Demographic variation in the U.K. serotine bat: filling gaps in knowledge for management

Investigating the emergence of a zoonotic virus: phylogenetic analysis of European bat lyssavirus 1 in the UK

European bat lyssavirus 1 (EBLV-1, Lyssavirus hamburg) is predominantly detected in serotine bats (Eptesicus serotinus) and is responsible for the majority of bat rabies cases in mainland Europe. A passive bat rabies surveillance scheme detected the virus in a serotine bat in the UK for the first time in October 2018. As of May 2024, 34 cases have been reported, 20 of which involved contact with an animal and 5 reported human contact. We investigated the emergence of EBLV-1 by undertaking comprehensive sequence analysis and Bayesian phylogenetics, based on complete virus genomes of 33 UK sequences and 108 sequences covering six countries in mainland Europe (1968-2023), including 21 French EBLV-1-positive RNA samples sequenced for this study. Sequence analysis revealed extreme similarity among UK EBLV-1 sequences (99.9%-100%), implying a single source of introduction rather than multiple independent introductions. Bayesian analysis revealed that the UK EBLV-1 sequences shared their most recent common ancestor with an EBLV-1 sequence from a serotine bat detected in Brittany, France, in 2001, with an estimated date of divergence of 1997. Within the UK sequences, the earliest divergence was estimated to occur in 2007. This study provides valuable insights into the molecular epidemiology of an emerging zoonotic pathogen and improved understanding of the risks posed to public and animal health.

Spring weather conditions influence breeding phenology and reproductive success in sympatric bat populations

Climate is known to influence breeding phenology and reproductive success in temperate-zone bats, but long-term population level studies and interspecific comparisons are rare. Investigating the extent to which intrinsic (i.e. age), and extrinsic (i.e. spring weather conditions), factors influence such key demographic parameters as the proportion of females becoming pregnant, or completing lactation, each breeding season, is vital to understanding of bat population ecology and life-history traits. Using data from 12 breeding seasons (2006-2017), encompassing the reproductive histories of 623 Myotis daubentonii and 436 Myotis nattereri adult females, we compare rates of recruitment to the breeding population and show that these species differ in their relative sensitivity to environmental conditions and climatic variation, affecting annual reproductive success at the population level. We demonstrate that (1) spring weather conditions influence breeding phenology, with warm, dry and calm conditions leading to earlier parturition dates and advanced juvenile development, whilst cold, wet and windy weather delays birth timing and juvenile growth; (2) reproductive rates in first-year females are influenced by spring weather conditions in that breeding season and in the preceding breeding season when each cohort was born. Pregnancy and lactation rates were both higher when favourable spring foraging conditions were more prevalent; (3) reproductive success increases with age in both species, but at different rates; (4) reproductive rates were consistently higher, and showed less interannual variation, in second-year and older M. daubentonii (mean 91.55% ± 0.05 SD) than M. nattereri (mean 72.74% ± 0.15 SD); (5) estimates of reproductive success at the population level were highly correlated with the size of the juvenile cohort recorded each breeding season. Improving understanding of the influence of environmental conditions, especially extreme climatic fluctuations, and the identification of critical periods (i.e. spring for reproductive female bats in temperate zones), which have disproportionate and lasting impacts on breeding phenology and reproductive success at a population level, is critical for improving predictions of the likely impact of climate change on bat populations.