Alternative reproductive tactics, sexual selection and the effects of inbreeding in the ant Hypoponera opacior

Inbreeding can lead to a fitness reduction due to the unmasking of deleterious recessive alleles and the loss of heterosis. Therefore, most sexually reproducing organisms avoid inbreeding, often by disperal. Besides the avoidance of inbreeding, dispersal lowers intraspecific competition on a local scale and leads to a spreading of genotypes into new habitats. In social insects, winged reproductives disperse and mate during nuptial flights. Therafter, queens independently found a new colony. However, some species also produce wingless sexuals as an alternative reproductive tactic. Wingless sexuals mate within or close to their colony and queens either stay in the nest or they found a new colony by budding. During this dependent colony foundation, wingless queens are accompanied by a fraction of nestmate workers. The production of wingless reproductives therefore circumvents the risks associated with dispersal and independent colony foundation. However, the absence of dispersal can lead to inbreeding and local competition.rnIn my PhD-project, I investigated the mating biology of Hypoponera opacior, an ant that produces winged and wingless reproductives in a population in Arizona. Besides the investigation of the annual reproductive cycle, I particularly focused on the consequences of wingless reproduction. An analysis of sex ratios in wingless sexuals should reveal the relative importance of local resource competition among queens (that mainly compete for the help of workers) and local mate competition among males. Further, sexual selection was expected to act on wingless males that were previously found to mate with and mate-guard pupal queens in response to local mate competition. We studied whether males are able to adapt their mating behaviour to the current competitive situation in the nest and which traits are under selection in this mating situation. Last, we investigated the extent and effects of inbreeding. As the species appeared to produce non-dispersive males and queens quite frequently, we assumed to find no or only weak negative effects of inbreeding and potentially mechanisms that moderate inbreeding levels despite frequent nest-matings.rnWe found that winged and wingless males and queens are produced during two separate seasons of the year. Winged sexuals emerge in early summer and conduct nuptial flights in July, when climate conditions due to frequent rainfalls lower the risks of dispersal and independent colony foundation. In fall, wingless sexuals are produced that reproduce within the colonies leading to an expansion on the local scale. The absence of dispersal during this second reproductive season resulted in a local genetic population viscosity and high levels of inbreeding within the colonies. Male-biased sex ratios in fall indicated a greater importance of local resource competition among queens than local mate competition among males. Males were observed to adjust mate-guarding durations to the competitive situation (i.e. the number of competing males and pupae) in the nest, an adaptation that helps maximising their reproductive success. Further, sexual selection was found to act on the timing of emergence as well as on body size in these males, i.e. earlier emerging and larger males show a higher mating success. Genetic analyses revealed that wingless males do not actively avoid inbreeding by choosing less related queens as mating partners. Further, we detected diploid males, a male type that is produced instead of diploid females if close relatives mate. In contrast to many other Hymenopteran species, diploid males were here viable and able to sire sterile triploid offspring. They did not differ in lifespan, body size and mating success from “normal” haploid males. Hence, diploid male production in H. opacior is less costly than in other social Hymenopteran species. No evidence of inbreeding depression was found on the colony level but more inbred colonies invested more resources into the production of sexuals. This effect was more pronounced in the dispersive summer generation. The increased investment in outbreeding sexuals can be regarded as an active strategy to moderate the extent and effects of inbreeding. rnIn summary, my thesis describes an ant species that has evolved alternative reproductive tactics as an adaptation to seasonal environmental variations. Hereby, the species is able to maintain its adaptive mating system without suffering from negative effects due to the absence of dispersal flights in fall.rn

Validity of an automatic measure protocol in distal femur for allograft selection from a three-dimensional virtual bone bank system

Osteoarticular allograft is one possible treatment in wide surgical resections with large defects. Performing best osteoarticular allograft selection is of great relevance for optimal exploitation of the bone databank, good surgery outcome and patient’s recovery. Current approaches are, however, very time consuming hindering these points in practice. We present a validation study of a software able to perform automatic bone measurements used to automatically assess the distal femur sizes across a databank. 170 distal femur surfaces were reconstructed from CT data and measured manually using a size measure protocol taking into account the transepicondyler distance (A), anterior-posterior distance in medial condyle (B) and anterior-posterior distance in lateral condyle (C). Intra- and inter-observer studies were conducted and regarded as ground truth measurements. Manual and automatic measures were compared. For the automatic measurements, the correlation coefficients between observer one and automatic method, were of 0.99 for A measure and 0.96 for B and C measures. The average time needed to perform the measurements was of 16 h for both manual measurements, and of 3 min for the automatic method. Results demonstrate the high reliability and, most importantly, high repeatability of the proposed approach, and considerable speed-up on the planning.

Neuronal polarity selection by topography-induced focal adhesion control

Interaction between differentiating neurons and the extracellular environment guides the establishment of cell polarity during nervous system development. Developing neurons read the physical properties of the local substrate in a contact-dependent manner and retrieve essential guidance cues. In previous works we demonstrated that PC12 cell interaction with nanogratings (alternating lines of ridges and grooves of submicron size) promotes bipolarity and alignment to the substrate topography. Here, we investigate the role of focal adhesions, cell contractility, and actin dynamics in this process. Exploiting nanoimprint lithography techniques and a cyclic olefin copolymer, we engineered biocompatible nanostructured substrates designed for high-resolution live-cell microscopy. Our results reveal that neuronal polarization and contact guidance are based on a geometrical constraint of focal adhesions resulting in an angular modulation of their maturation and persistence. We report on ROCK1/2-myosin-II pathway activity and demonstrate that ROCK-mediated contractility contributes to polarity selection during neuronal differentiation. Importantly, the selection process confined the generation of actin-supported membrane protrusions and the initiation of new neurites at the poles. Maintenance of the established polarity was independent from NGF stimulation. Altogether our results imply that focal adhesions and cell contractility stably link the topographical configuration of the extracellular environment to a corresponding neuronal polarity state.

Evidence for selection on coloration in a Panamanian poison frog: a coalescent-based approach

Aim The strawberry poison frog, Oophaga pumilio, has undergone a remarkable radiation of colour morphs in the Bocas del Toro archipelago in Panama. This species shows extreme variation in colour and pattern between populations that have been geographically isolated for < 10,000 years. While previous research has suggested the involvement of divergent selection, to date no quantitative test has examined this hypothesis. Location Bocas del Toro archipelago, Panama. Methods We use a combination of population genetics, phylogeography and phenotypic analyses to test for divergent selection in coloration in O. pumilio. Tissue samples of 88 individuals from 15 distinct populations were collected. Using these data, we developed a gene tree using the mitochondrial DNA (mtDNA) d-loop region. Using parameters derived from our mtDNA phylogeny, we predicted the coalescence of a hypothetical nuclear gene underlying coloration. We collected spectral reflectance and body size measurements on 94 individuals from four of the populations and performed a quantitative analysis of phenotypic divergence. Results The mtDNA d-loop tree revealed considerable polyphyly across populations. Coalescent reconstructions of gene trees within population trees revealed incomplete genotypic sorting among populations. The quantitative analysis of phenotypic divergence revealed complete lineage sorting by colour, but not by body size: populations showed non-overlapping variation in spectral reflectance measures of body coloration, while variation in body size did not separate populations. Simulations of the coalescent using parameter values derived from our empirical analyses demonstrated that the level of sorting among populations seen in colour cannot reasonably be attributed to drift. Main conclusions These results imply that divergence in colour, but not body size, is occurring at a faster rate than expected under neutral processes. Our study provides the first quantitative support for the claim that strong diversifying selection underlies colour variation in the strawberry poison frog.

Sexual selection and speciation: the comparative evidence revisited

The spectacular diversity in sexually selected traits in the animal kingdom has inspired the hypothesis that sexual selection can promote species divergence. In recent years, several studies have attempted to test this idea by correlating species richness with estimates of sexual selection across phylogenies. These studies have yielded mixed results and it remains unclear whether the comparative evidence can be taken as generally supportive. Here, we conduct a meta-analysis of the comparative evidence and find a small but significant positive overall correlation between sexual selection and speciation rate. However, we also find that effect size estimates are influenced by methodological choices. Analyses that included deeper phylogenetic nodes yielded weaker correlations, and different proxies for sexual selection showed different relationships with species richness. We discuss the biological and methodological implications of these findings. We argue that progress requires more representative sampling and justification of chosen proxies for sexual selection and speciation rate, as well as more mechanistic approaches.

Effect of Methodological and Ecological Approaches on Heterogeneity of Nest-Site Selection of a Long-Lived Vulture

The application of scientific-based conservation measures requires that sampling methodologies in studies modelling similar ecological aspects produce comparable results making easier their interpretation. We aimed to show how the choice of different methodological and ecological approaches can affect conclusions in nest-site selection studies along different Palearctic meta-populations of an indicator species. First, a multivariate analysis of the variables affecting nest-site selection in a breeding colony of cinereous vulture (Aegypius monachus) in central Spain was performed. Then, a meta-analysis was applied to establish how methodological and habitat-type factors determine differences and similarities in the results obtained by previous studies that have modelled the forest breeding habitat of the species. Our results revealed patterns in nesting-habitat modelling by the cinereous vulture throughout its whole range: steep and south-facing slopes, great cover of large trees and distance to human activities were generally selected. The ratio and situation of the studied plots (nests/random), the use of plots vs. polygons as sampling units and the number of years of data set determined the variability explained by the model. Moreover, a greater size of the breeding colony implied that ecological and geomorphological variables at landscape level were more influential. Additionally, human activities affected in greater proportion to colonies situated in Mediterranean forests. For the first time, a meta-analysis regarding the factors determining nest-site selection heterogeneity for a single species at broad scale was achieved. It is essential to homogenize and coordinate experimental design in modelling the selection of species' ecological requirements in order to avoid that differences in results among studies would be due to methodological heterogeneity. This would optimize best conservation and management practices for habitats and species in a global context.

Species-level selection reduces selfishness through competitive exclusion

Adaptation does not necessarily lead to traits which are optimal for the population. This is because selection is often the strongest at the individual or gene level. The evolution of selfishness can lead to a 'tragedy of the commons', where traits such as aggression or social cheating reduce population size and may lead to extinction. This suggests that species-level selection will result whenever species differ in the incentive to be selfish. We explore this idea in a simple model that combines individual-level selection with ecology in two interacting species. Our model is not influenced by kin or trait-group selection. We find that individual selection in combination with competitive exclusion greatly increases the likelihood that selfish species go extinct. A simple example of this would be a vertebrate species that invests heavily into squabbles over breeding sites, which is then excluded by a species that invests more into direct reproduction. A multispecies simulation shows that these extinctions result in communities containing species that are much less selfish. Our results suggest that species-level selection and community dynamics play an important role in regulating the intensity of conflicts in natural populations.

Wolf habitat selection at the territory level : seasonal and interannual variation and influence on reproductive success

Habitat selection has been one of the main research topics in ecology for decades. Nevertheless, many aspects of habitat selection still need to be explored. In particular, previous studies have overlooked the importance of temporal variation in habitat selection and the value of including data on reproductive success in order to describe the best quality habitat for a species. We used data collected from radiocollared wolves in Yellowstone National Park (USA), between 1996 and 2008, to describe wolf habitat selection. In particular, we aimed to identify i) seasonal differences in wolf habitat selection, ii) factors influencing interannual variation in habitat selection, and iii) the effect of habitat selection on wolf reproductive success. We used probability density functions to describe wolf habitat use and habitat coverages to represent the habitat available to wolves. We used regression analysis to connect habitat use with habitat characteristics and habitat selection with reproductive success. Our most relevant result was discovering strong interannual variability in wolf habitat selection. This variability was in part explained by pack identity and differences in litter size and leadership of a pack between two years (summer) and in pack size and precipitation (winter). We also detected some seasonal differences. Wolves selected open habitats, intermediate elevations, intermediate distances from roads, and avoided steep slopes in late winter. They selected areas close to roads and avoided steep slopes in summer. In early winter, wolves selected wetlands, herbaceous and shrub vegetation types, and areas at intermediate elevation and distance from roads. Surprisingly, the habitat characteristics selected by wolves were not useful in predicting reproductive success. We hypothesize that interannual variability in wolf habitat selection may be too strong to detect effects on reproductive success. Moreover, prey availability and competitor pressure may also have an influence on wolf reproductive success, which we did not assess. This project demonstrated how important temporal variation is in shaping patterns of habitat selection. We still believe in the value of running long-term studies, but the effect of temporal variation should always be taken into account.

Pollinator responses to variation in floral display and flower size in dioecious Sagittaria latifolia (Alismataceae)

In animal-pollinated plants with unisexual flowers, sexual dimorphism in floral traits may be the consequence of pollinator-mediated selection. Experimental investigations of the effects of variation in flower size and floral display on pollinator visitation can provide insights into the evolution of floral dimorphism in dioecious plants. Here, we investigated pollinator responses to experimental arrays of dioecious Sagittaria latifolia in which we manipulated floral display and flower size. We also examined whether there were changes in pollinator visitation with increasing dimorphism in flower size. In S. latifolia, males have larger flowers and smaller floral displays than females. Visitation by pollinators, mainly flies and bees, was more frequent for male than for female inflorescences and increased with increasing flower size, regardless of sex. The number of insect visits per flower decreased with increasing floral display in males but remained constant in females. Greater sexual dimorphism in flower size increased visits to male inflorescences but had no influence on the number of visits to female inflorescences. These results suggest that larger flower sizes would be advantageous to both females and males, and no evidence was found that females suffer from increased flower-size dimorphism. Small daily floral displays may benefit males by allowing extended flowering periods and greater opportunities for effective pollen dispersal.

Support for the predictions of the pollinator-mediated stabilizing selection hypothesis

Aims Floral traits are frequency used in traditional plant systematics because Of their assumed constancy. One potential reason for the apparent constancy of flower size is that effective pollen transfer between flowers depends oil the accuracy of the physical fit between the flower and pollinator. Therefore, dowels are likely to he under stronger stabilizing selection for uniform size than vegetative plant parts. Moreover, as predicted by the pollinator-mediated stabilizing selection (PMSS) hypothesis, all accurate fit between flowers and their pollinators is likely to he more important for specialized pollination systems as found in many species with bilaterally symmetric (zygomorphic) flowers than for species, with radially symmetric (actinomorphic) flowers. Methods In a comparative study of 15 zygomorphic and 13 actinomorphic species ill Switzerland, we tested whether variation in flower size, among and within individuals, is smaller than variation ill leaf size and whether variation in flower size is smaller ill zygomorphic compared to actinomorphic species. Important findings Indeed, variation ill leaf length was significantly larger than variation in flower length and width. Within-individual variation ill flower and leaf sizes did not differ significantly between zygomorphic and actinomorphic species. In line with the predictions of the PMSS, among-individual variation ill flower length and flower width was significantly smaller for zygomorphic species than for actinomorphic species, while the two groups did not differ in leaf length variation. This suggests that plants with zygomorphic flowers have undergone stronger selection for uniform flowers than plants with actinomorphic flowers. This supports that the uniformity of flowers compared to vegetative structures within species, as already observed in traditional plant systematics, is, at least in part, a consequence of the requirement for effective pollination.

Code-specific learning rules improve action selection by populations of spiking neurons

Population coding is widely regarded as a key mechanism for achieving reliable behavioral decisions. We previously introduced reinforcement learning for population-based decision making by spiking neurons. Here we generalize population reinforcement learning to spike-based plasticity rules that take account of the postsynaptic neural code. We consider spike/no-spike, spike count and spike latency codes. The multi-valued and continuous-valued features in the postsynaptic code allow for a generalization of binary decision making to multi-valued decision making and continuous-valued action selection. We show that code-specific learning rules speed up learning both for the discrete classification and the continuous regression tasks. The suggested learning rules also speed up with increasing population size as opposed to standard reinforcement learning rules. Continuous action selection is further shown to explain realistic learning speeds in the Morris water maze. Finally, we introduce the concept of action perturbation as opposed to the classical weight- or node-perturbation as an exploration mechanism underlying reinforcement learning. Exploration in the action space greatly increases the speed of learning as compared to exploration in the neuron or weight space.

Genome-wide analysis reveals selection for important traits in domestic horse breeds.

Intense selective pressures applied over short evolutionary time have resulted in homogeneity within, but substantial variation among, horse breeds. Utilizing this population structure, 744 individuals from 33 breeds, and a 54,000 SNP genotyping array, breed-specific targets of selection were identified using an F(ST)-based statistic calculated in 500-kb windows across the genome. A 5.5-Mb region of ECA18, in which the myostatin (MSTN) gene was centered, contained the highest signature of selection in both the Paint and Quarter Horse. Gene sequencing and histological analysis of gluteal muscle biopsies showed a promoter variant and intronic SNP of MSTN were each significantly associated with higher Type 2B and lower Type 1 muscle fiber proportions in the Quarter Horse, demonstrating a functional consequence of selection at this locus. Signatures of selection on ECA23 in all gaited breeds in the sample led to the identification of a shared, 186-kb haplotype including two doublesex related mab transcription factor genes (DMRT2 and 3). The recent identification of a DMRT3 mutation within this haplotype, which appears necessary for the ability to perform alternative gaits, provides further evidence for selection at this locus. Finally, putative loci for the determination of size were identified in the draft breeds and the Miniature horse on ECA11, as well as when signatures of selection surrounding candidate genes at other loci were examined. This work provides further evidence of the importance of MSTN in racing breeds, provides strong evidence for selection upon gait and size, and illustrates the potential for population-based techniques to find genomic regions driving important phenotypes in the modern horse.

Doppler Ultrasound Flow Evaluation of the Uterine Arteries Significantly Correlates with Tumor Size in Cervical Cancer Patients.

PURPOSE The aim of this present study was to evaluate the sonographic correlation between Doppler flow characteristics of the uterine arteries and tumor size in patients with cervical cancer, in order to establish a new potential marker to monitor treatment response. METHODS This was a retrospective cohort study of 25 patients who underwent a sonographic evaluation of Doppler flow characteristics of the uterine arteries before surgery or radiochemotherapy for early and locally advanced/advanced cervical cancer, respectively, was analyzed. The primary outcome was the correlation between Doppler flow characteristics of the uterine arteries and tumor size in patients with cervical cancer. RESULTS Median age was 49 (range 26-85) years, and mean tumor size was 40.8 ± 17 mm. A significant positive correlation was found between tumor diameter and the uterine artery end-diastolic velocity (r = 0.47, p < 0.05) as well as the peak systolic velocity (r = 0.41, p < 0.05). No correlation was found between tumor size and the pulsatility index or resistance index. CONCLUSIONS In cervical cancer, uterine artery velocity parameters are associated with tumor size. This finding could become particularly useful in the follow-up of locally advanced cervical cancer patients undergoing radiochemotherapy or in corroborating the selection of women with more possibility of a high response rate during neoadjuvant chemotherapy before surgery.

Single nucleotide polymorphism (SNP) selection for genotype-phenotype association studies

With hundreds of single nucleotide polymorphisms (SNPs) in a candidate gene and millions of SNPs across the genome, selecting an informative subset of SNPs to maximize the ability to detect genotype-phenotype association is of great interest and importance. In addition, with a large number of SNPs, analytic methods are needed that allow investigators to control the false positive rate resulting from large numbers of SNP genotype-phenotype analyses. This dissertation uses simulated data to explore methods for selecting SNPs for genotype-phenotype association studies. I examined the pattern of linkage disequilibrium (LD) across a candidate gene region and used this pattern to aid in localizing a disease-influencing mutation. The results indicate that the r2 measure of linkage disequilibrium is preferred over the common D′ measure for use in genotype-phenotype association studies. Using step-wise linear regression, the best predictor of the quantitative trait was not usually the single functional mutation. Rather it was a SNP that was in high linkage disequilibrium with the functional mutation. Next, I compared three strategies for selecting SNPs for application to phenotype association studies: based on measures of linkage disequilibrium, based on a measure of haplotype diversity, and random selection. The results demonstrate that SNPs selected based on maximum haplotype diversity are more informative and yield higher power than randomly selected SNPs or SNPs selected based on low pair-wise LD. The data also indicate that for genes with small contribution to the phenotype, it is more prudent for investigators to increase their sample size than to continuously increase the number of SNPs in order to improve statistical power. When typing large numbers of SNPs, researchers are faced with the challenge of utilizing an appropriate statistical method that controls the type I error rate while maintaining adequate power. We show that an empirical genotype based multi-locus global test that uses permutation testing to investigate the null distribution of the maximum test statistic maintains a desired overall type I error rate while not overly sacrificing statistical power. The results also show that when the penetrance model is simple the multi-locus global test does as well or better than the haplotype analysis. However, for more complex models, haplotype analyses offer advantages. The results of this dissertation will be of utility to human geneticists designing large-scale multi-locus genotype-phenotype association studies. ^

Effects of Study Area Size on Geographic Characterizations of Health Events: Prostate Cancer Incidence in Southern New England, USA, 1994-1998.

ABSTRACT : BACKGROUND : We consider how representations of geographic variation in prostate cancer incidence across Southern New England, USA may be affected by selection of study area and/or properties of the statistical analysis. METHOD : A spatial scan statistic was used to monitor geographic variation among 35,167 incident prostate cancer cases diagnosed in Massachusetts, Connecticut and Rhode Island from 1994 to 1998, in relation to the 1990 populations of men 20+ years of age living in that region. Results from the combined-states analysis were compared to those from single-states. Impact of scanning procedures set to examine up to 50% or no more than10% of at-risk populations also was evaluated. RESULTS : With scanning set to 50%, 5 locations in the combined-states analysis were identified with markedly distinct incidence rates. Fewer than expected cases were estimated for nearly all Connecticut, Rhode Island and West Central Massachusetts, whereas census tracts on and around Cape Cod, and areas of Southwestern Connecticut and adjacent to greater Boston were estimated to have yielded more than expected incidence. Results of single-state analyses exhibited several discrepancies from the combined-states analysis. More conservative scanning found many more locations with varying incidence, but discrepancies between the combined- and single-state analysis were fewer. CONCLUSION : It is important to acknowledge the conditional nature of spatial analyses and carefully consider whether a true cluster of events is identified or artifact stemming from selection of study area size and/or scanning properties.