Heritabilities and genetic correlation of shell thickness and shell length growth in a mussel, Mytilus chilensis (Bivalvia:Mytilidae)

Abstract

Heritabilities and genetic correlation of shellthickness and shell length growth in a mussel,Mytilus chilensis(Bivalvia:Mytilidae)Ricardo Gui~nez1, Jorge E Toro2, Sebasti an Krapivka3, Ang elica C Alcap an2&Pablo A Oyarz un21Instituto de Ciencias Naturales Alexander von Humboldt, Facultad de Ciencias del Mar y Recursos Biol ogicos,Universidad de Antofagasta, Antofagasta, Chile2Instituto de Ciencias Marinas y Limnol ogicas (ICML), Universidad Austral de Chile, Valdivia, Chile3Departamento de Antropolog ıa, Facultad de Ciencias Sociales, Universidad de Chile, Santiago, ChileCorrespondence:J E Toro, Instituto de Ciencias Marinas y Limnol ogicas (ICML), Universidad Austral de Chile, Valdivia, Chile.E-mail: jtoro@uach.clAbstractShell thickness in mollusks is generally consid-ered adaptive because of their effects on fitness.However, little is known about the genetic basisof shell thickness. This is important, because theresponse to selection and the subsequent adap-tive microevolution of a trait, such as thicknessis only possible when that trait exhibits additivegenetic variation. Here, we estimated the nar-row-sense heritability (h2: ratio between additivegenetic variance and phenotypic variance) forthe traits ‘shell thickness’ and ‘shell lengthgrowth’ in a 34-month-old cohort of the musselMytilus chilensisobtained by using a half-fullsib design and grown in the field. Also, pheno-typic and genetic correlations were estimatedbetween both traits. We found thath2showedsignificant values for shell thickness(0.294 0.194) and length (0.731 0.379).The phenotypic correlation between both traitswas positive and significant; however, thegenetic correlation between these traits was not.These results suggest both traits can evolveadaptively by selection, but because these traitsdid not show genetic correlation, it is possiblethat selection pressure affecting one trait maynot affect the other.