Interspecific Hybridization and Mitochondrial Introgression in Invasive Carcinus Shore Crabs

Interspecific hybridization plays an important role in facilitating adaptive evolutionary change. More specifically, recent studies have demonstrated that hybridization may dramatically influence the establishment, spread, and impact of invasive populations. In Japan, previous genetic evidence for the presence of two non-native congeners, the European green crab Carcinus maenas and the Mediterranean green crab C. aestuarii, has raised questions regarding the possibility of hybridization between these sister species. Here I present analysis based on both nuclear microsatellites and the mitochondrial cytochrome C oxidase subunit I (COI) gene which unambiguously argues for a hybrid origin of Japanese Carcinus. Despite the presence of mitochondrial lineages derived from both C. maenas and C. aestuarii, the Japanese population is panmictic at nuclear loci and has achieved cytonuclear equilibrium throughout the sampled range in Japan. Furthermore, analysis of admixture at nuclear loci indicates dramatic introgression of the C. maenas mitochondrial genome into a predominantly C. aestuarii nuclear background. These patterns, along with inferences drawn from the observational record, argue for a hybridization event pre-dating the arrival of Carcinus in Japan. The clarification of both invasion history and evolutionary history afforded by genetic analysis provides information that may be critically important to future studies aimed at assessing risks posed by invasive Carcinus populations to Japan and the surrounding region

The Whereabouts of an Ancient Wanderer: Global Phylogeography of the Solitary Ascidian Styela plicata

Genetic tools have greatly aided in tracing the sources and colonization history of introduced species. However, recurrent introductions and repeated shuffling of populations may have blurred some of the genetic signals left by ancient introductions. Styela plicata is a solitary ascidian distributed worldwide. Although its origin remains unclear, this species is believed to have spread worldwide by travelling on ship's hulls. The goals of this study were to infer the genetic structure and global phylogeography of S. plicata and to look for present-day and historical genetic patterns. Two genetic markers were used: a fragment of the mitochondrial gene Cytochrome Oxidase subunit I (COI) and a fragment of the nuclear gene Adenine Nucleotide Transporter/ADP-ATP Translocase (ANT). A total of 368 individuals for COI and 315 for ANT were sequenced from 17 locations worldwide. The levels of gene diversity were moderate for COI to high for ANT. The Mediterranean populations showed the least diversity and allelic richness for both markers, while the Indian, Atlantic and Pacific Oceans had the highest gene and nucleotide diversities. Network and phylogenetic analyses with COI and ANT revealed two groups of alleles separated by 15 and 4 mutational steps, respectively. The existence of different lineages suggested an ancient population split. However, the geographic distributions of these groups did not show any consistent pattern, indicating different phylogeographic histories for each gene. Genetic divergence was significant for many population-pairs irrespective of the geographic distance among them. Stochastic introduction events are reflected in the uneven distribution of COI and ANT allele frequencies and groups among many populations. Our results confirmed that S. plicata has been present in all studied oceans for a long time, and that recurrent colonization events and occasional shuffling among populations have determined the actual genetic structure of this species

Effectiveness of Sampling Techniques in Collecting the Polyp Stage of the Invasive Freshwater Hydrozoan Craspedacusta sowerbii

Current sampling methods for detecting the presence of the invasive freshwater hydrozoan Craspedacusta sowerbii rely mainly on visual confirmation of the medusa stage. Confirming the presence of the polyp stage is equally important for observing medusae since typical late summer/early fall occurrences or observations of medusae are sporadic though are becoming more frequent. The polyp stage is important as it is the organism’s primary stage and is present throughout the year depending on water temperatures. Therefore, sampling methods for the polyp stage are, commonly, the collection of substrates such as rocks, plants, or pieces of wood in a given body of water, and these can be cumbersome to examine. Polyps are also small, transparent, and difficult to see on natural substrates. Based on a preliminary culturing of the polyp stage on glass and plastic microscope slides in the laboratory, we designed a sampling methodology based on submerging four substrate types (glass and plastic microscope slides, Hester-Dendy discs, and small glass Petri dishes) to confirm the presence of C. sowerbii polyps in the field. We tested this method in three lakes in the Illinois–Indiana region (USA). Two of the lakes have recorded sightings of medusae but the third has no record of polyps or medusae. The sampling method we designed was effective in that C. sowerbii polyps were found on both plastic and glass slides. While this method can be sufficient for detection of the polyp stage, it also shows potential for improvement; we highlight abiotic and biotic ecological parameters as significant factors influencing the collection of C. sowerbii polyps to be considered for future methodologies

Microsatellite loci for the invasive colonial hydrozoan \u3ci\u3eCordylophora caspia\u3c/i\u3e

Cordylophora caspia, a colonial hydrozoan native to the Ponto-Caspian region, has become a common invader of both fresh and brackish water ecosystems of North America and Europe. We describe 11 polymorphic microsatellite loci for this species. Preliminary analyses indicate that population substructure may contribute to departures from Hardy–Weinberg equilibrium. In addition, new loci failed to consistently amplify Cordylophora samples known to be genetically distant from those utilized in this study, indicating the presence of cryptic diversity within the taxon

Life Cycle Transitions in the Freshwater Jellyfish Craspedacusta sowerbii

Craspedacusta sowerbii is an invasive hydrozoan found globally in freshwater habitats. C. sowerbii has a complex life cycle that includes benthic, pelagic, dispersal and dormant stages. The distribution of the medusa (jellyfish) stage has been well documented, but little is known about the other life cycle stages, which are suggested to be more widespread. In addition, the conditions required for growth, reproduction and dispersal of the different life cycle stages, as well as the environmental cues that regulate life cycle transitions, are not fully understood. The aim of this study was to determine laboratory conditions for growth of, and transition to, different life cycle stages in order to improve our ability to culture all life cycle stages of C. sowerbii. In addition, insight into the environmental triggers that promote life cycle transitions will enable us to better predict the potential negative effects C. sowerbii could impose on freshwater ecosystems