Post-glacial population history and genetic structure of the northern clingfish (Gobbiesox maeandricus), revealed from mtDNA analysis

Mitochondrial d-loop sequences were analyzed to characterize the phylogeographic and population genetic structure of the northern clingfish (Gobbiesox maeandricus Girard). Sequence analysis of 378 bp from 111 individuals sampled in 14 localities along the northeast Pacific coast and within the Strait of Georgia from 1996 to 1999 revealed marked genetic differentiation (Φ_ct=0.247) among regional population groupings. The gene genealogy distinguished two major clades of haplotypes separated by at least 1.1% sequence divergence. One clade with very low haplotype diversity (h=0.2095, n=18) occurred only within the recently unglaciated Strait of Georgia. The other clade had high haplotype diversity (h=0.8808, n=93) and was found in all populations. High haplotype diversity was found in open coastal populations, both north and south of the maximum extant of the Wisconsin ice sheet, suggesting that the clingfish range was not pushed to a southern refugium during the last glacial maximum. A nested clade analysis also did not detect a large northward expansion from a single southern refugium. The level of sequence divergence and coalescent-based analyses suggest that the observed patterns of polymorphism are the result of Pleistocene diversification within multiple refugia, followed by population expansion and asymmetrical lineage introgression. Received: 5 February 2000 / Accepted: 31 August 2000     

Genetic structure of round scad mackerel <Emphasis Type="Italic">Decapterus macrosoma</Emphasis> (Carangidae) in the Indo-Malay archipelago

Round scad mackerel sampled in 1995-1998 were analysed for genetic variation using mitochondrial-DNA and nuclear-DNA markers. Sequence variation for a fragment of the cytochrome b gene (mitochondrial), amplified by polymerase chain reaction, was screened across individuals using single strand conformation polymorphism (SSCP). Sequence analysis of all SSCP haplotypes indicated two mitochondrial clades separated by, on average, 2.3% nucleotide divergence. The geographic distribution of haplotypes was homogeneous (Weir and Cockerham's [^(q)] \hat \theta =-0.002). Also, no geographic heterogeneity was detected for length polymorphism of Intron 1 of the gene encoding aldolase B ([^(q)] \hat \theta =0.005). Although homogeneity in allele frequencies throughout the Indo-Malay archipelago conformed to the expectations for a widely distributed pelagic fish in a highly connected habitat, this was at variance with the sharp geographic structure previously uncovered in Indian scad mackerel, Decapterus russelli, a fish with life-history characteristics similar to D. macrosoma. A remarkable similarity, however, was the occurrence of two similarly distinct clades within each species, suggesting a common history of geographic isolation. Low sea levels in the Pleistocene might have caused the separation and vicariance of populations within both D. macrosoma and D. russelli. Subsequent genetic exchange between populations would then have erased allele-frequency differences at the cytochrome b and aldolase B loci in D. macrosoma while some barrier to gene flow was maintained in D. russelli.     

Effects of DDT sediment-contamination on macrofaunal community structure and composition in San Francisco Bay

The objectives of this study were to determine the effects of sediment contamination on the benthic macrofauna and to predict macrofaunal changes following remediation at a Superfund (uncontrolled hazardous waste) site in San Francisco Bay, California, USA. DDT and its metabolites (ΣDDT) were the contaminants of concern. With few small-scale exceptions, all (>100) other sediment contaminants ever measured at the site were present at background or non-toxic levels. In hierarchical regressions [Y=f(X ₁, X ₂, X ₃), where X ₁=sediment %silt + clay, X ₂=sediment total organic carbon (OC), and X ₃=log ₁₀ (ΣDDT μg g⁻¹ OC)] with data from samples collected at the study site, log₁₀(ΣDDT μg g⁻¹ OC) explained a highly significant amount of the variance in the infaunal index (II ) and log₁₀(number of Amphipoda excluding Grandidierella japonica + 1) after statistically controlling for the potential effects of sediment %silt + clay and OC. The ratios of change of II and log₁₀(number of Amphipoda excluding G. japonica + 1) with respect to log₁₀(ΣDDT μg g⁻¹ OC) were about −9:1 and −0.4:1, respectively. Most of the 92 species collected were present at low to moderate densities over the entire range of ΣDDT sediment concentrations. The bivalve Theora lubrica, tubificids, most polychaetes, a tanaid (Zeuxo normani), and an amphipod (G. japonica), were common, while four other amphipods (Ampelisca abdita, Corophium heteroceratum, Photis brevipes, Dulichia rhabdoplastis), a phoronid (Phoronis cf. pallida), a bivalve (Cryptomya californica), and a cumacean (Eudorella pacifica), were rare or absent from sites with high ΣDDT sediment-concentrations. Received: 1 August 1997 / Accepted: 13 August 1997     

Genetic evidence of the presence of two species of Crassostrea (Bivalvia: Ostreidae) on the coast of Brazil

 Although oysters are commercially very important in Brazil, there is still much dispute about the number of Crassostrea species occurring on the Brazilian coast. The dispute is centered around C. brasiliana, considered by some authors to be a junior synonym of C. rhizophorae. In this paper we compared, by allozyme electrophoresis, sympatric and allopatric populations of the two putative species. Of the 17 loci analysed, five were diagnostic for the two species in sympatry (gene identity = 0.46 to 0.47), clearly demonstrating that they are distinct biological species. Heterozygosity (h) levels were high for both species (h = 0.24 to 0.28), and no heterozygote deficiencies were observed in any population (local inbreeding, F _IS  = 0.141; P > 0.70). Levels of population structure in C. rhizophorae along 1300 km of coast were very low (population inbreeding, F _ST  = 0.026; P > 0.15), indicating that the planktonic, planktotrophic larvae of these species are capable of long-range dispersal. Received: 14 January 1999 / Accepted: 8 December 1999     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Phylogeographic structure of false clownfish, Amphiprion ocellaris, explained by sea level changes on the Sunda shelf

The phylogenetic structure of the anemonefish Amphiprion ocellaris was established based on sequence data generated for the 5′ end of the cytochrome b (cytb) gene at 11 sites throughout Southeast Asia. Considerable genetic structuring was observed throughout the range of A. ocellaris. The region has a complex geography, with the Sunda shelf having been exposed during the lower sea levels associated with periods of glaciation. The direction of subsequent flooding of the Sunda shelf, as a direct consequence of the retreating glacial sheets, can be predicted based on the major river drainage systems in the region. Much of the phylogeographic structure, including levels of intra-site genetic variation, can be explained in terms of the “seeding” of sites on the Sunda shelf, by those on the shelf rim, as sea levels rose. We often found surface ocean currents in the region, which should influence larval dispersal, to be poorly correlated with phylogeographic structure. Several geographically close sites, which appear to be connected by surface currents, showed significant genetic stratification. We hypothesise that the phylogeographic structure of A. ocellaris is more reminiscent of the Pleistocene sea level changes than surface currents. The high contribution of sea level changes to the phylogeographic structure was also supported by several missing haplotypes in the generated spanning network. Cytb DNA sequences generated for recently recruited A. ocellaris individuals sampled from Singapore indicate that, on a local scale, there is a directional inflow of recruits, which is dependent on the monsoon seasons. The nature of dispersal and genetic structure of reef fish species found on the Sunda shelf is clearly complex, and should take into consideration past phylogeographic events. Received: 13 November 1999 / Accepted: 12 July 2000     

Effects of municipal piers on the growth of juvenile fishes in the Hudson River estuary: a study across a pier edge

The growth rates of two fish species, the winter flounder Pseudopleuronectes americanus (Walbaum) (19.3 to 42.6 mm total length, TL) and the tautog Tautogaonitis (Linnaeus) (23.9 to 55.9 mm TL), were used to evaluate habitat quality under and around municipal piers in the Hudson River estuary, USA. Growth rates were measured in a series of 10 d field caging-experiments conducted at two large piers in the summers of 1996 and 1997. Cages (0.64 m²) were deployed along␣transects that stretched from underneath the piers to beyond them, encompassing the pier edge (the transitional zone between the pier interior and the outside). Growth in weight (G _w ) was determined at five locations along the transect, 40 m beneath the pier, 20 m beneath the pier, at the pier edge, 20 m beyond the pier edge, and 40 m beyond. Under piers, mean growth rates of winter flounder and tautogs were negative (xˉG _W = −0.02 d⁻¹), and rates were comparable to laboratory-starved control fishes (xˉG _W = −0.02 d⁻¹). In contrast, mean growth rates at pier edges and in open waters beyond piers were generally positive (xˉG _W ranged from −0.001 to +0.05 d⁻¹), with growth at pier edges often being more variable and less rapid than at open-water sites. Analyses of stomach contents upon retrieval of caged fishes revealed that dry weights of food were generally higher among fishes caged at open-water stations (xˉ range = 0.02 to 0.72 mg dry wt) than at pier-edge (xˉ range = 0.01 to 0.54 mg) or under-pier (xˉ range = 0.03 to 0.11 mg) stations, although it was apparent that benthic prey were available at all stations on the transect. Our results indicate poor feeding conditions among fishes caged under piers, and suboptimal foraging among fishes caged at pier edges. Inadequate growth rates can lead to higher rates of mortality, and, based on these and other earlier experiments, we conclude that under-pier environments are poor-quality habitats for some species of juvenile fishes. Received: 12 March 1998 / Accepted: 9 November 1998     

Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef

The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations. S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of multi-locus genotypes indicated a high number of unique genotypes (N _go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations indicated that gene flow is restricted between some reefs (F _ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F _ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation. Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further from the coast. Received: 10 July 2000 / Accepted: 5 October 2000     

Genetic differentiation in Hediste diversicolor (Polychaeta: Nereididae) for the North Sea and the Baltic Sea

Genetic differentiation between North Sea and Baltic Sea Hediste diversicolor (O.F. Müller, 1776) (Polychaeta: Nereididae) populations was studied by allozyme electrophoresis on starch gel. Thirteen loci were analyzed in eight populations. The level of genetic variation was very low (mean H _o = 0.000 to 0.015). Differentiation between H. diversicolor populations is quite high (F _ST = 0.892) and reflected by three enzyme loci (MDH-I*, MDH-II*, IDH-I*). The reduced gene flow (N _m<1) may be explained by the limited dispersal capacity of the species. Regardless of whether found in the North Sea or Baltic Sea, there appear to be two different genetic types which are parapatric or sympatric in some places. The two types hybridize at three localities, but no signs of hybridization have been found at one (Tallinn). Received: 26 June 1997 / Accepted: 10 September 1997     

Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa

Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O₂ and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O₂ concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness decreased the O₂ concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O₂ h⁻¹ foraminifer⁻¹. The net photosynthesis averaged 5.3 ± 2.7 nmol O₂ h⁻¹. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O₂h⁻¹, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O₂ h⁻¹). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross photosynthesis versus scalar irradiance curves (P vs E _o curves) showed light saturation irradiances (E _k) of 75 and 137 μmol photons m⁻² s⁻¹ in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m⁻² s⁻¹. The light compensation point of the symbiotic association was 50 μmol photons m⁻² s⁻¹. Radial profile measurements of scalar irradiance (E _o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E _d). Received: 26 January 1998 / Accepted: 11 April 1998     

Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands

An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H _e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F _is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F _st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time. Received: 24 July 1997 / Accepted: 31 October 1997     

Occurrence of the Kumamoto oyster Crassostrea sikamea in the Ariake Sea, Japan

The Kumamoto oyster Crassostrea sikamea is distinguished from the closely related Pacific oyster C. gigas by concordant differences in 16S rDNA, allozymes, and a one-way gametic incompatibility. After repeated failures to find this oyster in its native habitat, we speculated in 1994 that “the Kumamoto oyster may be extinct in Japan”. In September 1996, we sampled small, deep-cupped oysters from the Ariake Sea and typed these for 16S rDNA and ITS-1 DNA markers previously shown to be diagnostic for the three most common oysters in the Ariake Sea, C. gigas, C. sikamea and  C. ariakensis. Our earlier suggestion of the demise of  C. sikamea proved incorrect. Of the 256 oysters sampled, 181 (71%) were  C. gigas, 53 (21%) were C. sikamea, and 22 (9%) were  C. ariakensis; no interspecific hybrids were observed. The distributions of C. sikamea and  C. ariakensis are clumped in the Ariake Sea:  C. sikamea occurs on the eastern and northern shores,  C. ariakensis occurs only in the northern part. These results emphasize the value of molecular markers for discriminating these morphologically plastic species both in the field and in aquaculture. Received 6 July 1998 / Accepted 8 October 1998     

Effects of organochlorines on the ultrastructure of the liver of the damselfish Parma microlepis from reefs in New South Wales, Australia

  Parma microlepis (Günther) were collected from Malabar, an urban location close to the centre of Sydney, Australia, and from Jervis Bay, a reference location 170 km south of the city centre. At each location, fish were collected from two sites separated by 100 to 200 m. The ultrastructure of normal liver tissue is described based on 20 female fish collected from Jervis Bay, where fish are known to be exposed to low levels of organochlorine contaminants. Alterations in the endoplasmic reticulum, mitochondria, lysosomes and nuclei of hepatocytes were identified and quantified in the liver tissue of fish from this location and compared to alterations in 20 female fish collected from Malabar, where fish are exposed to higher concentrations of organochlorine pesticides such as DDT compounds. There were significant differences in the percentage of hepatocytes with swollen mitochondria (F = 124.025, df = 2, 2, P = 0.008) and atypical nuclei (F = 22.198, df = 2, 2, P = 0.043) between sites (100 to 200 m apart), but there were no clear differences between the percentage of structural alterations in the hepatocytes of P. microlepis from Jervis Bay and Malabar. Associations between liver morphology and the organochlorines aldrin, dieldrin, DDE and chlordane were examined using a Pearson correlation matrix. Significant correlations were detected between the percentage of hepatocytes with dilated endoplasmic reticulum and the concentrations of the pesticide aldrin (r = 0.600, df = 11, r _{crit(α = 0.05)} = 0.553). Significant associations were also detected between the percentage of hepatocytes with disorganised endoplasmic reticulum and the concentrations of dieldrin and DDE residues in fish (r = 0.576, r = 0.567, respectively, df = 13, r _{crit (α = 0.05)} = 0.514). However, there was little evidence that ultrastructural alterations in fish responded to increasing concentrations of these pesticides in a consistent dose-response manner. Received: 20 October 1998 / Accepted: 24 November 1999     

Kinetics of glucose and amino acid uptake by attached and free-living marine bacteria in oligotrophic waters

Kinetics of glucose and amino acid uptake by attached and free-living bacteria were compared in the upper 70 m of the oligotrophic north-western Mediterranean Sea. Potential uptake rates of amino acids were higher than those of glucose in all the samples analysed. Cell-specific potential uptake rates of attached bacteria were up to two orders of magnitude higher than those of total bacteria, both for amino acids and glucose (0.72–153 amol amino acids cell⁻¹ h⁻¹ and 0.05–58.42 amol glucose cell⁻¹ h⁻¹ for attached bacteria and 0.34–1.37 amol amino acids cell⁻¹ h⁻¹ and 0.07–0.22 amol glucose cell⁻¹ h⁻¹ for total bacteria). The apparent K _m values were also higher in attached bacteria than in total bacteria, both for amino acids and glucose. These results would reflect the presence of different uptake systems in attached and free-living bacteria, which is in accordance with the different nutrient characteristics of their microenvironments, ambient water and particles. Attached bacteria show transport systems with low affinity, which characterise a bacterial community adapted to high concentration of substrates. Received: 13 June 2000 / Accepted: 6 December 2000     

Distribution and diversity of mtDNA lineages among southern right whales (Eubalaena australis) from Australia and New Zealand

Using a biopsy dart system, samples of skin tissue were collected from southern right whales (Eubalaena australis) in 1995 on two wintering grounds, southwest Australia (n = 20) and the Auckland Islands of New Zealand (n = 20); and on offshore feeding grounds at Latitudes 40 to 43°, south of Western Australia (n = 5). A variable section of the mitochondrial DNA control-region (289 nucleotides) was amplified and sequenced from these 45 individuals (21 males, 20 females and 4 of unknown sex), distinguishing a total of seven unique sequences (i.e. mtDNA haplotypes). Two haplotypes were found on both wintering grounds (including a common type representing 45% of each sample), and five types were unique to only one wintering ground. An analysis of variance adapted for molecular information revealed significant genetic differentiation between the two wintering grounds (p = 0.017). The feeding-ground sample was too small for statistical comparison with the wintering grounds, but included two haplotypes found only in the Auckland Islands as well as the common haplotype found on both wintering grounds. The nucleotide diversity and differentiation of mtDNA among the right whales was similar to that among humpback whales (Megaptera novaeangliae) from the same regions (Baker et al. 1998), but haplotype diversity was significantly reduced, perhaps as a result of more intensive hunting during the last century and continued illegal hunting during this century. Received: 16 March 1998 / Accepted: 18 December 1998     

Respiration of the eggs of the giant cuttlefish Sepia apama

On the roofs of subtidal crevices, the giant cuttlefish (Sepia apama) of southern Australia lays clutches of lemon-shaped eggs which hatch after 3 to 5 mo. Diffusion of oxygen through the capsule and chorion membrane to the perivitelline fluid and embryo was modelled using the equation V˙ _O2 = G _O2(P _O2out−P _O2in), where V˙ _O2 = rate of oxygen consumption, G _O2 = oxygen conductance of the capsule, and P _O2 values = oxygen partial pressures across the capsule. During development, V˙ _O2 rose exponentially as the embryo grew, reaching 5.5 μl h⁻¹ at hatching. Throughout development, the capsule dimensions enlarged by absorption of water into the perivitelline space, increasing G _O2 by a combination of increasing surface area, and decreasing thickness of the capsule. These processes maintained P _O2in high enough to allow unrestricted V˙ _O2 until shortly before hatching. Diffusion limitation of respiration in hatching-stage embryos was demonstrated by (1) increased embryonic V˙ _O2 when P _O2out was experimentally raised, (2) greater V˙ _O2 of resting individuals immediately after hatching, and (3) reduced V˙ _O2 of hatchlings at experimental P _O2 levels higher than P _O2in before hatching. Thus, low P _O2in may be the stimulus to hatch. Potential problems of diffusive gas-exchange are mitigated by the relatively low incubation temperature (12 °C), which may be a factor limiting the distribution of the species to cool, southern waters. Received: 14 August 1999 / Accepted: 24 January 2000     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Distribution and ecology of leptocephali of the congrid eel, Ariosoma scheelei, around Sulawesi Island, Indonesia

A survey for leptocephali around Sulawesi Island in the central Indonesian Seas during May 2001 found that the leptocephali of the congrid eel, Ariosoma scheelei, were present in all seven areas that were sampled. A total of 551 leptocephali (22–166 mm TL) were collected, and A. scheelei was by far the most abundant species of leptocephali collected during the survey. The wide range of sizes in most areas indicated that spawning had occurred during a period of several months in many different areas, although the exact spawning locations were not determined. The larger size classes were more abundant in all areas except in Tomini Bay on the northeast side of Sulawesi Island. The highest catch rates were observed at the eastern edge of the Java Sea and to the north in the Celebes Sea near Makassar Strait. Premetamorphic leptocephali were also collected in surface samples at 11 stations (N=62), but metamorphosing leptocephali (N=86) were only caught in IKMT tows that fished from the surface to about 200 m. Metamorphosing leptocephali were collected primarily at two stations in the Java Sea and Makassar Strait where a surface layer of lower-salinity water was detected. Their total lengths (105.3–153.3 mm) and the largest premetamorphic individuals suggested that this species can reach maximum sizes of about 165 mm before beginning to metamorphose. It is hypothesized that this species may be abundant in the Indonesian Seas region and that it has ecological traits such as large size at recruitment and a small size at reproduction that have made it successful in many regions of the Indo-Pacific.     

Sociality,Bateman’s gradients,and the polygynandrous genetic mating system of round-tailed ground squirrels (<Emphasis Type="Italic">Xerospermophilus tereticaudus</Emphasis>)

Historically, most mammals have been classified as polygynous; although recent molecular evidence suggests that many mammals may be polygynandrous, particularly the ground-dwelling sciurids. We genotyped 351 round-tailed ground squirrels (Xerospermophilus tereticaudus) using seven microsatellite loci to determine paternity in 31 litters from 2004 to 2007. Polygyny was evident in all years except in 2007, when the population size was reduced. Multiple paternity occurred in the majority of litters (55%) with 2.5 ± 0.26 sires/litter (n = 31). Forty-nine percent of resident males (n = 114) sired offspring, and of males that sired offspring (n = 56) 27% sired young in multiple litters in a single breeding season. Litter size was positively correlated with the number of sires. Through an indirect analysis of paternity, we found 21 litters (68%) with an average relatedness of 0.5 or less. Males had a greater opportunity for sexual selection (I _s = 1.60) than females (I _s = 0.40); Bateman’s gradient was also greater in males (1.07 ± 0.04, n = 56) than females (0.82 ± 0.08, n = 31). The mating system in round-tailed ground squirrels defined through genetic analyses and Bateman’s gradients is polygynandrous compared to the previously suggested polygynous mating system as established by behavioral observations and fits within the predictions of the ground squirrel sociality models. Upon evaluating the predictions of the sociality models among sciurid species, we found a negative relationship between the level of sociality with litter size and the average percentage of multiple paternity within a litter. Thus, recent genetic information and reclassification of mating systems support the predictions of the ground-dwelling squirrel sociality models.     

Light and carbon balance in the seagrass Thalassia testudinum : evaluation of current production models

The production dynamics and carbon balance of Thalassia testudinum in the lower Laguna Madre, Texas, USA, were examined during the 1995 summer period based on in situ photosynthesis vs irradiance (PI) measurements and continuous measurements of underwater photon-flux density (PFD). The validity of applying the H _sat model, used to calculate production for Zostera marina as the product of the maximum rate of photosynthesis (P _max) and daily hours of saturating irradiance (H _sat) was assessed for T. testudinum by comparison with integrated production estimates derived through numerical integration. Gross integrated production values were combined with dark-respiration measurements of photosynthetic (PS) and non-photosynthetic (NPS) tissues and areal biomass to generate daily whole-plant carbon balance. Production and whole-plant carbon balance are discussed in relation to surface and underwater PFD measurements, biomass and other physical and chemical parameters collected during a 1 yr period from January to December 1995. The H _sat model significantly underestimated production during all summer months, averaging 70% of integrated production over the entire study period. Gross integrated production ranged between 11.5 mg C g⁻¹ leaf dry wt d⁻¹ in June (during a period of unseasonably low PFDs caused by a drift-alga mat covering the seagrass bed) to 26.7 mg C g⁻¹ leaf dry wt d⁻¹ in July. Modeled net carbon gain was highest in July at 454 mg C m⁻² d⁻¹ (1.4 g dry wt m⁻² d⁻¹), sufficient to account for measured rates of leaf production in the study area and representative of T. testudinum populations of low productivity. During part of the summer period, however, the population was in negative carbon balance. The relatively low productivity of this population and the periods of negative carbon balance are attributed to low net photosynthesis:dark respiration (P _net:R _d) ratios, sporadic low-light periods, the small fraction of PS tissue relative to whole-plant biomass (5 to 13%) and nutrient limitation. Production models are sensitive to both light availability and the proportion of PS tissue supporting NPS biomass as reflected in whole-plant P _net:R _d ratios. Received: 13 August 1997 / Accepted: 6 March 1998