BIO 171 1st Edition Lecture 11Outline of Last Lecture I. Population GeneticsII. InbreedingIII. Hardy-Weinberg Equilibrium Outline of Current Lecture I. Species Concepts II. Speciation (allopatric and sympatric) III. Reproductive Isolation: Mechanisms to Prevent Successful Reproduction Current LectureSpecies Concepts -A species is a group of individuals that actually or potentially interbreed in nature (fundamental biological unit)-Three major species concepts:oBiological Species Concept (BSC)= species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other organisms-Emphasis on reproductive isolation -The offspring that they produce must be fertile (able to pass their genetic information on to their own offspring)-More useful in theory than in practice because it cannot be applied to all speciesEx) Fossil species (extinct species) and asexual species oMorphospecies Concept= defines species based on similarities in morphological traits (appearance)-Can be applied to fossils -Does not work for species that are variable (members of the same species that don’t look alike/have different morphological traits), species that have sexual dimorphisms (males and females possessing different morphological traits), or species that are cryptic (a part of different species but look extremely alike) oPhylogenetic Species Concept= defines species based on their unique genetic history -Represented by a tip on a phylogenetic tree These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Can be applied to asexual organisms and fossils -Can be problematic because we don’t have phylogenetic trees for everything Speciation (allopatric and sympatric) -Speciation is the formation of distinct species by genetic divergence leading to reproductive isolation oIt begins when gene flow is interrupted by some barrier (causing genetic isolation) -This barrier can be in space (geographic), in time (species acting during day vs. night), or behavior.oThe genetic makeup of each population changes through selection, genetic drift, and/or mutation (causing genetic divergence)oReproductive isolating mechanisms evolve causing 2 different species (speciation)-Allopatric speciation is when a population of the same species becomes subdivided geographically into separate populations oThese populations may be separated by colonization of a new island, formation of a mountain, ocean, etc.oOnce the two populations are separated, evolution can proceed independently in each population through mutation, natural or sexual selection, or genetic drift. -Vicariance= physical splitting of a habitatoAllopatric speciation is the most common mode of speciation in animals -Sympatric speciation is speciation that occurs without geographic separation oMeaning the initial barrier to gene flow is biological -Can be genetic (chromosomal differences making them unable to mate) Ex) polyploidy which occurs when errors in meiosis can lead to extra setsof chromosomes in gametes-3N or 4N mutants are unable to breed with normal 2N individuals, causing them to be reproductively isolated from their diploid ancestors -Causes very rapid speciation (common in plants) Ex) autopolyploidy which is when both chromosome sets are from the same parental species, but they still have a different number of chromosomes than their predecessors -Can be ecological Ex) host shifts (when species start to lay their eggs/look for mates in new areas or new "hosts" causing gene flow to be interrupted between species on initial host and species on new host)-Can be behavioral Ex) change in mate preference oDisruptive selection plays a big role in sympatric speciation -Reduces fitness of heterozygotes eventually leading to enough genetic differences to prevent successful interbreeding Reproductive Isolation: Mechanisms to Prevent Successful Reproduction -Pre-Zygotic Isolating Mechanisms:oPrevent mating or fertilizationoNo hybrid zygotes form -Post-Zygotic Isolating Mechanisms: oFertilization occurs, and hybrid zygote forms oHybrid fails to thrive or it is unable to reproduce -Examples of pre-zygotic barriers:oBehavioral barriers (species use different courtship signals) oEcological barriers (species live in the same area, but use different habitats so rarely encounter each other) oTemporal barriers (species breed at different times)oMechanical barriers (anatomical differences between individuals that prevent mating) oGametic barriers (gametes of two species meet, but do not fuse) Continued in next