Thermal adaptation and clinal mitochondrial DNA variation of European anchovy

Abstract

Natural populations of widely distributed organisms often exhibit genetic clinal variation over their geographical ranges. The European anchovy, Engraulis encrasicolus, illustrates this by displaying a two-clade mitochondrial structure clinally arranged along the eastern Atlantic. One clade has low frequencies at higher latitudes, whereas the other has an anti-tropical distribution, with frequencies decreasing towards the tropics. The distribution pattern of these clades has been explained as a consequence of secondary contact after an ancient geographical isolation. However, it is not unlikely that selection acts on mitochondria whose genes are involved in relevant oxidative phosphorylation processes. In this study, we performed selection tests on a fragment of 1044 bp of the mitochondrial cytochrome b gene using 455 individuals from 18 locations. We also tested correlations of six environmental features: temperature, salinity, apparent oxygen utilization and nutrient concentrations of phosphate, nitrate and silicate, on a compilation of mitochondrial clade frequencies from 66 sampling sites comprising 2776 specimens from previously published studies. Positive selection in a single codon was detected predominantly (99%) in the anti-tropical clade and temperature was the most relevant environmental predictor, contributing with 59% of the variance in the geographical distribution of clade frequencies. These findings strongly suggest that temperature is shaping the contemporary distribution of mitochondrial DNA clade frequencies in the European anchovy.

Thermal acclimation and subspecies-specific effects on heart and brain mitochondrial performance in a eurythermal teleost (Fundulus heteroclitus)

“…Our data are consistent with these observations of limited subspecies effects (Figs 2-7). Modest subspecies differences are perhaps unsurprising as mitochondrial genes are often subject to neutral and purifying selection and functional differences may only be detected under specific conditions (MeloFerreira et al, 2014;Silva et al, 2014), and in general this is true among species of Fundulus as well (Whitehead, 2009). However, mitochondrial respirometry assays often assess function under saturating substrate conditions to ensure a maximum enzyme velocity.…”

Do relaxed selection and habitat temperature facilitate biased mitogenomic introgression in a narrowly endemic fish?

“…The amino acid differences between H. minckleyi and H. cyanoguttatus at site 155 in COX3, 368 in CYTB, and 12 in ND4 are locations that have been implicated in mitogenomic cold adaptation in other vertebrates (Silva et al. 2014; Welch et al. 2014).…”

“…This amino acid shows a strong association with the temperature adaptation in anchovies in the Atlantic Ocean (Silva et al. 2014). Furthermore, this amino acid site exhibits a threonine in H. cyanoguttatus and a valine in the colder regions of the anchovies range.…”

“…2014) although it is critical to the molecular evolution of the mitogenome (Silva et al. 2014; Welch et al. 2014).…”

“…Advantageously, a number of studies have already identified particular amino acids in mitochondrial proteins that are candidate adaptations to colder temperatures (Silva et al. 2014; Welch et al. 2014).…”