Evolutionary rescue can be impeded by temporary environmental amelioration

Rapid evolutionary adaptation has the potential to rescue from extinction populations experiencing environmental changes. Little is known, however, about the impact of short‐term environmental fluctuations during long‐term environmental deterioration, an intrinsic property of realistic environmental changes. Temporary environmental amelioration arising from such fluctuations could either facilitate evolutionary rescue by allowing population recovery (a positive demographic effect) or impede it by relaxing selection for beneficial mutations required for future survival (a negative population genetic effect). We address this uncertainty in an experiment with populations of a bacteriophage virus that evolved under deteriorating conditions (gradually increasing temperature). Periodic environmental amelioration (short periods of reduced temperature) caused demographic recovery during the early phase of the experiment, but ultimately reduced the frequency of evolutionary rescue. These experimental results suggest that environmental fluctuations could reduce the potential of evolutionary rescue.     

Perceived social isolation,evolutionary fitness and health outcomes: a lifespan approach

Sociality permeates each of the fundamental motives of human existence and plays a critical role in evolutionary fitness across the lifespan. Evidence for this thesis draws from research linking deficits in social relationship—as indexed by perceived social isolation (i.e. loneliness)—with adverse health and fitness consequences at each developmental stage of life. Outcomes include depression, poor sleep quality, impaired executive function, accelerated cognitive decline, unfavourable cardiovascular function, impaired immunity, altered hypothalamic pituitary–adrenocortical activity, a pro-inflammatory gene expression profile and earlier mortality. Gaps in this research are summarized with suggestions for future research. In addition, we argue that a better understanding of naturally occurring variation in loneliness, and its physiological and psychological underpinnings, in non-human species may be a valuable direction to better understand the persistence of a ‘lonely’ phenotype in social species, and its consequences for health and fitness.     

Unique evolutionary trajectories in repeated adaptation to hydrogen sulphide‐toxic habitats of a neotropical fish (Poecilia mexicana)

Replicated ecological gradients are prime systems to study processes of molecular evolution underlying ecological divergence. Here, we investigated the repeated adaptation of the neotropical fish Poecilia mexicana to habitats containing toxic hydrogen sulphide (H₂S) and compared two population pairs of sulphide‐adapted and ancestral fish by sequencing population pools of >200 individuals (Pool‐Seq). We inferred the evolutionary processes shaping divergence and tested the hypothesis of increase of parallelism from SNPs to molecular pathways. Coalescence analyses showed that the divergence occurred in the face of substantial bidirectional gene flow. Population divergence involved many short, widely dispersed regions across the genome. Analyses of allele frequency spectra suggest that differentiation at most loci was driven by divergent selection, followed by a selection‐mediated reduction of gene flow. Reconstructing allelic state changes suggested that selection acted mainly upon de novo mutations in the sulphide‐adapted populations. Using a corrected Jaccard index to quantify parallel evolution, we found a negligible proportion of statistically significant parallel evolution of J_corr = 0.0032 at the level of SNPs, divergent genome regions (J_corr = 0.0061) and genes therein (J_corr = 0.0091). At the level of metabolic pathways, the overlap was J_corr = 0.2545, indicating increasing parallelism with increasing level of biological integration. The majority of pathways contained positively selected genes in both sulphide populations. Hence, adaptation to sulphidic habitats necessitated adjustments throughout the genome. The largely unique evolutionary trajectories may be explained by a high proportion of de novo mutations driving the divergence. Our findings favour Gould's view that evolution is often the unrepeatable result of stochastic events with highly contingent effects.     

Novel genetic capacitors and potentiators for the natural genetic variation of sensory bristles and their trait specificity in Drosophila melanogaster

Cryptic genetic variation (CGV) is defined as the genetic variation that has little effect on phenotypic variation under a normal condition, but contributes to heritable variation under environmental or genetic perturbations. Genetic buffering systems that suppress the expression of CGV and store it in a population are called genetic capacitors, and the opposite systems are called genetic potentiators. One of the best‐known candidates for a genetic capacitor and potentiator is the molecular chaperone protein, HSP90, and one of its characteristics is that it affects the genetic variation in various morphological traits. However, it remains unclear whether the wide‐ranging effects of HSP90 on a broad range of traits are a general feature of genetic capacitors and potentiators. In the current study, I searched for novel genetic capacitors and potentiators for quantitative bristle traits of Drosophila melanogaster and then investigated the trait specificity of their genetic buffering effect. Three bristle traits of D. melanogaster were used as the target traits, and the genomic regions with genetic buffering effects were screened using the 61 genomic deficiencies examined previously for genetic buffering effects in wing shape. As a result, four and six deficiencies with significant effects on increasing and decreasing the broad‐sense heritability of the bristle traits were identified, respectively. Of the 18 deficiencies with significant effects detected in the current study and/or by the previous study, 14 showed trait‐specific effects, and four affected the genetic buffering of both bristle traits and wing shape. This suggests that most genetic capacitors and potentiators exert trait‐specific effects, but that general capacitors and potentiators with effects on multiple traits also exist.     

An evolutionarily conserved non-coding element in casein locus acts as transcriptional repressor

In mammals, the casein locus consists of stretches of non-coding DNA, the functions of most of which are unknown. These regions are believed to harbour elements responsible for spatio-temporally regulated expression of genes in this locus and so far, only a few such elements have been identified. In this study, we report a novel regulatory element in the casein locus. Comparative analysis of genomic DNA sequences of casein loci from different mammals identified a 147 bp long evolutionarily conserved region (ECR) upstream of Odam, a gene in this locus. The ECR was found in close proximity of Odam gene in all the mammals examined. In-silico analysis predicted the ECR as a potential regulatory element. Functional analysis in different cell lines identified it as a unidirectional repressor element. From our findings we speculate that the ECR may be involved in the repression of the Odam expression in the mammary gland during lactation.     

Genetic rescue of small inbred populations: meta‐analysis reveals large and consistent benefits of gene flow

Many species have fragmented distribution with small isolated populations suffering inbreeding depression and/or reduced ability to evolve. Without gene flow from another population within the species (genetic rescue), these populations are likely to be extirpated. However, there have been only ~ 20 published cases of such outcrossing for conservation purposes, probably a very low proportion of populations that would potentially benefit. As one impediment to genetic rescues is the lack of an overview of the magnitude and consistency of genetic rescue effects in wild species, I carried out a meta‐analysis. Outcrossing of inbred populations resulted in beneficial effects in 92.9% of 156 cases screened as having a low risk of outbreeding depression. The median increase in composite fitness (combined fecundity and survival) following outcrossing was 148% in stressful environments and 45% in benign ones. Fitness benefits also increased significantly with maternal ΔF (reduction in inbreeding coefficient due to gene flow) and for naturally outbreeding versus inbreeding species. However, benefits did not differ significantly among invertebrates, vertebrates and plants. Evolutionary potential for fitness characters in inbred populations also benefited from gene flow. There are no scientific impediments to the widespread use of outcrossing to genetically rescue inbred populations of naturally outbreeding species, provided potential crosses have a low risk of outbreeding depression. I provide revised guidelines for the management of genetic rescue attempts.     

Insights into the evolutionary history of Cervus (Cervidae,tribe Cervini) based on Bayesian analysis of mitochondrial marker sequences,with first indications for a new species

Molecular phylogeny and evolutionary history of Cervus, the most successful and widespread cervid genus, have been extensively addressed in Europe, fairly in eastern Asia, but scarcely in central Asia, where some populations have never been phylogenetically investigated with DNA‐based methods. Here, we applied a coalescent Bayesian approach to most Cervus taxa using complete mitochondrial cytochrome b gene and control region to provide a temporal framework for species differentiation and dispersal, with special emphasis on the central Asian populations from the Tarim Basin (C. elaphus bactrianus, C. elaphus yarkandensis) and Indian Kashmir (C. elaphus hanglu) aiming at assessing their phylogenetic and phylogeographic patterns. Red deer (C. elaphus), wapiti (C. canadensis) and sika deer (C. nippon) are confirmed as highly differentiated taxa, with genetic distances, divergence times and phylogenetic positions compatible with the rank of species. Similarly, the red deer of the Tarim group, hitherto considered as subspecies of C. elaphus, showed a comparable pattern of genetic distinction in the phylogeny and, according to our results, are thus worthy of being raised to the species level. The systematic position of the endangered red deer from Indian Kashmir is assessed here for the first time, and implications for its conservation are also outlined. Based on phylogeny and divergence time estimates, we propose a novel evolutionary pattern for the genus Cervus during the Mio/Pliocene, in the light of palaeo‐climatological information.     

Solution structure and properties of AlgH from Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the algH gene regulates the cellular concentrations of a number of enzymes and the production of several virulence factors, and is suggested to serve a global regulatory function. The precise mechanism by which the algH gene product, the AlgH protein, functions is unknown. The same is true for AlgH family members from other bacteria. In order to lay the groundwork for understanding the physical underpinnings of AlgH function, we examined the structure and physical properties of AlgH in solution. Under reducing conditions, results of NMR, electrophoretic mobility, and sedimentation equilibrium experiments indicate AlgH is predominantly monomeric and monodisperse in solution. Under nonreducing conditions intra and intermolecular disulfide bonds form, the latter promoting AlgH oligomerization. The high‐resolution solution structure of AlgH reveals alpha/beta‐sandwich architecture fashioned from ten beta strands and seven alpha helices. Comparison with available structures of orthologues indicates conservation of overall structural topology. The region of the protein most strongly conserved structurally also shows the highest amino acid sequence conservation and, as revealed by hydrogen‐deuterium exchange studies, is also the most stable. In this region, evolutionary trace analysis identifies two clusters of amino acid residues with the highest evolutionary importance relative to all other AlgH residues. These frame a partially solvent exposed shallow hydrophobic cleft, perhaps identifying a site for intermolecular interactions. The results establish a physical foundation for understanding the structure and function of AlgH and AlgH family proteins and should be of general importance for further investigations of these and related proteins. Proteins 2015; 83:1137–1150. © 2015 Wiley Periodicals, Inc.     

Affinity for natal environments by dispersers impacts reproduction and explains geographical structure of a highly mobile bird

Understanding dispersal and habitat selection behaviours is central to many problems in ecology, evolution and conservation. One factor often hypothesized to influence habitat selection by dispersers is the natal environment experienced by juveniles. Nonetheless, evidence for the effect of natal environment on dispersing, wild vertebrates remains limited. Using 18 years of nesting and mark–resight data across an entire North American geographical range of an endangered bird, the snail kite (Rostrhamus sociabilis), we tested for natal effects on breeding-site selection by dispersers and its consequences for reproductive success and population structure. Dispersing snail kites were more likely to nest in wetlands of the same habitat type (lacustrine or palustrine) as their natal wetland, independent of dispersal distance, but this preference declined with age and if individuals were born during droughts. Importantly, dispersing kites that bred in natal-like habitats had lower nest success and productivity than kites that did not. These behaviours help explain recently described population connectivity and spatial structure across their geographical range and reveal that assortative breeding is occurring, where birds are more likely to breed with individuals born in the same wetland type as their natal habitat. Natal environments can thus have long-term and large-scale effects on populations in nature, even in highly mobile animals.