Intro to Vertebrates/Evolution - The Basics

Transcription

1 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 1 of 12 Based on Pough et. al, Vertebrate Zoology - 3rd Ed. MacMillan Hickman et al., Integrated Principles of Zoology - 11th Ed. William C. Brown Publishers Intro to Vertebrates/Evolution - The Basics Theme: The turtle as a typical vertebrate. Demonstration - Turtle Question - what is a vertebrate? characteristics - size from 0.1 gram to 100,000 kg length to 60m all habitats all types of feeding strategies presence of a vertebral column (and associated brain, spinal cord, etc.) 50,000 extant species, up to 500,000 extinct species Some examples of vertebrates: Myxini - hagfish Cephalaspidomorphi - lampreys 50 species (with myxinoidea) Elasmobranchii - sharks, skates, rays species Holocephali - ratfish Cladista - bichers, reed fish Chondrostei - sturgeon, paddlefish Neopterygii - gar, bowfin Teleostei - other ray-finned fishes - 21,000 species of fish Actinistia - coelocanth - 1 species Dipnoi - lungfish - 6 species Microsauria/Caudata - salamanders & caecilians species Temnospondyli/Anura - frogs and toads - 3,500 species Testudomorpha/Testudines - turtles species Lepidosauria - tuatara, lizards, snakes - 5,800 species Archosauria - crocodiles - 21 species crocs Aves - birds - 9,000 birds Synapsida - mammals - 4,000 species (17 groups)

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3 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 3 of 12 Classification of the turtle: Kingdom Animalia (Plantae, Fungi, Protista, Monera) Phylum Chordata Class Anapsida Order Testudomorpha Family Emydidae Genus Terrapene - box turtles species carolina - eastern box turtle Terrapene carolina (Linnaeus, 1758) Note forms of order names, family names, proper handling of specific epithet (including author). Graptemys geographica (Le Seur) Note common names

4 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 4 of 12 Go to Board Taxa - any hierarchical grouping - a level Basic taxonomy - Holotype - part of species description must be deposited in museum must be mentioned in text is the basis for future assignment of the name paratype additional specimens representing the known variation of the species priority - first description is the valid one each species must have unique specific epithet Commission of Zoological Nomenclature Evolution gene - basic unit of selection - DNA code for protein AKA locus allele - differing form of gene - same protein, slightly different genotype - all the genes of an individual Haploid - only one allele for each gene - sex cell diploid - two alleles for each gene - somatic cell Homozygous - both alleles for a given locus are identical (diploid cell) Heterozygous - two different alleles at a given locus phenotype - the resulting traits (structural, behavioral, etc.) of a given genotype Variation - mutations are changes in the genetic code - they give rise to new alleles - alleles are combined into new genotypes (and phenotypes) through sexual reproduction and recombination. Variation is the basis for evolution.

5 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 5 of There are differences in organisms (evidence gathered on Beagle) 2. There is a struggle for existence (Malthus) 3. In the struggle, certain differences will give those organisms possessing them an advantage (Darwin's contribution) 4. These organisms will survive and reproduce in greater numbers (differential reproduction) 5. Over long periods of time (Lyell), the whole species will change (evolution) heritability - any variation must exist in the genes - be heritable - if natural selection is to act on it. Natural Selection - differential reproduction of differing alleles (genotypes, phenotypes) different levels selection of individuals (and associated genes) genic selection (alleles going into sex cells) group or interdemic selection - species selection (controversial) Types of natural selection: use bell drawings directional selection stabilizing selection - driving force of allopatric speciation disruptive selection - driving force of sympatric speciation

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7 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 7 of 12 Fitness - measure of the reproductive success (of an allele or individual) Inclusive fitness - fitness gained by the copies of your genes carried by relative's kin. sometimes one can maximize his own fitness by foregoing reproduction to help kin rear offspring - altruistic behavior

8 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 8 of 12 Types of variation : 1 - individual - each individual has a unique assortment of genes (genotype), and thus a unique phenotype. 2 - polymorphism - several discrete phenotypes exist in a population 3 - sexual dimorphism - a type of polymorphism where the phenotypes vary according to sex. Often reinforced by sexual selection 4 - geographic - variation in populations according to geographic location. polytypic - a species with geographic variants pronounced enough to be subspecies. monotypic - a species which shows little variation over its range. Speciation speciation - the separation of a population into distinct breeding groups via natural selection and other genetic processes, including chance. biological species - groups of actually (or potentially) interbreeding natural populations which are reproductively (genetically) isolated from other such groups. gene flow - the mixing of alleles in a population through breeding. if effective gene flow exists, then speciation cannot occur. reproductive isolating mechanisms - keep organisms of different species interbreeding from 1. premating a) habitat isolation b) temporal isolation c) behavioral isolation d) mechanical isolation 2. postmating a) gametic isolation b) zygote mortality c) hybrid sterility d) fitness of offspring

9 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 9 of 12 effects of size: if a population is large - becomes subdivided - strong (but different) natural selection on each "pocket" --> speciation (assuming low gene flow) if a population is small - genetic drift ---> speciation (assuming low gene flow. genetic drift - the tendency for random chance to change allelic frequencies within a population - pronounced in small populations. effective population size: the current population size may not be critical in the species' evolution. Often low population size is. bottleneck effect - powerful sorting and genetic drift effects from single period of low population size

10 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 10 of 12 founder effect - if a population is formed initially by few individuals, genetic diversity is low and subsequent evolution will be drastically affected. adaptive radiation - the evolution into many different niches by a single species (through speciation) - usually requires colonization of an ecologically void area (island) Models of speciation: allopatric - geographic isolation ---> genetic drift and/or natural selection --> speciation sympatric - no geographic isolation - mutation ---> reproductive isolation --> genetic drift and/or natural selection --> speciation Example: Galapagos finches - Figure 6-22 pg. 120

11 Biology 222 Vertebrate Zoology Evolution/Basics Lecture Outline Page 11 of 12 Isolation on continents: mountain ranges - rivers - deserts refugia and speciation gradualism vs. punctuated equilibria - use figure 6-24, 6-25, pg. 121

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