Chapter 24 - Biology - "Origin Of Species"

Speciation origination of a new species, shown in fossil record macroevolution Term that means an evolutionary change above the species level, including the appearance of evolutionary developments like flight that is used to define higher taxa 2 Basic Patterns of Evolutionary Change Anagenesis and Cladogenesis Anagenesis (Strictly Phyletic evolution, meaning it can only apply to one species) An accumulation of changes that gradually transform a given species with different characteristics. Cladogenesis (Branching evolution, meaning it can promote biodiversity by increasing the number of species) Splitting a gene pool into two or more separate pools and each gives rise to one or more species Biological Species Concept Follows Ersnt Mayr's definition of "a population or group of populations whose members have the potential top interbreed in nature and produce viable fertile offspring with members of other populations Types of Reproductive Isolation Prezygotic and Postzygotic Barriers make this up. Reproductive Isolation Occurs when the existence of biological factors impede individuals from two different species from producing fertile offspring Prezygotic Barriers Impede mating between species or hinder fertilization of ova if species do mate. Types of Prezygotic Barriers: pre-mating Temporal, Habitat, Behavioral Types of Prezygotic Barriers: pre-fertilization Mechanical and Gametic Habitat isolation Type of prezygotic barrier occurs before mating when two species that occupy different habitats within the same area may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers, such as mountain ranges. Temporal Isolation Type of prezygotic barrier that occurs before mating attempt when species that breed during different times of the day, or during different seasons, or different years cannot mix their gametes. Behavioral Isolation Type of prezygotic barrier that occurs before mating attempt because courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers even between closely related species. These enable mate recognition, a way to identify potential matches of the same species. Mehcanical Isolation Type of prezygotic barrier occurs after mating attempt when morphological differences between species prevent successful completion Gametic Isolation Type of prezygotic barrier occurs after mating attempt when sperm of one species may not be able to fertilize eggs of another species. Sperm may not be able to survive in the reproductive tract of females of other species, or biochemical mechanisms may prevent the sperm from penetrating the membrane surrounding other species' egg Types of postzygotic barriers reduced hybrid viability, reduced hybrid fertility, and reduced hybrid breakdown. Reduced Hybrid Viability Postzygotic barrier that occurs when the genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment Reduced hybrid fertility Postzygotic barrier that occurs when the chromosomes of the two parent species differ in number or structure causes meiosis in the hybrids to fails produce normal gametes. Since the infertile hybrids cannot produce offspring when they mate with either parent species, genes cannot flow freely between the species. Reduced hybrid breakdown Postzygotic barrier that occurs because some first generation hybrids are viable and fertile, but when they mate with one another or with either parent species, offspring of the next generation are feeble or sterile. Postzygotic Barriers if sperm from one species does overcome prezygotic barriers, these often prevent the hybrid from developing into a viable, fertile adult. Limitations of Biological Species Concept. These include fossils, asexual organisms, organisms that produce viable hybrids, and organisms whose mating strategies are still unknown. Morphological Species Concept This classification system characterizes body shape, size, and other structural features. It requires taxa based on subjective criteria, though it can be applied asexual and sexual organisms alike. Paleontological Species Concept This classification system focuses on morphologically discrete species only from fossil record, and works for those species whose mating strategies are still unknown. Ecological Species concept This classification system views a species based on its ecological role, like its diet, and works for asexual species as well. Phylogenetic Species Concept This classification system uses organisms with a unique genetic history, and traces physical appearances and molecular sequences with other organisms to reveal sibling species or species that looks so similar they cannot morphologically be told apart. Allopatric Speciation When gene flow is interrupted when a population is divided into geographically isolated populations. Example: lake levels subside, result in smaller lakes with separated populations. Sympatric Speciation This takes place in geographically overlapping populations and includes chromosomal changes and nonrandom mating that reduces flow of genes. Polyploidy A condition where some plant species have their origins in accidents during cell division that result in extra chromosome sets (mutation). Autopolyploidy When an individual that has more than 2 sets of chromosomes that are all derived from a single species. Interspecific hybrids of this sort are often sterile: their set of chromosomes for one species cannot pair meiosis with set of chromosomes of other species. Allopolyploidy A fertile polyploid of this sort represents a new species because it cannot mate with the parent. First polyploid wheat probably occured around 8000 yrs ago as a spontaneous hybrid of cultivated wheat and wild grass. Understanding this allows scientists to design wheat with higher yield. Adaptive radiation The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges. Punctuated equilibrium The fossil record includes many episodes of species appearing in a stratum, remaining unchanged, and then disappearing. This phenomena describes the periods of apparent stasis punctuated by sudden change. Cuvier used catastrophism to explain this. Not all modifications can be exposed in strata; there may just be no fossil record. Evolutionary novelties These are when occasional major morphological transformation occurs from simple basic versions to complicated ones that serve the same function. Example: the eye; simplest ones only have patches of photoreceptor cells. Exaptations These are structures that evolve in one context but become co-opted for another Heterochrony An evolutionary change in the rate or timing of developmental events; for example: an organism's shape depends in part on the relative growth rates of different body parts during development Allometric Growth Proportioning that helps give a body part its specific form. Example: most salamanders live on the ground, but some species live in trees. The feet of the tree-dwelling species are adapted for climbing vertically rather than walking 9they have shorter digits and extensive webbing provide better traction. The basis for this adaptation was a selection for alleles of genes that control the timing of foot development. Paedomorphosis This condition occurs when reproductive development accelerates compared to nonreproductive development, and leads to the sexually mature stages may retain body features that were juvenile structures in an ancestral species. Homoectic genes These determine spatial organization or placement of parts on a body Hox genes These are a class of homoectic genes thats provide positional information in an animal embryo and prompt cells to develop into structures appropriate for a particular location. They provide positional information about how far digits, for example, and other bones should extend from the body. pluralistic species concept This classification system is focused on how a scientist can apply a different concept based on which organism is being studied Microevolution Changes in allele frequency from one generation to the next. Novel features arise by modifications of existing structures Sexual Selection leads to sympatric speciation in animals