Ch 18 Species.docx

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University of Toronto Scarborough
Biological Sciences
Ivana Stehlik

Ch 18 Species 18.1 What’s in a Name? (Pg 396)  Communication affects both inter and intraspecific behavior o Like monkeys signaling for eagle or leopard  Names to distinguish between categories of objects o Each species has a scientific name  Latinized descriptions of the organism bearing the name 18.2 Definition of “Species” (Pg 396)  biologists use names to precisely identify species, subspecies, or varieties  traditionally, morphological features were most important to identify species, but now behavioural and genetic features are more commonly used  molecular markers are also becoming important to identify and separate species  Species = a Latin word meaning “kind” or “appearance”  Species are the fundamental taxonomic units of biological classification.  Biological species concept defines species as group of organisms that can successfully interbreed and produce fertile offspring but are unable to produce viable fertile offspring with members of other populations o problems  works with sexually reproducing species, does not work with those that reproduce asexually  species that hybridize and produce fertile offspring  Hybridization: two species interbreed and produce fertile offspring  Many hybridize naturally in the wild  10% of 8000 species of birds hybridize naturally and produce fertile offspring. o Genetic cohesiveness of species  Pops of same species are said to experience gene flow that mixes their genetic material and could be “glue” holding a species together o Pops of diff species are reproductively isolated, cannot exchange genetic info. o Process of speciation is frequently defined as the evolution of reproductive isolation between pops o This concept could explain why individuals of a species generally look alike  Share genetic traits (genotype) which is diff from other species.  Morphological Species Concept defines a species as all individuals that share measurable traits distinguishing them from individuals of other species o characterizes a species in terms of its body shape, size, and other structural features  Phylogenetic Species concept defines species as a group of organisms bound by a unique ancestry  Ecological Species concept defines species as a group of organisms that share a distinct ecological niche  No one definition of “species” in biology is uniformly used or subscribed to by all biologists!! 18.3 Gene Flow: Four examples (Pg 399)  Gene flow occurs within populations of single species o Species that reproduce sexually and whose geographic distributions are relatively continuous  Several influences that can affect gene flow have been revealed using DNA technology tools o Distribution  endemic species  Endemism is the ecological state of being unique to a particular geographic location  narrow or very localized distribution  cosmopolitan species  widespread (even global) distribution o Species Dependence  widespread distribution of egg-laying snail depends on migratory bird species  o Social Behaviour  social behaviour may affect degree of gene flow between potentially interacting populations  gene flow may depend on which members of a population carry the genetic variation  example of rat. It can interbreed but its social behavior doesn’t make it happen o Habitat  changes in the availability of habitat affects the distribution of populations 18.6 Geographic Variation (Pg 402)  Subspecies: geographically separated pops of a species exhibit dramatic, easily recognized phenotypic variation o Local variants of a species o Individuals from diff subspecies usually interbreed where their geographic distributions meet  Offspring often exhibit intermediate phenotypes o “race”(zoologists) or “variants”(botanists) or “cultivars” for domesticated stock.  Ring species: geographic distribution that surrounds uninhabitable terrain o Can exchange genetic material directly o Gene flow between distant pops occurs only though intermediary populations  Cline species: species distributed over a large environmentally diverse area exhibit pattern of smooth variation along the geographic gradient o Clinical variation results from gene flow btw adjacent pops that are each adapting to slightly diff conditions  Most species are morphologically or behaviourally distinct from other species o Local and geographic variation can mask interspecific diff How does Speciation occur? • speciation is often a gradual process • difficult to recognize species’ boundaries 18.7 Reproductive Isolation (Pg 404)  Reproductive isolating mechanism: biological characteristic that prevents the gene pools of two species from mixing even when they are sympatric (occupying the same spaces at the same time)  the existence of biological factors that impede members of two species from producing viable, fertile hybrids  prevent gene pools from mixing  Two ways o Prezygotic isolating mechanisms  Exert their effects before the production of a zygote or fertilized egg o Postzygotic isolating mechanisms  Operate after zygote formation. o These are not mutually exclusive and two or more may operate simultaneously  Prezygotic Isolating mechanisms o Ecological isolation  Live in different habitats but same geographic region o Temporal isolation  Species in the same habitat but mate at different times of the day or diff times of the year o Behavioural isolation  Signals used by one species are not recognized by another  Many animals rely on specific signals which often differ dramatically btw species to identify the species of a potential mate – courtship displays  Females that choose appropriate mates are likely to produce more surviving offspring than those that choose other species and hybridize  Natural selection plays a role?  Mate choice by females and sexual selection generally drive the evolution of mate recognition signals.  Overtime, # of males with recognizable traits and # of females able to recognize the traits increase in the population o Mechanical isolation  Different in structure of copulatory (sexual) organs prevent successful mating btw individuals of diff species  Example pollination of flowers in the same area by different birds. o Gametic isolation  Incompatibility between the sperm of one species and the eggs of another prevent fertilization  Eg marine species – invertebrates  Release gametes into env for external fertilization.  Sperm n egg of each species recognize another’s complementary surface proteins  Diff surface proteins on gametes of diff species do not match.  Postzygotic Isolating Mechanisms o Despite prezygotic isolation, sperm from one species sometimes fertilizes egg of another  The two species are reproductively isolated if their offspring called interspecific (btw species) hybrids have lower fitness than those produced by intraspecific (within species) matings o Hybrid inviability  Occur because many genes govern the complex processes that transform a zygote into a mature organism  Hybrids have two sets of developmental instructions which may not interact properly for the successful completion of embryonic development.  So, die as an embryo at an early age. o Hybrid Sterility  Although some hybrids btw closely related species develop into healthy and vigorous adults, they produce non-functional gametes  Results when parent species diff in the number or structure of their chromosomes which cannot pair properly during meiosis.  Zero fitness -> no descendants  Example mule: mating btw female horse (2n = 64) and male donkey (2n = 62).  Example zebroids: zebras and horses o Hybrid breakdown  Some F1 hybrids are healthy, vigorous and fully fertile and can breed with other hybrids and with both parental species  Sometimes F2 gen, produced by mating btw F1 or btw F1 and parental species, they may exhibit reduced survival or fertility  Reproductive isolation is maintained btw species because there is little long-term mixing of their gene pools 18.8 Geography of Speciation (Pg 407)  Geography has a huge impact on whether gene pools have the opportunity to mix  Three modes of speciation based on geographic relationship of pops as they become reproductively isolated Allopatric speciation o Occur when a physical barrier subdivide a large pop or when a small pop becomes separated from a species’ main geographic distribution  Hurricanes may create new channels that divide low coastal island and the pops inhabiting them  Uplif
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