Impact of pre-copulatory sexual cannibalism on genetic diversity and efficacy of selection.

Factors that increase reproductive variance among individuals act to reduce effective population size (Ne), which accelerates the loss of genetic diversity and decreases the efficacy of purifying selection. These factors include sexual cannibalism, offspring investment and mating system. Pre-copulatory sexual cannibalism, where the female consumes the male prior to mating, exacerbates this effect. We performed comparative transcriptomics in two spider species, the cannibalistic Trechaleoides biocellata and the non-cannibalistic T. keyserlingi, to generate genomic evidence to support these predictions. First, we estimated heterozygosity and found that genetic diversity is relatively lower in the cannibalistic species. Second, we calculated dN/dS ratios as a measure of purifying selection; a higher dN/dS ratio indicated relaxed purifying selection in the cannibalistic species. These results are consistent with the hypothesis that sexual cannibalism impacts operational sex ratio and demographic processes, which interact with evolutionary forces to shape the genetic structure of populations. However, other factors such as the mating system and life-history traits contribute to shaping Ne. Comparative analyses across multiple contrasting species pairs would be required to disentangle these effects. Our study highlights that extreme behaviours such as pre-copulatory cannibalism may have profound eco-evolutionary effects.

Stressful environments favor deceptive alternative mating tactics to become dominant.

BACKGROUND: Deceptive alternative mating tactics are commonly maintained at low frequencies within populations because males using them are less competitive and acquire lower fitness than those using dominant tactics. However, the successful invasion of a male deceptive tactic is plausible if deception carries no fitness cost to females. Among populations of the gift-giving spider Paratrechalea ornata, males very often offer females a deceptive worthless gift, rather than a nutritive gift. We tested the degree to which deceptive worthless gifts can occur in natural populations living under divergent environmental conditions (moderate and stressful). We examined the plasticity of morphological and behavioral traits and analyzed the fitness of females in relation to the gift type, also examining the paternity acquired by males offering either gift type. RESULTS: We demonstrated that worthless gifts can become dominant under highly stressful environmental conditions (84-100%). Individuals in such environment reach smaller sizes than those in moderate conditions. We suggest that the size reduction probably favors low metabolic demands in both sexes and may reduce the costs associated with receiving deceptive worthless gifts for females. In contrast, males living under moderate conditions varied the use of the deceptive tactic (0-95%), and worthless gifts negatively influenced female fecundity. Furthermore, male size, rather than gift content, positively impacted paternity success in the moderate but not in the stressful environment. CONCLUSIONS: Overall, this is the first empirical evidence that a reversible deceptive tactic can become dominant when the environment becomes harsh and mate choice becomes limited.

The contribution of incomplete lineage sorting and introgression to the evolutionary history of the fast-evolving genus Ctenomys (Rodentia, Ctenomyidae).

Incomplete lineage sorting (ILS) and introgression have been increasingly recognized as important processes involved in biological differentiation. Both ILS and introgression result in incongruences between gene trees and species trees, consequently causing difficulties in phylogenetic reconstruction. This is particularly the case for rapid radiations, as short internodal distances and incomplete reproductive isolation increase the likelihood of both ILS and introgression. Estimation of the relative frequency of these processes requires assessments across many genomic regions. We use transcriptomics to test for introgression and estimate the frequency of ILS in a set of three closely related and geographically adjacent South American tuco-tucos species (Ctenomys), a genus comprising 64 species resulting from recent, rapid radiation. After cleaning and filtering, 5764 orthologous genes strongly support paraphyly of C. pearsoni relative to C. brasiliensis (putatively represented by the population of Villa Serrana). In line with earlier phylogenetic work, the C. pearsoni - C. brasiliensis pair is closely related to C. torquatus, whereas C. rionegrensis is more distantly related to these three nominal species. Classical Patterson's d-statistic shows significant signals of introgression from C. torquatus into C. brasiliensis. However, a 5-taxon test shows no significant results. ILS was estimated to have involved about 9% of the loci, suggesting it represents an important process in the incipient diversification of tuco-tucos.

Adaptive evolution of ß-globin gene in subterranean in South America octodontid rodents.

The convergent evolution of subterranean rodents is an excellent model to study how natural selection operates and the genetic bases of these adaptations, but the study on the different taxa has been very uneven and still insufficient. In the octodontoid caviomorph rodent superfamily there are two independent lineages where they have recently evolved into totally underground lifestyles: the genera Ctenomys (tuco-tucos) and Spalacopus (coruro). The underground habitat is characterized by an hypoxic and hypercapnic atmosphere, thus gas exchange is one of the most important challenges for these animals. The invasion of the underground niche could have modified the selective regimes of proteins involved in the respiration and transport of O2 of these rodents, positively selecting mutations of higher affinity for O2. Here we examine the sequence variation in the beta globin gene in these two lineages, within a robust phylogenetic context. Using different approaches (classical and Bayesian maximum likelihood (PAML/Datamonkey) and alternatives methods (TreeSAAP)) we found at least three sites with evidence of positive selection in underground lineages, especially the basal branch that leads to the Octodontidae family and the branch that leads to the coruro, suggesting some adaptive changes to the underground life. We also found a convergence with another underground rodent, which cannot be identified by the above methods.

A new species of Edrabius Fauvel (Coleoptera, Staphylinidae, Staphylininae) from Uruguay.

A new rove beetle species, Edrabius uruguayensis Martínez-Villar, González-Vainer Tomasco, sp. nov., associated with the subterranean rodent Ctenomys rionegrensis in Uruguay, is described and illustrated. Photographs, scanning electron micrographs and drawings of the diagnostic character states are provided. The new species is compared with other species of the genus. Nucleotide sequence of the cytochrome oxidase subunit I was reported for the first time for the genus and phylogenetic reconstruction confirms their close relationship with the other genus used from the tribe Amblyopinini (Heterothops).

Unraveling Honey Bee-Varroa destructor Interaction: Multiple Factors Involved in Differential Resistance between Two Uruguayan Populations.

The ectoparasite Varroa destructor is the greatest biotic threat of honey bees Apis mellifera in vast regions of the world. Recently, the study of natural mite-resistant populations has gained much interest to understand the action of natural selection on the mechanisms that limit the mite population. In this study, the components of the A. mellifera-V. destructor relationship were thoroughly examined and compared in resistant and susceptible honey bee populations from two regions of Uruguay. Mite-resistant honey bees have greater behavioral resistance (hygienic and grooming behaviors) than susceptible honey bees. At the end of the summer, resistant honey bees had fewer mites and a lower deformed wing virus (DWV) viral load than susceptible honey bees. DWV variant A was the only detected variant in honey bees and mites. Molecular analysis by Short Tandem Repeat showed that resistant honey bees were Africanized (A. m. scutellata hybrids), whereas susceptible honey bees were closer to European subspecies. Furthermore, significant genetic differentiation was also found between the mite populations. The obtained results show that the natural resistance of honey bees to V. destructor in Uruguay depends on several factors and that the genetic variants of both organisms can play a relevant role.

Detection of Lotmaria passim in Africanized and European honey bees from Uruguay, Argentina and Chile.

Trypanosomatids affecting honey bees, Crithidia mellificae and Lotmaria passim, have been poorly studied in South America. We therefore analyzed their presence in Africanized and European honeybees from Uruguay, Argentina and Chile collected between 1990 and 2011 and assessed their association with other bee parasites and pathogens. Crithidia mellificae was not detected while L. passim was wide-spread. This report shows that L. passim has been present in this region at least since 2007 and it infects both Africanized and European honey bees. L. passim infected colonies showed high V. destructor parasitization levels, suggesting an association between them.

Molecular adaptive convergence in the α-globin gene in subterranean octodontid rodents.

Tuco-tucos (Ctenomys) and related coruros (Spalacopus) are South American subterranean rodents. An energetically demanding lifestyle within the hypoxic/hypercapnic underground atmosphere may change the selective regime on genes involved in O2 transport in blood. In addition, some species of tuco-tucos may be found at high altitude, thus facing additional reductions in changes O2 availabily. We examined sequence variation in the alpha globin subunit gene of hemoglobine in these lineages, within a robust phylogenetic context. Using different approaches (classical and Bayesian maximum likelihood (PAML/Datamonkey) and alternatives methods (TreeSAAP)) we found at least 2 sites with evidence of positive selection in the basal branch of Octodontidae, but not in tuco-tucos. These results suggest some adaptive changes associated to fossoriality, but not strictly to life underground.

Two mitochondrial genes under episodic positive selection in subterranean octodontoid rodents.

Tuco-tucos (Ctenomys) and related coruros (Spalacopus) are South American subterranean rodents. An energetically demanding lifestyle within the hypoxic, underground atmosphere may change the selective regime on oxidative phosphorylation. We examined whether weak and/or episodic positive directional selection affected the evolution of two mitochondrial genes (COX2, CytB), in a background of purifying selection in these lineages. We estimated rates of synonymous (dS) and non-synonymous (dN) substitutions and found: 1) significantly higher dN/dS ratio in subterranean groups relative to non-subterranean related species, and 2) two codons in each gene under episodic selection: 94 and 277 of COX2 and 269 and 307 of CytB.

The evolution of mitochondrial genomes in subterranean caviomorph rodents: adaptation against a background of purifying selection.

South American tuco-tucos (Ctenomys) and the related coruro (Spalacopus) are two rodent lineages that have independently colonised the subterranean niche. The energetically demanding lifestyles of these species, coupled with the hypoxic atmospheres characteristic of subterranean environments, may have altered the selective regimes on genes encoding proteins related to cellular respiration. Here, we examined the molecular evolution of 13 protein-coding genes in the mitochondrial genome of seven caviomorph rodents, including these two subterranean genera and their above-ground relatives. Using maximum-likelihood and Bayesian approaches, we estimated rates of synonymous (dS) and nonsynonymous (dN) substitutions. We found a significantly higher ω ratio (dN/dS) in subterranean groups as compared to their non-subterranean counterparts in 11 of 13 genes, although no ω ratio was larger than 1. Additionally, we applied a method based on quantitative physicochemical properties to test for positive selection. Amino acid changes implicated in radical structural or functional shifts in the protein property were found to be ubiquitous across the phylogeny, but concentrated in the subterranean lineages. Convergent changes were also found between the subterranean genera used in this study and other mammals adapted to hypoxia. The results of this study suggest a link between niche shifts and weak directional (or episodic) selection at the molecular level against a background of purifying selection.

Presence of Nosema ceranae in honeybees (Apis mellifera) in Uruguay.

The microsporidium Nosema ceranae is an emergent pathogen of European honeybees Apis mellifera. Using a PCR-RFLP diagnosis, 29 samples of infected honeybees obtained in 2007-2008 (N=26), 2004 (N=2) and before 1990 (N=1) were analyzed for the presence of Nosema apis and N. ceranae. Only N. ceranae was found in all samples, indicating that this species dispersed to Uruguay (and likely the region) at some time before 1990. The presence of N. ceranae in Uruguay is not associated with an increase of Nosemosis, and its role in colony loss seems to be irrelevant.

Toward a global database for the molecular typing of Saccharomyces cerevisiae strains.

Most of the yeast strains used in fermented beverages and foods are classified as Saccharomyces cerevisiae. However, different strains are suitable for different fermentation processes. The purpose of this work is the proposal of a standardized methodology for the molecular genotyping of S. cerevisiae strains based on polymorphisms at microsatellite loci and/or single nucleotide polymorphisms (SNPs). Single nucleotide variants in the coding region of FLO8, a key regulator of flocculation and pseudohyphae formation, were analyzed in a subset of Uruguayan wine strains. Polymorphism analysis at nine microsatellite loci (selected from 33 loci tested) was performed in a collection of 120 strains, mostly wine strains, from different origins. From a total of 184 different alleles scored, 50 were exclusive alleles that could identify 29 strains. Four selected microsatellite loci are located within or near genes of putative enological interest. The Uruguayan strains are highly diverse and evenly distributed in the phylogenetic reconstructions, suggesting an evolutionary history previous to human use. The Saccharomyces cerevisiae Microsatellites and SNPs Genotyping Database is presented (www.pasteur.edu.uy/yeast). Comparison of standardized results from strains coming from different settings (industrial, clinical, environmental) will provide a reliable and growing source of information on the molecular biodiversity of S. cerevisiae strains.

Evaluation of polymorphism in ten microsatellite loci in Uruguayan sheep flocks

The allele frequencies of 10 microsatellite loci previously described for sheep as BM1314, BM6526, OarFCB128, OarHH64, OarCP20, OarHH47, OarFCB48, OarHH35, OarHH72 and BM2508 were estimated for the Uruguayan flocks. A representative sample of 101 individuals composed by the two predominant breeds (76 percent Corriedale and 24 percent Australian Merino) was used. The sample did not show a significant tendency towards substructuring, in spite of presenting some significantly different allele frequencies between races. The Corriedale sample presents three loci in which the presence of null alleles is possible. The markers were highly variable, showing between 7 and 15 alleles each. The Polymorphism Information Content Index ranged from 0.63 to 0.87 and the Exclusion Probability from 0.39 to 0.75 for a cumulative Exclusion Probability of 99.98 percent. These results suggest the effectiveness of this set of loci for testing genetic relatedness. This is the first report of microsatellite variation in Corriedale