Search

Migration is typically associated with risk and uncertainty at the population level, but little is known about its cost¿benefit trade-offs at the species level. Migratory insects in particular often exhibit strong demographic fluctuations due to local bottlenecks and outbreaks. Here, we use genomic data to investigate levels of heterozygosity and long-term population size dynamics in migratory insects, as an alternative to classical local and short-term approaches such as regional field monitoring. We analyse whole-genome sequences from 97 Lepidoptera species and show that individuals of migratory species have significantly higher levels of genome-wide heterozygosity, a proxy for effective population size, than do nonmigratory species. Also, we contribute whole-genome data for one of the most emblematic insect migratory species, the painted lady butterfly (Vanessa cardui), sampled across its worldwide distributional range. This species exhibits one of the highest levels of genomic heterozygosity described in Lepidoptera (2.95 ± 0.15%). Coalescent modelling (PSMC) shows historical demographic stability in V. cardui, and high effective population size estimates of 2 -20 million individuals 10,000 years ago. The study reveals that the high risks associated with migration and local environmental fluctuations do not seem to decrease overall genetic diversity and demographic stability in migratory Lepidoptera. We propose a "compensatory" demographic model for migratory r-strategist organisms in which local bottlenecks are counterbalanced by reproductive success elsewhere within their typically large distributional ranges. Our findings highlight that the boundaries of populations are substantially different for sedentary and migratory insects, and that, in the latter, local and even regional field monitoring results may not reflect whole population dynamics. Genomic diversity patterns may elucidate key aspects of an insect's migratory nature and population dynamics at large spatiotemporal scales., This work was funded by the National Geographic Society (grant WW1-300R-18) and by the grant PID2020-117739GA-I00 from MCIN/AEI/10.13039/501100011033 to G.T., by fellowship FPU19/01593 to A.G.-B., by project LINKA20399 from the CSIC i-LINK-2021 programme to G.T., N.E.P., R.V. and N.B., by grants from the Putnam Expeditionary Fund of the Museum of Comparative Zoology to G.T. and N.E.P., by projects PID2019-107078GB-I00/MCIN/AEI/10.13039/501100011033 and 2017-SGR-991 (Generalitat de Catalunya) to R.V. and G.T., by the University of Malaya (grant H50001-A-000027) to K.G.C., by the Swedish Collegium for Advanced Science (SCAS; Natural Sciences Programme, Knut and Alice Wallenberg Foundation, Postdoc funding) to D.S., by NSF grant DEB-1541560 to N.E.P., and by the Swedish Research Council FORMAS (grant 2019-00670) to N.B., G.T. and R.V., 1 INTRODUCTION2 MATERIALS AND METHODS2.1 Heterozygosity estimates2.2 Behavioural scoring2.3 Comparative analyses2.4 Vanessa cardui sampling and sequencing2.5 Vanessa cardui reference-based assemblies2.6 Vanessa cardui demographic inference3 RESULTS3.1 Heterozygosity rates in Lepidoptera3.2 Vanessa cardui demographic history4 DISCUSSION4.1 Genomic heterozygosity, effective population size and migration4.2 Short-term migratory cost but long-term demographic stability4.3 Delimiting populations in migratory insect speciesAUTHOR CONTRIBUTIONSACKNOWLEDGEMENTSCONFLICT OF INTEREST

Migration is typically associated with risk and uncertainty at the population level, but little is known about its cost and benefit trade-offs at the species level. Migratory insects often exhibit strong demographic fluctuations due to local bottlenecks and outbreaks. Here, we use genomic data to investigate levels of heterozygosity and long-term population size dynamics in migratory insects, as an alternative to classical local and short-term approaches such as regional field monitoring. We analyze whole-genome sequences from 97 Lepidoptera species and show that migratory species have significantly higher levels of genome-wide heterozygosity, a proxy for effective population size, than non-migratory species. Also, we contribute whole-genome data for one of the most emblematic insect migratory species, the painted lady butterfly (Vanessa cardui), sampled across its worldwide distribution range. This species exhibits one of the highest levels of heterozygosity described in Lepidoptera (2.95% ± 0.15). Coalescent modeling (PSMC) shows historical demographic stability in V. cardui, and high effective population size estimates of 2 to 20 million individuals 10,000 years ago. The study reveals that the high risks associated with migration and local environmental fluctuations do not seem to decrease overall genetic diversity and demographic stability in migratory Lepidoptera. We propose a “compensatory” demographic model for migratory r-strategist organisms in which local bottlenecks are counterbalanced by reproductive success elsewhere within their typically large distributional ranges. Our findings highlight that the delimitations of populations are substantially different for sedentary and migratory insects, and that, in the latter, local and even regional field monitoring results may not reflect whole population dynamics. Genomic diversity patterns may elucidate key aspects of an insect’s migratory nature and population dynamics at large spatiotemporal scales.

Additional file 2: Figure S1. Rarefaction curves evaluating the richness of ASVs in the bacterial microbiome of faecal samples collected from the toilet chamber of the laboratory NMRs.

Additional file 6: Figure S3. The bacterial microbiomes of faecal samples from wild individual NMRs and the toilet chamber of a laboratory NMR colony. Barplot showing the relative abundance of bacterial taxa at the rank of family.

Additional file 5: Figure S2. The bacterial microbiomes of faecal samples from wild individual NMRs and the toilet chamber of a laboratory NMR colony. Barplot showing the relative abundance of bacterial taxa at the rank of phylum.

Additional file 3: Table S2. Alpha diversity analysis after rarefaction to 70,000 sequences per faecal sample from the toilet chamber of the laboratory NMR colony.

Additional file 4: Table S3. The number of 16S rRNA gene sequences in the bacterial microbiomes of faecal samples from wild individual NMRs and the toilet chamber of a laboratory NMR colony. The data for wild NMRs were obtained from previous studies (1. Debebe T, Biagi E, Soverini M, Holtze S, Hildebrandt TB, Birkemeyer C, et al. Unraveling the gut microbiome of the long-lived naked mole-rat. Sci Rep. 2017;7(1):1���9).

Additional file 1: Table S1. 16S rRNA gene sequences of bacteria in the microbiome of the faecal samples from the toilet chamber of the laboratory NMR colony.

Pseudomonads typically carry multiple non-identical alleles of the post-transcriptional regulator rsmA. In Pseudomonas aeruginosa, RsmN is notable in that its structural rearrangement confers distinct and overlapping functions with RsmA. However, little is known about the specificities of RsmN for its target RNAs and overall impact on the biology of this pathogen. We purified and mapped 503 transcripts directly bound by RsmN in P. aeruginosa. About 200 of the mRNAs identified encode proteins of demonstrated function including some determining acute and chronic virulence traits. For example, RsmN reduces biofilm development both directly and indirectly via multiple pathways, involving control of Pel exopolysaccharide biosynthesis and c-di-GMP levels. The RsmN targets identified are also shared with RsmA, although deletion of rsmN generally results in less pronounced phenotypes than those observed for ΔrsmA or ΔrsmArsmNind mutants, probably as a consequence of different binding affinities. Targets newly identified for the Rsm system include the small non-coding RNA CrcZ involved in carbon catabolite repression, for which differential binding of RsmN and RsmA to specific CrcZ regions is demonstrated. The results presented here provide new insights into the intricacy of riboregulatory networks involving multiple but distinct RsmA homologues.