Karine Berthier

Nuclear insertions and heteroplasmy of mitochondrial DNA as two sources of intra-individual genomic variation in grasshoppers

We examined the level of intra‐individual variation in a region of the mitochondrial genome coding for cytochrome oxydase 1 (COI) in two grasshopper species using a clone‐and‐sequence analysis of hundreds of sequences. In both Locusta migratoria and Chortoicetes terminifera, we found that 60–65% of the clones were unique COI‐like sequences. Among these COI‐like sequences, 70–75% diverged by less than 1% from the real mitochondrial haplotypes, and were likely to represent microheteroplasmic molecules. About 20% of the COI‐like sequences diverged by more than 9% from the mitochondrial haplotypes, and generally included stop codons, suggesting that these sequences were nuclear mitochondrial pseudogenes (NUMTs). Only six sequences, diverging by 2–6% from the mitochondrial haplotypes, were identified as potentially misleading in phylogenetic studies. In addition, we found that five sequences from C. terminifera were associated with mobile elements or repetitive DNA families.

Laboratory Populations as a Resource for Understanding the Relationship Between Genotypes and Phenotypes: A Global Case Study in Locusts

Publisher Summary The expression of phenotypic plasticity is widespread in insects. One of the most extraordinary and economically devastating examples of phenotypic plasticity is found in locusts. In contrast to typical grasshoppers, locust species express an extreme form of density-dependent phenotypic plasticity known as “phase polyphenism.” Environmental factors such as temperature, photoperiod, resource availability and population density, are known to affect the development of a myriad of phenotypic traits that have consequences for individual performance, ecology, life-history, fitness and subsequent evolution. Given their diversity of responses and amenability to experimental manipulation and rearing in the lab, insects continue to play an important role as model organisms in empirical analyses of the fundamental relationships between genotypes and phenotypes in animals. Critical conclusions and recommendations from the analysis of recent laboratory stocks, findings that are broadly applicable across taxa to any research program rearing organisms in the lab, are also given in the chapter.

Crosses prior to parthenogenesis explain the current genetic diversity of tropical plant-parasitic Meloidogyne species (Nematoda: Tylenchida).

The tropical and subtropical parthenogenetic plant-parasitic nematodes Meloidogyne are polyphagous major agricultural pests. Implementing proper pest management approaches requires a good understanding of mechanisms, population structure, evolutionary patterns and species identification. A comparative analysis of the mitochondrial vs nuclear diversity was conducted on a selected set of Meloidogyne lines from various geographic origins. Mitochondrial co2-16S sequences and AFLP markers of total DNA were applied because of their ability to evidence discrete genetic variation between closely related isolates. Several distinct maternal lineages were present, now associated with different genetic backgrounds. Relative discordances were found when comparing mitochondrial and nuclear diversity patterns. These patterns are most likely related to crosses within one ancestral genetic pool, followed by the establishment of parthenogenesis. In this case, they mirror the genetic backgrounds of the original individuals. Another aspect could be that species emergence was recent or on process from this original genetic pool and that the relatively short time elapsed since then and before parthenogenesis settlement did not allow for lineage sorting. This could also be compatible with the hypothesis of hybrids between closely related species. This genetic pool would correspond to a species as defined by the species interbreeding concept, but also including the grey area of species boundaries. This complex process has implications on the way genotypic and phenotypic diversity should be addressed. The phenotype of parthenogenetic lines is at least for part determined by the ancestral amphimictic genetic background. A direct consequence is, therefore, in terms of risk management, the limited confidence one can have on the direct association of an agronomic threat to a simple typing or species delineation. Risk management strategies and tools must thus consider this complexity when designing quarantine implementation, resistance breeding programmes or molecular diagnostic.

Modeling spatiotemporal dynamics of outbreaking species: influence of environment and migration in a locust

Many pest species exhibit huge fluctuations in population abundance. Understanding their large-scale and long-term dynamics is necessary to develop effective control and management strategies. Occupancy models represent a promising approach to unravel interactions between environmental factors and spatiotemporal dynamics of outbreaking populations. Here, we investigated population dynamics of the Australian plague locust, Chortoicetes terminifera, using density data collected between 1988 and 2010 by the Australian Plague Locust Commission over more than 3 million km2 in eastern Australia. We applied multistate and autologistic multi-season occupancy models to test competing hypotheses about environmental and demographic processes affecting the large-scale dynamics of the Australian plague locust. We found that rainfall and land cover predictors best explained the spatial variability in outbreak probability across eastern Australia. Outbreaks are more likely to occur in temperate than tropical regions, with a faster and more continuous response to rainfall in desert than in agricultural areas. Our results also support the hypothesis that migration tends to propagate outbreaks only locally (over distances lower than 400 km) rather than across climatic regions. Our study suggests that locust outbreak forecasting and management systems could be improved by implementing key environmental factors and migration in hierarchical spatial models. Finally, our modeling framework can be seen as a step towards bridging the gap between mechanistic and more phenomenological models in the spatial analysis of fluctuating populations.