A novel phase variation mechanism in the meningococcus driven by a ligand-responsive repressor and differential spacing of distal promoter elements

Phase variable expression, mediated by high frequency reversible changes in the length of simple sequence repeats, facilitates adaptation of bacterial populations to changing environments and is frequently important in bacterial virulence. Here we elucidate a novel phase variable mechanism for NadA expression, an adhesin and invasin of Neisseria meningitidis. The NadR repressor protein binds to operators flanking the phase variable tract of the nadA promoter gene and contributes to the differential expression levels of phase variant promoters with different numbers of repeats, likely due to different spacing between operators. It is shown that IHF binds between these operators, and may permit looping of the promoter, allowing interaction of NadR at operators located distally or overlapping the promoter. The 4-hydroxyphenylacetic acid, a metabolite of aromatic amino acid catabolism that is secreted in saliva, induces nadA expression by inhibiting the DNA binding activity of the NadR repressor. When induced, only minor differences are evident between NadR-independent transcription levels of promoter phase variants, which are likely due to differential RNA polymerase contacts leading to altered promoter activity. These results suggest that NadA expression is under both stochastic and tight environmental-sensing regulatory control, and both regulations are mediated by the NadR repressor that and may be induced during colonization of the oropharynx where it plays a major role in the successful adhesion and invasion of the mucosa. Hence, simple sequence repeats in promoter regions may be a strategy used by host-adapted bacterial pathogens to randomly switch between expression states that may nonetheless still be induced by appropriate niche-specific signals.

Genetic and environmental factors associated with the risk of cognitive decline and dementia

AD is the most common age related neurodegenerative disease in the industrialized world. Clinically AD is defined as a progressing decline of cognitive functions. Neuropathologically, AD is characterized by the aggregation of b-amyloid (Ab) peptide in the form of extracellular senile plaques, and hyperphosphorlylated tau protein in the form of intracellular neurofibrillary tangles. These neuropathological hallmarks are often accompanied by abundant microvascular damage and pronounced inflammation of the affected brain regions. In this thesis we investigated several aspects of AD focusing on the genetic aspect. We confirmed that Alpha 1 antichymotrypsin (ACT), an acute phase protein, was associated to AD subjects, being plasma levels higher in AD cases than controls. In addition, in a GWA study we demonstrated that two different gene, Clusterin and CR1 were strongly associated to AD. A single gene association not explain such a complex disease like AD. The goal should be to created a network of genetic, phenotypic and clinical data associated to AD. We used a new algorithm, the ANNs, aimed to map variables and search for connectivity among variables. We found specific variables associated to AD like cholesterol levels, the presence of variation in HMGCR enzyme and the age. Other factors such as the BMI, the amount of HDL and blood folate levels were also associated with AD. Pathogen infections, above all viral infections, have been previously associated to AD. The hypothesis suggests that virus and in particular herpes virus could enter the brain when an individual becomes older, perhaps because of a decline in the immune system. Our new hypothesis is that the presence of SNPs in our GWA gene study results in a genetic signature that might affect individual brain susceptibility to infection by herpes virus family during aging.

Relationships between plant diversity and environmental heterogeneity in rupicolous grasslands on gypsum. The case study of Alysso-Sedion albi (Habitat 6110).

Plant communities on weathered rock and outcrops are characterized by high values in species richness (Dengler 2006) and often persist on small and fragmented surfaces. Yet very few studies have examined the relationships between heterogeneity and plant diversity at small scales, in particular in poor-nutrient and low productive environment (Shmida and Wilson 1985, Lundholm 2003). In order to assess these relationships both in space and time in relationship, two different approaches were employed in the present study, in two gypsum outcrops of Northern Apennine. Diachronic and synchronic samplings from April 2012 to March 2013 were performed. A 50x50 cm plot was used in both samplings such as the sampling unit base. The diachronic survey aims to investigate seasonal patterning of plant diversity by the use of images analysis techniques integrated with field data and considering also seasonal climatic trend, the substrate quality and its variation in time. The purpose of the further, synchronic sampling was to describe plant diversity pattern as a function of the environmental heterogeneity meaning in substrate typologies, soil depth and topographic features. Results showed that responses of diversity pattern depend both on the resources availability, environmental heterogeneity and the manner in which the different taxonomic group access to them during the year. Species richness and Shannon diversity were positively affected by increasing in substrate heterogeneity. Furthermore a good turnover in seasonal species occurrence was detected. This vegetation may be described by the coexistence of three groups of species which created a gradient from early colonization stages, characterized by greater slope and predominance of bare rock, gradually to situation of more developed soil.

Technological trajectories and environmental policy: the transformation of the automobile

This thesis aims to fill the gap in the literature by examining the relationship between technological trajectories and environmental policy in the automotive industry, focusing on the role of environmental policies in unlocking the industry from fossil fuel path-dependence. It first explores the inducement mechanism that underpins the interaction between environmental policy and green technological advances, investigating under what conditions the European environmental transport policy portfolio and the intrinsic characteristics of assignees' knowledge boost worldwide green patent production. Subsequently, the thesis empirically analyses the dynamics of technological knowledge involved in technological trajectories assessing evolution patterns such as variation, selection and retention, in order to study the impact of policy implementation on technological knowledge related to electric and hybrid vehicle technologies. Finally, the thesis sheds light on the drivers that encourage a shift from incumbent internal combustion engine technologies towards low-emission vehicle technologies. This analysis tests whether tax-inclusive fuel prices and technological proximity between technological fields induce a shift from non-environmental inventions to environmentally friendly inventive activities and if they impact the competition between alternative vehicle technologies. The findings provide insights into the effectiveness of environmental policy in triggering inventive activities related to the development of alternative vehicle technologies. In addition, there is evidence that environmental policy redirects technological efforts towards a sustainable path and impacts the competition between low-emission vehicles.

Roman aqueducts and calcareous sinter deposits as a proxy for environmental changes

Die im Süden der Türkei gelegen, antiken Städte Aspendos und Patara, waren in der Römerzeit zwei bedeutende Handelszentren mit hoher Bevölkerungsdichte. Aquädukte versorgten beide Städte mit carbonathaltigem Wasser, wobei sich Kalksinter (Calciumcarbonat) in der Kanalrinne ablagerte. Dabei lagern sich im Wechsel eine hellere und dunklere Kalksinterlage ab, die als Sinterpaar bezeichnet wird. Um die Entstehung dieser Sinterpaare besser zu verstehen, und die beteiligten Prozesse mit saisonalen Veränderungen der Umwelt zu korrelieren, werden in der vorliegenden Arbeit laminierten Sinterablagerungen mit geochemischen und petrographischen Methoden untersucht.rnEntlang der Kanalrinne beider Aquädukte wurden an mehreren Stellen Proben entnommen. Es wurde untersucht in wieweit sich die Sinterstruktur aufgrund von Änderungen in der Neigung des Wasserkanals oder des Kanaltyps ändert. Um die Kristallform und die kristallografische Orientierung der Kristalle innerhalb der verschiedenen Sinterpaare zu untersuchen, wurden die entnommenen laminierten Kalksinterablagerungen mit Hilfe optischer Mikroskopie und EBSD (Electron Backscatter Diffraction) analysiert. Der Electron Probe Micro-Analyzer (EPMA) wurde verwendet, um saisonale Schwankungen der Hauptelementverteilung und den Anteil der stabilen Isotope im Wasser zu bestimmen. Die LA-ICP-MS (Laser Ablation-induktiv gekoppeltem Plasma-Massenspektrometrie) Spurenelementanalyse wurde durchgeführt, um kleinste Schwankungen der Spurenelemente zu finden. Basierend auf diesen Analysen wurde festgestellt, dass laminierten Kalksinterablagerungen laterale Änderungen in der Aquäduktstruktur und -neigung, jahreszeitliche Änderungen der Wasserchemie, der Temperatur sowie der Entgasungsrate während eines Jahres widerspiegeln. Die Kalksinterablagerungen zeigen eine deutliche Laminierung in Form von feinkörnig-porösen und grobkörnig-dichten Schichten, die trockene und nasse Jahreszeiten anzeigen. Feinkörnige Schichten zeigen eine hohe Epifluoreszenz aufgrund reichhaltiger organischer Inhalte, die vermutlich eine Folge der bakteriellen Aktivität während der warmen und trockenen Jahreszeit sind. Stabile Sauerstoff und Kohlenstoff-Isotop-Kurven entsprechen auch den jahreszeitlichen Schwankungen der verschiedenen Schichtenpaare. Vor allem δ 18O spiegelt jährliche Veränderungen in der Temperatur und jahreszeitliche Veränderungen des Abflusses wieder. Das wichtigste Ergebnis ist, dass die Periodizität von δ 18O durch Erwärmen des Wassers im Wasserkanal und nicht durch die Verdunstung oder der Brunnenwasser-Charakteristik verursacht wird. Die Periodizität von δ 13C ist komplexer Natur, vor allem zeigen δ 18O und δ 13C eine Antikorrelation entlang der Lamellenpaare. Dies wird wohl vor allem durch Entgasungsprozesse im Aquädukt verursacht. Die Ergebnisse der Spurenelemente sind meist inkonsistent und zeigen keine signifikanten Veränderungen in den verschiedenen Lamellenpaaren. Die Isotope Mg, Sr und Ba zeigen hingegen bei einigen Proben eine positive Korrelation und erreichen Höchstwerte innerhalb feinkörnig-poröser Schichten. Auch sind die Hauptelementwerte von Fe, K, Si und anderer detritischer Elemente innerhalb der feinkörnige-porösen Schichten maximal. Eine genaue Datierung der Kalksinterablagerungen ist wünschenswert, da der Zeitraum, in dem die Aquädukte aktiv waren, bereits archäologisch auf 200-300 Jahre festgelegt wurde. Paläomagnetische und 14C-Datierung geben keine brauchbare Ergebnisse. Die U/Th Isotopie wird durch eine hohe Anfangskonzentration von Th in den Proben behindert. Trotz dieser Schwierigkeiten war eine U/Th Datierung an einem Testbeispiel des Béziers Aquädukt erfolgreich. Mit Hilfe von analogen Untersuchungen an aktiven Wasserkanälen der heutigen Zeit, werden die Ablagerungsmechanismen und die geochemische Entwicklung der laminierten Sinterschichten besser verstanden. Ein weiteres laufendes Projekt dieser Doktorarbeit ist die Überwachung von Sinterabscheidungen und der saisonale Zusammensetzung des Wassers an einigen heute noch aktiven Aquädukten. Das Ziel ist die Untersuchung der jetzigen Calciumcarbonatabscheidungen in Aquäduktkanälen unter den heutigen Umgebungsbedingungen. Erste Ergebnisse zeigen, dass kleine regelmäßige jahreszeitliche Veränderungen in der Isotopenzusammensetzung des Wassers vorliegen, und dass die beobachtete Periodizität der stabilen Isotope aufgrund von Änderungen im eigentlichen Kanal entstanden ist. Die Untersuchung von Kalksinterablagerungen in römischen Aquädukten liefern vielversprechende Ergebnisse, für die Untersuchung des Paläöklimas, der Archaeoseismologie und anderer Umweltbedingungen in der Römerzeit. Diese Studie beschränkt sich auf zwei Aquädukte. Die Untersuchungen weiterer Aquädukte und einer Überwachung, der noch in Betrieb stehenden Aquädukte werden genauere Ergebnisse liefern.

Another Way of Saying Enough: Environmental Concern and Popular Mobilization in Kyrgyzstan

This article is a foray into the understudied issue of environmental protest politics in Central Asia. Specifically, it uses Kyrgyzstan as a case study to test the argument that environmental concerns mobilized people to engage in protest and in ways different from other kinds of protest. This essay presents the first systematic study of public opinion about the environment in Kyrgyzstan. It includes results from a 2009 nationwide survey, over 100 expert and elite interviews, and newspaper content analysis. Furthermore, it spatially analyzes these results to identify geographical variation in public perception and political event occurrence patterns. Protest engagement is a complex process determined by the interaction of several factors, and is not explained solely by affluence, rationality, or grievances. Eco-mobilization - collective political action about the environment - represents a class of protest events that offers a different view into mass discontent in the former Soviet Union and neo-patrimonial societies. The study finds that these political actions about the environment are not necessarily elite driven; there is a basic foundation of national concern and salience of these issues, and demonstrated environmental beliefs do help to explain protest behavior.

Temporal and spatial variation of nitrogen transformations in nitrogen-saturated soils of a central Appalachian hardwood forest

We studied temporal and spatial patterns of soil nitrogen (N) dynamics from 1993 to 1995 in three watersheds of Fernow Experimental Forest, W.V.: WS7 (24-year-old, untreated); WS4 (mature, untreated); and WS3 (24-year-old, treated with (NH4)2SO since 1989 at the rate of 35 kg Nha–1year–1). Net nitrification was 141, 114, and115 kg Nha–1year–1, for WS3, WS4, and WS7, respectively, essentially 100% of net N mineralization for all watersheds. Temporal (seasonal) patterns of nitrification were significantly related to soil moisture and ambient temperaturein untreated watersheds only. Spatial patterns of soil water NO3–of WS4 suggest that microenvironmental variabilitylimits rates of N processing in some areas of this N-saturated watershed, in part by ericaceous species in the herbaceous layer. Spatial patterns of soil water NO3–in treated WS3 suggest that later stages of N saturation may result inhigher concentrations with less spatial variability. Spatial variability in soil N variables was lower in treated WS3 versus untreated watersheds. Nitrogen additions have altered the response of N-processing microbes to environmental factors, becoming less sensitive to seasonal changes in soil moisture and temperature. Biotic processes responsible forregulating N dynamics may be compromised in N-saturated forest ecosystems.

A 700-year paleoecological record of boreal ecosystem responses to climatic variation from Alaska

Recent observations and model simulations have highlighted the sensitivity of the forest - tundra ecotone to climatic forcing. In contrast, paleoecological studies have not provided evidence of tree-line fluctuations in response to Holocene climatic changes in Alaska, suggesting that the forest - tundra boundary in certain areas may be relatively stable at multicentennial to millennial time scales. We conducted a multiproxy study of sediment cores from an Alaskan lake near the altitudinal limits of key boreal-forest species. Paleoecological data were compared with independent climatic reconstructions to assess ecosystem responses of the forest - tundra boundary to Little Ice Age (LIA) climatic. uctuations. Pollen, diatom, charcoal, macrofossil, and magnetic analyses provide the first continuous record of vegetation -. re - climate interactions at decadal to centennial time scales during the past 700 years from southern Alaska. Boreal-forest diebacks characterized by declines of Picea mariana, P. glauca, and tree Betula occurred during the LIA ( AD 1500 - 1800), whereas shrubs ( Alnus viridis, Betula glandulosa/nana) and herbaceous taxa (Epilobium, Aconitum) expanded. Marked increases in charcoal abundance and changes in magnetic properties suggest increases in. re importance and soil erosion during the same period. In addition, the conspicuous reduction or disappearance of certain aquatic ( e. g., Isoetes, Nuphar, Pediastrum) and wetland ( Sphagnum) plants and major shifts in diatom assemblages suggest pronounced lake-level. uctuations and rapid ecosystem reorganization in response to LIA climatic deterioration. Our results imply that temperature shifts of 1 - 2 degrees C, when accompanied by major changes in moisture balance, can greatly alter high-altitudinal terrestrial, wetland, and aquatic ecosystems, including conversion between boreal-forest tree line and tundra. The climatic and ecosystem variations in our study area appear to be coherent with changes in solar irradiance, suggesting that changes in solar activity contributed to the environmental instability of the past 700 years.

Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy

Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652ma.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitudedependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline.We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).

Analysis of Variation in Clubfoot Candidate Genes

Isolated clubfoot, a common birth defect occurring in more than 135,000 livebirths worldwide each year, is associated with significant health care and financial burdens. Clubfoot is defined by forefoot adduction, hindfoot varus, midfoot cavus and hindfoot equinus. Isolated clubfoot, which is the focus of these studies, is distinct from syndromic clubfoot because there are no other associated malformations. Population, family, twin and segregation analysis studies provide evidence that genetic and environmental factors play an etiologic role in isolated clubfoot. The studies described in this thesis were performed to define the role of genetic variation in isolated clubfoot. Interrogation of a deletion region associated with syndromic clubfoot, suggested that CASP8 and CASP10, two apoptotic genes, play a role in isolated clubfoot. To explore the role of apoptotic genes in clubfoot, SNPs spanning genes involved in the apoptotic pathway in the six chromosomal deletion regions, and limb patterning genes, HOXD and HOXA, were interrogated. SNPs in mitochondrial mediated apoptotic genes and several SNPs in HOXA and HOXD genes were modestly associated with clubfoot with the most significant SNP, rs3801776, located in the basal promoter of HOXA9. Several significant associations were found with SNPs in NFAT2 and TNIP2. Significant gene interactions were detected between SNPs in HOX and apoptotic genes. These findings suggest a model for clubfoot in which variation in one gene is not sufficient to cause the malformation but requires variation several genes to perturb protein expression sufficiently to alter muscle and foot development. These results significantly impact our knowledge base by delineating underlying mechanisms causing clubfoot.

Genetic variation in genes for the xenobiotic-metabolizing enzymes CYP1A1, EPHX1, GSTM1, GSTT1, and GSTP1 and susceptibility to colorectal cancer in Lynch syndrome.

Individuals with Lynch syndrome are predisposed to cancer due to an inherited DNA mismatch repair gene mutation. However, there is significant variability observed in disease expression likely due to the influence of other environmental, lifestyle, or genetic factors. Polymorphisms in genes encoding xenobiotic-metabolizing enzymes may modify cancer risk by influencing the metabolism and clearance of potential carcinogens from the body. In this retrospective analysis, we examined key candidate gene polymorphisms in CYP1A1, EPHX1, GSTT1, GSTM1, and GSTP1 as modifiers of age at onset of colorectal cancer among 257 individuals with Lynch syndrome. We found that subjects heterozygous for CYP1A1 I462V (c.1384A>G) developed colorectal cancer 4 years earlier than those with the homozygous wild-type genotype (median ages, 39 and 43 years, respectively; log-rank test P = 0.018). Furthermore, being heterozygous for the CYP1A1 polymorphisms, I462V and Msp1 (g.6235T>C), was associated with an increased risk for developing colorectal cancer [adjusted hazard ratio for AG relative to AA, 1.78; 95% confidence interval, 1.16-2.74; P = 0.008; hazard ratio for TC relative to TT, 1.53; 95% confidence interval, 1.06-2.22; P = 0.02]. Because homozygous variants for both CYP1A1 polymorphisms were rare, risk estimates were imprecise. None of the other gene polymorphisms examined were associated with an earlier onset age for colorectal cancer. Our results suggest that the I462V and Msp1 polymorphisms in CYP1A1 may be an additional susceptibility factor for disease expression in Lynch syndrome because they modify the age of colorectal cancer onset by up to 4 years.

Habitat-dependent geographical variation in ontogenetic allometry of the shiner perch Cymatogaster aggregata Gibbons (Teleostei: Embiotocidae)

Studies of intraspecific morphological variation in fishes have traditionally focused on freshwater rather than marine species. In addition, such studies typically focus on adults, although causes and intensities of selective pressures most likely vary through an individual’s lifetime. In this study, body and head shape of a marine species, shiner perch Cymatogaster aggregata Gibbons were compared among localities along the Pacific Northwest coast of North America. Evidence was found for intraspecific variation in ontogenetic allometry, and for a closer correlation of body shape with environment rather than geographical proximity. This correlation with environment was more evident in younger fish, thereby demonstrating the importance of analysing multiple life stages. A common garden experiment suggests both environmental and genetic bases for the observed differences. Recognizing intraspecific ecomorphological complexity and its specificity to habitat and/or life stage can have important consequences for understanding the role of local adaptation and population dynamics in macroecology.

Genetic diversity, phenotypic variation and local adaptation in the alpine landscape: case studies with alpine plant species

Plant survival in alpine landscapes is constantly challenged by the harsh and often unpredictable environmental conditions. Steep environmental gradients and patchy distribution of habitats lead to small size and spatial isolation of populations and restrict gene flow. Agricultural land use has further increased the diversity of habitats below and above the treeline. We studied the consequences of the highly structured alpine landscape for evolutionary processes in four study plants: Epilobium fleischeri, Geum reptans, Campanula thyrsoides and Poa alpina. The main questions were: (1) How is genetic diversity distributed within and among populations and is it affected by altitude, population size or land use? (2) Do reproductive traits such as allocation to sexual or vegetative reproduction vary with altitude or land use? Furthermore, we studied if seed weight increases with altitude. Within-population genetic diversity of the four species was high and mostly not related to altitude and population size. Nevertheless, genetic differentiation among populations was pronounced and strongly increasing with distance. In Poa alpina genetic diversity was affected by land use. Results suggest considerable genetic drift among populations of alpine plants. Reproductive allocation was affected by altitude and land use in Poa alpina and by succession in Geum reptans. Seed weight was usually higher in alpine species than in related lowland species. We conclude that the evolutionary potential to respond to global change is mostly intact in alpine plants, even at high altitude. Phenotypic variability is shaped by adaptive as well as by random evolutionary processes; moreover plastic responses to growth conditions seem to be crucial for survival of plants in the alpine landscape.

Seasonal Variation in the Capacity for Plant Trait Measures to Predict Grassland Carbon and Water Fluxes

There is a need for accurate predictions of ecosystem carbon (C) and water fluxes in field conditions. Previous research has shown that ecosystem properties can be predicted from community abundance-weighted means (CWM) of plant functional traits and measures of trait variability within a community (FDvar). The capacity for traits to predict carbon (C) and water fluxes, and the seasonal dependency of these trait-function relationships has not been fully explored. Here we measured daytime C and water fluxes over four seasons in grasslands of a range of successional ages in southern England. In a model selection procedure, we related these fluxes to environmental covariates and plant biomass measures before adding CWM and FDvar plant trait measures that were scaled up from measures of individual plants grown in greenhouse conditions. Models describing fluxes in periods of low biological activity contained few predictors, which were usually abiotic factors. In more biologically active periods, models contained more predictors, including plant trait measures. Field-based plant biomass measures were generally better predictors of fluxes than CWM and FDvar traits. However, when these measures were used in combination traits accounted for additional variation. Where traits were significant predictors their identity often reflected seasonal vegetation dynamics. These results suggest that database derived trait measures can improve the prediction of ecosystem C and water fluxes. Controlled studies and those involving more detailed flux measurements are required to validate and explore these findings, a worthwhile effort given the potential for using simple vegetation measures to help predict landscape-scale fluxes.

Parent – environmental interactions shape acoustic signatures in tree swallows: a cross-fostering experiment.

Acoustic signatures are common components of avian vocalizations and are important for the recognition of individuals and groups. The proximate mechanisms by which these signatures develop are poorly understood, however. The development of acoustic signatures in nestling birds is of particular interest, because high rates of extra-pair paternity or egg dumping can cause nestlings to be unrelated to at least one of the adults that are caring for them. In such cases, nestlings might conceal their genetic origins, by developing acoustic signatures through environmental rather than genetic mechanisms. In a cross-fostering experiment with tree swallows Tachycineta bicolor, we investigated whether brood signatures of nestlings that were about to fledge were attributable to their genetic/maternal origins or to their rearing environment. We found that the calls of cross-fostered nestlings did not vary based on their genetic/maternal origin, but did show some variation based on their rearing environment. Control nestlings that were not swapped, however, showed stronger brood signatures than either experimental group, suggesting that acoustic signatures develop through an interaction between rearing environment and genetic/maternal effects.