Differentiation and adaptive radiation of amphibious gobies (Gobiidae: Oxudercinae) in semi-terrestrial habitats

During several surveys made in the region of the lower Fly River and delta, Papua New Guinea, nine species of oxudercine gobies (Gobiidae: Oxudercinae) were recorded: Boleophthalmus caeruleomaculatus, Oxuderces wirzi, Periophthalmodon freycineti, Periophthalmus darwini, Periophthalmus novaeguineaensis, Periophthalmus takita, Periophthalmus weberi, Scartelaos histophorus and Zappa confluentus. An exploratory multivariate analysis of their habitat conditions discriminated five guilds, differentially distributed in habitats with different quantities of environmental water and three guilds corresponding to different levels of salinity. A partial correspondence between phylogenetic and ecological categories suggested the presence of parallel adaptive radiations within different genera. In particular, the species found in the most terrestrial habitats (P. weberi) was also found in the widest range of conditions, suggesting that colonization of extreme semi-terrestrial and freshwater habitats by this species was facilitated by eurytypy. It is proposed that these findings provide insight into convergent adaptations for the vertebrate eco-evolutionary transition from sea to land.     

Phylogeography of Walton’s Mudskipper,Periophthalmus waltoni Koumans, 1941 (Perciformes: Gobiidae), from the Persian Gulf and Gulf of Oman

Mudskippers are amphibious air breathing fish with terrestrial adaptations in contrast to entirely aquatic fish. They are adapted to living on mudflats and show morphological, physiological, and behavioural features that could affect their phylogeny and phylogeography. A comparative genetic analysis was carried out on 100 specimens of the mudskipper Periophthalmus waltoni Koumans, 1941 from eight different sites along the coast of the Persian Gulf and Gulf of Oman. Phylogeographic inference based on two mitochondrial markers (Cyt b and D-loop) suggests that P. waltoni populations are divided into two well-divergent clades western and eastern. This is likely related to the geohydrological history of the area during the last Pleistocene glaciations. The regional phylogeographies are apparently also influenced by ecological and geographical barriers such as salinity, water current, and the geographic position of the Strait of Hormuz.     

Periophthalmus spilotus, a new species of mudskipper from Sumatra (Gobiidae: Oxudercinae)

A new species of mudskipper,Periophthalmus spilotus, is described on the basis of 16 specimens from Sumatra, Indonesia. It differs from other species ofPeriophthalmus by the following combination of characters: pelvic fins totally united into rounded disk; first dorsal fin high, greyish, no spots on fin nor elongate spines; second dorsal fin typically with 14 total elements; anal fin typically with either 14 or 15 total elements; length of anal-fin base 21.8–29.0% SL; and length of second dorsal-fin base 22.5–26.7% SL. This species is most similar to, and probably most closely related to,P. chrysospilos.     

Gross and fine anatomy of the respiratory vasculature of the mudskipper,Periophthalmodon schlosseri (Gobiidae: Oxudercinae)

To illustrate vascular modification accompanying transition from aquatic to amphibious life in gobies, we investigated the respiratory vasculatures of the gills and the bucco‐opercular cavities in one of the most terrestrially‐adapted mudskippers, Periophthalmodon schlosseri, using the corrosion casting technique. The vascular system of Pn. schlosseri retains the typical fish configuration with a serial connection of the gills and the systemic circuits, suggesting a lack of separation of O₂‐poor systemic venous blood and O₂‐rich effluent blood from the air‐breathing surfaces. The gills appear to play a limited role in gas exchange, as evidenced from the sparsely‐spaced short filaments and the modification of secondary lamellar vasculature into five to eight parallel channels that are larger than red blood cell size, unlike the extensive sinusoidal system seen in purely water‐breathing fishes. In contrast, the epithelia of the bucco‐opercular chamber, branchial arches, and leading edge of the filaments are extensively laden with capillaries having a short (<10 μm) diffusion distance, which strongly demonstrate the principal respiratory function of these surfaces. These capillaries form spiral coils of three to five turns as they approach the epithelial surface. The respiratory capillaries of the bucco‐opercular chamber are supplied by efferent blood from the gills and drained by the systemic venous pathway. We also compared the degree of capillarization in the bucco‐opercular epithelia of Pn. schlosseri with that of the three related intertidal‐burrowing gobies (aquatic, non‐air‐breathing Acanthogobius hasta; aquatic, facultative air‐breathing Odontamblyopus lacepedii; amphibious air‐breathing Periophthalmus modestus) through histological analysis. The comparison revealed a clear trend of wider distribution of denser capillary networks in these epithelia with increasing reliance on air breathing, consistent with the highest aerial respiratory capacity of Pn. schlosseri among the four species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.