MtDNA copy number variation in male Littorina saxatilis. Association between mtDNA copy number and ecotypes.

Abstract

Mitochondria are not only the powerhouse of the cell, but the organelle also store its own genetic material, mitochondrial DNA (mtDNA). The amount of mtDNA is referred to as mtDNA copy number and has been found to reflect both energy demand and physiological adaptations of tissues. However, there are a limited number of studies that have examined if this pattern can be seen in marine invertebrates. To expand this knowledge, I examined how mtDNA copy number varies between tissues among males of a small marine invertebrate named Littorina saxatilis. Since the species L. saxatilis consists of different ecotypes that exhibit adaptation to different microhabitats, it was hypothesized that variation in mtDNA copy number would reflect these adaptive differences. DNA was extracted from different tissues (mantle, foot, head, seminal vesicles and testes), and mtDNA copy number was quantified in each tissue through qPCR. Comparisons were performed between ecotypes within a single population and between ecotypes across two different populations. The results were analyzed using a linear mixed effects model (LMM), which showed a significant effect of Tissue (p < 0.001) and Population (p < 0.001), but the effect of Ecotype was not significant. Significance was also shown in the interactions Ecotype x Tissue and Ecotype x Tissue x Population. Post-hoc comparisons using EMM showed the crab ecotype from Ängklåvbukten had significantly higher mtDNA copy number in the mantle and seminal vesicles. From Inre Arsklovet, the wave ecotype exhibited significantly higher mtDNA copy number in the head. Results showed variations in mtDNA copy number depend on the type of tissue, and that in turn is influenced by both ecotype and population.