Biological Species Concept Lecture PDF

Biological Species Concept What is a species?  Can we use morphological traits (shape, coloration, etc.) to determine a species? Eastern Spotte d Skunk Western Spotted Skunk  On the previous slide, there are 2 skunks that look very similar to me.  However, they are completely differen...

Biological Species Concept What is a species?  Can we use morphological traits (shape, coloration, etc.) to determine a species? Eastern Spotte d Skunk Western Spotted Skunk  On the previous slide, there are 2 skunks that look very similar to me.  However, they are completely different species.  Obviously, all 6 people on the previous slide were the same species: Homo sapiens (the scientific name for human beings)  If a Martian came down to Earth in a flying saucer & had never seen humans before, it might think that those people represented 6 different species because there are plenty of visual differences. I. Biological Species Concept  A. Species = a group of populations whose members have the potential to interbreed and produce viable offspring  viable offspring: healthy juveniles who mature into fertile adults  Please note that this definition of species only applies to sexual organisms.  It does not apply to asexual reproducers such as bacteria or an amoeba  B. Reproductive Isolation  Reproductive barriers separate species  A reproductive barrier is something that prevents two individuals from producing viable offspring  1. Prezygotic Barriers  Obstructions that prevent gametes from fusing and producing a zygote  2. Postzygotic Barriers  Obstructions that prevent a zygote from developing into a viable adult II. Prezygotic Barriers  A. Spatial Isolation: species living in the same area may never encounter each other  Occupy different habitats White-throated sparrow  Dense Thickets White Crowned Sparrow  Open meadows  The 2 sparrows would rarely have the chance to reproduce together, because they would hardly ever come into contact Fig. 14-3a  The land snake would rarely ever meet the water snake.  Note: this type of barrier is not perfect. What about on the shore where the land & water meet?  B. Behavioral Isolation: Breeding does not occur due to incorrect mating behavior  Examples: courtship rituals (dances, songs, fireflies …) Fig. 14-3b Mating dance of blue-footed boobies differs between species  C. Temporal Isolation: members of closely related species breed at different times  Different times of the day (nocturnal or diurnal)  Different times of the year (example: plants) Monterey pine releases pollen in February (Pollen contains sperm Bishop’s pine releases pollen in April Orchids in the rainforest, only release pollen on 1 day out of the entire year!  D. Mechanical Isolation: similar species cannot breed because they are anatomically different  Plants and pollinators  Insects: sex organs do not fit Smells like Dull color, dung! Yum! strong aroma Plants & pollinators  Notice on the previous slide that the flowers are very different depending on the animal that will pollinate it  Example: Beetles have an excellent sense of smell, but they don’t see bright colors.  So, the flowers have a strong scent, but dull color I look & smell like a female wasp to trick males into pollinating me as they attempt to mate! Fig. 14-3c shells spiral in opposing directions: genital openings cannot align  It is common for insect species that look almost identical to have very different genitalia.  Mating can only occur if the male & female genitalia are compatible  The next 2 slides show 2 examples of insect male genitalia that look very different. The female genital shape must match for sex to work.  E. Gametic Isolation: Gametes meet, but fail to fuse and produce a zygote III. Postzygotic Barriers  A. Reduced Hybrid Viability: fertilization occurs and produces a zygote, but the offspring do not survive or are very sickly Ranunculus plants  one species adapted to wet habitat  the other to a dry habitat  hybrids are not well adapted to either B. Hybrid Sterility  1. Hybrid is healthy, but sterile  B.Hybrid Sterility: related species may breed, but there offspring are sterile  Different numbers of chromosomes  Chromosomes of different size and function (homologous chromosomes do not match C. Hybrid Breakdown  1st generation hybrids are fertile, 2nd generation hybrids are sterile or unhealthy  Example: cotton  Hybrids are fertile, offspring of hybrids die as seed or grow into weak, defective plants IV. Speciation  A. Process by which one species diverges into two species B. Two requirements  1. Populations become isolated from each other  2. Genetic divergence  Mutations occur, cause reproductive barriers (pre- &/or postzygotic) to form  There are multiple ways that the 1st requirement (populations becoming isolated from each other can occur)  We will only discuss one method called allopatric speciation, which is explained on the next slide C. Allopatric Speciation  Members of the same species become separated due to a geographic barrier & develop into 2 species Fig. 14-4 A. harrisi A. leucurus South North Allopatric Speciation (fig 10-11)  Notice from the previous slide that new speciation does not always occur when populations are geographically separated  For example, human populations became separated from each other on the various continents. We did exhibit genetic changes through mutations, which caused the development of different levels of skin pigments, & other differences that we see in different ethnic groups.  However, while we did change genetically from each other in some ways, we did not mutate to develop reproductive barriers. A human from one part of the world can have babies with a human from any other part of the world V. Evolutionary relatedness  When we talk about species being related to each other, we are actually speaking about sharing a common ancestor.  Species that are closely related have a recent common ancestor  Species are distantly related if their common ancestor lived a very long time ago.  On the next slide, you will see that humans are closely related to chimpanzees.  Humans are more distantly related to lemurs  VI. Convergent Evolution A. The independent evolution of similar structures that were not inherited from the same ancestor Similar adaptations to similar environments  Example: Desert plants  Small leaves or lack leaves  Prevent loss of water  Spines are modified leaves  Provide shade and prevent predation  Thorns are modified branches  Prevent predation  Fleshy stems  Store water  On the next slide, you will notice that Hoodia & Cholla share many similar characteristics. However, they are not closely related. The Hoodia is not a cactus, even though it looks like one. VII. Divergent Evolution  A. Groups from the same common ancestor evolve and accumulate differences, resulting in the formation of new species that can be quite different. VIII. Rates of Evolution  A. Gradualism  the slow speciation of organisms brought about by the slow accumulation of favorable characteristics over a period of time  Examples:  Beak size of finches  Horses  The fossil record indicates that the ancestors of modern horses had more toes. These toes gradually grew smaller in the descendants until they finally disappeared (through mutation)  There is some debate. They may not have disappeared; there is evidence that some of the toes may have fused  Also notice that the size increased. The ancestors were smaller than today’s horse. Divergent Evolution B. Punctuated Equilibrium  Quick, fast burst of new species followed by longer periods with little evolution  Examples:  Bacteria  Insects  (antibiotic / pesticide resistance) IX. Classification A. Every organism is assigned to one of three categories called Domains Bacteria, Archaea, and Eukarya  Domain Bacteria Domain Eukarya Bacteria Domain Archaea Protists Kingdom Plantae (multiple kingdoms) Archaea Kingdom Fungi Kingdom Animalia  B. In turn each organism is assigned to successive categories, which provide more precision Kingdom, Phylum, Class, Order, Family, Genus, and Species Each category is more exclusive  EUKARYA Figure 7.11-1a Domain Eukaryotes ANIMALIA Kingdom Animals CHORDATA Phylum Chordates MAMMALIA Class Mammals Order CARNIVORA Carnivores Family FELIDAE Felines PANTHERA Genus Big cats PANTHERA TIGRIS Species Tiger © 2015 Pearson Education, Inc.  To help you memorize the classification system, here is something to remember  Dear King Phillip Came Over For Great Soup  The 1st letter of each word represents:  Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species C. Binomial Nomenclature Every organism is given two names Genus Species Example: Homo sapiens Escherichia coli  The 1st letter of the genus is capitalized. The species name is not capitalized.  If typing: both words italicized  If writing by hand: both words are underlined  Staphylococcus aureus Dictionary definition  Homo is a Latin word that means man, or human.  When it is used as a prefix it comes from the Greek word homos, meaning the same.  I wanted to point out the definition of homo as it relates to our genus.  The reason is because there was a woman a while back that protested her child’s school calling people Homo sapiens, because she thought that meant homosexual  She was literally protesting the fact that the school was teaching her kids that humans are called human (since homo is Latin for human) X. Eukaryotic cells evolved from prokaryotic cells  A. Endomembrane system developed from infolding (folding inwards) of the plasma membrane  (Nucleus, ER, Golgi) Figure 8.6-1a_3 Nuclear Plasma membrane envelope Endoplasmic Cytoplasm Nucleus reticulum DNA ANCESTRAL INFOLDING CELL WITH NUCLEUS AND PROKARYOTE ENDOMEMBRANE SYSTEM © 2015 Pearson Education, Inc.  B. Endosymbiosis  1. One species lives inside another host species  2. Mitochondria and Chloroplasts started out as separate cells  Have their own DNA  Resembles prokaryotic DNA more than eukaryotic DNA  These smaller cells were engulfed by a larger cell  This happens all the time. This is how cells eat.  Normally, the engulfed cell would be destroyed. Sometimes this process fails  The smaller cell provided a benefit for the larger cell  The cells that became mitochondria were very efficient at turning food energy into ATP  The cells that became chloroplasts could carry out photosynthesis & produce sugars using CO2 & energy from the sun Figure 8.6-2_5 CELL WITH NUCLEUS AND ENDOMEMBRANE SYSTEM ANCESTRAL CELL WITH AN Photosynthetic ENDOMEMBRANE SYSTEM prokaryote ENGULFING A BACTERIUM Later, this cell engulfs a photosynthetic Oxygen- prokaryote. metabolizing bacterium © 2015 Pearson Education, Inc. Please watch the following video https://www.youtube.com/watch?v=FGnS-Xk0ZqU