Variation in digestive performance between geographically disjunct populations of Atlantic salmon: countergradient in passage time and digestion rate

Abstract

European Atlantic salmon (Salmo salar) populations inhabit rivers from northern Portugal to northern Norway across a wide spectrum of environmental variability. To address whether single physical factors might lead to genetic divergence of isolated populations, we compared the digestive performances total digestibility, relative nitrogen digestibility, passage time, and digestion rate (g dry matter · h) - of northern (Scotland) and southern (Asturias, northern Spain) populations at three temperature regimes (5, 12, and 20° C). Total dry matter digestibilities increased directly with temperature but were similar for both populations at each of the three trials. Relative nitrogen digestibility did not differ between populations nor among temperature regimes. In contrast, passage time was significantly longer for low-than for high-latitude fish at both 5 and 20° C. When the percentage of food digested and the passage time were integrated as digestion rates (food digested per unit time), a significant population × temperature interaction consistent with a genotype × environment interaction was detected in addition to the population and temperature effects. This implies that not only is the digestive performance of the high-latitude population higher throughout the range of temperatures examined, but moreover the difference is reinforced at high temperatures, where the digestion rate of high-latitude fish was 1.6 times greater. Taken together, these two results provide preliminary evidence for countergradient variation in digestive rates of salmonids in response to variation in growth opportunity. The data support our previous work on the same two populations showing differences in growth rates, and underlie one of the possible mechnisms leading to more rapid growth of the high-latitude fish when both populations are reared in a common environment.

Assimilation efficiency in Bufo spinulosus tadpoles (Anura: Bufonidae): effects of temperature, diet quality and geographic origin

“…While AE for the LQD increased at 25 o C, the HQD did not present and significant differences between the two temperatures. Environmental temperature has traditionally been considered as one of the most relevant factors affecting the physiology of poikilotherms (Rome et al 1992, Duellman & Trueb 1994, Schmidt-Nielsen 1997 and its effect on digestive physiology has received considerable attention (e.g., Coulson 1990, Nicieza et al 1994, McConnachie & Alexander 2004). It has been described that an increase in temperature increases assimilation of food (Altig & McDearman 1975, Nicieza et al 1994, McKinon & Alexander 1999, McConnachie & Alexander 2004.…”

Evolution of Intrinsic Growth and Energy Acquisition Rates. Ii. Trade-Offs With Vulnerability to Predation in Menidia Menidia

“…It is becoming increasingly apparent that countergradient variation and other forms of adaptive variation in juvenile growth rate are common in various taxonomic groups, including reptiles, amphibians, gastropods, insects, and plants (Nicieza et al 1994;Conover and Schultz 1995;James and Partridge 1995;Schultz et al 1996;Arendt and Wilson 1999;DiMichele and Westerman 1997;Parsons 1997;Dittman et al 1998;Arnett and Gotelli 1997;Jonassen et al 2000). These emerging patterns suggest that trade-offs countering the benefits of rapid juvenile growth are widespread in nature.…”

Possible countergradient variation in growth of juvenile cod Gadus morhua from the northwest Atlantic

“…However, no significant difference in standard length or wet mass among the 3 populations at the end of the experiment indicates a trend toward faster growth of cod juveniles from the most northern population. Our northernmost cod population grew 20 or 50% faster at (Nicieza et al 1994). Northern fish populations of Atlantic silverside (Present & Conover 1992) and Atlantic salmon (Nicieza et al 1994) have a higher FCE than southern populations.…”

“…Our northernmost cod population grew 20 or 50% faster at (Nicieza et al 1994). Northern fish populations of Atlantic silverside (Present & Conover 1992) and Atlantic salmon (Nicieza et al 1994) have a higher FCE than southern populations. Further evidence in support of a CnGV in FCE was reported in juvenile turbot and Atlantic halibut Hippoglossus hippoglossus (Jonassen et al 2000).…”

“…In temperature-controlled studies, faster growth rates at higher latitudes have also been found in largemouth bass Micropterus salmoides (Williamson & Carmichael 1990), Atlantic salmon Salmo salar (Nicieza et al 1994), and striped bass (Conover et al 1997). Seasonality, as measured by the length of the growing season, has a significant evolutionary effect on growth rates whereby intrinsic rates of growth tend to be greater in populations adapted to higher latitudes (Conover & Schultz 1995).…”