Ecological niche and phylogeny: the highly complex echolocation behavior of the trawling long-legged bat, Macrophyllum macrophyllum

Bats produce echolocation signals that reflect the sensory tasks they perform. In open air or over water, bats encounter few or no background echoes (clutter). Echolocation of such bats is the primary cue for prey perception and varies with the stage of approach to prey, typically comprising search, approach, and terminal group calls. In contrast, bats that glean stationary food from rough surfaces emit more uniform calls without a distinct terminal group. They use echolocation primarily for orientation in space and mostly need additional sensory cues for finding food because clutter echoes overlap strongly with food echoes. Macrophyllum macrophyllum is the only Neotropical leaf-nosed bat (Phyllostomidae) that hunts in clutter-poor habitat over water. As such, we hypothesized that, unlike all other members of its family, but similar to other trawling and aerial insectivorous bats, M. macrophyllum can hunt successfully by using only echolocation for prey perception. In controlled behavioral experiments on Barro Colorado Island, Panamá, we confirmed that echolocation alone is sufficient for finding prey in M. macrophyllum. Furthermore, we showed that pattern and structure of echolocation signals in M. macrophyllum are more similar to aerial and other trawling insectivorous bats than to close phylogenetic relatives. Particularly unique among phyllostomid bats, we found distinct search, approach, and terminal group calls in foraging M. macrophyllum. Call structure, however, consisting of short, multiharmonic, and steep frequency-modulated signals, closely resembled those of other phyllostomid bats. Thus, echolocation behavior in M. macrophyllum is shaped by ecological niche as well as by phylogeny.     

Multimodal signals,imperfect information,and identification of sex in red-backed salamanders (<Emphasis Type="Italic">Plethodon cinereus</Emphasis>)

Theoretical treatments and empirical studies both suggest that signals that occur in multiple sensory modes have superior detectabilities, discriminabilities, and memorabilities. There is also an intuitive link between signal detectability, discriminability, and memorability and the quality of information that is transferred via the signaler. We investigated the role of information quality and sensory modality in the sexual identification of intruding conspecifics by territorial male red-backed salamanders (Plethodon cinereus). Our results imply that these salamanders are able to discriminate between intruding male and female conspecifics (based on the allocation of aggression) in bimodal scenarios (vision and olfaction) even under situations in which the information available about the intruders sexual identities is reduced in quality. In unimodal scenarios (olfaction only), male residents exhibited heightened levels of aggression toward male secretions and reduced levels of aggression toward female secretions. In unimodal scenarios where information pertaining to the sex of the stimulus was reduced in quality, male residents displayed intermediate levels of aggression relative to the responses that male and female stimuli received respectively. Although resident males touched bimodal stimuli significantly more than they touched unimodal stimuli, we were unable to find support for the notion that sensory modality greatly influences how male resident red-backed salamanders allocate aggression toward intruding male versus female stimuli.Communicated by H. Kokko     

Cave molly females (Poecilia mexicana, Poeciliidae, Teleostei) like well-fed males

We examined the preference of Atlantic molly females (Poecilia mexicana) to associate with a well-fed or a starved male in simultaneous choice tests. Females from three different populations were tested in three treatments: (1) the females could choose on the basis of multiple cues from the males (visual plus non-visual); (2) only non-visual cues could be perceived in darkness, (3) only visual cues were presented. The three tested populations differ clearly in their ecology: one population occurs in a typical river habitat, the second one in a milky sulfur creek outside a cave, and the third population occurs in a cave habitat (cave molly). In the river-dwelling population, females never showed a preference. In the population from the sulfur creek, females preferred to associate with the well-nourished male when visual cues from the males were available. Only cave molly females exhibited a strong preference for well-nourished males in all treatments. A morphological comparison demonstrated that wild-caught males from river habitats are typically in a good nutritional state. In the sulfur creek, males showed signs of starvation. Cave molly males were in an even worse nutritional state. In the cave population, saturated males probably indicate high fitness, thereby driving the evolution of the preference for good male nutritional state.Communicated by K. Lindström     

Will Simplified Modalities and Procedures Make More Small-Scale Forestry Projects Viable Under the Clean Development Mechanism?

Simplified modalities and procedures (M&P) are expected to increase the viability of small-scale project activities under the Clean Development Mechanism (CDM). A small-scale afforestation or reforestation (AR) project is defined as a project removing less than 8 kilotons of carbon dioxide equivalent (CO₂e) per year. Depending on the project type and the method for measuring scale, 8 kilotons of CO₂e per year correspond to highly diverse areas, possibly ranging from 200 to 6000 ha. Using a model to calculate the minimum project scale above which the CDM is a positive financial incentive for eligible AR project activities, the paper analyzes whether a reduction of transaction costs under simplified M&P will be a sufficient incentive to motivate small-scale participation in the CDM. Model results show that, even under optimistic assumptions on carbon market conditions and transaction costs, small-scale project activities will not benefit from simplified M&P. Results also show that project activities removing more than 8 kilotons of CO₂e per year and registered as small-scale would be the ones that could benefit the most from simplified M&P. It is concluded that the participation of small-scale project activities to the CDM requires more than simplified M&P, the price of expiring Certified Emission Reductions being one of the most critical parameters.     

The evolutionary origin of auditory receptors in Tettigonioidea: the complex tibial organ of Schizodactylidae

Audition in insects is of polyphyletic origin. Tympanal ears derived from proprioceptive or vibratory receptor organs, but many questions of the evolution of insect auditory systems are still open. Despite the rather typical bauplan of the insect body, e.g., with a fixed number of segments, tympanal ears evolved at very different places, but only ensiferans have ears at the foreleg tibia, located in the tibial organ. The homology and monophyly of ensiferan ears is controversial, and no precursor organ was unambiguously identified for auditory receptors. The latter can only be identified by comparative study of recent atympanate taxa. These atympanate taxa are poorly investigated. In this paper, we report the neuroanatomy of the tibial organ of Comicus calcaris (Irish 1986), an atympanate Schizodactylid (splay-footed cricket). This representative of a Gondwana relict group has a tripartite sensory organ, homologous to tettigoniid ears. A comparison with morphology-based cladistic phylogeny indicates that the tripartite neuronal organization present in the majority of Tettigonioidea presumably preceded evolution of a hearing sense in the Tettigonioidea. Furthermore, the absence of a tripartite organ in Grylloidea argues against a monophyletic origin and homology of the cricket and katydid ears. The tracheal attachment of sensory neurons typical for ears of Tettigonioidea is present in C. calcaris and may have facilitated cooption for auditory function. The functional auditory organ was presumably formed in evolution by successive non-neural modifications of trachea and tympana. This first investigation of the neuroanatomy of Schizodactylidae suggests a non-auditory chordotonal organ as the precursor for auditory receptors of related tympanate taxa and adds evidence for the phylogenetic position of the group.     

Use of heterospecific cues by the lizard Platysaurus broadleyi for food location

Flat lizards (Platysaurus broadleyi) at Augrabies Falls National Park, South Africa, are restricted to rocky terrain where the predominant tree is the Namaqua fig (Ficus cordata cordata). P. broadleyi readily feeds on Namaqua figs when they are available, and the lizards sometimes form large (maximum recorded=134) congregations under fruiting fig trees. The distance lizards travel to fruiting trees also exceed normal daily foraging distances. Location of fruiting fig trees by a lizard can have a high pay-off because figs are energetically rich and trees fruit irregularly and asynchronously, resulting in a resource that is available, but unpredictable in time and space. The prediction that bird activity in fig trees provides a cue to the presence of ripe figs was tested experimentally. By placing cages containing birds and empty control cages in trees devoid of fruit, we demonstrated that P. broadleyi are drawn to fig trees with high bird congregations. We also tested if the presence of a fig tree was necessary to draw lizards to bird congregations by placing cages containing birds and empty control cages in a matched-pairs design on rock away from trees. Namaqua fig trees were not necessary to draw lizards to bird congregations. Received: 12 May 1998 / Accepted after revision: 30 November 1998     

Why do <Emphasis Type="Italic">Manduca sexta</Emphasis> feed from white flowers? Innate and learnt colour preferences in a hawkmoth

Flower colour is an important signal used by flowering plants to attract pollinators. Many anthophilous insects have an innate colour preference that is displayed during their first foraging bouts and which could help them locate their first nectar reward. Nevertheless, learning capabilities allow insects to switch their colour preferences with experience and thus, to track variation in floral nectar availability. Manduca sexta, a crepuscular hawkmoth widely studied as a model system for sensory physiology and behaviour, visits mostly white, night-blooming flowers lacking UV reflectance throughout its range in the Americas. Nevertheless, the spectral sensitivity of the feeding behaviour of naïve moths shows a narrow peak around 450 nm wavelengths, suggesting an innate preference for the colour blue. Under more natural conditions (i.e. broader wavelength reflectance) than in previous studies, we used dual choice experiments with blue- and white-coloured feeders to investigate the innate preference of naïve moths and trained different groups to each colour to evaluate their learning capabilities. We confirmed the innate preference of M. sexta for blue and found that these moths were able to switch colour preferences after training experience. These results unequivocally demonstrate that M. sexta moths innately prefer blue when presented against white flower models and offer novel experimental evidence supporting the hypothesis that learning capabilities could be involved in their foraging preferences, including their widely observed attraction to white flowers in nature.     

Natterer’s bat (Myotis nattereri Kuhl, 1818) hawks for prey close to vegetation using echolocation signals of very broad bandwidth

We present a hitherto unknown prey perception strategy in bats: Myotis nattereri (Vespertilionidae, Chiroptera) is able to perceive prey by echolocation within a few centimeters of echo-cluttering vegetation, by using frequency-modulated search signals of very large bandwidth (up to 135 kHz). We describe the species’ search behavior and echolocation repertoire from the field and from experiments in a flight tent. In the field, bats varied signal parameters in relation to their distance from vegetation and usually flew close to vegetation. In the flight tent, M. nattereri detected and localized prey by echolocation alone as close as 5 cm from vegetation. Apparently, the bats were able to tolerate some overlap between prey and clutter echoes. Passive prey cues (vision, olfaction, prey-generated sounds) were not used in prey perception. The bats selected prey by size. The animals performed aerial catches and produced approach sequences typical for aerial hawking bats, but were able to do so within a few centimeters of the substrate. M. nattereri thus has access to silent, suspended prey very close to vegetation (e.g., spiders, and caterpillars on threads). Received: 29 September 1999 / Received in revised form: 12 February 2000 / Accepted: 12 February 2000     

Fruit detection and discrimination by small fruit-eating bats (Phyllostomidae): echolocation call design and olfaction

We studied the role of echolocation and other sensory cues in two small frugivorous New World leaf-nosed bats (Phyllostomidae: Artibeus watsoni and Vampyressa pusilla) feeding on different types of fig fruit. To test which cues the bats need to find these fruit, we conducted behavioral experiments in a flight cage with ripe and similar-sized figs where we selectively excluded vision, olfaction, and echolocation cues from the bats. In another series of experiments, we tested the discrimination abilities of the bats and presented sets of fruits that differed in ripeness (ripe, unripe), size (small, large), and quality (intact(infested with caterpillars). We monitored the bats' foraging and echolocation behavior simultaneously. In flight, both bat species continuously emitted short (<2 ms), multi-harmonic, and steep frequency-modulated (FM) calls of high frequencies, large bandwidth, and very low amplitude. Foraging behavior of bats was composed of two distinct stages: search or orienting flight followed by approach behavior consisting of exploration flights, multiple approaches of a selected fruit, and final acquisition of ripe figs in flight or in a brief landing. Both bat species continuously emitted echolocation calls. Structure and pattern of signals changed predictably when the bats switched from search or orienting calls to approach calls. We did not record a terminal phase before final acquisition of a fruit, as it is typical for aerial insectivorous bats prior to capture. Both bat species selected ripe over unripe fruit and non-infested over infested fruit. Artibeus watsoni preferred larger over smaller fruit. We conclude from our experiments, that the bats used a combination of odor-guided detection together with echolocation for localization in order to find ripe fruit and to discriminate among them.     

Experimental assessment of sensory modalities of coral-reef fish larvae in the recognition of their settlement habitat

One of the great mysteries of coral-reef fish ecology is how larvae locate the relatively rare patches of coral-reef habitat on which they settle. The present study aimed to estimate, by experiments in aquaria, the sensory modalities of coral-reef fish larvae for senses used in searching for their species settlement habitat. Larval recognition of settlement habitat can be based on the detection of conspecifics and/or of characteristics of coral habitat using visual, chemical and mechanical cues. For this study, larvae were captured with crest nets and were then introduced into experimental tanks that allowed testing of each type of cue separately (visual, chemical or mechanical cues). Among the 18 species studied, 13 chose their settlement habitat due to the presence of conspecifics and not based on the characteristics of coral habitat, and 5 species did not move toward their settlement habitat (e.g. Scorpaenodes parvipinnis, Apogon novemfasciatus). Among the different sensory cues tested, two species used the three types of cues (Parupeneus barberinus and Ctenochaetus striatus: visual, chemical and mechanical cues), six used two types (e.g. Myripristis pralinia: visual and chemical cues; Naso unicornis: visual and mechanical cues), and five used one type (e.g. Chrysiptera leucopoma: visual cues; Pomacentrus pavo: chemical cues). These results demonstrate that many coral-reef fish larvae could in practice use sensory cues for effective habitat selection at settlement, and have the ability to discriminate species-specific sensory cues.Communicated by J. Krause