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Relative importance of plastic and genetic responses to weather conditions in long-lived bats
(2022)
In the light of the accelerating pace of environmental change, it is imperative to understand how populations and species can adapt to altered environmental conditions. This is a crucial step in predicting current and future population persistence and limits thereof. Genetic adaption and phenotypic plasticity are two main mechanisms that can mediate the process of adaptation and are of particular importance for non-dispersing species. While phenotypic plasticity may enable individuals to cope with short term environmental changes, genetic adaptation will often be required for populations to survive in situ over longer time spans. However, a rapid genetic response is expected particularly in species with fast life histories or large population sizes, leaving species with slow life histories potentially at higher extinction risk. The Bechstein’s bat (Myotis bechsteinii) is a mammal of 10 g weight that - despite its small size - is characterized by a slow life history, with low reproductive output and long lifespan, and is already considered to be of high conservation concern. Past work demonstrated body size to be a highly fitness-relevant trait in Bechstein’s bats. Body size is further known to be a pivotal trait shaping the pace of life histories in numerous species. Simultaneously, many studies reported noteworthy changes in body size as a response to shifting environments across different taxa. This suggested a potential for high plasticity in this trait in Bechstein’s bats as well; however, changes in body size could have vital impacts on demographic rates.
Therefore, this dissertation investigated the following questions: firstly, what shapes the fundamental development of body size in M. bechsteinii, and, specifically, is there an impact of weather conditions on body size? If so, in what form and magnitude? Secondly, how does body size subsequently influence the pace of life in females? What is the cost of a faster or slower pace of life, and how does fitness compare across individuals with slow and fast life histories? And finally, to what extent can changes in body size be attributed to either phenotypic plasticity or genetic adaptation? What is the evolutionary potential of body size in the populations? And, consequently, what implications can we draw regarding population persistence of these colonies?
To answer these questions, we analyzed a long-term dataset of over two decades collected from four wild Bechstein’s bat colonies. We used individual-based data on survival, reproduction and body size, built multi-generational pedigrees, and combined everything with meteorological data. In Manuscript 1 we found that, in contrast to the declining body size observed in many species, body size in Bechstein’s bats increased significantly over the last decades. We demonstrated that ambient temperature was linked to the development of body size and identified a sensitive time period in the prenatal growth phase, in which body size was most susceptible to the impact of temperature. We established that warmer summers resulted in larger bats, but that these large bats had higher mortality risks throughout their lives. Manuscript 2 then revealed the influence of body size on the pace of life in Bechstein’s bats and demonstrated high plasticity in intraspecific life history strategies. Large females were characterized by a faster pace of life and shorter lifespans, but surprisingly, lifetime reproductive success remained remarkably stable across individuals with different body sizes. The acceleration of their pace of life means that larger females compensated for their reduced longevity by an earlier reproduction and higher fecundity to reach similar overall fitness. Ultimately, differences in body size resulted in changes in population growth rate via the impact of size on generation times. Results of Manuscript 3 were then able to clarify the extent to which changes in body size were founded on either phenotypic plasticity or genetic adaptation. We demonstrated a particularly low heritability in hot summers, indicating that variance in body size was mostly driven by phenotypic plasticity, with few genetic constraints. During cold summers, behavioural adaptations by reproducing bats seem to be able to mitigate negative effects of cold temperatures. These behaviours, such as social aggregation or preference for warm roosts, are, however, essentially irrelevant in hot environments. In addition, a low evolvability of forearm length points to a low capacity to respond to selection pressures associated with the trait.
We can conclude that body size in M. bechsteinii has increased over the last two decades as a response to global warming and is only slightly constrained by its genetic underpinnings. We can further demonstrate a direct link between body size and the pace of life histories in the Bechstein’s bat populations and how changes in body size impact demographic rates via this linkage. In the context of climate change and hotter summers, our findings consequently suggest that body size will likely increase further if warm summers continue to become more frequent. Whether this plastic response of body size proves to be adaptive in the long term, however, remains to be seen. While, up to this point, switching to a faster life history has been successful in compensating fitness losses, this strategy requires sufficient habitat quality and is likely risky in times when extreme weather events are becoming more frequent, as predicted by most climate change scenarios.
Durch zymografische Untersuchungen und Massenspektrometrie (MS) wurden neun Proteasen vom Subtilisin-Typ im Wurzelexsudat von Nicotiana tabacum identifiziert. Ein Peptid-Antikörper wurde produziert, der die affinitätschromatografische Anreicherung einer tobacco root exuded subtilase (TREXS, XP_016501597.1) und zweier Isoformen sowie eines Peroxidase-artigen und eines SERK2-artigen Proteins ermöglichte. Basierend auf dem Subtilase-EST, der in der MS identifiziert worden war, wurde die full-length cDNA von TREXS durch 5'RACE und 3'RACE sequenziert und die gDNA kloniert. Das intronfreie TREXS-Gen codiert eine 756 Aminosäuren lange Subtilase mit Signalpeptid, I9-Inhibitordomäne, PA- und Fn-III-artiger Domäne. Der Nachweis von TREXS-mRNA in Blattgewebe zeigte, dass TREXS nicht exklusiv auf Wurzeln beschränkt ist. Phylogenetische Analysen zeigten, dass SDD1 die ähnlichste Subtilase aus A. thaliana zu TREXS ist. Mit großer Wahrscheinlichkeit ist TREXS jedoch nicht das Ortholog zu SDD1, weil zum einen strukturähnlichere Subtilasen zu SDD1 in Tabak existieren und zum anderen SDD1 an der Ausprägung von Stomata in der Blattepidermis beteiligt ist, TREXS hingegen im Wurzelexsudat vorkommt. Das
MS-identifizierte SERK2-artige Protein, das bei der Peptid-Antikörper-Affinitätschromatografie zusammen mit TREXS angereichert wurde, ist Kandidat als Substrat für TREXS, weil es potenziell durch IgG–TREXS–SERK2-like-Interaktion co-angereinigt wurde, die in-silico docking-Vorhersagen zwischen den modellierten Molekülen von TREXS und SERK2-like einen proteolytisch relevanten Bindungszustand vorhersagt und es strukturelle Ähnlichkeit mit LRP, einem bekannten Substrat der Subtilase P69C, hat. Die transiente Expression rekombinanter TREXS in N. benthamiana war möglich, zeigte sich jedoch kritisch gegenüber C- und N-terminal fusionierten Anhängen: Transiente Transformation mit TREXS oder TREXS:Strep-tag führte zu proteolytisch aktivem Protein. Jedoch war der C-terminale Strep-tag nicht funktionell. Längere C-terminale Anhänge und auch TREXS-Mutanten mit inaktiviertem katalytischen Zentrum erbrachten kein Genprodukt. C-terminales GFP erbrachte – auch bei mutiertem katalytischen Zentrum – stets nur den GFP-Anteil des Fusionsproteins.