pleiotropy
Zhang X-S 2012 Fisher's geometrical model of fitness landscape and variance in fitness within a changing environment. Evolution 66:2350-2368.
- predictions from Fisher's geometrical model are consistent with empirical estimates, implying that multivariate stabilizing selection is a reasonable fitness landscape model
- the U-shaped relationship of VG(F) with n indicates that a very complex organism can also have a high rate of adaptation in accordance with Fisher's fundamental theorem
- this finding is in sharp contrast to that predicted in the so-called "cost of complexity" theory (Orr 2000) in which the rate of adaptation decreases quickly with increasing organismal complexity
- adaptation relies not only on new mutations but also on the standing genetic variance
- as the contribution from all mutations (i.e., the first component of (16)) increases with organismal complexity, the rate of adaptation does not correspondingly decrease monotonically
- for organisms that have a high mutation rate, say one mutation per genome per generation, standing quantitative genetic variation is the main source of VG(F) when organismal complexity is low
- with increasing organismal complexity, its contribution decreases but that from mutation increases
- for very complex organisms, the main contribution to adaptation is from mutations
- pleiotropy is a common phenomenon
- the degree of pleiotropy cannot be large
- the number of independent traits could be very small (n < 3) for some model species
- complicated models that include correlation in mutational effects and selection on multiple traits can be reduced to the simple model considered here by a transformation that simultaneously diagonalizes both matrices M and S
