Biology subjects

Lilley, T.

Publications and source records attributed to Lilley, T..

12 recordsLinked to original sources

bioRxiv2026

The geography of nocturnality: emergence patterns of bats on a latitudinal gradient

Animals often attempt to resolve the trade-off between foraging and predation by regulating their activity timings and patterns. Driven by individual energetic requirements and the local environment, onset of activity in a species varies across space and time. These differences are particularly enhanced on a latitudinal gradient, influenced by varying lengths of daylight, temperature and seasonality. For a nocturnal mammal like the bat, such patterns translate to shorter activity windows at higher latitudes, both on a nightly and a seasonal basis. This constructs the timing of activity onset as a crucial variable for a successful night of foraging. While roost exit timings and influence of local conditions on bat activity have been extensively studied across species inhabiting a variety of locations around the world, our understanding of bat emergence behaviour on a global scale remains limited. To investigate emergence patterns in bats across a latitudinal gradient, we conducted a meta-analysis spanning 91 species from across 13 Chiropteran families. We evaluated how timing and luminosity (i.e., sun altitude) at exit varied across latitudes and species. Results revealed that bats across the globe tended to emerge under conserved thresholds of brightness, a pattern that was facilitated by a temporal delay in roost exits at higher latitudes. By maintaining emergence within the confines of nautical twilight (sun altitude between 0{degrees} to -12{degrees}), bats across the phylogeny thus seemed to balance the dilemma of predation versus foraging. This pattern was mirrored across the two broad dietary types (frugivores and insectivores) as well as different social structures (maternal v. non-maternal colonies). Furthermore, our models indicated that while local conditions dictate final exit decisions, shared ancestry was potentially influencing the extent of plasticity seen in emergence patterns. Taken together, these results highlight how broad-scale latitudinal gradients of light can influence the foraging strategies in a globally distributed nocturnal mammal.

ecology↗

bioRxiv2026

Hibernation site dimensions influence bat abundance and diversity in the boreal zone

Hibernation is a critical phase in the annual cycle of boreal bats, especially near the northern limit of their range where winter conditions are severe and suitable hibernacula are limited. In Finland, anthropogenic structures, such as abandoned bunkers, commonly serve as hibernacula for bats. In this research, we investigate how the size characteristics of bunkers affect species composition and abundance of hibernating bats. The length of the bunker was the best predictor of the presence and abundance of bats. The longest sites ([~]25-26 m) had the highest probability to host all studied species, or group of species of bats, specifically Eptesicus nilssonii, Plecotus auritus, and Myotis bats. Eptesicus nilssonii appeared to be a generalist species, utilizing a variety of bunkers regardless of their length or temperature regime. Still, its number per bunker was relatively low. The highest numbers of Myotis bats were observed in the longest bunkers with stable temperature. The number of P. auritus was positively related to the bunker length; however, it was rare in the studied hibernacula. Different species showed different patterns in hibernacula space usage. Eptesicus nilssonii hibernated in any part of the bunker, while Myotis bats used the most remote from the entrances areas in small sites, and occupied the whole area of the longest bunkers.

ecology↗

bioRxiv2025

Behavioural changes in female northern bats (Eptesicus nilssonii) across gestation and lactation.

Unpredictable environmental conditions affecting prey availability and short summer nights reducing foraging time present nocturnal insectivorous mammals with an energetic dilemma at northerly latitudes during gestation and lactation. This is pronounced for aerial hawking bat species, for which prey activity is highly dependent on ambient temperature. Here, we describe changes in activity of female Eptesicus nilssonii, the northernmost breeding bat species, during gestation and lactation over several years at a roost site in southern Norway (60.1{degrees}N). Roost exits and returns were recorded using an infrared barrier at the entrance, and parturition dates were registered via a camera set inside the roost. Our results indicate significant temporal changes in body mass and behaviour throughout the breeding season. Lactating bats both setting out to forage earlier than during gestation and returning later. This behaviour is dependent on ambient temperature, with bats extending foraging time at elevated temperatures. These behaviours may occur as a response to the increased energetic needs of lactation, and the effect of increased temperature to reflect increased food availability which allows females to avoid increased predation pressure as a consequence of advanced roost exit or delayed return. The mass of females also decreases during lactation, suggesting high energetic demands during this period. Our study reveals insights into underlying mechanisms in high latitude insectivorous bats that can assist in coping with a short season with fluctuating resources.

animal behavior and cognition↗

bioRxiv2024

Population structure of the endangered Siberian flying squirrel (Pteromys volans) revealed by genomic and mitochondrial data

The Siberian flying squirrel (Pteromys volans) is an arboreal rodent with a distribution range that covers large parts of the Eurasian taiga forest zone. However, extensive forestry has resulted in widespread local population declines and extinctions in recent decades. Even though it is widely distributed in Eurasia, almost nothing is known about its phylogeography. Here we used genome-wide single nucleotide polymorphisms (SNPs) and mitochondrial DNA (mtDNA) to investigate population structure, connectivity and genetic diversity in different sites throughout its distribution. Overall, the species shows low nucleotide diversity and heterozygosity. Locations in Finland, on the western edge of the distribution, had the lowest diversities in genomic SNPs and mtDNA, while individuals in the Far East (Sikhote-Alin, Russia) show the highest diversity. These findings fit with a rapid range expansion from the Far East to the west. We found a strong genetic differentiation between Sikhote-Alin and all other populations investigated, which might warrant a revision of their taxonomic classification. The inferred low genetic diversities at the western edge of their distribution are especially worrisome as they are currently experiencing strong population declines and major habitat changes, which can be especially detrimental when standing variation is low. Thus, stressing the need for the revision of the species conservation status.

evolutionary biology↗

bioRxiv2024

Supersize me: torpor assists pre-hibernation fattening in a boreal bat

Hibernators face an energetic dilemma in the autumn at northern latitudes; while temperatures and food availability decrease, hibernating species need to build fat deposits to survive the winter. During this critical fattening phase, insectivorous boreal bats use torpor to build and conserve their reserves. However, we still know little about temporal variability in torpor use employed by bats in autumn and how decreasing temperatures and food availability in combination with increasing individual body mass impact this. Here we present two general hypotheses for explaining temporal torpor patterns observed in a boreal bat (Eptesicus nilssonii), in which torpor use I) facilitates rapid mass gain or II) conserves stored body mass. Although temporally separated in our dataset, temperature, insect abundance and body mass throughout autumn in the study system indicate that E. nilssonii reaches a majority of its overwintering mass before the onset of increasing daily and nightly torpor use. In combination with generally low food availability by this point in time, these observations suggest that torpor expression might be intended to conserve gained reserves. Our study is intended as a first proof-of-concept for disentangling temporal drivers of torpor in bats during the pre-hibernation fattening phase.

ecology↗

bioRxiv2024

Thermoregulation and Diurnal Roost Selection of Boreal Bats During Pre-Hibernation Period

Living in a seasonal environment poses challenges for small mammals, such as bats, reliant on insects as their primary food source. Bats may adeptly navigate these energetic challenges by reducing their metabolism and body temperature, entering a state of torpor. Particularly during the winter, bats remain torpid for extended periods, but are dependent on sufficient energy reserves to survive until spring. With the onset of autumn and declining temperature, bats face the challenge of building their fat deposits during a time of decreasing food availability. Bats may therefore transition to cooler roosts to initiate torpor, thereby reducing energy expenditure. However, little is still known about torpor use or roost selection by bats in autumn. This study explores the factors influencing roost selection and torpor use and -duration in two bat species during this critical transition period between the breeding and overwintering season. We show that date in autumn is a stronger driver of torpor use than prevailing ambient temperature, and that bats employ specific strategies in which they first increase daytime torpor use before also increasing the use of night-time torpor during the pre- hibernation fattening period, most likely to facilitate rapid fat accumulation. Notably, bats commenced night-time torpor use after spending entire days in torpor. These findings underscore the dynamic nature of torpor and the energy-saving strategies employed during the crucial pre- hibernation period, marking the transition from summer to winter.

ecology↗

bioRxiv2023

Signals of positive selection in Palearctic bat species coexisting with a fungal pathogen

Traits that directly influence the survival of an organism are suspect to positive selection. Disease can act as a driving force in shaping the genetic makeup across populations, even species, if the impacts are influencing a particularly sensitive part of their life cycles. White-nose syndrome is a fungal disease that affects bats during hibernation. The mycosis has caused massive population declines of susceptible species in North America, whereas in Eurasia, where the fungal pathogen has coevolved with its hosts for an extended period of time, bats appear to tolerate infection. Here, we adopted both whole-genome sequencing approaches and a literature search to compile a set of 300 genes from which to investigate for signals of positive selection in genomes of 11 Eurasian bats at the codon-level. Our results indicate significant positive selection in 38 genes, many of which have a marked role in responses to infection. Our findings suggest the fungal disease known as white-nose syndrome may have applied a significant selective pressure on hibernatory Eurasian Myotis-bats in the past, which can partially explain their survival in the presence of the pathogen.

evolutionary biology↗

bioRxiv2021

Next-generation ultrasonic recorders facilitate effective bat activity and distribution monitoring by citizen scientists

Time and budgetary resources are often a limiting factor in the collection of large-scale ecological data. If data collected by citizen scientists were comparable to data collected by researchers, it would allow for more efficient data collection over a broad geographic area. Here, we compare the quality of data on bat activity collected by citizens (high school students and teachers) and researchers. Both researchers and citizen scientists used the same comprehensive instructions when choosing study sites. We found no differences in total bat activity minutes recorded by citizens and researchers. Instead, citizen scientists collected data from a wider variety of habitats than researchers. Involvement of citizens also increased the geographical coverage of data collection, resulting in the northernmost documentation of the Nathusiuss pipistrelle so far in Finland. Therefore, bat research can benefit from the use of citizen science when participants are given precise instructions and calibrated data collection equipment. Citizen science projects also have other far-reaching benefits, increasing, for example, the scientific literacy and interest in natural sciences of citizens. Involving citizens in science projects also has the potential to enhance their willingness to conserve nature. Open Research StatementData are not yet provided, but will uploaded Dryad upon publication.

ecology↗

bioRxiv2020

Winter activity of boreal bats

Natural hibernation sites used by bats in areas that lack cave features have long remained unresolved. To investigate hibernation site selection and winter activity of boreal bats, we recorded bat calls using passive acoustic monitoring on 16 sites. These sites included four rock outcrops with crevices and cave features, three glacial erratics or boulder fields, three ancient shores, three root cellars and three control sites where we did not expect bats to be overwintering. Our results revealed echolocation calls of Eptesicus nilssonii, Plecotus auritus and Myotis sp. We recorded significantly more activity near rock outcrops and root cellars compared to other habitats. We also found that ambient temperature had a positive effect on bat activity and found evidence that P. auritus may be using low barometric pressure as a proxy for suitable foraging conditions during the winter. Our results suggest that rock outcrops may be more important to bats than previously acknowledged, highlighting the need to take these sites in account in planning of conservation measures. Furthermore, our findings underline the suitability of using acoustic monitoring in homing on hibernation sites that are not otherwise accessible.

zoology↗

bioRxiv2020

Roosting ecology of the southernmost bats, Myotis chiloensis and Histiotus magellanicus, in southern Tierra del Fuego, Chile

There are few studies of day-roosting ecology of bats inhabiting the southernmost forests of South America, where cool summer temperatures and land management practices pose several challenges. The goal of the present study was to describe day-roosting habitats and patterns of thermoregulation in two bat species occurring on Tierra del Fuego, Myotis chiloensis (Chilean myotis) and Histiotus magellanicus (southern big-eared brown bat), during late spring. To do so, we tagged 17 bats with temperature-sensitive radio-transmitters, located 17 day-roosts, and collected 81 days of skin temperature data. We concurrently recorded ambient air temperature to determine its effect on torpor use. Both species were found roosting in large diameter (77.8 {+/-} 6 cm), typically live, Nothofagus pumilio trees (lenga) located on the edges of forest gaps or within stands primarily composed of smaller, younger trees. Bats of both species frequently used torpor, with skin temperatures dropping below a torpor threshold on 89% of days (n = 72) and daily minimum skin temperatures averaging 16.5 {degrees}C over the course of our study. Average daily air temperature was a significant predictor of torpor use, with lower skin temperatures and more time spent in torpor observed on colder days. Minimum skin temperature and time spent torpid did not vary between bat species, nor did the characteristics of day-roosts. These data show that spring temperatures in Tierra del Fuego pose an energetic challenge that bats meet through frequent use of torpor, and likely, habitat selection. We recommend local conservation efforts keep these thermal challenges in mind by retaining large trees, which may provide warmer microclimates or room for social groups.

ecology↗

bioRxiv2020

Population connectivity predicts vulnerability to white-nose syndrome in the Chilean myotis (Myotis chiloensis) - a genomics approach

Despite its peculiar distribution, the biology of the southernmost bat species in the world, the Chilean myotis (Myotis chiloensis), has garnered little attention so far. The species has a north-south distribution of c. 2800 km, mostly on the eastern side of the Andes mountain range. Use of extended torpor occurs in the southernmost portion of the range, putting the species at risk of bat white-nose syndrome (WNS), a fungal disease responsible for massive population declines in North American bats. Here, we examined how geographic distance and topology would be reflected in the population structure of M. chiloensis along the majority of its range using a double digestion RAD-tag method. We sampled 66 individuals across the species range and discovered pronounced isolation-by-distance. Furthermore, and surprisingly, we found higher degrees of heterozygosity in the southernmost populations compared to the north. A coalescence analysis revealed that our populations may still not have reached secondary contact after the Last Glacial Maximum. As for the potential spread of pathogens, such as the fungus causing WNS, connectivity among populations was noticeably low, especially between the southern hibernatory populations in the Magallanes and Tierra del Fuego, and more northerly populations. This suggests the probability of geographic spread of the disease from the north through bat-to-bat contact to susceptible populations is low. The study presents a rare case of defined population structure in a bat species and warrants further research on the underlying factors contributing to this.

evolutionary biology↗

bioRxiv2019

Genome-wide changes in genetic diversity in a Myotis lucifugus population affected by white-nose syndrome

Novel pathogens can cause massive declines in populations, and even extirpation of hosts. But disease can also act as a selective pressure on survivors, driving the evolution of resistance or tolerance. Bat white-nose syndrome (WNS) is a rapidly spreading wildlife disease in North America. The fungus causing the disease invades skin tissues of hibernating bats, resulting in disruption of hibernation behavior, premature energy depletion, and subsequent death. We used whole-genome sequencing to investigate changes in allele frequencies within a population of Myotis lucifugus in eastern North America to search for genetic resistance to WNS. Our results show low FST values within the population across time, i.e. prior to WNS (Pre-WNS) compared to the population that has survived WNS (Post-WNS). However, when dividing the population with a geographical cut-off between the states of Pennsylvania and New York, a sharp increase in values on scaffold GL429776 is evident in the Post-WNS samples. Genes present in the diverged area are associated with thermoregulation and promotion of brown fat production. Thus, although WNS may not have subjected the entire M. lucifugus population to selective pressure, it may have selected for specific alleles in Pennsylvania through decreased gene flow within the population. However, the persistence of remnant sub-populations in the aftermath of WNS is likely due to multiple factors in bat life history.

evolutionary biology↗