bio c exam 4

what is a species?

species include all individuals of the “same kind”

what is the process in which species form

Speciation is the process by which species form

• populations connected by gene flow over time become isolated and diverge

  • barrier is introduced, and gene flow continues in respective environments without interbreeding

Biological species concept

Def: all individuals who can interbreed and form viable offspring

Hybrid sterility stops gene flow (offspring formed from 2 different species that can’t reproduce

mechanisms of reproductive isolation

prezygotic barriers

• habitat isolation

• temporal isolation

• behavior isolation

• mechanical isolation

• gametic isolation

postzygotic barriers

• reduced hybrid viability

• reduced hybrid fertility

• hybrid breakdown

habitat isolation

potentially interbreeding populations occupy different habitats so they dont come into contact to mate

prezygotic barrier mating attempt

temporal isolation

interbreeding populations which do not reproduce at the same time (like if they breed seasonally they likely wont produce offpsring because they are breeding during different seasons)

prezygotic barrier mating attempt

behavior isolation

thye have different behavior cues to identify mates, like a mating call so if these don’t match it prevents sexual contact

prezygotic barrier mating attempt

mechanical isolation

interbreeding populations cannot mate due to physical barriers like sperm not meeting egg, or genitalia doesn’t match

prezygotic barrier fertilization

gametic isolation

sperm of one species can’t fertilize the egg of the other species

prezygotic barrier fertilization

reduced hybrid viability

reduced hybrid viability means the hybrids are much less likely to survive with them dying before birth

postzygotic barrier

hybrid breakdown

F1 populations (the first birth generation) is healthy and good and can reproduce but the following generations have very reduced fitness and don’t even hatch

postzygotic barrier

total reproductive isolation

no individuals can and will mate with eachother

biological SC does not apply to all species

it cant explaine verything — other flashcard has the different species concepts

defining species through using species concepts

biological SC - all individulas who can interbreed and form viable offpsring

morphological/phenetic SC - all individuals who meet a specific morphological diagnostic criterion

ecological SC — organisms that occupy an additive zone/niche within its range

phylogenetic SC — smallest population or lineage of individuals diagnosabe by unique character combinations

morphological/phenetic SC

all individuals who meet a specific morphological diagnostic criterion

ockham’s razor if they look the same they are the same

ecological SC

all individuals who occupy the same adaptive zone/niche within the range of the zone/niche

ex: polar and grizzly bears occupy diff niches which keeps them seperate in terms of species if you ignore biological SC (double check)

phylogenetic species concept

the smallest population or lineage of individuals diagnosable by unique character combinations

useful for asexual organisms, phylogeny off archaeans and butterfly lizards

types of speciation

allopatric (different fatherland): a physical barrier causes species to diverge and prevent gene flow

sympatric (same fatherland): species diverge in situ meaning that the speciation occurs while both populations still occupy the same geographic area

allopatric speciation

(different fatherland): a physical barrier causes species to diverge and prevent gene flow

• vicariance event: a barrier that splits the population

  • river,

  • highway,

  • habitat loss,

  • land bridge disappears or forms

• Dispersal (founder effect)

  • small number of individuals colonize an isolated location

  • the “barrier” or how far they are is determined by dispersal ability

  • adaptive radiation (result of founder effect)

    • rapid speciation after colonization

      • species in an adaptive radiation are more closely related to eachother despite them being phenotypically different

here mutations or changes in allele frequencies accumulate

Sympatric speciation

mating from same geographic region

here mutations stop gene flow

• polyploidy: uneven chromosome numbers prevent fertiliation between specis with different ploidy

• autopolyploidy: result of cell division error changing number of chromosomes

• allopolyploidy: result of meiosis independent assortment resulting in only some gametes being viable because they’ll have an unbalanced set of chromosomes

• sexual selection: differences in mating preference causes population to diverge

• habitat differentiation: some mutations can cause differences in habitat preferences

speciation can be fast or slow

Punctuated model: not a gradual shift to different phenotype

gradual model: represents a slow shift from the original to a different phenotypes

• forms in between are transitional forms

polyploidy can cause reproductive isolation of many plants super quick in one or two generation

bacteria can evolve drug resistance in days

niche

niche - an ecological role or place

4 outcomes to post-divergence contact

populations making secondary contact will hybridize if not reproductively isolated

• reinforcement ?

• fusion ?

• stability?

• hybrid speciation ?

reinforcement

if hybrids are less fit than parents things that prevent hybridization will be selected for

• sympatric females choose conspecific males (preventing hybridization)

• allopatric females choose heterospecific males (they are more likely to hybridize)

Fusion

if hybrids are as fit as their parents the 2 species fuse back into one

stability

constant production of hybrids as a result of hybridization between ecologically divergent species

hybrid speciation

hybrids are reproductively isolated promoting speciation

All life descends from which common ancestor

LUCA

Systematics???

Systematics is the study of organismal diversity and grouping

synapomorphies

shared derived characters

• ex: feathers, milk, amniotic egg these can encompass an entire clade

phylogenies

def: represent a hypothesis about evolutionary relationships

Nodes: represent a hypothetical common ancestor; they look like the branch points

sister taxa: have the most recent common ancester (MRCA)

an outgroup- a species known to be distently related (many branches ago)

clades

Cladistics: grouping species into clades, which encompass an ancestor and its descendants

when making a clade you have to include all descendants from the starting branch point

methods of constructing phylogenies

1. input data

   • morphological (using the shapes or physical characteristics of the organisms)

   • genomic (nucleotides)

2. analysis method

   • maximum parsimony

     • relationships inferred by minimizing the number of evolutionary steps required to explain the data

     • All steps have equal weight

     • used for morphological data sets

   • maximum likelihood

     • relationships inferred with a substitution model (probability that a specific nucleotide substitution or morphological change occurred)

     • accounts for nucleotide chemistry, codon redundancy, morphological complexity

     • used for genomic data sets

morphological—> maximum parsimony

genomic—>maximum likelihood

methods of constructing phylogenies

come back to this slide 9 lecture 18

homology

homologous traits are those shared because of descent from a common ancestory

analogy

analogous traits are those shared due to convergent evolution

convergent evolution

organisms with similar ecology develop similar adaptations

loci accumulation of mutation

some loci accumulate mutation in rates

molecular clock:locus/loci with constant rate of neutral substitution, useful for estimating divergence time (uneven branch lengths)

time error refers to the deviation ideal assumption of a constnat rate of molecular evolution time scale

time scale are the units of time that are used to measure evolutionary distance between different species or lineages

when a phylogeny is time-calibrated it emans that the branch legnths represent time rather than evolutionary changes

microevolution

change within a population (mutations and changes in allele frequencies)

• change within a taxon

macroevolution

evolution of higher taxonomic groups (species, genera, famiies, orders, & phyla)

• change between taxa

think of this as the entire phylogeny tree

macroevolution isn’t seperated from microevolution but its just microevolution plus more time

• it is a field of study of organisms that share a common ancestor

pattern of macroevolution

evolutionary trends reflect survivorship bias due to natural selection

• species are born and die the same way individuals do

  • individuals who are most fit persist and continue to speciate

evolution isn’t goal oriented

• selection will only favor traits that result in higher fitness at that moment of time not looking towards the future

• evolution if the most complex structures still followed the rules of smaller increments resulting in higher fitness

• complex structures can be lost if there is no selection for them

• for example ability to fly can be lost, or color vision can be lost if it isn’t needed

small mutations can become large changes in phenotype

macromutations: mutations that cause large phenotypic differences

• things like hox (homeotic) genes if mutated can result in a completely different organism

neoteny — sexual maturity reached while retaining juvenile features

• if the metamorphosis into becoming a terrestrial adult that means they don’t have neoteny

evolutionary innovation

evolution of a new functional trait, body part, or big change in an existing body part

poorly adapted species go extinct

5 billion eukaryotic species are thought to have ever lived but only 8.7 million live now meaning many lineages are permanently lost

mass extinctions

def: periods of very high extinction rate

• usually species will naturally go extinct but there can be sudden changes that result in mass extinctions

• living fossils (lazarus taxa)

  • lazarus taxa are fossils before discovery of modern examples

  • living fossils resemble ancestral forms

  • all lineages have been evolving for the same amount of time so a lineage can’t be more evolved than another but can be better suited for an environment than another

hybrid

offspring of two parents of different species

reduced hybrid fertility

hybrids are much less likely to reproduce