Predictive capability of a leaf optical meter for determining leaf pigment status during senescence

We conducted an experiment to assess the predictive capability of a leaf optical meter for determining leaf pigment status of Acer mono Maxim., A. ginnala Maxim., Quercus mongolica Fisch., and Cornus alba displaying a range of visually different leaf colors during senescence. Concentrations of chlorophyll (Chl) a, Chl b, and total Chl [i.e., Chl (a+b)] decreased while the concentration of carotenoids (Car) remained relatively static for all species as leaf development continued from maturity to senescence. C. alba exhibited the lowest average concentration of Chl (a+b), Chl a, and Car, but the highest relative anthocyanin concentration, while Q. mongolica exhibited the highest Chl (a+b), Chl b, and the lowest relative anthocyanin concentration. A. mono exhibited the highest Chl a and Car concentrations. The relationships between leaf pigments and the values measured by the optical meter generally followed an exponential function. The strongest relationships between leaf pigments and optical measurements were for A. mono, A. ginnala, and Q. mongolica (R ² ranged from 0.64 to 0.95), and the weakest relationships were for C. alba (R ² ranged from 0.13 to 0.67). Moreover, optical measurements were more strongly related to Chl a than to Chl b or Chl (a+b). Optical measurements were not related to Car or relative anthocyanin concentrations. We predicted that weak relationships between leaf pigments and optical measurements would occur under very low Chl concentrations or under very high anthocyanin concentrations; however, these factors could not explain the weak relationship between Chl and optical measurements observed in C. alba. Overall, our results indicated that an optical meter can accurately estimate leaf pigment concentrations during leaf senescence — a time when pigment concentrations are dynamically changing — but that the accuracy of the estimate varies across species. Future research should investigate how species-specific leaf traits may influence the accuracy of pigment estimates derived from optical meters.     

The taxonomic challenge posed by the Antarctic echinoids <Emphasis Type="Italic">Abatus bidens</Emphasis> and <Emphasis Type="Italic">Abatus cavernosus</Emphasis> (Schizasteridae,Echinoidea)

Cryptic species have been repeatedly described for two decades among the Antarctic fauna, challenging the classic model of Antarctic species with circumpolar distributions and leading to revisit the richness of the Antarctic fauna. No cryptic species had been so far recorded among Antarctic echinoids, which are, however, relatively well diversified in the Southern Ocean. The R/V Polarstern cruise PS81 (ANT XXIX/3) came across populations of Abatus bidens, a schizasterid so far known by few specimens that were found living in sympatry with the species Abatus cavernosus. The species A. cavernosus is reported to have a circum-Antarctic distribution, while A. bidens is only recorded with certainty in South Georgia and at the northern tip of the Antarctic Peninsula. Based on genetic and morphological analyses, our results clearly show that A. bidens and A. cavernosus are two distinct species. The analyzed specimens of A. bidens group together in two haplogroups separated from one another by 2.7 % of nucleotide differences. They are located in the Weddell Sea and in the Bransfield Strait. Specimens of A. cavernosus form one single haplogroup separated from haplogroups of A. bidens by 5 and 3.5 % of nucleotide differences, respectively. The species was collected in the Drake Passage and in the Bransfield Strait. Morphological analyses differentiate A. bidens from A. cavernosus. In contrast, the two genetic groups of A. bidens cannot be differentiated from one another based on morphology alone, suggesting that they may represent a case of cryptic species, common in many Antarctic taxa, but not yet reported in Antarctic echinoids. This needs to be confirmed by complementary analyses of independent genetic markers.     

Isolation of <Emphasis Type="Italic">Campylobacter</Emphasis> spp. from Three Species of Antarctic Penguins in Different Geographic Locations

The presence of Campylobacter species was studied in three Antarctic penguin species, Adélie (Pygoscelis adeliae), chinstrap (Pygoscelis antarctica) and gentoo (Pygoscelis papua). A total of 390 penguins were captured in 12 different rookeries along the Antarctic Peninsula with differences in the amount of human visitation: six colonies were highly visited [Stranger Point, King George Island (P. papua and P. adeliae); Hannah Point, Livingston Island (P. papua and P. antarctica); Deception Island (P. antarctica); and Paradise Bay, Antarctic Peninsula (P. papua)], and six colonies were rarely visited [Devil’s Point, Byers Peninsula, Livingston Island (P. papua); Cierva Cove, Antarctic Peninsula (P. papua); Rongé Island (P. papua and P. antarctica); Yalour Island (P. adeliae); and Avian Island (P. adeliae)]. A total of 23 strains were isolated from penguins from nine different rookeries. Campylobacter lari subsp. lari was isolated from eight samples (seven from P. papua and one from P. adeliae); C. lari subsp. concheus from 13 (ten from P. adeliae and three from P. antarctica) and C. volucris from two samples (both from P. papua). We did not find any significant differences in the prevalence of Campylobacter spp. between the populations in highly and rarely visited areas. This is the first report of C. lari subsp. concheus and C. volucris isolation from penguins in the Antarctic region.     

Distribution,habitat and trophic ecology of Antarctic squid Kondakovia longimana and Moroteuthis knipovitchi: inferences from predators and stable isotopes

Cephalopods have a key role in the marine environment though knowledge of their distribution and trophic ecology is limited by a lack of observations. This is particularly true for Antarctic species. Toothfish species are key predators of cephalopods and may be viewed as ideal biological samplers of these species. A total of 256 cephalopod lower beaks were identified from the stomachs of Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni), captured in fisheries of South Georgia and the South Sandwich Islands in the South Atlantic between March and April 2009. Long-armed octopus squid (Kondakovia longimana) and smooth-hooked squid (Moroteuthis knipovitchi) were the main cephalopod prey and both were predated upon wherever toothfish were captured, though this cephalopod species appear to inhabit deeper waters at the South Sandwich Islands than at South Georgia. Measurements of δ¹³C from beak material indicated a clear segregation of habitat use comparing adult and sub-adult sized K. longimana. Variation in δ¹⁵N with size indicated an ontogenetic shift in the diet of cephalopods and also suggested some trophic plasticity among years. This study provides new insights into the private life of some elusive Antarctic cephalopods in an underexplored region of the South Atlantic.     

Natively oxidized amino acid residues in the spinach cytochrome <Emphasis Type="Italic">b</Emphasis><Subscript><Emphasis Type="Italic">6</Emphasis></Subscript><Emphasis Type="Italic">f</Emphasis> complex

The cytochrome b ₆ f complex of oxygenic photosynthesis produces substantial levels of reactive oxygen species (ROS). It has been observed that the ROS production rate by b ₆ f is 10–20 fold higher than that observed for the analogous respiratory cytochrome bc₁ complex. The types of ROS produced (O₂^{??, 1}O₂, and, possibly, H₂O₂) and the site(s) of ROS production within the b ₆ f complex have been the subject of some debate. Proposed sources of ROS have included the heme b _p , PQ _p ^?? (possible sources for O₂^??), the Rieske iron–sulfur cluster (possible source of O₂^?? and/or ¹O₂), Chl a (possible source of ¹O₂), and heme c _n (possible source of O₂^?? and/or H₂O₂). Our working hypothesis is that amino acid residues proximal to the ROS production sites will be more susceptible to oxidative modification than distant residues. In the current study, we have identified natively oxidized amino acid residues in the subunits of the spinach cytochrome b ₆ f complex. The oxidized residues were identified by tandem mass spectrometry using the MassMatrix Program. Our results indicate that numerous residues, principally localized near p-side cofactors and Chl a, were oxidatively modified. We hypothesize that these sites are sources for ROS generation in the spinach cytochrome b ₆ f complex.     

Horizontal niche partitioning of humpback and fin whales around the West Antarctic Peninsula: evidence from a concurrent whale and krill survey

A dedicated aerial cetacean survey was conducted concurrently to a standardised net trawl survey for krill in order to investigate distribution patterns of large whales and different krill species and to investigate relationships of these. Distance sampling data were used to produce density surface models for humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) around the West Antarctic Peninsula (WAP). Abundance for both species was estimated over two strata in the Bransfield Strait and Drake Passage. Distinct distribution patterns suggest horizontal niche partitioning of the two whale species around the WAP, with fin whales aggregating at the shelf edge of the South Shetland Islands in the Drake Passage and humpback whales in the Bransfield Strait. Krill biomass estimated from the concurrent krill survey was used along with CTD data from the same expedition, bathymetric parameters and satellite data on chlorophyll-a and ice concentration to model krill distribution. Comparisons of the predicted distributions of both whale species with the predicted distributions of Euphausia superba, Euphausia crystallorophias and Thysanoessa macrura suggest a complex relationship rather than a straightforward correlation between krill and whales. However, results indicate that fin whales were feeding in an area dominated by T. macrura, while humpback whales were found in areas of higher E. superba biomass. Our results provide abundance estimates for humpback whales and, for the first time, fin whales in the WAP and contribute important information on feeding ecology and habitat use of these two species in the Southern Ocean.     

Length-weight and length-length relationships of <Emphasis Type="Italic">Cirrhinus mrigala</Emphasis> (Cyprinidae) and <Emphasis Type="Italic">Xenentodon cancila</Emphasis> (Belonidae) from the river Ganga

Length-weight and length-length relationships are presented for two fish species collected during May 2015 to August 2016 from Narora site of the river Ganga. The parameters a and b of the length-weight relationships were estimated after the logarithmic transformation of the equation: W = aL ^b . The lengthlength relationships were also estimated using linear regressions. The coefficients of determination (R ²) values were >0.9 for both target fish species and linear regressions were highly significant (p < 0.001). Length-weight relationship indicated positive allometric growth pattern for Cirrhinus mrigala and negative allometric growth pattern for Xenentodon cancila. Length-length relationships for the selected fish species were also highly significant (R ² > 0.9, p < 0.001).     

Soluble carbohydrates in developing and mature diaspores of polar Caryophyllaceae and Poaceae

The accumulation of soluble carbohydrates in maturing diaspores of flowering plants comprising Arctic populations of Cerastium alpinum, indigenous Antarctic species Colobanthus quitensis and Deschampsia antarctica, and cosmopolitan Poa annua from the Antarctic was investigated. For comparative purposes, the diaspores of two species of flowering plants growing in the area of Olsztyn (Poland), Poa annua (Poaceae) and Cerastium arvense (Caryophyllaceae) were used. A qualitative and quantitative analysis of soluble carbohydrates conducted by means of high-resolution gas chromatography showed that monosaccharides (glucose and fructose), maltose and sucrose, raffinose, myo-inositol and galactinol are ubiquitous in developing and mature diaspores among investigated species. Moreover, D. antarctica and P. annua caryopses additionally contained stachyose and 1-kestose; the seeds of Caryophyllaceae studied were found to contain d-pinitol and d-ononitol. The development and maturation of the seeds of polar Caryophyllaceae and Poaceae were accompanied by the changes in the concentration of their soluble carbohydrates. During maturation, seeds accumulated galactinol and raffinose family of oligosaccharides (RFOs), except C. quitensis. Although seeds of the studied Caryophyllaceae contained d-pinitol and lower amounts of d-ononitol, they did not accumulate α-d-galactoside derivatives of mentioned cyclitols. P. annua caryopses, occurring in the Antarctic, were found to accumulate considerably higher amounts of sucrose and 1-kestose than those developed in Olsztyn.     

Higher phenotypic plasticity does not confer higher salt resistance to <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> than <Emphasis Type="Italic">Amorpha fruticosa</Emphasis>

A greenhouse experiment was conducted in which two leguminous species commonly used in the Yellow River Delta for vegetation restoration, Robinia pseudoacacia and Amorpha fruticosa, were subjected to five salt treatments: 0, 50, 100, 150, and 200 mmol L^?1. We aimed to determine which of the two species would be better suited for growth in a saline environment, and whether the acclimation capacity to salinity resulted from an inherently higher phenotypic plasticity. The results showed that salinity affected most growth and biomass parameters but had no effects on most leaf traits and physiological parameters of the two species. Height, relative growth rate of crown area, root biomass, and leaf mass ratio of R. pseudoacacia were reduced by higher salinity, while A. fruticosa was not affected. Chlorophyll a-to-chlorophyll b ratio and total antioxidative capacity of A. fruticosa increased with higher salinity, whereas those of R. pseudoacacia remained unchanged. Root mass ratio and vitamin C concentration of both species were not affected by salinity, whereas vitamin C concentration of A. fruticosa was higher than that of R. pseudoacacia. The root-to-shoot ratio of A. fruticosa was higher than that of R. pseudoacacia in most salt treatments. Of all leaf traits, only leaf area differed between treatments. R. pseudoacacia generally exhibited a greater plasticity than A. fruticosa in response to salinity, but A. fruticosa was more resistant to the higher salinities than R. pseudoacacia, and was thus a better candidate for vegetation restoration in saline areas.     

Interspecific variation in extracellular polysaccharide content and colony formation of <Emphasis Type="Italic">Microcystis</Emphasis> spp. cultured under different light intensities and temperatures

Single cells of five different Microcystis species (M. ichthyoblabe, M. viridis, M. flos-aquae, M. wesenbergii, and M. aeruginosa) were batch-cultured at different temperatures and light intensities: (a) 25 °C and 50 μmol photons m^?2 s^?1 (control culture); (b) 25 °C and 10 μmol photons m^?2 s^?1; and (c) 15 °C and 50 μmol photons m^?2 s^?1. The extracellular polysaccharide content was significantly higher in treatments b and c than in the control treatment. All Microcystis species existed as single cells under the control treatment but formed colonies in treatments b and c. All of the colonies were irregular with indistinct margins. M. ichthyoblabe, M. viridis, M. flos-aquae, and M. wesenbergii formed colonies with similar morphologies and their cells were loosely aggregated. In contrast, M. aeruginosa formed denser colonies with no distinct holes. The colony morphologies differed from the classic morphology of M. ichthyoblabe field-grown colonies but resembled that of small colonies found in Lake Taihu (Yangtze Delta Plain, China) during early spring. This indicates that field- and laboratory-grown colonies are governed by similar formation processes. We suggest that in laboratory and field environments, M. ichthyoblabe (or M. flos-aquae) colonies are representative of small colonies formed from single Microcystis cells, whereas the morphology of older colonies evolves to resemble M. wesenbergii and M. aeruginosa colonies.     

Construction of flavocytochrome <Emphasis Type="Italic">b</Emphasis><Subscript>2</Subscript>-overproducing strains of the thermotolerant methylotrophic yeast <Emphasis Type="Italic">Hansenula polymorpha</Emphasis> (<Emphasis Type="Italic">Pichia angusta</Emphasis>)

L-Lactate cytochrome c oxidoreductase (flavocytochrome b ₂, FC b ₂) from the thermotolerant methylotrophic yeast Hansenula polymorpha (Pichia angusta) is, unlike the enzyme form baker’s yeast, a thermostable enzyme potentially important for bioanalytical technologies for highly selective assays of L-lactate in biological fluids and foods. This paper describes the construction of flavocytochrome b ₂ producers with over-expression of the H. polymorpha CYB2 gene, encoding FC b ₂. The HpCYB2 gene under the control of the strong H. polymorpha alcohol oxidase promoter in a plasmid for multicopy integration was transformed into the recipient strain H. polymorpha C-105 (grc1 catX), impaired in glucose repression and devoid of catalase activity. A method was developed for preliminary screening of the transformants with increased FC b ₂ activity in permeabilized yeast cells. The optimal cultivation conditions providing for the maximal yield of the target enzyme were found. The constructed strain is a promising FC b ₂ producer characterized by a sixfold increased (to 3 μmol min^?1 mg^?1 protein in cell-free extract) activity of the enzyme.     

Molecular phylogeny of pectinase genes <Emphasis Type="Italic">PGU</Emphasis> in the yeast genus <Emphasis Type="Italic">Saccharomyces</Emphasis>

Using yeast genome databases and literature data, phylogenetic analysis of pectinase PGU genes from 112 Saccharomyces strains assigned to the biological species S. arboricola, S. bayanus (var. uvarum), S. cariocanus, S. cerevisiae, S. kudriavzevii, S. mikatae, S. paradoxus, and the hybrid taxon S. pastorianus (syn. S. carlsbergensis) was carried out. A superfamily of divergent PGU genes was found. Natural interspecies transfer of the PGU gene both from S. cerevisiae to S. bayanus and from S. paradoxus to S. cerevisiae may, however, occur. Within the Saccharomyces species, identity of the PGU nucleotide sequences was 98.8–100% for S. cerevisiae, 86.1–95.7% for S. bayanus (var. uvarum), 94–98.3% for S. kudriavzevii, and 96.8–100% for S. paradoxus/S. cariocanus. For the first time, a family of polymeric PGU1b, PGU2b, PGU3b and PGU4b genes is documented for the yeast S. bayanus var. uvarum, a variety important for winemaking.     

Two distinct <Emphasis Type="Italic">waxy</Emphasis> alleles impact the granule-bound starch synthase in sorghum

The granule-bound starch synthase (GBSS) is the enzyme responsible for amylose synthesis in starch granules. Loss of GBSS activity results in starch granules containing mostly amylopectin and little or no amylose, a phenotype described as waxy. Previously, two phenotypic classes of waxy alleles were identified in sorghum (Sorghum bicolor L. Moench) characterized by the absence (waxy ^a ; wx ^a ) or presence (waxy ^b ; wx ^b ) of the GBSS protein in the endosperm. To characterize these alleles, we examined endosperm architecture using scanning electron microscopy (SEM), assayed GBSS enzymatic activities, and identified DNA lesions associated with the mutations in the GBSS (Sb10g002140) gene. wx ^a , the allele present in B Tx630 and R Tx2907, contained a large insertion in the third exon, which was consistent with the absence of the GBSS protein previously observed. wx ^b , the allele present in B 9307 and B TxARG1, contained a missense mutation that resulted in conversion of glutamine 268 to histidine in a conserved domain in starch synthases. In wx ^b , GBSS activity was less than 25% that of the non-waxy line B Wheatland, and GBSS activity was not detected in wx ^a . SEM showed that endosperm architecture was very similar in both wx ^a and wx ^b alleles, but altered in comparison to non-waxy lines R Tx430 and B Wheatland. Both alleles may have a range of potential applications in grain sorghum because of low amylose content in their starch and the presence or absence of the GBSS protein. PCR based markers were developed for both the wx ^a and the wx ^b alleles to aid in molecular breeding of low amylose sorghum.     

Thermal Preference of the Bush Cricket <Emphasis Type="Italic">Isophya rizeensis</Emphasis>; Testing the Effect of Countergradient Selection

Thermal preference is one of the most crucial components of behavioral thermoregulation in ectotherms, and documenting the adaptation of thermal preference carries great importance for studying the evolution of thermal biology. However there are not many studies focusing on the adaptation of thermal preference in elevational and latitudinal gradients. Isophya rizeensis is a color polymorphic bush cricket species endemic to the mountainous region of northeastern Turkey. Populations of this species are distributed in a wide elevational range between 350 and 2300 m. In this study, we hypothesized that the thermal preference of Isophya rizeensis might follow a countergradient variation where crickets from higher altitudes have higher temperature preferences compared to crickets from lower altitudes. To test this hypothesis, thermal preference values (T _pref ) of crickets from three altitudes groups (low, middle and high) were measured with a thermal gradient experiment. Additionally, body temperatures (T _b ) and environmental temperatures (T _a ) were measured in field. Deviation values of T _b and T _a from T _pref were calculated to investigate the extent of thermoregulation. As Isophya rizeensis is color polymorphic species where morphology pattern changes from lighter to darker types with increasing altitude we also tested whether coloration has any effect on temperature excess (T _ex ) and thermoregulation. Thermal preference values did not differ significantly between three groups and also colouration does not influence the extent of thermoregulation in this species. These results indicate that there is not sufficient evidence for the existence of a countergradient selection related with thermal behavior. However, the deviation of body (D _b ) and environmental (D _a ) temperatures suggest that at higher altitudes thermoregulation might be more efficient than lower altitudes.     

Competition between native Antarctic vascular plants and invasive <Emphasis Type="Italic">Poa annua</Emphasis> changes with temperature and soil nitrogen availability

Over the last decades human have introduced non-native organisms to Antarctica, including the grass species Poa annua. This non-native grass under constant growth temperatures has been shown negatively affect the growth of the only two native Antarctic vascular plants, Deschampsia antarctica and Colobanthus quitensis, under constant growth temperatures. However, whether there are changes in the interaction between these species under warmer conditions is an important question. In cold ecosystems, soil nutrient status directly affects plant responses to increases in temperature and Antarctic soils are highly variable in nutrient supply. Thus, in this study we experimentally assessed the interaction between the non-native Poa with the two native Antarctic vascular plant species at two different temperatures and levels of nutrient availability. Individual mats of the study species were collected in King George Island, and then transported to Concepcion where we conducted competition experiments. In the first experiment we used soil similar to that of Antarctica and plants in competition were grown at two temperatures: 5°/2° and 11°/5 °C (day/night temperature). In a second experiment plants were grown in these two temperature regimes, but we varied nitrogen (N) availability by irrigating plants with Hoagland solutions that contained 8000 or 300 µM of N. Overall, Poa exerted a competitive effect on Deschampsia but only at the higher temperature and higher N availability. At 5°/11 °C the competitive response of Deschampsia to Poa was of similar magnitude to the competitive effect of P. Deschampsia, and the competitive effect was greater with at low N. The competitive effect of Poa was similar to the competitive response of Colobanthus to Poa at both temperatures and N levels. Thus, at low temperatures and N soil content the native Antarctic species might withstand Poa invasion, but this might change with climate warming.     

Fine-scale differences in genetic and census population size ratios between two stream fishes

Comparing the ratio of effective number of breeders (N _b ) to adult population size (N) among closely related coexisting species can provide insights into the role of life history on N _b /N ratios and inform conservation programs towards limiting the loss of evolutionary potential in natural populations. We estimated N _b and N in two coexisting salmonid fishes (Brook trout and Atlantic salmon) for 3–4 consecutive years in two small, adjacent streams in Newfoundland, Canada, using mark-recapture (N), linkage disequilibrium (N _b(LD)), and sibship frequency approaches (N _b(Sib) ). We found that N _b /N ratios were about 20-fold greater in Atlantic salmon than in brook trout (mean 0.20, range 0.06–0.56 vs. mean 0.02, range 0.01–0.05, respectively). This difference was consistent across N _b estimators. In addition, we found that removing migrants reduced N _b : the strength of the effect was weak for N _b(LD) and much stronger for N _b(Sib). Our results highlight the importance of subtle ecological differences and gene flow in shaping N _b /N. They also provide some evidence that the linkage between demographic and evolutionary processes varies between closely related taxa and suggest that a more complete understanding of the N _b /N range across various species is an important component of conservation genetics and management.     

Check of Gene Number during the Process of rDNA Magnification

THE multiple sequences of rDNA (DNA complementary to ribosomal RNA) of the Drosophila genome are localized at the bobbed locus, located in the X chromosome, position 66 and in the short arm of the Y chromosome^1,2. Wild bobbed (bb⁺) is that locus which, without a partner, gives rise to a normal phenotype. That locus which in similar conditions is incapable of giving rise to a normal phenotype is called a bobbed mutation (bb) and contains fewer genes for rRNA. The number of genes for rRNA in different individuals can vary considerably. One mechanism for rDNA variation is unequal crossing over³. Another mechanism, described by Tartof⁴, becomes apparent when individual flies, carrying only one bobbed locus, are constructed and only if such a locus is on the X chromosome; that is, if one constructs Xbb⁺/O males (and also Xbb/O males) or Xbb⁺/X_NO- females. Such individuals show a higher rDNA content than expected from the analysis of the same locus in Xbb⁺/Xbb⁺ females or in Xbb⁺/Ybb⁺ males. The increase of rDNA in this case is not inheritable⁴.     

The diet of the Antarctic fur seal <Emphasis Type="Italic">Arctocephalus gazella</Emphasis> at the South Orkney Islands in ten consecutive years

To improve the knowledge on the Antarctic fur seal foraging behavior, evaluate whether changes in its diet are associated with changes in prey availability, and evaluate whether fisheries had negative impacts on Antarctic fur seal populations, a total of 1359 scats of non-breeding males were collected in ten consecutive sampling periods between 1994 and 2003 at Laurie Island, South Orkney Islands. Antarctic krill was the most numerous prey throughout the sampling period followed in importance by fish prey. Antarctic krill also predominated by reconstructed mass, except during 1994 and 1998 when penguins were the most important prey, and during 1995 when fish dominated. Among fish, demersal-benthic species (mainly Gobionotothen gibberifrons, Chaenocephalus aceratus and Chionodraco rastrospinosus) dominated the diet except in 1997, 1998, 1999 and 2002 when myctophids (mainly Gymnoscopelus nicholsi and Electrona antarctica) were the most important fish prey. In seasons when fish dominated the diet, the diet was primarily comprised of demersal species. Although our results are in overall agreement with previous studies, the contribution to the diet of the main preys changed throughout the sampling period, probably in parallel with changes in prey abundance. According to historical results on fish consumption, the fisheries carried out in the past have had negative impacts on seal populations from the South Orkney Islands.