Diet of bluegill Lepomis macrochirus in a South African reservoir during winter and summer

Alien fishes are considered a major threat to aquatic biodiversity in South Africa, yet relatively little regional information on their biology and ecology is available for many of these species. Seasonal changes in the diet of the bluegill Lepomis macrochirus in Howieson’s Poort Dam, Grahamstown, were assessed during summer and winter in 2014–2015, using stomach content analysis. In winter, juvenile and adult fish diets were dominated by crustacean zooplankton and insects, respectively. In summer, juvenile fish fed on crustaceans and insects, whereas adults consumed mostly fish eggs, indicating a potential impact by these invasive fish on native fish through oophagy.     

DEVELOPMENTAL CONSEQUENCES OF AN EVOLUTIONARY CHANGE IN EGG SIZE: AN EXPERIMENTAL TEST

Larvae of two species of sea urchins (Strongylocentrotus droebachiensis and S. purpuratus) differ in initial form and in the rate of development. To determine whether these differences are attributable to the large interspecific difference in egg size, we experimentally reduced egg size by isolating blastomeres from embryos. The rate of development of feeding larvae derived from isolated blastomeres was quantified using a novel morphometric method. If the differences early in the life histories of these two species are due strictly to differences in egg size, then experimental reduction of the size of S. droebachiensis eggs should yield an initial larval form and rate of development similar to that of S. purpuratus. Our experimental manipulations of egg size produced three clear results: 1) smaller eggs yielded larvae that were smaller and had simpler body forms, 2) smaller eggs resulted in slower development through the early feeding larval stages, and 3) effects of egg size were restricted to early larval stages. Larvae from experimentally reduced eggs of the larger species had rates of development similar to those of the smaller species. Thus, cytoplasmic volumes of the eggs, not genetic differences expressed during development, account for differences in larval form and the rate of form change. This is the first definitive demonstration of the causal relationship between egg size (parental investment per offspring) and life-history characteristics in marine benthic invertebrates. Because larval form influences feeding capability, the epigenetic effects of egg size on larval form are likely to have important functional consequences. Adaptive evolution of egg size may be constrained by the developmental relationships between egg size and larval form: evolutionary changes in egg size alone can result in concerted changes in larval form and function; likewise evolutionary changes in larval form and function can be achieved through changes in egg size. These findings may have broader implications for other taxa in which larval morphology and, consequently, performance may be influenced by changes in egg size.     

Molecular phylogenetic and biogeochemical studies of sulfate-reducing bacteria in the rhizosphere of spartina alterniflora

The population composition and biogeochemistry of sulfate-reducing bacteria (SRB) in the rhizosphere of the marsh grass Spartina alterniflora was investigated over two growing seasons by molecular probing, enumerations of culturable SRB, and measurements of SO42- reduction rates and geochemical parameters. SO42- reduction was rapid in marsh sediments with rates up to 3.5 &mgr;mol ml-1 day-1. Rates increased greatly when plant growth began in April and decreased again when plants flowered in late July. Results with nucleic acid probes revealed that SRB rRNA accounted for up to 43% of the rRNA from members of the domain Bacteria in marsh sediments, with the highest percentages occurring in bacteria physically associated with root surfaces. The relative abundance (RA) of SRB rRNA in whole-sediment samples compared to that of Bacteria rRNA did not vary greatly throughout the year, despite large temporal changes in SO42- reduction activity. However, the RA of root-associated SRB did increase from <10 to >30% when plants were actively growing. rRNA from members of the family Desulfobacteriaceae comprised the majority of the SRB rRNA at 3 to 34% of Bacteria rRNA, with Desulfobulbus spp. accounting for 1 to 16%. The RA of Desulfovibrio rRNA generally comprised from <1 to 3% of the Bacteria rRNA. The highest Desulfobacteriaceae RA in whole sediments was 26% and was found in the deepest sediment samples (6 to 8 cm). Culturable SRB abundance, determined by most-probable-number analyses, was high at >10(7) ml-1. Ethanol utilizers were most abundant, followed by acetate utilizers. The high numbers of culturable SRB and the high RA of SRB rRNA compared to that of Bacteria rRNA may be due to the release of SRB substrates in plant root exudates, creating a microbial food web that circumvents fermentation.     

Codon use and the rate of divergence of land plant chloroplast genes

Codon fitnesses for chloroplast genes were estimated using the relative synonymous codon use of psbA, which has a different pattern of codon use than other chloroplast genes and is the major translation product of the chloroplast. These estimates were used to calculate the codon adaptation index (CAI) of chloroplast genes from Marchantia polymorpha, Nicotiana tabacum, and Chlamydomonas reinhardtii. The genes with the highest CAI values in M. polymorpha correspond to those that are expressed at the highest levels. The rate of divergence between M. polymorpha and both C. reinhardtii and N. tabacum is inversely related to the CAI value of the M. polymorpha gene. The data suggest that selection is acting on the synonymous codon use of the highly expressed genes of the M. polymorpha chloroplast genome. The data set is inconclusive about N. tabacum genes, but, as there is a weaker correspondence between CAI value and expression level, it suggests that selection is not operating in this lineage.      

Fine with heat,problems with water: microclimate alters water loss in a thermally adapted insular lizard

Global change, including habitat isolation and climate change, has both short‐ and long‐term impacts on wildlife populations. For example, genetic drift and inbreeding result in genetic impoverishment in small, isolated populations, while species undergo range shifts or adaptive phenotypic change in response to shifts in environmental temperatures. In this study, we utilize a model system in which Holocene landscape changes have occurred to examine long‐term effects of population isolation. To examine how isolation may constrain responses to climate change, we characterized ecophysiology across land‐bridge island populations of Erhard's wall lizard Podarcis erhardii. We hypothesized that 1) small, isolated populations that are likely genetically depauperate would exhibit lower phenotypic variability; and 2) populations would be adapted to local microhabitat conditions. We compared a population at a low elevation site on the large island of Naxos with two small populations on nearby islets to determine the effects of population fragmentation. We further compared the low elevation Naxos population with two high elevation sites characterized by disparate microclimates to examine the effects of microclimate. To assess the thermal biology and ecophysiological limits of the study species we measured operative body temperatures (T_e), field body temperatures (T_b), preferred temperatures (T_p), thermal tolerances (CT_max and CT_min), and evaporative water loss (EWL). Our results indicate that small, isolated populations did not exhibit thermal biology or evaporative water loss, while EWL and thermoregulatory effort varied according to microhabitat characteristics. This study integrates fine‐scale measurements with environmental data to provide a holistic view of the relationships between ecophysiology, fragmentation, and microclimate. Our methods can be applied to other ectotherms to gain a better understanding of potential impacts of global change on natural populations.     

Physiological epistasis, ontogenetic conflict and natural selection on physiology and life history

Ontogenetic conflict arises when optima for alleles governingfitness variation differ between juveniles and adults or betweenadult sexes. Loci that govern development of alternative phenotypesin the sexes, hereafter termed morph-determining loci, mediatedevelopment through the endocrine system. Morphotypic selectionis defined to be multivariate selection favoring discrete alternativemorphotypes (e.g., optima). When the optimal combinations ofalleles for alternative morphs differ between the sexes, itgenerates conflicting selection pressure and thus ontogeneticconflict. Selection on morph alleles promotes ontogenetic conflictbecause it perturbs physiological epistasis that governs theexpression of male versus female traits. Expression of physiologicaltraits arises from homeostasis that maintains trait expressionwithin a normal range. The genetic basis of homeostasis is likelyto arise from interactions among several genes (e.g., geneticepistasis) or protein products (e.g., physiological epistasis).For example, endocrine regulation arises from interactions betweengondatropins, which are protein hormones produced by the hypothalamic-pituitaryglands, and steroid hormones, which are produced by the gonads(e.g., HPG axis). The side-blotched lizard system is discussedwith respect to physiological bases of ontogenetic conflict.We also describe a novel molecular marker strategy for uncoveringgenome-wide physiological epistasis in nature. Finally, ontogeneticconflict exerts selection on females to evolve mate selectionor cryptic choice that is reflected in different sires beingchosen for son versus daughter production. We describe how side-blotchedlizard females ameliorate ontogenetic conflict by cryptic choiceof male genotypes to produce sons versus daughters.     

Purification and characterization of maltooligosaccharide-forming amylase from Bacillus circulans GRS 313

A maltooligosaccharide-forming amylase that hydrolyzes starch into maltotriose and maltopentaose was found in the culture filtrate of a strain of Bacillus circulans GRS 313 isolated from local soil. The enzyme was purified by organic solvent fractionation, Sephadex G-100 gel filtration and CM-Sephadex column chromatography. Optimum pH and temperature of amylase were evaluated using response surface methodology (RSM) and were found to be 48°C and 4.9, respectively. The enzyme was stable up to 60°C and its pH stability was in the range of 5.0–8.0. The K _m and V _max of the amylase with starch were 11.66 mg/ml and 68.97 U, respectively, and the energy of activation, E _a, was 7.52 kcal/mol. Dextrin inhibited the enzyme competitively, with a K _i of 6.1 mg/ml, and glucose caused noncompetitive inhibition with a K _i of 9.5 mg/ml. The enzyme was inhibited by Hg²⁺, Mn²⁺, Fe³⁺ and Cu²⁺ and enhanced by Co²⁺ and Mg²⁺. EDTA reversed the inhibitory effect of the metals. Paper chromatographic and high-performance liquid chromatography analysis of the products of the amylolytic reaction showed the presence of maltotriose, maltotetraose, maltopentaose, maltose and glucose in the starch hydrolysate. Journal of Industrial Microbiology & Biotechnology (2002) 28, 193–200 DOI: 10.1038/sj/jim/7000220 Received 11 December 2000/ Accepted in revised form 22 October 2001     

Thermal biology of genus Liolaemus: A phylogenetic approach reveals advantages of the genus to survive climate change

The trends of body temperatures in the field (T_b) and preferred body temperatures in the laboratory (T_pref) of the genus Liolaemus relative to reproductive mode, air temperature (T_air), precipitation, latitude, and elevation were studied using phylogenetic comparative analysis. Results were discussed in the framework of the evolution of thermal physiology and vulnerability to global climate change. Reproductive mode affects T_b but not T_pref. Whereas T_b and T_pref showed a significant association with T_air, there was no relationship with latitude or elevation.     

Correlational selection on lay date and life-history traits: experimental manipulations of territory and nest site quality

Abundant evidence suggests that females may engage in mate choice to gain nongenetic (material) benefits from high-quality territories; however, the selective consequences that influence those choices are not well understood. We studied the fitness effects of territory quality and incubation temperature on juvenile lizards in nature. We manipulated territory quality by redistributing rocks between pairs of neighboring home ranges. Rock manipulations set up adjacent plots that were either experimentally improved or reduced in quality. We incubated eggs from field-caught gravid females in each of three temperature treatments in the laboratory (low, medium, and high temperature). Progeny were released in either experimentally improved or reduced-quality plots upon hatching, and the following spring we measured survival as a function of egg size and laying date. We conducted concurrent studies of the thermal environment on experimental territories. Improved territories provided significantly more hours for lizards to behaviorally thermoregulate at their preferred body temperature and also provided nest sites with incubation conditions that were closer to optimal compared with reduced-quality plots. Reduced-quality plots were significantly more variable in quality. Finally, we measured significant correlational selection between egg mass and laying date on manipulated plots in two separate years. Results indicate the influence of environmental variation on correlational selection on life-history traits.     

Integrating ecophysiological models into species distribution projections of European reptile range shifts in response to climate change

Uncertainty in projections of global change impacts on biodiversity over the 21st century is high. Improved predictive accuracy is needed, highlighting the importance of using different types of models when predicting species range shifts. However, this is still rarely done. Our approach integrates the outputs of a spatially‐explicit physiologically inspired model of extinction and correlative species distribution models to assess climate‐change induced range shifts of three European reptile species (Lacerta lepida, Iberolacerta monticola, and Hemidactylus turcicus) in the coming decades. We integrated the two types of models by mapping and quantifying agreement and disagreement between their projections. We analyzed the relationships between climate change and projected range shifts. Agreement between model projections varied greatly between species and depended on whether or not they consider dispersal ability. Under our approach, the reliability of predictions is greatest where the predictions of these different types of models converge, and in this way uncertainty is reduced; sites where this convergence occurs are characterized by both current high temperatures and significant future temperature increase, suggesting they may become hotspots of local extinctions. Moreover, this approach can be readily implemented with other types of models.