organisms and evolution Flashcards
definition of a hazard
something with potential to cause harm
definition of a risk
the likelihood of harm arising from exposure to a hazard
what does risk assessing involve?
identifying control measures to minimise risk
how should sampling wild organisms be carried out?
- in a way that minimises the impact on wild species and habitats
- consideration should be given to rare and vulnerable species and habitats that are protected by legislation
4 different sampling techniques
- point count
- transect line
- remote detection
- capture techniques
capture techniques
- traps and nets
- used for mobile species like mice
remote detection
- used to detect elusive species
- camera traps/scat sampling
point count
- involves recording all individuals seen from a fixed location
- can be compared to other locations or same location at a different time
transect line using quadrats
- line along which different samples can be taken, set up along an area with variable terrain or abiotic factors
- allows sessile organism abundance to be recorded
- abiotic features can also be measured to determine habitat features of organisms
two ways in which organisms can be classified
taxonomy and phylogenetics
what is taxonomy?
identification and naming of organisms and classifying them based on shared characteristics
- based on morphology
what is phylogenetics?
the study of evolutionary history and relationships among individuals or groups of organisms
- uses heritable traits to make inferences about an organisms evolutionary history
what is a phylogenetic tree?
a diagrammatic hypothesis of an organism’s relatedness to other organisms
what does genetic evidence reveal?
relatedness obscured by divergent or convergent evolution
three taxonomic groups needed
nematodes: round worms which show great variety, often parasitic
arthropods: joint-legged invertebrates which are identified by their segmented body, typically paired with appendages (wasps, spiders, butterflies)
chordates: sea squirts and vertebrates (birds, reptiles, amphibians, fish)
what are model organisms?
organisms which have been well studied or are easily studied
- used to obtain information that can be applied other species which are more difficult to study directly
methods of monitoring populations
- banding
- tagging
- surgical implantation
- painting
- hair clipping
indicator species
presence, absence/abundance of them can give info of environmental qualities such as the presence of pollutants
what does an absence of indicator species suggest?
a species is susceptible to some factor in the environment
what does an abundance of indicator species suggest?
a species is favoured by the conditions
what is ethology?
the study of animal behaviour
ways of quantifying animal behaviour?
latency, frequency, duration
what is latency?
time between stimulus occurring and the response behaviour
what is frequency?
number of times a behaviour occurs within the observation period
what is duration?
the length of time each behaviour occurs for during the observation period
what is an ethogram?
a method of recording animal behaviours over a set period of time
what is recorded in an ethogram?
- specific behaviours observed and recorded
- duration of each behaviour and total time of observation are recorded
- time budget can be constructed to show the percentage of time spent on each behaviour
what is anthropomorphism?
assigning human emotions to animal behaviour
why should anthropomorphism be avoided when performing an ethogram?
it can lead to invalid conclusions
what is evolution?
the change over time in the proportion of individuals in a population differing in one or more inherited trait
2 ways changes in allele frequency can occur
selection (natural or sexual)
genetic drift
what is natural selection and how does it arise?
- non-random increase in frequency of advantageous alleles and non-random decrease in frequency of deleterious alleles
- acts on genetic variation
- arises as a result of mutation
what will happen when more offspring are produced than the environment can handle?
only the best adapted will survive
what is sexual selection?
non-random process involving the selection of alleles that increase the chance of mating and producing offspring
- doesn’t increase chances of survival
what is sexual selection due to?
either male to male rivalry or female choice
what is male to male rivalry
- males compete aggressively to defend territories and gain access to females
what is female choice?
females will choose a male based on traits he displays, if males cannot control access to females
what is genetic drift?
random process which results in an increase or decrease in the frequency of inherited traits
when does genetic drift occur?
when a chance event such as a natural disaster causes unpredictable fluctuations in allele frequency from one generation to the next
examples of genetic drift
- population bottlenecks
- founder effects (isolation of a few members of a population from a larger one - gene pool is therefore not representative of the original pool)
what are selection pressures?
environmental factors that influence which individuals in a population pass on their alleles
- can be biotic or abiotic
what does the Hardy-Weinberg principle state?
in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations
what is fitness in evolution?
a measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species
two ways in which fitness can be defined
absolute or relative terms
definition of absolute fitness
ratio between the number of individuals of a particular genotype after selection, to that before selection
definition of relative fitness
ratio of number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype.
what is co-evolution?
the process by which two or more species evolve in response to selection pressures imposed by each other
where is co-evolution seen?
in pairs of species that have symbiotic relationships
what is symbiosis? + 3 types
co-evolved intimate relationship between members of two different species
- mutualism, commensalism, parasitism
sexual reproduction definition
offspring arise from the combination of male and female gametes after the process of fertilisation
asexual reproduction
offspring arise from a single organism and share the DNA of that parent only
costs of sexual reproduction
- only half the population are able to produce offspring
- only half of each parents’ genome is passed onto offspring, disrupting successful parental genomes
benefits of sexual reproduction
- outweigh the costs due to increase in genetic variation of the population
- this provides raw material for adaptation which gives sexually reproducing organisms a better chance of survival under changing selection pressures
benefits of asexual reproduction
- one parent can produce a colony of virtually unlimited size
- offspring can be reproduced more often and in larger numbers
- whole genomes are passed onto offspring
- maintaining genome of parent is an advantage in very narrow, stable niches/when recolonising disturbed habitats
costs of asexual reproduction
- not able to adapt easily to changes in their environment
- mutations can occur that provide some degree of variation and enable natural selection to occur
- organisms often have mechanisms for horizontal gene transfer, which results in faster evolutionary change than in those that use vertical transfer
parthenogenesis definition
type of asexual reproduction in which an unfertilised female gamete develops into a new individual
where is parthenogenesis most common?
in cooler climates or areas with low parasite density or diversity
meiosis definition
division of the nucleus that results in the formation of haploid gametes from a diploid gamete
what are gametocytes?
cells in eukaryotes which give rise to gamete
M1 - pairing of homologous chromosomes
- prior to M1, during interphase, homologous chromosomes duplicate so each is now made of two sister chromatids
- chromosomes condense and the homologous chromosomes pair up so that they are aligned gene by gene
M1 - crossing over
- a chiasma forms at a random position between the homologous pairs
- sections of DNA can be exchanged at these points
- this crossing over of DNA is random and produces genetically different recombinant chromosomes
- this can result in new combinations of the alleles of these genes, which increases variation
M1 - alignment on the metaphase plate
- spindle fibres attach to the homologous pairs and line them up at the equator of the cell
- the orientation of the pairs of homologous chromosomes at the equator is random
- this means each pair is positioned independently of the others, irrespective of whether they came from the mother or father
- known as independent assortment
M1 - separating homologous chromosomes
- microtubules begin to shorten
- the chromosomes of each homologous pair are separated and move to opposite poles of the cell
- the chromosomes group in each end of the cell and a nuclear membrane forms around them
- cytokinesis occurs and two daughter cells are formed
- sister chromatids are no longer identical due to the crossing over
- two haploid cells are formed
meiosis II
- each of the two cells from meiosis I undergoes a further division
- sister chromatids of each chromosome are separated
- total of four haploid cells are produced
what is the SRY gene?
the sex determining region on the Y chromosome
- determines development of male characteristics in most mammals
what does the Y chromosome lack?
many genes found on its homologous X chromosome
what is sex linkage?
- in XX females, a recessive allele on one X can be masked by a dominant allele on the other X
- in XY males, a recessive allele on the X has no second copy to mask its effects
- this can lead to carrier females and affected males
what does X chromosome inactivation prevent?
a double dose of gene products which could be harmful to cells
what is a hermaphrodite?
species that have functioning male and female reproductive organs in each individual
benefits of hermaphrodites
- there is no requirement for a partner to be of the opposite sex
what can cause changing of sex in an individual?
environmental factors such as size, competition, parasitic infection and temperature
clearest sexual dimorphism in vertebrates
gamete size
which parent provides greater investment?
females/mother
how are organisms classified (r and K)
based on their level of parental investment in offspring, and the number of offspring produced
where does r-selection occur?
in unstable environments where the species has not reached its reproductive capacity
where does K-selection occur?
in stable environments
benefits of internal fertilisation
- increased chance of internal fertilisation
- fewer eggs needed
- offspring can be retained internally for production and/or development
- higher offspring survival rate
costs of internal fertilisation
- a mate must be located, requires energy expenditure
- requires direct transfer of gametes of gametes from one partner to another
benefits of external fertilisation
very large number of offspring can be produced
costs of external fertilisation
- many gametes predated, not fertilised
- no/limited parental care
- few offspring survive
4 types of mating system
monogamy, polygamy, polygyny, polyandry
monogamy definition
mating of a pair of animals to the exclusion of all others
polygamy definition
individuals of one sex have more than one mate
polygyny definition
one male mates exclusively with a group of females
polyandry definition
one female mates with a number of males in the same breeding season
what is sexual selection
selects for characteristics that have little survival benefit for the individual, but increase their chances of mating
are males of females more conspicuous?
males - they often have more obvious markings, structures and behaviours
what does female choice involve?
females assessing honest signals of the fitness of males
what do honest signals indicate?
favourable alleles that increase chances of survival of offspring, or a low parasite burden suggesting a healthy individual
what do males do in lekking species?
- gather to display at a lek, where female choice occurs
- dominant males occupy the centre of the lek, with subordinates and juveniles at the fringes
what is an ecological niche?
a multi-dimensional summary of tolerances and requirements of a species
when is a fundamental niche occupied?
in the absence of interspecific competition
when is a realised niche occupied?
in response to interspecific competition
what is competitive exclusion
where the niches of two species are so similar that one declines to local extinction
when can competitors co-exist?
when the realised niches are sufficiently different, so resource partitioning can occur
what does degenerate mean (parasites) and why does this occur?
- lacking in structures and organs found in other organisms
- occurs because a host provides so many of the parasite’s needs
ectoparasites
live on the surface of the host
endoparasites
live within the tissues of the host
what is a definitive host?
organism on or in which the parasite reaches sexual maturity
what is an intermediate host?
may also be required for the parasite to complete its life cycle
what do vectors do?
play an active role in the transmission of the parasite and may also be a host
plasmodium (process)
- infected mosquito acts as a vector, bites a human
- plasmodium enters bloodstream, asexual reproduction occurs in the liver and red blood cells
- red blood cells burst and gametocytes are released into the bloodstream
- another mosquito bites an infected human and the gametocytes enter the mosquito, maturing into male and female gametes, allowing sexual reproduction to occur
- mosquito can then infect another human host
what are viruses?
parasites that can only replicate inside a host cell
- they contain genetic material in the form of DNA or RNA, packaged in a protein coat
- outer surface contains antigens that a host cell may or may not be able to detect as foreign
viral life cycle - stages
1 - infection of host cell with genetic material
2 - host cell enzymes replicate viral genome
3 - transcription of viral genes and translation of viral proteins
4 - assembly and release of new viral particles
what are RNA retroviruses?
viruses with RNA rather than DNA
what happens when RNA retroviruses inject their RNA into a host cell?
the also inject an enzyme - reverse transcriptase
what does reverse transcriptase do?
- synthesises DNA from the RNA
- the DNA is then inserted into genome of the host cell
- the viral genes can then be expressed to form new viral particles
transmission definition
the spread of a parasite to the host
virulence definition
the harm cause to a host by a parasite
methods of transmission - ectoparasites
- direct contact
- consumption of intermediate host
methods of transmission - endoparasites
often via vector
factors influencing transmission
- overcrowding of hosts
- mechanisms such as vectors and waterborne dispersal stages that allow parasites to spread even if the host is at full capacity
- host behaviour is often exploited by parasite to maximise transmission
non-specific immune responses
- physical barriers
- chemical secretions (saliva, tears)
- inflammatory response (enhanced blood flow to injury site, brings phagocytes)
- natural killer cells (release chemicals which cause cell death by apoptosis)
- phagocytes (engulf the parasites and store them in a vacuole)
what happens when tissues become damaged or invaded?
cytokines are released, causing increased blood flow, resulting in white blood cells accumulating at the site of infection
what do lymphocytes have on their surface?
a receptor which can potentially recognise a parasite antigen
what happens when an antigen binds to a lymphocyte?
the receptor selects that lymphocyte to divide and produce a clonal population
what gives an antibody its specificity for the binding antigen?
variable region of amino acid sequence
what can the antibody-antigen complex result in?
inactivation of the parasite, making it susceptible to a phagocyte
or can stimulate a response that results in cell lysis
what do memory lymphocytes do?
- produce a secondary response when the antigen enters the body in the future
- this results in enhanced antibody production
which type of parasite has demonstrated the most success in evading the immune system
endoparasites
how do endoparasites evade the immune system?
they don’t stimulate an immune response, despite possessing foreign antigens, they mimic host antigens to avoid detection.
they are also capable of modifying the host immune response to reduce their chances of destruction
antigenic variation
some parasites show antigenic variation, which allows them to change between different antigens during the course of an infection
what does antigenic variation allow?
- parasites to evolve faster than the host immune system can respond to the new antigens
- re-infection of the same host with the new variant
what’s another method of evading immune surveillance?
by integrating the virus’ genome into host genomes existing in an inactive state called latency
- the virus becomes active again when favourable conditions arise
what is epidemology?
the study of the outbreak and spread of infectious diesease
what do vaccinations do?
- reduce the spread of disease, as they contain antigens that can elicit an immune response
what is the herd immunity threshold?
the density of resistant hosts in the population required to prevent an epidemic
challenges to overcome in the successful treatment and control of parasites?
- some parasites are difficult to culture on the lab, making it difficult to design vaccines
- rapid antigenic variation
- the similarities between host and parasite metabolism make it difficult to find drug compounds which only target the parasite
