Species and taxonomy

courtship

• Organisms belong to the same species if they interbreed in their natural habitat to produce fertile offspring

• The process of successful interbreeding or mating is preceded by some form of courtship behaviour

  • Courtship in animals is a behaviour that eventually results in mating and reproduction

  • It can be a very simple process that involves a small number of visual, chemical or auditory stimuli

  • It can also be a highly complex sequence of acts by two or more individuals, who are using several modes of communication

    • Many birds of paradise have intricate and impressive courtship rituals

• Courtship can play a major role in species recognition

courtship example - Drosophila (fruit fly)

• Fruit fly species in the genus Drosophila are hard to distinguish by appearance, but each has a unique, genetically controlled courtship ritual

• Males perform species-specific "dances" involving wing vibrations, body movements, and licking

• Females only respond to the correct sequence and signal disinterest through specific behaviours that the male recognises

what is phylogenetics

• the study of how organisms are evolutionarily related — often shown using a phylogenetic tree

• The phylogenetic system of taxonomy arranges organisms into groups based on their evolutionary origins and relationships

what is under the phylogenetic classification system

• there is a hierarchy of groups, in which smaller groups are placed within larger groups

• there is no overlap between groups

• each group is called a taxon (plural taxa)

how phylogenetic systems work

• Phylogenetic systems use DNA, RNA, and protein similarities to identify evolutionary links

• For example, two species with more similar DNA sequences are assumed to have a more recent common ancestor

why is phylogenetics useful

• Grouping organisms in this way is helpful for several reasons

  • Scientists can communicate clearly about different species

  • Knowledge that relates to one species can often be partially applied to other, closely related species, e.g. if one species in a taxon has medicinal properties then it is likely that other species will too

  • It allows scientists to gain an accurate count of the number of species, which is useful for conservation purposes

how does phylogenetics become more accurate

• Biological classification changes as more molecular analysis is completed; this means that phylogenetic classification is becoming more accurate over time

  • E.g. the five kingdoms classification system (animals, plants, fungi, protists, bacteria) has now been incorporated into the three domains system (below)

hierarchy of the taxa

• The hierarchical classification system of organisms in biology is used to organise and group similar organisms together so that they can be more easily understood

  • A hierarchical system is one in which larger groups contain smaller groups with no overlap between groups

• All taxonomic ranks or 'taxa' make up a 'taxonomic hierarchy'

what is the hierarchy of the taxa made of

• One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species

• Species is the lowest taxonomic rank in the system and domains are the highest taxonomic rank in the system

  • Similar species can be grouped in a genus

  • Similar genera can be grouped in a family

  • Similar families can be grouped into an order

  • Similar orders can be grouped into a class

  • Similar classes can be grouped into a phylum

  • Similar phyla can be grouped into a kingdom

  • Similar kingdoms can be grouped into a domain

binomials

• Binomials are the scientific name of a species

  • A species is a group of organisms that can reproduce to produce fertile offspring

• It consists of the organism’s genus and species name in modern Latin

• For example, the binomial for humans is Homo sapiens and the binomial for dogs is Canis familiaris

• Binomials are extremely useful for scientists as they allow for species to be universally identified - the binomial for a species is the same across the entire globe

evolutionary relationships

• In the past, scientists encountered many difficulties when trying to determine the evolutionary relationships of species

• Using the physical features of species (such as colour/shape/size) has many limitations and can often lead to the wrong classification of species

• Advances in genome sequencing and immunology have allowed scientists to further investigate the evolutionary relationships between species

genome sequencing

• Sequencing technology can determine the order of DNA bases, mRNA bases and amino acids within an organism's genome

• This technology is especially useful for comparison with an extinct species (using ancient DNA) or when distinguishing between species that are very physically similar

• Scientists will choose specific proteins or sections of the genome for comparison between organisms

  • Looking at multiple proteins or multiple regions of the genome will allow for a more accurate estimate of evolutionary relatedness

  • Note that the protein used needs to be present in a wide range of organisms and show sufficient variation between species

    • Cytochrome c is often used as it is an integral protein to respiration (in the electron transport chain) which is used by all eukaryotic organisms

• For all types of sequence data, it can be said that the more similar the sequences, the more closely related the species are

• Two groups of organisms with very similar sequences will have separated into separate species more recently than two groups with less similarity in their sequences

• Species that have been separated for longer have had a greater amount of time to accumulate mutations and changes to their DNA,mRNA and amino acid sequences

• Sequence analysis and comparison can be used to create family trees that show the evolutionary relationships between species

immunology

• The proteins of organisms can also be compared using immunological techniques

• The protein albumin is found in many species and is commonly used for these experiments

immunology method

• Pure albumin is extracted from various species and injected into separate rabbits

• Each rabbit produces antibodies specific to that albumin

• These antibodies are then mixed with different albumin samples, and the resulting precipitate (antigen–antibody complexes) is weighed

immunology results and interpretations

• The heavier the precipitate, the greater the similarity between the antibody and albumin

• For example, antibodies to human albumin form more precipitate with chimpanzee albumin than with rat albumin, reflecting closer evolutionary relatedness