Effects of parasitism on antipredatory responses and defensive behaviors in the subterranean rodent Ctenomys talarum.

Predation represents an important evolutionary force shaping specific adaptations. Prey organisms present behavioral adaptations that allow them to recognize, avoid and defend themselves from their predators. In addition to predation, there is a growing consensus about the role of parasitism in the structuring of biological communities. In vertebrates, the effects on hosts include changes in daily activity, feeding, mate selection, reproduction, and modifications in responses to environmental stimuli. These behavioral variations can benefit the parasite (parasitic manipulation), benefit the host, or appear as a side effect of the infection. We evaluated the influence of parasitism on the behavioral and physiological response of Ctenomys talarum (Thomas 1898) to predator cues. We found that individuals exposed to cat odors and immobilization entered less often and stayed less time in the transparent arms of elevated maze, exhibiting a preference for protected areas (anxiogenic response). Additionally, we evaluated if the presence of parasites affected antipredatory behaviors in tuco-tucos (naturally parasitized, deparasitized or inoculated with Eimeria sp.). We did not find differences among the groups as regards responses to predator cues. Therefore, while exposure to predator cues triggered a stress response, the manipulation of parasite loads did not modify homeostasis under these experimental conditions.

The effects of introgression across thousands of quantitative traits revealed by gene expression in wild tomatoes

It is now understood that introgression can serve as powerful evolutionary force, providing genetic variation that can shape the course of trait evolution. Introgression also induces a shared evolutionary history that is not captured by the species phylogeny, potentially complicating evolutionary analyses that use a species tree. Such analyses are often carried out on gene expression data across species, where the measurement of thousands of trait values allows for powerful inferences while controlling for shared phylogeny. Here, we present a Brownian motion model for quantitative trait evolution under the multispecies network coalescent framework, demonstrating that introgression can generate apparently convergent patterns of evolution when averaged across thousands of quantitative traits. We test our theoretical predictions using whole-transcriptome expression data from ovules in the wild tomato genus Solanum. Examining two sub-clades that both have evidence for post-speciation introgression, but that differ substantially in its magnitude, we find patterns of evolution that are consistent with histories of introgression in both the sign and magnitude of ovule gene expression. Additionally, in the sub-clade with a higher rate of introgression, we observe a correlation between local gene tree topology and expression similarity, implicating a role for introgressed cis-regulatory variation in generating these broad-scale patterns. Our results reveal a general role for introgression in shaping patterns of variation across many thousands of quantitative traits, and provide a framework for testing for these effects using simple model-informed predictions.

Long-term balancing selection in highly dynamic mating loci generates trans-species polymorphisms in fungi

Balancing selection, an evolutionary force that retains genetic diversity, has been detected in multiple genes and organisms, such as the sexual mating loci in fungi. In tetrapolar basidiomycete fungi, sexual type is determined by two unlinked loci, MATA and MATB. These loci are usually highly diverse, but with conserved domains. Previous studies have revealed that species of the genus Trichaptum (Hymenochaetales, Basidiomycota) possess a tetrapolar mating system, with multiple inferred alleles for MATA and MATB. Here, we sequenced a total of a hundred and eighty specimens of three Trichaptum species. We characterized the chromosomal location of MATA (chromosome 2) and MATB (chromosome 9), the molecular structure of MAT regions and their allelic richness. We found multiple MAT alleles segregating in both multiple Trichaptum specimens, and the non-Trichaptum species included for comparison. Phylogenetic analyses and various nucleotide statistics suggested that long-term balancing selection has generated trans-species polymorphisms. Mating sequences were classified in different allelic classes based on an identity threshold of higher than 86%. The observed allelic classes could potentially generate 14,560 different mating types. The inferred allelic information mirrored the outcome of in vitro crosses, thus allowing us to support the degree of allelic divergence needed for successful mating. Even with the high amount of divergence, key amino acids in functional domains are conserved. We conclude that the genetic diversity of mating in Trichaptum loci is due to long-term balancing selection that likely promote sexual outcrossing, with limited recombination and duplication activity. Our large number of sequenced specimens highlighted the importance of sequencing multiple individuals from different species to detect the mating-related genes, the mechanisms generating diversity and the evolutionary forces maintaining them.

Sexual selection and sexual size dimorphism in animals

Sexual selection is often considered as a critical evolutionary force promoting sexual size dimorphism (SSD) in animals. However, empirical evidence for a positive relationship between sexual selection on males and male-biased SSD received mixed support depending on the studied taxonomic group and on the method used to quantify sexual selection. Here, we present a meta-analytic approach accounting for phylogenetic non-independence to test how standardized metrics of the opportunity and strength of pre-copulatory sexual selection relate to SSD across a broad range of animal taxa comprising up to 95 effect sizes from 59 species. We found that SSD based on length measurements was correlated with the sex difference in the opportunity for sexual selection but showed a weak and statistically non-significant relationship with the sex difference in the Bateman gradient. These findings suggest that pre-copulatory sexual selection plays a limited role for the evolution of SSD in a broad phylogenetic context.

Host Colonization as a Major Evolutionary Force Favoring the Diversity and the Emergence of the Worldwide Multidrug-Resistant Escherichia coli ST131

Until now, there has been no indication that the evolutionary dynamics of Escherichia coli ST131 may reflect independent and host-specific adaptation of this lineage outside humans. In contrast, the limited number of ST131 reports in animals supported the common view that it rather reflects a spillover of the human sector.

Reaction to Snakes in Wild Moor Macaques (Macaca maura)

Snake predation is considered an important evolutionary force for primates. Yet, very few studies have documented encounters between primates and snakes in the wild. Here, we provide a preliminary account of how wild moor macaques (Macaca maura) respond to seven species of real and model snakes. Snakes could be local and dangerous to the macaques (i.e., venomous or constricting), local and nondangerous, and novel and dangerous. Macaques reacted most strongly to constrictors (i.e., pythons), exploring them and producing alarm calls, and partially to vipers (both local and novel), exploring them but producing no alarm calls. However, they did not react to other dangerous (i.e., king cobra) or nondangerous species. Our results suggest that moor macaques discriminate local dangerous snakes from nondangerous ones, and may use specific cues (e.g., triangular head shape) to generalize their previous experience with vipers to novel species.

Coupled protein synthesis and ribosome-guided piRNA processing on mRNAs

PIWI-interacting small RNAs (piRNAs) protect the germline genome and are essential for fertility. Previously, we showed that ribosomes guide the biogenesis of piRNAs from long non-coding RNAs (lncRNAs) after translating the short open reading frames (ORFs) near their 5' cap. It remained unclear, however, how ribosomes proceed downstream of ORFs and how piRNA precursors distinguish from other RNAs. It is thus important to test whether a short ORF length is required for substrate recognition for ribosome guided-piRNA biogenesis. Here, we characterized a poorly understood class of piRNAs that originate from the 3' untranslated regions (3'UTRs) of protein coding genes in mice and chickens. We demonstrate that their precursors are full-length mRNAs and that post-termination 80S ribosomes guide piRNA production on 3'UTRs after translation of upstream long ORFs. Similar to non-sense mediated decay (NMD), piRNA biogenesis degrades mRNA right after pioneer rounds of translation and fine-tunes protein production from mRNAs. Interestingly, however, we found that NMD, along with other surveillance pathways for ribosome recycling are temporally sequestered during the pachytene stage to allow for robust piRNA production. Although 3'UTR piRNA precursor mRNAs code for distinct proteins in mice and chickens, they all harbor embedded transposable elements (TEs) and produce piRNAs that cleave TEs, suggesting that TE suppression, rather than the function of proteins, is the primary evolutionary force maintaining a subset of mRNAs as piRNA precursors. Altogether, we discover a function of the piRNA pathway in fine-tuning protein production and reveal a conserved, general piRNA biogenesis mechanism that recognizes translating RNAs regardless of their ORF length in amniotes.

A Case of Intragenic Recombination Dramatically Impacting the Phage WO Genetic Diversity in Gall Wasps

The phage WO was characterized in Wolbachia, a strictly intracellular bacterium causing several reproductive alterations in its arthropod hosts. This study aimed to screen the presence of Wolbachia and phage WO in 15 gall wasp species from six provinces of southern China to investigate their diversity and prevalence patterns. A high incidence of Wolbachia infection was determined in the gall wasp species, with an infection rate of 86.7% (13/15). Moreover, seven species had double or multiple infections. All Wolbachia-infected gall wasp species were found to harbor phage WO. The gall wasp species infected with a single Wolbachia strain were found to harbor a single phage WO type. On the contrary, almost all species with double or multiple Wolbachia infections harbored a high level of phage WO diversity (ranging from three to 27 types). Six horizontal transfer events of phage WO in Wolbachia were found to be associated with gall wasps, which shared identical orf7 sequences among their respective accomplices. The transfer potentially took place through gall inducers and associated inquilines infected with or without Wolbachia. Furthermore, 10 putative recombination events were identified from Andricus hakonensis and Andricus sp2, which harbored multiple phage WO types, suggesting that intragenic recombination was the important evolutionary force, which effectively promoted the high level of phage WO diversity associated with gall wasps.

Broad geographic sampling reveals the shared basis and environmental correlates of seasonal adaptation in Drosophila

To advance our understanding of adaptation to temporally varying selection pressures, we identified signatures of seasonal adaptation occurring in parallel among Drosophila melanogaster populations. Specifically, we estimated allele frequencies genome-wide from flies sampled early and late in the growing season from 20 widely dispersed populations. We identified parallel seasonal allele frequency shifts across North America and Europe, demonstrating that seasonal adaptation is a general phenomenon of temperate fly populations. Seasonally fluctuating polymorphisms are enriched in large chromosomal inversions and we find a broad concordance between seasonal and spatial allele frequency change. The direction of allele frequency change at seasonally variable polymorphisms can be predicted by weather conditions in the weeks prior to sampling, linking the environment and the genomic response to selection. Our results suggest that fluctuating selection is an important evolutionary force affecting patterns of genetic variation in Drosophila.