Flashcards in Species Deck (58):
what are the three types of species concept?
1) biological species concept
2) morphological species concept
3) phylogenetic species concept
what is the biological species concept?
there is a TON of variation among members of a species (look at dogs)
species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups
much of the intraspecific variation is geographically structured
can species be defined by morphological differences?
biological species concept
species cannot be defined by the degree of morphological difference --> morphology is important but it's not necessarily what differentiates species
what are species?
species are population(s) of variable individuals connected through gene flow
species are systems of populations; the gene exchange between these systems is limited or prevented in nature by a reproduction isolating mechanism or several such mechanisms
what observations led to the biological species concept?
- variation within populations -->genetic differences
- geographic variation between populations --> look different in different regions, but interbreed where populations meet
- sibling ("cryptic") species --> reproductively these are different species but the look alike
what is another name for sibling species? what are they?
reproductively different species, but they look alike
what are limits to the biological species concept?
1) emphasis on sexual reproduction makes it difficult to address organisms whose life history is not defined by that process (e.g. parthenogenic or asexual species)
2) interbreeding is not "all or nothing"
- ex. hybrid zones
3) extinct species
biological species concept and extinct species
there's limits in this concept when it comes to extinct species because if interbreeding is the key, how can we determine the species boundaries of animals about whom we have no data on reproductive habits and capabilities (this is relevant to extinct and extant species)
how can we determine if geographically separated populations can potentially interbreed
how do we know if populations have the potential to interbreed?
what is the morphological species concept?
species are defined on the basis of physical features (morphology)
ex. body size, shape, color
what is the phylogenetic species concept?
The concept of a species as an irreducible group whose members are descended from a common ancestor and who all possess a combination of certain defining, or derived, traits
"an irreducible (basal) cluster of organisms, diagnosably distinct from other such clusters, and within which there is a parental pattern of ancestry and descent"
"the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals"
what is synapomorphy?
shared, derived (homologous) features
a character or trait that is shared by two or more taxonomic groups and is derived through evolution from a common ancestral form.
may be transformed over time with a newly transformed "state" characterizing a less inclusive group
fins --> arms --> wings or flippers
what is monophyly?
groups of species or populations characterized by synapomorphy
a monophyletic group is group of organisms which forms a clade which consists of an ancestral species and all its descendants
what is a clade?
a monophyletic group that consists of a complete lineage: ALL the descendants of a common ancestors
fish --> tetrapods --> birds or mammals
what is a synapomorphies?
shared, derived features that group and differentiate each named species
what is a solenobiella?
a population cluster that is diagnosable by a unique combination of features
all populations of solenobiella share a common ancestor
what is a monophyletic group?
contains an ancestor and all of its descendants
what is a paraphyletic group?
contains an ancestor but only some of its descendants
what's a polyphyletic group?
contains various organisms with no recent common ancestor
how do you interpret a phylogenetic tree/clydogram?
trees specify relationships between terminal groups --> these do not change when the node flips
what are commonalities of all species concepts?
species are populations linked by history
characterized by shared, derived attributes
genetic and morphological continuity maintained by interbreeding
what is speciation?
the mechanisms by which populations attain reproductive isolation
what are isolating mechanisms?
phenomena that prevent gene flow between populations or members of the same population
what are prezygotic barriers?
they prevent mating between populations
may outright prevent or just decrease the frequency or incidence of mating
what is positive assortative mating? what kind of barrier is it?
non-random mating based on genotype or phenotype
like mates with like
what is reproductive isolation?
all these species concept imply
physical barriers between populations are not enough
the physical barriers between populations could interbreed
biologically based reproductive barrier accompany speciation
what is temporal isolation?
incipient/cryptic/sibling species in the same place but they mate at different times of the year or day
effect of temporal isolation on spawners
for spawners this will effectively eliminate opportunity for gene flow if the offset in mating time is greater than gamete competence because gametes won't come into contact
effect of temporal isolation on copulators
for copulators, mate searching or aggregating at specific times of day or year
trout and temporal isolation example
brown trout and rainbow trout live in the same streams but brown trout breed in the fall and rainbow trout breed in the spring
what is habitat isolation?
spending your whole life in a single place or on a single host and so you don't get a chance to meet
examples of habitat isolation
ex. epilachna spend their whole life in a single kind of plant
the european mosquito consists of six morphologically indistinguishable species but they breed in different habitats: brackish water, running fresh water, stagnant water, etc.
lack of interest
may be most critical barrier in animals
when the males don't engage females or when females don't respond to males
- specific mate recognition system
- mating behavior or song
- pheromone responses
what is behavioral isolation? what's another name for it?
an important evolutionary mechanism that helps members of the same species identify each other as proper mates
morphologically indistiguishable, but don’t reproduce as the don’t recognize the song…perform a duet…
what is a post-mating prezygotic barrier?
mating of gamete transfer occurs but zygotes are not formed
what are types of post-mating prezygotic barriers?
lack of fertilization
what is lack of fertilization?
post-mating prezygotic barrier
- parts don't fit (no sperm transfer)
- eggs and sperm mechanically incompatible
what is gametic isolation?
important for many marine invertebrates and nearly all plants
egg may not recognize sperm due to incompatible receptors
nuclei may not fuse
what are postzygotic barriers?
fertilization takes place but may not result in a successful offspring
hybrid zygotes are formed but have reduced fitness
what are some examples of postzygotic barriers?
interaction of incompatible genes
disruption of meiosis
different number/structure of chromosomes
what is the outcome of reproductive isolation?
zygote or hybrid mortality if the embryo dies shortly after fertilization
embryo dies shortly after fertilization:
- may not successfully complete development
-embryos of hybrids often fail to undergo metamorphosis successfully
hybrid mortality if hybrid offspring develop but then die
hybrid viability may differ depending on environment
selection against hybrids in both parental habitats
asymmetry in hybrid succes
hybrids viable but not fertile:
-asymmetry between crosses --> heterogametic sex most often sterile
- chromosomes have different genes or morphologies, and so can't segregate properly
what is an example of hybrid sterility?
horse + donkey = mule
what are models of speciation?
speciation is not the purpose but a by-product of other processes and events
what are the three types of models of speciation?
what is allopatry
*most important mode of speciation for animals*
non-overlapping distribution by vicariance or by dispersal (peripatry)
one island: island splits and now there's two populations of the same species on two different islands and they mutation
Allopatric speciation is speciation that results when a population is separated by a physical barrier. It is also referred to as geographic speciation
A population is subdivided; during the separation, mutations arise in each subset such that each subset changes from the original in terms of morphology, behavior, etc --> the differences that arise are sufficient to maintain distinctiveness even in the absence of physical barrier
what what is sympatry?
Sympatric speciation is speciation that occurs without physical separation of members of the population
what is parapatry?
"isolation by distance"
the relationship between organisms whose ranges do not significantly overlap but are immediately adjacent to each other; they do not occur together except in a narrow contact zone.
two islands: some organisms travel from one island to another --> that's peripatetic
allopatric speciation vs. peripatric speciation
allopatric speciation by vicariance
peripatric speciation by dispersal
allopatric speciation: when the physical barrier is removed or the new species disperses over it, it re-establishes sympatry
peripatric speciation: range expansion re-establishes sympatry
what is vicariance?
the geographical separation of a population, typically by a physical barrier such as a mountain range or river, resulting in a pair of closely related species
allopatry that arises because extrinsic factors act to subdivide population
what is dispersal?
allopatry that arises because a subset of the population disperses to a new, isolated place --> peripatetic speciation or founder effect
subsets differentiate while separated --> small size of founding population spurs change (genetic drift)
what is parapatric speciation?
Speciation that occurs when the groups that evolve to be separate species are geographic neighbors; they are in different areas, but the areas are next to each other and individuals can move between the areas (gene flow)
strong selection to counteract the effect of gene flow, usually strong difference in environment
widespread species undergo local differentiation that leads to isolation --> 2 instances of change independent of one another
physical distance acts are the initial barrier to gene flow: isolation by distance
NOT THE SAME AS PERIPATRIC
what are secondary contact zones?
Areas of overlap in range AFTER speciation
Hybrids may form if isolation is incomplete.
what is sympatric speciation?
Speciation without physical or spatial barrier
Subsets each specialize on particular resource within ecosystem --> Niche partitioning and adaptive radiation
what is an example of sympatric speciation?
an entomologist discovers that the apple maggot was Rhagoletis pomonella, an insect normally found on wild hawthorn
a certain set of flies changes their host causing reproductive isolation