Application of a Temperature‐Dependent Mitotic Interval (τ o ) for Induction of Diploid Meiotic Gynogenetic Paddlefish

We tested the application of mitotic interval (tau [τ o ]) unit in comparison with absolute time to help standardize preshock timing for a consistent production of diploid meiotic gynogenetic paddlefish Polyodon spathula . The diploid gynogenetic larvae were produced by applying heat shock (35°C; 2 min) at different times after activation of paddlefish eggs with irradiated sperm of shovelnose sturgeon Scaphirhynchus platorynchus at two different preshock temperatures (15°C and 20°C). When the timing of heat shock (minutes after activation) was expressed in absolute time, the yield of gynogenetic diploid larvae was distinctly different between the two preshock incubation temperatures. At 20°C, the highest yield was observed when the timing of the heat shock was 12‐ 13 min after activation, whereas at 15°C the highest yield was observed when the timing of the heat shock was 17‐ 22 min after activation. However, when the timing of heat shock was expressed in terms of τ o , the yield of gynogenetic diploid larvae for the two preshock incubation temperatures coincided completely at each time point tested. The highest yield (about 30%) of diploid gynogenetic larvae was obtained when the timing of heat shock was between 0.22τ o and 0.26τ o . Reporting of heat shock timing in terms of τ o provides the opportunity to standardize the preshock time interval for any preshock temperature. This could help to identify the optimal timing of heat shock for a specific experiment and allow comparison of data among different experiments in which different preshock temperatures were used.