Defining a species
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The document discusses the distinct species classification of the black stilt (Himantopus novaezelandiae) and the pied stilt (Himantopus himantopus), believed to have originated from separate colonizations in New Zealand with significant differences in plumage and morphology. It outlines various definitions of species, including the biological, morphological, recognition, phylogenetic, and concordance species concepts, highlighting the challenges of classification due to hybridization and genetic divergence. Overall, it emphasizes that the black and pied stilts are generally accepted as two distinct species, with the phylogenetic and concordance concepts being most relevant.
Defining a species
- 1. Defining a species What defines two organisms as being two different species? A case study with black and pied stilts
- 2. Speciation of the black and pied stilts • Generally excepted that they are two distinct species • Black stilt - Himantopus novaezelandiae • Pied stilt – Himantopus himantopus http://basicbiology.net/gallery/animals/pied_stilt.jpghttp://www.mattjoneswildlifeimages.com/page40.htm
- 3. Background to their relationship • Believed to have originated from two separate colonisations from Australia pied stilts to New Zealand. • Black stilts - potentially 1 million years ago • Pied stilts – possilby as recent as 150 years ago • Differences – plumage (black vs black & white) – other morphological difference – behavioural differences.
- 4. Background to their relationship • IUCN red list status Black stilt – critically endangered Pied stilt – least concern • Black stilts mate for life • Due to a very low population size - between 58-78 adult birds - will sometimes mate and hybridize with pied stilts.
- 5. Definitions of species • Biological species concept – species defined as populations of individuals that can produce viable offspring. – Probably the most well-known definition of a species – Hybridisation? • Morphological species concept – classified as the same species if organisms fit into the same morphological criteria. – Classical definition going back to the days on Carl Linnaeus – the father of taxonomy
- 6. Definitions continued • Recognition species concept – species defined as organisms that recognise each other as potential mates. • Not well accepted due to hybridisation and phylogenetic • Phylogenetic species concept – species are a group of organisms that share a single common ancestor. • Concordance species concept – takes into account a range of diagnostic markers such as breeding, morphology, DNA markers. • Plus many more...
- 7. How do pied and black stilts fit in? • Morphological species concept: • The two species are similar in many ways. • Main difference in is the colour of plumage. • Black stilts - larger body size, longer beaks, shorter legs, longer wings. • But all are expected adaptations to a colder climate.
- 8. How do pied and black stilts fit in? • Phylogenetic species concept: • Pied stilt and black stilt have been shown to have two different haplotypes for mtDNA • i.e. two genetically different species • Mitochondrial genome <0.001% of the nuclear genome • Potentially not very representative • Concordance species concept: • The combination of morphological, mtDNA, isozyme and plumage markers indicate two distinct species
- 9. What does this all mean? • Firstly, as I said at the start – it is generally accepted that they are two distinct species. • It seems the phylogenetic and concordance species concepts hold more weight than other species definitions. • Illustrates how difficult it can be to classify a species. • Scratches the surface of the difficulties encountered by taxonomists.