Browsing by Person "Steidle, Johannes"

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Habitat use and morphological adaptations of endemic rodents (Muroidea: Nesomyinae) of East Madagascar
(2014) Marquart, Kathrin; Steidle, Johannes
In an adaptive radiation, Madagascar’s endemic rodents colonised a variety of different habitats. In this thesis, ecological and morphological aspects of the frequently sympatric nesomyines of East Madagascar were analysed. In the first part of the study, vegetation analyses were conducted in a model rainforest in East Madagascar and compared with species distribution to describe the species ecology. The results represent a preliminary ecological classification of the habitat use of nesomyines. In the second part of the study, the morphology of the hands and feet (chiridia) was correlated with ecological parameters and habitat use for the first time. Adaptive differentiations of the chiridia give evidence of a species’ ecological niche. Certain patterns of the volar integument, epidermal structures as well as length and area ratios are discussed in respect of their functional and ecological adaptive value. Seven endemic rodent species (Eliurus grandidieri, E. minor, E. tanala, E. webbi, Nesomys rufus, Gymnuromys roberti, Brachytarsomys albicauda) were trapped with live traps in different microhabitats. Ecological data and information on habitat structures were collected along five 1 km long trails. The specialised rodents were found in different ecological niches: on trees, lianas, underneath wood and thick roots, in dead wood or rotten logs. Some were found close to small rivers, some in humid valleys, whereas others seemed to prefer the higher mountain slopes or misty ridges, up to 1200 m a.s.l. Microhabitat analyses were conducted and trails where a species was significantly more abundant were compared with those where it was rare. The presence of an endemic rodent species was strongly connected with forest type, forest structure and vegetation density. In contrast, the deforested and cleared areas were species-poor. For the morphological studies, detailed microscopic drawings of the hands and feet were prepared of voucher specimens to be compared between the species. The chiridian structures differed clearly between the seven species. Slender hind feet with small thenar pads were significantly correlated with a terrestrial locomotion and a ground-dwelling ecology. Species with a predominantly arboreal locomotion exhibit large and prominent pads, covering a great area of the chiridian surface. Large-tree-climbers have larger pads in relation to foot size than bamboo-grass and small-branch-climbers which possess relatively longer feet with longer toes. Climbing on large trees needs good adhesive properties and climbing on grass or thin branches needs good grasping abilities. In conclusion, certain morphological structures of the rodents chiridia are evidence of a special way of life and foot-pad morphology in particular mirrors special adaptations to a species habitat. These adaptations are regarded as important to understand niche occupation, certain ecological aspects and locomotion forms of sympatric species. Thus, habitat preferences and special habitat requirements of the endemic nesomyines of East Madagascar could be analysed in details. In this thesis, it could be documented for the first time by the combination of these ecological and morphological results that the chiridian morphology allows to differentiate nesomyine taxa on ecological level.
Reproductive success and escape behaviour in urban greylag geese (Anser anser)
(2023) Mai, Sabrina; Steidle, Johannes
Urbanisation and its effect on animals and plants is an important factor to analyse in behavioural studies. Warmer temperatures and an increased availability of food provide benefits to animals occurring in urban habitats. In contrast, these animals also have to tolerate the disturbance caused by artificial lights or noise. This work studies an urban local population of greylag geese Anser anser. Greylag geese live in wetland landscapes, but also in urban parks with wide lawns and water bodies. Since the nineties, the city of Stuttgart in southwest Germany is home to a breeding population of greylag geese. As a result of a long-term ringing project, a large percentage of the population is ringed. This data shows that the population is non-migratory, as the geese generally remain in the area year-round. The individual identification offers the opportunity of tracing data, such as reproduction or behaviour, for the same animal over a longer period. This data can then be individually connected to genetic information, which is a large benefit in behavioural studies. The first chapter of this work focuses on reproductive success as one of the two key parameters which influence population change. As reproductive success itself is influenced by a variety of factors, this study analysed the effect of factors such as population size, brood size or dispersal by using two different measures of reproductive success: fledging success (the relation between hatched and fledged young of a brood ) and hatchling survival (the likelihood of a hatchling to survive to fledging). Fledging success of pairs initially increased with the number of times pairs bred together but decreased again in later broods. While the experience of a pair is therefore beneficial for their reproductive success, the subsequent decrease may be caused by the increasing age of the parents. The brood size also influenced reproductive success, as fledging success was higher in larger broods and hatchling survival was also positively influenced by brood size. In some years, several goose families dispersed from the breeding ground to a different brood rearing area. Hatchling survival was higher in these families, though this effect decreased again when the broods were large. The total population size had a negative effect on hatchling survival, indicating density dependence. To determine if there is a genetic basis for escape behaviour in greylag geese, the second chapter of this work compares Stuttgart’s urban local population of greylag geese with a rural local population in the countryside near Ludwigsburg. Animals occurring in urban habitats need a higher tolerance towards disturbance. This tolerance may be due to the animal’s personality. Animal personality is defined as consistent behaviour across time or context and is expressed for example through risk-prone behaviour. Urban animals are likely more risk-prone than their rural counterparts and thus have a bolder personality. There is increasing evidence that personality and thus behaviour have a genetic basis. This study analyses the dopamine D4 receptor (DRD4) as a candidate gene associated with boldness / shyness and fear. The gene showed a high variation with eleven alleles and 35 genotypes being detected in the analysed greylag geese. Allele and genotype frequencies were skewed, with one allele and two genotypes occurring more often than the others. Based on the detected frequencies, these two genotypes were defined as common and the remaining 33 as rare genotypes. Common genotypes were found more frequently in geese from urban areas, while rare genotypes were found more frequently in geese from rural areas. To determine if the detected genotypes could be associated with behaviour, the flight initiation distance (FID) of individual geese was measured. As the geese are ringed, FID measurements could be directly assigned to a specific goose and thus to its genotype. A high FID indicates geese which are more cautious, while a low FID indicates boldness. Indeed, greylag geese of the rural location show increased FID, while those in urban areas in Stuttgart have lower FIDs and thus a bolder personality. Despite these results, there was no significant correlation between DRD4 genotype frequency and FID. This may be explained by methodological effects. Alternatively, DRD4 has also been associated with other behaviours such as novelty seeking and exploratory behaviour. These behaviours may also differ between urban and rural animals and may thus be the reason for the detected frequencies. It is therefore likely that local habitat selection may be influenced by the DRD4 genotype. Overall, this work demonstrates that different factors, including genetics, should be taken into account when managing urban populations of wild animals, as their behaviour can differ significantly from their rural counterparts, even within a single species.
Reproduktionsbiologie und olfaktorisches Verhalten des Kleinen Beutenkäfers Aethina tumida MURRAY 1867 (Nitidulidae)
(2014) Mustafa, Sandra Gabriele; Steidle, Johannes
This dissertation aimed to investigate the olfactory behaviour and reproductive biology of the small hive beetle (Aethina tumida, Nitidulidae). Our investigations focused on the second part of the small hive beetle life cycle, after beetles emerged from the ground and invaded a honeybee (Apis mellifera) hive. Once in the hive, beetles show strong developed aggregation behaviour and start reproducing. We suspected the involvement of aggregation- and/or sexual pheromones in these social interactions. Our goal was to identify or at least to prove the existence of the latter. Three laboratory bioassays were developed on this purpose: aggregation-assay, filter-assay and choice-assay. Gender and age independent aggregation behaviour was revealed by the aggregation assay. The choice assay revealed a gender and age dependent preference for the opposite sex in both genders. The involvement of chemical substances in this system was proved by the filter-assay. Pieces of filter paper, which were left with certain beetle stages to leave marks on, proved to be attractive when offered to other beetles. A detailed description of the mating behaviour was supposed to reveal further information about chemical communication in the small hive beetle. Therefore an ethogram and flow diagram were compiled through video analysis of the mating behaviour. Several behaviours observed before, after and during copulation indicated chemical communication on tactile level; this included tapping, thrilling or rubbing of the cuticle surface of fellow mates. Electron microscopy pictures showed a high density of sensillae and pores on the areas involved in frequent behavioural interactions. The description of the mating behaviour revealed several indications for cryptic female choice mechanisms. One was the distinct aggressive behaviour of females in contrast to males. They pushed other beetles in high frequency and often interrupted matings this way. Comparison of matings in single pairs and aggregations showed that small hive beetles only copulate in aggregations and sexual behaviours reaches its peak at the ages from two to three weeks. It is further the only age in which more hetero- than homosexual matings occur. All these facts added up indicated female pheromone emission from the age of two weeks on. This feature might be seen as an extraordinary and unique adaption to their honey bee host. Single pairs would never be able to compete with the hygienic behaviour of the honeybees and all their offspring and eggs would be cleaned out immediately. It further helps in synchronizing reproduction of all beetles in an aggregation which in turn favours mass reproduction and surrendering the host. The central role of this mass reproduction strategy became further obvious when investigating the susceptibility of small nucleus hives to invasion of the small hive beetle. Nucleus hives were far more vulnerable to invasion of the small hive beetle than full sized colonies. After a four week study period under moderate invasion pressure, half of all 24 nucleus colonies showed signs of small hive beetle reproduction, namely they either collapsed or were infected with larvae in their final development stage. In contrast, none of the full-sized colonies showed any symptoms. Beekeepers in affected areas should consider this in their daily tasks and avoid using too-small nucleus colonies for queen rearing or colony propagation. The small hive beetle depends on the collapse of the colony to ensure its reproduction in contrast to many other parasites which try to keep their host alive as long as possible. In the first stage of the adult live cycle, after pupation and emergence from the ground, foraging and host-finding behaviour have first priority. Volatiles from fermenting honey might be a key trigger during this time. Infection with larvae incites fermentation of honey and pollen which produces the typical slimy combs in the end. Colonies in the stage between collapse and symptom-free infestation are supposed to be the most attractive. There are still food resources available but the honey bee host is already weak and vulnerable. In a preliminary trial under canvas we investigated the effect of various ferment products. They seemed to be attractive and could be considered as lure for traps in the field after further experiments. In conclusion one can say that it was possible to prove the existence of chemical- probably chemotactical communication via pheromones in the small hive beetle A. tumida. Olfactory orientation is present in all stages of the life cycle and aggregation and a mass reproduction strategy is closely connected to it on the reproductive and behavioural level. Thereby, this effective mass reproduction strategy may be the key to the success of this invasive species.
Speciation and isolating barriers in a parasitoid wasp focusing on the role of reproductive isolation caused by endosymbionts
(2023) Pollmann, Marie; Steidle, Johannes
Hymenoptera are one of the most speciose animal taxa, presumably caused by a high rate of speciation. The investigation of evolutionary processes is predominantly based on the biological species concept (BSC), which defines species as groups of interbreeding individuals which are reproductively isolated from individuals of other groups. As an alternative approach, species are delimitated by predetermined threshold distances in the so-called barcode segment of the mitochondrial COI gene. Many arthropods are infected with endosymbiotic bacteria, some of which have been shown to manipulate their hosts’ reproduction via mechanisms like cytoplasmic incompatibility (CI). It occurs between infected males and uninfected females and results in the reduction or absence of diploid offspring. Due to their ability to interfere with the reproduction of their hosts, endosymbionts have been suggested to be potential drivers of their hosts’ speciation processes. Lariophagus distinguendus is a parasitoid wasp which uses larvae of multiple coleopteran species as hosts. In past studies, two distinct species of L. distinguendus have been discovered. They are separated by different barriers including unidirectional CI caused by an unknown bacterium. Here, the nature of the CI inducer in crosses between untreated males and tetracycline-treated females of the L. distinguendus strain STU was investigated. Additionally, diversity and speciation processes were investigated within the L. distinguendus species complex by constructing phylogenetic trees with COI and nuclear genes as well as by conducting crossing experiments with different strain combinations. The bacterium Spiroplasma, termed sDistinguendus (sDis) for its L. distinguendus host, was identified to be the causative agent of this CI. Despite being known for multiple types of interactions with various hosts, Spiroplasma had not been demonstrated to cause CI before. None of the other bacteria identified within STU were associated with CI and none of the known CI inducers and other bacteria manipulating reproduction were found. The potential for maternal transmission was shown by the presence of sDis in the ovaries of STU females. Transferring sDis and CI from infected to uninfected STU females via hemolymph microinjection solidified the connection between CI and sDis. The simplicity of this transfection technique could prove to be valuable for applicable purposes in future. CI strength varying between male offspring of the injected females was not linked to the titer of sDis. All available L. distinguendus strains were analyzed with the barcode segment of COI as well as five nuclear genes to infer their phylogenetic relationships. Furthermore, five pairs of strains covering a gradient of genetic divergence were selected for crossing experiments investigating their reproductive isolation. The nuclear genes recovered two clusters identical to the previously known species, whereas three distinct clusters were found based on barcoding. These three clusters were revealed as separate species due to very high to complete reproductive isolation in crossing experiments between strains representing each of them. Threshold values of COI distances commonly used for species delimitation relying predominantly on barcodes, i.e. 2% to 2.2%, were shown to be not applicable for L. distinguendus due to the divergence between strains of the same species exceeding these thresholds. This calls the faith in these pre-set thresholds and the barcode-only approach to species delimitation into question and suggests the consideration of additional data along with those obtained by barcoding for species delimitation. Reproductive isolation between the strains was found to span a continuum of divergence from no reproductive isolation and low genetic divergence to complete isolation and high genetic divergence. The first barrier, present in all strain pairs, was sexual isolation, ranging from weak and unidirectional to complete and near complete in both directions. In the untreated cross between BIR females and STU males, sDis-induced CI was present along with sexual isolation. The reduced fertility of hybrid males was the next barrier to appear in the three more distantly related strain pairs along with behavioral sterility of hybrid females in the one strain pair among them where it was measured. These barriers were followed by the behavioral sterility, inviability, and physiological sterility of hybrid males and as last barrier by the reduced fertility of hybrid females. Due to the majority of barriers affecting hybrid males, but not females, speciation in L. distinguendus follows Haldane’s rule, stating that a fitness loss present in the hybrids of only one sex will be affecting the heterogametic sex, i.e. the males in L. distinguendus. In conclusion, the CI between infected males and uninfected females of L. distinguendus was found to be caused by Spiroplasma, termed sDis, marking the first time for CI to be demonstrated as phenotype of Spiroplasma. It was also one reproductive barrier present in crossings of different L. distinguendus strains, apparently contributing to their divergence. The diversity within the L. distinguendus species complex was shown to be greater than detected before, as seen by the discovery of a third species. The studied pairs of strains covered a wide range of both genetic divergence and strength of reproductive isolation, suggesting L. distinguendus to be currently in the process of ongoing speciation. The commonly used threshold distances in COI were not applicable for species delimitation in L. distinguendus, challenging their unconditional use.