Orientador: Estevam Guilherme Lux Hoppe / Banca: Daniel Fontana Ferreira Cardia / Banca: Marcos Rogério André / Resumo: A Amazônia é o maior Bioma brasileiro, com uma das maiores biodiversidades mundial. Foram descritas 167 espécies de morcegos no Brasil, com 120 espécies registradas no Estado do Pará, das quais 10 têm registro exclusivo neste estado. Entretanto, apesar da elevada diversidade, são raros os estudos voltados para a descrição de endoparasitas em quirópteros pertencentes a este Bioma. Diante disso, o presente estudo teve como objetivo estudar a helmintofauna de diferentes espécies de quirópteros amazônicos, calcular os índices de infecção comparando-os com aspectos fenotípicos dos hospedeiros e avaliar os índices ecológicos populacionais e de cada guilda alimentar. Para tal, foram utilizados 67 morcegos de 21 espécies provenientes de várias cidades do Estado do Pará. Os animais foram separados em guildas alimentares e necropsiados. Os parasitas obtidos foram identificados taxonomicamente e quantificados. Dos animais estudados, 20,89% (14/67) encontraram-se parasitados. No total, foram recuperados 182 exemplares de helmintos das seguintes espécies: Anenterotrema eduardocaballeroi, Anenterotrema liliputianum, Ochoterenatrema caballeroi, Tricholeiperia sp., Parahistiostrongylus octacanthus, Litomosoides guiterasi, Litomosoides brasiliensis, Capillariinae gen. sp. e Hymenolepididae gen. sp. Pelos resultados obtidos verificou-se que não houve impacto do endoparasitismo na condição corporal dos quirópteros e não foram observadas diferenças entre a intensidade parasitária de machos e de ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Amazonia, the largest Brazilian Biomes, is one of the most biodiverse Biomes around the world. Considering the Brazilian chiropteran species, 120 of out 167 are registered in Pará State, with 10 endemic species. Despite the high diversity of bats in Amazonia, studies on their parasites, especially on helminths, are scarce. Therefore, the present study aims to study the helminthfauna of different bat species from the Pará State, Amazon Biome, determine the descriptors of infection and evaluate the host-parasite relationship, as well as evaluate diferences in ecological indexes in accord to the alimentary guilds. The study was developed on 67 bats of 21 species captured in several áreas of the Pará State. The animals were identified, divided in alimentary guilds and necropsied. The parasites obtained were identified and quantified. Parasites were found in 20.89% of the bats, a total of 182 specimens belonging to Anenterotrema eduardocaballeroi, Anenterotrema liliputianum, Ochoterenatrema caballeroi, Tricholeiperia sp., Parahistiostrongylus octacanthus, Litomosoides guiterasi, Litomosoides brasiliensis, Capillariinae gen. sp. and Hymenolepididae gen. sp. The results indicate that there was no impact of endoparasitism on host body condition and no relationship between sex and parasite intensity. In relation to the alimentary guilds, the omnivores showed higher prevalence and mean intensity. Animals from regions closer to the equator tend to have greater richness parasites species... (Complete abstract click electronic access below) / Mestre

O gênero Myotis é extremamente diverso, sendo atualmente reconhecidas 103 espécies, além de 94 subespécies as quais não foram avaliadas satisfatoriamente quanto seu status taxonômico. Para a América do Sul são reconhecidas 12 espécies, das quais cinco são consideradas politípicas, dentre elas Myotis nigricans, táxon considerado um complexo de espécies. Com o objetivo de caracterizar, morfologicamente e molecularmente, os táxons do gênero Myotis que ocorrem no Brasil e aqueles relacionados a Myotis nigricans, examinei 1.018 exemplares depositados em coleções científicas nacionais e internacionais. Analisei 25 caracteres de morfologia externa e craniana, e aferi 13 medidas corporais e 19 cranianas. Submeti as medidas cranianas a testes estatísticos uni e multivariados com o intuito de investigar variações inter e intraespecíficas, e verificar a existência de dimorfismo sexual em cada táxon analisado. Selecionei um gene mitocondrial, citocromo b (402pb), e um gene nuclear, RAG2 (620pb), com a finalidade de caracterizar a diversidade genética intra e interespecífica dos táxons de Myotis, dos quais obtive 78 seqüências: 58 mitocondriais e 20 nucleares. A partir deste conjunto de dados reconheci 8 espécies válidas para o gênero Myotis no Brasil (Myotis albescens, Myotis alter, Myotis levis, Myotis nigricans, Myotis riparius, Myotis ruber, Myotis simus, e Myotis sp.n.). Elevei Myotis osculati ao nível específico, táxon até então considerado uma subespécie de Myotis nigricans; e considerei Myotis punensis e Myotis chiriquensis espécies válidas, as quais eram consideradas sinonímias de Myotis nigricans nigricans. Neste contexto, reconheço 15 espécies sul-americanas do gênero Myotis, o que representa um acréscimo de 25% na diversidade anteriormente reconhecida para o grupo na região. Não encontrei dimorfismo sexual significativo nas medidas cranianas de M. albescens, M. levis, M. nigricans, M. riparius e M. ruber. Para melhor delimitar morfometricamente os táxons estudados, em especial M. nigricans de M. riparius, propus a utilização de dois índices: um craniano e outro maxilar. Os caracteres qualitativos cranianos, como a presença de crista sagital e o posicionamento dos pré-molares superiores, associados aos de morfologia externa, como a disposição de pêlos ao longo do uropatágio, o formato do pavilhão auditivo, e a angularidade da porção distal da maxila inferior, apresentaram-se como os mais robustos na delimitação dos táxons com ocorrência no Brasil. As relações filogenéticas entre as espécies de Myotis após inclusão dos táxons validados neste trabalho, ainda permanecem imprecisas. Através dos métodos de Máxima Parcimônia (MP), de distância de Neighbor-Join (NJ) e análise Bayesiana (B), houve o resgate de dois grandes clados compostos por espécies com crista sagital ausente ou discreta (clado A), e crista sagital presente (clado B). Atribuí a politomia encontrada dentro do clado A à rápida diversificação do grupo na região, com possíveis eventos simultâneos de especiação. Associo a inclusão de M. levis no clado de M nigricans com um evento de introgressão mitocondrial dado a natureza do gene, e ao número de mutações, incompatível com homoplasia do gene. O tempo de divergência estimado em 1,2Ma (±0,8), coincide com os eventos de mudanças climáticas e de retração de florestas durante o Pleistoceno, que propiciariam a hibridização destas duas linhagens. Apliquei o Teste de Mantel nas populações de M. nigricans e M. riparius presente nos domínios da Mata Atlântica, com o intuito de verificar a existência de correlação entre distância genética e distância geográfica entre as populações, testando a hipótese de isolamento por distância, a qual foi rejeitada tanto para M. nigricans (p=0,9449; r=0,23) como para M. riparius (p=0,9997; r=0,60). As populações de Myotis riparius apresentaram uma baixa divergência genética (0,8 a 1,5%) ao longo da distribuição, com compartilhamento de haplótipos entre as populações de Paraíba, São Paulo, Paraná e Paraguai. Em relação à Myotis nigricans destaco o compartilhamento de haplótipos entre as populações da Bahia, São Paulo e Paraná, e a baixa divergência (1,9 a 2,4%) entre as populações ao leste da Serra do Mar. Contudo, os níveis de divergência entre estas populações e as populações provenientes da Serra do Japi e Serra da Mantiqueira são acentuados (5,7 a 8,1%), similares aos níveis interespecíficos para o gênero. Estes dados sugerem um alto fluxo gênico no sentido Norte-Sul da Mata Atlântica ao leste da Serra do Mar, podendo esta atuar como barreira para as populações interioranas. A compreensão dos processos envolvidos na diversificação do grupo será favorecida com a inclusão a estas análises de amostras provenientes de outras populações distribuídas nas porções Leste Oeste da Mata Atlântica. / Myotis is a highly diverse genus, with 103 species recognized so far, in addition to another 94 subspecies whose taxonomical status has not yet been completely evaluated. Twelve species are known to South America, among which five are considered polytypic, including Myotis nigricans. This taxon in considered a species complex. In order to characterize, both morphologically and molecularly, the taxa of the genus Myotis, I examined 1,018 individuals from national and foreign scientific collections. Twenty-five characters from external and cranial morphology were analyzed and 13 body and 19 cranial measures were checked. In order to investigate inter and intraspecific variations and the existence of sexual dimorphism in each taxon analyzed, I submitted the cranial measures to uni and multivariate statistic tests. To characterize intra and interspecific genetic diversity of the taxa in the genus Myotis, I selected one mitochondrial gene, cytochrome b (402pb), and a nuclear gene, RAG2 (602pb). From these two genes, I obtained 78 sequences: 58 mitochondrial and 20 nuclear. From the data obtained, I recognized as valid eight Brazilian species in the genus Myotis (Myotis albescens, Myotis alter, Myotis levis, Myotis nigricans, Myotis riparius, Myotis ruber, Myotis simus, and Myotis sp.n.). I elevated Myotis osculati, a taxon hitherto considered a subspecies of Myotis nigricans, to specific level and diagnosed Myotis punensis and Myotis chiriquensis as valid species, which were previously considered synonyms of Myotis nigricans nigricans. In this context, I recognize 15 species for the genus Myotis in South America, representing an increase of 25% in the previously known diversity for the group in the continent. I have not found significant sexual dimorphism in the cranial measures for M. albescens, M. levis, M. nigricans, M. riparius and M. ruber. To better delimitate morphometricaly the taxa herein studied, specially M. nigricans from M. riparius, I proposed the use of two indexes: one cranial and one maxillary. Qualitative characters from skull, such as presence or absence of a sagittal crest and the arrangement of upper premolars, associated to those from external morphology, such as the arrangement of the hair along the uropatagium, the shape of external ear, and the angling from the distal portion of the lower maxillae, were fundamental for diagnosing the taxa occurring in Brazil. The phylogenetic relationship among the species of genus Myotis is still imprecise, even after the inclusion of those taxa diagnosed as valid in this thesis. Through Maximum Likelihood (ML), Neighbor-Join (NJ) and Bayesian analysis methods, two clades were defined, one formed by species with absent or shallow sagittal crest (clade A), and another (clade B) with the presence of sagittal crest. I correlate the polytomy found within clade A with a fast diversification of this group in the region, possibly with simultaneous events of speciation. I correlate the inclusion of M. levis in the clade of M. nigricans with an event of mitochondrial introgression, given the nature of this gene and the number of mutations, which are not compatible with the homoplasy for this gene. The estimated divergence time of 1.2 Ma (±0.8), coincides with climatical changes and forest retraction during the Pleistocene, which allowed the hybridization of these two lineages. I ran the Test of Mantel for the populations of M. nigricans and M. riparius from the Atlantic Forest dominium, aiming at verifying the existence of a correlation between genetic distance and geographical distance in the populations, testing the hypothesis of isolation by distance, which was rejected both for M. nigricans (p=0.9449; r=0.23) and for M. riparius (p=0.9997; r=0.60). The populations of Myotis riparius showed a low genetic divergence (0.8 to 1.5%) along their distribution, with the populations from Paraíba, São Paulo, Paraná and Paraguay sharing haplotypes. Regarding Myotis nigricans, I point out that populations from Bahia, São Paulo and Paraná share haplotypes and low divergence (1.9 to 2.4%) between the populations from the western portion of Serra do Mar. Yet, the level of divergence between such populations and those from Serra do Japi and Serra da Mantiqueira is high (5.7 to 8.1%), therefore similar to the interspecific levels for the genus. These data suggest a high gene flow from the North-South direction to eastern Serra do Mar, which may be acting as a barrier to interior populations. The understanding of the processes involved in the diversification of the group will be favored by the inclusion of samples of other populations distributed in the East-West portions of the Atlantic Forest.

Chrotopterus auritus is a phyllostomid bat with a wide distribution in the Neotropics. It has been recorded in Brazil’s 6 biomes but with few records in the Caatinga. We provide the first record of C. auritus for Rio Grande do Norte state, northeastern Brazil, based on records from 2 caves, Três Inchu and Gruta da Carrapateira. The nearest records are ca. 400 km southeast in Ceará state and ca. 350 km northwest in Pernambuco state. Our new records fill the northeastern distributional gap of C. auritus in Brazil and South America.

Different cognitive processes underlie the perception of vocalizations in many mammals, including humans. This perception now extends to a highly specialized form of sonar called echolocation. In habituation-dishabituation experiments, a high duty cycle echolocating bat, Rhinolophus clivosus, dishabituated significantly when echolocation calls of a different gender or individual were played to the habituation. Strong individual and gender signatures but weak geographic signatures were found in both the CF and FM components of their echolocation calls. In the individual discrimination trials reactions were more pronounced to an individual that was less acoustically similar to the habituation than to one that was more similar. Bats reacted to playbacks with a variety of social behaviours. Prior to the analysis of the experiment an ethogram was done on three groups of captive R. clivosus bats. This ethogram was used to categorize the behavioural responses of these bats to the acoustic stimuli in the experiments. The reactions to the habituation-dishabituation experiments show bats perceive gender and individual-specific signatures found in their conspecifics echolocation calls. This is the first study to show behavioural evidence for individual discrimination and second to show gender discrimination of echolocation calls in high duty cycle bats. This evidence supports the theory that echolocation, a system thought to have evolved solely for orientation and foraging, has been coopted for intra-specific communication and mate recognition in bats.

Bats asymptomatically host a number of viruses that are the cause of recently emergent infectious diseases in humans. While the mechanisms underlying this asymptomatic infection are currently not known, studies of sequenced bat genomes help uncover genetic adaptations in bats that may have functional importance in the antiviral response of these animals. To identify differences between antiviral mechanisms in humans and bats, we sequenced, assembled, and analyzed the genome of the Egyptian rousette bat (ERB; Rousettus aegyptiacus), a natural reservoir of Marburg virus and the only known reservoir for any filovirus. We used this genome to understand the evolution of immune genes and gene families in bats, and describe several observations relevant to defense against viruses. We observed an unusual expansion of the NKG2/CD94 natural killer (NK) cell receptor gene families in Egyptian rousette bats relative to other species, and found genomic evidence of unique features and expression of these receptors that may result in a net inhibitory balance within bat NK cells. The expansion of NK cell receptors is matched by an expansion of potential major histocompatibility complex (MHC) class I ligands, which are distributed both within and, surprisingly, outside the canonical MHC loci. We also observed that the type I interferon (IFN) locus is considerably expanded and diversified in the ERB, and that the IFN-ω subfamily contributes most to this expansion. To understand the functional implications of this expansion, we synthesized multiple IFN-ω proteins and examined their antiviral effects. Members of this subfamily are not constitutively expressed but are induced after viral infection, and show antiviral activity in vitro, with different antiviral potencies observed for different IFN-ω proteins. Taken together, these results show that multiple bats, including the ERB, have expanded and diversified numerous antiviral loci, and potentially developed unique adaptations in NK cell receptor signaling, and type I IFN responses. The concerted evolution of so many key components of immunity in the ERB is strongly suggestive of novel modes of antiviral defense that may contribute to the ability of bats to asymptomatically host viruses that are pathogenic in humans.

No description available.

In this study I assessed bat (Chiroptera) diversity on Kwalata Game Ranch (KGR) in Gauteng, South Africa. I investigated the influence of habitat heterogeneity, specifically vegetation type and level of cover, on the local bat assemblage structure. I sampled bats within three vegetation types (savanna-woodland, riparian and ecotone) on KGR and estimated percentage vegetation cover at sample sites as a proxy for vegetation structural complexity. I used passive sampling with bat detectors and active trapping with mistnets, harp-traps and roost searches to ensure as thorough an inventory as possible. Sample-based rarefaction revealed that the KGR bat assemblage is relatively species-poor and bat diversity is equivalent among the different vegetation types (confirmed with Whittaker’s β diversity index). A total of only eight insectivorous species was recorded and pteropodids appear to be absent from KGR. Moreover, species richness estimators indicated sampling was exhaustive. I attributed the low bat diversity to the impacts of known land use, particularly historical grazing by cattle (during 1980’s) and land clearing by humans that have resulted in a relatively fragmented savannah-woodland . In addition to the diversity assessment I evaluated effects of the deterministic processes of interspecific competition and prey defences on the ensemble structure of insectivorous bats . I measured the parameters of size, wing morphology and echolocation call structure for each species. These are the primary traits governing the habitat in which insectivorous bats can forage and the types of prey they can handle. Competition should result in size assortment of species that minimizes their similarity while defences of insect prey should result in a narrow range of effective echolocation parameters. Taking size into account is important as size can govern the type of prey able to be handled thus differently sized sympatric bat species may have similar echolocation characteristics but do not compete for prey. I used null models to test for the effects of competition and prey defences. I compared the insectivorous bat ensemble of KGR with random ensembles constructed from regional species pools of insectivorous bats. My results suggest evidence for competition – minimum size differences were larger and more evenly distributed than expected from chance. Moreover, my results are unlikely to be reflecting the “ghost of competition past” as the majority of insectivorous bat species at KGR are generalists thus making resource overlap more likely. Prey defences, on the other hand, appear to have no influence on the KGR ensemble structure – echolocation call parameters were clumped rather than more similar than chance would expect. Evidence for competition was surprising given the species-poor nature of the ensemble. Thus alternative factors potentially contributing to assortment of size and wing morphology parameters are discussed. KGR is bordered by large peri-urban settlements with numerous street lamps and large spotlights that produce substantial light pollution. High-duty cycle bats are often the main contributors to the prey defence hypothesis as they usually echolocate outside of the hearing range of tympanate insects. However, they may actively avoid artificially lit areas as a result of the slow flight making them more susceptible to predation. Also, artificial lights can interfere with the defence mechanisms of many tympanate insects thus allowing low-duty cycle echolocating bats to take advantage of a usually unavailable resource. The lack of evidence for the influence of prey defences was thus attributed to impacts of ecological light pollution.

This experiment was run to see whether the educational presentations done at zoos and other educational facilities are effectively changing patrons' negative misconceptions about the animals they were seeing. Participants were invited to attend one of three educational presentations, where they were exposed to either a low, intermediate or high level of interaction involving a bat. I hypothesized that regardless of the level of interaction, participants would learn the information, but that a higher level of interaction would cause the biggest perceptual change in terms of how participants felt about the bat and the highest degree of learning. Across the board, participants increased their factual knowledge, with no significant differences between the baseline, taxidermy or live bat conditions. The taxidermy group had the largest difference in attitude change, but the live bat did have a role in influencing participants' views as to whether bats were beneficial to the environment. These results imply that educational facilities can use a taxidermy bat or a live bat with their patrons and depending on how they utilize the inclusion of the interactive stimulus, it will cause perceptual and educational differences.

The biosonar system of bats has many unique adaptations which allow for navigation in extremely cluttered environments. One such adaptation is the rapid motion of the pinna and noseleaf observed in certain families of old-world bats (Rhinolophidae and Hipposiderae). Little is known about the physical properties about this adaptation affects emitted pulses or incoming echoes. To explore the physical properties of biosonar systems utilizing dynamic peripheries, biomimetic sonar systems have been devised, which can be used to simulate the structural characteristics of the pinna and noseleaf geometry as well as the motor characteristics. Using this method, it was determined that the changing conformations of the biomimetic baffles were responsible for time-variant signatures in echoes. These signatures could be seen in echoes from a variety of both simple and complex target shapes. Then to further the capabilities of the device, an improved actuation system was devised using pneumatic actuation. This allowed for the baffles to make several unique motions as opposed to being restricted to one previously. It was also shown that the distinct motion profiles of the system led to distinct differences in the received acoustic signal. The features encoded by this system could lead to improvements in the development of improved sensing of smaller autonomous systems. GRANT INFORMATION: This work was supported by grants from the Office of Naval Research (ONR) and the Naval Engineering Education Consortium (NEEC). Additional support was provided by an East Asia and Pacific Summer Institutes (EAPSI) fellowship from the National Science Foundation (NSF). / Doctor of Philosophy / Bats are known for using echolocation in addition to sight for hunting and navigating at night. The capabilities of bats and their ``sonar'' systems vary widely, as each species has evolved to survive in its specific environment. Certain species of bats indigenous to Eurasia are observed to perform complex motions of the outer ear and noseleaf (a ridged structure which sits atop the nostrils and acts like a ``megaphone'' of sorts). These bats are noted to be able to live in particularly cluttered environments and could be a particularly useful model organism for improving sonar. This is because since they are able to acquire detailed information about its surroundings with only their nostrils and ears, are able to outperform complicated man-made devices with thousands more sensing elements. To be able to better understand how a fast-moving ear and noseleaf can improve the sonar capabilities of bats, robots which mimic these bats have been devised, with the main purpose being to replicate the sensing elements of the bat. There have been significant changes made to the robotic sonar head in order to allow for us to expand the capabilities of our research. Using CT-scans as reference, the design of the baffles was redesigned to become more realistic and to have more features observed in the bats. A new method was designed in order to move the ``ears'' and ``noseleaf'' of the robot, using pneumatic actuators, which allowed for better control of the system. Finally, prototype sensors were developed to aid in the development of a motion feedback system to ensure a stable system. The robotic sonar has been used in several experiments to study the effects of a fast-moving, flexible anatomy on the physical properties of echoes. This is first illustrated by studying the echoes from various targets with changes in ear and noseleaf shape. Additionally, with the use of the improved actuation system, it was shown that different motion profiles lead to different responses. The continued development of this system and the changes to the signals explored provide new opportunities for furthering the fields of adaptive sensing as they apply to robots and other platforms. Being able to use a few ``smart'' sensors will help reduce the size, power, and weight costs of traditional sensing designs and allow for more robust and efficient technology to be produced.

Horseshoe bats (family Rhinolophidae) are among the bat species that dynamically deform their reception baffles (pinnae) and emission baffles (noseleaves) during signal reception and emissions, respectively. These dynamics are a focus of prior studies that demonstrated that these effects could introduce time-variance within emitted and received signals. Recent lab based experiments with biomimetic hardware have shown that these dynamics can also inject time-variant signatures into echoes from simple targets. However, complex foliage echoes, which comprise a large portion of the received echoes and contain useful information for these bats, have not been studied in prior research. We used a biomimetic sonarhead which replicated these dynamics, to collect a large dataset of foliage echoes (>55,000). To generate a neuromorphic representation of echoes that was representative of the neural spikes in bat brains, we developed an auditory processing model based on Horseshoe bat physiological data. Then, machine learning classifiers were employed to classify these spike representations of echoes into distinct groups, based on the presence or absence of dynamics' effects. Our results showed that classification with up to 80% accuracy was possible, indicating the presence of these effects in foliage echoes, and their persistence through the auditory processing. These results suggest that these dynamics' effects might be present in bat brains, and therefore have the potential to inform behavioral decisions. Our results also indicated that potential benefits from these effects might be location specific, as our classifier was more effective in classifying echoes from the same physical location, compared to a dataset with significant variation in recording locations. This result suggested that advantages of these effects may be limited to the context of particular surroundings if the bat brain similarly fails to generalize over variation in locations. / Master of Science / Horseshoe bats (family Rhinolophidae) are an echolocating bat species, i.e., they emit sound waves and use the corresponding echoes received from the environment to gather information for navigation. This species of bats demonstrate the behavior of deforming their emitter (noseleaf), and ears (pinna), while emitting or receiving echolocation signals. Horseshoe bats are adept at navigating in the dark through dense foliage. Their impressive navigational abilities are of interest to researchers, as their biology can inspire solutions for autonomous drone navigation in foliage and underwater. Prior research, through numerical studies and experimental reproductions, has found that these deformations can introduce time-dependent changes in the emitted and received signals. Furthermore, recent research using a biomimetic robot has found that echoes received from simple shapes, such as cube and sphere, also contain time-dependent changes. However, prior studies have not used foliage echoes in their analysis, which are more complex, since they include a large number of randomly distributed targets (leaves). Foliage echoes also constitute a large share of echoes from the bats' habitats, hence an understanding of the effects of the dynamic deformations on these foliage echoes is of interest. Since echolocation signals exist within bat brains as neural spikes, it is also important to understand if these dynamic effects can be identified within such signal representations, as that would indicate that these effects are available to the bats' brains. In this study, a biomimetic robot that mimicked the dynamic pinna and noseleaf deformation was used to collect a large dataset (>55,000) of echoes from foliage. A signal processing model that mimicked the auditory processing of these bats and generated simulated spike responses was also developed. Supervised machine learning was used to classify these simulated spike responses into two groups based on the presence or absence of these dynamics' effects. The success of the machine learning classifiers of up to 80% accuracy suggested that the dynamic effects exist within foliage echoes and also spike-based representations. The machine learning classifier was more accurate when classifying echoes from a small confined area, as compared to echoes distributed over a larger area with varying foliage. This result suggests that any potential benefits from these effects might be location-specific if the bat brain similarly fails to generalize over the variation in echoes from different locations.