Editing Neoteny (section)

== In other species ==

[[File:Axolotl ganz.jpg|thumb|alt=A green salamander with four short legs|The axolotl is a neotenous [[salamander]], often retaining gills throughout its life.]]

Neoteny has been observed in many other species. It is important to note the difference between partial and full neoteny when looking at other species, to distinguish between juvenile traits which are advantageous in the short term and traits which are beneficial throughout the organism's life; this might provide insight into the cause of neoteny in a species. Partial neoteny is the retention of the larval form beyond the usual age of maturation, with possible sexual development (progenesis) and eventual maturation into the adult form; this is seen in the frog ''[[Lithobates clamitans]]''. Full neoteny is seen in ''[[Axolotl|Ambystoma mexicanum]]'' and some populations of ''[[Tiger salamander|Ambystoma tigrinum]]'', which remain in larval form throughout their lives.<ref name="Swingle, W. 1922 pp.397-421">{{cite journal |last=Swingle |first=W. |year=1922 |title=Experiments on the metamorphosis of neotenous amphibians |url=https://zenodo.org/record/1426890|journal=Journal of Experimental Zoology |volume=36 |issue=4 |pages=397–421 |doi=10.1002/jez.1400360402 |bibcode=1922JEZ....36..397S }}</ref><ref>{{cite web |url=http://amphibiaweb.org/species/3850 |title=Ambystoma tigrinum |publisher=Amphibia Web}}</ref> ''Lithobates clamitans'' is partially neotenous; it delays maturation during the winter as fewer resources are available; it can find resources more easily in its larval form. This encompasses both of the main causes of neoteny; the energy required to survive in the winter as a newly-formed adult is too great, so the organism exhibits neotenous characteristics until it can better survive as an adult. ''Ambystoma tigrinum'' retains its neoteny for a similar reason; however, the retention is permanent due to the lack of available resources throughout its lifetime. This is another example of an environmental cause of neoteny. Several avian species, such as the [[manakin]]s ''[[Long-tailed manakin|Chiroxiphia linearis]]'' and ''[[Blue manakin|Chiroxiphia caudata]]'', exhibit partial neoteny. The males of both species retain juvenile plumage into adulthood, losing it when they are fully mature.<ref>{{cite journal |last=Foster |first=M. |year=1987 |title=Delayed maturation, neoteny, and social system differences in two manakins of genus ''Chiroxyphia'' |url=https://zenodo.org/record/1235115|journal=Evolution |volume=41 |issue=3|pages=547–558 |doi=10.2307/2409256|pmid=28563802 |jstor=2409256 }}</ref> 

Neoteny is commonly seen in flightless insects, such as the females of the order [[Strepsiptera]]. Flightlessness in insects has evolved separately a number of times; factors which may have contributed to the separate evolution of flightlessness are high altitude, geographic isolation (islands), and low temperatures.<ref name="Barbosa, P. 1989">{{cite journal |last1=Barbosa |first1=P. |display-authors=etal |year=1989 |title=Life-history traits of forest-inhabiting flightless Lepidoptera |journal=American Midland Naturalist |volume=122 |issue=2|pages=262–274 |jstor=2425912 |doi=10.2307/2425912}}</ref> Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates. The [[Larviform female|females]] of certain insect groups become sexually mature without metamorphosis, and some do not develop wings. Flightlessness in some female insects has been linked to higher [[fecundity]].<ref name="Barbosa, P. 1989" /> [[Aphid]]s are an example of insects which may never develop wings, depending on their environment. If resources are abundant on a host plant, there is no need to grow wings and disperse. If resources become diminished, their offspring may develop wings to disperse to other host plants.<ref name="Harrison1980" />

Two environments which favor neoteny are high altitudes and cool temperatures, because neotenous individuals have more fitness than individuals which metamorphose into an adult form. The energy required for metamorphosis detracts from individual fitness, and neotenous individuals can utilize available resources more easily.<ref name="Snyder, R. 1956">{{cite journal |last=Snyder |first=R. |year=1956 |title=Comparative Features of the Life Histories of ''Ambystoma gracile'' (Baird) from Populations at Low and High Altitudes |journal=Copeia |volume=1956 |issue=1|pages=41–50 |jstor=1439242 |doi=10.2307/1439242}}</ref> This trend is seen in a comparison of salamander species at lower and higher altitudes; in a cool, high-altitude environment, neotenous individuals survive more and are more fecund than those which metamorphose into adult form.<ref name="Snyder, R. 1956" /> Insects in cooler environments tend to exhibit neoteny in flight because wings have a high surface area and lose heat quickly; it is disadvantageous for insects to metamorphose into adults.<ref name="Barbosa, P. 1989" />

Many species of salamander, and amphibians in general, exhibit environmental neoteny. [[Axolotl]] and [[olm]] are [[perennibranchiate]] salamander species which retain their juvenile aquatic form throughout adulthood, examples of full neoteny. Gills are a common juvenile characteristic in amphibians which are kept after maturation; examples are the tiger salamander and rough-skinned newt, both of which retain gills into adulthood.<ref name="Swingle, W. 1922 pp.397-421" />

[[Bonobo]]s share many physical characteristics with humans, including neotenous skulls.<ref name="ReferenceA">{{cite journal |last1=Shea |first1=B. T. |year=1983 |title=Paedomorphosis and Neoteny in the Pygmy Chimpanzee |journal=Science |volume=222 |issue=4623 |pages=521–522 |jstor=1691380 |doi=10.1126/science.6623093 |pmid=6623093 |bibcode=1983Sci...222..521S }}</ref> The shape of their skull does not change into adulthood (only increasing in size), due to [[sexual dimorphism]] and an evolutionary change in the timing of development.<ref name="ReferenceA" /> 

In some groups, such as the insect families [[Gerridae]], [[Delphacidae]] and [[Ground beetle|Carabidae]], energy costs result in neoteny; many species in these families have [[brachyptery|small]], neotenous wings or [[aptery|none at all]].<ref name="Harrison1980">{{cite journal |last1=Harrison |first1=R. |year=1980 |title=Dispersal polymorphisms in insects |journal=Annual Review of Ecology and Systematics |volume=11 |issue=1 |pages=95–118 |jstor=2096904 |doi=10.1146/annurev.es.11.110180.000523|bibcode=1980AnRES..11...95H }}</ref> Some cricket species shed their wings in adulthood;<ref name="jstor.org">{{cite journal |last1=Harrison |first1=R. |year=1980 |title=Dispersal Polymorphisms in Insects |journal=Annual Review of Ecology and Systematics |volume=11 |issue=1 |pages=95–118 |jstor=2096904 |doi=10.1146/annurev.es.11.110180.000523|bibcode=1980AnRES..11...95H }}</ref> in the genus ''[[Ozopemon]]'', males (thought to be the first example of neoteny in [[beetle]]s) are significantly smaller than females due to [[inbreeding]].<ref>{{cite journal |last1=Jordal |first1=B. H. |last2=Beaver |first2=R. A. |last3=Normark |first3=B. B. |last4=Farrell |first4=B. D. |year=2002 |title=Extraordinary sex ratios and the evolution of male neoteny in sib-mating ''Ozopemon'' beetles |journal=Biological Journal of the Linnean Society |volume=75 |issue=3|pages=353–360 |doi=10.1046/j.1095-8312.2002.00025.x |doi-access=free }}</ref> In the termite ''[[Kalotermes flavicollis]]'', neoteny is seen in molting females.<ref name="dx.doi.org">{{cite journal |last1=Soltani-Mazouni |first1=N. |last2=Bordereau |first2=C. |year=1987 |title=Changes in the cuticle, ovaries and colleterial glands during the pseudergate and neotenic molt in ''Kalotermes flavicollis'' (FABR.) (Isoptera : Kalotermitidae) |journal=International Journal of Insect Morphology and Embryology |volume=16 |issue=3–4|pages=221–225 |doi=10.1016/0020-7322(87)90022-5 }}</ref>

In other species, such as the [[northwestern salamander]] (''Ambystoma gracile''), environmental conditions{{snd}}high altitude, in this case{{snd}}cause neoteny.<ref>{{cite journal |last1=Eagleson |first1=G. |last2=McKeown |first2=B. |year=1978 |title=Changes in thyroid activity of ''Ambystoma gracile'' (Baird) during different larval, transforming, and postmetamorphic phases |journal=Canadian Journal of Zoology |volume=56 |issue=6|pages=1377–1381 |doi= 10.1139/z78-190|bibcode=1978CaJZ...56.1377E }}</ref> Neoteny is also found in a few species of the crustacean family [[Asellota#Classification|Ischnomesidae]], which live in deep ocean water.<ref>{{cite journal |last1=Brokeland |first1=W. |last2=Brandt |first2=A. |year=2004 |title=Two new species of Ischnomesidae (Crustacea: Isopoda) from the Southern Ocean displaying neoteny |journal=Deep-Sea Research Part II |volume=51 |issue=14–16|pages=1769–1785 |doi=10.1016/j.dsr2.2004.06.034 |bibcode=2004DSRII..51.1769B }}</ref>

Neoteny is an ancient, pervasive phenomenon. In [[urodeles]], many extant taxa are neotenic,<ref name="Wiens et al. 2005">{{cite journal |last1=Wiens |first1=John J. |last2=Bonett |first2=Ronald M. |last3=Chippindale |first3=Paul T. |last4=Anderson |first4=Frank (Andy) |title=Ontogeny Discombobulates Phylogeny: Paedomorphosis and Higher-Level Salamander Relationships |journal=Systematic Biology |date=1 February 2005 |volume=54 |issue=1 |pages=91–110 |doi=10.1080/10635150590906037 |pmid=15805013 |url=https://doi.org/10.1080/10635150590906037}}</ref> and both morphological <ref name="Evans et al. 1988">{{cite journal |last1=Evans |first1=Susan E. |last2=Milner |first2=Andrew R. |last3=Mussett |first3=Frances |title=The earliest known Salamanders (Amphibia, Caudata):A record from the Middle Jurassic of England |journal=Geobios |date=1 January 1988 |volume=21 |issue=5 |pages=539–552 |doi=10.1016/S0016-6995(88)80069-X |bibcode=1988Geobi..21..539E |url=https://doi.org/10.1016/S0016-6995(88)80069-X |issn=0016-6995}}</ref> and histological data suggest that the Middle [[Jurassic]] taxon ''[[Marmorerpeton]]'' was neotenic.<ref name="de Buffrénil et al. 2015">{{cite journal |last1=de Buffrénil |first1=Vivian |last2=Canoville |first2=Aurore |last3=Evans |first3=Susan E. |last4=Laurin |first4=Michel |title=Histological study of karaurids, the oldest known (stem) urodeles |journal=Historical Biology |date=2 January 2015 |volume=27 |issue=1 |pages=109–114 |doi=10.1080/08912963.2013.869800 |bibcode=2015HBio...27..109D |url=http://dx.doi.org/10.1080/08912963.2013.869800}}</ref>