Models of a dual inheritance system

In higher plants, animals and fungi, there are two inheritance systems: the familiar system, depending on DNA sequence, used in transmitting information between sexual generations, and an epigenetic inheritance system, depending on gene activation, responsible for the transmission of states of differentiation during development. Occasionally, epigenetic changes are transmitted in sexual reproduction. A formal model of such a dual inheritance system is presented, and it is shown how the separation between the two systems can sometimes break down. The evolutionary significance of such breakdowns is discussed.     

Dietary salt intake and its relevance to ionic regulation in freshwater salmonids

Dietary sodium intake for freshwater salmonids feeding in the wild (invertebrate diet) or in captivity (pellet diet) was calculated and compared with published branchial sodium influx values. Dietary sodium intake (mmol kg⁻¹ per month) increases from winter minimum values of 5 and 30-40 to reach maximum values in summer of 175 and 240 for invertebrate and pellet diet, respectively. In summer, dietary sodium intake for fish feeding in the wild was of the same magnitude as branchial sodium influx. The implications of dietary sodium intake for sodium balance in freshwater fish are discussed.