Evidence of auditory insensitivity to vocalisation frequencies in two frogs

The emergence and maintenance of animal communication systems requires the co-evolution of signal and receiver. Frogs and toads rely heavily on acoustic communication for coordinating reproduction and typically have ears tuned to the dominant frequency of their vocalizations, allowing discrimination from background noise and heterospecific calls. However, we present here evidence that two anurans, Brachycephalus ephippium and B. pitanga, are insensitive to the sound of their own calls. Both species produce advertisement calls outside their hearing sensitivity range and the inner ear is partly undeveloped, which accounts for their lack of high-frequency sensitivity. Unheard by the intended receivers, calls are not beneficial to the emitter and should be selected against because of the costs associated with signal production. We suggest that protection against predators conferred by their high toxicity might help to explain why calling has not yet disappeared, and that visual communication may have replaced auditory in these colourful, diurnal frogs

Finding a place to live: conspecific attraction affects habitat selection in juvenile green and golden bell frogs

Conspecific attraction plays an important role in habitat selection of several taxa and can affect and determine distribution patterns of populations. The behaviour is largely studied and widespread among birds, but in amphibians, its occurrence seems limited to breeding habitats of adults and gregarious tadpoles. The Australian green and golden bell frogs (<i>Litoria aurea</i>) have suffered considerable shrinking of their original distribution in south-eastern Australia since the 1970s. Currently, with only about 40 populations remaining, the species is considered nationally threatened. In natural conditions, these frogs are aggregated in the landscape and do not seem to occupy all suitable ponds within the occurrence area. To date, studies focusing on the frogs' habitat have failed in finding a general habitat feature that explains current or past occupancy. This led us to the hypothesis that social cues may play a key role in habitat selection in this species. Using two choice experiments, we tested the preference of juvenile green and golden bell frogs for habitats containing cues of conspecifics of similar size versus habitats without conspecific cues. Tested frogs did not show a preference for habitats containing only scent from conspecifics but did prefer habitats where conspecifics were present. Our results show that conspecific attraction is a determining factor in juvenile green and golden bell frog habitat selection. To our knowledge, this is the first time the behaviour is shown to occur in juvenile frogs in the habitat selection context. From a conservation management point of view, the behaviour may help to explain the failure of reintroductions to areas where the frogs have been extinct, and the non-occupation of suitable created habitats in areas where they still inhabit and develop appropriated management strategies

Nesseltalgraben, a new reference section of the last glacial period in southern Germany

In the northern Alpine region only a few lacustrine sediment sequences are known from the period of the last glacial, regionally assigned as Würmian. Even less is known about Alpine palaeoenvironments prior to the last glacial maximum (LGM). The recently discovered sediment sections at the Nesseltalgraben site (northern Alps, southern Germany) presented here, comprise an approximately 27-m-high, predominantly lacustrine composite profile below coarse clastic sediments assigned to the LGM and underlain by Permian–Triassic evaporitic and sandy clayey sediments of the Haselgebirge and Werfen-Formation. The Würmian lake sediments consist of carbonate mud layers representing cooler phases, and organic rich layers (compressed peat, organic mud), that were deposited during warmer periods. Bulk organic geochemical analyses suggest that predominantly algal organic matter was deposited during the cooler periods, while higher fractions of terrestrial vascular plants were admixed during warmer phases. A diamict represents an erosional unconformity and cuts the sediment sequence into a lower and an upper part. Paleomagnetic, palynostratigraphic and radiocarbon analyses place the lower part into the Marine Isotope Stage (MIS) 5c (Lower Würmian), while the upper part covers at least the period from 45 to 31 ka cal BP (MIS 3, Middle Würmian). Different explanations for the origin and spatiotemporal extent of the palaeolake are discussed. The most plausible sedimentary deposition is the formation of the small-scaled lake in a sinkhole in the evaporitic Haselgebirge Formation. The results highlight the significance of the Nesseltalgraben site as a new reference section of the last glacial period in the Northern Calcareous Alps and call for the necessity of further geochronological and paleoenvironmental studies at that site