Scientists from Canada and the USA have gained further insight into how gliding evolved in flying fishes (Exocoetidae).
The first comprehensive study of the molecular phylogeny of the group, conducted by Eric Lewallen and coauthors, is to be published in a forthcoming issue of the Biological Journal of the Linnean Society.
The authors conducted their species-level analysis on 31 species of flying fishes in seven genera, based on data from the mitochondrial cytochrome b gene (1137 base pairs) and the nuclear RAG2 gene (882 base pairs).
Their results indicated that flying fishes are monophyletic (ie. they all shared a most recent common ancestor), but not the genus Cheilopogon; this implied that gliding evolved only once in the flying fishes.
More importantly, the study confirmed the results of previous studies that examined how gliding originated and evolved in flying fishes.
Flying fishes can be divided into two-wing (those with enlarged pectoral fins only) and four-wing (those with enlarged pectoral and pelvic fins) forms and exhibit a range of gliding capabilities, from weak gliders like Fodiator, to the two-winged Exocoetus that glide short distances (tens of metres), to the four-winged members of the Cypselurinae that can glide hundreds of metres.
They are thought to have evolved the ability to glide in two stages: two-winged gliding first and four-winged gliding more recently, which the results of this study supported.
Previous studies have further subdivided this scenario of flying fish evolution into a three-step pattern:
(1) enlarged pectoral fins in all flying fishes; (2) even more greatly enlarged pectoral fins in Exocoetus+Cypselurinae and (3) enlarged pelvic fins in Cypselurinae. The molecular phylogeny presented in this study agrees with the three-step scenario of gliding evolution.
Even more studies are needed to fully understand the evolution of gliding in flying fishes. We still do not understand the selective pressures that led to the origination and elaboration of gliding strategies. The general consensus among scientists is that flying fishes evolved the ability to glide to escape from predators.
Although it is difficult to test hypotheses of how gliding originated within the group, the authors state that it is possible to test for correlations between the presence of particular types of predators and types of gliding behaviour.
Field observations indicate that Exocoetus is frequently found with tunas, whereas members of the Cypselurinae are frequently preyed on by dolphinfishes. Tunas (Scombridae) hunt in large, fast-swimming schools, and may be avoided best by two-wing flying fishes that are able to exit the water quickly without the need to taxi. On the other hand, dolphinfishes (Coryphaenidae) actively pursue prey (and may be evaded best by the longer glides, faster speeds, and abrupt changes in direction achieved by four-wing flying fish species.
For more information, see the paper: Lewallen, EA, RI Pitman, Sl Kjartanson and NR Lovejoy (2011) Molecular systematics of flyingfishes (Teleostei: Exocoetidae): evolution in the epipelagic zone. Biological Journal of the Linnnean Society DOI: 10.1111/j.1095-8312.2010.01550.x