Remodeling of membrane lipids in gills of adult hard clam Mercenaria mercenaria during declining temperature

Abstract

In a previous study, a major remodeling of lipids, consistent with the theory of homeoviscous adaptation, was observed in the juvenile hard clam Mercenaria mercenaria during a temperature reduction from 24 to -1°C. In addition, the lipid remodeling varied between genetically distinct lines of hard clams. The present study examined whether adult hard clams originating from different locations and a selectively bred variety show differences related to their genetic characteristics in the remodeling of lipids that normally occur during decreasing temperatures. Wild hard clams from 4 locations in Atlantic Canada and the selectively bred M. mercenaria var. notata were held at an aquaculture growout site located at the northern distribution limit of the species in the Gulf of St. Lawrence from August to December 2006. Gills were sampled monthly for lipid analyses. Hard clams from the 5 groups showed an increase in the unsaturation index, mainly attributable to 22:6n-3 and 20:5n-3 as temperature decreased during the fall, followed by an increase in the phospholipid to sterol ratio in December. Although hard clams from the wild showed a lower unsaturation index than the selectively bred clams, there was no effect of location on the lipid remodeling. This result coincided with low genetic differentiation among hard clams from the 5 groups. Interestingly, the levels of 20:5n-3, 20:4n-6 and 22:6n-3 -3 fatty acids obtained from the diet -were generally lower in the environment compared to the levels in hard clams, thus suggesting some mechanisms for the selective incorporation of these fatty acids in hard clams.

Lipids in Marine Ecosystems

“…Ectotherms can counteract the ordering effects of reduced temperature or increased pressure by changing the structure of their membranes [65,66], a process known as homeoviscous adaptation [67]. This biochemical adaptation involves remodeling membrane lipids: changes in phospholipid to sterol ratios and acyl chain length and saturation have been observed in bivalves and finfish [68,69]. Hard clams in Atlantic Canada increased the level of unsaturation of fatty acids in their gills throughout the fall and then increased their phospholipid to sterol ratio in December [68].…”

“…This biochemical adaptation involves remodeling membrane lipids: changes in phospholipid to sterol ratios and acyl chain length and saturation have been observed in bivalves and finfish [68,69]. Hard clams in Atlantic Canada increased the level of unsaturation of fatty acids in their gills throughout the fall and then increased their phospholipid to sterol ratio in December [68]. Although it is generally accepted that ectothermic animals increase membrane content of unsaturated fatty acids in response to cold to maintain fluidity [70], few studies have shown a clear and direct relationship between unsaturated fatty acids and membrane fluidity in marine organisms [67,71].…”

Age-related cellular changes in the long-lived bivalve A. islandica

“…We speculate that higher observed F 2 IsoPs in Icelandic A. islandica may be the result of higher total lipid uptake in the Icelandic environment. Many clams get most of their polyunsaturated fatty acids from their diets (Langdon and Waldock 1981;Parent et al 2008), and Icelandic A. islandica may have a richer available diet than Baltic Sea A. islandica (Ridgway and Richardson 2010). Analyses and comparisons of lipid and proteome compositions of the two investigated A. islandica populations could give more insights into underlying mechanisms of lipid peroxidation and protein stability.…”

Scale-dependent natural variation in larval nutritional reserves in a marine invertebrate: implications for recruitment and cross-ecosystem coupling

“…In S. balanoides, cyprid size increases towards colder regions over continental scales (Crisp 1962). In other organisms, cholesterol responds negatively to temperature as part of a mechanism to regulate membrane fluidity (Crockett 1998), and studies in marine species have found seasonal or spatial patterns in cholesterol that are consistent with the existence of such mechanisms (Parent et al 2008). However, we did not find consistent evidence of latitudinal thermal gradients in the studied area (Fig.…”