Phylogeny and Jaw Ontogeny of Beloniform Fishes1

Integrative and Comparative Biology, Nov 2004 by Lovejoy, Nathan R, Iranpour, Mahmood, Collette, Bruce B

DISCUSSION

Phytogeny

The expansion of the Lovejoy (2000) matrix by 1 kilobase of nuclear gene sequence and 14 new taxa confirms the main conclusions of that study regarding beloniform relationships. The family Belonidae is not monophyletic without the inclusion of sauries, traditionally regarded as a distinct family (Scomberesocidae). Halfbeaks are also non-monophyletic; however, salvaging the family Hemiramphidae is more problematic. Halfbeaks are divided into three main clades: Zenarchopteridae (the Indo-West Pacific freshwater halfbeaks), the Hemiramphus clade (which includes Euleptorhamphus and Oxyporhamphus), and the Hyporhamphus/Arrhamphus clade. Perhaps the most surprising result is the sister group relationship between Zenarchopteridae and needlefishes/sauries. This relationship is supported by high decay indices and bootstrap proportions, and by its presence in separate ,analyses of the nuclear genes. Similarly, the sister group relationship between the Hemiramphus clade and fiyingfishes is quite strong. The position of the Hyporhamphus clade is less clear. In the most parsimonious tree, it is placed as the sister group to the zenarchopterids and needlefishes/sauries; however, in trees two steps longer (and in separate analyses of the nuclear genes), it is grouped with the Hemiramphus clade and flyingfishes. Increased taxonomic sampling of halfbeaks may resolve this issue; Hyporhamphus, the most taxonomically diverse halfbeak genus, with two distinct subgenera, is represented by only two species in this study.

The hypothesized division of halfbeaks into three groups has implications for patterns of morphological evolution. The fusion of the third pair of upper pharyngeal bones has been considered a synapomorphy of Hemiramphidae (Collette et al., 1984). In light of the topology presented here, these bones either fuse independently in two or more halfbeak lineages, or become unfused in needlefishes and flyingfishes Similarly, homoplasy is required in the evolution of the fourth upper pharyngeal toothplates. The plates are absent in halfbeaks and flyingfishes (Rosen and Parenti, 1981; Collette et al, 1984), thus the present topology requires their independent loss in the three halfbeak/flyingfish lineages, or their reappearance in the needlefish/saury lineage. Before more definitive hypotheses concerning the evolution of the characters can be made, a complete anatomical survey needs to be undertaken for beloniforms, and incorporated into the matrix.

The inclusion of additional halfbeak and flyingfish taxa provides some interesting results concerning the evolution of gliding. Parin (1961), Collette et al., (1984), Dasilao et al. (1997), and Dasilao and Sasaki (1998) have presented phylogenetic hypotheses for flyingfishes. The results presented here are largely in agreement with these previous studies. Fodlator is generally considered the least sophisticated glider, along with Parexocoetus, and Exocoetus. These three genera are "monoplane" gliders, having greatly expanded pectoral fins but not pelvics. Cypselurus, Prognichthys, and Hirundichthys, and Cheilopogon (the Cypselurinae) are "biplane" gliders, and have expanded pelvic as well as pectoral fins, which help to control gliding stability (Davenport, 1992). Morphological studies place the monoplane gliders at the base of the exocoetid tree, suggesting a progressive refinement of gliding ability. The molecular data support this idea. Dasilao et al. (1997) also showed that, based on morphology, the halfbeak Oxyporhamphus, should be considered the basal flyingfish taxon. The molecular data presented here strongly disagree with this hypothesis, placing Oxyporhamphus deeply within the Hemiramphus clade. Several of the characters used by Dasilao et al. (1997) are related to gliding (in particular, a strengthened caudal complex for take-offs), and might be convergent features of gliding behavior.