Seminar: “Micro- and macroevolution of fork tails in swallows” by Dr. Masaru Hasegawa
Dr. Masaru Hasegawa, SOKENDAI, the Graduate University for Advanced Studies, Japan
Micro- and macroevolution of fork tails in swallows
Deep fork tail of the barn swallow Hirundo rustica (Fig. 1, left) is a classic example of sexual trait. Sexual selection via female choice would favor the evolution of this ornament that seem to have rather negative effects on survivorship. This explanation, however, has been challenged by "aerodynamic advantage" hypothesis, which predicts that aerodynamic advantage for capturing prey item rather than sexually selected advantage is the main selection force driving deep fork tails: deeper fork tails would provide better flight maneuverability than shallower fork tails. Although a series of experiments suggest that only a small portion of tail feather is costly part (while the remaining can be explained by aerodynamic advantage), their approach accompanying tail manipulation upsets an original co-adapted character set, limiting the validity of the findings. Here, to study the evolution of fork tails in swallows, we used two alternative approaches: 1) within-species pattern of fork tails in the Pacific swallow Hirundo tahitica, which has shallow fork tails (Fig. 1, right), in a once-in-a-century severe winter; 2) interspecific pattern of fork tails across hirundine species using phylogenetic comparative approaches. Results from both approaches showed that deep fork tails are costly in swallows, which is inconsistent with the aerodynamic advantage hypotheses. The evolution of deep fork tails may be explained by sexual selection.