Plague dynamics and population genetics of the desert locust: can turnover during recession maintain population genetic structure?

Insights into the neutral and adaptive processes shaping the spatial distribution of genomic variation in the economically important Moroccan locust (Dociostaurus maroccanus)

Understanding the processes that shape neutral and adaptive genomic variation is a fundamental step to determine the demographic and evolutionary dynamics of pest species. Here, we use genomic data obtained via restriction site-associated DNA sequencing to investigate the genetic structure of Moroccan locust (Dociostaurus maroccanus) populations from the westernmost portion of the species distribution (Iberian Peninsula and Canary Islands), infer demographic trends, and determine the role of neutral versus selective processes in shaping spatial patterns of genomic variation in this pest species of great economic importance. Our analyses showed that Iberian populations are characterized by high gene flow, whereas the highly isolated Canarian populations have experienced strong genetic drift and loss of genetic diversity. Historical demographic reconstructions revealed that all populations have passed through a substantial genetic bottleneck around the last glacial maximum (~21 ka BP) followed by a sharp demographic expansion at the onset of the Holocene, indicating increased effective population sizes during warm periods as expected from the thermophilic nature of the species. Genome scans and environmental association analyses identified several loci putatively under selection, suggesting that local adaptation processes in certain populations might not be impeded by widespread gene flow. Finally, all analyses showed few differences between outbreak and nonoutbreak populations. Integrated pest management practices should consider high population connectivity and the potential importance of local adaptation processes on population persistence.

Locust Collective Motion and Its Modeling

Over the past decade, technological advances in experimental and animal tracking techniques have motivated a renewed theoretical interest in animal collective motion and, in particular, locust swarming. This review offers a comprehensive biological background followed by comparative analysis of recent models of locust collective motion, in particular locust marching, their settings, and underlying assumptions. We describe a wide range of recent modeling and simulation approaches, from discrete agent-based models of self-propelled particles to continuous models of integro-differential equations, aimed at describing and analyzing the fascinating phenomenon of locust collective motion. These modeling efforts have a dual role: The first views locusts as a quintessential example of animal collective motion. As such, they aim at abstraction and coarse-graining, often utilizing the tools of statistical physics. The second, which originates from a more biological perspective, views locust swarming as a scientific problem of its own exceptional merit. The main goal should, thus, be the analysis and prediction of natural swarm dynamics. We discuss the properties of swarm dynamics using the tools of statistical physics, as well as the implications for laboratory experiments and natural swarms. Finally, we stress the importance of a combined-interdisciplinary, biological-theoretical effort in successfully confronting the challenges that locusts pose at both the theoretical and practical levels.

Demographic processes shaping genetic variation of the solitarious phase of the desert locust

Between plagues, the solitarious desert locust (Schistocerca gregaria) is generally thought to exist as small populations, which are particularly prone to extinction events in arid regions of Africa and Asia. Given the high genetic structuring observed in one geographical area (the Eritrean coast) by former authors, a metapopulation dynamics model involving repeated extinction and colonization events was favoured. In this study, we assessed the validity of a demographic scenario involving temporary populations of the solitarious phase of the desert locust by analysing large-scale population genetic data. We scored 24 microsatellites in 23 solitarious population samples collected over most of the species range during remission. We found very little genetic structuring and little evidence of declining genetic diversity. A Bayesian clustering method distinguished four genetically differentiated units. Three groups were largely consistent with three population samples which had undergone recent bottleneck events. Nevertheless, the last genetically homogeneous unit included all individuals from the remaining 18 population samples and did not show evidence of demographic disequilibrium. An approximate Bayesian computation treatment indicated a large population size for this main genetic group, moderately reduced between plague and remission but still containing tens of thousands of individuals. Our results diverge from the hypothesis of a classical metapopulation dynamics model. They instead support the scenario in which large populations persist in the solitarious phase of the desert locust.

Molecular mechanisms of phase change in locusts

Phase change in locusts is an ideal model for studying the genetic architectures and regulatory mechanisms associated with phenotypic plasticity. The recent development of genomic and metabolomic tools and resources has furthered our understanding of the molecular basis of phase change in locusts. Thousands of phase-related genes and metabolites have been highlighted using large-scale expressed sequence tags, microarrays, high-throughput transcriptomic sequences, or metabolomic approaches. However, only several key factors, including genes, metabolites, and pathways, have a critical role in phase transition in locusts. For example, CSP (chemosensory protein) and takeout genes, the dopamine pathway, protein kinase A, and carnitines were found to be involved in the regulation of behavioral phase change and gram-negative bacteria-binding proteins in prophylaxical disease resistance of gregarious locusts. Epigenetic mechanisms including small noncoding RNAs and DNA methylation have been implicated. We review these new advances in the molecular basis of phase change in locusts and present some challenges that need to be addressed.

The structure of biodiversity - insights from molecular phylogeography

DNA techniques, analytical methods and palaeoclimatic studies are greatly advancing our knowledge of the global distribution of genetic diversity, and how it evolved. Such phylogeographic studies are reviewed from Arctic, Temperate and Tropical regions, seeking commonalities of cause in the resulting genetic patterns. The genetic diversity is differently patterned within and among regions and biomes, and is related to their histories of climatic changes. This has major implications for conservation science.