Biology subjects

Łukasik, P.

Publications and source records attributed to Łukasik, P..

3 recordsLinked to original sources

bioRxiv2018

Changes in endosymbiont complexity drive host-level compensatory adaptations in cicadas

For insects that depend on one or more bacterial endosymbionts for survival, it is critical that these bacteria are faithfully transmitted between insect generations. Cicadas harbor two essential bacterial endosymbionts, Sulcia muelleri and Hodgkinia cicadicola. In some cicada species, Hodgkinia has fragmented into multiple distinct cellular and genomic lineages that can differ in abundance by more than two orders of magnitude. This complexity presents a potential problem for the host cicada, because low-abundance-but-essential Hodgkinia lineages risk being lost during the symbiont transmission bottleneck from mother to egg. Here we show that all cicada eggs seem to receive the full complement of Hodgkinia lineages, and that in cicadas with more complex Hodgkinia this outcome is achieved by increasing the number of Hodgkinia cells transmitted by up to six-fold. We further show that cicada species with varying Hodgkinia complexity do not visibly alter their transmission mechanism at the resolution of cell biological structures. Together these data suggest that a major cicada adaptation to changes in endosymbiont complexity is an increase in the number of Hodgkinia cells transmitted to each egg. We hypothesize that the requirement to increase the symbiont titer is one of the costs associated with Hodgkinia fragmentation.

evolutionary biology↗

bioRxiv2017

Idiosyncratic genome degradation in a bacterial endosymbiont of periodical cicadas

When a free-living bacterium transitions to a host-beneficial endosymbiotic lifestyle, it almost invariably loses a large fraction of its genome [1, 2]. The resulting small genomes often become unusually stable in size, structure, and coding capacity [3-5]. Candidatus Hodgkinia cicadicola (Hodgkinia), a bacterial endosymbiont of cicadas, sometimes exemplifies this genomic stability. The Hodgkinia genome has remained completely co-linear in some cicadas diverged by tens of millions of years [6, 7]. But in the long-lived periodical cicada Magicicada tredecim, the Hodgkinia genome has split into dozens of tiny, gene-sparse genomic circles that sometimes reside in distinct Hodgkinia cells [8]. Previous data suggested that other Magicicada species harbor similarly complex Hodgkinia populations, but the timing, number of origins, and outcomes of the splitting process were unknown. Here, by sequencing Hodgkinia metagenomes from the remaining six Magicicada species and two sister species, we show that all Magicicada species harbor Hodgkinia populations of at least twenty genomic circles each. We find little synteny among the 256 Hodgkinia circles analyzed except between the most closely related species. Individual gene phylogenies show that Hodgkinia first split in the common ancestor of Magicicada and its closest known relatives, but that most splitting has occurred within Magicicada and has given rise to highly variable Hodgkinia gene dosages between cicada species. These data show that Hodgkinia genome degradation has proceeded down different paths in different Magicicada species, and support a model of genomic degradation that is stochastic in outcome and likely nonadaptive for the host. These patterns mirror the genomic instability seen in some mitochondria.

evolutionary biology↗

bioRxiv2017

Dramatic differences in gut bacterial densities help to explain the relationship between diet and habitat in rainforest ants

Abundance is a key parameter in microbial ecology, and important to estimates of potential metabolite flux, impacts of dispersal, and sensitivity of samples to technical biases such as laboratory contamination. However, modern amplicon-based sequencing techniques by themselves typically provide no information about the absolute abundance of microbes. Here, we use fluorescence microscopy and quantitative PCR as independent estimates of microbial abundance to test the hypothesis that microbial symbionts have enabled ants to dominate tropical rainforest canopies by facilitating herbivorous diets, and compare these methods to microbial diversity profiles from 16S rRNA amplicon sequencing. Through a systematic survey of ants from a lowland tropical forest, we show that the density of gut microbiota varies across several orders of magnitude among ant lineages, with median individuals from many genera only marginally above detection limits. Supporting the hypothesis that microbial symbiosis is important to dominance in the canopy, we find that the abundance of gut bacteria is positively correlated with stable isotope proxies of herbivory among canopy-dwelling ants, but not among ground-dwelling ants. Notably, these broad findings are much more evident in the quantitative data than in the 16S rRNA sequencing data. Our results help to resolve a longstanding question in tropical rainforest ecology, and have broad implications for the interpretation of sequence-based surveys of microbial diversity.

ecology↗