The contribution of differential hatching success to the fitness of species and interspecific hybrids

Resting egg banks of microcrustaceans have been used to reconstruct the evolutionary and ecological history of species. However, recent studies provided evidence for a discrepancy between dormant propagules in the sediment and the planktonic population. This pattern raises two questions: First, what is the value of data on resting egg banks for population dynamics over time and second, which component of the reproductive cycle causes the observed inconsistency? In our study we focussed on the second question by comparing the taxon composition of a resting egg bank with the reproductive success of ex-ephippial hatchlings. Species and interspecific hybrid identification of dormant and hatched stages was achieved through the application of restriction fragment length polymorphism analysis of an internal transcribed spacer region. We found no significant deviation between the proportion of hatched Daphnia galeata, D. galeata x hyalina and D. hyalina individuals and the observed taxon composition of the resting egg bank. However, species and hybrids differed in their mode and relative success of reproduction. We conclude that the components of reproductive success in Daphnia contribute differentially to the fitness of species and interspecific hybrids. The discrepancy between resting egg banks and "active" planktonic populations results not from differential hatching of species but from the reproductive success of ex-ephippial females and the timing and frequency of sexual reproduction of the different taxa

Envisioning a Literacy Partnership: The University of Nebraska at Omaha’s Criss Library and Girls Inc.

The history of academic library involvement in service learning is varied. This paper provides an overview of service learning and the literature on academic libraries’ participation in service learning activities. A vision of service learning participation is described, as well as the implementation of service learning activities in two library science courses. Strategies for future library contributions to service learning are presented to encourage more widespread involvement across the profession

Introduction. Extent, processes and evolutionary impact of interspecific hybridization in animals

Since the time of Charles Darwin, studies of interspecific hybridization have been a major focus for evolutionary biologists. Although this phenomenon has often been viewed as problematic in the fields of ecology, taxonomy and systematics, it has become a primary source of data for studies on speciation and adaptation. Effects from genetic/evolutionary processes, such as recombination and natural selection, usually develop over extended periods of time; however, they are accelerated in cases of hybridization. Interspecific hybrids exhibit novel genomes that are exposed to natural selection, thus providing a key to unravel the ultimate causes of adaptation and speciation. Here we provide firstly a historic perspective of hybridization research, secondly a novel attempt to assess the extent of hybridization among animals and thirdly an overview of the reviews and case studies presented in this theme issue

The reconstruction of evolutionary patterns from daphnia resting egg banks

In this study I analysed past and recent Daphnia populations from Lake Constance and Greifensee. Herefore, I first established a set of microsatellite markers applicable to European Hyalodaphnia species (chapter 1). Primers were also identified for species specific fragment lengths. 32 markers were then available to characterize the resting egg banks of Daphnia galeata and D. hyalina. Chapter 2 presents the reconstruction of the taxonomic composition in these two ecologically different lakes. This part of my work shows that the eutrophication that occurred in both lakes in the mid of the last century has strongly influenced the Daphnia populations. In both lakes Daphnia galeata established and hybridized with the indigenous D. hyalina. Interspecific hybridization resulted in introgression on the mitochondrial and nuclear level. In chapter 3 resting eggs from the sediments of the 1960s, 1970s, 1980s, 1990s and 2000s were characterized with microsatellite markers. The aim was to specify the extent of interspecific hybridization and nuclear introgression assuming that the genetic exchange between both species has an impact on their adaptation to their habitat. In life history experiments D. galeata and D. galeata x hyalina clones hatched from different time periods showed significant differential responses to food quality. Therefore, the question had to be answered how the Daphnia resting egg bank and the planktonic population are connected. In chapter 4 hatching experiments were conducted to bridge this gap of scientific knowledge in the life cycle of cyclic parthenogenetic waterfleas. Only D. galeata individuals were able to establish a clonal lineage after maturity. All observed recombinant individuals did not reproduce at all or firstly went through another sexual phase of reproduction i.e. produced resting eggs. In order to compare the findings of chapter 4 with the taxon composition of the recent planktonic population of Daphnia in Lake Constance, samples were taken over one season (between May 2005 and September 2006). During the season, the taxonomic composition of Daphnia changes severely with D. galeata being most abundant during the warm season and D. hyalina in the cold season. Moreover, some individuals were detected, that did not follow this pattern. With mitochondrial analysis those individuals were identified as mitochondrial introgressants and processed to life history experiments. Significant differences in the somatic growth rate under different temperatures (5°C, 12.5°C and 20°C) were related to the origin of the mitochondrial genome rather than the nuclear taxonomic assignment of the individual. The findings of this study show that all organisms exposed to rapid ecological changes and their microevolutionary reaction to those.Viele Seen in Europa waren in den letzten Jahrzehnten starken anthropogenen, ökologischen Veränderungen ausgesetzt, wobei die Einschleppung von Neobiota, Einbringung von Medikamenten-Rückständen und Chemikalien und die Eutrophierung dieser Habitate einen besonders gravierenden Einfluss auf deren natürliches Gleichgewicht haben. Die weit verbreitete Eutrophierung der Gewässer durch den Eintrag von phosphorhaltigen Waschmitteln und Düngemitteln wurde in den letzten Jahrzehnten durch Umweltschutzmaßnahmen und Kläranlagen grösstenteils annähernd rückgängig gemacht, um in diesen Habitaten einen ursprünglichen ökologischen Status wieder herzustellen. Für die Erforschung der durch Eutrophierung ausgelösten Prozesse wurden Arten aus der Familie Daphniidae (Untergattung Hyalodaphnia) zur Untersuchung ausgewählt. Während sich Daphnien unter optimalen Lebensbedingungen, wie sie im Frühjahr und Sommer herrschen, asexuell vermehren, werden zu anderen Zeiten nicht nur sexuelle Weibchen sondern auch Männchen gebildet. Im sexuellen Reproduktionszyklus bilden Daphnien Dauereier, die in eine cuticuläre Hülle eingebettet sind. Diese Ephippien sind resistent gegen Austrocknung, Frost und Druck und können so Zeiten überstehen, in denen das Überleben für ein adultes Tier nicht mehr möglich ist. Die Dauereier sind auch nach mehreren Jahrzehnten noch in der Lage, sich zu entwickeln und bilden in ihrer Gesamtheit im Sediment eine resting egg bank (Dauerstadienbank), in der das genetische Material der vergangenen Jahre konserviert vorliegt. In dieser Doktorarbeit werden die Prozesse innerhalb von Populationen mehrerer Hyalodaphnien-Arten rekonstruiert, die anthropogenen Einflüssen ausgesetzt waren. Im Bodensee (Deutschland, Schweiz und Österreich) und Greifensee (Schweiz) kommen die drei untersuchten Arten Daphnia galeata, D. hyalina und D. cucullata (nur in letzterem) vor, die, seit sie zusammen vorkommen, hybridisieren. Die Prozesse, die sich innerhalb dieser Populationen abgespielt haben, wurden anhand der Dauerstadienbanken dieser Arten rekonstruiert, teils durch direkte Anwendung von molekular-genetischen Methoden, teils durch Life-History-Versuche an Tieren, die aus Dauerstadien schlüpften und bis zu 40 Jahre alte Genotypen repräsentieren. Auf der einen Seite wurde besonderer Wert auf die Analyse der Auswirkungen der Eutrophierung und Reoligotrophierung dieser physikalisch unterschiedlichen Seen auf die Daphnia Populationen gelegt. Auf der anderen Seite wurde verfolgt, welchen evolutionären Effekt interspezifische Hybride und Introgression zwischen den Arten über die Zeit haben..