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1

speciation

origin of new species

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_______ is the source of biological diversity

appearnace of new species

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______ is at the focal point of evolutionary theory

speciation

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microevolution

evolutionary change below the species level; change in the genetic makeup of a population from generation to generation

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___ reveals the cumulative effects of speciation over vast tracts of time

the fossil record

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macroevolution

evolutionary change above the species level, including the appearance of major evolutionary developments, such as flight, that was use to define higher taxa

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2 basic patterns of evlutionary change

cladogenesis and anagenesis

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anagensis

(ana - new ; genos - race)
accumulation of changes that gradually transform a given species into a species w/ different characteristics

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anagensis is aka as

phyletic evolution

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cladogensis is aka as

branching evolution

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cladogenssi

(klados - branch)
the splitting of a gene pool into two or more separate pools, which each give rise to one or more new species

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only cladogensis can

promote biological diversity by increasing the number of species

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species is a latin word meaning

kind / appearance

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biological species concept

defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but are unable to produce viable, fertile offspring w/ other members of other populations

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reproductive isolation

the existence of biological factors that impede members of 2 species from producing viable, fertile hybrids

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reproductive barriers are classified according to whether

they contribute to reproductive isolation before or after fertilization

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prezygotic barriers

"before the zygote"
impede mating between species or hinder the fertilization of ova if members of different species attempt to mate

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postzygotic barriers

often prevent the hybrid zygote from developing into a viable, fertile adult

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5 types of prezygotic barriers

habitat
temporal
behavioral
mechanical
gametic isolation

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3 types of postzygotic barriers

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

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habitat isolation

2 species that occupy diff habitats w/in the same area may encounter e/o rarely, if at all, even though they aren't islated by obvious physical barriers

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temporal isolation

species that breed during diff times of day, seasons, or years; ==> they cant mix their gametes

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behavioral isolation

courtship rituals that attract mates and other behaviors unique

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mechanical isolation

morphological differences can prevent successful mating

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gametic isolation

sperm of one species may not be able to fertilize the eggs of another species. ex: sperm can't survive in other species' female reproductive tract, biochemical mechanisms may prevent sperm from penetrating the membrane surrounding other species' eggs

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reduced hybrid viability

genes of diff parent species may interact and impair the hybrid's development

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reduced hybrid fertility

vigorous hybrids may be sterile. if chromosomes of the 2 parent species differ in number of structure, meiosis in the hybrids may fail to produce normal gametes. since the infertile hybrids can't produce offspring when they mate w/ other parental species, genes can't flow freely

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hybrid breakdown

some first-generation hybrids are viable and fertile, but when they mate w/ one another or w/ either parent species, offspring of the next generation are feeble/sterile

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limitations of biological species concept (2)

1. there's no way to evaluate the reproductive isolation of fossils or asexual organisms (such as prokaryotes)
2. it's difficult to apply the concept to the many sexual organisms about which little is known regarding their ability to mate w/ diff kinds of organisms

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the biological species concept emphasizes

the separateness of species from one another due to reproductive barriers

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morphological species concept

characterizies a species by its body shape, size, and other structural features

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advantages of morph. species concept: (2)

1. can be applied to sexual and asexual organisms
2. can be useful even w/o info on the extent of gene flow

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disadvantage of morph species concept

definition relies on subjective criteria; researchers may disagree on which structural features distinguish a species

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paleontological species concept

focuses on morphologically discrete species known only from the fossil record

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we are forced to distinguish many species using the paleon. species concept b/c

there's little or no info on their mating compatibility

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ecological species concept

views a species in terms of its ecological niche, its role in a biological community

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unlike the biological species concept, the ecol. species concept

can accommodate asexual as well as sexual species

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phylogenetic species concept

defines a species as a set of organisms w/ a unique genetic history -- that is, as one branch on te tree of life

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biologists trace the phylogenetic history of a species by

comparing its physical characteristics or its molecular sequences w/ those of other organisms

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phylogenetic info sometimes reveals

the existence of sibling species

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sibling species

species that appear so similar that they cannot be distinguished on morphological grounds

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the ___ species concept is partcularly valuable for studying how species originate

biological

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speciation can occur in 2 main ways:

allopatric, sympatric

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allopatric speciation

(allos - other; patra - homeland)
gene flow is interrupted when a population is divided into geographically isolated subpopulations

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_____ are more likely to experience allopatric speciation

small, isolated populations

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to confirm a case of allopatric speciation, it is necessary to determine

whether the allopatric populations have changed enough that they no longer have the potential to interbreed and produce fertile offspring

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isolating mechanisms are intrinsic

to the organisms themelves

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____ is not in itself a biological isolating mechanism

geographic isolation

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isolating mechanisms prevent interbreeding even

in the absence of geograhpic isolation

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sympatric speciation

(syn - together)
speciation takes place in geographically overlapping populations

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machanisms of sypmpatric speciation include

chromosomal changes
nonrandom mating that reduces gene flow

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polyploidy

condition caused by a mutational change that results in extra sets of chromosomes

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autopolyploid

an individual that has more than 2 chromosome sets, all derived from a single species

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the triploid (3n) offspring of tetraploid (4n) and diploid (2n) parents are sterile b/c

their unpaired chromosomes result in abnormal meiosis

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a common form of polyploidy

when 2 diff species interbreed and produce a hybrid

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interspecific hybrids are often sterile b/c

the set of chromosomes from one species can't pair during meiosis w/ the set of chromosomes from the other species

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though infertile, hybrids may be able to ____, as many _____ do

propagate itself asexually, as many plants do

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allopolyploid

A polyploid organism, usually a plant, that contains multiple sets of chromosomes derived from different species.

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many important agricultural crops such as potatoes, tobacco, wheat, oats, and coton are

polyploids

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today, plant geneticists create new polyploids in the laboratory by

using chemicals that induce meiotic and mitotic errors

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polyploid speciation is more common in

plants than in animals

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in allopatric speciation, the isolated population evolves by __ and __

natural selection and genetic drift

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what is another way sympatric speciation can occur?

when a subset of a population becomes reproductively isolated b/c of a switch to a habitat, food source, or other resource not used by the parent population

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adaptivve radiation

the evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges

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adaptive radiation typically occurs when

a few organisms make their way to new, often distant areas when environmental changes cause numerous extinctions, opening up ecological niches for the survivors

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punctuated equilibrium

in evolutonary theory, long periods of apparent stasis (no change) interrupted by relatively brief periods of sudden change

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by necessity, paleontologists base hypotheses about descent almost entirely on __ and __

external anatomy and skeletons

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during periods of apparent equilibrium, changes in __, __, and __ may go undetected

behavior, internal anatomy, and physiology

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exaptations

structures that evolve in one context but become co-opted for another function