Figure 1.

Schematic illustration of temporal sequence of oocyte RYD phase, ovulation and egg-laying in a bird. (a) Traditional view: hierarchical order of oocyte sequestration (F1–F4) into RYD phase is maintained at ovulation and egg-laying (E1–E4) because of similar RYD growth pattern among oocytes. The sigmoid growth of F1 shows growth parameters measured in this study: K₁, initial growth rate; K₂, late growth rate; T_max, time of maximum growth, the horizontal line shows total duration of RYD phase of F1 and is the same for all oocytes. In this example, during its RYD growth, F1 overlaps with growth of F2 for 24 h, with growth of F2+F3 for 24 h, and with growth of F2+F3+F4 for 24 h. (b) Hypothetical view: when RYD growth rate and duration differ among oocytes, the hierarchical order of sequestration (F1–F4) might not be maintained at ovulation (in this example, F2, F1, F4, F3). Growing oocytes would differ in the duration of overlap with RYD phase of other oocytes, and variation in RYD growth patterns could expose growing oocytes to distinct maternal hormonal profiles and lead to accumulation of distinct hormonal concentrations in oocyte yolk prior to ovulation.