Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae)

Habitat shifts are implicated as the cause of many vertebrate radiations, yet relatively few empirical studies quantify patterns of diversification following colonization of new habitats in fishes. The pufferfishes (family Tetraodon‐tidae) occur in several habitats, including coral reefs and freshwater, which are thought to provide ecological opportunity for adaptive radiation, and thus provide a unique system for testing the hypothesis that shifts to new habitats alter diversification rates. To test this hypothesis, we sequenced eight genes for 96 species of pufferfishes and closely related porcupine fishes, and added 19 species from sequences available in GenBank. We time‐calibrated the molecular phylogeny using three fossils, and performed several comparative analyses to test whether colonization of novel habitats led to shifts in the rate of speciation and body size evolution, central predictions of clades experiencing ecological adaptive radiation. Colonization of freshwater is associated with lower rates of cladogenesis in pufferfishes, although these lineages also exhibit accelerated rates of body size evolution. Increased rates of cladogenesis are associated with transitions to coral reefs, but reef lineages surprisingly exhibit significantly lower rates of body size evolution. These results suggest that ecological opportunity afforded by novel habitats may be limited for pufferfishes due to competition with other species, constraints relating to pufferfish life history and trophic ecology, and other factors.     

First record of Potamogeton×salicifolius for Italy,with isozyme evidence for plants collected in Italy and Sweden

Abstract

Potamogeton×salicifolius, a hybrid between P. lucens and P. perfoliatus, is identified as a new taxon for Italy. This is the first record of this hybrid from southern Europe. The Italian sample was studied in cultivation and compared with a living specimen of P.×salicifolius from Sweden, where the hybrid is rather widespread. In addition to morphological features, the most compelling evidence for the hybrid origin of these plants came from the isozyme analysis. The additive “hybrid” banding patterns of the five enzyme systems studied indicate inheritance from P. lucens and P. perfoliatus. The distribution of this hybrid in Europe coincides with the areas most severely affected by the Late Pleistocene glaciation. The relationships between environmental conditions, history of the habitat and rise of hybrids are discussed.     

Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes,Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge

We describe two new, closely related species of toothed Brachyhypopomus (Hypopomidae: Gymnotiformes: Teleostei) from the central Amazon basin and create a new subgenus for them. Odontohypopomus, new subgenus of Brachyhypopomus, is diagnosed by (1) small teeth present on premaxillae; (2) medialmost two branchiostegal rays thin with blades oriented more vertically than remaining three rays; (3) background color in life (and to lesser extent in preservation) distinctly yellowish with head and sides peppered with small, widely spaced, very dark brown stellate chromatophores that greatly contrast with light background coloration; (4) a dark blotch or bar of subcutaneous pigment below the eye; (5) electric organ discharge waveform of very long duration (head-positive phase approx. 2 milliseconds or longer, head-negative phase shorter or absent) and slow pulse repetition rate (3–16 Hz). The type species of the new subgenus, Brachyhypopomus (Odontohypopomus) walteri sp. n., is diagnosed by the following additional character states: (1) subcutaneous dark pigment at base of orbit particularly prominent, (2) body semi-translucent and nearly bright yellow background coloration in life, (3) a biphasic electric organ discharge (EOD) waveform of very long duration (between 3.5 and 4 milliseconds at 25° C) with head-positive first phase significantly longer than second head-negative phase in both sexes. Brachyhypopomus (Odontohypopomus) bennetti sp. n. is diagnosed by two character states in addition to those used to diagnose the subgenus Odontohypopomus: (1) a deep electric organ, visible as large semi-transparent area, occupying approximately 14–17% body depth directly posterior to the abdominal cavity in combination with a short, but deep, caudal filament, and (2) a monophasic, head-positive EOD waveform, approximately 2.1 milliseconds in duration in both sexes. These are the only described rhamphichthyoid gymnotiforms with oral teeth, and Brachyhypopomus bennetti is the first Brachyhypopomus reported to have a monophasic (head-positive) EOD waveform. Unlike biphasic species, the waveform of its EOD is largely unaffected by tail damage from predators. Such injuries are common among specimens in our collections. This species’ preference for floating meadow habitat along the major channels of the Amazon River basin may put it at particularly high risk of predation and “tail grazing.”     

Systematics of a widely distributed western North American springsnail,Pyrgulopsis?micrococcus (Caenogastropoda,Hydrobiidae), with descriptions?of?three new congeners

We describe three new species of springsnails (genus Pyrgulopsis) from the Amargosa River basin, California and Nevada (P. licina sp. n., P. perforata sp. n., P. sanchezi sp. n.), each of which was previously considered to be part of P. micrococcus. We also restrict P. micrococcus to its type locality area (Oasis Valley) and redefine a regional congener, P. turbatrix, to include populations from the central Death Valley region and San Bernardino Mountains that had been previously identified as P. micrococcus. The five species treated herein form genetically distinct lineages that differ from each other by 4.2–12.6% for mtCOI and 5.2–13.6% for mtNDI (based on previously published and newly obtained data), and are diagnosable by shell and/or penial characters. The new molecular data presented herein confirm sympatry of P. licina and P. sanchezi in Ash Meadows (consistent with morphological evidence) and delineate an additional lineage of P. micrococcus (in the broad sense) that we do not treat taxonomically owing to the paucity of morphological material. Conservation measures are needed to ensure the long term persistence of populations of P. micrococcus and a genetically differentiated lineage of P. sanchezi which live in disturbed habitats on private lands.     

A new species of Gyraulus (Gastropoda: Planorbidae) from Ancient Lake Lugu,Yunnan-Guizhou Plateau,Southwest China

A new aberrant species of the planorbid genus Gyraulus, Gyraulus luguhuensis n. sp., is described from Lake Lugu (Lugu-hu, in Chinese), Southwest China. The generic assignment with Gyraulus is based on features of the genital anatomy that are characteristic for members of that genus, in particular the presence of a chitinized penial stylet. Gyraulus luguhuensis n. sp. differs from most other congeners by its large, thick shell with an elevated spire. Similarly, aberrant shells are known from congeners in other Ancient Lakes worldwide indicating a potentially convergent evolution of shell characteristics in exclusively lacustrine species. Gyraulus luguhuensis differs from other lacustrine Gyraulus species with similarly large shells in having a sub-terminal penis pore and an unkeeled shell.     

Morphological and morphometrical description of the glochidia of Westralunio carteri Iredale, 1934 (Bivalvia: Unionoida: Hyriidae)

Most freshwater mussel (Bivalvia: Unionoida) larvae (glochidia in Margaritiferidae, Hyriidae and Unionidae) are fish parasites. Knowledge of the larval morphology and the mechanism of release in freshwater mussels is useful in species systematics and ecology. Westralunio carteri is the only unionoid from south-western Australia. Little information is available on its biology and its glochidia have never been described. The aim of this study was to describe the glochidia of W. carteri and method of their release. Glochidia within vitelline membranes were embedded in mucus which extruded from exhalent siphons of females during spring/summer; they then hatched from vitelline membranes but remained tethered by a larval thread and began characteristically “winking”. Shells (n=120) were subtriangular, 308 μm long (±0.83 SE), 251 μm high (±0.73 SE) and had a hinge length of 212 μm (±0.78 SE). Larval teeth were singular with interlocking cusps and convex or concave basal protuberances on opposing valves.     

THE DISTRIBUTION AND ECOLOGY OF TWO MULLET SPECIES IN SOME FRESH WATER RIVERS IN THE EASTERN CAPE,SOUTH AFRICA

SUMMARY

Data on the relative abundance, penetration and breeding biology of the freshwater mullet Mugil cephalus and the flathead mullet Mugil cephalus in the freshwater reaches of some Eastern Cape coastal rivers are described. The differences found between the two species indicate that Myxus capensis is more specialized for a catadromous life history in an unstable riverine environment. Evidence showing the importance of the freshwater phase for the latter species is given and the disastrous effects of the erection of barriers to fish movement are stressed.