Impact of rifting and hydrography on the genetic structure of Clarias gariepinus in eastern Africa

In a study of the genetic structure of Clarias gariepinus at the ND5 and ND6 loci of mitochondrial DNA using RFLP–PCR in 16 populations (267 fish), a total of 18 haplotypes was detected. The most common haplotype was EA1 and represented 46% of all genotypes. Three phylogenetic groups characterized the region, with the East African clade occurring between the western rift in the west, Lake Baringo in the north, the Indian Ocean in the east and the Rufiji River in the south. The Lower Tana River (unlike the Upper Tana River) and Lake Kamnarok grouped with the North clade, while the Ruaha River (tributary of the Rufiji River) represented a contact zone between the East and the South-central African clade. Genetic structure was distinct ( F _ST=0·66), with the Lower Tana River and Lake Mtera forming specific units. Within the East clade, the Oloibortoto River, Upper Tana River and Lake Victoria each formed a distinct population. Lake Baringo grouped either with the eastern rift or the western rift depending on the analysis. Lake Jipe, the Pangani River, Rusizi River, Lake Edward, Nyabugogo River and the Luiche River clustered together. Among group variance explained 66·8% of the total variance; the impact of vicariance (rifting and uplifting) on the phylogeography was considerable. A distribution model of the catfish is proposed which combines the separation by rifting several million years ago with a high gene flow in the western rift due to historical connectivity among lakes and rivers.     

Rare and asymmetrical hybridization of the endemic Barbus carpathicus with its widespread congener Barbus barbus

In endemic species that co-occur with widespread congeners, hybridization can lead to an influx of novel and beneficial genetic variation, but high rates of introgression may cause genetic swamping of the endemic species and have detrimental effects on its survival potential. This study examines hybridization between sympatric populations of the Carpathian barbel Barbus carpathicus , a recently discovered cryptic species with a restricted range, and the widespread common barbel Barbus barbus . Based on six diagnostic allozyme loci, a microsatellite locus and mtDNA, hybrids were found to be present at multiple localities within the Vistula River drainage (Baltic Sea) as well as in the Tisza River system of the Danube River drainage (Black Sea). However, the numbers of hybrids were very low; four individuals of 230 fish sampled from the Vistula drainage. Bayesian assessment of their nuclear genotypes suggested that two hybrids in the Vistula drainage and nine in the Tisza system were F₁ generation, and one in the Vistula drainage and one in the Tisza system were backcrosses (BC) to B. barbus , while no F₂ or BC to B. carpathicus were detected. No hybrid carried B. carpathicus mtDNA and cytonuclear linkage disequilibria showed significant positive associations between hybrid genotypes and B. barbus mtDNA, suggesting unidirectionality in the interspecific mating with a disproportionate contribution of B. barbus mothers. Despite geographically broad occurrence of hybrids, these data provide evidence of strong constraints on hybridization in the native breeding habitats and the lack of introgression towards B. carpathicus .     

赣江下游及其支流浮游甲壳动物的群落结构

2009年6月、11月和2010年4月对赣江下游浮游甲壳动物的群落结构和时空变化进行研究.共记录浮游甲壳动物21种,其中枝角类14种、桡足类7种.脆弱象鼻溞Bosmina fatalis、微型裸腹溞Moina micrura和中剑水蚤Mesocyclops sp.为优势种.赣江下游干流浮游甲壳动物的最大平均密度和生物量(11.1ind.·L^-1和0.127mg·L^-1)均出现在6月,最小值(1.59ind.·L^-1和0.01mg·L^-1)均出现在4月.袁河支流的枝角类和桡足类密度在6月(4.97±13.28ind.·L^-1和2.07±4.85ind.·L^-1)和11月(2.07±5.21ind.·L^-1和2.24±5.22ind.·L^-1)高于赣江下游干流和锦江支流.香农-威纳指数(H')和马加利夫指数(d)表明赣江下游及其支流水质为中度污染或重污染.水温和小型浮游植物生物量是影响赣江下游浮游甲壳动物密度时空变化的重要因素.     

Iteroparity in complex mating systems of steelhead Oncorhynchus mykiss (Walbaum)

This study investigated diverse reproductive types in complex mating systems of steelhead Oncorhynchus mykiss . Postspawned steelhead (kelts) were sampled during attempted downstream migration over Lower Granite Dam on the Snake River, U.S.A. Multilocus microsatellite genotypes (14 loci) were used to assign unknown origin, kelt individuals to upstream populations of origin. Results indicated that iteroparity is a life-history trait that remains in several tributaries of the Snake River basin despite strong selection against downstream adult passage because of hydroelectric dams. The largest populations of steelhead in the Snake River, however, were only weakly represented (Clearwater River = 7·5% and Salmon River = 9·4%, respectively) in the kelt steelhead mixture relative to the Grande Ronde River (18·2%), Imnaha River (17·4%), Pahsimeroi Hatchery (25·2%) and Asotin Creek (22·2%). A lack of correlation between population escapement size and kelt proportions ( P > 0·05) suggests that iteroparity was not uniformly expressed across populations, but was significantly negatively correlated with body size ( P < 0·05). Iteroparity may be a valuable source of genetic variability and a conservation priority, especially in years with poor recruitment or in recently bottlenecked populations.     

Genic diversity in Red River pupfish Cyprinodon rubrofluviatilis (Atheriniformes: Cyprinodontidae) and its implications for the conservation genetics of the species

Starch gel electrophoresis of proteins was used to study geographic variation at 26 gene loci in the Red River pupfish ( Cyprinodon rubrofluviatílís ), a species restricted to west Texas and Oklahoma. Marked differences were detected between populations in the Red and Brazos river drainages, with fixed or nearly fixed differences occurring at five gene loci. In addition, mean heterozygosity was uniformly high for the Red River form ( = 0·076–0·101) while samples of the Brazos River form were genetically depauperate ( =0·00–0·017). Introduced populations in the South Canadian and Colorado river drainages appear to have been derived from the Red River drainage. The presence of alleles diagnostic of the Red and Brazos river forms supports the suggestion from previous work that they may represent cryptic species. Regardless of taxonomy, however, the presence of two genetically distinct forms must be taken into consideration by those concerned with maintenance of biotic diversity.     

Variation in behavioural response to oxygen stress by egg-tending males of parapatric fluvial and lacustrine populations of a landlocked goby

The behavioural response of egg-tending males from parapatric fluvial and lacustrine populations of a landlocked goby Rhinogobius sp. (the orange form) to oxygen stress was compared in laboratory experiments. The natural spawning locations of these populations (rapids of tributary rivers and lakeshore of Lake Biwa, respectively) differ in dissolved oxygen concentration and its variability. Males of both populations spent a longer period of time in fanning behaviour under low dissolved oxygen conditions (4·5–5·0 mg l⁻¹), where >90% of eggs without paternal care died before reaching eyed stage, relative to fully saturated dissolved oxygen conditions (8·0–8·5 mg l⁻¹). Lacustrine males, who occasionally encounter oxygen stress (<2 mg l⁻¹) in their natural habitat, fanned eggs for a longer time period than fluvial males. The time difference in fanning behaviour between the two oxygen conditions was greater for lacustrine than fluvial males. Survival rate in the lower oxygen condition was higher for eggs tended by lacustrine males than those tended by fluvial males, probably due to this difference in fanning activity. These results showed that the response to oxygen stress differs between the two populations and, moreover, as both populations behaved adaptively in responding to the reduction in dissolved oxygen, contiguous habitats may have distinct natural selective pressures. It is suggested that regulation of egg fanning activity is strongly favoured by natural selection in unpredictable environments.     

Historic speciation and recent colonization of Eurasian monkey gobies (Neogobius fluviatilis and N. pallasi) revealed by DNA sequences,microsatellites, and morphology

Aim Hidden diversity within an invasive ‘species’ can mask both invasion pathways and confound management goals. We assessed taxonomic status and population structure of the monkey goby Neogobius fluviatilis across Eurasia, comparing genetic variation across its native and invasive ranges. Location Native populations were analysed within the Black and Caspian Sea basins, including major river drainages (Dnieper, Dniester, Danube, Don and Volga rivers), along with introduced locations within the upper Danube and Vistula river systems. Methods DNA sequences and 10 nuclear microsatellite loci were analysed to test genetic diversity and divergence patterns of native and introduced populations; phylogenetic analysis of mtDNA cytochrome b and nuclear RAG‐1 sequences assessed taxonomic status of Black and Caspian Sea lineages. Multivariate analysis of morphology was used to corroborate phylogenetic patterns. Population genetic structure within each basin was evaluated with mtDNA and microsatellite data using F_ST analogues and Bayesian assignment tests. Results Phylogenetic analysis of mitochondrial and nuclear sequences discerned a pronounced genetic break between monkey gobies in the Black and Caspian Seas, indicating a long‐term species‐level separation dating to c. 3 million years. This pronounced separation further was confirmed from morphological and population genetic divergence. Bayesian inference showed congruent patterns of population structure within the Black Sea basin. Introduced populations in the Danube and Vistula River basins traced to north‐west Black Sea origins, a genetic expansion pattern matching that of other introduced Ponto‐Caspian gobiids. Main conclusions Both genetic and morphological data strongly supported two species of monkey gobies that were formerly identified as subspecies: N. fluviatilis in the Black Sea basin, Don and Volga Rivers, and the Kumo‐Manych Depression, and Neogobius pallasi in the Caspian Sea and Volga River delta. Genetic origins of introduced N. fluviatilis populations indicated a common invasion pathway shared with other introduced Ponto‐Caspian fishes and invertebrates.     

Structure of the gut of the racer goby Neogobius gymnotrachelus (Kessler, 1857)

The morphological and histological features of the gut of juvenile racer goby Neogobius gymnotrachelus [range of body mass 0·2–0·9 g and standard length ( L _S) 20·0–38·8 mm] were examined in fish collected from the Włocławek Reservoir on the Vistula River, Poland. Evidence is provided of the stomachless nature of the gut of the racer goby. The intestine of the juveniles lacks the intestinal bulb. A particular feature of the racer goby gut is the secretory oesogaster (the transitional region where the secretory oesophagus merges into the intestine) with multicellular alveolar glands that secrete via a common duct to the surface between the mucosal folds. The cells in the secretory oesogaster alveolar glands are periodic-acid-Schiff (PAS) positive indicating the presence of neutral mucopolysaccharides. It is hypothesized that the secretory oesogaster is evidence of the loss of the functional stomach in this species. There are two sphincters: the oesogaster–intestinal and the intestinal–rectal in the racer goby gut. It can be concluded that the oesogaster–intestinal sphincter is functionally related to the gastro-intestinal sphincter described in many fish species having a stomach. Enterocytes with a distinct brush border and only a few goblet cells are observed in the epithelium along the whole intestine. The existence of vacuoles in the supranuclear region of the rectal enterocytes is also confirmed.     

The Chinese sleeper (Perccottus glenii Dybowski, 1877) in Ukraine: New data on distribution

The Chinese sleeper Perccottus glenii Dybowski, 1877 is one of the most successful alien species in Europe today. This article is a review of the current distribution of the species in Ukraine using published data, own field studies (2005–2016) and collections from museums and colleagues. The Chinese sleeper has been confirmed in the Vistula, Danube, Dniester, Southern Bug and Dnipro river basins, with earlier occurrence (1970s–90s) in the Vistula, Danube and Dniester river basins. As a result, the species is distributed more evenly in these river basins. The Chinese sleeper was first recorded in the Dnipro and Southern Bug river basins in the 21st century; hence, its occurrence is still irregular. Present data suggest that, in some regions, the species could inhabit not only floodplains and bays but also fluvial river sections.     

Relationships among tributary length,census population size,and genetic variability of white-spotted charr, <Emphasis Type="Italic">Salvelinus leucomaenis</Emphasis>, in the Lake Biwa water system

The relationships between census population size and tributary length and between haplotype diversity of the mitochondrial DNA and census population size in ten white-spotted charr populations in the Lake Biwa water system and its adjacent basins were investigated. The census population size (number of fish with ≥100 mm in standard length) significantly increased with the tributary length. In the eastern part of the Lake Biwa water system, haplotype diversity increased with the census population size. On other hand, in the western part of the water system and adjacent basins, haplotype diversity was zero irrespective of the census population size. These results suggest that white-spotted charr populations in the eastern and western part of the Lake Biwa water system have undergone different levels of bottlenecks related to the habitat size in the postglacial warming.     

Change of strategy or always overlooked? Third recent record of the beardless tadpole goby Benthophiloides brauneri from an inland location far from the coast

The present study documents three specimens of Benthophiloides brauneri from the River Dniester. It is one of the rarest freshwater fishes in Europe, living along the western coast of the Black and Asov Seas, but these new records are 200 river km from the coast. We discuss whether the species has recently started to establish inland populations or inland specimens have previously been overlooked.     

Isolation by distance and selection effects on genetic structure of sardines Sardina pilchardus Walbaum

Allozyme data were used to analyse the genetic structure of Sardina pilchardus populations. Fifty samples from 15 locations between the North Sea and Mauritania, including samples from the Azores, Madeira and the Mediterranean Sea, were surveyed. A weak but significant structure was found between all samples ( F _ST= 0.057, P < 0·001). This structure results from a change in the most common allele of SOD* between the North African and the Azores populations separated by the greatest distance. This locus seemed to be under selective pressure according to the test of neutrality, and the variations in allele frequencies may be explained due to isolation by distance (IBD) of coastal populations (from Mauritania to the North Sea) ( r = 0·86, P < 0·001). When SOD* was removed from the analyses, IBD was not observed in coastal populations ( r = 0·236, P > 0·05) but was observed over the whole range ( r = 0·321, P = 0·05). The genetic structure of S. pilchardus is driven by both IBD and selective processes.     

Back from the Brink: The Holocene History of the Carpathian Barbel Barbus carpathicus

As a result of specific adaptations and habitat preferences strongly rheophilic fish species may show high levels of endemism. Many temperate rheophilic fish species were subjected to a series of range contractions during the Pleistocene, and then successfully expanded during the Holocene, colonising previously abandoned areas. The Carpathian barbel (Barbus carpathicus Kotlík, Tsigenopoulos, Ráb et Berrebi 2002) occurs in the montane streams in three basins of the main Central European rivers in the northern part of the Carpathian range. We used genetic variation within 3 mitochondrial and 9 microsatellite loci to determine a pattern of postglacial expansion in B. carpathicus. We found that overall genetic variation within the species is relatively low. Estimate of time to the most recent common ancestor (tMRCA) of mitochondrial sequences falls within the Holocene. The highest levels of genetic variation found in upper reaches of the Tisa river in the Danube basin suggest that glacial refugia were located in the south-eastern part of the species range. Our data suggest that the species crossed different watersheds at least six times as three genetically distinct groups (probably established in different expansion episodes) were found in northern part of the species range. Clines of genetic variation were observed in both the Danube and Vistula basins, which probably resulted from subsequent bottlenecks while colonizing successive habitats (south eastern populations) or due to the admixture of genetically diverse individuals to a previously uniform population (Vistula basin). Therefore, B. carpathicus underwent both demographic breakdowns and expansions during the Holocene, showing its distribution and demography are sensitive to environmental change. Our findings are important in the light of the current human-induced habitats alterations.     

The trout (Salmo trutta) population of the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales

Data are presented from a 10-year (1984 to 1993) study of a Salmo trutta population in the Afon Cwm, a small tributary of the Afon Dyfi, mid-Wales. The stream is a spawning and nursery area for sea trout. Growth of trout within the stream can be summarized by a von Bertalanffy growth coefficient ( K ) of 0·310, with asymptotic length (1∞) 21·6 cm and with length at age 1 of 7·6 cm. Mean population density in the whole stream varied from year to year between 0·05 and 0·60 0-group trout m⁻² and between 0·05 and 0·70 older trout m⁻². Mean biomass varied, between years, from 0·1 to 3·5 g m⁻² for 0-group and from 1·3 to 10·4g m⁻² for older trout. Loss between 3 and 5 months of age appeared to be proportionate at about 50 to 60% and instantaneous loss rate from 5 to 53 months of age varied from 0·04 to 0·10 month⁻¹ and was positively correlated with cohort number at 3 months of age. Production between 3 and 53 months of age varied between cohorts from 3 to 8 g m ⁻² live weight.     

European geography of Alnus incana leaf variation

The intra- and inter-population and geographic differentiation of Alnus incana were examined biometrically on the basis of morphological character of the leaves. The study results only partly confirmed the assumption that Carpathian and Alpine populations of the species differ significantly. This may indicate that gene exchange continued during glacial periods as these regions were not sufficiently isolated from each other. The geographic variation of grey alder along the Balkans–Scandinavia axis is more eminent. It is debatable whether A. incana has migrated northwards from montane refugia, along Central European rivers, mostly the Vistula and Oder. It can be, however, noted that the Masurian, Sudetan and East Carpathian populations are similar to one another.     

Population genetic structure and effective population size of ayu (Plecoglossus altivelis), an amphidromous fish

The temporal and spatial population genetic structure of ayu Plecoglossus altivelis (Salmoniformes: Plecoglossidae), an amphidromous fish, was examined using analysis of variation at six microsatellite DNA loci. Intracohort genetic diversities, as measured by the number of alleles and heterozygosity, were similar among six cohorts (2001–2006) within a population (Nezugaseki River), with the mean number of alleles per cohort ranging from 11·0 to 12·5 and the expected heterozygosity ranging from 0·74 to 0·77. Intrapopulational genetic diversities were also similar across the three studied populations along the 50 km coast, with the mean number of alleles and the expected heterozygosity ranging from 11·33 to 11·67 and from 0·75 to 0·76, respectively. The authors observed only one significant difference in pair-wise population differentiation ( F _ST-value) between the cohorts within a population and among three populations. Estimates of the effective population size ( N _e) based on maximum-likelihood method yielded small values (ranging from 94·8 to 135·5), whereas census population size ranged from c. 4800 to 24 000. As a result, the ratio of annual effective population sizes to census population size ( N _e/ N ) ranged from 0·004 to 0·023. These estimates of N _e/ N agree more closely with estimates for marine fishes than that of the larger estimates for freshwater fishes. The present study suggests that ayu which is highly fecund and shows low survival during the early life stages is also characterized by having low value of N _e/ N , similar to marine species with a pelagic life cycle.     

Using 18O/16O data to examine the mixing of water masses in floodplain wetlands

Oxygen isotopic data were used to assess how far waters from the Savannah River, a major river in the Southeastern United States, backed up and inundated the wetlands along a small Coastal Plain tributary during a flood. This approach worked because the water of this tributary, Unper Three Runs, had an oxygen isotopic composition (¹⁸O = –4.9 ) distinct from Savannah River water (¹⁸O = –3.2 ).Two sample surveys were taken from the mouth of Upper Three Runs to 2 km upstream. Waters were isotopically uniform along the length of the sample transect when both river and tributary water levels were below bankfull. Visual estimates of turbidity taken when both the river and tributary overflowed their channels and inundated adjacent wetlands indicated that Savannah River water extended about 300 meters up the tributary channel. In contrast, the isotopic data indicated that a mixing zone of river and tributary waters extended about 1100 meters upstream. Although this mixing zone was documented only in the channel of Upper Three Runs, it probably extended into adjacent parts of the riparian wetland, potentially affecting ecological processes due to the differing water quality. This study was conducted in a single river-tributary system and the approach is probably applicable in other large rivers.Corresponding Editor: R. SharitzTo Whom Correspondence should be sent     

Population structure of lake‐type and river‐type sockeye salmon in transboundary rivers of northern British Columbia

The population structure of 'lake‐type' and 'river‐type' sockeye salmon Oncorhynchus nerka , primarily in transboundary rivers in northern British Columbia, was examined with a survey of microsatellite variation. Variation at 14 microsatellite loci was surveyed from c . 3000 lake‐type and 3200 river‐type sockeye salmon from 47 populations in six river drainages in British Columbia. The mean F _ST for the 14 microsatellite loci and 47 populations was 0·068, and 0·034 over all river‐type populations. River‐type sockeye salmon were more genetically diverse than lake‐type sockeye salmon, with expected heterozygosity of river‐type sockeye salmon 0·72 and with an average 12·7 alleles observed per locus, whereas expected heterozygosity of lake‐type sockeye salmon was 0·65 with and average 10·5 alleles observed per locus. River drainage of origin was a significant unit of population structure. There was clear evidence of genetic differentiation among river‐type populations of sockeye salmon from different drainages over a broad geographic range in British Columbia.     

Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.     

Differences in temperature conditions and somatic growth rate of larval and early juvenile spring-spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith to fish size relationship

Larval and juvenile herring Clupea harengus collected in the Polish part of the Vistula Lagoon in May-July 1997 had hatched between 17 April and 9 June and originated from three cohorts. The spawning season began on 1 March at 3·8° C and was completed on 3 June at 12·7° C. Mortality among larvae was high in the first 2 weeks of April, probably associated with significant temperature decrease at the beginning of the spawning season. The growth of 10–48 mm L _S herring was linear, highest for larvae and juveniles from the first cohort (0·58 mm mm^-1 day^-1), slower for the second cohort (0·55 mm mm^-1 day^-1) and the slowest for the third cohort (0·45 mm mm day^-1). Temperature effects on the growth were inconclusive and potentially unfavourable feeding conditions in June might have been responsible for the relatively slow growth of third cohort larvae and juveniles.
Relationships between otolith size (perimeter, length, width, area, and weight) and fish size ( L _S) differed among the three cohorts, related mostly to the positive temperature effect on otolith growth, individuals growing in warmer water had larger otoliths. Although a negative growth rate effect was observed as well, it was less significant.