墨西哥麗脂鯉：修订间差异

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{{In use}}
{{Taxobox
{{redirect|Blind cave fish|cavefish in general|cavefish}}
| status = NE
{{Speciesbox
| status_system = IUCN3.1
| name = Mexican tetra
| image = Astyanax mexicanus.JPG
| image = Mexican Tetra (Astyanax mexicanus) (2687270083).jpg
| regnum = [[動物界]] Animalia
| image2 = Astyanax mexicanus 01.jpg
| phylum = [[脊索動物門]] Chordata
| image2_caption = Mexican tetra, normal form (above) and blind cave form (below)
| classis = [[輻鰭魚綱]] Actinopterygii
| status = LC
| ordo = [[脂鯉目]] Characiformes
| status_system = IUCN3.1
| subordo = [[脂鲤亞目]] Characoidei
| status_ref = <ref name=IUCN>{{cite journal | author = NatureServe | title = ''Astyanax mexicanus'' | journal = <!-- [[IUCN Red List of Threatened Species]] -->[[國際自然保護聯盟瀕危物種紅色名錄]] | volume= 2013 | page = e.T62191A3109229 | year = 2013 | doi = 10.2305/IUCN.UK.2013-1.RLTS.T62191A3109229.en }}</ref>
| familia = [[脂鯉科]] Characidae
| genus = [[麗脂鯉屬]] ''Astyanax''
| taxon = Astyanax mexicanus
| authority = ({{tsl|en|Filippo de' Filippi|}}, 1853)
| species = '''墨西哥麗脂鯉 ''A. mexicanus'''''
| range_map = PeixecegoMAPA.gif
| binomial = ''Astyanax mexicanus''
| range_map_caption = Approximate range in red
| binomial_authority = [[De Filippi]], 1853
| synonyms_ref = <ref>http://www.fishbase.se/Nomenclature/SynonymsList.php?ID=2740&SynCode=23916&GenusName=Astyanax&SpeciesName=mexicanus</ref>
| synonyms = *''Tetragonopterus mexicanus''<br /><small>De Filippi, 1853</small>
| synonyms = {{Specieslist|Tetragonopterus mexicanus|De Filippi, 1853|Astyanax fasciatus mexicanus|(De Filippi, 1853)|Astyanax argentatus|Baird & Girard, 1854|Tetragonopterus brevimanus|Günther, 1864|Tetragonopterus petenensis|Günther, 1864|Tetragonopterus fulgens|Bocourt, 1868|Tetragonopterus nitidus|Bocourt, 1868|Tetragonopterus streetsii|Cope, 1872}}
*''Astyanax fasciatus mexicanus''<br /><small>De Filippi, 1853</small>
*''Astianax mexicanus''<br /><small>De Filippi, 1853</small>
*''Astyanax argentatus''<br /><small>Baird & Girard, 1854</small>
*''Tetragonopterus brevimanus''<br /><small>Günther, 1864</small>
*''Tetragonopterus petenensis''<br /><small>Günther, 1864</small>
}}
}}
'''墨西哥麗脂鯉'''，為[[輻鰭魚綱]][[脂鯉目]][[脂鯉亞目]][[脂鯉科]]的其中一個[[種]]，為熱帶淡水魚，分布於[[北美洲]][[格蘭特河]]、[[佩科斯河]]及[[墨西哥]]中部的淡水流域，體長可達12公分，棲息在沙石底質的溪流，以[[昆蟲]]、[[甲殼類]]及[[蠕蟲]]為食，生活習性不明，可作為觀賞魚。


'''墨西哥麗脂鯉'''（學名：''{{lang|la|Astyanax mexicanus}}''）為[[輻鰭魚綱]][[脂鯉目]][[脂鯉亞目]][[脂鯉科]]的其中一個[[物種]]，為[[熱帶]][[淡水]][[鱼]]{{r|FishBase|itis}}，也是[[麗脂鯉屬]]的[[模式種]]。本物種是[[新北界]][[生物地理分布区]]的[[特有種]]，分佈於[[北美洲]][[格蘭特河]]及{{tsl|en|Nueces River|}}的下游、[[德克萨斯州]]的[[佩科斯河]]及[[墨西哥]]東部與中部的淡水流域{{r|FishBase}}。
==参考文献==
{{refbegin}}
*{{FishBase_species|genus=Astyanax|species=mexicanus|year=2013|month=11}}
{{refend}}


成長後本物種的體長可達12公分, the Mexican tetra is of typical characin shape, with unremarkable, drab coloration{{r|FishBase}}。棲息在沙石底質的溪流，以[[昆蟲]]、[[甲殼類]]及[[蠕蟲]]為食，生活習性不明，可作為觀賞魚。
== 扩展阅读 ==

{{refbegin}}
Its {{tsl|en|Blind fish|}} cave form, however, is notable for having no eyes or pigment; it has a pinkish-white color to its body (resembling an <!-- [[Albinism in biology|albino]] -->[[白化症]]).<ref name=Keene2016>{{cite book | authors=Keene; Yoshizawa; and McGaugh | title=Biology and Evolution of the Mexican Cavefish | year=2016 | pages=68–69, 77–87 | isbn=978-0-12-802148-4}}</ref>
{{wikispecies-inline|Astyanax mexicanus|墨西哥麗脂鯉}}

{{refend}}
This fish, especially the blind variant, is reasonably popular among <!-- [[aquarist]] -->[[水族饲养]]s.<ref name=seriouslyfish>{{cite web | publisher=SeriouslyFish | title=Astyanax mexicanus | url=http://www.seriouslyfish.com/species/astyanax-mexicanus/ | accessdate=2 May 2017}}</ref>
{{魚類小作品}}

[[Category:觀賞魚]]
''A. mexicanus'' is a peaceful species that spends most of its time in midlevel water above the rocky and sandy bottoms of pools and backwaters of creeks and rivers of its native environment. Coming from a <!-- [[subtropical]] -->[[亚热带]] climate, it prefers water with 6.5&ndash;8 <!-- [[pH]] -->[[PH值]], a <!-- [[Hard water|hardness]] -->[[硬水]] of up to 30 {{tsl|en|dGH|}}, and a temperature range of {{convert|20|to|25|C|F}}. In the winter, some populations migrates to warmer waters. Its natural diet consists of <!-- [[crustacean]] -->[[甲殼亞門]]s, <!-- [[insect]] -->[[昆虫]]s, and <!-- [[annelid]] -->[[环节动物门]]s, although in captivity it is <!-- [[omnivorous]] -->[[雜食動物]].<ref name="fishbase"/><ref name=seriouslyfish/>
[[Category:麗脂鯉屬|mexicanus]]

The Mexican tetra has been treated as a subspecies of ''<!-- 页面不存在 -->[[Astayanax faciatus|A. fasciatus]]'', but this is not widely accepted.<ref name="fishbase" /> Additionally, the blind cave form is sometimes recognized as a separate species, ''<!-- [[Astyanax jordani|A. jordani]] -->[[盲鱼]]'', but this directly contradicts <!-- [[Phylogenetics|phylogenetic]] -->[[系统发生学]] evidence.<ref name=Keene2016/><ref name="gross12">{{cite journal|last=Gross|first=J.B.|title=The complex origin of Astyanax cavefish|journal=BMC Evolutionary Biology|date=June 2012|volume=12|pages=105|doi=10.1186/1471-2148-12-105|pmid=22747496|pmc=3464594}}</ref><ref name=Jeffrey2009>{{cite journal | last1 = Jeffery | first1 = W | year = 2009 | title = Regressive evolution in Astyanax cavefish | url = | journal = Annu. Rev. Genet. | volume = 43 | issue = | pages = 25–47 | doi=10.1146/annurev-genet-102108-134216| pmid = 19640230 | pmc = 3594788}}</ref><ref name=Bradic2012>{{cite journal | last1 = Bradic | first1 = M. | last2 = Beerli | first2 = P. | last3 = Garcia-de Leon | first3 = F. J. | last4 = Esquivel-Bobadilla | first4 = S. | last5 = Borowsky | first5 = R. L. | year = 2012 | title = Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus) | url = | journal = BMC Evol. Biol. | volume = 12 | issue = | page = 9 | doi=10.1186/1471-2148-12-9| pmid = 22269119 | pmc = 3282648 }}</ref><ref name=Dowling2002>{{cite journal | last1 = Dowling | first1 = T. E. | last2 = Martasian | first2 = D. P. | last3 = Jeffery | first3 = W. R. | year = 2002 | title = Evidence for multiple genetic forms with similar eyeless phenotypes in the blind cavefish, Astyanax mexicanus | url = | journal = Mol. Biol. Evol. | volume = 19 | issue = 4| pages = 446–455 | doi=10.1093/oxfordjournals.molbev.a004100| pmid = 11919286 }}</ref><ref name=Strecker2004>{{cite journal | last1 = Strecker | first1 = U. | last2 = Faúndez | first2 = V. H. | last3 = Wilkens | first3 = H. | year = 2004 | title = Phylogeography of surface and cave Astyanax (Teleostei) from Central and North America based on cytochrome b sequence data | url = | journal = Mol. Phylogenet. Evol. | volume = 33 | issue = 2| pages = 469–481 | doi=10.1016/j.ympev.2004.07.001| pmid = 15336680 }}</ref>

==Blind cave form==
[[Image:Mexican Tetra as Blind Cave Fish.jpg|thumb|left|225px|Mexican tetra in blind cave fish form]]
''A. mexicanus'' is famous for its blind {{tsl|en|Cavefish|}}, which is known by such names as '''blind cave tetra''', '''blind tetra''' (leading to easy confusion with the Brazilian ''<!-- [[Stygichthys typhlops]] -->[[盲眼冥脂鯉]]''), '''blind cave characin''' and '''blind cavefish'''. Depending on the exact population, cave forms can have degenerated <!-- [[visual perception|sight]] -->[[视知觉]] or have total loss of sight and even their <!-- [[eye]] -->[[眼]]s. The fish in the Pachón caves have lost their eyes completely whilst the fish from the Micos cave only have limited sight.<ref name="gross">{{cite journal|author=Moran|author2=Softley|author3=Warrant|last-author-amp=yes|title=The energetic cost of vision and the evolution of eyeless Mexican cavefish|journal=Science Advances|date=2015|volume=1|issue=8|pages=e1500363|doi=10.1126/sciadv.1500363|pmid=26601263}}</ref>
Cave fish and surface fish are able to produce fertile offspring.<ref name="gross"/>

These fish can still, however, find their way around by means of their <!-- [[lateral line]] -->[[体侧线]]s, which are highly sensitive to fluctuating <!-- [[water pressure]] -->[[压强]].<ref name="yoshizawa">{{cite journal|last=Yoshizawa|first=M.|author2=Yamamoto, Y.|author3= O'Quin, K. E.|author4= Jeffery, W. R.|title=Evolution of an adaptive behavior and its sensory receptors promotes eye regression in blind cavefish|journal=BMC Biology|date=December 2012|volume=10|pages=108|doi=10.1186/1741-7007-10-108|pmid=23270452}}</ref> Currently, about 30 cave populations are known, dispersed over three geographically distinct areas in a <!-- [[karst]] -->[[喀斯特地形]] region of <!-- [[San Luis Potosí]] -->[[聖路易斯波托西州]] and far southern <!-- [[Tamaulipas]] -->[[塔毛利帕斯州]], northeastern Mexico.<ref name="gross12"/><ref name=Romero2009>{{cite book | author=Romero, A. | title=Cave Biology: Life in Darkness | year=2009 | publisher=Cambridge University Press |pages=147–148 | isbn=978-0-521-82846-8}}</ref><ref name=Espinasa2001>{{cite journal | authors=Espinasa; Rivas-Manzano; and Espinosa Pérez | title=A New Blind Cave Fish Population of Genus Astyanax: Geography, Morphology and Behavior |journal=Environmental Biology of Fishes | year=2001 | volume=62 | issue=1 | pages=339–344 | doi=10.1023/A:1011852603162}}</ref> Among the various cave population are at least three with only full cave forms (blind and without pigment), at least eleven with cave, "normal" and intermediate forms, and at least one with both cave and "normal" forms but no intermediates.<ref name=Romero2009/> Studies suggest at least two distinct genetic {{tsl|en|Lineage (evolution)|}} occur among the blind populations, and the current distribution of populations arose by at least five independent invasions.<ref name="gross12"/>

The eyed and eyeless forms of ''A. mexicanus'', being members of the same species, are closely related and can interbreed<ref name="retaux">{{cite journal|last=Retaux|first=S.|author2=Casane, D.|title=Evolution of eye development in the darkness of caves: adaptation, drift, or both?|journal=Evodevo|date=September 2013|volume=4|pages=26|doi=10.1186/2041-9139-4-26}}</ref> making this species an excellent <!-- [[model organism]] -->[[模式生物]] for examining <!-- [[convergent evolution|convergent]] -->[[趋同演化]] and <!-- [[parallel evolution]] -->[[平行演化]], regressive evolution in cave animals, and the genetic basis of regressive traits.<ref name="soares">{{cite journal|last=Soares|first=D.|author2=Niemiller, M. L.|title=Sensory Adaptations of Fishes to Subterranean Environments|journal=BioScience|date=April 2013|volume=63|issue=4|pages=274–283|doi=10.1525/bio.2013.63.4.7}}</ref> This, combined with the ease of maintaining the species in captivity, has made it the most studied cavefish and likely also the most studied {{tsl|en|List of troglobites|}} overall.<ref name=Romero2009/>

The blind and colorless cave form of ''A. mexicanus'' is sometimes recognized as a separate species, ''<!-- [[Astyanax jordani|A. jordani]] -->[[盲鱼]]'', but this leaves the remaining ''A. mexicanus'' as a <!-- [[paraphyletic]] -->[[並系群]] species and ''A. jordani'' as <!-- [[polyphyletic]] -->[[多系群]].<ref name=Keene2016/><ref name="gross12"/><ref name=Jeffrey2009/><ref name=Bradic2012/><ref name=Dowling2002/><ref name=Strecker2004/> The Cueva Chica Cave in the southern part of the Sierra del Abra system is the {{tsl|en|Type locality (biology)|}} for ''A. jordani''.<ref name=Keene2016/> Other blind populations were initially also recognized as separate species, including ''antrobius'' described in 1946 from the Pachón Cave and ''hubbsi'' described in 1947 from the Los Sabinos Cave (both subsequently merged into ''jordani''/''mexicanus'').<ref name=Keene2016/> The most {{tsl|en|Genetic divergence|}} cave population is the one in Los Sabinos.<ref name=Keene2016/><ref name=Coghill2014>{{cite journal | authors=Coghill; Hulsey; Chaves-Campos; García de Leon; and Johnson | title=Next Generation Phylogeography of Cave and Surface Astyanax mexicanus|journal=Molecular Phylogenetics and Evolution | year=2014 | volume=79 | pages=368–374 | doi=10.1016/j.ympev.2014.06.029| pmid=25014568}}</ref>

Another cave-adapted population of ''Astyanax'', varying from blind and depigmented to individuals showing intermediate features, is known from the Granadas Cave, part of the <!-- [[Balsas River]] -->[[巴爾薩斯河]] drainage in <!-- [[Guerrero]] -->[[格雷羅州]], southern Mexico, but it is a part of ''<!-- 页面不存在 -->[[Astyanax aeneus|A. aeneus]]'' (itself sometimes included in ''A. mexicanus'').<ref name=Keene2016/><ref name=Espinasa2001/><ref>{{cite journal | authors=Jeffery; Strickler; and Yamamoto | title=To See or Not to See: Evolution of Eye Degeneration in Mexican Blind Cavefish | journal=Integr Comp Biol | year=2003 | volume=43 | issue=4 | pages=531–541 | doi=10.1093/icb/43.4.531| pmid=21680461 }}</ref>

===Evolution research===
The surface and cave forms of the Mexican tetra have proven powerful subjects for scientists studying <!-- [[evolution]] -->[[演化]].<ref name="retaux" /> When the surface-dwelling ancestors of current cave populations entered the subterranean environment, the change in ecological conditions rendered their <!-- [[phenotype]] -->[[表型]]—which included many biological functions dependent on the presence of light—subject to <!-- [[natural selection]] -->[[自然选择]] and <!-- [[genetic drift]] -->[[遗传漂变]].<ref name="soares" /><ref name="wilkens">{{cite journal|last=Wilkens|first=H|title=Genes, modules and the evolution of cave fish|journal=Heredity|date=November 2012|volume=105|issue=5|pages=413–422|doi=10.1038/hdy.2009.184|pmid=20068586}}</ref> One of the most striking changes to evolve was the loss of eyes. This is referred to as a "regressive trait" because the surface fish that originally colonized caves possessed eyes.<ref name="retaux" /> In addition to regressive traits, cave forms evolved "constructive traits". In contrast to regressive traits, the purpose or benefit of constructive traits is generally accepted.<ref name="soares" /> Active research focuses on the mechanisms driving the evolution of regressive traits, such as the loss of eyes, in ''A. mexicanus''. Recent studies have produced evidence that the mechanism may be direct selection,<ref name="Goss08">{{cite journal|last=Protas|first=M|author2=Tabansky, I.|author3= Conrad, M.|author4= Gross, J. B. |author5=Vidal, O.|author6= Tabin, C. J. |author7=Borowsky, R.|title=Multi-trait evolution in a cave fish, ''Astyanax mexicanus''|journal=Evolution & Development|date= April 2008|volume=10|issue=2|pages=196–209|doi=10.1111/j.1525-142x.2008.00227.x|pmid=18315813}}</ref> or indirect selection through {{tsl|en|Antagonistic pleiotropy hypothesis|}},<ref>{{cite journal|last=Jeffery|first=WR|title=Regressive Evolution in Astyanax Cavefish|journal=Annual Review of Genetics|year=2009|volume=43|pages=25–47|doi=10.1146/annurev-genet-102108-134216|pmc=3594788|pmid=19640230}}</ref> rather than genetic drift and neutral mutation, the traditionally favored hypothesis for regressive evolution.<ref name="wilkens" />

The blind form of the Mexican tetra is different from the surface-dwelling form in a number of ways, including having unpigmented skin, having a better <!-- [[olfaction|olfactory]] -->[[嗅觉]] sense by having <!-- [[taste bud]] -->[[味蕾]]s all over its head, and by being able to store four times more energy as fat, allowing it to deal with irregular food supplies more effectively.<ref>Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 315, 1997, {{ISBN|0-86542-256-7}}</ref>

Darwin said of sightless fish:{{Quote|By the time that an animal had reached, after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will often have affected other changes, such as an increase in the length of antennae or palpi, as compensation for blindness.|Charles Darwin|Origin of Species (1859)}}

Modern genetics has made clear that the lack of use does not, in itself, necessitate a feature's disappearance.<ref>{{cite web|url=http://www.findarticles.com/p/articles/mi_m1134/is_5_114/ai_n13811128 |title=Archived copy |accessdate=2007-02-13 |deadurl=yes |archiveurl=https://web.archive.org/web/20060515160857/http://findarticles.com/p/articles/mi_m1134/is_5_114/ai_n13811128 |archivedate=2006-05-15 |df= }}</ref> In this context, the positive genetic benefits have to be considered, i.e., what advantages are obtained by cave-dwelling tetras by losing their eyes? Possible explanations include:
*Not developing eyes allows the individual more energy for growth and reproduction. However the species does use other methods to locate food and detect danger, which also consume energy that would be conserved if it had eyes or transparent eyelids.
*There remains less chance of accidental damage and infection, since the previously useless and exposed organ is sealed with a flap of protective skin. It is unknown why this species did not develop transparent skin or eyelids instead, as some species of reptiles did.
*The lack of eyes disables the "body clock", which is controlled by periods of light and dark, conserving energy. However sunlight does have minimal impact on the "body clock" in caves.{{cn|date=April 2018}}

Another likely explanation for the loss of its eyes is that of selective neutrality and genetic drift; in the dark environment of the cave, the eyes are neither advantageous nor disadvantageous and thus any genetic factors that might impair the eyes (or their development) can take hold with no consequence on the individual or species. Because there is no selection pressure for sight in this environment, any number of genetic abnormalities that give rise to the damage or loss of eyes could proliferate among the population with no effect on the fitness of the population.

Among some <!-- [[creation-evolution controversy|creationists]] -->[[创造论与科学]], the cave tetra is seen as evidence 'against' evolution. One argument claims this is an instance of "{{tsl|en|Biological devolution|}}"—showing an evolutionary trend of decreasing complexity. But evolution is a non-directional process, and while increased complexity is a common effect, there is no reason why evolution cannot tend towards simplicity if that makes an organism better suited to its environment.<ref>Dawkins, R.: Climbing Mount Improbable, W. W. Norton & Co, 1997, {{ISBN|0-393-31682-3}}</ref>

Inhibition of the {{tsl|en|Hsp90|}} has a dramatic effect in the development of the blind tetra.<ref>{{cite journal|last1=Rohner|first1=N.|last2=Jarosz|first2=D. F.|last3=Kowalko|first3=J. E.|last4=Yoshizawa|first4=M.|last5=Jeffery|first5=W. R.|last6=Borowsky|first6=R. L.|last7=Lindquist|first7=S.|last8=Tabin|first8=C. J. |year=2013 |title=Cryptic variation in morphological evolution: HSP90 as a capacitor for loss of eyes in cavefish | journal=Science|volume=342 |issue=6164 |pages=1372–1375 |doi=10.1126/science.1240276|hdl=1721.1/96714 |pmid=24337296 |pmc=4004346}}</ref>

===In the aquarium===
The blind cave tetras seen in the <!-- [[aquarium]] -->[[水族箱]] trade are all based on stock collected in the Cueva Chica Cave in the southern part of the Sierra del Abra system in 1936.<ref name=Keene2016/> These were sent to an aquarium company in Texas, who soon started to distribute them to aquarists. Since then, these have been <!-- [[selectively bred]] -->[[人工選擇]] for their {{tsl|en|troglomorphic|}} traits.<ref name=Keene2016/> Today large numbers are bred at commercial facilities, especially in Asia.<ref name=seriouslyfish/>

The blind cave tetra is a hardy species.<ref name=Keene2016/> Their lack of sight does not hinder their ability to get food. They prefer subdued lighting with a rocky substrate, like gravel, mimicking their natural environment. They become semi-aggressive as they age, and are by nature schooling fish.{{Citation needed|date=January 2014}} Experiments have shown that keeping these fish in bright aquarium set-ups has no effect on the development of the skin flap that forms over their eyes as they grow.

==參考文獻==
{{Reflist|25em|refs=
<ref name="FishBase">{{FishBase |genus=Astyanax |species=mexicanus |year=2015 |month=October}}</ref><ref name="itis">{{ITIS |id=162850 |taxon=''Astyanax mexicanus'' |access-date=2006-07-01}}</ref>
}}

==參看==
*{{tsl|en|List of freshwater aquarium fish species|水族缸淡水魚類列表}}

==外部連結==
{{Taxonbar|from=Q135378}}
<!-- 没有链接 -->[[Category:Tetras]]
<!-- 没有链接 -->[[Category:Astyanax (fish)]]
<!-- 没有链接 -->[[Category:Freshwater fish of Mexico]]
<!-- 没有链接 -->[[Category:Freshwater fish of the United States]]
<!-- 没有链接 -->[[Category:Cave fish]]
<!-- 没有链接 -->[[Category:Blind animals]]
<!-- 没有链接 -->[[Category:Least concern biota of the United States]]
<!-- 没有链接 -->[[Category:Fish described in 1853]]

2019年2月17日 (日) 14:21的版本

  「Blind cave fish」重定向至此。关于cavefish in general，请见「cavefish」。
Mexican tetra
Mexican tetra, normal form (above) and blind cave form (below)
科学分类 编辑
界： 动物界 Animalia
门： 脊索动物门 Chordata
纲： 辐鳍鱼綱 Actinopteri
目： 脂鯉目 Characiformes
科： 脂鲤科 Characidae
属： 麗脂鯉屬 Astyanax
种：
Mexican tetra A. mexicanus
二名法
Astyanax mexicanus
Approximate range in red
異名[2]
  • Tetragonopterus mexicanus De Filippi, 1853
  • Astyanax fasciatus mexicanus (De Filippi, 1853)
  • Astyanax argentatus Baird & Girard, 1854
  • Tetragonopterus brevimanus Günther, 1864
  • Tetragonopterus petenensis Günther, 1864
  • Tetragonopterus fulgens Bocourt, 1868
  • Tetragonopterus nitidus Bocourt, 1868
  • Tetragonopterus streetsii Cope, 1872

墨西哥麗脂鯉（學名：Astyanax mexicanus）為輻鰭魚綱脂鯉目脂鯉亞目脂鯉科的其中一個物種，為熱帶淡水鱼[3][4]，也是麗脂鯉屬的模式種。本物種是新北界生物地理分布区的特有種，分佈於北美洲格蘭特河及Nueces River（英语：Nueces River）的下游、德克萨斯州的佩科斯河及墨西哥東部與中部的淡水流域[3]。

成長後本物種的體長可達12公分, the Mexican tetra is of typical characin shape, with unremarkable, drab coloration[3]。棲息在沙石底質的溪流，以昆蟲、甲殼類及蠕蟲為食，生活習性不明，可作為觀賞魚。

Its Blind fish（英语：Blind fish） cave form, however, is notable for having no eyes or pigment; it has a pinkish-white color to its body (resembling an 白化症).[5]

This fish, especially the blind variant, is reasonably popular among 水族饲养s.[6]

A. mexicanus is a peaceful species that spends most of its time in midlevel water above the rocky and sandy bottoms of pools and backwaters of creeks and rivers of its native environment. Coming from a 亚热带 climate, it prefers water with 6.5–8 PH值, a 硬水 of up to 30 dGH（英语：dGH）, and a temperature range of 20至25 °C（68至77 °F）. In the winter, some populations migrates to warmer waters. Its natural diet consists of 甲殼亞門s, 昆虫s, and 环节动物门s, although in captivity it is 雜食動物.[7][6]

The Mexican tetra has been treated as a subspecies of A. fasciatus, but this is not widely accepted.[7] Additionally, the blind cave form is sometimes recognized as a separate species, 盲鱼, but this directly contradicts 系统发生学 evidence.[5][8][9][10][11][12]

Blind cave form

Mexican tetra in blind cave fish form

A. mexicanus is famous for its blind Cavefish（英语：Cavefish）, which is known by such names as blind cave tetra, blind tetra (leading to easy confusion with the Brazilian 盲眼冥脂鯉), blind cave characin and blind cavefish. Depending on the exact population, cave forms can have degenerated 视知觉 or have total loss of sight and even their 眼s. The fish in the Pachón caves have lost their eyes completely whilst the fish from the Micos cave only have limited sight.[13] Cave fish and surface fish are able to produce fertile offspring.[13]

These fish can still, however, find their way around by means of their 体侧线s, which are highly sensitive to fluctuating 压强.[14] Currently, about 30 cave populations are known, dispersed over three geographically distinct areas in a 喀斯特地形 region of 聖路易斯波托西州 and far southern 塔毛利帕斯州, northeastern Mexico.[8][15][16] Among the various cave population are at least three with only full cave forms (blind and without pigment), at least eleven with cave, "normal" and intermediate forms, and at least one with both cave and "normal" forms but no intermediates.[15] Studies suggest at least two distinct genetic Lineage (evolution)（英语：Lineage (evolution)） occur among the blind populations, and the current distribution of populations arose by at least five independent invasions.[8]

The eyed and eyeless forms of A. mexicanus, being members of the same species, are closely related and can interbreed[17] making this species an excellent 模式生物 for examining 趋同演化 and 平行演化, regressive evolution in cave animals, and the genetic basis of regressive traits.[18] This, combined with the ease of maintaining the species in captivity, has made it the most studied cavefish and likely also the most studied List of troglobites（英语：List of troglobites） overall.[15]

The blind and colorless cave form of A. mexicanus is sometimes recognized as a separate species, 盲鱼, but this leaves the remaining A. mexicanus as a 並系群 species and A. jordani as 多系群.[5][8][9][10][11][12] The Cueva Chica Cave in the southern part of the Sierra del Abra system is the Type locality (biology)（英语：Type locality (biology)） for A. jordani.[5] Other blind populations were initially also recognized as separate species, including antrobius described in 1946 from the Pachón Cave and hubbsi described in 1947 from the Los Sabinos Cave (both subsequently merged into jordani/mexicanus).[5] The most Genetic divergence（英语：Genetic divergence） cave population is the one in Los Sabinos.[5][19]

Another cave-adapted population of Astyanax, varying from blind and depigmented to individuals showing intermediate features, is known from the Granadas Cave, part of the 巴爾薩斯河 drainage in 格雷羅州, southern Mexico, but it is a part of A. aeneus (itself sometimes included in A. mexicanus).[5][16][20]

Evolution research

The surface and cave forms of the Mexican tetra have proven powerful subjects for scientists studying 演化.[17] When the surface-dwelling ancestors of current cave populations entered the subterranean environment, the change in ecological conditions rendered their 表型—which included many biological functions dependent on the presence of light—subject to 自然选择 and 遗传漂变.[18][21] One of the most striking changes to evolve was the loss of eyes. This is referred to as a "regressive trait" because the surface fish that originally colonized caves possessed eyes.[17] In addition to regressive traits, cave forms evolved "constructive traits". In contrast to regressive traits, the purpose or benefit of constructive traits is generally accepted.[18] Active research focuses on the mechanisms driving the evolution of regressive traits, such as the loss of eyes, in A. mexicanus. Recent studies have produced evidence that the mechanism may be direct selection,[22] or indirect selection through Antagonistic pleiotropy hypothesis（英语：Antagonistic pleiotropy hypothesis）,[23] rather than genetic drift and neutral mutation, the traditionally favored hypothesis for regressive evolution.[21]

The blind form of the Mexican tetra is different from the surface-dwelling form in a number of ways, including having unpigmented skin, having a better 嗅觉 sense by having 味蕾s all over its head, and by being able to store four times more energy as fat, allowing it to deal with irregular food supplies more effectively.[24]

Darwin said of sightless fish:

By the time that an animal had reached, after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will often have affected other changes, such as an increase in the length of antennae or palpi, as compensation for blindness.

——Charles Darwin，Origin of Species (1859)

Modern genetics has made clear that the lack of use does not, in itself, necessitate a feature's disappearance.[25] In this context, the positive genetic benefits have to be considered, i.e., what advantages are obtained by cave-dwelling tetras by losing their eyes? Possible explanations include:

  • Not developing eyes allows the individual more energy for growth and reproduction. However the species does use other methods to locate food and detect danger, which also consume energy that would be conserved if it had eyes or transparent eyelids.
  • There remains less chance of accidental damage and infection, since the previously useless and exposed organ is sealed with a flap of protective skin. It is unknown why this species did not develop transparent skin or eyelids instead, as some species of reptiles did.
  • The lack of eyes disables the "body clock", which is controlled by periods of light and dark, conserving energy. However sunlight does have minimal impact on the "body clock" in caves.[來源請求]

Another likely explanation for the loss of its eyes is that of selective neutrality and genetic drift; in the dark environment of the cave, the eyes are neither advantageous nor disadvantageous and thus any genetic factors that might impair the eyes (or their development) can take hold with no consequence on the individual or species. Because there is no selection pressure for sight in this environment, any number of genetic abnormalities that give rise to the damage or loss of eyes could proliferate among the population with no effect on the fitness of the population.

Among some 创造论与科学, the cave tetra is seen as evidence 'against' evolution. One argument claims this is an instance of "Biological devolution（英语：Biological devolution）"—showing an evolutionary trend of decreasing complexity. But evolution is a non-directional process, and while increased complexity is a common effect, there is no reason why evolution cannot tend towards simplicity if that makes an organism better suited to its environment.[26]

Inhibition of the Hsp90（英语：Hsp90） has a dramatic effect in the development of the blind tetra.[27]

In the aquarium

The blind cave tetras seen in the 水族箱 trade are all based on stock collected in the Cueva Chica Cave in the southern part of the Sierra del Abra system in 1936.[5] These were sent to an aquarium company in Texas, who soon started to distribute them to aquarists. Since then, these have been 人工選擇 for their troglomorphic（英语：troglomorphic） traits.[5] Today large numbers are bred at commercial facilities, especially in Asia.[6]

The blind cave tetra is a hardy species.[5] Their lack of sight does not hinder their ability to get food. They prefer subdued lighting with a rocky substrate, like gravel, mimicking their natural environment. They become semi-aggressive as they age, and are by nature schooling fish.[來源請求] Experiments have shown that keeping these fish in bright aquarium set-ups has no effect on the development of the skin flap that forms over their eyes as they grow.

參考文獻

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  2. ^ http://www.fishbase.se/Nomenclature/SynonymsList.php?ID=2740&SynCode=23916&GenusName=Astyanax&SpeciesName=mexicanus
  3. ^ 3.0 3.1 3.2 Froese, R. & Pauly, D. (eds.) (2015). Astyanax mexicanus. FishBase. Version 2015-10.
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  5. ^ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 Keene; Yoshizawa; and McGaugh. Biology and Evolution of the Mexican Cavefish. 2016: 68–69, 77–87. ISBN 978-0-12-802148-4. 
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