Phenotypic disparity

The phenotypic disparity, also known as morphological diversity, morphological variety, morphological disparity, morphodisparity or simply disparity, refers to the phenotypic differentiation within groups. It was originally proposed in paleontology, and has also been introduced into the study of extant organisms. Some biologists view phenotypic disparity as an important aspect of biodiversity, while others believe that they are two different concepts.

## History[edit]

Biologists' concern with phenotypic disparity appeared before the concept, with Douglas Erwin arguing that it had been central to the organismal biology since Georges Cuvier, who used it as the criteria for animal classification.[1]

This concept was first proposed in the 1980s, utilized to explore the evolutionary patterns of variation in anatomy, function, and ecology.[2] It arose from the efforts by paleobiologists to define the evolutionary origins of the body plans of animals and by comparative developmental biologists to offer causal explanations for the emergence of these body plans.[2] In 1989, Stephen Jay Gould published Wonderful Life, in which he used the fossils from the Middle Cambrian Burgess Shale to contend that the ancient arthropods at this site has a greater phenotypic disparity than all living arthropods.[1] It has been introduced into the study of extant organisms.[3][4]

Initially, phenotypic disparity was considered a sub-concept of biodiversity, referred to as "morphological diversity"[5], subsequently it acquired its own name "disparity", also known as "morphological diversity",[5] "phenotypic disparity", "morphological disparity", "morphological variety" or "morphodisparity"[3]

## Summary[edit]

In the narrower sense, the currently widely accepted concept of biodiversity meant only the taxonomic diversity, or the species richness. However, some groups have a large number of species, while all of them are very similar in morphology; other groups have very little species, while they are highly heterogeneous. Therefore, focusing only on the species richness is one-sided.[6]

The disparity is defined as the phenotypic differentiation within groups.[4][7] "Groups" usually refers to the taxonomic groups, including species or higher taxa.[7] Some biologists believe that the concept of disparity should also be applied to other groups, including sexes, ages, biomorphs and the castes of social insects.[8]

Disparity has changed at different rates and independently of species richness in the evolutionary history. There are two main patterns in how disparity develops over time. Some groups have developed high disparity early on in their evolution (called "early-disparity"), while others take longer to reach their maximum disparity (called "later-disparity"). The early-disparity boom may happen because species quickly explore new habitats or take advantage of new ecological niches. On the other hand, later-disparity groups may have develop new morphological forms slowly, resulting in a delay in reaching their maximum disparity.[5]

Species richness does not necessarily correlate with disparity; a small group can have high or low disparity, and so can a large group. Birds, with more than 10,000 species, have greater species richness than mammals, which have approximately 5,600 species. However, birds are relatively more uniform in morphology, reproductive biology, and developmental biology. Even including some rare groups, such as penguins and ratites (ostriches and their relatives), the range of body plans in birds is much narrower than in mammals, which include apes, whales, bats, giraffes, moles, the platypus, marsupials and armadillos.[6]

## Measuring disparity[edit]

The morphospace of the plant kingdom. Taxa with higher disparity occupy larger areas.[4]

Initially, there was no consensus on how to measure disparity.[9] Currently, disparity is usually quantified using the morphospace, which is a multidimensional space covering the morphological variation within a taxon.[10] Due to the use of different mathematical tools, morphospaces may have different geometric structures and mathematical meanings.[11]

The initial step involves selecting multiple phenotypic descriptors (characteristics described in appropriate ways) that vary among different taxa.[7] All phenotypic characteristics can be used to evaluate the disparity of a group, but the morphological characteristics are mostly used, because they are more accessible than others.[6] Secondly, use the selected descriptors to construct a morphospace. Then, use standard statistical dispersion indicators, such as total range or total variance, to describe the dispersion and distribution of groups in morphospace. The morphospace is a multidimensional space, which is almost impossible to visualize, so the dimensionality of the morphospace should be reduced using principal component analysis, principal coordinate analysis, or other mathematical methods. Therefore, it could be projected onto a two-dimensional space to visualize it.[7]

## References[edit]

1. ^ a b Erwin, Douglas H. (2007). "Disparity: Morphological pattern and developmental context". Palaeontology. 50 (1): 57–73. doi:10.1111/j.1475-4983.2006.00614.x. ISSN 0031-0239.
2. ^ a b Guillerme, Thomas; Cooper, Natalie; Brusatte, Stephen L.; Davis, Katie E.; Jackson, Andrew L.; Gerber, Sylvain; Goswami, Anjali; Healy, Kevin; Hopkins, Melanie J.; Jones, Marc E. H.; Lloyd, Graeme T.; O'Reilly, Joseph E.; Pate, Abi; Puttick, Mark N.; Rayfield, Emily J. (2020). "Disparities in the analysis of morphological disparity". Biology Letters. 16 (7): 20200199. doi:10.1098/rsbl.2020.0199. ISSN 1744-9561. PMC 7423048. PMID 32603646.
3. ^ a b Oyston, Jack W.; Hughes, Martin; Gerber, Sylvain; Wills, Matthew A. (2016). "Why should we investigate the morphological disparity of plant clades?". Annals of Botany. 117 (5): 859–879. doi:10.1093/aob/mcv135. ISSN 0305-7364. PMC 4845799. PMID 26658292.
4. ^ a b c Clark, James W.; Hetherington, Alexander J.; Morris, Jennifer L.; Pressel, Silvia; Duckett, Jeffrey G.; Puttick, Mark N.; Schneider, Harald; Kenrick, Paul; Wellman, Charles H.; Donoghue, Philip C. J. (2023). "Evolution of phenotypic disparity in the plant kingdom". Nature Plants. 9 (10): 1618–1626. doi:10.1038/s41477-023-01513-x. ISSN 2055-0278. PMID 37666963.
5. ^ a b c López-Martínez, Andrea M.; Magallón, Susana; von Balthazar, Maria; Schönenberger, Jürg; Sauquet, Hervé; Chartier, Marion (2024). "Angiosperm flowers reached their highest morphological diversity early in their evolutionary history". New Phytologist. 241 (3): 1348–1360. doi:10.1111/nph.19389. ISSN 0028-646X. PMC 10952840. PMID 38029781.
6. ^ a b c Minelli, Alessandro (2019). "Biodiversity, disparity and evolvability". In Casetta, Elena; da Silva, Jorge Marques; Vecchi, Davide (eds.). From assessing to conserving biodiversity: Conceptual and practical challenges. Switzerland: Springer Open. pp. 233–246. ISBN 978-3-030-10990-5.
7. ^ a b c d Hopkins, Melanie J.; Gerber, Sylvain (2017), Nuno de la Rosa, Laura; Müller, Gerd (eds.), "Morphological Disparity", Evolutionary Developmental Biology: A Reference Guide, Cham: Springer International Publishing, pp. 1–12, doi:10.1007/978-3-319-33038-9_132-1, ISBN 978-3-319-33038-9, retrieved 2024-05-08
8. ^ Pavlinov, Igor (2008). "Morphological disparity: general conceptions and basic characteristics". Archive of Zoological Museum of Moscow University (in Russian). 48: 343–388. ISSN 0134-8647.
9. ^ Wills, Matthew A.; Briggs, Derek E. G.; Fortey, Richard A. (1994). "Disparity as an evolutionary index: a comparison of Cambrian and Recent arthropods". Paleobiology. 20 (2): 93–130. Bibcode:1994Pbio...20...93W. doi:10.1017/S009483730001263X. ISSN 0094-8373.
10. ^ McClain, Craig R.; Johnson, Nicholas A.; Rex, Michael A. (2004). "Morphological disparity as a biodiversity metric in lower bathyal and abyssal gastropod assemblages". Evolution. 58 (2): 338–348.
11. ^ Gerber, Sylvain (2017). "The geometry of morphospaces: lessons from the classic R aup shell coiling model". Biological Reviews. 92 (2): 1142–1155. doi:10.1111/brv.12276. ISSN 1464-7931.