Exam two so far

what exactly is a species

• some concepts are based on patterns that can be used to recognize species

  • morphological species concept

  • polyogenic species concept

• others are based on biological processes underlying speciation

  • ecological species concept

  • biological species concept

morphological species concept

• experts in different groups that do studies on anthropology and more

• this definition of species emphasizes the morphological similarities between species

• relies on comparative morphology and anatomy

what are the PROs to morphological species

• applies to both asexual and sexual organisms

• may be used for both extant (claims that are not supported) and extinct organisms (part of the fossil record)

what are the CONs to morphological species

• relies on subjective criteria: how much difference are necessary to qualify as a different species?

• polyphenism, sexual dimorphism, and cryptic species are problematic

cryptic species

two or more distinct species that are classified as a single species because they are morphologically identical or nearly indistinguishable, despite being genetically distinct and reproductively isolated

ecological species concept

this defintion of species emphasizes the concept of ecological niche

ecological niche

the specific, functional role and position a species occupies within an ecosystem, encompassing how it survives, reproduces, and interacts with both biotic (living) and abiotic (non-living) factors

polyphenism

a biological phenomenon where a single genotype (the same set of genes) produces two or more distinct, discrete phenotypes (forms or morphs) in response to environmental cues, such as diet, temperature, or season

what are the PROs of ecological species concept

• applies to both asexual and sexual organisms

• emphasizes on ecosystem approach (environment variation)

what are the CONs of ecological species concept

• presupposes that ecological niches are discrete and non-overlapping

• doesn’t really incorporate evolutionary history

biological species concept

• a group of populations, the members of which can interbreed producing viable fertile offspring

• gene flow pressures reproductive compatibility between pop of a species

• conversely, absence of sufficent gene flow can lead to speciation

what are the PROs of biological species concept

it relates directly to the process by which speciation occurs: reproductive isolation(ties off gene flow)

incorporates pop genetic

what are the CONs of biological species concept

• doesn’t easily extend to organisms that reproduce asexually

• hard to apply to fossil organisms, or geographically separated species/pop

• some species pairs can hybridize (produce hybrids)

parthenogenesis

in some species, females can produce offspring without genetic contribution from males

gynogenetic females

generally produce triploid eggs that require activation by sperm cells, but without genetics combination from males

hybridogenetic females

produce haploid eggs that are fertilized by sperm cells from the males, but the male contribution will be discarded during gamete genetics

reproductive isolation

barriers that prevent members of two species from interbreeding and producing viable, fertile offspring

prezygotic barriers

• prevent fertilization from occurring

• before fertilization

postzygotic barriers

• mechanisms that affect the survival and/or fitness of the embryo/offspring

• chemical/physical homozygote

what are they two different types of reproductive isolation

• prezygotic barriers

• postzygotic barriers

what are the different types of prezygotic barriers

• habitat isolation

• temporal isolation

• behavioral isolation

• mechanical isolation

• gametic isolation

what are the different types of post zygotic barriers

• reduced hybrid viability

• reduced hybrid fertility

• hybrid breakdown

habitat isolation

• two species occupy could reproduce but different habitats

• consequently, they may encounter each other only rarely

temporal isolation

• two species differ in the times when they breed

• this can be annual, seasonal, or time-of-day differences

behavioral isolation

species-specific mating rituals can create extremely strong reproductive barriers

courtship

• type of behavioral isolation

• stepwix process that typically requires coordinated behavioral responses from both parents

mechanical isolation

• not compactiable in shapes

• mating is attempted but morphological in compatibilities prevent its successful completion

gametic isolation

• sperm may pass but won’t be able to reproduce

• sperm from one species may not be able to fertilize the ovum of another species

reduced hybrid viability

• genetic incompatibilities impair development and/or survival in the hybrid offspring

• but … ring species can provide a window into the evolutionary process of speciation

reduced hybrid fertility

• hybrids may be viable, yet sterile

• differences in the number and structures of parental chromosomes may prevent the formation of normal gametes during meiosis

• gene flow, therefore can’t be maintained between the hybrids and either parental species

hybrid breakdown

• hybrid may be viable and fertile

• however, when they mate with each other or with either parent, offspring of the next generation feeble or stable

what is the importance of gene flow

• the inherent complexities of defining “species”

• central to most species concepts is that gene flow is interrupted, thus allowing populations to diverge

• prior to reproductive barriers emerging, there are different scenarios in which pop may become increasing isolated from one another

• the main difference between these scenarios is the degree to which populations are geographically isolated from one another

allopatric speciation

• gene flow is interrupted when a population is divided into geographically isolated subpopulations

• the separated gene pools may then diverge

• different mutations may arise, and natural selection and genetic drift may alter allele frequencies differently between subpopulations

• eventually, reproductive isolation sets in as a byproduct of genetic divergence

vicariance

• geographical barrier

• fragmentation of the environment such that a species’ range become divided

sympatric speciation

• diverge with a geographical barrier

• speciation occurring in pop that occupy the same geographical area

• gene flow is reduced because of factors such as polyploidy, sexual selection or ecological differentiation

what are three ways that gene flow is reduced

• polyploidy

• sexual selection

• ecological differentiation

autopolyploids

• they are individuals that have more than two sets of chromosomes dervied from a single species

• can result from an error in cell division

• fertile with similar polyploids, but reproductively isolated from parental diploid species

allopolyploids

• common in plants

• they happen through hybridization

• they can arise when two species hybridize

• the inital offspring is infertile but may be capable of self-propagating asexually

• various genetic mechanisms can subsequently produce fertile allopolyploid over time

polyploidy

• many important agricultural crops are ___

• modern wheat used to produce bread is an allohexaploid (six sets of chromosomes, two sets from each three species)

• can happen with animals but rarely

• species can be identified acoustically be differences in their advertisements (mating) and encounter cells

habitat differentiation

• among horseshoe bats, the constant frequency of echolocation calls determines prey size and is involved in social communication

• in the large earned horseshoe, abrupt differences in call frequencies correlate with reproductive isolation

ecological differentiation and sexual selection

• Lakes Malawi and Victoria each contain about 500 species of cichlids

• the radiation of these cichlids species involve 3 steps

1) adaptation to either rockey habitats

2) adaptation to different diets

3) changes in male color patterns owing to sexual selection

phylogeny

the evolutionary history of a group of organisms can be represented by branching diagram

phylogenetic tree

• a hypothesis of the interrelationships between organisms in a tree

• can be constructed based on criteria such as morphology, or biochemistry

tip

each ___ represents taxa that descend from a common ancestor

taxa

organism were interested in only skill in existence

root

• the branching point at the ___ representing the common ancestor to all taxa in the tree

• position of the most common ancestor of the organisms

nodes

represent speciation events that lead to two different linages

branch

represent an evolutionary lineage. they can be either internodel or terminal (proportional to time)

sister groups (species)

taxa that share a common ancestor (not in the same species) that is not shared by an other group

clade

a grouping that includes a common ancestor and all descendants of that ancestor

monophyletic

type of clade that consists of a common ancestor and all of its descendants

paraphyletic

a group that shares a common ancestor, but which excludes some of the descendants of that common ancestor

polyphyletic

a group of distantly related taxa, excluding their common ancestor

plesiomorphy

• old

• primitive state of character

apomorphy

• new

• dervied state of character

• new character, novel trait

synapomorphy

• shared

• dervied state of that is shared by all members of clades

• more shared characteristics

autapomorphy

dervied state that is unique to a single trait

homoplasy

• due to convergent evolution

• superficial similarities that aren’t inherited from a common ancestor

synapomorphies

• shared dervied characters from nested patterns that provide information about when branching events occured

• and outgroup is often used to polarize characters states

outgroup

organism that is ancestral to everything else

parsimonious

trait that should only evolve once

constructing phylogenies

• the basic principle is the same, except that we are comparing sequences for genes or proteins across species

• fewer differences mean more closely related species

• larger numbers of differences mean more distantly related species

what are the two types of temperature and modes of evolution

• rates

• modes

tempo and modes of evolution

phylogenies can be used to study patterns of evolutionary change

rates

• speciation and extinction

• molecular change

• morphological change

modes

• gradualism

• punctuated equilibrium

diversification rates

• net difference new/old species and how they adapt

• clade diversify when there are more new species produced than the number lost to extinction

• the reverse occurs when a group is in decline

what are the 4 types of evolutionary temp

• evolutionary radiations

• mass extinction

• punctuated equilibrium

• gradualism

evolutionary radiations

• dramatic increase in taxonomic diversity due to high rates of speciation

• if these events are associated with ecological specialization, they are known as adaptive radiations

adaptive radiations

events are associated with ecological specialization

mass extinction

The Big Five: punctual events in the history of Earth where extinction rates were extremely high

punctuated equilibrium

• ancestral lineage

• long periods of time with no change

• long periods of stasis are interrupted by sudden bursts of morphological diversification

• changes occur mostly when new species branch from their parent species

• after their inception, new species change little over the rest of their existence

gradualism

• species change gradually over long periods of time

• morphological changes occur slowly and steadily

• morphological changes are uncorrelated with speciation events