biological species concept

species are groups of potentially interbreeding populations that are reproductively isolated from other such groups (work pretty well for sexually reproducing animals)

phylogenetic species concept

smallest possible group descending from a common ancestor and recognizable by unique, derived traits (useful for systematics; focuses on phylogenetic history)

general lineage species concept

species are metapopulations that exchange alleles frequently enough to compreise the same gene pool

metapopulation

group of spatially separated populations of the same species that interact at some level

biologist generally agree that

no single definition of a "species" will fit all taxa

speciation

evolutionary process by which new species arise (key step in the evolution of new species is the splitting in two of an original population)

isolating barrier

an aspect of the environment, genetics, behavior, physiology, or ecology of a species that reduces or impedes gene flow from individuals of other species (geographic or reproductive)

geographic

extrinsic properties of landscape that prevent gene flow (allopatry)

reproductive

features of organisms that prevent interbreeding (barriers effective even in sympatry)

prezygotic barriers

pre-mating:

-behavioral isolation

-ecological isolation: habitat, temporal, pollinator

-mechanical isolation

prezygotic barriers

post-mating:

-copulatory behavioral isolation

-gametic isolation

prezygotic barriers

intrinsic:

-hybrid inviability

-hybrid sterility: physiological and behavioral

prezygotic barriers

extrinsic:

-ecological inviability

-behavioral sterility

elk and red deer

two populations are geographically isolated but will reproduce when brought together

total population of free-ranging elk in trans-pecos as estimated in 1995 at

330 but 2014 was 3.5k

premating barriers

timing of reproduction

corals reproduce by releasing gametes into the water, the graph shows

two species of Montastraea corals remain reproductively isolated due to spawning times

some animals have

distinct courtship rituals

some rituals reinforce recent speciation events for

closely related animals

females only respond to

specific courtship displays for mating

premating barriers

pollinator isolation (two species of partially sympatric monkey flowers are pollinated, not hybridized in nature as pollinators aren't interested in the other species)

copulatory behavioral isolation

mating between species results in damage to the female reproductive tract; different species males' copulatory courtship results in eggs not fertilized by deposited sperm

gametic incompability

sperm or pollen from one species fails to penetrate and fertilize the egg of another species

hybrids are produced but have

low fitness

hybrid inviability

the hybrid embryos of sheep and goats, for example, die in the early developmental stages birth

hybrid sterility

mules

ecological inviability (outbreeding depression)

outbreeding depression can lead to coadapted gene complexes being broken apart without the forging of new coadapted gene complexes to take their place

behavioral sterility

e.g., behavioral sterility of hybrid males in acoustically communicating grasshoppers

bateson-dobzhansky-muller incompability

genetic incompatibility in hybrid offspring arising from epistatic interactions at two or more loci

dobzhanksy-muller incompatibility arises if

one population evolves the A1B0 genotype and the other evolves the A0B1 hybrids if the populations were to come into contact

Example of B-D-M incompatibility (epistatic interaction)

QTL was used to identify Hms1 on chromosome 6 and Hms2 on chromosome 13. Hybrids with M. guttatus alleles for Hms1 produce viable pollen if they also inherit at least one M. guttatus allele at Hms2. if they get M. nasutus the pollen is sterile.

allopatric speciation

result of geographic isolation, after a geographic boundary separate them, the populations become increasingly divergent

reinforcement refers to

the increase of reproductive isolation between populations through selection against hybrid offspring

consequences of secondary contact

-fusion of incipient populations back into one species

-reinforcement

-stable or transient hybrid zone formation

-speciation of hybrids

reinforcement increases

prezygotic reproductive isolation

reinforcement (definition)

natural selection favors prezygotic isolation mechanisms that prevent the formation of hybrids with reduced fitness (postzygotic isolation must evolve in allopatry)

reinforcement outcomes

-extinction of one of the initial populations

-the initial populations can hybridized

-the initial populations can speciate, are determined by both initial divergence and level of fitness of the hybrids

sympatric speciation

reproductive isolation evolves without geographic isolation (requires nonrandom mating based on genetic or phenotypic factors )

parapatric speciation

geographic barrier only partially separates populations (some gene flow possible), for example, grass Agrostis tenuis, individuals are tolerant to heavy metals, a heritable trait, survive well on contaminated soil, but poorly on non-contaminated soil (the reverse occurs for intolerant populations)

isolation by distance

populations tend to breed with those in close proximity (causes variation across the range of the species)

ring species

is a connected series of neighboring populations, each of which interbreed with closely sited related populations, but for which there exist at least two "end" populations

ecological speciation

selection for different ecological traits in different niches creates reproductive barriers (can lead to pre- ad postzygotic isolation

magic traits

traits that simultaneously confer divergent local adaptation and act as reproductive barriers

a species population of pink-petal flowers becomes isolated in allopatry or parapatry. novel pollinators drive the selection of new traits (purple petals) in the isolated populations eventually leading to

speciation of the flower populations

phylogentic evidence for allopatric speciation

a land bridge from north america to south america only arose 3mya. allopatric speciation resulted.

palm trees evolved due to soil types (one liked basic while the other liked acidic), therefore

there was also a shift in flowering times

islands provide

opportunity for allopatric speciation

colonization leads to

speciation

(Laupala crickets only found in hawaii) QTL mapping suggests that

loci associated with male pulse rate also maps to female song preference

populations on the same island often differ in male songs and female preferences for the songs

polar bears evolved into a distinct species beginning

500,000 years ago

ecological speciation and interspecies gene flow between polar bears and brown bears

polar bears and brown bears

genes under strong selection in polar bears linked to ecological niche

-APOB proteins (to handle high levels of cholesterol from diet rich in fatty acids)

-heart function (long-distance swimming)

-hair pigmentation

(interbreeding has occurred since divergence)

when D=1 Drosophila spp. can

no longer interbreed, using molecular clocks, it takes hundreds of thousands of years for them to diverge into new biological species.

allopolyploidy can lead to

extremely rapid speciation

allopolyploid

an individual having two or more complete sets of chromosomes derived from different species

cryptic species

compromise two or more taxa that are grounded under a single name because they are more-or-less indistinguishable morphologically (important for detailed biodiversity assessments)

skippers in costa rica has caterpillars with different patters, and were apparantly

cryptic species

cryptic meadowlarks (eastern meadowlark, western meadowlark, and chihuahuan meadowlark) in

texas

16S rRNA genes vary by up to

3% in microbial species

is microbes are 97% similar to 16S rRNA, they are the

same species

single spoonful of soil may contain

10,000 different species of bacteria (soil has one trillion species by locey and lennon 2016)

horizontal gene transfer in

E.coli, however, core genome is only 3188 genes, but there are 90,000+ gene across the entire E.coli genome

horizontal gene transfer makes classification difficult

the mixing genes makes it difficult, if not impossible, to delineate species boundaries

horizontal gene transfer is

common

bacterial species often defined by

specific adaptations

stable ecotype model

species concept for microbes, species is long-lived population of genetically related individuals that share a stable set of adaptations for hte same ecological niche, yet scientist criticize this method

taking horizontal gene transfer into account

shapiro et al. suggests that gene acquired from other lineages can be important for the emergence of lineages with new adaptations

geographic barriers to gene flow

physically separate populations (important for all species concepts)

reproductive barriers are

intrinsic features of organisms that reduce likelihood of interbreeding

separation of populations over time will

reduce gene flow

divergent floral traits can cause

pollinator isolation and reduce interbreeding

genetic incompabilities that reduce hybrid fitness can be

important barriers to gene flow

specitation can occur in symatry when

populations rarely interbreed

identifying cryptic species is important for

measures of biodiversity

cryptic species may diverge from ancestral populations without

easily distinguishable morphologies

microbial organisms present challenges to species concepts

developed eaukaryotes