Foraging behavior and Doppler shift compensation in echolocating hipposiderid bats, I-Iipposideros bicolor and I-Iipposideros speoris

1. Two hipposiderid bats,H. bicolor andH. speoris, were observed in their natural foraging areas in Madurai (South India). Both species hunt close together near the foliage of trees and bushes but they differ in fine structure of preferred hunting space:H. bicolor hunts within the foliage, especially whenH. speoris is active at the same time, whereasH. speoris never flies in dense vegetation but rather in the more open area (Fig. 1, Table 1). 2. Both species emit CF/FM-sounds containing only one harmonic component in almost all echolocation situations. The CF-parts of CF/FM-sounds are species specific within a band of 127–138 kHz forH. speoris and 147–159 kHz forH. bicolor (Tables 2 and 3). 3. H. speoris additionally uses a complex harmonic sound during obstacle avoidance and during laboratory tests for Doppler shift compensation.H. bicolor consistently emits CF/FM-sounds in these same situations (Fig. 2). 4. Both hipposiderid bats respond to Doppler shifts in the returning echoes by lowering the frequency of the emitted sounds (Fig. 3). However, Doppler compensations are incomplete as the emitted frequencies are decreased by only 55% and 56% (mean values) of the full frequency shifts byH. speoris andH, bicolor, respectively. 5. The differences in Doppler shift compensation, echolocating and hunting behavior suggest thatH. speoris is less specialized on echolocation with CF/FM-sounds thanH. bicolor

Ontogeny of sounds in the echolocating bat Hipposideros speoris

1. Young Hipposideros speoris emit multiharmonic sounds in groups of three to four notes. Newborns emit a relatively uniform pattern of FM- and FM/CF/FM-sounds. From ten days of age onwards the initial sound (first note) of a group is a FM-sound whereas the successive ones are CF/FM-sounds of consistently higher frequencies. At prevolant and volant stages of the bat's development most of the sound energy is concentrated in the second harmonic which is raised to the frequency range of the adults' CF/FM-sounds (127-138 kHz). Subsequently other harmonics disappear. 2. Harmonic components are suppressed or filtered out when they fall in a frequency range of approximately 65-75 kHz. This was found for bats of different ages regardless which fundamental frequency the suppressed harmonic components corresponded to, indicating a mechanical filtering process. These measurements coincide with the absence of the first harmonics in the same frequency range in the sounds of adults. 3. Temporal sound emission patterns were measured for bats of different ages. There was an increase in sound duration and an increase in the number of sounds (notes) per group as the bat matured to adulthood. 4. The sound emission of juveniles aids mothers in finding their young ones. Mothers located their infants even when the juveniles were displaced far from where they were left behind by their mothers. Behavioral experiments under both natural and captive conditions showed that the sound emission of young ones attracts mothers but do not give sufficient cues to allow the mother to discriminate their own from a group of young. 5. The ontogeny of the two types of sounds (CF/FM and complex harmonic FM) of adult Hipposideros speoris is discussed and compared with the vocalisations of other bat species

Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation

Bats ( Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one- fifth of extant species(1). Although recent studies unambiguously support bat monophyly(2-4) and consensus is rapidly emerging about evolutionary relationships among extant lineages(5-8), the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood(5,7-9). Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute(7-18), and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non- flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a 'flight first' hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding - fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under- branch hanging behaviour.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62816/1/nature06549.pd

The basipodium of Anthracobunodon weigelti HELLER, 1934 (Artiodactyla, Mammalia) from the middle Eocene Geiseltal near Halle (Germany): Das Basipodium von Anthracobunodon weigelti HELLER, 1934 (Artiodactyla, Mammalia) aus dem mittleren Eozän des Geiseltales bei Halle (Deutschland)

The carpus and tarsus are described of the middle Eocene haplobunodontid Anthracobunodon weigelti from the lignite beds of the Geiseltal (MP 13). The study is based on new methods of microradiography and computer-tomography which allow a classic and a three-dimensional investigation of morphological details. The reconstructed morphology of the basipodium is compared with other artiodactyls of the Eocene and interpreted phylogenetically. Anthracobunodon displays a paraxonic foot with typical artiodactyl astragalus and calcaneum. Navicular and cuboid are unfused. An entocuneiform and an ectocuneiform exist distally, which are probably fused with the mesocuneiform. The carpus displays the beginning of the paraxonic arrangement still without any fusion. The carpals are in two rows with four bones each. Five metacarpals are retained, the first of which is reduced to half the length of the others, the third is the longest. In the foot the main metatarsals have about the same length, the first metatarsus is reduced. Both extremities are characterised by hooflike third digits.Es werden die Hand- und Fußknochen des mitteleozänen Haplobunodontiden Anthracobunodon weigelti aus den Braunkohlenschichten des Geiseltales beschrieben (MP 13). Die Studie basiert auf neuen Methoden der Mikroradiographie und Computertomographie, die sowohl eine klassische als auch eine dreidimensionale Untersuchung morphologischer Details erlauben. Die rekonstruierte Morphologie des Basipodiums wird mit anderen Artiodactylen des Eozäns verglichen und phylogenetisch interpretiert. Anthracobunodon zeigt einen paraxonischen Fuß mit den für Artiodactylen typischen Astragalus und Calcaneus. Naviculare und Cuboid sind nicht verwachsen. Distal existiert ein Endocuneiforme und ein Ectocuneiforme, dasvermutlich mit dem Mesocuneiforme verwachsen ist. In der Handwurzel zeichnet sich der Beginn einer paraxonische Anordnung ab, die noch keine Verschmelzungen erkennen läßt. Der Carpus besteht aus zwei Reihen mit jeweils 4 Knochen. Es sind noch fünf Metacarpalia erhalten, wobei das erste auf die halbe Länge der anderen reduziert ist. Längstes Metacarpale ist das dritte. Am Fuß sind drittes und viertes Metatarsale fast gleich lang, das erste ist reduziert. Beide Extremitäten sind durch Hufe als Endphalangen charakterisiert

Substrate-triggered position switching of TatA and TatB during Tat transport in <i>Escherichia coli</i>

The twin-arginine protein transport (Tat) machinery mediates the translocation of folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. The Escherichia coli Tat system comprises TatC and two additional sequence-related proteins, TatA and TatB. The active translocase is assembled on demand, with substrate-binding at a TatABC receptor complex triggering recruitment and assembly of multiple additional copies of TatA; however, the molecular interactions mediating translocase assembly are poorly understood. A 'polar cluster' site on TatC transmembrane (TM) helix 5 was previously identified as binding to TatB. Here, we use disulfide cross-linking and molecular modelling to identify a new binding site on TatC TM helix 6, adjacent to the polar cluster site. We demonstrate that TatA and TatB each have the capacity to bind at both TatC sites, however in vivo this is regulated according to the activation state of the complex. In the resting-state system, TatB binds the polar cluster site, with TatA occupying the TM helix 6 site. However when the system is activated by overproduction of a substrate, TatA and TatB switch binding sites. We propose that this substrate-triggered positional exchange is a key step in the assembly of an active Tat translocase

Apolipoprotein E mediates evasion from hepatitis C virus−neutralizing antibodies

Background &#38; Aims Efforts to develop an effective vaccine against hepatitis C virus (HCV) have been hindered by the propensity of the virus to evade host immune responses. HCV particles in serum and in cell culture associate with lipoproteins, which contribute to viral entry. Lipoprotein association has also been proposed to mediate viral evasion of the humoral immune response, though the mechanisms are poorly defined. Methods We used small interfering RNAs to reduce levels of apolipoprotein E (apoE) in cell culture−derived HCV−producing Huh7.5-derived hepatoma cells and confirmed its depletion by immunoblot analyses of purified viral particles. Before infection of naïve hepatoma cells, we exposed cell culture−derived HCV strains of different genotypes, subtypes, and variants to serum and polyclonal and monoclonal antibodies isolated from patients with chronic HCV infection. We analyzed the interaction of apoE with viral envelope glycoprotein E2 and HCV virions by immunoprecipitation. Results Through loss-of-function studies on patient-derived HCV variants of several genotypes and subtypes, we found that the HCV particle apoE allows the virus to avoid neutralization by patient-derived antibodies. Functional studies with human monoclonal antiviral antibodies showed that conformational epitopes of envelope glycoprotein E2 domains B and C were exposed after depletion of apoE. The level and conformation of virion-associated apoE affected the ability of the virus to escape neutralization by antibodies. Conclusions In cell-infection studies, we found that HCV-associated apoE helps the virus avoid neutralization by antibodies against HCV isolated from chronically infected patients. This method of immune evasion poses a challenge for the development of HCV vaccines