Adaptive mechanisms underlying the bat biosonar behavior

For survival, bats of the suborder Microchiropetra emit intense ultrasonic pulses and analyze the weak returning echoes to extract the direction, distance, velocity, size, and shape of the prey. Although these bats and other mammals share the common layout of the auditory pathway and sound coding mechanism, they have highly developed auditory systems to process biologically relevant pulses at the expense of a reduced visual system. During this active biosonar behavior, they progressively shorten the pulse duration, decrease the amplitude and pulse-echo gap as they search, approach and finally intercept the prey. Presumably, these changes in multiple pulse parameters throughout the entire course of hunting enable them to extract maximal information about localized prey from the returning echoes. To hunt successfully, the auditory system of these bats must be less sensitive to intense emitted pulses but highly sensitive to weak returning echoes. They also need to recognize and differentiate the echoes of their emitted pulses from echoes of pulses emitted by other conspecifics. Past studies have shown the following mechanical and neural adaptive mechanisms underlying the successful bat biosonar behavior: (1) Forward orienting and highly mobile pinnae for effective scanning, signal reception, sound pressure transformation and mobile auditory sensitivity; (2) Avoiding and detecting moving targets more successfully than stationary ones; (3) Coordinated activity of highly developed laryngeal and middle ear muscles during pulse emission and reception; (4) Mechanical and neural attenuation of intense emitted pulses to prepare for better reception of weak returning echoes; (5) Increasing pulse repetition rate to improve multiple-parametric selectivity to echoes; (6) Dynamic variation of duration selectivity and recovery cycle of auditory neurons with hunting phase for better echo analysis; (7) Maximal multiple-parametric selectivity to expected echoes returning within a time window after pulse emission; (8) Pulse-echo delaysensitive neurons in higher auditory centers for echo ranging; (9) Corticofugal modulation to improve on-going multiple-parametric signal processing and reorganize signal representation, and (10) A large area of the superior colliculus, pontine nuclei and cerebellum that is sensitive to sound for sensori-motor integration. All these adaptive mechanisms facilitate the bat to effectively extract prey features for successful hunting.     

吸血蝙蝠食性特化及其研究现状

翼手目动物（蝙蝠）的食性多样性丰富,其食物包括昆虫、鱼类、两栖动物、爬行动物、鸟类、哺乳动物、植物果实、花、花粉、花蜜、叶片和血液等。其中,大约70%的蝙蝠主要以昆虫为食,而以血液为食的吸血蝙蝠只有3种,它们是哺乳动物中唯一的仅以血液为食的动物类群。因此,吸血蝙蝠是研究动物食性演化的重要模式动物。本文综述了吸血蝙蝠在形态学、生理学、行为学、感觉系统和肠道微生物等方面的研究,指出了吸血蝙蝠食性特化的适应性特征。随着普通吸血蝠高质量基因组的公布,我们将有机会探究食性相关基因在吸血蝙蝠中的功能改变,阐明动物食性转变的分子机理。本文将为吸血蝙蝠和其它动物食性转变的研究提供有益的参考。     

云南蒙自钳嘴鹳夜栖地利用及夜栖树选择

动物对夜栖地选择的灵活程度是其分布和扩散的重要因素之一。钳嘴鹳(Anastomus oscitans)为中国新分布种,要了解其扩散趋势,掌握其夜栖地需求至关重要。2015年11月至2018年7月在云南蒙自坝区,使用卫星跟踪技术对6只钳嘴鹳进行了夜栖地利用和夜栖树选择研究,结果表明:(1)钳嘴鹳可以在多种生境中夜栖,包括林地、沼泽、岛屿等。从群体水平上分析,钳嘴鹳主要夜栖于沼泽中,利用率为(51.19±12.34)%,其次为林地(31.55±11.34)%和岛屿(17.26±5.70)%;从个体水平上来看,不同钳嘴鹳的夜栖地利用方式差异较大,其中4只主要利用沼泽,而另外2只主要利用林地;(2)随机森林分析表明:影响钳嘴鹳夜栖树选择的首要因子为距觅食地距离,其次为树高、地径和最低枝高度,而人为干扰因子的影响较弱。综合来看,钳嘴鹳对夜栖地类型以及夜栖树均表现出了极强的适应性和可塑性,这可能是其能够快速扩散的重要原因之一。同时也表明夜栖树并不能成为一个有力的限制因子,钳嘴鹳有可能继续向国内的南方湿地区扩散。     

ACOUSTIC SIGNALS OF THE NOCTURNAL LIZARD GEKKO GECKO: ANALYSIS OF THE ‘LONG COMPLEX SEQUENCE’

ABSTRACT

Four types of vocalizations of the nocturnal lizard Gekko gecko (the ‘Tokay’) are described. A bark of intimidation, distress calls, a short not very intense call, apparently related to sexual inter-action, and a long, complex sequence. This ‘long sequence’ is considered to be a territorial proclamation which also functions as a mating-call. It has been analysed in detail with special emphasis on the intra-individual variations. The mean duration of this sequence is 22.3 s, the intensity is 70 dB at 1m and the maximum of energy is between 300 and 4000 Hz. This sequence is composed of three phases. The first one consists of several multipulse sounds called ‘rattles’, the second of bi-motifs which sound like a two syllable tok-kay, and the third, not always present, is a kind of ‘grumble’. The number of motifs and the occurrence of the third phase may vary but the duration of the motifs is relatively stable.     

Resource selection by Indiana bats during the maternity season

Little information exists on resource selection by foraging Indiana bats (Myotis sodalis) during the maternity season. Existing studies are based on modest sample sizes because of the rarity of this endangered species and the difficulty of radio-tracking bats. Our objectives were to determine resource selection by foraging Indiana bats during the maternity season and to compare resource use between pregnant and lactating individuals. We used an information theoretic approach with discrete choice modeling based on telemetry data to evaluate our hypotheses that land cover, percent canopy cover, distance to water, and prescribed fire affected the relative probability a point was used by a foraging Indiana bat. We fit models for individual bats and a population-level model based on all individuals with a random factor to account for differences in sample size among individuals. We radio-tracked 29 individuals and found variation in resource selection among individuals. However, among individuals with the same supported covariates, the magnitude and direction of the covariates were similar. Eighteen bats selected areas with greater canopy closure and 5 of 6 bats that had areas burned by low-intensity prescribed fire in their home range selected burned areas. Resource selection was related to land cover for 13 individuals; they selected forest and shrubland over agricultural land, which composed >50% of the landscape within 10 km. We found no support for our hypothesis that resource selection was related to individual reproductive condition or Julian date in our population-level model indicating habitat selection was not determined by reproductive status or date within the maternity season. Land use or forest management that greatly reduces canopy cover may have a negative impact on Indiana bat use. Maintaining forest cover in agricultural landscapes is likely critical to persistence of maternity colonies in these landscapes. Sites managed with low severity prescribed fire may be selected by some individuals because of reduced understory vegetation. © 2013 The Wildlife Society.     

Species richness and assemblages of bats along a forest elevational transect in Papua New Guinea

Over the past decades, elevational gradients have become a powerful tool with which to understand the underlying cause(s) of biodiversity. The Mt. Wilhelm elevational transect is one such example, having been used to study the birds, insects, and plants of Papua New Guinea (PNG). However, a survey of mammals from this forest elevational transect was lacking. We thus aimed to investigate patterns in the community structure and species richness of bats (Chiroptera) along the transect, link the species to available regional data, and explain the observed patterns by including environmental characteristics. Bat assemblages were surveyed between 200 m and a timberline at 3700 m a.s.l. at eight study sites separated by 500 m in elevation. We conducted mist-netting and acoustic surveys to detect and identify species at each site. Regional data were compiled to compare local with regional diversity. Finally, biotic (i.e., food availability, habitat features) and abiotic (i.e., mean daily temperature) factors were included in our analyses to disentangle the ecological drivers underlying bat diversity. Results revealed that species richness decreases with ascending elevation and was best explained by a corresponding decrease in temperature. We observed both turnover and nestedness of the species composition at regional scale whereas turnover was dominant at local scale. Extensions and shifts of bat elevational ranges were also found in Mt. Wilhelm. Consequently, despite that the study was restricted to one mountain in PNG, it demonstrates how basic inventory surveys can be used to address ecological questions in other similar and undisturbed tropical mountains.     

Species variation in the localisation of esterases in the cerebellar cortex of mouse and bat

A comparative study of the distribution of a simple esterase and acetylcholinesterase in the cerebellar cortex of mouse and bat has been made. The Purkinje layer is intensely positive for simple esterase in both species. The granular and molecular layers showed mild to moderate activity in mouse and intense activity in bat. Acetylcholinesterase in cerebellar layers of bat is more intense than in mouse. In bat cerebellum, acetylcholinesterase is observed in the dendrites of Purkinje cells, but not in their cell bodies. Acetylcholinesterase was not found in Purkinje cells of mouse.     

Population structure of wild bananas, Musa balbisiana, in China determined by SSR fingerprinting and cpDNA PCR-RFLP

Both demographic history and dispersal mechanisms influence the apportionment of genetic diversity among plant populations across geographical regions. In this study, phylogeography and population structure of wild banana, Musa balbisiana, one of the progenitors of cultivated bananas and plantains in China were investigated by an analysis of genetic diversity of simple sequence repeat (SSR) fingerprint markers and cpDNA PCR-RFLP. A chloroplast DNA (cpDNA) genealogy of 21 haplotypes identified two major clades, which correspond to two geographical regions separated by the Beijiang and Xijiang rivers, suggesting a history of vicariance. Significant genetic differentiation was detected among populations with cpDNA markers, a result consistent with limited seed dispersal in wild banana mediated by foraging of rodents. Nuclear SSR data also revealed significant geographical structuring in banana populations. In western China, however, there was no detected phylogeograpahical pattern, possibly due to frequent pollen flow via fruit bats. In contrast, populations east of the Beijiang River and the population of Hainan Island, where long-range soaring pollinators are absent, are genetically distinct. Colonization-extinction processes may have influenced the evolution of Musa populations, which have a metapopulation structure and are connected by migrating individuals. Effective gene flow via pollen, estimated from the nuclear SSR data, is 3.65 times greater than gene flow via seed, estimated from cpDNA data. Chloroplast and nuclear DNAs provide different insights into phylogeographical patterns of wild banana populations and, taken together, can inform conservation practices.     

Optimum effort to estimate habitat use when the individual animal is the sampling unit

• 1 Studies of habitat use in which the individual animal is the sampling unit should ideally sample each individual sufficiently to achieve a stable estimate of its habitat use. Data are typically obtained by radio-tracking, which can be labour-intensive. Hence, optimization of sampling effort is desirable. A method to determine optimum sampling effort is described with reference to an example from a study of Natterer's bat Myotis nattereri, in which data were collected by radio-tracking with individual bats followed continuously for entire nights.
• 2 Habitat use by Natterer's bat was assessed by compositional analysis, which compares the composition of habitats used with those potentially available. Therefore, we plotted running per cent foraging time spent over a range of habitat types against the cumulative foraging time recorded. We visually estimated the optimum sum of foraging time required to determine stable estimates of the composition of habitat use from the plots. Then, by reference to the full-time budget, the total tracking effort expended at the point when this optimum amount of foraging data had been recorded was determined and expressed in units of the number of nightly tracking sessions that had been undertaken to collect that amount of foraging data.
• 3 Stable estimates of habitat use were attained after a mean of 22 ± 7.7 h of foraging time, which were obtained in a mean of 4.6 ± 1.9 nights of radio-tracking effort. Thus, in this Natterer's bat study, where habitat preference was assessed by compositional analysis, it was appropriate to aim to collect foraging data during five nights of radio-tracking for each bat sampled.
• 4 The method presented is also applicable to studies where tracking data are discontinuous. A variation of the method can be applied in studies where a Euclidean distance method is to be used for the analysis of habitat use.

     

Serotonin modulates responses to species-specific vocalizations in the inferior colliculus

Neuromodulators such as serotonin are capable of altering the neural processing of stimuli across many sensory modalities. In the inferior colliculus, a major midbrain auditory gateway, serotonin alters the way that individual neurons respond to simple tone bursts and linear frequency modulated sweeps. The effects of serotonin are complex, and vary among neurons. How serotonin transforms the responses to spectrotemporally complex sounds of the type normally heard in natural settings has been poorly examined. To explore this issue further, the effects of iontophoretically applied serotonin on the responses of individual inferior colliculus neurons to a variety of recorded species-specific vocalizations were examined. These experiments were performed in the Mexican free-tailed bat, a species that uses a rich repertoire of vocalizations for the purposes of communication as well as echolocation. Serotonin frequently changed the number of recorded calls that were capable of evoking a response from individual neurons, sometimes increasing (15% of serotonin-responsive neurons), but usually decreasing (62% of serotonin-responsive neurons), this number. A functional consequence of these serotonin-evoked changes would be to change the population response to species-specific vocalizations.