Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the world's largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the world's great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.     

The collapse of benthic macroalgal blooms in response to self‐shading

1. Our goal was to use physiological indicators [photosynthesis–irradiance (P–I) response, nutrient status], population level feedbacks (self‐shading) and ambient environmental conditions (dissolved nutrients, light, temperature) to improve our understanding of the seasonal and spatial population dynamics of Cladophora. 2. Cladophora grew in three distinct phases, rapid growth early in the season (May–July), a mid‐season population collapse (July–August) and autumn re‐growth. Across all sites and dates, mean net maximal photosynthesis [P_M (NET)] was 6.9 ± 3.9 mg O₂ g DM^?1 h^?1, and α was 0.055 ± 0.025 mg O₂ g DM^?1 μm photons^?1 m^?2. Mean values for critical irradiance (I_CR) and the half‐saturation light intensity (I_K), were 42.9 ± 32.1 and 189.3 ± 123.8 μm photons^?1 m^?2 s^?1 respectively. 3. At most sites growth was phosphorus‐limited. Values of α were significantly higher at a site influenced by a nutrient enriched river plume, where algal growth was phosphorus‐sufficient. 4. Photoinhibition was not apparent in any of our P–I experiments. Even if photoinhibition had been apparent during in vitro P–I experiments, population level photosynthetic rates in the field would be little affected because intense self‐shading restricts inhibiting irradiances to the upper few mm–cm of the algal canopy. 5. Our physiological (P–I response) experiments contradicted previous assertions that high ambient temperatures, or nutrient deficiency, were primary causes of mid‐summer sloughing. In our study, sloughing occurred simultaneously at nutrient enriched and nutrient deficient sites, at temperatures well below critical values found during in vitro experiments, and our indicator of physiological condition (P–I response) remained unchanged leading up to, or immediately after, the sloughing event. 6. Self‐shading can reduce the convexity of the P–I response within in vitro incubations, even when the amount of algal material is low. Our experiments used 0.08 g DM of algal material that formed clumps c. 1 cm thick. Under these conditions, we estimated negligible (<1%) effects on P_M, a 12% reduction in apparent values of α, and 14% and 17% increases in values of the α‐dependent terms I_CR and I_K, respectively. 7. Our results are consistent with the hypothesis that a population‐level negative feedback (self‐shading) is responsible for sloughing in dense macroalgal beds. Sloughing was probably inevitable once macroalgal bed density and thickness surpassed a critical threshold. Cells towards the base of the bed received insufficient light to maintain metabolic balance, began to decay and weaken, and became increasingly susceptible to physical detachment from shear stress.     

Low Genotyping Error Rates and Noninvasive Sampling in Bighorn Sheep

Abstract Noninvasive DNA sampling allows studies of natural populations without disturbing the target animals. Unfortunately, high genotyping error rates often make noninvasive studies difficult. We report low error rates (0.0–7.5%/locus) when genotyping 18 microsatellite loci in only 4 multiplex polymerase chain reaction amplifications using fecal DNA from bighorn sheep (Ovis canadensis). The average locus-specific error rates varied significantly between the 2 populations (0.13% vs. 1.6%; P < 0.001), as did multi-locus genotype error rates (2.3% vs. 14.1%; P < 0.007). This illustrates the importance of quantifying error rates in each study population (and for each season and sample preservation method) before initiating a noninvasive study. Our error rates are among the lowest reported for fecal samples collected noninvasively in the field. This and other recent studies suggest that noninvasive fecal samples can be used in species with pellet-form feces for nearly any study (e.g., of population structure, gene flow, dispersal, parentage, and even genome-wide studies to detect local adaptation) that previously required high-quality blood or tissue samples.     

Clutch size manipulation, hatching success and offspring phenotype in the ball python (Python regius)

In a diverse array of avian and mammalian species, experimental manipulations of clutch size have tested the hypothesis that natural selection should adjust numbers of neonates produced so as to maximize the number of viable offspring at the end of the period of parental care. Reptiles have not been studied in this respect, probably because they rarely display parental care. However, females of all python species brood their eggs until hatching, but they do not care for their neonates. This feature provides a straightforward way to experimentally increase or reduce clutch size to see whether the mean clutch size observed in nature does indeed maximize hatching success and/or optimize offspring phenotypes. Eggs were removed or added to newly laid clutches of Ball Pythons ( Python regius ) in tropical Africa (nine control clutches, eight with 50% more eggs added, six with 42% of eggs removed). All clutches were brooded by females throughout the 2-month incubation period. Experimental manipulation of clutch-size did not significantly affect the phenotypes (morphology, locomotor ability) of hatchlings, but eggs in 'enlarged' clutches hatched later, and embryos were more likely to die before hatching. This mortality was due to desiccation of the eggs, with females being unable to cover 'enlarged' clutches sufficiently to retard water loss. Our results support the notion of an optimal clutch size, driven by limitations on parental ability to care for the offspring. However, the proximate mechanisms that generate this optimum value differ from those previously described in other kinds of animals. © 2003 The Linnean Society of London . Biological Journal of the Linnean Society 2003, 78 , 263–272.     

Genetic structure among populations in the endemic Hawaiian Plantago lineage: insights from microsatellite variation

Endemic Hawaiian species in the genus Plantago show considerable morphological and ecological diversity. Despite their variation, a recent phylogenetic analysis based on DNA sequence data showed that the group is monophyletic and that sequence variation among species and morphotypes is low. This lack of sequence polymorphisms resulted in an inability to resolve species and population affinities within the most recently derived clade of this lineage. To assess species boundaries, population genetic structure and interpopulation connectivity among the morphologically and ecologically distinct populations within this clade, genetic variation was examined using eight microsatellite loci. Within‐population genetic diversity was found to be lowest in the Maunaiu, Hawai'i population of the endangered P. hawaiensis, and highest in the large P. pachyphylla population from 'Eke, West Maui. Isolation by distance across the range of populations was detected and indicated restricted dispersal. This result is likely to be attributable to few interisland dispersal events in the evolutionary history of this lineage. Genetic differentiation within islands tended to be higher among populations occurring in contrasting bog and woodland habitats, suggesting ecological barriers to gene flow and the potential role of ecological divergence in population diversification. Overall, these results are consistent with findings from phylogenetic analysis of the entire lineage. Our data bring new insights regarding patterns of dispersal and population genetic structure to this endemic and endangered group of island taxa. As island environments become increasingly fragmented, information of this type has important implications for the successful management of these fragile populations and habitats.     

Morphological functions of gibberellins in leptosporangiate fern gametophytes: insights into the evolution of form and gender expression

In addition to genetic load, the induction of maleness in leptosporangiate gametophytes by the pheromone antheridiogen may facilitate rates of outcrossing similar to those found in angiosperms. The antheridiogens that have been chemically identified are similar to gibberellins and probably evolved from this common plant hormone. The purposes of this study were to determine the functions of endogenous gibberellins in morphological development and gender expression in leptosporangiate fern gametophytes and to elucidate how antheridiogens may have evolved from gibberellin precursors. We grew gametophytes of Osmunda regalis and Athyrium filix‐femina on nutrient agar enriched with APOGEE, which blocks gibberellin synthesis. Osmunda regalis is a member of Osmundaceae, the only family in Osmundales, the sister group of all remaining extant leptosporangiate ferns. This family possesses a male‐first gender in isolation and lacks any known antheridiogen systems. In contrast, A. filix‐femina is a member of a derived family, Woodsiaceae, which possesses antheridiogen systems. Disruption of gibberellin synthesis retarded notch development and expression of both maleness and femaleness (i.e. gender status) in both species. On the basis of these results, we offer a simple model of gametophyte evolution driven by gender‐based fitness gain curves and the influence of exogenous gibberellins. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 599–615.     

Contrasting patterns of population structure in the montane caddisflies Hydropsyche tenuis and Drusus discolor in the Central European highlands

1. In this study, we compared mitochondrial sequence data (cytochrome oxidase I) to infer the population structure of the two montane caddisflies Hydropsyche tenuis and Drusus discolor. The two species are contrasting examples of montane aquatic insects with insular distributions: D. discolor is restricted to altitudes above 600 m, H. tenuis is limited to the same mountain ranges in Central Europe but inhabits lower altitudes. 2. In particular, we ask whether these two species with similar regional distributions show similar patterns of population structure and haplotype diversity, and whether any differences can be attributed to population history and/or autecology. 3. To determine the population structure of both species, we applied conventional population genetics analyses to mitochondrial sequence data. We collected and sampled 121 specimens of H. tenuis from 29 sites in 10 different regions of the Central European highlands and 138 individuals of D. discolor from 40 sites in 11 different regions. 4. Nine unique haplotypes were identified for H. tenuis and 34 for D. discolor. There were eight variable positions in H. tenuis and 41 in D. discolor. The maximum difference between haplotypes was 0.8% (4 bp) for H. tenuis and 4.2% (21 bp) for D. discolor. We observed haplotype overlap between geographic regions for both species. Analysis of molecular variance showed that two‐thirds of the total variance in H. tenuis was found among regions while in D. discolor, a larger portion of variance was found within regions and populations due to a higher number of haplotypes observed within regions. Mantel test showed a significant relationship between genetic and geographic distance in D. discolor, but no significant relationship in H. tenuis. 5. Our analyses show that, despite their very similar overall distribution pattern in Europe, the two species exhibit distinct population structures, which may reflect differences in phylogeographic history, dispersal capabilities, habitat specifity or within‐region geographic occurrence.     

Exploitation of prey by a river bird, the dipper Cinclus cinclus (L.), along acidic and circumneutral streams in upland Wales

SUMMARY. 1. The diet of the Eurasian dipper Cinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time-activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem. 2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr^?1 depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m²), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m^?2. 3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium-rich prey such as fish prior to egg formation. 4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m^?2 for Plecoptera. 0.02–0.22 g m^?2 for Ephemeroptera. 0.59–1.11 g m^?2 for Trichoptera and 0–0.78 g m^?2 for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce. 5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds. 6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of considerable research effort.     

Ecology of leaf pack macroinvertebrate communities in streams of the Fraser River Basin, British Columbia

1. To characterise geographic and small scale variation in the structure of macroinvertebrate communities in stream leaf packs, we collected one to three natural leaf pack communities from 119 reference streams in the Fraser River Basin and quantified their variability and correlation with aspects of the stream environment at several scales. We also sampled leaf packs in 19 test streams in the same geographic area exposed to stressors (nine logged, seven farmed, three mined catchments) to evaluate the leaf pack community as a tool for bioassessment. 2. There was substantial variation in the composition of invertebrate communities in leaf packs among reference streams of the Fraser River Basin. Capnia and Zapada (stoneflies), Baetis and Ephemerella (mayflies) and Tvetnia (midge) were the most common taxa found in the leaf packs. There were three types of assemblages identified by non‐metric multidimensional scaling; Capnia, Baetis and Ephemerella communities. 3. Leaf pack communities from the 19 test streams were plotted on a non‐metric multidimensional scaling ordination of the reference communities, and 14 of 19 sites fell outside the 80% confidence ellipse of the reference sites, including eight of nine logged, four of seven farmed and one of three mined catchments. Most of these streams plotted on the ordination near the Ephemerella reference communities. Reference stream communities had a similar number of genera per leaf pack (12.0) and genera per site (18.7) as the test streams (12.6 genera per leaf pack and 18.7 genera per site). Among the test sites, the farmed catchments had higher genera per leaf pack (17.8) and genera per site (21.9) than either the logged (11.5 genera per leaf pack; 19.9 genera per site) or mined (3.4 genera per leaf pack; 7.7 genera per site) catchments. 4. Heterogeneity of leaf pack communities within a site decreased as the number of genera found at the site increased. This was determined by allometric regression of the number of genera found at a site on the maximum number of genera possible, given the average number found per leaf pack. 5. There was a significant relationship between the composition of the leaf pack invertebrate community and stream geography (latitude, longitude, altitude, stream order). Canonical correspondence analysis showed differences among ‘big river’, ‘mountain stream’ and ‘southern’ communities. 6. There was no relationship between the composition of the leaf pack invertebrate community and stream channel and flow characteristics (bank dimensions, flow, slope). There was a significant relationship between the composition of the leaf pack invertebrate community and water quality of the stream (oxygen, nitrogen, phosphorus, conductivity, pH, temperature). ‘Cold, oxygen rich water’ communities were distinguishable from communities in streams with warmer, lower oxygen concentration. ‘High nutrient water’ communities were also distinct from communities in low nutrient streams. There was no relationship between the composition of the leaf pack invertebrate community and the nature of the leaf pack itself (i.e. morphology, decomposition, coniferous needle content). 7. Invertebrate communities in leaf packs show substantial, interpretable variation among reference streams. They are sensitive to human stressors at a landscape scale such as forestry and agriculture. Their diversity and composition varies at different spatial scales in a way that is at least partially explained by the environment of the stream and its catchment area.     

Extracellular Matrix Constituents and Pigment Cell Expression in Primary Cell Culture

Three types of pigment cells were isolated and cultured from larval Rana pipiens, and their attachment, maintenance, and proliferation were examined in the presence of extra-cellular matrix constituents (ECMs) in primary cell culture. The initial profile of pigment cell types present on day 2 of culture reflects the relative attachment of the cells to the dishes. Changes in the numbers of cells present after day 2 reflects the influence of factors present in the culture media on the maintenance, proliferation, or detachment of each type of pigment cell. Fetal bovine serum (FBS) promoted melanophore expression, but inhibited iridophore expression. FBS had no effect on xanthophores. In contrast, ventral skin conditioned medium (VCM), which contains melanization inhibiting factor, strongly stimulated iridophore expression, while it markedly inhibited melanophore expression. VCM had little effect on xanthophores. Of the ECMs tested, collagen type I had no effect on pigment cells. Fibronectin slightly inhibited melanophore expression, while it moderately stimulated iridophores and xanthophores. The stimulatory effect of fibronectin was not as strong as that of FBS or VCM. Laminin was also tested; however, it did not allow pigment cells to attach to the dishes, at least under the culture conditions utilized. The results of these experiments are discussed in terms of the general mechanisms of pigment pattern formation.