Where do adaptive shifts occur during invasion? A multidisciplinary approach to unravelling cold adaptation in a tropical ant species invading the Mediterranean area

Evolution may improve the invasiveness of populations, but it often remains unclear whether key adaptation events occur after introduction into the recipient habitat (i.e. post‐introduction adaptation scenario), or before introduction within the native range (i.e. prior‐adaptation scenario) or at a primary site of invasion (i.e. bridgehead scenario). We used a multidisciplinary approach to determine which of these three scenarios underlies the invasion of the tropical ant Wasmannia auropunctata in a Mediterranean region (i.e. Israel). Species distribution models (SDM), phylogeographical analyses at a broad geographical scale and laboratory experiments on appropriate native and invasive populations indicated that Israeli populations followed an invasion scenario in which adaptation to cold occurred at the southern limit of the native range before dispersal to Israel. We discuss the usefulness of combining SDM, genetic and experimental approaches for unambiguous determination of eco‐evolutionary invasion scenarios.     

Early life antibiotic-driven changes in microbiota enhance susceptibility to allergic asthma

Allergic asthma rates have increased steadily in developed countries, arguing for an environmental aetiology. To assess the influence of gut microbiota on experimental murine allergic asthma, we treated neonatal mice with clinical doses of two widely used antibiotics--streptomycin and vancomycin--and evaluated resulting shifts in resident flora and subsequent susceptibility to allergic asthma. Streptomycin treatment had little effect on the microbiota and on disease, whereas vancomycin reduced microbial diversity, shifted the composition of the bacterial population and enhanced disease severity. Neither antibiotic had a significant effect when administered to adult mice. Consistent with the 'hygiene hypothesis', our data support a neonatal, microbiota-driven, specific increase in susceptibility to experimental murine allergic asthma.     

Chimeric β-Lactamases: Global Conservation of Parental Function and Fast Time-Scale Dynamics with Increased Slow Motions

Enzyme engineering has been facilitated by recombination of close homologues, followed by functional screening. In one such effort, chimeras of two class-A β-lactamases – TEM-1 and PSE-4 – were created according to structure-guided protein recombination and selected for their capacity to promote bacterial proliferation in the presence of ampicillin (Voigt et al., Nat. Struct. Biol. 2002 9:553). To provide a more detailed assessment of the effects of protein recombination on the structure and function of the resulting chimeric enzymes, we characterized a series of functional TEM-1/PSE-4 chimeras possessing between 17 and 92 substitutions relative to TEM-1 β-lactamase. Circular dichroism and thermal scanning fluorimetry revealed that the chimeras were generally well folded. Despite harbouring important sequence variation relative to either of the two ‘parental’ β-lactamases, the chimeric β-lactamases displayed substrate recognition spectra and reactivity similar to their most closely-related parent. To gain further insight into the changes induced by chimerization, the chimera with 17 substitutions was investigated by NMR spin relaxation. While high order was conserved on the ps-ns timescale, a hallmark of class A β-lactamases, evidence of additional slow motions on the µs-ms timescale was extracted from model-free calculations. This is consistent with the greater number of resonances that could not be assigned in this chimera relative to the parental β-lactamases, and is consistent with this well-folded and functional chimeric β-lactamase displaying increased slow time-scale motions.     

Evidence of plasticity in the reproduction of a trematode parasite: the effect of host removal

The parasitic trematode Proctoeces lintoni requires 3 hosts (intertidal mussels, keyhole limpets, and clingfish) to complete its life cycle. The densities and size structure of host communities are modified by selective human harvesting. This study examined clutch and egg size of P. lintoni in 3 adjacent sites in rocky intertidal areas of central Chile presenting differences in the levels of human disturbance (i.e., from a fully protected marine reserve to free open-access areas). We found significant differences in parasite fecundity among sites. An increase in number of eggs was observed inside protected marine areas compared with open-access areas, suggesting a plastic response of the parasite reproductive strategies to the host community modification. These results show that host removal by humans in coastal ecosystems can strongly influence parasite life history traits.     

Competition,predation and flow rate as mediators of direct and indirect effects in a stream food chain

Using semi-natural stream channels, we estimated the effects of competition and predation exerted by juvenile and adult exotic rainbow trout (Oncorhynchus mykiss) on the diel activity pattern of juvenile native Atlantic salmon (Salmo salar), a secondary consumer. We also evaluated the direct and indirect effects of competition, predation and abiotic factors (water depth and velocity) on the growth rate of salmon, the biomass of invertebrate grazers (primary consumers) and the biomass of periphytic algae (primary producers; chlorophyll a). The presence of chemical cues emanating from adult predatory trout reduced the daily activity of juvenile Atlantic salmon. In contrast, competition imposed by juvenile rainbow trout forced Atlantic salmon to be more active during the day, even if adult rainbow trout were also present. We found no effect of either competition or of predatory cues on the growth rate of Atlantic salmon, and no evidence of indirect effects on either the biomass of invertebrates or the biomass of chlorophyll a. In contrast, we demonstrated that this food chain (fish--invertebrate grazers--periphytic algae) was under the control of a critical abiotic factor, the water velocity, and of bottom-up processes. We concluded that the exotic species directly increases the risk of predation of the native Atlantic salmon, but behavioral compensation probably limits the effects on growth rate. The competition and predation imposed by the invaders had no indirect effects on lower trophic levels. Top-down effects may have been mitigated by the dominant influence of water velocity controlling all components of the food chain and by elevated levels of primary production.     

Persistent nuclear ribosomal DNA sequence polymorphism in the Amelanchier agamic complex (Rosaceae)

Individual plants of several Amelanchier taxa contain many polymorphic nucleotide sites in the internal transcribed spacers (ITS) of nuclear ribosomal DNA (nrDNA). This polymorphism is unusual because it is not recent in origin and thus has resisted homogenization by concerted evolution. Amelanchier ITS sequence polymorphism is hypothesized to be the result of gene flow between two major North American clades resolved by phylogenetic analysis of ITS sequences. Western North American species plus A. humilis and A. sanguinea of eastern North America form one clade (A), and the remaining eastern North American Amelanchier make up clade B. Five eastern North American taxa are polymorphic at many of the nucleotide sites where clades A and B have diverged and are thought to be of hybrid origin, with A. humilis or A. sanguinea as one parent and various members of clade B as the other parent. Morphological evidence suggests that A. humilis is one of the parents of one of the polymorphic taxa, a microspecies that we refer to informally as A. "erecta." Sequences of 21 cloned copies of the ITS1- 5.8S gene-ITS2 region from one A. "erecta" individual are identical to A. humilis sequence or to the clade B consensus sequence, or they are apparent recombinants of A. humilis and clade B ITS repeats. Amelanchier "erecta" and another polymorphic taxon are suspected to be relatively old because both grow several hundred kilometers beyond the range of one of their parents. ITS sequence polymorphisms have apparently persisted in these two taxa perhaps because of polyploidy and/or agamospermy (asexual seed production), which are prevalent in the genus.      

Behavioural and Growth Responses of a Territorial Fish (Atlantic Salmon, Salmo salar, L.) to Multiple Predatory Cues

Antipredatory behaviours are important fitness components. The probability of survival decreases if animals fail to respond to signs of danger, but in contrast, energetic costs increase if the response to the threat is exaggerated. We conducted a laboratory experiment designed to examine the behavioural and growth responses of a territorial fish (Atlantic salmon fry, Salmo salar, L.) to different predatory cues (no predatory cues, chemical cues alone, physical cues alone and combined chemical and physical cues). We evaluated the response of Atlantic salmon, focussing on behaviours linked to predator avoidance and to other fitness‐enhancing activities (territory defence and energy acquisition) both during the day and the night. The cost of such responses in terms of growth was assessed and we compared the relative contributions of behaviours in explaining individual growth rate, according to each predation treatment. We demonstrated that the magnitude and nature of behavioural modification varied according to the response variables we considered. An index of predator avoidance and the distance from the food source were affected in an additive fashion by predatory cues (interaction term, p = 0.469 and p = 0.888 for the index of predator avoidance and the distance from the food source respectively); the effect of physical cues was stronger than the effect of chemical cues and the effect of the combined cues was highest. An index of territoriality was affected in a threshold‐like fashion (interaction term, p = 0.040); chemical or physical cues alone had no effect but when both cues were combined, Atlantic salmon significantly reduced their territorial defence. An index of foraging activity was not significantly affected by predatory cues (alone or combined). We detected no effect on the growth rate of Atlantic salmon (p = 0.328). Finally, we found that the relative contribution of behaviours in explaining individual growth rate changed according to the treatments we considered. Overall, these results demonstrated that fish were able to accurately integrate multiple predatory cues and that this information was used to modulate their antipredatory response. Behaviours involved in the response were relatively independent of each other, allowing fish to adopt behavioural tactics that maximized the ratio of net energy gain to predator avoidance.     

Effects of biotic interactions on modeled species' distribution can be masked by environmental gradients

A fundamental goal of ecology is to understand the determinants of species' distributions (i.e., the set of locations where a species is present). Competition among species (i.e., interactions among species that harms each of the species involved) is common in nature and it would be tremendously useful to quantify its effects on species' distributions. An approach to studying the large‐scale effects of competition or other biotic interactions is to fit species' distributions models (SDMs) and assess the effect of competitors on the distribution and abundance of the species of interest. It is often difficult to validate the accuracy of this approach with available data. Here, we simulate virtual species that experience competition. In these simulated datasets, we can unambiguously identify the effects that competition has on a species' distribution. We then fit SDMs to the simulated datasets and test whether we can use the outputs of the SDMs to infer the true effect of competition in each simulated dataset. In our simulations, the abiotic environment influenced the effects of competition. Thus, our SDMs often inferred that the abiotic environment was a strong predictor of species abundance, even when the species' distribution was strongly affected by competition. The severity of this problem depended on whether the competitor excluded the focal species from highly suitable sites or marginally suitable sites. Our results highlight how correlations between biotic interactions and the abiotic environment make it difficult to infer the effects of competition using SDMs.     

Hosts are more important than destinations: What genetic variation in Microctonus aethiopoides (Hymenoptera: Braconidae) means for foreign exploration for natural enemies

Nucleotide sequence data were generated from the gene regions COI, 16S, and arginine kinase to assess genetic variation within the Palearctic parasitoid, Microctonus aethiopoides, reared from Sitona discoideus, S. hispidulus, and Hypera postica collected from two proximate locations in Mediterranean France. Partitioned Bayesian phylogenetic analyses of the molecular data provided strong support for the presence of at least two M. aethiopoides biotypes, one associated with Hypera species and the other with Sitona species. These new results combined with previously published data from 14 countries show that M. aethiopoides genetic variation is much more strongly correlated with host taxon than with sampling location. This contrasts with earlier perceptions that M. aethiopoides exhibits significant geographic variation, and helps to explain the widely varying biological control outcomes that have been obtained following the introductions of M. aethiopoides to Australia, New Zealand, and North America. The results strongly suggest that success rates and environmental safety in biological control would both be improved by ensuring that parasitoids collected in the native range are reared from the same host species as the one being targeted for control in the region of introduction. The results also provided insights both on the evolution of M. aethiopoides' host range, and on its evolutionary transition between solitary and gregarious larval development.