Individual escape flight performance is repeatable and differs between long-tailed finch (Poephila acuticauda) subspecies but not as predicted by asymmetrical introgression

An emerging question in evolutionary research is the extent to which mitochondrial variation across species and populations drives functional differences in fitness-related traits. The asymmetric introgression and narrow mitochondrial clines seen in long-tailed finch (Poephila acuticauda) subspecies is suggestive of selection but there is no direct evidence of fitness related differences in admixed birds. Asymmetric introgression of the eastern P. a. hecki mito-type into P. a. acuticauda, suggests that the former may possess a selective energetic advantage such as superior escape flight performance. We employed a spatial tracking software, Argus, to quantify the take-off flight performance of 158 wild-derived, captive long-tailed finches as they were released repeatedly, from which we obtained nine flight metrics. Average force and maximum vertical distance travelled were repeatable across all individuals and significantly lower in P. a. hecki compared to P. a. acuticauda males. Hence, contrary to predictions, P. a. hecki did not display escape flight performance superior to P. a. acuticauda suggesting take-off flight performance in wild long-tailed finches is not related to the observed asymmetry in the introgression of mito-type between the subspecies. Furthermore, in intraspecific female hybrids, in which we might theoretically expect a mismatch between mitochondrial haplotype and mitonuclear genes, we also found no evidence of impaired flight take-off performance, relative to those with matched mitochondrial and mitonuclear genes (here: female P. a. acuticauda). Finally, male and female hybrids did not differ in the average force and maximum vertical distance travelled, again suggesting that take-off performance is not significantly worse in the heterogametic sex, as predicted by Haldane's rule. The angle of the take-off flight was a key determinant of our flight performance metrics and consequently, future work could benefit from better directing the flight path of tracked birds.