Alžbeta Darolová

Composition of Bacterial Assemblages in Different Components of Reed Warbler Nests and a Possible Role of Egg Incubation in Pathogen Regulation

Bacteria play a central role in animal health. Yet, little is known about the acquisition of bacteria and the extent to which bacteria are acquired from different environmental sources. For example, bird nests host diverse bacteria associated with the eggs, nestlings and nesting material, but previous research has typically focussed on only a limited number of nest components at a time. It therefore remains unknown to what extent bacteria are transmitted between these components. Using both molecular and culture techniques, we characterised nest-associated bacterial assemblages throughout the entire nesting cycle of reed warblers by sampling bacteria on eggs before and during incubation, within nestling faeces, and on the nesting material of post-breeding nests. We found that bacterial assemblages clustered by nest component. Yet some overlap existed between nest components, suggesting that bacterial transmission across components is likely to occur. Eggs and nestlings from the same nest harboured more similar bacteria than expected by chance, suggesting an influence of environment or genetics on bacterial assemblages. Bacterial loads were not lower on incubated eggs. Instead, incubation was associated with a change in the structure of assemblages, including a decrease in potentially-harmful Gram-negative bacteria. In addition we show for the first time, that incubation is associated with the complete extinction of harmful haemolytic bacteria. Overall, our study appears to be the first to demonstrate differences in bacterial assemblages between bird nest components. In addition, we highlight the complexity of nest bacterial assemblages and provide new insights into the benefits of incubation.

Reproductive success decreases with colony size in the European bee-eater

The evolution of coloniality is usually explained by a benefit/cost ratio greater than one. Alternatively, when costs exceed benefits, a clumped or restricted availability of limiting resources is used to explain coloniality. In this study we examine the relation between reproductive success and colony size in the European bee-eater (Merops apiaster). In our study population in Slovakia colony size varied from solitary breeding pairs up to 79 pairs per colony. We found no seasonal effects on reproductive success, however, there was a negative correlation between colony size and chick condition and survival. This relationship, although not significant, tended to be the same when examining only the earliest breeding pair of each colony site. There was no relation between reproductive parameters and age of parents and no indication for age related settlement or any effect of the nest hole position within a colony. Limitation of nesting sites and distribution of food are probably two important determinants for colonial breeding in this species. Different aspects, including the rare occurrence of helpers, are discussed as possible factors explaining the negative relationship between annual reproductive success and colony size.

Does egg colouration signal female and egg quality in reed warbler (Acrocephalus scirpaceus)

To explain the evolution of egg colouration in open cup nesting species, a number of functions have been suggested. Recent studies focus on the role of eggshell colour as a postmating sexually selected trait of females which manipulates male parental investment. A basic prediction of this hypothesis is that egg pigmentation reflects female quality. In this study we examine whether there is a relationship between eggshell colouration and either female quality or egg quality in reed warblers. This open cup nesting species has eggs that are heavily spotted with brownish marks on a bluish-green background. We used several parameters describing female and egg quality, and measured eggshell colouration at the blunt pole and the egg centre, deriving four colour variables from colour spectrometry. To determine egg quality parameters, the third egg of each clutch was sampled and analysed. To determine female quality, females were trapped shortly after egg laying, and several morphological and a single conditional variable were determined. Additionally, a blood sample was taken to determine blood parasites (avian malaria and Trypanosoma spp.) and a faecal sample to determine intestinal parasites (Isospora spp). Our results revealed that eggshell pigmentation appears to be independent of female condition and parasites, but reflects concentrations of egg compounds such as testosterone and lysozyme. Egg colouration is also related to yolk weight and egg size. Our results further suggested that the information about colour varies depending on the position on the egg (blunt pole or egg centre). The only relationship with females was between female size (tarsus length) and egg colouration, which suggests a genetic component. We discuss reasons for the absence of a relationship between egg colouration and female quality.

Do females invest more into eggs when males sing more attractively? Postmating sexual selection strategies in a monogamous reed passerine.

Maternal investment can play an important role for offspring fitness, especially in birds, as females have to provide their eggs with all the necessary nutrients for the development of the embryo. It is known that this type of maternal investment can be influenced by the quality of the male partner. In this study, we first verify that male song is important in the mate choice of female Eurasian reed warblers, as males mate faster when their singing is more complex. Furthermore, female egg investment varies in relation to male song characteristics. Interestingly, clutch size, egg weight, or size, which can be considered as an high-cost investment, is not influenced by male song characteristics, whereas comparably low-cost investment types like investment into diverse egg components are adjusted to male song characteristics. In line with this, our results suggest that female allocation rules depend on investment type as well as song characteristics. For example, egg white lysozyme is positively correlated with male song complexity. In contrast, a negative correlation exists between-song speed and syllable repetitiveness and egg yolk weight as well as egg yolk testosterone concentration. Thus, our results suggest that female egg investment is related to male song performance in several aspects, but female investment patterns regarding various egg compounds are not simply correlated.

Are parasite intensity and related costs of the milichiid fly Carnus hemapterus related to host sociality

Ectoparasites have often been shown to have detrimental effects on their host. Not much is known, however, about determinants of infestation, e.g. the question of which factors affect distribution and occurrence of parasites on different host species (degree of host specificity) and their infestation rates. In this study we examine possible effects of host determinants on parasite intensity of Carnus hemapterus (Carnidae), an ectoparasitic fly on nestling birds, in the European bee-eater (Merops apiaster), which is a common host of C. hemapterus. Our results show that European bee-eaters seem to be one of the most heavily infested host species of C. hemapterus. We found that brood size, nestling age, and colony size are the most important determinants of infestation by C. hemapterus. This parasite seems to prefer medium-sized bee-eater chicks and to select them according to their condition. Our results further suggest a negative effect of C. hemapterus on chick development.

Experimental evidence for costs due to chewing lice in the European bee-eater (Merops apiaster).

Animals frequently host organisms on their surface which can be beneficial, have no effect or a negative effect on their host. Ectoparasites, by definition, are those which incur costs to their host, but these costs may vary. Examples of avian ectoparasites are chewing lice which feed exclusively on dead feather or skin material; therefore, costs to their bird hosts are generally considered small. Theoretically, many possible proximate effects exist, like loss of tissue or food, infected bites, transmission of microparasitic diseases or reduced body insulation due to loss of feathers, which may ultimately also have fitness consequences. Here, we experimentally examined a possible negative impact of 2 feather-eating louse species (Meropoecus meropis and Brueelia apiastri) on male and female European bee-eaters (Merops apiaster) by removing or increasing louse loads and comparing their impact to a control group (lice removed and immediately returned) after 1 month. A negative effect of chewing lice was found on body mass and sedimentation rate and to a lesser extent on haematocrit levels. Males and females lost more weight when bearing heavy louse loads, and were more susceptible to infestations as indicated by the higher sedimentation rate. Our results further suggest differences in sex-specific susceptibility.

Vegetation type variation in marsh habitats: does it affect nest site selection, reproductive success, and maternal investment in Reed Warblers?

AbstractHabitat choice may have an important impact on survival and fitness of an individual. Besides an individual’s intrinsic features, such as resource-holding potential, experience, age, and habitat characteristics like habitat heterogeneity may play a role. In line with this, we investigate the importance of vegetation type for habitat choice, reproductive investment, and success within one population of the Reed Warbler (Acrocephalus scirpaceus), a common Palearctic marsh bird that nests in reed (Phragmites australis) and reed mace (Typha spp.) stands. In particular, we want to know whether individuals differ in the use of the nesting habitat and whether choosing a different habitat, namely reed and reed mace, may have consequences for reproductive success and/or reproductive investment. Our results suggest clear differences in vegetation structure between reed and reed mace territories. Reed mace provided denser vegetation for nest sites, and, consequently, breeding density was higher and nest predation lower. Although reproductive success was significantly lower in reed nests, we did not find a directional habitat preference. We also found some indication for size-dependent habitat choice, as bigger males (with longer tarsi) settle in reed mace. Differences in vegetation type could also be observed in regard to maternal investment. Females reproducing in reed mace produced larger and heavier eggs. The results are further discussed in regard to the possibility of sympatric speciation.ZusammenfassungBeeinflusst die Vegetation Nistplatzwahl, Bruterfolg und mütterlichen Aufwand bei Teichrohrsängern? Habitatwahl kann einen wichtigen Einfluss auf das Überleben und die Fitness eines Individuums haben. Neben qualitativen Unterschieden zwischen Individuen, die z.B. durch Faktoren wie Erfahrung, Alter, „resource holding potential“beeinflusst werden, können auch Lebensraumcharakeristika von Bedeutung sein. In diesem Zusammenhang untersuchen wir die Bedeutung der Vegetation für die Habitatwahl, Investition und Erfolg bei der Fortpflanzung bei einer Teichrohrsängerpopulation Acrocephalus scirpaceus. Der Teichrohrsänger ist ein häufiger Bewohner von Feuchtgebieten der seine Nester gerne in Schilf (Phragmites australis) und Rohrkolben (Typha spp.) baut. Hier untersuchen wir ob Individuen sich in der Wahl ihres Bruthabitats unterscheiden und ob die Benutzung der zwei unterschiedlichen Vegetationstypen, nämlich Schilf und Rohrkolben, Auswirkungen auf den Fortpflanzungserfolg und/oder die Investition in die Fortpflanzung hat. Unsere Ergebnisse zeigen eindeutige Unterschiede in der Vegetationsstruktur von Schilf- und Rohrkolbenterritorien. Rohrkolben bieten dichtere Vegetationsstrukturen für den Nestbau. Die Brutdichte in Rohrkolbenterritorien ist höher und der Raubdruck auf die Nester geringer. Obwohl der Fortpflanzungserfolg in Schilfnestern signifikant niedriger war fanden wir keine ausgeprägte Präferenz für Rohrkolbenhabitate. Außerdem fanden wir einen Hinweis auf größenabhängige Habitatwahl. Männchen in Rohrkolbenterritorien hatten längeren Tarsi. Unterschiede zwischen den zwei Vegetationstypen, scheinen auch in der mütterlichen Investition in die Gelege zu existieren. Weibchen in Rohrkolbenterritorien produzieren größere und schwerere Eier. Die Ergebnisse werden auch in Bezug auf die Möglichkeit sympatrischer Speziation diskutiert.

Determinants of population biology of the chewing louse Brueelia apiastri (Mallophaga, Philopteridae) on the European bee-eater (Merops apiaster).

In this study we examine the population biology of Brueelia apiastri, a chewing louse living on the European bee-eater (Merops apiaster). We investigate the relationships between parasite intensity of infestation, sex ratio, reproductive output, parasite size and their environment i.e. the morphology, condition, age and sex of the host. Chewing lice were collected, their sex and age (developmental stage) identified and parasite body size determined as a measure of parasite condition (larger individuals consume larger meals and larger females may produce larger clutches). The data show that there is variation in intensity as well as body size of B. apiastri between individual bee-eaters and this variation is independent of the sex of the birds. However, size, condition and age of the birds seem to influence the infestation rates with B. apiastri. The study suggested size-dependent depredation, since more, smaller chewing lice (usually nymphs) living on birds in better condition and birds having longer bills. Furthermore, more male chewing lice (males are smaller than females) live on older birds. Intraspecific competition between parasites seems to have a negative effect on female but not male body size but this result could be also explained by size-dependent depredation.

Experimentally Simulating Paternity Uncertainty: Immediate and Long-Term Responses of Male and Female Reed Warblers Acrocephalus scirpaceus

In many socially monogamous species, both sexes seek copulation outside the pair bond in order to increase their reproductive success. In response, males adopt counter-strategies to combat the risk of losing paternity. However, no study so far has tried to experimentally prove the function of behaviour for paternity assurance. Introducing a potential extra-pair partner during the female fertile period provides a standardised method to examine how pair members respond immediately (e.g. increase mate guarding or copulation frequency) or long term (e.g. later parental investment and paternity uncertainty). In this study on a socially monogamous passerine species, we experimentally confronted pairs of reed warblers with a conspecific male (caged male simulating an intruder) during egg-laying. Our results revealed that occurrence of an intruder during that period triggered aggression against the intruder, depending on the presence of the female. The male territory owner also attacked the female partner to drive her away from the intruder. Thus territory defence in reed warblers also serves to protect paternity. The increase in paternity uncertainty did not affect later paternal investment. Paternal investment was also independent of the actual paternity losses. In females, the experiment elicited both, immediate and long-term responses. E.g. female copulation solicitations during the intruder experiment were only observed for females which later turned out to have extra-pair chicks in their nest. In relation to long term response females faced with an intruder invested later less in offspring feeding, and had less extra-pair chicks in their nests. Extra-pair paternity also seems to be affected by female quality (body size). In conclusion female reed warblers seem to seek extra-pair fertilizations but we could demonstrate that males adopt paternity assurance tactics which seems to efficiently help them to reduce paternity uncertainty.

Food preferences and mound-building behaviour of the mound-building mice Mus spicilegus

Optimal foraging strategies and food choice are influenced by various factors, e.g. availability, size and caloric content of the food type and predation risk. However, food choice criteria may change when food is not eaten immediately but has to be carried to a storage site for later use. For example, handling time in terms of harvesting and transport time should be optimized, particularly when the risk of predation is high. Thus, it is not clear whether food selected by hoarding animals reflects their food preference due to intrinsic features of the food type, e.g. size, caloric or lipid content, or whether the food type selected is a compromise that also considers the handling time required for harvesting and transport. We investigate this question in relation to food hoarding behaviour in mound-building mice. In autumn, mound-building mice Mus spicilegus collect seeds and other plant material and cover it with soil. Such above-ground storage is quite unusual for rodents. Here, we investigated whether there is a relationship between the seed species preferred as building materials and those preferred for food. We conducted a seed preference test using three most collected weed species for mound building. Controlling factors like food availability or predation risk, mice prefer Setaria spp. as food, although Amaranthus spp. and Chenopodium spp. were preferentially harvested and stored. By including the availability of the three species, our experimental results were confirmed, namely, a clear preference for Setaria spp. Also, handling time and seed size revealed to influence plant choice.