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Lesa - skrifa - spjalla: Af hverju eru húsdýr svona marglit?

Af hverju eru húsdýr svona marglit?

Úr tímaritinu Lifandi vísindi 7. tölublað 2010.

 

Feldur dýra og hár manna hafa mismunandi lit vegna þess að í hárunum eru litarefnin eumelanín og phoemelanín, sem annars vegar gefa svartan og brúnan lit, en hins vegar gulan og rauðan, allt eftir magni. Hár albínóa hefur ekkert af þessum litarefnum.

Hjá villtum dýrum sker litur feldsins úr um hversu vel felubúin dýrin eru og það skiptir máli bæði fyrir rándýrið og bráðina. Gott dæmi eru heimskautarefir og hérar sem fara úr hárum tvisvar á ári og eru þess vegna hvítir á veturna en gráir eða brúnir á sumrin. Litur feldsins hefur einnig þýðingu varðandi líkamshitann. Rannsóknir á stökkhjörtum í Suður Afríku, sem yfirleitt eru brúnir og hvítir að lit, hafa sýnt að hin alsvörtu dýr hafa hærri líkamshita þegar heitt er í veðri, en ámóta sjaldgæf hvít dýr hafa lægri líkamshita að vetri til. Bæði þessi óvenjulegu litaafbrigði eru sem sagt galli og einmitt þess vegna eru þau óvenjuleg. Þessi dýr lifa síður af vegna þess að þau hafa ekki aðlagast aðstæðum nógu vel. Húsdýrin þurfa ekki að aðlagast náttúrunni á sama hátt, heldur er þróun þeirra ákveðin af manninum, sem velur saman dýr til undaneldis á grundvelli eiginleika sem taldir eru eftirsóknarverðir. Og þar eð húsdýr eru fóðruð og vernduð gegn rándýrum, geta afbrigði sem ekki myndu lifa í náttúrunni, sem best þrifist.

Hundar eru ágætt dæmi. Öfugt við úlfa eru hundar til í öllum mögulegum litum og litamynstrum, sumir jafnvel deplóttir. Öldum saman hafa ýmsir hundar verið ræktaðir út frá litnum, fremur en öðrum eiginleikum, svo sem veiðihæfni eða getu til að halda kindum í hnapp. Þar eð hundar stunda ekki veiðar sér til matar, þurfa þeir ekki á neinum felulitum að halda. Það er sem sé í rauninni sameiginlegt með villtum og tömdum dýrum að þau þróast eftir aðstæðum, en aðstæðurnar eru gerólíkar. Í náttúrunni verða lífsbjargareiginleikarnir ofan á, en hjá húsdýrum eru það eiginleikar sem maðurinn kýs.

Síðast breytt: mivikudagur, 27 jl 2011, 09:16 eh