The gap in our knowledge is understanding why WNS is tolerated in European bats but pathogenic in North American bat populations. Being able to identify factors that predict tolerant individuals is important for the conservation of populations threatened by WNS. Recently, some surviving populations of little brown myotis have been discovered in North America at sites where the fungus was first detected nearly ten years ago. The objective of this project was to reveal and validate specific genes associated with tolerance to infection firstly by contrasting allele selection in tolerant/resistant (hereafter WNS-survivors) and susceptible (hereafter WNS-susceptible) little brown myotis populations in North America and secondly, by contrasting the selection patterns in North American WNS-survivors with a European closely related Myotis, the greater mouse-eared bat (Myotis myotis), a species infected by the pathogen but not suffering mortality. Because the fungal pathogen, Pseudogymnoascus destructans (Pd) originates from Europe, Myotis myotis has likely already gone through a similar WNS-caused bottleneck, hence its genome was expected to show similar signatures of selection as the WNS-survivors. Furthermore, the proposal examined genome-wide patterns of genetic diversity that could underpin resilience to infectious disease and the effects of a population bottleneck on genetic diversity in populations that have survived WNS.
WP 1.
Novel pathogens can cause massive declines in populations, but seldom lead to extirpation of hosts. Rather, disease acts as a selective pressure on survivors, driving the evolution of resistance. 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 use whole-genome sequencing to investigate changes in allele frequencies within (temporal variation) and across (geographical variation) genomes of three populations (PA, NY and MI) of Myotis lucifugus, to scan for genetic resistance to WNS. Our results show minor decrease in heterozygosity within the populations across time, i.e. prior to WNS (Pre-WNS) compared to populations that have survived WNS (Post-WNS). We also see low FST -values between Pre-WNS populations, except for a sharp increase in values on scaffold GL429776 between PA and MI. These values are even higher in comparisons between Post-WNS PA and MI populations and NY and PA populations. Thus, WNS has not subjected M. lucifugus to selective pressure, but may have allowed the rise of a local adaptation in PA through weakening the connectedness of populations. However, the existence of remnant populations is thus likely due to other factors in bat life history besides genetic adaption.
Work package 2
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. European species appear to be tolerant/resistant to the fungus, and do not suffer from the pathological consequences of the disease. We collected both infected and uninfected tissue samples from two bat species during the hibernation period: the Palearctic Myotis myotis, and the Nearctic M. lucifugus, to compare responses to local infection. M. myotis showed much lower fold changes in gene expression due to local infection with P. destructans, despite similar levels of infection. Only 5 transcripts were differentially expressed in M. myotis at an FDR cutoff of 0.05 while 1981 transcripts were differentially expressed in the M. lucifugus samples. Gene ontology analysis revealed that that the differentially expressed genes in the latter were involved in muscle cell development/function, cell communication/signaling, and immune responses. These results, in conjunction with our previous studies, enforce the view that local immune reactions play an important function in WNS-associated pathology.
Submitted manuscripts:
Lilley TM, Wilson IW, Field KA, Reeder DM,Turner G, Kurta A, Hoff S,Herzog C, Paterson S."Genome-wide changes in genetic diversity among populations of Myotis lucifugus affected by white-nose syndrome" In Review, Molecular Ecology.
In preparation
Lilley TM, Prokkola JM, Blomberg AS, Paterson S, Johnson JS, Turner GT, Bartonička T, Bachorek E Reeder DM, Field KF. "True survivors: host response to bat fungal pathogen varies according to past exposure"
