Investigating the association two large effect loci vgll3 and six6 have on the maturation timing in Wild Atlantic salmon

Abstract

Maturation timing is a key life history trait in Atlantic salmon (Salmo salar), influencing population resilience through variation in age at maturity. Identifying the genetic basis of this trait is a central goal in conservation biology of the species. Two candidate loci, vestigial-like family member 3 (vgll3) and SIX homeobox 6 (six6), have previously been identified with a genetic predisposition towards age at maturity due to differences in a single SNP indicating ‘early’ or ‘late; maturation timing. In this project, DNA was extracted from fin clips of wild Atlantic salmon from nine rivers across six regions in Iceland. Genotype frequencies associated with maturation timing were determined using quantitative PCR (qPCR) analysis. Overall, results indicated a genetic predisposition towards earlier maturation at both loci when samples were grouped across all sample sites. Although statistical significance was marginal, an association was detected between sea age and vgll3*EE the most frequently observed genotype at the vgll3 locus. Additional significant relationships were observed between vgll3 and body length, where vgll3*EE individuals were longer than vgll3*LL individuals and overall males were shorter than females. A significant association was found between sea age and length indicating 2SW individuals were longer compared to 1SW individuals. Life history traits showed a significant association between vgll3*EE and precocious males and a marginally significant association between vgll3*LL and iteroparous spawners. When populations were separated by river, a linear model reveled location was a significant determinant of body length compared to genotype and sex at vgll3 while at six6 sex and genotype were significant determinants of body length while river showed no statistical significance. Genotype frequencies varied markedly within and among rivers, even after accounting for geographic proximity, possibly due to population differentiation or even local adaptation. Additionally, the genotype frequency of farmed salmon differed significantly from wild salmon at six6 but not at vgll3.These findings are highly relevant in establishing how a gene targeted management approach can inform the conservation and management of Atlantic salmon populations in Iceland.

Kynþroskaaldur er mikilvægur lífssögueiginleiki hjá Atlantshafslaxinum (Salmo salar) og hefur breytileiki hans áhrif á stöðugleika stofna og getur greining á erfðum þessa eiginleika nýst við verndun tegundarinnar. Sýnt hefur verið fram á að breytileiki í tveimur genum, vestigial-like family member 3 (vgll3) og SIX homeobox 6 (six6), sýni sterk tengsl við kynþroskaaldur, þar sem mismunandi samsætur tengjast snemm- og síðkynþroska. Í þessu verkefni var DNA einangrað úr uggasýnum villtra laxa frá níu ám af sex svæðum innan Íslands. Arfgerðir sem hafa verið tengdar við kynþroskatíma voru greindar með magnbundnu PCR (qPCR) og tíðni gerðanna og samsætanna metin. Niðurstöður, sameinaðar frá ólíkum ám, sýna að erfðabreytileiki sem tengist snemmkynþrosaka er algengari en sem valda síðkynþroska. Vísbending var um tengsl aldurs í sjó og breytileika í vgll3 við kynþroska, vgll3*EE greindist frekar hjá löxum sem voru lengri tíma í sjó og þeir voru lengri en vgll3*LL og almennt voru hængar minni en hrygnur. Vgll3*EE reyndist algengari meðal snemmkynþroska laxa og væg vísbending var um aukna tíðni vgll3*LL hjá löxum sem æxluðust endurtekið (e. iterparous). Við greiningu á lengd laxanna með línulegu líkani kom í ljós að árnar höfðu meiri áhrif á lengd fiskanna en arfgerð vgll3 arfgerðarinnar og kyn, hinsvegar þegar lengdin var skoðuð m.t.t. arfgerðar six6 gensisins var skoðuð reyndist áhrif arfgerðarinnar matktæk auk þess sem kynið hafði áhrif en ekki árnar. Tíðni arfgerðanna meðal villtu laxanna var marktæk frábrugðin arfegrðum eldislaxa í six6 en ekki í vgll3. Þessi rannsókn sýnir hvernig greiningar á breytileika einstakra gena getur veitt upplýsingar fyrir verndun og stjórnun á villtum laxastofnum á Íslandi.