Zoology Lecture Notes PDF

ZOOLOGY Lecture 2: Sep 12 The theories behind the Evolution theory 1 The five theories within the theory of evolution: 1. Perpetual change 2. Common descent...

ZOOLOGY Lecture 2: Sep 12 The theories behind the Evolution theory 1 The five theories within the theory of evolution: 1. Perpetual change 2. Common descent 3. Multiplication of species 4. Gradualism 5. Natural selection 2 1  COMMON DESCENT 2 There is a common ancestor for all the living forms (current or extinct) This theory saw life as a branching tree… where large branches split in small (derived) ones… The issue was… it also implied that humans descended from monkeys…. If this theory is correct, we can look for common / similar features to find relationships among animals And we can introduce two related concepts: Homology and Analogy 3 COMMON DESCENT 2 There is a common ancestor for all the living forms (current or extinct) Evidence of ancestry and relationships among groups? Plenty: HOMOLOGY Fossils, molecular studies, etc. 4 2  COMMON DESCENT 2 There is a common ancestor for all the living forms (current or extinct) HOMOLOGIES: ANALOGIES: Characters derived from a Not from a common ancestor; common ancestor independent origin Differences between homologies Similarities between analogies come from Divergent evolution come from Convergent evolution 5 COMMON DESCENT 2 There is a common ancestor for all the living forms (current or extinct) Homologies allow the study of ancestry and relatedness among animal groups. It also let us propose a hierarchy of classification: CLADOGRAM: A nested hierarchy of groups in a branching diagram It tells when groups are related And how closely related Common characteristics 6 3  MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms Poor Rich The issue with biodiversity: To state that one system is richer than other, we need a unit to measure that… The Arabian fox Such unit is the species But then, what exactly is a species? 7 MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms Species are not that simple to define… here is an example: Zoology recognizes several different concepts of species. We will distinguish four of them 8 4  MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms THE FOUR MAIN CONCEPTS OF SPECIES A) TYPOLOGICAL concept of species: Based on morphological similarity. Individuals that look similar are grouped together as one species. The most classic concept; in practice, it continues to be used by museums and collections Are there limitations to this concept? Yes, species change, they evolve… 9 MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms THE FOUR MAIN CONCEPTS OF SPECIES B) BIOLOGICAL concept of species: Based on similarity, niche, and the ability of individuals to interbreed and produce viable offspring Probably the most popular concept… Any limitations? Yes, what about species with asexual reproduction? What about hybrid creatures? Horse + donkey = mule 10 5  MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms THE FOUR MAIN CONCEPTS OF SPECIES C) EVOLUTIONARY concept of species: Based on biological concept + evidence of ancestry (a common ancestor) Limitations? What about species without ancestry information? 11 MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms THE FOUR MAIN CONCEPTS OF SPECIES D) PHYLOGENETIC concept of species: Based on the evolutionary concept + any recognizable genetic variation resulting from isolation Problems? “Recognizable variation” is an ambiguous concept, hard to judge… Let’s compare the four species concepts using an example: The Atlantic frog 12 6  MULTIPLICATION OF SPECIES 3 A branching tree that diversifies: an ancestral form splits into two or more derived forms Distributed all across the region until… PEI split from the mainland The original Today: do these four frog populations belong to the same species? Atlantic frog QB Typological concept: Yes, they belong to the same species PE NB as long as they are similar Biological concept: NS Yes, as long as they are similar, have same niche, and interbreed. Evolutionary concept: Yes, as long as they are similar, interbreed, have similar niche, and share a common ancestor Phylogenetic concept: PEI population will be judged a different species if there is a diagnosable evidence of genetic variation with respect to blue populations 13 MULTIPLICATION OF SPECIES 3 A branching tree implies diversification: an ancestral form split into two or more derived species How does speciation proceed? Normally, the rise of reproductive barriers and speciation occurs by one of the following mechanisms: 1) Spatial and temporal isolation (allopatric process) Allopatry = separate / distant areas 2) Niche specialization (sympatric process) Sympatry = coexistence / in a same area 3) Mutations (allopatric or sympatric) 14 7  MULTIPLICATION OF SPECIES 3 A branching tree implies diversification: an ancestral form split into two or more derived species The formal recognition of a new species requires three elements: 1. An official name (written in binomial system, eg. Apis mellifera) 2. An official description (in a scientific publication) 3. An official type or preserved specimen (in a collection or museum) 15 GRADUALISM 4 Change among populations and species occurs as a gradual process over time Remember Lyell, the geologist? Change occurs as a continuous cumulative process over a long time Two issues: What about mutations? It is difficult to explain What about those gaps in the fossil record? these using Gradualism… 16 8  GRADUALISM 4 Change among populations and species occurs as a gradual process over time We really need an alternative view: Eldredge & Gould (1972): There are periods of abrupt change and periods of slow or no change… Based on this view, speciation is a “sudden” event… that happens only occasionally (and that explains why the fossil record is incomplete)... 17 GRADUALISM 4 Change among populations and species occurs as a gradual process over time These are two alternative views of how evolution takes place over time Coronation street Entourage 18 9  NATURAL SELECTION 5 Change is driven by natural selection and the survival of the fittest Four key observations: o Populations are fertile (they can produce many eggs) o Resources are limited, so numbers cannot raise endlessly o Traits are hereditary but descendants are no identical to parents o So survival is differential and favour the fittest All these observations suggest that there is a constant competition for resources, and that only the best fitted survive, reproduce, and prevail… 19 NATURAL SELECTION 5 Change is driven by natural selection and the survival of the fittest When habitat changes… this creates opportunities and one original species may become various species Adaptive radiation: The formation of various species from a common ancestral form Example: Darwin’s finches underwent adaptive radiation by colonizing new islands and using different ecological niches 20 10  55 NATURAL NATURAL SELECTION SELECTION Change is driven by natural selection and the survival of the fittest Adaptive radiation also occurs after drastic environmental phenomena called “massive extinctions”… Pre-Cretaceous: Dinosaurs dominated Post cretaceous: Mammals diversified by adaptive radiation 21 Next week: Animal concept and architecture From small to big, from simple to complex… The real reason dinosaurs became extinct 22 11