Life cycle parameters
Life cycle parameters, for example the rate of maturation, length of life, number of progeny and the related biodemographic parameters of the population (life history characters), for example population size and rate of growth, can apparently easily change as a consequence of various mutations. With a certain degree of simplification, it can be stated that almost every mutation is manifested to a certain degree in the life-cycle parameters of its carrier. Simultaneously, the life-cycle parameters can very substantially affect the fitness of an individual. The level of investment into reproductive organs in plants or into reproductive conduct in animals can very readily reduce or increase the number of progeny left by a particular individual by an order of magnitude and thus proportionally change the probability that the mutation that caused the particular change is passed on to the next generation. The importance of the individual types of mutations for the fitness of an individual can be indirectly estimated on the basis of the degree of inheritability of the relevant phenotype differences (Houle 1992). Genetically determined traits that very strongly affect the fitness cannot survive for long in the population in the polymorphic state, as one or the other form of the particular trait can be eliminated relatively easily in the population through natural selection. This is manifested at the population level in that most of the intra-population variability in the particular trait or in the particular category of traits is of nongenetic nature or, if it is of genetic nature, it has very low inheritability, i.e. degree (or probability) with which it is transferred from parents to progeny. Numerous observations in nature and the laboratory have shown that life cycle parameters and biodemographic parameters in general have, on an average, much lower inheritability than morphological parameters (Mousseau & Roff 1987) (Fig. XII.11).