
- may form skeleton of calcium carbonate
- always aquatic
Phylum Cnidaria
- include jellyfish, corals and anemones
- 2 basic body forms: swimming medusae and sessile polyps
- have radial symmetry
- mouth present
- single opening into a body cavity used for digestion and waste disposal
- simple nervous system composed of a decentralised nerve net
Phylum Platylhelmintha
- flatworms
- bilateral symmetry
- 3 layers of tissue in their body
- no body cavity
- mouth present
- no anus
- found in water and sometimes as parasites in other animals
Phylum Annelida
- include segmented worms and leeches
- have bilateral symmetry
- has a mouth and anus
- body is divided into ringed segments w/ some specialisation of segments
- found in marine environments
eg. earthworms
Phylum Mollusca
- snails, slugs, octopus, oysters, mussels
- has a mantle w/ a significant cavity used for breathing and excretion
- has a radula
- simple nervous system
- may have a calcareous shell
- has a mouth and anus
Phylum Arthropoda
- includes insects, crustaceans, spiders
- all have an exoskeleton made of chitin
- bilateral symmetry
- jointed appendages
- all have segmented bodies
Phylum Chordata
- mammals, fish, amphibians, reptiles, birds
- animals that have a notochord
- have a hollow dorsal nerve cord
- all have bilateral symmetry
- separate mouth and anus
Vertebrates
- subphylum of chordata
Five classes (MR FAB):
Mammals
Reptiles
Fish
Amphibians
Birds
Mammals
- are endothermic; maintain their body at a metabolically favourable temp.
- have hair, 3 middle ear bones and mammary glands in females
- all give birth to live young (except for the 5 species of montremes)
- rely on internal fertilisation for reproduction
Reptiles
- includes turtles, crocodiles, snakes and lizards
- have scales
- are ectothermic
- have dry scaly skin
- reproduce through internal fertilisation but lay eggs
Fish
- an animals w/ gills that lacks limbs w/ digits
- most are ectothermic
- bodies are covered w/ scales
- possess a swim bladder for buoyancy
- most species rely on external fertilisation for reproduction
Amphibians
- ectothermic
- found in a wide variety of habitats: terrestrial, arboreal or freshwater aquatic ecosystems
- use their skin as a secondary respiratory surface
- rely on external fertilisation for reproduction
Birds
- have feathers, wings and two legs
- are endothermic
- lay eggs
- rely on internal fertilisation for reproduction
Monotremes
egg-laying mammals
eg. platypus
Ectothermic
animals that regulate their body temp. using external sources eg. basking in the sun
- makes them cold-blooded
How can the ancestry of a group of species be deduced?
Deduced by comparing base or amino acid sequences
Cladistics
A system of classifying organisms according to shared characteristics, based on ancestry
Cladogram
A diagram that shows the evolutionary relationship of a group of organisms
Clade
A group of organisms, both extant and extinct that share an ancestor
- based on similarity of DNA or amino acid sequences
Analogous structures
structures that have similar functions but have evolved separately, through convergent evolution, from different ancestral features
Homologous structures
structures that are similar because of shared ancestry, but that may have different actions due to divergent evolution
Evidence for which species are part of a clade
- compare the morphological features, analyse DNA of a particular gene or ribosomal RNA of these species
- comparing amino acid sequence of certain proteins
- DNA analysis and protein analysis will allow them to describe relationships between DNA or protein sequences
- closer the relationship more recent these species diverged from each other
NB/ Evidence for which species are part of a clade is obtained from base sequences of a gene or corresponding amino acid sequence of a protein
Process of the molecular clock
- DNA can mutate
- So, over time, small changes occur in the DNA, ultimately leads to speciation
- mutations accumulate gradually and are an indication of how much time has passed since two species diverged from their common ancestor
- There is a positive correlation between no. of differences between two species and time since they diverged from a common ancestor
- longer the time period since two species separated, more differences there will be when DNA of two species is compared
Formation of a cladogram
- a tree diagram that shows most probable sequence of divergence within a group that shares characteristics, commonly known as a clade
- mostly based on sequence analysis of either DNA bases or amino acids from proteins
- DNA sequence analysis gives most accurate results
- certain genes for analysis gives a better result
- some genes are more conserved- they evolve more slowly because any mutation might be lethal to the organism
- these conserved genes allow even distantly related species to be compared
- computer programs analyse DNA sequences to arrive at cladogram w/ lowest possible number of nodes
Node
a point on the cladogram that represents where two species diverged
Analysis of cladograms- assumptions and definitions made
- Branching pattern is assumed to represent evolutionary relationship between species
- If extinct species are included, information must be given on whether cladogram is based on morphology only (DNA generally isn’t available for analysis, although there are exceptions)
- More nodes there are between species, the more distant their relationship
- Changes at DNA and protein level are assumed to occur at a constant rate
- Some cladograms are drawn to scale; length of branches is proportional to time since divergence
NB/ cladogram can be used to estimate when species diverged and when the common ancestor existed
Classificaiton errors
- classification based on traditional methods; morphology, feeding patterns and other behavioural aspects,
hasn’t given accurate results for relationships between organisms - new evidence has shown that classification of some groups didn’t correspond w/ evolutionary origins of a group or species
- use of protein and DNA sequence technologies allows analysis of these biochemicals and improvs accuracy of cladistic analysis immensely
- technology has caused reclassification of many plant and animal
- some groups have merged, and others have been split
Classification of the figwort family
- an example of how DNA sequence analysis has changed classification
- plants are difficult to classify, and arrival of modern DNA sequencing techniques makes it possible to assess relationships between some plants w/ relative confidence
- figwort family (Scrophulariaceae) included more than 275 genera w/ around 5,000 species, based on shared morphological features
- scientists compared chloroplast DNA, observed that what was once thought to be 1 clade- all descendants from 1 ancestor, was actually 5 clades
- until this analysis, it was impossible to distinguish between the 5 clades, as their morphology was so similar (due to convergent evolution)
- now figwort family has around 200 species
- several figwort genera have been moved to other families eg/ plantain and broomrape
