Genomic admixture increases fitness during a biological invasion

Abstract During biological invasions, multiple introductions can provide opportunities for admixture among genetically distinct lineages. Admixture is predicted to contribute to invasion success by directly increasing fitness through hybrid vigour or by enhancing evolutionary potential within populations . Here, we demonstrate genome‐wide admixture during an invasion that substantially boosted fitness in the cosmopolitan weed, Silene vulgaris. We identified three divergent demes in the native European range that expanded from glacial refugia and experienced historical admixture in a well‐known suture zone. During recent invasion of North America, multiple introductions created additional opportunities for admixture. In common garden experiments, recombinant genotypes from North America experienced a two‐fold increase in fitness relative to nonrecombinants, whereas recombinant genotypes from Europe showed no lasting fitness benefits. This contrast implicates hybrid vigour behind the boost in fitness and supports the hypothesis that admixture can lead to fitness increases that may catapult invasion into a new range.     

Do landscape barriers affect functional connectivity of populations of an endangered damselfly?

1. Landscape genetic approaches were used to assess functional connectivity of populations of the endangered damselfly Coenagrion mercuriale in a fragmented agricultural landscape in Switzerland. Spatial genetic clustering methods combined with interpolation by kriging and landscape genetic corridor analysis were applied to identify landscape elements that enhance or hinder dispersal and gene flow. 2. Spatial genetic clustering analysis divided the sampled populations into a northern and a southern genetic group. The boundary between the two groups coincided with a hill ridge intersecting the study area. Landscape corridor analysis identified five landscape elements that significantly affected gene flow. Elevation change, Euclidian distance, patches of forest and flowing waterbodies acted as barriers, whereas open agricultural land enhanced gene flow between populations of C. mercuriale. 3. This study showed that movement of C. mercuriale was not restricted to its preferred habitat (i.e. streams). Populations linked via continuous open agricultural land were functionally well connected if they were not more than about 1.5–2 km apart. In contrast, substantial elevation change and larger forest patches separated populations. These findings may serve as a basis to define conservation units and should be considered when planning connectivity measures, such as determining the locations of stepping stones, or the restoration of streams.     

Statistical Confusion Among Graduate Students: Sickness or Symptom?

Abstract: Statistics is one of the most important yet difficult subjects for many ecology and wildlife graduate students to learn. Insufficient knowledge about how to conduct quality science and the ongoing debate about the relative value of competing statistical ideologies contribute to uncertainties among graduate students regarding which statistical tests are most appropriate. Herein, we argue that increased education of the available statistical tests alone is unlikely to ameliorate the problem. Instead, we suggest that statistical uncertainties among graduate students are a secondary symptom of a larger problem. We believe the root cause lies in the lack of education on how to conduct science as an integrated process from hypothesis creation through statistical analysis. We argue that if students are taught to think about how each step of the process will affect all other steps, many statistical uncertainties will be avoided.     

Genomic diversity,population structure,and migration following rapid range expansion in the Balsam Poplar,Populus balsamifera

Rapid range expansions can cause pervasive changes in the genetic diversity and structure of populations. The postglacial history of the Balsam Poplar, Populus balsamifera, involved the colonization of most of northern North America, an area largely covered by continental ice sheets during the last glacial maximum. To characterize how this expansion shaped genomic diversity within and among populations, we developed 412 SNP markers that we assayed for a range‐wide sample of 474 individuals sampled from 34 populations. We complemented the SNP data set with DNA sequence data from 11 nuclear loci from 94 individuals, and used coalescent analyses to estimate historical population size, demographic growth, and patterns of migration. Bayesian clustering identified three geographically separated demes found in the Northern, Central, and Eastern portions of the species’ range. These demes varied significantly in nucleotide diversity, the abundance of private polymorphisms, and population substructure. Most measures supported the Central deme as descended from the primary refuge of diversity. Both SNPs and sequence data suggested recent population growth, and coalescent analyses of historical migration suggested a massive expansion from the Centre to the North and East. Collectively, these data demonstrate the strong influence that range expansions exert on genomic diversity, both within local populations and across the range. Our results suggest that an in‐depth knowledge of nucleotide diversity following expansion requires sampling within multiple populations, and highlight the utility of combining insights from different data types in population genomic studies.     

The pay-off from superparasitism in the egg parasitoid Trissolcus basalis, in relation to patch defence

1. In species such as quasi-gregarious egg parasitoids, which exploit defendable patches, the fitness pay-off from superparasitism is an important factor in considering the evolution of patch defence and optimal patch defence strategies.
2. When oviposition in a previously parasitized host has a non-zero fitness pay-off, competing parasitoids are not only able to diminish the future value of a patch to other females by depleting unparasitized hosts, but also devalue the previous investment of other females in the patch by superparasitizing.
3. In Trissolcus basalis , an egg parasitoid of pentatomid bugs, the fitness pay-off from superparasitism is higher than 0.5 when the time interval between ovipositions is less than 3 h, suggesting that defending a previous investment will be an important component of patch defence behaviour.
4. The data suggest a mechanism for the high early pay-off, which involves the superparasitizing female adjusting the sex ratio of its offspring in favour of males. Males develop more quickly than females and thus may have a competitive advantage.     

Microsatellite markers for European Daphnia

We present 32 polymorphic microsatellite markers for species of the European Daphnia longispina group: D. galeata, D. hyalina, D. rosea, D. cucullata and D. curvirostris. Microsatellite markers were either isolated from genomic libraries or optimized based on previously published sequence information of sister taxa. Cross‐species tests revealed that all but one of the polymorphic markers are applicable to more than one species, which allows intra‐ and interspecific genetic studies on, i.e. population structure, hybridization events and introgression.     

Sugar demand of ripening grape berries leads to recycling of surplus phloem water via the xylem

We tested the common assumption that fleshy fruits become dependent on phloem water supply because xylem inflow declines at the onset of ripening. Using two distinct grape genotypes exposed to drought stress, we found that a sink‐driven rise in phloem inflow at the beginning of ripening was sufficient to reverse drought‐induced berry shrinkage. Rewatering accelerated berry growth and sugar accumulation concurrently with leaf photosynthetic recovery. Interrupting phloem flow through the peduncle prevented the increase in berry growth after rewatering, but interrupting xylem flow did not. Nevertheless, xylem flow in ripening berries, but not berry size, remained responsive to root or shoot pressurization. A mass balance analysis on ripening berries sampled in the field suggested that phloem water inflow may exceed growth and transpiration water demands. Collecting apoplastic sap from ripening berries showed that osmotic pressure increased at distinct rates in berry vacuoles and apoplast. Our results indicate that the decrease in xylem inflow at the onset of ripening may be a consequence of the sink‐driven increase in phloem inflow. We propose a conceptual model in which surplus phloem water bypasses the fruit cells and partly evaporates from the berry surface and partly moves apoplastically to the xylem for outflow.