Annotated mitochondrial genome assemblies for two sand lances (genus: Ammodytes) from the northwest Atlantic.

Complete mitochondrial genomes of two northwest Atlantic sand lances (Ammodytes americanus and Ammodytes dubius) were sequenced, assembled, and annotated. Both genomes were 16 519 bp in length and were differentiated by a genetic distance of only 0.01. Furthermore, mitochondrial gene annotations were identical for both species. Phylogenetic analysis revealed that divergence between the two species was shallow, relative to other members of the genus.

Complete mitochondrial genomes for Icelus spatula, Aspidophoroides olrikii and Leptoclinus maculatus: pan-Arctic marine fishes from Canadian waters.

Three Arctic marine fishes Icelus spatula, Aspidophoroides olrikii and Leptoclinus maculatus have been identified as target species for investigating the effects of ocean warming on population patterns in high-latitude marine habitats around Canada. In preparation for this research, we have resolved whole mitochondrial genome sequences of 16 384, 17 200 and 16 384 bp for each species, respectively. GC content for each species was 47.5%, 44.2% and 45.3%, respectively. Mitogenome gene composition included 13 protein-encoding genes, 2 rRNA and 22 tRNA genes, for I. spatula and L. maculatus, consistent with other teleosts. Only 20 tRNA genes were annotated for A. olrikii, because tRNA-Pro and tRNA-Thr are poorly characterized and aberrantly located in this species.

Risk assessment of inbreeding and outbreeding depression in a captive-breeding program.

Captive-breeding programs can be implemented to preserve the genetic diversity of endangered populations such that the controlled release of captive-bred individuals into the wild may promote recovery. A common difficulty, however, is that programs are founded with limited wild broodstock, and inbreeding can become increasingly difficult to avoid with successive generations in captivity. Program managers must choose between maintaining the genetic purity of populations, at the risk of inbreeding depression, or interbreeding populations, at the risk of outbreeding depression. We evaluate these relative risks in a captive-breeding program for 3 endangered populations of Atlantic salmon (Salmo salar). In each of 2 years, we released juvenile F(1) and F(2) interpopulation hybrids, backcrosses, as well as inbred and noninbred within-population crosstypes into 9 wild streams. Juvenile size and survival was quantified in each year. Few crosstype effects were observed, but interestingly, the relative fitness consequences of inbreeding and outbreeding varied from year to year. Temporal variation in environmental quality might have driven some of these annual differences, by exacerbating the importance of maternal effects on juvenile fitness in a year of low environmental quality and by affecting the severity of inbreeding depression differently in different years. Nonetheless, inbreeding was more consistently associated with a negative effect on fitness, whereas the consequences of outbreeding were less predictable. Considering the challenges associated with a sound risk assessment in the wild and given that the effect of inbreeding on fitness is relatively predictable, we suggest that risk can be weighted more strongly in terms of the probable outcome of outbreeding. Factors such as genetic similarities between populations and the number of generations in isolation can sometimes be used to assess outbreeding risk, in lieu of experimentation.

Human disturbance causes the formation of a hybrid swarm between two naturally sympatric fish species.

Most evidence for hybrid swarm formation stemming from anthropogenic habitat disturbance comes from the breakdown of reproductive isolation between incipient species, or introgression between allopatric species following secondary contact. Human impacts on hybridization between divergent species that naturally occur in sympatry have received considerably less attention. Theory predicts that reinforcement should act to preserve reproductive isolation under such circumstances, potentially making reproductive barriers resistant to human habitat alteration. Using 15 microsatellites, we examined hybridization between sympatric populations of alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis) to test whether the frequency of hybridization and pattern of introgression have been impacted by the construction of a dam that isolated formerly anadromous populations of both species in a landlocked freshwater reservoir. The frequency of hybridization and pattern of introgression differed markedly between anadromous and landlocked populations. The rangewide frequency of hybridization among anadromous populations was generally 0-8%, whereas all landlocked individuals were hybrids. Although neutral introgression was observed among anadromous hybrids, directional introgression leading to increased prevalence of alewife genotypes was detected among landlocked hybrids. We demonstrate that habitat alteration can lead to hybrid swarm formation between divergent species that naturally occur sympatrically, and provide empirical evidence that reinforcement does not always sustain reproductive isolation under such circumstances.