24 Flashcards
speciation
origin of new species
_______ is the source of biological diversity
appearnace of new species
______ is at the focal point of evolutionary theory
speciation
microevolution
evolutionary change below the species level; change in the genetic makeup of a population from generation to generation
___ reveals the cumulative effects of speciation over vast tracts of time
the fossil record
macroevolution
evolutionary change above the species level, including the appearance of major evolutionary developments, such as flight, that was use to define higher taxa
2 basic patterns of evlutionary change
cladogenesis and anagenesis
anagensis
(ana - new ; genos - race)
accumulation of changes that gradually transform a given species into a species w/ different characteristics
anagensis is aka as
phyletic evolution
cladogensis is aka as
branching evolution
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
only cladogensis can
promote biological diversity by increasing the number of species
species is a latin word meaning
kind / appearance
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
reproductive isolation
the existence of biological factors that impede members of 2 species from producing viable, fertile hybrids
reproductive barriers are classified according to whether
they contribute to reproductive isolation before or after fertilization
prezygotic barriers
“before the zygote”
impede mating between species or hinder the fertilization of ova if members of different species attempt to mate
postzygotic barriers
often prevent the hybrid zygote from developing into a viable, fertile adult
5 types of prezygotic barriers
habitat temporal behavioral mechanical gametic isolation
3 types of postzygotic barriers
reduced hybrid viability, reduced hybrid fertility, hybrid breakdown
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
temporal isolation
species that breed during diff times of day, seasons, or years; ==> they cant mix their gametes
behavioral isolation
courtship rituals that attract mates and other behaviors unique
mechanical isolation
morphological differences can prevent successful mating
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
reduced hybrid viability
genes of diff parent species may interact and impair the hybrid’s development
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
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
limitations of biological species concept (2)
- there’s no way to evaluate the reproductive isolation of fossils or asexual organisms (such as prokaryotes)
- 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
the biological species concept emphasizes
the separateness of species from one another due to reproductive barriers
morphological species concept
characterizies a species by its body shape, size, and other structural features
advantages of morph. species concept: (2)
- can be applied to sexual and asexual organisms
2. can be useful even w/o info on the extent of gene flow
disadvantage of morph species concept
definition relies on subjective criteria; researchers may disagree on which structural features distinguish a species
paleontological species concept
focuses on morphologically discrete species known only from the fossil record
we are forced to distinguish many species using the paleon. species concept b/c
there’s little or no info on their mating compatibility
ecological species concept
views a species in terms of its ecological niche, its role in a biological community
unlike the biological species concept, the ecol. species concept
can accommodate asexual as well as sexual species
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
biologists trace the phylogenetic history of a species by
comparing its physical characteristics or its molecular sequences w/ those of other organisms
phylogenetic info sometimes reveals
the existence of sibling species
sibling species
species that appear so similar that they cannot be distinguished on morphological grounds
the ___ species concept is partcularly valuable for studying how species originate
biological
speciation can occur in 2 main ways:
allopatric, sympatric
allopatric speciation
(allos - other; patra - homeland)
gene flow is interrupted when a population is divided into geographically isolated subpopulations
_____ are more likely to experience allopatric speciation
small, isolated populations
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
isolating mechanisms are intrinsic
to the organisms themelves
____ is not in itself a biological isolating mechanism
geographic isolation
isolating mechanisms prevent interbreeding even
in the absence of geograhpic isolation
sympatric speciation
(syn - together)
speciation takes place in geographically overlapping populations
machanisms of sypmpatric speciation include
chromosomal changes
nonrandom mating that reduces gene flow
polyploidy
condition caused by a mutational change that results in extra sets of chromosomes
autopolyploid
an individual that has more than 2 chromosome sets, all derived from a single species
the triploid (3n) offspring of tetraploid (4n) and diploid (2n) parents are sterile b/c
their unpaired chromosomes result in abnormal meiosis
a common form of polyploidy
when 2 diff species interbreed and produce a hybrid
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
though infertile, hybrids may be able to ____, as many _____ do
propagate itself asexually, as many plants do
allopolyploid
A polyploid organism, usually a plant, that contains multiple sets of chromosomes derived from different species.
many important agricultural crops such as potatoes, tobacco, wheat, oats, and coton are
polyploids
today, plant geneticists create new polyploids in the laboratory by
using chemicals that induce meiotic and mitotic errors
polyploid speciation is more common in
plants than in animals
in allopatric speciation, the isolated population evolves by __ and __
natural selection and genetic drift
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
adaptivve radiation
the evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges
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
punctuated equilibrium
in evolutonary theory, long periods of apparent stasis (no change) interrupted by relatively brief periods of sudden change
by necessity, paleontologists base hypotheses about descent almost entirely on __ and __
external anatomy and skeletons
during periods of apparent equilibrium, changes in __, __, and __ may go undetected
behavior, internal anatomy, and physiology
exaptations
structures that evolve in one context but become co-opted for another function
