Migratory singers dynamically overlap the signal space of a breeding warbler community

Migratory species inhabit many communities along their migratory routes. Across taxa, these species repeatedly move into and out of communities, interacting with each other and locally breeding species and competing for resources and niche space. However, their influence is rarely considered in analyses of ecological processes within the communities they temporarily occupy. Here, we explore the impact of migratory species on a breeding community using the framework of acoustic signal space, a limited resource in which sounds of species within communities co-exist. Migrating New World warblers (Parulidae, hereafter referred to as migrant species) often sing during refueling stops in areas and at times during which locally breeding warbler species (hereafter breeding species) are singing to establish territories and attract mates. We used eBird data to determine the co-occurrence of 19 migrant and 11 breeding warbler species across spring migration in SW Michigan, generated a signal space from song recordings of these species, and examined patterns of signaling overlap experienced by breeding species as migrants moved through the community. Migrant species were present for two-thirds of the breeding season of local species, including periods when breeding species established territories and attracted mates. Signaling niche overlap experienced by individual breeding species was idiosyncratic and varied over time, yet niche overlap between migrant and breeding species occurred more commonly than between breeding species or between migrant species. Nevertheless, the proportion of niche overlap between migrant and breeding warblers was similar to overlap among breeding species. Our findings showed that singing by migrant species overlapped the signals of many breeding species, suggesting that migrants could have unexplored impacts on communication in breeding species, potentially affecting song detection and song evolution. Our study contributes to a growing body of research documenting the impacts of migratory species on communities and ecosystems.

Host gene expression in wildlife disease: making sense of species-level responses

Emerging infectious diseases are significant threats to wildlife conservation, yet the impacts of pathogen exposure and infection can vary widely among host species. As such, conservation biologists and disease ecologists have increasingly aimed to understand species-specific host susceptibility using molecular methods. In particular, comparative gene expression assays have been used to contrast the transcriptomic responses of disease-resistant and disease-susceptible hosts to pathogen exposure. This work usually assumes that the gene expression responses of disease-resistant species will reveal the activation of molecular pathways contributing to host defence. However, results often show that disease-resistant hosts undergo little gene expression change following pathogen challenge. Here, we discuss the mechanistic implications of these "null" findings and offer methodological suggestions for future molecular studies of wildlife disease. First, we highlight that muted transcriptomic responses with minimal immune system recruitment may indeed be protective for nonsusceptible hosts if they limit immunopathology and promote pathogen tolerance in systems where susceptible hosts suffer from genetic dysregulation. Second, we argue that overly narrow investigation of responses to pathogen exposure may overlook important, constitutively active molecular pathways that underlie species-specific defences. Finally, we outline alternative study designs and approaches that complement interspecific transcriptomic comparisons, including intraspecific gene expression studies and genomic methods to detect signatures of selection. Collectively, these insights will help ecologists extract maximal information from conservation-relevant transcriptomic data sets, leading to a deeper understanding of host defences and, ultimately, the implementation of successful conservation interventions.

Social context and noise affect within and between male song adjustments in a common passerine

Across populations, animals that inhabit areas with high anthropogenic noise produce vocalizations that differ from those inhabiting less noisy environments. Such patterns may be due to individuals rapidly adjusting their songs in response to changing noise, but individual variation is seldom explored. Therefore, we tested the hypothesis that male house wrens (Troglodytes aedon) immediately adjust their songs according to changing noise and that social context further modifies responses. We recorded songs, quantified noise, and defined social context within pairs as female fertile status and between males as number of conspecific neighbors. We used a reaction-norm approach to compare song trait intercepts (between-male effects) and slopes (within-male effects) as a function of noise. Individuals immediately adjusted song duration in response to changing noise. How they achieved adjustments varied: some sang shorter and others longer songs with greater noise, and individuals varied in the extent to which they adjusted song duration. Variation in song duration could be affected by competition as between-male noise levels interacted with number of neighbors to affect syllable duration. Neither within- nor between-male noise effects were detected for frequency traits. Rather, males with fertile mates sang lower-frequency songs and increased peak frequency with more neighbors. Among males, social context but not noise affected song frequency, whereas temporal structure varied between and within individuals depending on noise and social factors. Not all males adjusted signals the same way in response to noise, and selection could favor different levels of variation according to noise.

Antibiotic resistant bacteria are widespread in songbirds across rural and urban environments

The widespread use of antibiotics in human and veterinary medicine to treat pathogenic bacteria has resulted in the rapid emergence of antibiotic-resistant bacteria (ARB). Wild animals may enable the spread of pathogenic and non-pathogenic ARB when they are exposed to reservoirs (e.g., contaminated soil, water, or crops) and carry ARB in and on their bodies to other environments. We tested for the presence of ARB in four songbird species in southwest Michigan across a gradient of land use. Our specific objectives were to: 1) quantify the prevalence of ARB found in the gut microbiome of birds; 2) identify the specific bacteria exhibiting resistance; 3) assess whether ARB prevalence and identity varied among bird species; and 4) assess whether anthropogenic land use influenced the prevalence and identity of ARB found on birds. We sampled birds across a land use gradient consisting of urban, agricultural, and natural land covers using a randomized, spatially-balanced sampling design and cultured bacteria from fecal samples in the presence of three different antibiotics (amoxicillin, tetracycline, and ciprofloxacin). Overall prevalence of ARB was high, with 88% of total birds carrying ARB resistant to one of three antibiotics that we tested. Resistance to amoxicillin was more common (83% of sampled birds) than resistance to tetracycline (15%) or ciprofloxacin (1%). Identified ARB were diverse, and included 135 isolates representing 5 bacterial phyla and 22 genera. There was no effect of land use on ARB prevalence, with 90% of sampled birds captured in rural sites and 85% of sampled birds in urban sites carrying ARB. We provide the first analysis of ARB prevalence across multiple bird species and land uses utilizing a spatially-balanced, randomized study design. Our results demonstrate that nearly all sampled birds carried at least some ARB, and that they may serve as important dispersal agents of ARB across large spatial scales.

Nestedness in assemblages of helminth parasites of bats: a function of geography, environment, or host nestedness?

Nested subsets occur in ecological communities when species-poor communities are subsets of larger, species-rich communities. Understanding this pattern can help elucidate species colonization abilities, extinction risks, and general structuring of biological communities. Here, we evaluate nestedness in a poorly studied host-parasite system, bats and their helminths, across the Japanese archipelago and within its different bioclimatic regions. We hypothesized that (1) if helminth communities are nested across geographic sites at the level of the archipelago, then broad-scale processes, like colonization-extinction dynamics, mainly structure parasite assemblages; (2) if helminth communities are nested across geographic sites at the level of the bioclimatic region, then fine-scale environmental variation plays a significant role in species nestedness; (3) if helminth community nestedness mirrors host species nestedness, then communities are nested because the habitats they occupy are nested; and (4) if nestedness does not occur or if it is not correlated with any geographical or host data, then passive sampling could be responsible for the patterns of parasite assemblage in our sample. We found that helminth communities were nested across host species throughout the archipelago but, when considering each bioclimatic region, helminths in only one region were significantly more nested than the null model. Helminth communities were also nested across sites within all four bioclimatic regions. These results suggest that helminths form nested subsets across the archipelago due to broad-scale processes that reflect the overall lineages of their mammalian hosts; however, at the regional scale, environmental processes related to nestedness of their habitats drive parasite community nestedness.

Host association influences variation at salivary protein genes in the bat ectoparasite Cimex adjunctus

Parasite-host relationships create strong selection pressures that can lead to adaptation and increasing specialization of parasites to their hosts. Even in relatively loose host-parasite relationships, such as between generalist ectoparasites and their hosts, we may observe some degree of specialization of parasite populations to one of the multiple potential hosts. Salivary proteins are used by blood-feeding ectoparasites to prevent hemostasis in the host and maximize energy intake. We investigated the influence of association with specific host species on allele frequencies of salivary protein genes in Cimex adjunctus, a generalist blood-feeding ectoparasite of bats in North America. We analysed two salivary protein genes: an apyrase, which hydrolyses ATP at the feeding site and thus inhibits platelet aggregation, and a nitrophorin, which brings nitrous oxide to the feeding site, inhibiting platelet aggregation and vasoconstriction. We observed more variation at both salivary protein genes among parasite populations associated with different host species than among populations from different spatial locations associated with the same host species. The variation in salivary protein genes among populations on different host species was also greater than expected under a neutral scenario of genetic drift and gene flow. Finally, host species was an important predictor of allelic divergence in genotypes of individual C. adjunctus at both salivary protein genes. Our results suggest differing selection pressures on these two salivary protein genes in C. adjunctus depending on the host species.

Prevalence and diversity of avian Haemosporida infecting songbirds in southwest Michigan

Avian blood parasites from the genera Plasmodium, Haemoproteus, and Leucocytozoon (Haemosporida) affect hosts in numerous ways. They influence species interactions, host behavior, reproductive success, and cause pathology and mortality in birds. The Great Lakes region of North America has extensive aquatic and wetland habitat and supports a diverse vector community. Here we describe the community of bird-infecting Haemosporida in southwest Michigan and their host associations by measuring parasite prevalence, diversity, and host breadth across a diverse community of avian hosts. Over 700 songbirds of 55 species were screened for Haemosporida infection across southwest Michigan, including 11 species that were targeted for larger sample sizes. In total, 71 parasite lineages infected over 40% of birds. Of these, 42 were novel, yet richness estimates suggest that approximately half of the actual parasite diversity in the host community was observed despite intensive sampling of multiple host species. Parasite prevalence varied among parasite genera (7-24%) and target host species (0-85%), and parasite diversity was consistently high across most target species. Host breadth varied widely across the most prevalent parasite lineages, and we detected around 60% of host species richness for these parasite lineages. We report many new lineages and novel host-parasite associations, but substantial parasite diversity remains undiscovered in the Midwest.

Population structure in two geographically sympatric and congeneric ectoparasites (Cimex adjunctus and Cimex lectularius) in the North American Great Lakes region

Subdivided populations can be described by different models of population structure that reflect population organization, dynamics, and connectivity. We used genetic data to investigate population structure in two geographically sympatric, congeneric species of generalist ectoparasites of warm-blooded animals. We characterized the spatial genetic structure of the eastern bat bug (Cimex adjunctus Barber, 1939), an understudied and fairly abundant species, using microsatellite markers at a spatial scale representing contemporary dispersal of the species. We found seven genetic clusters, global [Formula: see text] of 0.2, 33% of genetic variation among sites, and nonsignificant isolation-by-distance. We compared these results with the common bed bug (Cimex lectularius L., 1758), a closely related but conversely well-known species, in the same geographic area. We found stronger genetic structuring in C. lectularius than in C. adjunctus, with 11 genetic clusters, [Formula: see text] of 0.7, 57% of genetic variation among sites, and significant but weak isolation-by-distance (R2 = 0.09). These results suggest that while both species can be described as having classic metapopulation structure, C. adjunctus leans more towards a patchy population and C. lectularius leans more towards a nonequilibrium metapopulation. The difference in population structure between these species may be attributable to differences in movement potential and extinction–colonization dynamics.

Decomposing an urban soundscape to reveal patterns and drivers of variation in anthropogenic noise

Continuous and intermittent noise may have different effects on humans and wildlife, therefore distinguishing temporal patterns of noise and their drivers is important for policy regarding both public health and wildlife management. We visualized patterns and explored land-use drivers of continuous and high-amplitude intermittent sound pressure levels (SPLs) on an urban campus in Michigan, U.S.A. To visualize patterns of SPLs, we introduce decibel duration curves (DDCs), which show the cumulative frequency distribution of SPLs and aid in the interpretation of statistical SPLs (L_n values) that reflect continuous versus intermittent sounds. DDCs and L_n values reveal that our 24 recording locations varied in the intensity of both continuous and intermittent noise, with intermittent high-amplitude sound events in particular contributing to variability in SPLs over the study site. Time of day influenced both continuous and intermittent SPLs, as locations relatively close to manmade structures (buildings, roads and parking lots) experienced higher SPLs as the day progressed. Continuous SPLs increased with decreasing distance to manmade structures, whereas intermittent SPLs increased with decreasing distance to roads and increasing distance to buildings. Thus, different land-use factors influenced patterns of continuous and intermittent noise, which suggests that different policy and strategies may be needed to ameliorate their effects on the public and wildlife.

Comparative analysis of landscape effects on spatial genetic structure of the big brown bat and one of its cimicid ectoparasites

Identification of landscape features that correlate with genetic structure permits understanding of factors that may influence gene flow in a species. Comparing effects of the landscape on a parasite and host provides potential insights into parasite‐host ecology. We compared fine‐scale spatial genetic structure between big brown bats (Eptesicus fuscus) and their cimicid ectoparasite (Cimex adjunctus; class Insecta) in the lower Great Lakes region of the United States, in an area of about 160,000 km². We genotyped 142 big brown bat and 55 C. adjunctus samples at eight and seven microsatellite loci, respectively, and inferred effects of various types of land cover on the genetic structure of each species. We found significant associations between several land cover types and genetic distance in both species, although different land cover types were influential in each. Our results suggest that even in a parasite that is almost entirely reliant on its hosts for dispersal, land cover can affect gene flow differently than in the hosts, depending on key ecological aspects of both species.

Host association and selection on salivary protein genes in bed bugs and related blood-feeding ectoparasites

Reciprocal selective pressures can drive coevolutionary changes in parasites and hosts, and result in parasites that are highly specialized to their hosts. Selection and host co-adaptation are better understood in endoparasites than in ectoparasites, whose life cycles may be more loosely linked to that of their hosts. Blood-feeding ectoparasites use salivary proteins to prevent haemostasis in the host, and maximize energy intake. Here we looked for signals of selection in salivary protein genes of ectoparasite species from a single genus (Cimex) that associate with a range of hosts including mammals (bats and humans) and birds (swallows). We analysed two genes that code for salivary proteins that inhibit platelet aggregation and vasoconstriction and may directly affect the efficiency of blood feeding in these species. Significant positive selection was detected at five codons in one gene in all bat-associated species groups. Our results suggest association with bats, versus humans or swallows, has posed a selective pressure on the salivary apyrase gene in species of Cimex.

Range-wide genetic structure and demographic history in the bat ectoparasite Cimex adjunctus

Background

Evolutionary histories of parasite and host populations are intimately linked such that their spatial genetic structures may be correlated. While these processes have been relatively well studied in specialist parasites and their hosts, less is known about the ecological and evolutionary consequences of relationships between generalist ectoparasites and their hosts. The aim of this study was to investigate the genetic structure and demographic history of a bat ectoparasite, Cimex adjunctus, whose host affinity is weak but the biology of the potential hosts have been well studied. This ectoparasite has been hypothesized to rely on its hosts for dispersal due to its low inherent dispersal potential. Here we describe genetic diversity and demographic history in C. adjunctus through most of its range in North America. We investigated variation at the cytochrome c oxidase 1 mitochondrial gene and nine microsatellite markers, and tested the prediction that genetic diversity in C. adjunctus is spatially structured. We also tested the prediction that demographic history in C. adjunctus is characterized by range and demographic expansion as a consequence of post-Pleistocene climate warming.

Results

We found stronger spatial structuring of genetic diversity in C. adjunctus than has been quantified in two of its hosts, but contrast in amount of variation explained by host association with different genetic markers (i.e., nuclear vs mitochondrial DNA). Also, C. adjunctus’ history is not primarily characterized by demographic and range expansion, as is the case with two of its key hosts.

Conclusions

Our study shows different patterns of genetic structure and demographic history in C. adjunctus than have been detected in two of its key hosts. Our results suggest an effect of a loose parasite-host relationship and anti-parasitism strategies on genetic structure and post-Pleistocene recovery of population size.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0839-1) contains supplementary material, which is available to authorized users.

Quantifying Global Drivers of Zoonotic Bat Viruses: A Process-Based Perspective

Emerging infectious diseases (EIDs), particularly zoonoses, represent a significant threat to global health. Emergence is often driven by anthropogenic activity (e.g., travel, land use change). Although disease emergence frameworks suggest multiple steps from initial zoonotic transmission to human-to-human spread, there have been few attempts to empirically model specific steps. We create a process-based framework to separate out components of individual emergence steps. We focus on early emergence and expand the first step, zoonotic transmission, into processes of generation of pathogen richness, transmission opportunity, and establishment, each with its own hypothesized drivers. Using this structure, we build a spatial empirical model of these drivers, taking bat viruses shared with humans as a case study. We show that drivers of both viral richness (host diversity and climatic variability) and transmission opportunity (human population density, bushmeat hunting, and livestock production) are associated with virus sharing between humans and bats. We also show spatial heterogeneity between the global patterns of these two processes, suggesting that high-priority locations for pathogen discovery and surveillance in wildlife may not necessarily coincide with those for public health intervention. Finally, we offer direction for future studies of zoonotic EIDs by highlighting the importance of the processes underlying their emergence.

Range-Wide Genetic Analysis of Little Brown Bat (Myotis lucifugus) Populations: Estimating the Risk of Spread of White-Nose Syndrome

The little brown bat (Myotis lucifugus) is one of the most widespread bat species in North America and is experiencing severe population declines because of an emerging fungal disease, white-nose syndrome (WNS). To manage and conserve this species effectively it is important to understand patterns of gene flow and population connectivity to identify possible barriers to disease transmission. However, little is known about the population genetic structure of little brown bats, and to date, no studies have investigated population structure across their entire range. We examined mitochondrial DNA and nuclear microsatellites in 637 little brown bats (including all currently recognized subspecific lineages) from 29 locations across North America, to assess levels of genetic variation and population differentiation across the range of the species, including areas affected by WNS and those currently unaffected. We identified considerable spatial variation in patterns of female dispersal and significant genetic variation between populations in eastern versus western portions of the range. Overall levels of nuclear genetic differentiation were low, and there is no evidence for any major barriers to gene flow across their range. However, patterns of mtDNA differentiation are highly variable, with high ΦST values between most sample pairs (including between all western samples, between western and eastern samples, and between some eastern samples), while low mitochondrial differentiation was observed within two groups of samples found in central and eastern regions of North America. Furthermore, the Alaskan population was highly differentiated from all others, and western populations were characterized by isolation by distance while eastern populations were not. These data raise the possibility that the current patterns of spread of WNS observed in eastern North America may not apply to the entire range and that there may be broad-scale spatial variation in the risk of WNS transmission and occurrence if the disease continues to spread west.

Two Tickets to Paradise: Multiple Dispersal Events in the Founding of Hoary Bat Populations in Hawai'i

The Hawaiian islands are an extremely isolated oceanic archipelago, and their fauna has long served as models of dispersal in island biogeography. While molecular data have recently been applied to investigate the timing and origin of dispersal events for several animal groups including birds, insects, and snails, these questions have been largely unaddressed in Hawai'i’s only native terrestrial mammal, the Hawaiian hoary bat, Lasiurus cinereus semotus. Here, we use molecular data to test the hypotheses that (1) Hawaiian L. c. semotus originated via dispersal from North American populations of L. c. cinereus rather than from South American L. c. villosissimus, and (2) modern Hawaiian populations were founded from a single dispersal event. Contrary to the latter hypothesis, our mitochondrial data support a biogeographic history of multiple, relatively recent dispersals of hoary bats from North America to the Hawaiian islands. Coalescent demographic analyses of multilocus data suggest that modern populations of Hawaiian hoary bats were founded no more than 10 kya. Our finding of multiple evolutionarily significant units in Hawai'i highlights information that should be useful for re-evaluation of the conservation status of hoary bats in Hawai'i.

Genetic approaches to the conservation of migratory bats: a study of the eastern red bat (Lasiurus borealis)

Documented fatalities of bats at wind turbines have raised serious concerns about the future impacts of increased wind power development on populations of migratory bat species. However, for most bat species we have no knowledge of the size of populations and their demographic trends, the degree of structuring into discrete subpopulations, and whether different subpopulations use spatially segregated migratory routes. Here, we utilize genetic data from eastern red bats (Lasiurus borealis), one of the species most highly affected by wind power development in North America, to (1) evaluate patterns of population structure across the landscape, (2) estimate effective population size (Ne ), and (3) assess signals of growth or decline in population size. Using data on both nuclear and mitochondrial DNA variation, we demonstrate that this species forms a single, panmictic population across their range with no evidence for the historical use of divergent migratory pathways by any portion of the population. Further, using coalescent estimates we estimate that the effective size of this population is in the hundreds of thousands to millions of individuals. The high levels of gene flow and connectivity across the population of eastern red bats indicate that monitoring and management of eastern red bats must integrate information across the range of this species.

Genetic structure of little brown bats (Myotis lucifugus) corresponds with spread of white-nose syndrome among hibernacula

Until recently, the little brown bat (Myotis lucifugus) was one of the most common bat species in North America. However, this species currently faces a significant threat from the emerging fungal disease white-nose syndrome (WNS). The aims of this study were to examine the population genetic structure of M. lucifugus hibernating colonies in Pennsylvania (PA) and West Virginia (WV), and to determine whether that population structure may have influenced the pattern of spread of WNS. Samples were obtained from 198 individuals from both uninfected and recently infected colonies located at the crest of the disease front. Both mitochondrial (636bp of cytochrome oxidase I) and nuclear (8 microsatellites) loci were examined. Although no substructure was evident from nuclear DNA, female-mediated gene flow was restricted between hibernacula in western PA and the remaining colonies in eastern and central PA and WV. This mitochondrial genetic structure mirrors topographic variation across the region: 3 hibernating colonies located on the western Appalachian plateau were significantly differentiated from colonies located in the central mountainous and eastern lowland regions, suggesting reduced gene flow between these clusters of colonies. Consistent with the hypothesis that WNS is transmitted primarily through bat-to-bat contact, these same 3 hibernating colonies in westernmost PA remained WNS-free for 1-2 years after the disease had swept through the rest of the state, suggesting that female migration patterns may influence the spread of WNS across the landscape.

When genes move farther than offspring: gene flow by male gamete dispersal in the highly philopatric bat species Thyroptera tricolor

For species characterized by philopatry of both sexes, mate selection represents an important behaviour for inbreeding avoidance, yet the implications for gene flow are rarely quantified. Here, we present evidence of male gamete-mediated gene flow resulting from extra-group mating in Spix's disc-winged bat, Thyroptera tricolor, a species which demonstrates all-offspring philopatry. We used microsatellite and capture-recapture data to characterize social group structure and the distribution of mated pairs at two sites in southwestern Costa Rica over four breeding seasons. Relatedness and genetic spatial autocorrelation analyses indicated strong kinship within groups and over short distances (<50 m), resulting from matrilineal group structure and small roosting home ranges (~0.2 ha). Despite high relatedness among-group members, observed inbreeding coefficients were low (FIS  = 0.010 and 0.037). Parentage analysis indicated mothers and offspring belonged to the same social group, while fathers belonged to different groups, separated by large distances (~500 m) when compared to roosting home ranges. Simulated random mating indicated mate choice was not based on intermediate levels of relatedness, and mated pairs were less related than adults within social groups on average. Isolation-by-distance (IBD) models of genetic neighbourhood area based on father-offspring distances provided direct estimates of mean gamete dispersal distances (r^) > 10 roosting home range equivalents. Indirect estimates based on genetic distance provided even larger estimates of r^, indicating direct estimates were biased low. These results suggest extra-group mating reduces the incidence of inbreeding in T. tricolor, and male gamete dispersal facilitates gene flow in lieu of natal dispersal of young.

Social calls used by a leaf-roosting bat to signal location

Social calls in bats have many functions, including mate attraction and maintaining contact during flight. Research suggests that social calls may also be used to transfer information about roosts, but no studies have yet demonstrated that calls are used to actively attract conspecifics to roosting locations. We document the social calls used by Spix's disc-winged bat (Thyroptera tricolor) to actively recruit group members to roosts. In acoustic trials, we recorded two sets of calls; one from flying individuals termed 'inquiry calls', and another from roosting bats termed 'response calls'. Inquiry calls were emitted by flying bats immediately upon release, and quickly (i.e. 178 ms) elicited production of response calls from roosting individuals. Most flying bats entered the roost when roosting individuals responded, while few bats entered the roost in the absence of a response. We argue that information transfer concerning roost location may facilitate sociality in T. tricolor, given the ephemeral nature of roosting structures used by this species.

Host phylogeny constrains cross-species emergence and establishment of rabies virus in bats

For RNA viruses, rapid viral evolution and the biological similarity of closely related host species have been proposed as key determinants of the occurrence and long-term outcome of cross-species transmission. Using a data set of hundreds of rabies viruses sampled from 23 North American bat species, we present a general framework to quantify per capita rates of cross-species transmission and reconstruct historical patterns of viral establishment in new host species using molecular sequence data. These estimates demonstrate diminishing frequencies of both cross-species transmission and host shifts with increasing phylogenetic distance between bat species. Evolutionary constraints on viral host range indicate that host species barriers may trump the intrinsic mutability of RNA viruses in determining the fate of emerging host-virus interactions.

Bat orientation using Earth's magnetic field

Bats famously orientate at night by echolocation, but this works over only a short range, and little is known about how they navigate over longer distances. Here we show that the homing behaviour of Eptesicus fuscus, known as the big brown bat, can be altered by artificially shifting the Earth's magnetic field, indicating that these bats rely on a magnetic compass to return to their home roost. This finding adds to the impressive array of sensory abilities possessed by this animal for navigation in the dark.

Production of ultrasonic vocalizations by Peromyscus mice in the wild

BACKGROUND

There has been considerable research on rodent ultrasound in the laboratory and these sounds have been well quantified and characterized. Despite the value of research on ultrasound produced by mice in the lab, it is unclear if, and when, these sounds are produced in the wild, and how they function in natural habitats.

RESULTS

We have made the first recordings of ultrasonic vocalizations produced by two free-living species of mice in the genus Peromyscus (P. californicus and P. boylii) on long term study grids in California. Over 6 nights, we recorded 65 unique ultrasonic vocalization phrases from Peromyscus. The ultrasonic vocalizations we recorded represent 7 different motifs. Within each motif, there was considerable variation in the acoustic characteristics suggesting individual and contextual variation in the production of ultrasound by these species.

CONCLUSION

The discovery of the production of ultrasonic vocalizations by Peromyscus in the wild highlights an underappreciated component in the behavior of these model organisms. The ability to examine the production of ultrasonic vocalizations in the wild offers excellent opportunities to test hypotheses regarding the function of ultrasound produced by rodents in a natural context.

A tale of two siblings: multiple paternity in big brown bats (Eptesicus fuscus) demonstrated using microsatellite markers

In many bat species, the opportunity for sperm competition or other mechanisms of post-copulatory paternity biasing is thought to be great, due to the long delay between copulation and fertilization, demonstrated sperm storage capabilities, and observed promiscuity. We present the results of the first study to assess whether litters of big brown bats (Eptesicus fuscus) containing dizygotic twins share the same father. We sampled 26 mother-offspring triads from three colonies in Indiana and Illinois, as well as 299 additional adults (237 females and 62 males) from these colonies and six other maternity colonies in the same area in 1997-1998. All individuals were genotyped at nine highly variable autosomal microsatellite loci and one X-linked locus. We assessed multiple paternity using autosomal and X-linked locus exclusions, and using maximum-likelihood methods. All methods confirmed multiple paternity within litters, and the maximum-likelihood analyses indicated that almost half of the sampled litters were composed of maternal half-siblings rather than full-siblings. Our results highlight the potential importance of post-copulatory mechanisms of paternity determination in the mating system of big brown bats, and have important implications for gene flow and population structuring in this species.

Ectoparasitic insects of bats in British Columbia, Canada

One species of parasitic bug (Hemiptera : Cimicidae), 3 species of fleas (Siphonaptera: Ischnopsyllidae), and 2 species of parasitic flies (Diptera : Nycteribiidae) were collected from 9 species of bats (Chiroptera : Vespertilionidae) in southern interior and northeastern British Columbia, Canada. Female bats that return daily to maternity roosts were more frequently infested with both cimicids and ischnopsyllids than were male bats. Some differences in ectoparasite infestation can be attributed to differences in roosting behavior of the host. New national records for 2 parasite species, and 8 new host records are established for Canada.

Constant-frequency and frequency-modulated components in the echolocation calls of three species of small bats (Emballonuridae, Thyropteridae, and Vespertilionidae)

The echolocation calls of Rhychonycteris naso (Emballonuridae), Thyroptera tricolor (Thyropteridae), and Myotis riparius (Vespertilionidae) were recorded at the Cãno Palma Field Station in Costa Rica in February 1998. All three species produced echolocation calls at low duty cycle (signal on ~10% of the time). While T. tricolor produced low-intensity echolocation calls that were barely detectable when the bats were <0.5 m from the microphone, the other two species produced high-intensity calls, readily detectable at distances >5 m. Myotis riparius produced calls that swept from about 120 kHz to just over 50 kHz in about 2 ms. We found no evidence of harmonics in these calls. Rhynchonycteris naso and T. tricolor produced multiharmonic echolocation calls. In R. naso the calls included narrowband and broadband components and varied in bandwidth, sweeping from just under 100 kHz to around 75 kHz in over 5 ms. Most calls were dominated by the higher harmonic (ca. 100 kHz), but some also included a lower one (ca. 50 kHz). The calls of T. tricolor were 5-10 ms long and dominated by a single frequency (ca. 45 kHz), sometimes with a ca. 25 kHz component. The echolocation calls of all three species included frequency-modulated and constant-frequency components. While these terms describe the components of the echolocation calls, they do not necessarily describe the bats' echolocation behaviour.

Roost-site selection and roosting ecology of forest-dwelling bats in southern British Columbia

We used radiotelemetry to examine the roost-site preferences of four species of tree-roosting bats (Eptesicus fuscus, Lasionycteris noctivagans, Myotis evotis, and M. volans) in southern British Columbia, Canada, by radio-tracking bats to their day roosts. We found a total of 21 roost trees: 14 roosts were beneath loose bark, 5 were in cavities excavated by woodpeckers, and 2 were in natural cavities. Entrance height increased with tree height, but roost entrances tended to be situated below the level of the canopy. Of the 22 tree and site variables examined, only 3 significantly discriminated between roost trees and available trees: tree height, distance to the nearest available tree, and percent canopy closure. Bats preferred tall trees associated with low percent canopy closure and a short distance to the nearest available tree. Bats roosted in western white pine, and to a lesser extent ponderosa pine and western larch, in intermediate stages of decay more often than would be expected at random. Bats switched roosts frequently. The distance between subsequent roost trees was short, suggesting a degree of fidelity to a particular group of trees or area of forest. The number of days of rain during the roosting period significantly influenced the number of days spent in a particular roost, and thus ambient conditions may restrict the frequency with which bats can switch roosts.