Joana Sabino Pinto
Dr. rer. nat.
Fungus, Frogs and MHC: The role of sexual selection in the evolution of disease resistance
In order to survive, populations have to deal with constant threats, one of them being pathogens. One way of dealing with pathogens is by detecting them immunologically an eliminating invading organisms. The MHC is a complex of functionally related genes that present pathogens to the immune system and ultimately activate it.
Here, I explore whether amphibians select mates based on this trait (MHC genotype), and whether infection alters preferences. I do this by performing mate choice trials with poison frogs (in a collaboration with the University of French Guiana), and by comparing allelic frequencies in green frogs between parents and offspring.
Environmental factors and the presence of Bd
Pathogen-host-environment interactions determine pathogen distribution ranges. In order to make better predictions of pathogen spreading potential it is essential to determine the effect of environment in pathogen presence. We explored the differences between infected and uninfected sites in the province of Groningen and observed that the presence of rotifers (small zooplankton) and high amounts of NO3 is strongly correlated with Bd absence, and that the presence of copepods (big zooplankton) is correlated with Bd presence.
Filling the gaps: is the chytrid fungus Bd really not present in the province of Groningen?
While the chytrid fungus Bd is generally described as being present everywhere, there are certain areas where, either due to actually not being present or due to under-sampling, the fungus has not been found. One of this Bd-free zones is the province of Groningen, which was last screened in 2010 and no evidence of the fungus was found.
In an exciting collaboration with the Dutch herpetological association RAVON, I, with the help of students and volunteers, am conducting a province-wide screening for this pathogen.
Are fire salamanders aware that they are infected with chytrid?
Infectious chytrid fungi (Batrachochytrium dendrobatidis and B. salamandrivorans, Bsal) are among the main drivers of the worldwide amphibian decline. In Europe, Bsal is an invasive emerging infectious pathogen with devastating effects on the native Caudata communities – particularly on the common and widely distributed fire salamander (Salamandra salamandra) which is highly susceptible and is experiencing mass extinction of natural populations. Currently, we are lacking fundamental knowledge on the reasons for this high susceptibility. Are the individuals not aware of the infection or do they lack the tools to mount a proper immune response? We studied therefore gene expression patterns on Bsal-infected S. salamandra by microarray analysis and RNA sequencing under natural conditions and experimental setups.
Phenotypic plasticity and local adaptation via genetic change are two major mechanisms of response to dynamic environmental conditions. These mechanisms are not mutually exclusive, since genetic change can establish similar phenotypes to plasticity. This connection between both mechanisms raises the question of how much of the variation observed between species or populations is plastic and how much of it is genetic. We use a structured population of fire salamanders (Salamandra salamandra), in which two subpopulations differ in terms of physiology, genetics, mate- and habitat preferences to explore these two mechanisms in terms of morphology and transcriptomics.
Phenotypic plasticity vs. local adaptation
In this project I investigated the composition and dynamics of the skin microbial communities of several amphibians in Germany, Spain, and Japan. Communities were sampled and their composition identified through Illumina sequencing. Communities were found to differ between species, even when hosted under the same exact environmental conditions; at the same time communities differed within species when the environment was not so strictly controlled. In addition community structure shifted with developmental stage and season. Furthermore, species differed in the percentage of chytrid inhibiting OTUs, which is likely associated with differential species susceptibility to infection.
Amphibian skin microbiota
During my PhD I sampled thousands of amphibians and processed (DNA extraction and qPCR) the same amount of skin swabs for the detection of pathogens. This lead me to explore alternatives in order to accelerate the process.
I designed an pool-extraction method that without loosing detection efficiency allowed to reduce the number of extractions and sample processing costs by a quarter. This method was confirmed both in vitro and in vivo, and with multiple DNA extraction kits commonly used in chytridiomycosis studies. The ability to pool samples was dependent on the extraction kit.
More recently, and in order to minimize project costs, I explored the efficiency of DNA extraction kits that are not commonly used in chytridiomycosis research, and was happy to confirm that cheaper alternatives do exist. This allows to increase project sample sizes without having to increase project costs.
Chytridiomycosis methodologies improvements
Amphibians worldwide have been experiencing declines and extinction at an unprecedented rate. One factor leading to the declines is the emerging infectious disease chytridiomycosis. Recently a second fungus has been discovered in the Netherlands, with the ability to induce the same disease, which is extremely lethal to Salamandra salamandra.
Due to the proximity of Germany to the outbreak area we started screening german amphibian populations for the pathogen. In collaboration with several universities, environmental groups and nature enthusiasts we have been monitoring populations all over Germany and have detected the fungus in one location.
Additionally, concerned private amphibian keepers have reached out to us and we have included their collections in our screening with the surprising outcome of a relatively widespread presence of the pathogen in captivity.
Batrachochytrium salamandrivorans in Europe
Understanding individual variation in terms of resistance is incredibly important when it comes to the identification of mechanisms that can contribute to the survival of populations. However, the traditional method to identify susceptibility requires infecting individuals with dangerous pathogens and waiting to see the disease outcome.
My Master thesis aimed to develop an alternative method to identify susceptibility without having to subject individuals to the harms of infection and disease. I explored whether the killing capacity of the skin secretions of amphibians correlates with their known susceptibility. I was happy to discover that the correlation indeed exists!
Using amphibian skin secretions to predict host susceptibility to Batrachochytrium dendrobatidis
