BIOLOGY SPECIATION

Adaptations Phenotypes that allow an organism to better survive in its environment.

Adaptive radiation The process of a single ancestral species evolving into a diverse array of descendant species, each adapted to a specific ecological niche. Also called divergent evolution.

Allele frequency The proportion of an allele for a specific gene in a gene pool.

Alleles Alternative forms of a gene. For example, black or chestnut coat colour in horses.

Allopatric speciation A type of speciation where geographic isolation disrupts gene flow between two populations of a species, resulting in evolution into different species.

Allopatric species Similar species that are reproductively isolated due to geographic separation.

Allopolyploid An organism that contains two or more sets of chromosomes from two or more different species.

Amphiploid (sterile hybrid) An amphiploid is formed by crossing two different species and is sterile. It undergoes nondisjunction in meiosis to become fertile, having two sets of homologous chromosomes and becoming an allopolyploid.

Analogous structures Traits in different and unrelated species that have similar functions but have evolved independently due to similar selection pressures. For example, wings in birds and insects.

Asexual reproduction A single parent copies itself to form a genetically identical offspring.

Autopolyploid Having more than two sets of chromosomes from a single species.

Biogeography The study of the geographical distribution of extinct and modern species.

Bottleneck effect The phenomenon in which a population is dramatically reduced in size but then rebounds. A consequence is the loss of alleles, reducing genetic diversity.

Behavioural adaptation A way of responding to the environment that is specific to a species of organisms and allows the organism to better survive in its environment.

Characteristics A feature of an organism, such as a trait or phenotype.

Clade A grouping or branch of a taxonomic tree that includes a common ancestor and all the descendants, both living and extinct, of that ancestor.

Cline A gradual change in the frequency of an allele or the average value of a phenotype across a geographical area.

Co-evolution Where two or more species affect each other's evolution by acting as selection pressures on each other. For example, tūī beak shape and harakeke flower shape.

Convergent evolution The evolution of similar phenotypes by species of different ancestral origins due to similar selection pressures. For example, penguins and fish both have torpedo shapes but have no genetic common ancestor.

Deme A sub-population within a larger population that is partly isolated from interbreeding with other sub-populations.

Directional selection A type of natural selection where individuals at one extreme of a phenotype distribution have higher survival and reproduction rates than the rest of the population.

Disruptive selection A type of natural selection where extreme phenotypes are favoured over average phenotypes, potentially leading to a population splitting into distinct groups.

Divergent evolution The process where two or more populations of a species are exposed to different selection pressures and evolve distinct phenotypes over time, becoming increasingly different. This process can lead to speciation.

Ecological equivalents Species that inhabit the same niche but in different geographical areas. They will compete if put in the same environment. For example, katipō and white-tailed spiders.

Endemic Species found naturally occurring in only a particular location. For example, kiwi in New Zealand.

Evolution Gradual change in the genetic code of populations over a long period. May result in the formation of new species.

Extant Species with members still living.

Extinct Species with no living members.

Fertilisation The combining of sperm and egg to form a single-celled zygote.

Fitness The ability of an individual to successfully reproduce and pass on their genetics.

Fitness Cost The loss of non-target alleles from a gene pool during the process of natural selection.

Foetus Unborn developing offspring.

Founder effect A new colony is started by a few members of an original population in a new location. Allele frequencies of the new population are not representative of the original population and rare alleles may become fixed or lost.

Gametes Sex cells containing half the chromosomes of the parent.

Gause's Competitive Exclusion Principle No two species can occupy the same ecological niche. One will either die or change niches.

Gene flow Occurs when individuals migrate between different populations and cause changes in the genetic composition of the resulting populations. This includes immigration into and emigration out of the population.

Gene pool The complete set of genes and their various alleles in a breeding population.

Genome The complete genetic composition of an individual or species.

Genotype An individual's allele combination for a particular phenotype.

Genetic diversity The variation of alleles and heritable traits in a population.

Genetic drift The random change in a small population's allele frequency from one generation to the next due to chance. Alleles may then become fixed or lost.

Genetic variation/diversity The variation of alleles and heritable traits in a population of organisms.

Geographical isolation Where any physical feature of the Earth prevents gene flow. For example, mountains, rivers or glaciers.

Gradualism The evolution of new species by gradual accumulation of small genetic changes over long periods of time.

Homologous structures Features with a similar ancestral origin but different functions due to differing selection pressures. For example, the arm of a human and the wing of a bat.

Hybrid An individual formed through crossing two different species where the offspring may be sterile or show hybrid vigour.

Hybrid breakdown A reproductive isolating mechanism where there is a decline in the fitness or viability of hybrid offspring in later generations, F2 and beyond, compared to the first generation, F1, hybrids.

Hybrid inviability A reproductive isolating mechanism where hybrids fail to develop into healthy, mature adults, either in utero or after birth.

Hybrid sterility A reproductive isolating mechanism where the hybrid reaches maturity but cannot produce viable offspring. For example, a mule.

Introduced species A species moved by humans from a native ecosystem to another ecosystem.

Reproductive isolating mechanism An inherited feature that tends to prevent species from interbreeding with other species.

Mitochondrial DNA Circular DNA found in the mitochondria. Passed down through the maternal line and does not undergo crossing-over. It can be used to compare the relatedness of species.

Mutation A permanent change in DNA or genetic material. It is only important to evolution if it is heritable.

Natural selection The process by which selection pressures act on members of a population and individuals with heritable traits better suited to their environment survive and reproduce more successfully than others. This leads to an increase in advantageous alleles over multiple generations.

Niche The habitat and ecological role of an organism.

Non-Random Mating Occurs when individuals with specific phenotypes are mated preferentially.

Organism A living thing.

Ovulation Cyclical production of one or more ova, or eggs.

Phenotype How a gene is expressed as a protein, characteristic or trait.

Phylogenetic tree A diagram that describes the evolutionary relationships among various species.

Polyploidy Where an organism has three or more sets of homologous chromosomes.

Population The number of organisms of the same species living in a defined area.

Prezygotic isolating mechanism A reproductive isolating mechanism that keeps species separate by acting before fertilisation occurs. For example, courtship differences.

Post-zygotic mechanism A reproductive isolating mechanism that keeps species separated by acting after fertilisation. For example, an infertile hybrid.

Punctuated equilibrium Long periods of little change in a species' evolution followed by short bursts of speciation due to rapid changes in the environment or selection pressures.

Reproduction The production of offspring, allowing genes to be passed on to subsequent generations.

Reproductive Isolating Mechanism An evolutionary mechanism that prevents different species from interbreeding and producing viable, fertile offspring. It may be temporal, behavioural, mechanical or gametic.

Ring species A series of geographically distributed populations that exhibit a gradual change in phenotypes away from the oldest population. Neighbouring populations can interbreed, but the extreme ends of the series cannot interbreed.

Selection pressures Environmental factors that affect the fitness and survival of individuals within a population and change allele frequencies. For example, resource scarcity, predation or environmental pressures.

Sexual reproduction The combining of genetic information from two parents, resulting in genetically unique offspring.

Sexual selection Some individuals are more successful at attracting mates and therefore produce more offspring. For example, peacocks with larger tails get more mating opportunities.

Speciation The process by which one species gives rise to two or more new species.

Species A group of organisms that can breed with each other and produce fertile offspring.

Stabilising selection A type of natural selection where individuals with average or moderate phenotypes are more fit than those with extreme phenotypes, leading to a narrowing of phenotypic variation.

Morphological isolating barrier When reproductive structures between related species are incompatible.

Sympatric speciation The process by which new species evolve from a single ancestral species by reproductive isolation while both still inhabit the same geographical region.

Sympatric species Similar species living in the same geographical area but are reproductively isolated. For example, gazelle and springbok on savannah.

Taxonomy The branch of science involved in naming, describing and classifying organisms.

Temporal isolating mechanism When groups are reproductively isolated because they are active at different times of the day or seasons.

Trait A feature of an organism, such as a protein, phenotype or characteristic.

Vestigial structure An anatomical feature that has no apparent function but resembles a structure of a presumed ancestor. For example, the kiwi wing.

Y-chromosome A nuclear chromosome passed down through the male line. It does not undergo crossing-over and can be used to compare the relatedness of extant and extinct species.

Zygote The fertilised egg or ovum.