Variation in F1 viability among different animal crosses.

See references listed below for details on how viability was estimated in each case. Data for this table were obtained from studies focused on postzygotic isolation and not on hybrid inviability; as a result, we could not include examples in which inviability and hybrid infertility were combined into a unified metric of isolation [50], [51]. Cases listed in this table should be taken as examples of partial inviability and not as an exhaustive review of known cases. Many cases (e.g., butterflies) involve partial inviability arising from Haldane's Rule. Because different studies use different methods to quantify inviability, values across studies are not necessarily comparable. Data from each source are as follows a: “Inviability index” data from Presgraves [52]. b: mean hybrid viability from supplemental material to Bolnick et al. [41] and see Bolnick & Near [17]. c: Based on “Percentage of embryos hatched” and “percentage of larvae metamorphosed” from Sasa et al. [53] (Appendix). d: Based on viability categories from supplemental data to Price and Bouvier [54]; estimates of partial viability and complete inviability are based on crosses in categories 3.5 to 5; crosses in categories 1 to 3 vary in degree of hybrid fertility but were considered completely viable for the purpose of this summary.