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Livestock domestication has long been a part of agriculture, estimated to have first occurred approximately 10 000 years ago. Despite the plethora of traits studied, there is little understanding of the possible impacts domestication has had on internal organs, which are key determinants of survival. Moreover, the genetic basis of observed associated changes in artificial environments is still puzzling. Here we examine impacts of captivity on two organs in Atlantic salmon ( Salar salar ) that have been domesticated for approximately 50 years: heart and liver, in addition to growth. We studied multiple families of wild, domesticated, F 1 and F 2 hybrid, and backcrossed strains of S. salar in replicated common garden tanks during the freshwater and marine stages of development. Heart and liver weight were investigated, along with heart morphology metrics examined in just the wild, domesticated and F 1 hybrid strains (heart height and width). Growth was positively linked with the proportion of the domesticated strain, and recombination in F 2 hybrids (and the potential disruption of co-adapted gene complexes) did not influence growth. Despite the influence of domestication on growth, we found no evidence for domestication-driven divergence in heart or liver morphology. However, sexual dimorphism was detected in heart morphology, and after controlling for body size, females exhibited significantly larger heart weight and heart width when compared with males. Wild females also had an increased heart height when compared with wild males, and this was not observed in any other strain. Females sampled in saltwater showed significantly larger heart height with rounder hearts, than saltwater males. Collectively, these results demonstrate an additive basis of growth and, despite a strong influence of domestication on growth, no clear evidence of changes in heart or liver morphology associated with domestication was identified.

Despite increasing threats to the marine environment, only a fraction of the biodiversity of the oceans has been described, owing in part to the widespread occurrence of cryptic species. DNA-based barcoding through screening of an orthologous reference gene has been proposed as a powerful tool to uncover biological diversity in the face of dwindling taxonomic expertise and the limitations of traditional species identification. Although DNA barcoding should be particularly useful in the sea, given the prevalence of marine cryptic species, the link between taxa identified through DNA barcodes and reproductively isolated taxa (biological species) has rarely been explicitly tested. Here, we use an integrated framework comparing breeding compatibility, morphology and mitochondrial (cytochromecoxidase 1) and nuclear (elongation factor-1-alpha) DNA sequence variation among globally distributed samples of the cosmopolitan marine bryozoanCelleporella hyalina(L.). Our results reveal thatC. hyalinacomprises numerous deep, mostly allopatric, genetic lineages that are reproductively isolated, yet share very similar morphology, indicating rampant cryptic speciation. The close correspondence between genetic lineages and reproductively isolated taxa in the context of minimal morphological change suggests that DNA barcoding will play a leading role in uncovering the hidden biodiversity of the oceans and that the sole use of morphologically based taxonomy would grossly underestimate the number of marine species.

Despite increasing evidence that current exploitation rates can contribute to shifts in life-history traits and the collapse of marine fish stocks, few empirical studies have investigated the likely evolutionary impacts. Here, we used DNA recovered from a temporal series of archived North Sea cod (Gadus morhua) otoliths, to investigate genetic diversity within the Flamborough Head population between 1954 and 1998, during which time the population underwent two successive declines. Microsatellite data indicated a significant reduction in genetic diversity between 1954 and 1970 (total number of alleles: 1954, 46; 1960, 42; 1970, 37), and a subsequent recovery between 1970 and 1998 (total number of alleles: 1970, 37; 1981, 42; 1998, 45). Furthermore, estimates of genetic differentiation (F(ST) and R(ST)) showed a significant divergence between 1998 and earlier samples. Data are consistent with a period of prolonged genetic drift, accompanied by a replacement of the Flamborough Head population through an increased effective migration rate that occurred during a period of high exploitation and appreciable demographic and phenotypic change. Other studies indicate that diversity at neutral microsatellite loci may be correlated with variability at selected genes, thus compromising a population's subsequent recovery and adaptive potential. Such effects are especially pertinent to North Sea cod, which are threatened by continuing exploitation and rising sea temperatures.

Allopatric processes of speciation have routinely been presented to explain the extraordinary radiation of the East African Great Lakes cichlid fish species flocks. The 21 or more species of pelagic cichlids within the Lake Malawi flock appear to have lake-wide distributions that challenge such a concept. Data from six microsatellite DNA loci indicate single, panmictic populations across the lake of three Diplotaxodon species. Levels of variability at these loci suggest that populations have been large and stable. Mitochondrial DNA sequence data (872 bp of control region + 981 bp of the NADH-2) from 90 species, representing all major clades within the Lake Malawi flock, indicate reciprocal monophyly of the pelagic clade. We suggest that these data support a hypothesis that speciation in sympatry is more plausible (and widespread) within the cichlid species flocks than previously thought.

Populations of the intertidal isopod Jaera albifrons from three sites in South Wales (U.K.), each containing animals from ten `rock populations9 separated by an average of 3 m, were examined by using starch gel electrophoresis to determine their degree of genetic divergence. Nine enzyme-coding loci were found to be polymorphic (P

The population genetic consequences of intraspecific introductions are not well understood. In the present study we verify the success of a 34-year-old transplantation of guppies, Poecilia reticulata , in Trinidad, and document the spread of the introduced fish. Gene frequencies in the introduced population are in accord with the stochastic effects of a founder event. Gene frequencies downstream of the transplant site suggest that the introduced fish have replaced the native guppy population throughout a substantial stretch of the river. There is strong evidence that the enzyme loci studied here are selectively neutral in the face of selection pressures known to have modified behaviour since the introduction.

An RNA derivative (pSPT 18.15) of Jeffreys' 33.15 human minisatellite core sequence was used to probe DNA from individuals of the peach-potato (Myzus persicae) and grain (Sitobion avenae) aphid. Sufficient and reproducible quantities of DNA (M. persicae = 0.90 $\pm $ 0.19 $\mu $g DNA individual$^{-1}$; S. avenae = 1.50 $\pm $ 0.30 $\mu $g DNA individual$^{-1}$) were extracted from individuals by whole-body homogenization to produce complex multi-locus DNA fingerprints. Profiles contained 19.5 $\pm $ 2.4 (M. persicae) and 14.8 $\pm $ 1.2 (S. avenae) fragments per individual, mainly within the 0.6-6.6 kb range, and exhibited marked endonuclease-specific variations in complexity. Individuals from six clones of S. avenae found to be monomorphic at 11 putative allozymic loci could be distinguished using their DNA fingerprint profiles. Fingerprints from a clone of M. persicae were stable over nine parthenogenetic generations showing the absence of major genetic rearrangements (`endomeiosis') during apomictic parthenogenesis. The demonstration that sequences homologous to human minisatellite regions are both present and polymorphic in an invertebrate, coupled with the ability to characterize clones from individuals yielding small quantities of DNA show that genetic fingerprinting should be especially valuable for monitoring the diversity and dynamics of clonal animals in the field.

Allopatric divergence in peripheral habitats may lead to rapid evolution of populations with novel phenotypes. In this study we provide the first evidence that isolation in peripheral habitats may have played a critical role in generation of Lake Malawi's cichlid fish diversity. We show that Lake Chilingali, a satellite lake 11.5 km from the shore of Lake Malawi, contains a breeding population of Rhamphochromis , a predatory genus previously thought to be restricted to Lake Malawi and permanently connected water bodies. The Lake Chilingali population is the smallest known Rhamphochromis , has a unique male nuptial colour pattern and has significant differentiation in mitochondrial DNA from Lake Malawi species. In laboratory mate choice trials with a candidate sister population from Lake Malawi, females showed a strong tendency to mate assortatively indicating that they are incipient biological species. These data support the hypothesis that isolation and reconnection of peripheral habitats due to lake level changes have contributed to the generation of cichlid diversity within African lakes. Such cycles of habitat isolation and reconnection may also have been important in evolutionary diversification of numerous other abundant and wide-ranging aquatic organisms, such as marine fishes and invertebrates.