Understanding origins of present-day genetic structure in marine fish: biologically or historically driven patterns?

Determining the origin of genetic structure is of wide interest because of its use in stock discrimination in marine organisms. Schematically, genetic differentiation can result from historical patterns maintained over geological time or from present-day isolation attributable to biological characteristics of the species. We used a comparative approach to population genetic analysis based on allozyme polymorphism to determine the impact of reproductive strategy (i.e. biological origin) and habitat (i.e. historical origin) on the genetic structure of individuals sampled from five isolated islands in French Polynesia. Eight species of coral reef fishes from two families (Chaetodontidae and Pomacentridae) were selected to test the impact of sea-level change (historical origin) and reproductive strategy (biological origin) on genetic structure. Seven of the eight study species showed significant divergence in allelic frequencies computed over all sites. For these seven species, multilocus F_stvalues ranged from 0.0114 to 0.0287. None of the eight species showed a significant relationship between genetic divergence and geographical distance between sites. Significant divergence (difference in allozyme frequencies) between some pairs of sites occurred but was unrelated to distances between them. These results suggest that the genetic structure of coral reef fish in French Polynesia is likely to be driven according to an island model in which migrations between populations are rare and random in space and time. Overall, none of the species showed congruent genetic structures between sites sampled. Genetic structure of the eight species did not appear significantly related either to reproductive strategy or habitat preference. Genetic diversity (heterozygosity) was significantly correlated with these two factors, with species laying benthic eggs and/or inhabiting lagoons showing significantly higher multilocus heterozygosity than species laying pelagic eggs and/or living on the outer reef slope. Overall, the absence of differences according to habitat and/or reproductive strategy did not provide any conclusive pattern regarding the origin of the genetic structure, but the limited divergence in allelic frequencies suggests recent differentiations.     

Relationships between inner ear and sagitta growth during ontogenesis of three Carapini species,and consequences of life-history events on the otolith microstructure

Three species of Carapidae have in common a tenuis larval stage, during which they settle in the lagoon and take refuge in the same species of holothuroid. From the juvenile stage, Carapus homei and C. boraborensis are commensal, whereas Encheliophis gracilis is parasitic. The aims of this study were to analyse to what extent the ontogenetic changes of the otic capsule affected the shape of the inner ear and how environmental cues, due to the above-mentioned life history and the style, could influence the structure of the sagitta. Sagittal sections revealed a three-dimensional asymmetry with a nucleus close to the proximal surface. Observations of the growth axis of the sagitta suggest it has a morphogenetic impact on the otic cavity. Each sagitta contains three main zones related to the life stages of the fish. Bands and checks were observed in the third zone in C. homei and C. boraborensis, but this pattern was less discernible in E. gracilis. These structural differences in zone 3 could be related to the commensal and parasitic life styles of these fishes. Further studies dealing with otosac features and otolith functions are suggested.     

Comparison of Zn, Cu, Pb, Ni, Cr, Sn, Mo Concentrations in Tissues of Fish (Roach and Perch) from Lake Baikal and Bratsk reservoir, Russia

Data on Zn, Cu, Pb, Ni, Cr, Sn, Mo concentrations in some food fish in Baikal Lake and Bratsk reservoir have been compared. The muscles, skin and gills of roach and perch (Rutilus rutilus and Perca fluviatis L.) were analysed. The conditions of atomic-emission analysis, detection limits, reproducibility, coefficients of transformation from the wet to dry mass and to an ash residue are reported. To verify accuracy, the results of reference samples OK-1 (Baikal perch) and OM-1 (Baikal roach) were used along with atomic-absorption and neutron-activation results of ashed and dried samples. The observed range of concentrations in tissues exceeds the probable analytical errors and reflects natural variability. The content of Zn, Cu, Pb, Ni and Cr in tissues of fish collected in the Bratsk reservoir from the conventionally uncontaminated and polluted sites correspond to the concentrations in tissues of similar fish from Lake Baikal. The latter are normal for fish of weakly mineralised oligotrophic reservoirs. The ranges of concentration in studied fish (roach and perch) consist of mg kg^–1 dry wt: in muscles-Zn(14–28), Cu(2.2–4.7), Pb(0.30–0.61); in skin-Zn(94–119), Cu(1.2–1.4), Pb(0.16–0.08); in gills-Zn(70–280), Cu(2.0–7.4), Pb(0.19–1.2).     

Genetic monogamy in the common loon (Gavia immer)

We conducted behavioral observations and genetic analysis on breeding pairs of common loons in the upper Great Lakes region from 1993 through 1995 to look for behavioral evidence of extrapair copulations (EPCs) and to determine parentage of young. Pairs remained close to each other (usually within 20 m) during the pre-laying period, leaving little opportunity for EPCs to occur. Males and females both maintained physical proximity by approaching each other when they became separated. Copulations were obvious but infrequent, occurring about once every other day during the pre-laying period. Multilocus DNA fingerprinting was consistent with behavioral findings: 58 young from 47 different families were all genetic offspring of parents that raised them. Perfect genetic monogamy (genetic parentage of young by parents that rear them) in loons might arise as a consequence of the need for vigorous territorial defense to prevent territorial takeover. Received: 8 August 1996 / Accepted after revision: 22 March 1997     

Determination of canthaxanthin in the red coral (<Emphasis Type="Italic">Corallium rubrum</Emphasis>) from Marseille by HPLC combined with UV and MS detection

Corallium rubrum is the most famous and precious coral due to the intense characteristic red colour of its skeleton. We have determined the presence of carotenoids in natural samples of C. rubrum from Marseille, Riou, and investigated their chemical composition. Analysis was performed both on soft tissues and hard tissues including spicules and skeleton. Since hard tissues are made of a mineral fraction and an organic fraction obtained after demineralization, extraction was performed both with and without demineralization by EDTA. The extracts were analyzed by complementary methods of TLC, HPLC/DAD and HPLC/MS. The components were separated by RP-18 chromatography column using acetonitrile/methanol for HPLC/DAD and acetonitrile/water gradient for HPLC/MS analysis. Our results give the first evidence of the presence of canthaxanthin, 4,4′-diketo-β-carotene, as the major carotenoid in all samples. Spicules exhibited higher content in carotenoids than skeleton. Demineralization treatment improved the efficiency of carotenoid extraction by an average factor of 5 and showed that organic matrix contains canthaxanthin.     

Broad-band versus narrow-band irradiance for estimating latitude by archival tags

The relative effectiveness of different bands of irradiance to estimate the latitude of archival tags was evaluated. These tags are placed on fishes in order to describe their movements during long distance migrations. Measurements were recorded of broad-band irradiance with and without a cosine collector and narrow-band irradiance of seven narrow bands with 50% attenuation 30 nm on either side of their central wavelength of 400 (violet), 450 (blue), 500 (blue–green), 550 (green), 600 (yellow), 650 (orange), and 700 nm (red). A holographic, cosine collector was used to reduce the vertical transmission of irradiance to the sensor and to increase horizontal transmission of irradiance so the sensor detected more of the diffuse irradiance penetrating the water at dawn and dusk. Daily measurements were made during seven periods of 1–2 days each, beginning 28 June (after 21 June solstice) and ending on 6 October 1999 (after September 23 equinox) of submarine irradiance at 15-s intervals at a fixed depth (10 m) and location (38.31°N; 123.08°W) in Horseshoe Cove, California. Irradiance transmission at this site is intermediate between the clearest offshore waters, where blue irradiance (450 nm) penetrates farther with depth than green irradiance (550 nm) and most oceanic and coastal waters, where green penetrates farther than blue irradiance. Two algorithms were used to estimate latitude, the maximum slope method and the maximum logarithmic difference method. The broad-band, cosine-corrected light, excluding those deployments near the equinox when error is highest, produced an estimate of latitude of 38.30° for both methods and a latitudinal error of ±34.4 km for the former and ±27.2 km for the latter. The mean latitudinal error for non-cosine-collected, broad-band irradiance was ±190.9 km, using the slope algorithm and ±184.8 km using the difference algorithm. The blue band of irradiance, which attenuates least with increasing depth in clear, oceanic water, also produced a comparatively high-latitudinal error of ±163.8 km error for the former algorithm and ±170.4 km for the latter algorithm. Tag designers should consider using cosine-collectors over the irradiance sensors on their archival tags to increase the accuracy of position estimates.     

Spatial and temporal genetic homogeneity in the Arctic surfclam (<Emphasis Type="Italic">Mactromeris polynyma</Emphasis>)

Commercially harvested marine bivalve populations show a broad range of population-genetic patterns that may be driven by planktonic larval dispersal (gene flow) or by historical (genetic drift) and ecological processes (selection). We characterized microsatellite genetic variation among populations and year classes of the commercially harvested Arctic surfclam, Mactromeris polynyma, in order to test the relative significance of gene flow and drift on three spatial scales: within commercially harvested populations in the northwest Atlantic; among Atlantic populations; and between the Atlantic and Pacific oceans. We found small nonsignificant genetic subdivision among eight populations from the northwest Atlantic (F _ST = 0.002). All of these Atlantic populations were highly significantly differentiated from a northeast Pacific population (F _ST = 0.087); all populations showed high inbreeding coefficients (F _IS = 0.432). We tested one likely source of heterozygote deficits by aging individual clams and exploring genetic variation among age classes within populations (a temporal Wahlund effect). Populations showed strikingly different patterns of age structure, but we found little differentiation among age classes. In one case, we were able to analyze genetic diversity between age classes older or younger than the advent of intensive commercial harvesting. The results generally suggest spatially broad and temporally persistent genetic homogeneity of these bivalves. We discuss the implications of the results for the biology and management of surfclam populations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Density,size structure and aspergillosis prevalence in <Emphasis Type="Italic">Gorgonia ventalina</Emphasis> at six localities in Puerto Rico

Gorgonia ventalina’s density, size structure and lesion prevalence was measured at six sites in Puerto Rico that exhibited variation in horizontal water transparency, sedimentation rates, suspended particle matter, scleractinian and macroalgal cover. G. ventalina density varied significantly among sites (between 0.84 and 0.007 colonies/m²), and was positively correlated with water transparency. Size structure did not vary much among sites, and reflects high mortality among the smaller size classes and high survivorship in large colonies. Prevalence of active fungi-induced lesions (type I) did not vary significantly among sites and was density-independent. However, prevalence of old lesions of unknown origin (type II) did vary among reefs and was negatively correlated with water transparency. Prevalence of types I or II lesions was independent of colony size. Our results suggest that (1) turbidity and sedimentation are important abiotic factors controlling the abundance of sea fans, (2) variation in settlement success and early survivorship of recruits has more impact on the sea fan populations than variation in the survivorship of large colonies and (3) prevalence of aspergillosis (type I) at the studied sites is similar to that reported for other Caribbean reefs and supports the epizootic nature of the disease and (4) lesions with exposed skeleton are more likely to be colonized by fouling organisms at impacted reefs. The combined effects of anthropogenic impacts and aspergillosis may cause local extinctions of sea fans, as is becoming evident in many reefs in Puerto Rico.