Grain trade between China and the United States shapes the spatial genetic pattern of common ragweed populations in East China cities

Common ragweed (Ambrosia artemisiifolia L.) is an invasive alien species (IAS) that can cause severe allergies among urban residents. Understanding its invasion pathways is critical for designing effective control programs. However, studies on the invasion of common ragweed normally skip urban areas. Results from a few studies based on analyzing occurrence records contain high uncertainties. We attempted to address this knowledge gap through a case study in East China cities by combining the population genetic method with the occurrence records. We first collected leaf samples of 37 common ragweed populations from 15 cities. We then quantified the spatial genetic pattern of common ragweed populations by analyzing genomic and chloroplast DNA extracted from the leaf samples. Combined with the analysis of occurrence data and trade data, we discovered that multiple introductions have impacted the spatial genetic pattern of common ragweed populations in East China Cities. We inferred that the modern-day grain trade between the United States and China could be the primary invasion source while the bridgehead introduction passage through Japan played a minor role. Among the studied cities, Nanjing and Shenyang dispersed more gene flows than other cities. The two cities' central roles in transportation and grain importation might explain the observed pattern. Based on our findings, we suggest that invasive species control programs should consider the potential role of cities as landing points and dispersal hubs of common ragweed in invaded countries.

Effect of the Landscape on Functional and Spatial Connectivity in Magnolia Cubensis (Magnoliaceae) in Two Mountain Massifs of Cuba

Landscape features impact gene flow and the spatial patterns of genetic variation between populations of a species. Because many Magnoliaceae species occur in fragmented and highly disturbed landscapes, the family is an excellent model for landscape genetic studies. This research focuses on the subspecies and localities of Magnolia cubensis and aims to: (1) compare the genetic diversity, (2) search for genetic patterns, (3) describe the functional connectivity and (4) access the structural connectivity of the landscape. This study employs 21 microsatellite markers on two subspecies, complemented with landscape characteristics of the Guamuhaya and Sierra Maestra massifs in Cuba. Magnolia cubensis subsp. acunae does not have a well-defined spatial genetic pattern: there is no evidence of isolation by distance or spatial autocorrelation and the little genetic differentiation between the two localities does not reflect the characteristics of the landscape that separates them or the cost values to cross it. Magnolia cubensis subsp. cubensis presents evidence of isolation by distance and the autocorrelation analyses indicate that the approximate scale of the genetic neighborhood is between 35 and 40 km. There is a marked genetic structure with probability values that indicate the existence of three genetic groups. Large genetic differentiation was only found between Gran Piedra and the other localities, which reflects low gene flow. Our results support the recognition of these subspecies at the species level. We define one evolutionary significant unit in Magnolia cubensis subsp. acunae and two evolutionary significant units in Magnolia cubensis subsp. cubensis. These results must be combined with ecological, social and distribution data, in order to obtain a more accurate and realistic perspective of the conservation management strategies for these taxa.

Micromorphological character expression of the hybrid Quercus × dysophylla and its parental species (Q. crassifolia and Q. crassipes)

<p><strong>Background:</strong> Hybridization leads to individuals with atypical phenotypes, leading to taxonomic confusion when hybridizing populations are studied. Micromorphological characters may enable taxonomists to discriminate between parental and hybrid categories due to their simple genetic inheritance.</p><p><strong>Species study:</strong> Three oak taxa distributed in the montane regions of the Mexico were studied: <em>Quercus crassifolia</em>, <em>Q. crassipes</em> and their hybrid <em>Q</em>. × <em>dysophylla</em>.</p><p><strong>Hypothesis:</strong> We describe the leaf micromorphological and macromorphological variation of these taxa. Specifically, we searched for a unique combination of micromorphological characters in hybrids. We hypothesize that spatial micromorphological variation will match the spatial pattern revealed by a previous genetic study.</p><p><strong>Study sites:</strong> Two allopatric stands for each parental species and seven hybrid zones were studied. Individuals within each stand were identified as belonging to parental or hybrid categories following previous genetic analyses.</p><p><strong>Methods:</strong> Stomata and trichome types for each taxa were determined through Scanning Electron Microscopy. Eight micromorphological characters for trichomes and stomata and four foliar macromorphological characters were measured.</p><p><strong>Results: </strong>We found the presence of both multirradiate and simple stellate non-glandular trichomes as a diagnostic feature of <em>Q</em>. × <em>dysophylla.</em> Overall populations, <em>Q</em>. × <em>dysophylla</em> showed intermediate phenotypes in 70 % of morphological characters. However, hybrid phenotype exhibited geographical variation. Lastly, spatial hybrid’s phenotype variation did not correlate with the spatial genetic pattern previously identified.</p><p><strong>Conclusions: </strong>The micromorphological features of <em>Q.</em> × <em>dysophylla</em> may enable taxonomists to accurately discriminate between this taxon and its parental species. Finally, we suggest that micromorphological expression of both parental species and hybrids may be influenced by environmental gradients and microclimates.</p>

Spatial genetic pattern in the land mollusc Helix aspersa inferred from a ‘centre-based clustering’ procedure

The present work provides the first broad-scale screening of allozymes in the land snail Helix aspersa. By using overall information available on the distribution of genetic variation between 102 populations previously investigated, we expect to strengthen our knowledge on the spread of the invasive aspersa subspecies in the Western Mediterranean. We propose a new approach based on a centre-based clustering procedure to cluster populations into groups following rules of geographical proximity and genetic similarity. Assuming a stepping-stone model of diffusion, we apply a partitioning algorithm which clusters only populations that are geographically contiguous. The algorithm used, which is actually part of leading methods developed for analysing large microarray datasets, is that of the k-means. Its goal is to minimize the within-group variance. The spatial constraint is provided by a list of connections between localities deduced from a Delaunay network. After testing each optimal group for the presence of spatial arrangement in the genetic data, the inferred genetic structure was compared with partitions obtained from other methods published for defining homogeneous groups (i.e. the Monmonier and SAMOVA algorithms). Competing biogeographical scenarios inferred from the k-means procedure were then compared and discussed to shed more light on colonization routes taken by the species.