a4.1 (natural selection) Flashcards
define speciation
the process by which a population of one species diverges to become two distinct species
allopatric speciation vs sympatric speciation
allo = populations become geographically separated
symp = can occur within the same geographic area
3 steps to allopatric speciation
- populations begin to be geographically separated (eg. uplift of land, the movement of a glacier, or formation of a body of water)
- two populations independently evolve, accumulating different gene mutations and being subjected to different selective pressures
- the populations evolve to the point of not being able to interbreed and exchange genes. they are now separate species according to the biological species concept
example of allopatric speciation - panama and atlantic porkfish
panama and atlantic porkfish being separated by the isthmus of panama (the narrow strip of land above coloumbia and below costa rica formed by tectonic plate movement)
example of allopatric speciation - squirrels
kaibab (north of canyon) and abert’s (south of canyon, original species) squirrel in the colorado plateau in the grand canyon
how are groups separated sympatric speciation
groups are separated by differences in behavior or timing of life cycles
define polyploidy
another cause of sympatric speciation that is common in plants
when does behavioural isolation occur? & examples of how this may occur
when a behavior prevents reproduction between individuals.
for example, different individuals may have different preferences for breeding calls, mating dances, pheromones, or feeding locations within a habitat.
example of behavioural sympatric speciation - cichlid
(2 species names & changes)
littoral vs benthic cichlid fish (tanzania)
body color, shape, size, jaw & tooth structure
females preferentially mating with males that are more similar to themselves
separating as bottom vs top feeders
example of behavioural sympatric speciation - killer whales (2 species names & differences)
resident vs biggs killer whales
resident killer whales maintain tight-knit family pods and prey on salmon and other marine fish.
bigg’s killer whales roam in smaller groups, preying on other marine mammals such as seals and whales
example of temporal sympatric speciation - palm trees (2 species names & cause of speciation)
in australia (lord howe island)
howea forsteriana & howea belmoreana
speciation due to a substantial disjunction in flowering time
example of temporal sympatric speciation - cicadas (2 species names & cause of speciation)
in eastern united states
m. tredicim & m. septendecim
m. tredecim emerge every 13 years, while adults of m. septendecim emerge every 17 years
define species biodiversity
the number and relative abundance of species found in an area
define ecological niche
the role of a species in an ecosystem
4 characteristics of an ecological niche
the abiotic environmental conditions a species can tolerate (i.e. temperature, precipitation and terrain)
the biotic interactions a species has with other species (i.e. competition, predation and mutualism)
the activity pattern of the species (i.e. nocturnal, diurnal or crepuscular)
how the species obtains energy and nutrients from the environment (what and how it eats)
define adaptive radiation
a pattern of speciation in which many species rapidly evolve from a common ancestor to occupy a range of vacant ecological niches (a source of considerable biodiversity)
natural selection results in multiple related species exhibiting different ________, ________ and ________ adaptations to the new niches.
morphological, physiological, behavioral
how may niches become available? x2
mass extinctions leave behind a host of empty niches. any remaining species can rapidly evolve to fill the niches without competition from the other (now-extinct) species.
because new species rarely make it to isolated islands, the few pioneering species that first arrive and colonize find a wide-open ecosystem with many niche vacancies and lack of competition with other species for available resources.
how did dinosaur extinction impact adaptive radiation of mammals (before & after)? what did this lead to?
before the extinction, mammals were small and occupied few ecological niches
after the extinction, mammals evolved and adapted to the the newly available niches with few competitors for resources
this led to a “sudden” expansion of species diversity, including the first fully aquatic mammals, flying mammals, rodents and primates
what were cynodonts (200+ million years ago)
a group of mammal-like reptiles
3 characteristics of the early true mammals (~175 million years ago)
mainly small insect-eating creatures
adapted to nighttime activity
ranged in size from scarcely bigger than a bumblebee to squirrel-sized (keeping out of the way of the predatory dinosaurs)
3 mamillian groups at ~140 million years ago
monotremes (platypus and spiny anteater), which lay eggs externally
marsupials (kangaroos, opossums), which carry their young in a pouch
placental mammals (humans, cows, horses), which retain the fetus internally during long gestation period
what was the dinosaur extinction called? how many species of earth did it elimintate?
the cretaceous–paleogene
killed ~three-quarters of the plant & animal species
watch this video on adaptive radiation https://www.youtube.com/watch?v=IPlOLaY5xbA
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how did the galapagos finches experience adaptive radiation? & video to watch https://www.youtube.com/watch?v=mcM23M-CCog
one species of finch migrated to the galapagos from the mainland of central/south america
this one migrant species would gives rise to multiple species that exploit different niches
species have adapted for different diets: seeds, insects, flowers, the blood of seabirds, and leaves
how have madagascar’s ant nest beetles gone through adaptive radiation?
beetles imitate the sounds of an ant queen, permitting them access to the nest without alarming the other ants
secretions on their antennae and body allow them to interact with ant workers without being detected
how have hawaii’s silversword plants gone through adaptive radiation?
have a range of anatomical and ecological adaptations but are very genetically similar
are found in a range of terrestrial habitats (wet forests, dry forests, near sea level, in alpines, etc)
how have the caribbean’s anoles gone through adaptive radiation?
spread out across the islands once they arrived from south america
anatomical differences in leg length and toe pad size, primarily related to moving on the substrate they most frequently encounter (eg. lizards that live on the ground have long legs for sprinting whereas twig dwelling lizards have short legs for grasping)
define hybrid
the offspring resulting from the sexual reproduction between two closely related, but separate species
why are hybrid plants often bred for?
increased yield and improved quality traits such as size, color, and flavor
define prezygotic barriers
prevent fertilization of egg and sperm between two seperate species. these prevent any energy being wasted on the formation of a hybrid offspring.
what do barriers to hybridization ensure?
energy is not spent producing sterile hybrids and preventing the mixing of alleles between species
define postzygotic barriers
barriers that occur after fertilization that prevent the zygote from developing into a viable, fertile adult.
examples of prezygotic barriers & definitions x5
habitat isolation (two species occupy different habitat and/or niche)
temporal isolation (two species breed at different times of the day, season or year)
behavioural isolation (two species have unique behaviours that attract only the like-kind species)
mechanical isolation (differences in the anatomy of the reproductive organs may prevent successful breeding)
gametic isolation (the proteins on the surface of the gametes will not be complementary, preventing successful fertilization)
examples of postzygotic barriers & definitions x3
reduced hybrid viability (prevent the hybrid offspring from surviving)
reduced hybrid fertility (prevent the hybrid from itself successfully reproducing)
hybrid breakdown (see separate flashcard)
define hybrid breakdown
if a first-generation (F1) hybrid is able to survive and reproduce with another hybrid or with either parent species, the offspring of the hybrid (F2) may be feeble or sterile due to incompatibility between interacting genes of the two species.
define polyploidy. in what is it commonly seen?
there are more than two sets of chromosomes in each cell. most common in flowering plants (>70%)
why are polyploidy usually bigger in size than diploid ones?
the nucleus has to expand to accommodate the extra genetic material
how are polyploidy offspring different from their parents?
survive better than their parents in harsh environments, such as cold climates and high altitudes and latitudes
define the condition of autopolyploidy
a polyploid individual will have two or more complete sets of chromosomes from its own species
how may a diploid (2n) gamete be produced?
if there is an error in meiosis that results in all of the chromosomes moving into one cell instead of separating
how are triploid (3n) and tetraploid (4n) zygotes created?
the diploid (2n) gamete can then fuse with a haploid gamete from the same species to create a triploid (3n) zygote, or with another diploid gamete of the same species to create a tetraploid (4n) zygote
define allopolyploid
a polyploid with multiple chromosome sets derived from two different species
how are allopolyploids created?
gametes from two species, at least one of which has had an error in meiosis, combine to form allopolyploid offspring
why are polyploids immediately reproductively isolated?
as chromosome number is a shared trait within a species, polyploid offspring have a different number of chromosomes than the parent species, and as a result the offspring is unable to breed with members of the parent species
speciation due to polyploidy is a mechanism of what?
sympatric speciation
examples of polyploidy species x2
allium (onion, garlic, chives, scallion, shallot and leek)
coast redwood (hexaploid) (long lived tall trees)
lamarckism 2 main ideas (state & explain) & an example
use and disuse: structures that are used frequently and continuously will strengthen, develop, and enlarge, while structures that are not used will weaken and deteriorate.
inheritance of acquired characteristics: the physical changes to the structures of an organism that result from use/disuse during their lifetime are inherited by its offspring
ancestral giraffes stretching necks caused offspring to inherit stretched necks
charles darwin proposed a mechanism of evolution called what?
natural selection
how is lamarckism’s proposal of inheritance replaced by darwin through a paradigm shift?
because we now understand that physical changes that occur during an organism’s lifetime are not passed to offspring
define homologous structures
structures derived from the same body part of a common ancestor. they may not always have the same function
define analogous structures
structures that have different evolutionary origins, but perform the same function. does not imply a recent common ancestor
speciation is often depicted using what type of diagram?
a branching line diagram
why can it be hard to distinguish genetically diverging populations as the speciation process is occurring?
because there is a continuum from merely somewhat restricted gene flow within the ancestral species and the complete reproductive isolation of the 2 resulting species
define reproductive isolation as the first step in speciation. how can it be seen?
populations stop interbreeding with each other (for speciation to occur there must be barriers that prevent gene flow between the gene pools of two populations)
can be geographic, behavioural or temporal
define gene flow
the movement of genes into or out of a population
define how differential selection acts as the second step in speciation
if the divergence in traits results in the populations not being able to interbreed should they once again overlap then the populations are now different species according to the biological species concept
videos on slides 18, 19 and 23
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