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The next few questions refer to the following description.
In the ocean, on either side of the Isthmus of Panama, are 30 species of snapping shrimp; some are shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15 different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago.
In the following figure, the isthmus separates the Pacific Ocean on the left (side A) from the Atlantic Ocean on the right (side B). The seawater on either side of the isthmus is separated into five depth habitats (1—5), with 1 being the shallowest.
6 In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat A4?
7 Which of these habitats is likely to harbor the youngest species?
8 Which habitats should harbor snapping shrimp species with the greatest degree of genetic divergence from each other?
9 The Panama Canal was completed in 1914, and its depth is about 50 feet. After 1914, snapping shrimp species from which habitats should be most likely to form hybrids as the result of the canal?
10 Which factor is most important for explaining why there are equal numbers of snapping shrimp species on either side of the isthmus?
A) the relative shortness of time they have been separated
B) the depth of the ocean
C) the number of actual depth habitats between the surface and the sea floor
D) the elevation of the isthmus above sea level
E) the depth of the canal
Why a Scientific Classification System?
• Ambiguity of terms
• Latin “dead language”
• Categorization of relationships:
7 Classification Groups:
• Kingdom (most inclusive)
Species (most specific)
5 Major Kingdoms:
1 cell, prokaryotes
1 cell, eukaryotes & algae
Multicelled, absorptive feeders
Which is the most difficult to assign?
Which group has the largest # organisms?
• Common names
– Have evolved over centuries in a multitude of languages
– Sometimes used only in a limited geographical area
– Problem with common nameOne plant may be known by several names in different regions, and the same name may be used for several different plants…
Similar plant species form a group called a genus (plural: genera)…
Genera are grouped into families…
Families into orders, classes, phyla and kingdoms
“King Phillip Came Over For Great Spaghetti”
“King Phillip Conquered Our Fifty Great States”
Each species has a single correct scientific name in Latin called a binomial (two names) – it is always italicized or underlined.
First name is genus name.
Second name is species name
Human: Homo sapiens
Cat: Felis catus
Dog: Canis familiaris Wolf: Canis lupus
Genus of maple trees is Acer
It has many species including:
Common name Scientific name
“Red maple” Acer rubrum
“Sugar maple” Acer saccharum
“Black maple” Acer nigrum
Species that have many characteristics in common are grouped into a genus.
Related genera that share combinations of traits are grouped into families.
Families are grouped into orders.
Orders into classes
Classes into phyla
Related divisions/phyla are grouped into kingdoms
(e.g. house, street, city, county, state, country, continent, planet)
What is a species?
Species: a set of individuals that are closely related by descent from a common ancestor and ordinarily can reproduce with each other, but not with members of any other species.
Biological species: group of interbreeding populations. Offspring are fertile.
Pleonosporium flexuosum (C.Agardh) Bornet ex De Toni
Plocamium coccineum var. flexuosum Hooker & Harvey
Plocamium flexuosum (Hooker & Harvey) Harvey
Plocamium leptophyllum var. flexuosum J.Agardh
Pseudophormidium flexuosum (Gardner) Anagnostidis & Komárek
Schizonema flexuosum (Cleve) Kuntze
cytonema flexuosum Meneghini
Stigonema flexuosum W.West & G.S.West
Triceratium flexuosum Greville - Unchecked
Some members of same species look very different…
Definition of species
Or, plants look the same, but due to polyploidy
(more than the diploid number of chromosomes), they cannot interbreed.
For example: Ferns; evening primrose
Swedish scientist – Carl von Linne
(doctor and botanist)
born in 1707.
Called the “Father of Systematic Botany”
Established modern system of nomenclature
His binomial system of nomenclature, in which the genus and species names are used.
He classified 12,000 plants and animals, and many of the names he first proposed are still in use today…
Hypoglossum subslmplex Wynne sp. nov.
• Fasciculus lamina rum simplicium aut subsimplicium erectarum delicatarum e base disciformi orientium; ranNflcatio tantum ad unum ordinem; laminae tantum usque 6 mm altae; margins laminae laeves; costa corticata destituta; omnes cellulae serierum cellularum secundi ordinis series cellularum tertii ordinis procreant; tetrasporangia tantum in una lamina procreant, cellulis ambo serierum secundi ordinis et tertii ordinis abscissa, vicina costa laminae, sic laterales cellulas pericentrales includentibus; sorus tetrasporangiorum non discretus in longitudino sed ad aliquot distanciam currens; sori spermatangiorum plerumque in turmis diagonaliter aut irregulariter dispositi, parvi et sejuneti aut confluentes; uno aut duo cystocarpiae in quoque femina lamina, in costa locatae.
• Diagnosis: A cluster of simple or subsimple erect, delicate blades arising from a discoid base; branching to one order only; blades only up to 6 mm tall; margins of blade smooth; corticated midrib lacking; all second-order row cells producing thirdorder rows; tetrasporangia produced in only the primary layer, cut off by cells of both second- and third-order rows in vicinity of midline of blade, thus including lateral pericentral cells; tetrasporangial sorus not discrete in length but running continuously for some distance; spermatangial sori arranged usually in diagonal or irregular groups, small and isolated or becoming confluent; I or 2 cystocarps per female blade, located on the midline.
• Holotype: Wynne 9959 (slide in MICH), on Halimeda tuna, collected by M. D. Hanisak, 19 June 1994, Content Keys, lee side of Florida Keys, Florida, U.S.A. Isotypes: slides deposited in MEL, PC, UC, US.
Italics or underlined
Family or Genus Relations?
• Less closely related
• Larger group
• More closely related
• Precedes species=
• Lions, tigers, leopards
• house cats,cheetahs, ocelots
• Leopards (pardus)
• Lion (leo)
• Tigers (tigris)
Feline Family Members:
Genus: Panthera (Lions &Tigers)
The Permian Mass Extinction
- Permian Period (286-248 million years ago)
- Terrestrial faunal diversification occurred in the Permian
- 90-95% of marine species became extinct in the Permian
With the formation of the super-continent Pangea in the Permian, continental area exceeded that of oceanic area for the first time in geological history. The result of this new global configuration was the extensive development and diversification of Permian terrestrial vertebrate fauna and accompanying reduction of Permian marine communities. Among terrestrial fauna affected included insects, amphibians, reptiles (which evolved during the Carboniferous), as well as the dominant terrestrial group, the therapsids (mammal-like reptiles).
The terrestrial flora was predominantly composed of gymnosperms, including the conifers. Life in the seas was similar to that found in middle Devonian communities following the late Devonian crisis. Common groups included the brachiopods, ammonoids, gastropods, crinoids, bony fish, sharks, and fusulinid foraminifera. Corals and trilobites were also present, but were exceedingly rare.
The Permian mass extinction occurred about 248 million years ago and was the greatest mass extinction ever recorded in earth history; even larger than the previously discussed Ordovician and Devonian crises and the better known End Cretaceous extinction that felled the dinosaurs. Ninety to ninety-five percent of marine species were eliminated as a result of this Permian event
The primary marine and terrestrial victims included the fusulinid foraminifera, trilobites,rugose and tabulate corals, blastoids, acanthodians, placoderms, and pelycosaurs, which did not survive beyond the Permian boundary. Other groups that were substantially reduced included the bryozoans, brachiopods, ammonoids, sharks, bony fish, crinoids, eurypterids, ostracodes, and echinoderms
Speculated Causes of the Permian Extinction
Although the cause of the Permian mass extinction remains a debate, numerous theories have been formulated to explain the events of the extinction. One of the most current theories for the mass extinction of the Permian is an agent that has been also held responsible for the Ordovician and Devonian crises, glaciation on Gondwana.
A similar glaciation event in the Permian would likely produce mass extinction in the same manner as previous, that is, by a global widespread cooling and/or worldwide lowering of sea level.
The Formation of Pangea
Another theory which explains the mass extinctions of the Permian is the reduction of shallow continental shelves due to the formation of the super-continent Pangea. Such a reduction in oceanic continental shelves would result in ecological competition for space, perhaps acting as an agent for extinction.
However, although this is a viable theory, the formation of Pangea and the ensuing destruction of the continental shelves occurred in the early and middle Permian, and mass extinction did not occur until the late Permian.
A third possible mechanism for the Permian extinction is rapid warming and severe climatic fluctuations produced by concurrent glaciation events on the north and south poles. In temperate zones, there is evidence of significant cooling and drying in the sedimentological record, shown by thick sequences of dune sands and evaporites, while in the polar zones, glaciation was prominent..
This caused severe climatic fluctuations around the globe, and is found by sediment record to be representative of when the Permian mass extinction occurred.
The fourth and final suggestion that paleontologists have formulated credits the Permian mass extinction as a result of basaltic lava eruptions in Siberia. These volcanic eruptions were large and sent a quantity of sulphates into the atmosphere. Evidence in China supports that these volcanic eruptions may have been silica-rich, and thus explosive, a factor that would have produced large ash clouds around the world.
The combination of sulphates in the atmosphere and the ejection of ash clouds may have lowered global climatic conditions. The age of the lava flows has also been dated to the interval in which the Permian mass extinction occurred.
• A giant volcanic eruption in what is today’s Emeishan province in China unleashed half a million cubic kilometers of lava and tossed massive quantities of sulphur dioxide into the stratosphere 260 million years ago. The sulphur dioxide caused cloud formations across the entire planet. This cooled the Earth while subsequently dropping acid rain across the globe, leading to the planet’s most pervasive extinction.
Fortunately, the researchers, publishing their findings in Science, were able to determine the exact time of the massive eruption in China, thereby linking it to the Permian extinction. Since the eruption occurred in a shallow sea it left a layer of igneous rock in-between two layers of sedimentary rock which were able to be identified with their epochs by their marine fossils.
"The abrupt extinction of marine life we can clearly see in the fossil record firmly links giant volcanic eruptions with global environmental catastrophe, a correlation that has often been controversial," says Wignall.
The scientists believe their findings confirms several studies over the years
that have suggested volcanic activity as the cause of the Permian extinction
Speculated Causes of the Precambrian and Vendian Extinctions
The first extinction of the Precambrian, which largely affected stromatolites and acritarchs, has been correlated with a large glaciation event that occurred about 600 million years ago. This event was of such severity that almost all microorganisms were completely wiped out.
The Vendian extinction, occurring near the close of the Vendian period, is currently under debate as to whether an extinction event occurred or not. Many paleontologists believe that the Vendian fauna were the progenitors of the Cambrian fauna
However, others believe that the Vendian fauna have no living representatives. Under this latter hypothesis, the Vendian fauna is believed to have an undergone an extinction, after which the Cambrian fauna evolved. Until more information can be collected, details on the Vendian extinction event will remain open to debate.
Speculated Causes For the Cambrian Extinction
The two most accepted current hypotheses for the Cambrian extinction are:
Glaciation in the early Ordovician
Cooling and depletion of oxygen in marine waters
Glacial Cooling Hypothesis
The advancement of the theory of glaciation as the predetermining agent for the Cambrian extinctions has been developed by James F.Miller of Southwest Missouri State University. Through research undertaken by Miller, evidence of early Ordovician sediment of glacial origin has been uncovered in South America. Miller suggests in his hypothesis that this evidence of continental glaciation at the Cambrian-Ordovician boundary is responsible for a decrease in global climatic conditions. Such a decline in temperature is implied by Miller to destroy Cambrian fauna which are intolerant of cooler conditions, producing a mass extinction of mostly warm water species
He also suggests that a significant continental glaciation would bring large amounts of ocean water onto the land in the form of frozen glacial ice. This trapping of ocean water inevitably results in the decrease of sea-level and the withdrawal of shallow seas. Miller implicates that this reduction in sea-level would produce reduced habitat for marine species as continental shelves are obliterated. Ecological competition would consequently ensue, perhaps acting as a driving agent for extinction.
Oxygen Depletion Hypothesis
The development of a hypothesis invoking the cooling and depletion of water in marine waters as a causative agent for the Cambrian extinctions has been advanced by several geologists, primarily Allison Palmer and Michael Taylor of the U.S. Geological Survey and James Stilt of the University of Missouri.
The cooling and oxygen depletion would occur when cool waters from deep zones of the ocean spread up onto the continent, eliminating all organisms not able to tolerate cool conditions. The cooling would also result in stratification of the water column. Thus, species would ultimately perish due to their inability to tolerate dramatic shifts in such limiting factors as temperature and oxygen availibility. Further research is required to more fully test the validity of the above outlined Cabrian extinction hypotheses.
Speculated Causes of the Ordovician Extinction
Glaciation and Sea-Level Lowering Hypothesis
The Ordovician mass extinction has been theorized by paleontologists to be the result of a single event; the glaciation of the continent Gondwana at the end of the period. Evidence for this glaciation event is provided by glacial deposits discovered by geologists in the Saharan Desert. By integrating rock magnetism evidence and the glacial deposit data, paleontologists have proposed a cause for this glaciation.
When Gondwana passed over the north pole in the Ordovician, global climatic cooling occured to such a degree that there was global large-scale continental resulting in widespread glaciation. This glaciation event also caused a lowering of sea level worldwide as large amounts of water became tied up in ice sheets. A combination of this lowering of sea-level, reducing ecospace on continental shelves, in conjunction with the cooling caused by the glaciation itself are likely driving agents for the Ordovician mass extinction.
Speculated Causes of the Devonian Extinction
Evidence supporting the Devonian mass extinction suggests that warm water
marine species were the most severely affected in this extinction event. This
evidence has lead many paleontologists to attribute the Devonian extinction to
an episode of global cooling, similar to the event which is thought to have
cause the late Ordovician mass extinction. According to this theory,the
extinction of the Devonian was triggered by another glaciation event on
Gondwana, as evidenced by glacial deposits of this age in northern Brazil.
Similarly to the late Ordovician crisis, agents such as global cooling and
widespread lowering of sea-level may have triggered the late Devonian crisis.
Meteorite impacts at the Frasnian-Famennian boundary have also been suggested
as possible agents for the Devonian mass extinction. Currently, the data
surrounding a possible extra-terrestrial impact remains inconclusive, and the
mechanisms which produced the Devonian mass extinction are still under debate.
Speculated Causes of the End-Cretaceous Extinction
The End-Cretaceous mass extinction has generated considerable public interest in recent years, in response to the controversial debates in the scientific community over its cause. The more prominent of these new hypotheses invoke extra-terrestrial forces, such as meteorite impacts or comet showers as the causative extinction agent. Older hypotheses cite earthly mechanisms such as volcanism or glaciation as the primary agent behind this mass extinction.
The K-T Boundary
Evidence for catastrophism at the Cretaceous-Tertiary boundary is found in a
layer of sediment which was deposited at the same time that the extinction
occurred. This layer contains unusually high concentrations of Iridium, found
only in the earth's mantle, and in extra-terrestrial meteors and comets. This
layer has been found found in both marine and terrestrial sediments, at numerous
boundary sites around the world.
Some paleontologists believe that the widespread distribution of this Iridium layer could have only been caused by meteorite impact. Further, these researchers cite the abundance of small droplets of basalt, called spherules, in the boundary layer as evidence that basalt from the earth's crust that were melted and flung into the air upon impact. The presence of shocked quartz - tiny grains of quartz that show features diagnostic of the high pressure of impact - found in the boundary layer provides additional evidence of an extra- terrestrial impact at the Cretaceous-Tertiary boundary layer. Recent research suggests that the impact site may have been in the Yucatan Peninsula of Mexico.
The high concentrations of Iridium in the boundary layer has also been attributed to another source, the mantle of the earth. It has been speculated by some scientists that the Iridium layer may be the result of a massive volcanic eruption, as evidenced by the Deccan Traps - extensive volcanic deposits laid down at the Cretaceous-Tertiary boundary - of India and Pakistan. These lava flows came about when India moved over a "hot spot" in the Indian Ocean, producing flows that exceeded one hundred thousand square kilometers in area and one hundred and fifty meters in thickness. Such flows would have produced enormous amounts of ash, altering global climatic conditions and changing ocean chemistry. Evidence that volcanism was a primary extinction agent at this boundary is also relatively strong. In addition, and the presence of spherules and shocked quartz worldwide in the boundary layer may also have been the result of such explosive volcanism. Thus at present, both the volcanic and meteorite impact hypotheses are both viable mechanisms for producing the Cretaceous mass extinction, although the latter is more popular.
he Holocene Mass Extinction?
The Holocene epoch is the geologically brief interval of time encompassing the last 10,000 years.
With the evolution of humans beginning in the Neogene, humans have evolved into a significant agent of extinction. For example, David Western of the New York Zoological Society, has speculated that for the destruction of every two hundred square kilometers of tropical forest and one hundred thousand square kilometers of rangeland there is a resultant loss of hundreds, if not thousands, of species.
• Most of these have never been (or ever will be) documented by science.
Deforestation, agricultural practices, pollution, overhunting, and numerous other human activities result in numerous species being threatened everyday. However, more information is required to see if the level of extinctions being experienced today are the harbringer of a mass extinction or merely reflect natural background levels of species replacement.
•.Taxonomists during the 18th through the first part of the 19th century
worked to pigeon-hole all species, because it was thought that this would give
them insight into the Mind of the Creator.
•During the 18th and 19th century, species were thought to be immutable, unchanging, and fixed. Species don't mix, and when they do hybridize, the progeny are usually sterile -
• Overview: The “Mystery of Mysteries”
• Darwin explored the Galápagos Islands
– And discovered plants and animals found nowhere else on Earth
• The origin of new species, or speciation
– Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity
• Evolutionary theory
– Must explain how new species originate in addition to how populations evolve
– Refers to evolutionary change above the species level
• Two basic patterns of evolutionary change can be distinguished
• The biological species concept emphasizes reproductive isolation
– Is a Latin word meaning “kind” or “appearance”
• The biological species concept
– Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations
• Reproductive isolation
– Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids
– Is a combination of various reproductive barriers
• Prezygotic barriers
– Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate
• Postzygotic barriers
– Often prevent the hybrid zygote from developing into a viable, fertile adult
• 1. Habitat Isolation
• 2. Temporal Isolation
• 3. Behavioral Isolation
• 4. Mechanical Isolation
• 5. Gametic Isolation
• Habitat Isolation – live in same range (area) but occupy different niches
– Land vs water
• Temporal Isolation – species breed at different times
– Breeding season
• Behavioral Isolation – courtship rituals and other signals, may be pheromone controlled
• Mechanical Isolation – sex organs are not compatible (coevolution of plants and pollinators)
• Gametic Isolation – copulation (or interaction) occurs, but gametes do not fuse – gametes may not survive or lack specific recognition molecules for fertilization
• 1. Reduced Hybrid Viability
• 2. Reduced Hybrid Fertility
• 3. Hybrid breakdown
• Hybrid inviability (or reduced viability) – zygote fails to survive embryonic development (genetic incompatibilities)
• Hybrid sterility – viable hybrid is sterile, often due to inability to produce normal gametes by meiosis (two parents often differ in # or structure)
– Mule à female horse + male donkey
• Hybrid breakdown – 1st generation viable and fertile, but when mate with hybrid or parental species à offspring weak and feeble
How Do Reproductive Barriers Evolve?
• Geographical Isoaltion à does not equal Reproductive Isolation
– Reproductive isolation is how we define a species so needs to prevent the interbreeding even in the absence of geographic isolation.
– Speciation is not do to some drive toward reproductive isolation à reproductive barriers are probably coincidental changes in gene pools due to natural selection and genetic drift
• Prezygotic and postzygotic barriers
• Prezygotic and postzygotic barriers
•. Consequently when the gonads of a mule attempts to produce gametes (a process made possible through meiosis – chromosomes don't necessarily have a partner or homologue to pair with during Prophase I and separate from during Metaphase I).
. The result are gametes with varying numbers of chromosomes, hence these are incompetent and are likely not to form a viable zygote when combined with their counterpart (i.e., an egg with a sperm).
•Mind set of people prior and early into the 19th century - species do not evolve, they are static or constant. A dog is always a dog, a cat is always a cat ...........
• The biological species concept cannot be applied to
– Asexual organisms
– Organisms about which little is known regarding their reproduction
Other Definitions of Species
• The morphological species concept
– Characterizes a species in terms of its body shape, size, and other structural features
• The paleontological species concept
– Focuses on morphologically discrete species known only from the fossil record
• The ecological species concept
– Views a species in terms of its ecological niche
• The phylogenetic species concept
– Defines a species as a set of organisms with a unique genetic history
• : Speciation can take place with or without geographic separation
• Speciation can occur in two ways
– Allopatric speciation
– Sympatric speciation
• In allopatric speciation
– Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations
• Once geographic separation has occurred
– One or both populations may undergo evolutionary change during the period of separation
• In order to determine if allopatric speciation has occurred
– Reproductive isolation must have been established
Sympatric (“Same Country”) Speciation
• In sympatric speciation
– Speciation takes place in geographically overlapping populations
– Is the presence of extra sets of chromosomes in cells due to accidents during cell division
– Has caused the evolution of some plant species
• An autopolyploid
– Is an individual that has more than two chromosome sets, all derived from a single species
• An allopolyploid
– Is a species with multiple sets of chromosomes derived from different species
Habitat Differentiation and Sexual Selection
• Sympatric speciation
– Can also result from the appearance of new ecological niches
• In cichlid fish
– Sympatric speciation has resulted from nonrandom mating due to sexual selection
Allopatric and Sympatric Speciation: A Summary
• In allopatric speciation
– A new species forms while geographically isolated from its parent population
• In sympatric speciation
– The emergence of a reproductive barrier isolates a subset of a population without geographic separation from the parent species
• Adaptive radiation
– Is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities
Adaptive Radiation on Island Chains
• Islands are living islands of speciation
• Small founding populations evolve in isolation under different environmental condition
• New species can recolonize the original island and coexeist with the parental species
• Adaptive radiation - the emergence of numerous species from a common ancestor introduced to new and diverse environments
– Darwin’s Finches (Galapagos Islands)
• The Hawaiian archipelago
– Is one of the world’s great showcases of adaptive radiation
Studying the Genetics of Speciation
• The explosion of genomics
– Is enabling researchers to identify specific genes involved in some cases of speciation
The Tempo of Speciation
• The fossil record
– Includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear
• Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe these periods of apparent stasis punctuated by sudden change
• The punctuated equilibrium model
– Contrasts with a model of gradual change throughout a species’ existence
• : Macroevolutionary changes can accumulate through many speciation events
• Macroevolutionary change
– Is the cumulative change during thousands of small speciation episodes
• Most novel biological structures
– Evolve in many stages from previously existing structures
• Some complex structures, such as the eye
– Have had similar functions during all stages of their evolution
Evolution of the Genes That Control Development
• Genes that program development
– Control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult
Changes in Rate and Timing
– Is an evolutionary change in the rate or timing of developmental events
– Can have a significant impact on body shape
• Allometric growth
– Is the proportioning that helps give a body its specific form
• Different allometric patterns
– Contribute to the contrasting shapes of human and chimpanzee skulls
– Has also played a part in the evolution of salamander feet
• In paedomorphosis
– The rate of reproductive development accelerates compared to somatic development
– The sexually mature species may retain body features that were juvenile structures in an ancestral species
Changes in Spatial Pattern
• Substantial evolutionary change
– Can also result from alterations in genes that control the placement and organization of body parts
• Homeotic genes
– Determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a flower’s parts are arranged
• The products of one class of homeotic genes called Hox genes
– Provide positional information in the development of fins in fish and limbs in tetrapods
• The evolution of vertebrates from invertebrate animals
– Was associated with alterations in Hox genes
• Tunicate tadpoles mature extremely quickly, in a matter of just a few hours. Since the tadpoles do not feed at this stage of their lives, they have no mouths. Their sole job is to find a suitable place to live out their lives as adults. When ready to settle, a sticky secretion helps them attach head first to the spot they have chosen. They then reabsorb all the structures within their tail and recycle them to build new structures needed for their adult way of life.
• Whence cometh the vertebrates and their chordate ancestors?
• One theory holds that Amphioxus-like chordates arose from the neotonic larvae of sessile urochordates such as living tunicates (Figure 4.)
• When the larva settles, the "swimming parts," which include a notochord and a dorsal nerve cord, degenerate and are resorbed.
• The neotonic theory of chordate origins imagines that the larvae became sexually competent (neotony) with the consequent loss of the sessile adult phase.
– According to this, an important theme of chordate / early vertebrate evolution was progressive integration of the visceral and somatic parts of the body.
– These parts respecively derive from
• Gill basket
• Larval tail
Evolution Is Not Goal Oriented
• The fossil record
– Often shows apparent trends in evolution that may arise because of adaptation to a changing environment
• According to the species selection model
– Trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics
• The appearance of an evolutionary trend
– Does not imply that there is some intrinsic drive toward a particular phenotype
• Both models are probably useful in interpreting the fossil record
• Different populations and different features may evolve differently
• An evolutionary change does not mean that evolution is goal oriented
• Evolutionary trends are ultimately dictated by environmental conditions, if conditions change, an evolutionary trend may end or change
From Speciation to Macroevolution
• Macroevolution includes the genetic changes that result in reproductive isolation of new species as well as the evolution of the defining characteristics of higher taxonomic groups.
•Introgression=transplantation of alleles between species
•Allopatric speciation=Speciation that occurs when the initial lock to gene flow is a geographical barrier that physically isolates the population.
•Adaptive radiation=the evolution of many diversity adapted species from a common ancestor.
Conditions for Allopatric Speciation
• Geographical isolation
– How formidable? Depends on the organisms ability to move about or disperse
• Colonization of a new area can also geographically isolate populations
• Likelihood of allopatric speciation increases when a population is small and isolated
– Gene pool more easily changed
• Geographical isolation creates opportunities for speciation, but does NOT necessarily lead to new species.
• Most “new” populations more likely become extinct rather than evolving into a new species.
• Allopatric speciation in progress??
• Ring Species à is distributed around some geographical barrier, populations are separated and have diverged most of their evolutionary time, but eventually meet where the ring closes
– North Am. Salamander – Ensatina eschscholtzii
• Northern an middle part of the ring interbreed as single species
• Southern end as ring closes – no hybridization occurs where the populations overlap
• There are several ring species, but the most famous example is the herring gull. In Britain, these are white. They breed with the herring gulls of eastern America, which are also white. American herring gulls breed with those of Alaska, and Alaskan ones breed with those of Siberia. But as you go to Alaska and Siberia, you find that herring gulls are getting smaller, and picking up some black markings. And when you get all the way back to Britain, they have become Lesser Black-Backed Gulls.
• So, the situation is that there is a big circle around the world. As you travel this circle, you find a series of gull populations, each of which interbreeds with the populations to each side. But in Britain, the two ends of the circle are two different species of bird. The two ends do not interbreed: they think that they are two different species.
Distribution of Organisms
• Different factors may determine the distribution of a species on different scales
– Worldwide to microhabitat
• Most species have small geographical ranges à plants or animals
– Biologists don’t really know why
• Most species are relatively rare in nature, and only common organisms tend to have widespread geographic range
Factors Affecting the Distribution of Organisms
• Biogeography is the study of the past and present distribution of individual species
• To determine what limits geographic distribution of any particular species can ask a series of questions.
• Is the species absent because of:
– Biotic factors à predation, parasitism, competition or disease
– Abiotic factors chemical or physical
• One way to determine if dispersal is the limiting factor à observation of species transplants
– Transplant successful à Yes, area inaccessible or insufficient time to reach the area
– Transplant unsuccessful limited by other species, or abiotic factors
• Even if transplant is successful à potential range may be different then actual range
• A proper transplant experiment should have a CONTROL à transplants done within the existing distribution to provide data on the effects of handling and transplanting of organisms
• Observation of “Introduced Species”
– The African Honeybee (1957)
– The Zebra Mussel (1988) à efficient suspension feeders, make water much clearer but alter the native community of organisms
The Tens Rule
• Statistical prediction that an average of one out of ten introduced species become established
• One out of ten established species become common enough to become pests
• The ability of species to disperse is important on a global scale but rarely an important factor limiting the local distribution of organisms.
• Behavior and habitat selection contribute to the distribution of organisms
– Often keeps them from occupying their potential range
• Ovipositing insects à only choose certain host plants, may limit distribution
• Changing environmental conditions à evolved habitat selection behaviors may no longer be adaptive
Affect the distribution of organisms
– Inability of transplanted organisms to survive and reproduce may be due to
• Predation, disease, competition, lack of mutual symbiosis, food resources
“Removal and Addition” experiments test whether predators limit the distribution of prey species
– Sea urchins were shown to limit the abundance of seaweeds in subtidal zones
Some of the most dramatic cases occur when humans (accidentally or intentionally) introduce exotic predators or disease à wipes out native species
• Terrestrial à not most important factor
• Aquatic quality of light is very limiting
– Wind à amplifies the effects of environmental temp by increasing heat loss due to evaporation and convection, also contributes to water loss, effect morphology
– Soil Structure
Chemical water, oxygen, salinity, pH, soil nutrients
Climate also varies on a vary fine scale
Every environment on Earth is similarly characterized by a mosaic of small-scale differences in the abiotic factors that influence the local distribution of organisms.
Climate of a small area, such as a woodland, lake, or even a hedgerow. Significant differences can exist between the climates of two neighboring areas – for example, a town is usually warmer than the surrounding countryside (forming a heat island), and a woodland cooler, darker, and less windy than an area of open land.
Examples of The Process
Evolution of a Prezygotic Barrier
– Diane Dodd (Yale) à reproductive barriers in allopatric populations evolve as a by-product of the populations adaptive divergence to different environments
– Examined Drosophila mating in allopatric populations raised on different nutritional sources
• Maltose vs Starch medium
Taxonomy employs a hierarchical system of classification.
The Binomial (Linnaeus – 18th century)
– Each species given a two part name (binomial)
– Genus and species
– Genera à Families Orders Classes Phyla Kingdoms– Phylogenetic tree represents this taxonomic ordering
Considers the origin of new taxonomic groups from species to kingdom
– Microevolution – explains evolutionary change within a population
Begins with speciation – the origin of new species
Evidence often from fossil record
Tempo of speciation can be steady or jumpy
Two Models of Speciation
Gradualist Model ( Anagenesis or phyletic evolution)
– Transformation of one species into a new species
– Steady transition in inherited features, with populations changing little by little over time
• Divergence of new lineage from parent line (more common) à begins as a small isolated population
• Gradual evolutionary change in an unbranched lieage
– Evolve differences gradually as they become adapted to their local environment
Models of Speciation
• Punctuated Equilibrium (Cladogenesis or branching evolution) – last 50 yrs
– Most fossil species appear suddenly, without transition forms
– Isolated populations diverge from the ancestral form
– Changes occur abruptly in a relatively brief evolutionary time
– Abrupt episodes of speciation followed by long periods of little change or equilibrium
– Cladogenesis is the process that INCREASES biological diversity.
Dodd’s Drosophila Experiments
• Greater tendency for females to mate with males reared on the same medium
• Control à no preference for flies from their own population vs different population
• This discrimination is an example of a behavioral prezygotic barrier
– How could adaptation to a certain diet affect mate choice?
• One allele with multiple effects on phenotype à effect both nutrient digestion and mate choice where diet may effect “odor” cues during mating
Example of the Process
• Evolution of Postzygotic Barrier
– Robert Vickery (Univ of Utah) àtested the ability of plants from different populations of monkey flowers (Mimulus glabratu) to interbreed
– Large range throughout the Americas
– Cross-pollinated plants from different regions
• Most of the offspring were fertile when crosses were between plants from nearby populations
• Proportion of fertile offspring decreased when crossed plants from distant populations
• Crosses b/w Wisconsin and Mexican populations were almost all sterile
– Example of postzygotic à hybrid breakdown
. BIOLOGICAL EVOLUTION
Does life evolve (change over time)?
Can a species give rise over time to new species?
For that matter, what is a species?
Concept of species is pre-dates the birth of the Greek philosopher, Aristotle.
Basic unit of classifying different organisms, whether you use scientific or common names. The Latin word specere, from which our word "species" is derived, means "to look at." The word originally referred to the outward appearance of an organism.
Examples of different species that the average person recognizes include cardinals, bluebirds, snow geese, cats, dogs, petunias, roses, and so on.
Greek species concept. Aristotle (384-322 B.C.) and Theophrastus (late fourth and early third centuries B.C.) conceived of species as unstable and highly changeable.
Aristotle believed in spontaneous generation of species, and regarded all kinds of crosses between species as feasible, likely, and a means for the creative construction of new species.
For example: Rampant hybridization could produce a new species. A camel could hybridize with a panther to produce a giraffe. An Arabian camel crossed with a wild boar produced the two-humped Bactrian camel.
Oppian argued that a camel crossed with a sparrow produced an ostrich.
Some Greek philosophers, including Aristotle and Plato, believed in idealism.
For every thing in the universe (e.g., shapes), there existed the ideal or perfect form. All other objects were variations of the ideal form and drew their properties from such entities.
Consequently, when idealism was applied to the human concept of species (particularly by theologians and naturalists towards the end of the Middle Ages), these became seen as merely variations of ideal forms.
These forms were arranged in continuum of complexity from simple to more complex.
In the 1750's, the naturalist Buffon contributed to the idea that species were discrete entities. Theologians and naturalists of the time argued for the fixity of species, the view that each species remained as created by God, according to the accounts given in the Book of Genesis in the Judeo-Christian Bible.
. By the middle of the 18th century, the discreteness and stability of species were generally recognized, setting the scene for Linnaeus and other taxonomists to
collect representative members of each species,
preserve these in collections as the representative or type specimen of that species,
. provide it with a Latin binomial (two word, i.e., genus and specific epithet) species name, and
describe its physical appearance in Latin.
Thus, developed the typological species concept in which all members of a species were of one basic type. This type did not vary significantly from place to place or through time.
Classification by taxonomists were also arranged into a hierarchy
Kingdom =>Division (Phylum) =>Class=>Order=>Family=>Genus=> Specific epithet
*The genus and the specific eptithet when combined represents the two word (binomial) name of the species - e.g., like Quercus alba (the white oak tree) .
*Sometimes the name(s) or the intitial(s) of the person(s) responsible for describing the species appear after the name - e.g., Quercus alba L. (L. stands for Linnaeus).
Another prevailing idea of the time - Great Chain of Being - species were fixed into place by God (each species being created separately).
. - HYBRID STERILITY (fertile donkey and fertile horse = sterile mule). Mules are sterile because female horses (mares) are 2N = 64 (egg = 32 chromosomes) and the male donkey is 2N = 62 (sperm = 31) which combine during fertilization to produce a mule zygote with a chromosome number of 2N = 61.
Sponge Activity-What did you learn today?
• 1. Two animals are considered members of different species if they _____. (Concept 24.1)
• 2. The evolution of numerous species, such as Darwin's finches, from a single ancestor is called _____. (Concept 24.2)
• 3. If the wings of extant flying birds originally arose as thermoregulatory devices in ancestral reptiles, then the bird wings could be accurately described as _____. (Concept 24.3)
• 4. Individuals of different species living in the same area may be prevented from interbreeding by responding to different mating dances. This is called ________isolation.
• 5. Three species of frogs- Rana pipiens, Rana clamitans, and Rana sylvatica -all mate in the same ponds, but they pair off correctly because they have different calls. This is a specific example of a _____ barrier, called _______isolation .