4.4 Taxonomy - a special challenge for data integr… 4.4.1. What is a species? (1/2)
The concept of a species is a multifaceted and often controversial matter, as illustrated by Charles Darwin's observation in 1859 that the distinction between species and varieties can be somewhat vague and arbitrary [1]. Main concepts on defining species include:
- Biological Species Concept
This approach defines a species as a group of natural populations that either interbreed or have the potential to do so [2], while being reproductively isolated from other such groups. It suits sexually reproducing organisms but is insufficient in cases like asexual reproduction, fossils, hybridization, species complexes. - Morphological Species Concept
Species are identified based on similar physical traits [3]. While intuitive, this method can be subjective due to varying trait expressions, phenotypic plasticity, and cryptic species with nearly identical appearances. - Phylogenetic Species Concept
It defines a species as the smallest aggregation of populations or lineages distinguishable by unique genetic characteristics [4]. It is well-suited for asexual species but might lead to "taxonomic inflation" and conservation challenges. - DNA Barcoding
DNA barcoding relies on genetic sequences, using markers like cytochrome c oxidase for animals, 16S rRNA for bacteria, and internal transcribed spacer (ITS) 28S rRNA for fungi. It's a powerful tool for species identification, including eDNA [5]. However, it relies on reference sequences and can suffer from incomplete databases and misidentified species.
Other noteworthy concepts include the evolutionarily significant unit (conservation purposes), recognition and cohesion species (behavioural isolation), chronospecies in paleobiology, and ecological species occupying the same niche.
These concepts illuminate the diverse ways species are defined and have significant implications in various fields of biology and conservation.
[1] Darwin, C. (1859). On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. John Murray, London.
[2] Mayr, E. (1942). Systematics and the origin of species, from the viewpoint of a zoologist. Columbia University Press, New York.
[3] Linnaeus, C. (1753). Species plantarum. 1st edition. Laurentius Salvius, Stockholm, Sweden.
[4] Nixon, K.C. & Wheeler, Q.D. (1990). An amplification of the phylogenetic species concept. Cladistics, 6, 211–223. https://www.doi.org/10.1111/j.1096-0031.1990.tb00541.x
[5] Hebert, P.D.N., Cywinska, A., Ball, S.L. & DeWaard, J.R. (2003). Biological identifications through DNA barcodes. Proceedings of the Royal Society B-Biological Sciences, 270. https://www.doi.org/10.1098/rspb.2002.2218