Figure 1.

Effects of breeding values for clutch size on survival of female and male progeny partitioned by the first versus later clutch progeny. (a) First-clutch female progeny, (b) first-clutch male progeny, (c) later clutch female progeny, (d) later clutch male progeny. The linear relationship between survival and breeding values are shown (e.g. selection gradient) along with the confidence limits. However, statistical tests are based on the univariate selection differential, s, which is computed from the difference between the distribution of breeding values of survivors after the process of maturation (e.g. production of the first clutch) and distribution for breeding values (pooling distributions from the top, survival=1 and bottom, survival=0) when progeny emerge from winter hibernacula and begin to mature (table 1). See table 1 for selection differentials (s) and selection gradients (β) and p-values for individual tests, as well as ANCOVA (ordinary and logistic regression) of clutch and sex and interactions with breeding values for clutch size.