Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

We describe the draft genome of the microcrustacean Daphnia pulex, which is only 200 megabases and contains at least 30,907 genes. The high gene count is a consequence of an elevated rate of gene duplication resulting in tandem gene clusters. More than a third of Daphnia's genes have no detectable homologs in any other available proteome, and the most amplified gene families are specific to the Daphnia lineage. The coexpansion of gene families interacting within metabolic pathways suggests that the maintenance of duplicated genes is not random, and the analysis of gene expression under different environmental conditions reveals that numerous paralogs acquire divergent expression patterns soon after duplication. Daphnia-specific genes, including many additional loci within sequenced regions that are otherwise devoid of annotations, are the most responsive genes to ecological challenges.

/pdf/the-ecoresponsive-genome-of-daphnia-pulex-bywdhwk6v1.pdf

The ecoresponsive genome of Daphnia pulex

A recent trend in invasion ecology relates the success of non-indigenous species (NIS) to reduced control by enemies such as pathogens, parasites and predators (i.e. the enemy release hypothesis, ERH). Despite the demonstrated importance of enemies to host population dynamics, studies of the ERH are split – biogeographical analyses primarily show a reduction in the diversity of enemies in the introduced range compared with the native range, while community studies imply that NIS are no less affected by enemies than native species in the invaded community. A broad review of the invasion literature implies at least eight non-exclusive explanations for this enigma. In addition, we argue that the ERH has often been accepted uncritically wherever (i) NIS often appear larger, more fecund, or somehow ‘better’ than either congeners in the introduced region, or conspecifics in the native range; and (ii) known enemies are conspicuously absent from the introduced range. However, all NIS, regardless of their abundance or impact, will lose natural enemies at a biogeographical scale. Given the complexity of processes that underlie biological invasions, we argue against a simple relationship between enemy ‘release’ and the vigour, abundance or impact of NIS.

Is invasion success explained by the enemy release hypothesis

https://dialnet.unirioja.es/descarga/articulo/4511387.pdf

The origins of order. Self-organization and selection in evolution

There is mounting evidence that reduced genetic diversity in invasive populations is not as commonplace as expected. Recent studies indicate that high propagule vectors, such as ballast water and shellfish transplantations, and multiple introductions contribute to the elimination of founder effects in the majority of successful aquatic invasions. Multiple introductions, in particular, can promote range expansion of introduced populations through both genetic and demographic mechanisms. Closely related to vectors and corridors of introduction, propagule pressure can play an important role in determining the genetic outcome of introduction events. Even low-diversity introductions have numerous means of avoiding the negative impact of diversity loss. The interaction of high propagule vectors and multiple introductions reveal important patterns associated with invasion success and deserve closer scrutiny.

/pdf/paradox-lost-genetic-diversity-and-the-success-of-aquatic-539b94olwf.pdf

Paradox lost: genetic diversity and the success of aquatic invasions

DNA barcoding has revealed unrecognized species in several animal groups. In this study we have employed DNA barcoding to examine Hyalella, a taxonomically difficult genus of amphipod crustaceans, from sites in the southern Great Basin of California and Nevada, USA. We assessed the extent of species diversity using a species screening threshold (SST) set at 10 times the average intrapopulation cytochrome c oxidase subunit I (COI) haplotype divergence. Despite the fact that this threshold approach is more conservative in delineating provisional species than the phylogenetic species concept, our analyses revealed extraordinary levels of cryptic diversity and endemism. The SST discriminated two provisional species within Hyalella sandra, and 33 provisional species within Hyalella azteca. COI nucleotide divergences among these provisional species ranged from 4.4% to 29.9%. These results have important implications for the conservation of life in desert springs - habitats that are threatened as a result of groundwater over-exploitation.

DNA barcoding reveals extraordinary cryptic diversity in an amphipod genus: implications for desert spring conservation

Many benthic freshwater invertebrates are strong candidates for diversification as a result of their short generation times, the divergent selection pressures that they encounter across habitat gra...

Cryptic species diversity and evolution in the amphipod genus Hyalella within central glaciated North America: a molecular phylogenetic approach

The scale of divergence: a phylogenetic appraisal of intercontinental allopatric speciation in a passively dispersed freshwater zooplankton genus.

The predatory cladoceran Cercopagis pengoihas extended its range over the past decade from the Ponto-Caspian basin into the Baltic Sea and the Laurentian Great Lakes. This study employs mitochondrial DNA (mtDNA) sequence analysis to elucidate the invasion corridors exploited during this range expansion. The Caspian and Black Sea populations of C. pengoi exhibit marked genetic divergence, enabling their discrimination as potential sources of the Baltic and Great Lakes populations. The limited mtDNA haplotype diversity detected in the Baltic populations suggests they were founded by a small number of colonists from the Black Sea. The colonization of North America was apparently a result of the transfer of animals from the Baltic Sea in ballast water. Transoceanic shipping activities and canals linking naturally segregated watersheds on single continents are provoking a massive redistribution of freshwater life. Euryhaline organisms are well positioned to exploit these dispersal corridors, because shipping often occurs via waters of varying salinity. The Ponto-Caspian basin has had a turbulent history of salinity fluctuation and, consequently, many elements of its fauna have evolved broad salinity tolerances (Banarescu 1991; Dumont 1998). Hence, it is not surprising that many prominent invaders such as the hydrozoan Cordylophora caspia, the mollusks Dreissena polymorpha and Dreissena bugensis, the amphipod Echinogammarus ischnus, and the cladoceran Cercopagis pengoiwere derived from this region (MacIsaac et al. in press). Each of these species first extended its distribution into Eastern Europe (Olenin and Lep

/pdf/an-invasion-history-for-cercopagis-pengoi-based-on-5bawu3etoy.pdf

Jonathan D. S. Witt

Papers

DNA barcoding reveals extraordinary cryptic diversity in an amphipod genus: implications for desert spring conservation

Cryptic species diversity and evolution in the amphipod genus Hyalella within central glaciated North America: a molecular phylogenetic approach

The scale of divergence: a phylogenetic appraisal of intercontinental allopatric speciation in a passively dispersed freshwater zooplankton genus.

An invasion history for Cercopagis pengoi based on mitochondrial gene sequences

Distribution of the Ponto-Caspian Amphipod Echinogammarus ischnus in the Great Lakes and Replacement of Native Gammarus fasciatus