Fig. 3.

The effect of early-acting post-mating barriers to hybridization in all possible cross combinations between E. globulus (glob), E. nitens (nit) and their F₁ hybrid. Barriers assessed were (A) seed set, (B) time to first germination, (C) germination success (number of germinates/number of seeds sown) and (D) survival of pot-grown germinates after 6 months. Cross types with different letters were significantly different at P < 0·05 based on the Tukey–Kramer adjustment for multiple comparisons. Note that the unilateral mechanical barrier to zygote formation between E. nitens (pollen) and E. globulus (flowers) was lost in the F₁, i.e. crosses in both directions involving the F₁ were successful. There was also no evidence of reduced intrinsic post-zygotic fitness in seed produced from hybrid mothers or fathers in these early life history stages.