Estelle Rochat

Simple Rules for an Efficient Use of Geographic Information Systems in Molecular Ecology

Geographic Information Systems (GIS) are becoming increasingly popular in the context of molecular ecology and conservation biology thanks to their display options efficiency, flexibility and management of geodata. Indeed, spatial data for wildlife and livestock species is becoming a trend with many researchers publishing genomic data that is specifically suitable for landscape studies. GIS uniquely reveal the possibility to overlay genetic information with environmental data and, as such, allow us to locate and analyze genetic boundaries of various plant and animal species or to study gene-environment associations (GEA). This means that, using GIS, we can potentially identify the genetic bases of species adaptation to particular geographic conditions or to climate change. However, many biologists are not familiar with the use of GIS and underlying concepts and thus experience difficulties in finding relevant information and instructions on how to use them. In this paper, we illustrate the power of free and open source GIS approaches and provide essential information for their successful application in molecular ecology. First, we introduce key concepts related to GIS than are too often overlooked in the literature, for example coordinate systems, GPS accuracy and scale. We then provide an overview of the most employed open-source GIS-related software, file formats and refer to major environmental databases. We also reconsider sampling strategies as high costs of Next Generation Sequencing (NGS) data currently diminish the number of samples that can be sequenced per location. Thereafter, we detail methods of data exploration and spatial statistics suited for the analysis of large genetic datasets. Finally, we provide suggestions to properly edit maps and to make them as comprehensive as possible, either manually or trough programming languages.

Persistence of butterfly populations in fragmented habitats along urban density gradients: motility helps

In a simulation study of genotypes conducted over 100 generations for more than 1600 butterfly’s individuals, we evaluate how the increase of anthropogenic fragmentation and reduction of habitat size along urbanisation gradients (from 7 to 59% of impervious land cover) influences genetic diversity and population persistence in butterfly species. We show that in areas characterised by a high urbanisation rate (>56% impervious land cover), a large decrease of both genetic diversity (loss of 60–80% of initial observed heterozygosity) and population size (loss of 70–90% of individuals) is observed over time. This is confirmed by empirical data available for the mobile butterfly species Pieris rapae in a subpart of the study area. Comparing simulated data for P. rapae with its normal dispersal ability and with a reduced dispersal ability, we also show that a higher dispersal ability can be an advantage to survive in an urban or highly fragmented environment. The results obtained here suggest that it is of high importance to account for population persistence, and confirm that it is crucial to maintain habitat size and connectivity in the context of land-use planning.

Indication of spatially random infection of chlamydia-like organisms in Bufo bufo tadpoles from ponds located in the Geneva metropolitan area

Occurrence of bacteria belonging to the order Chlamydiales was investigated for the first time in common toad (Bufo bufo) tadpole populations collected from 41 ponds in the Geneva metropolitan area, Switzerland. A Chlamydiales-specific Real-Time PCR was used to detect and amplify the Chlamydiales 16S rRNA-encoding gene from the tails of 375 tadpoles. We found the studied amphibian populations to be infected by “Chlamydia-like organisms” (CLOs) attributable to the genera Similichlamydia, Neochlamydia, Protochlamydia and Parachlamydia (belonging to the family Parachlamydiaceae), Simkania (family Simkaniaceae) and Estrella (family Criblamydiaceae); additionally, DNA from the genus Thermoanaerobacter (family Thermoanaerobacteriaceae) was detected. A global autocorrelation analysis did not reveal a spatial structure in the observed CLOs infection rates, and association tests involving land cover characteristics did not evidence any clear effect on CLOs infection rates in B. bufo. Despite preliminary, these results suggest a random and ubiquitous distribution of CLOs in the environment, which would support the biogeographical expectation “everything is everywhere” for the concerned microorganisms and their amoeba vectors.

Open computational landscape genetics

Geographical Information Systems (GIS) are considered to be applications-led technology. Consequently, geographic information scientists commonly find themselves as guest in host disciplines in order to best exploit spatial analysis tools and methods, appropriately guided by experts in the field. An example is population genetics in evolutionary biology. Genetic information being linked to living organisms can be partially characterized by geographic coordinates. A research field named landscape genetics emerged at the intersection of genetics, environmental and geographic information science. Geocomputation and programming efforts carried out with the help of open sources technologies and dedicated to the analysis of genetic data gather together a key scientific community whose goal is to extract new knowledge from the present data tsunami caused by the advent of high throughput molecular data and of new sources of high resolution environmental data. While the level of sophistication of the population genetics functions included in the analytical frameworks developed until now are cutting-edge, advanced geo-competences are also required to reinforce the spatial side of this discipline. They will be particularly useful in conservation programmes for wildlife preservation, but also in farm animal genetic resources conservation.

Relationship between land cover type and Body Mass Index in Geneva

Past studies conducted in urban areas analyzed the impact of the presence of green spaces on public health, and highlighted in particular the psychological benefits of interacting with nature. To investigate a supposed relationship between overweight and dense built environment, we focused on the State of Geneva, Switzerland, and calculated the correlation between Body Mass Index (BMI) in a representative sample of 6663 adults and the percentage of natural areas at the locations where these individuals were living. To this end, we used population-based health data from the “Bus Santé” study (Geneva University Hospitals) and multi-scale land cover maps obtained by means of satellite images and LiDAR data classification. We found little correlation between BMI (as a proxy for health) and land cover data and were not able to verify the working hypothesis at local and regional scales. However, an important phenomenon highlighted here is the difference in the results obtained between the city center and the whole State.