Spatial distribution of aquatic marine fungi across the western Arctic and sub‐arctic

Fungi are important parasites of primary producers and nutrient cyclers in aquatic ecosystems. In the Pacific‐Arctic domain, fungal parasitism is linked to light intensities and algal stress that can elevate disease incidence on algae and reduce diatom concentrations. Fungi are vastly understudied in the marine realm and knowledge of their function is constrained by the current understanding of fungal distribution and drivers on global scales. To investigate the spatial distribution of fungi in the western Arctic and sub‐Arctic, we used high throughput methods to sequence 18S rRNA, cloned and sequenced 28S rRNA and microscopically counted chytrid‐infected diatoms. We identified a broad distribution of fungal taxa predominated by Chytridiomycota and Dikarya. Phylogenetic analysis of our Chytridiomycota clones placed Arctic marine fungi sister to the order Lobulomycetales. This clade of fungi predominated in fungal communities under ice with low snowpack. Microscopic examination of fixed seawater and sea ice samples revealed chytrids parasitizing diatoms collected across the Arctic that notably infected 25% of a single diatom species in the Bering Sea. The Pezizomycotina comprised > 95% of eukaryotic sequence reads in Greenland, providing preliminary evidence for osmotrophs being a substitute for algae as the base of food webs.     

Comparison of sterol and fatty acid profiles of chytrids and their hosts reveals trophic upgrading of nutritionally inadequate phytoplankton by fungal parasites

Chytrids are ubiquitous fungal parasites in aquatic ecosystems, infecting representatives of all major phytoplankton groups. They repack carbon from inedible phytoplankton hosts into easily ingested chytrid propagules (zoospores), rendering this carbon accessible to zooplankton. Grazing on zoospores may circumvent bottlenecks in carbon transfer imposed by the dominance of inedible or poorly nutritious phytoplankton (mycoloop). We explored qualitative aspects of the mycoloop by analysing lipid profiles (fatty acids, sterols) of two chytrids infecting two major bloom-forming phytoplankton taxa of contrasting nutritional value: the diatom Asterionella formosa and the filamentous cyanobacterium Planktothrix agardhii. The polyunsaturated fatty acid composition of chytrids largely reflected that of their hosts, highlighting their role as conveyors of otherwise inaccessible essential lipids to higher trophic levels. We also showed that chytrids are capable of synthesizing sterols, thus providing a source of these essential nutrients for grazers even when sterols are absent in their phytoplankton hosts. Our findings reveal novel qualitative facets of the mycoloop, showing that parasitic chytrids, in addition to making carbon and essential lipids available from inedible sources, also upgrade their host's biochemical composition by producing sterols de novo, thereby enhancing carbon and energy fluxes in aquatic food webs.     

The ecology of chytrids in aquatic ecosystems: roles in food web dynamics

Chytrids are very important components of freshwater ecosystems, but the ecological significance of this group of fungi is not well understood. This review considers some of the significant environmental factors affecting growth and population composition of chytrids in aquatic habitats. The physical factors include primarily salinity, dissolved oxygen concentration and temperature. The biological factors include the role of chytrids as saprobes and parasites and methods of dispersal of propagules throughout the ecosystem. Dispersal depends upon both zoospores for short range and whole thalli for long range dispersal. Five roles for chytrids in food-web dynamics are proposed: (1) chytrid zoospores are a good food source for zooplankton, (2) chytrids decompose particulate organic matter, (3) chytrids are parasites of aquatic plants, (4) chytrids are parasites of aquatic animals and (5) chytrids convert inorganic compounds into organic compounds. New molecular methods for analysis of chytrid diversity in aquatic environments have the potential to provide accurate quantitative data necessary for better understanding of ecological processes in aquatic ecosystems.     

The parasitic chytrid, Zygorhizidium, facilitates the growth of the cladoceran zooplankter, Daphnia, in cultures of the inedible alga, Asterionella

In food-web studies, parasites are often ignored owing to their insignificant biomass. We provide evidence that parasites may affect trophic transfer in aquatic food webs. Many phytoplankton species are susceptible to parasitic fungi (chytrids). Chytrid infections of diatoms in lakes may reach epidemic proportions during diatom spring blooms, so that numerous free-swimming fungal zoospores (2-3 microm in diameter) are produced. Analysis shows that these zoospores are rich in polyunsaturated fatty acids and sterols (particularly cholesterol), which indicates that they provide excellent food for zooplankters such as Daphnia. In life-table experiments using the large diatom Asterionella formosa as food, Daphnia growth increased significantly in treatments where a parasite was present. By grazing on the zoospores, Daphnia acquired important supplementary nutrients and were able to grow. When large inedible algae are infected by parasites, nutrients within the algal cells are consumed by these chytrids, some of which, in turn, are grazed by Daphnia. Thus, chytrids transfer energy and nutrients from their hosts to zooplankton. This study suggests that parasitic fungi alter trophic relationships in freshwater ecosystems and may be the important components in shaping the community and the food-web dynamics of lakes.     

Light‐driven tipping points in polar ecosystems

Some ecosystems can undergo abrupt transformation in response to relatively small environmental change. Identifying imminent ‘tipping points’ is crucial for biodiversity conservation, particularly in the face of climate change. Here, we describe a tipping point mechanism likely to induce widespread regime shifts in polar ecosystems. Seasonal snow and ice‐cover periodically block sunlight reaching polar ecosystems, but the effect of this on annual light depends critically on the timing of cover within the annual solar cycle. At high latitudes, sunlight is strongly seasonal, and ice‐free days around the summer solstice receive orders of magnitude more light than those in winter. Early melt that brings the date of ice‐loss closer to midsummer will cause an exponential increase in the amount of sunlight reaching some ecosystems per year. This is likely to drive ecological tipping points in which primary producers (plants and algae) flourish and out‐compete dark‐adapted communities. We demonstrate this principle on Antarctic shallow seabed ecosystems, which our data suggest are sensitive to small changes in the timing of sea‐ice loss. Algae respond to light thresholds that are easily exceeded by a slight reduction in sea‐ice duration. Earlier sea‐ice loss is likely to cause extensive regime shifts in which endemic shallow‐water invertebrate communities are replaced by algae, reducing coastal biodiversity and fundamentally changing ecosystem functioning. Modeling shows that recent changes in ice and snow cover have already transformed annual light budgets in large areas of the Arctic and Antarctic, and both aquatic and terrestrial ecosystems are likely to experience further significant change in light. The interaction between ice‐loss and solar irradiance renders polar ecosystems acutely vulnerable to abrupt ecosystem change, as light‐driven tipping points are readily breached by relatively slight shifts in the timing of snow and ice‐loss.     

Phylogenetic Position of Parasitic Chytrids on Diatoms: Characterization of a Novel Clade in Chytridiomycota

Chytrids are true fungi that reproduce with posteriorly uniflagellate zoospores. In the last decade, environmental DNA surveys revealed a large number of uncultured chytrids as well as undescribed order‐level novel clades in Chytridiomycota. Although many species have been morphologically described, only some DNA sequence data of parasitic chytrids are available from the database. We herein discuss five cultures of parasitic chytrids on diatoms Aulacoseira spp. and Asterionella formosa. In order to identify the chytrids examined, thallus morphologies were observed using light microscopy. We also conducted a phylogenetic analysis using 18S, 5.8S, and 28S rDNA sequences to obtain their phylogenetic positions. Based on their morphological characteristics, two cultures parasitic on As. formosa were identified as Rhizophydium planktonicum and Zygorhizidium planktonicum. The other three cultures infecting Aulacoseira spp. (two on Aulacoseira ambigua and the other on Aulacoseira granulata) were regarded as Zygorhizidium aff. melosirae. The results of the molecular phylogenetic analysis revealed that R. planktonicum belonged to the known order Chytridiales, while the two species of Zygorhizidium were placed in a novel clade that was previously reported as an undescribed clade composed of only the environmental sequences of uncultured chytrids.     

Origin and diversification of the cryptic ant genus Stenamma Westwood (Hymenoptera: Formicidae), inferred from multilocus molecular data,biogeography and natural history

The genus Stenamma Westwood comprises a group of cryptic, cold tolerant ants that occur throughout the Holarctic and Middle American regions. Traditional approaches to taxonomy and phylogeny are confounded by multiple factors, including the conservative and often convergent morphology of workers and the rarity of reproductive castes in collections. Monophyly of Stenamma and relationships within the genus are uncertain as nearly all previous taxonomic work has been regional in scope. Furthermore, the sister group to Stenamma has not been well established. Here an extensive molecular dataset consisting of ten genes (～8 kb of data), 48 ingroup taxa (20 Nearctic, 6 Palaearctic and 22 Neotropical) and 8 outgroup taxa (6 closely related non‐Stenamma and 2 additional myrmicines) is used to investigate the broad‐scale phylogeny and evolutionary history of Stenamma. Phylogenetic analysis is performed under maximum likelihood and Bayesian frameworks on individual genes and several alternate concatenated datasets, which are used to investigate the effects of inclusion or exclusion of COI and intronic regions. The timing of Stenamma evolution is inferred in beast and ancestral areas are reconstructed using both the s‐diva and DEC methods, as implemented in the programs rasp and lagrange , respectively. Stenamma is revealed as monophyletic with high support and tentatively is sister to a group of New World species placed currently in Aphaenogaster Mayr and Messor Forel. Within Stenamma, two major clades are recovered: a ‘Holarctic clade’ (HOC) and a ‘Middle American clade’ (MAC). The HOC consists of the European S. striatulum Emery sister to two well‐supported groups, the informal ‘debile’ and ‘brevicorne’ clades. The ‘brevicorne’ clade is entirely Nearctic, whereas the ‘debile’ clade includes both Nearctic and Palaearctic representatives. The MAC occurs from the southern United States to northern South America and, with the exception of S. huachucanum Smith, is almost completely isolated geographically from the HOC. It includes a depauperate northern clade and the ‘MAC core’, which is a diverse assemblage of wet forest adapted species found throughout Central America. Divergence dating and biogeographic reconstruction show that Stenamma is most likely to have originated in the Nearctic at the Eocene–Oligocene boundary (～35 Ma) and diversified more rapidly at 16 and 8 Ma for the HOC and MAC, respectively. Potential environmental factors affecting the evolution of Stenamma include the intense global cooling of the late Eocene combined with aridification and mountain building. The phylogenetic results are discussed in relation to the current Stenamma species groups and several new morphological characters are presented to help in identification.     

Hydrurus‐related golden algae (Chrysophyceae) cause yellow snow in polar summer snowfields

In polar regions, melting snow fields can be occupied by striking blooms of chrysophycean algae, which cause yellowish slush during summer. Samples were harvested at King George Island (South Shetland Islands, Maritime Antarctica) and at Spitsbergen (Svalbard archipelago, High Arctic). The populations live in an ecological niche, where water‐logged snow provides a cold and ephemeral ecosystem, possibly securing the survival of psychrophilic populations through the summer. A physiological adaptation to low temperatures was shown by photosynthesis measurements. The analysis of soluble carbohydrates showed the occurrence of glycerol and sugars, which may play a role in protection against intracellular freezing. Although both populations were made of unicells with Ochromonas‐alike morphology, investigation by molecular methods (18S rDNA sequencing) revealed unexpectedly a very close relationship to the mountain‐river dwelling Hydrurus foetidus (Villars) Trevisan. However, macroscopic thalli typical for the latter species were never found in snow, but are known from nearby localities, and harvested samples of snow algae exposed to dryness evolved a similar pervading, ‘fishy’ smell. Moreover, in both habitats tetrahedal zoospores with four elongate spikes were found, similar to what is known from Hydrurus. Our molecular results go along with earlier reports, where chrysophycean sequences of the same taxonomic affiliation were isolated from snow. This points to a distinct group of photoautotrophic, Hydrurus‐related chrysophytes, which are characteristic for long‐lasting, slowly melting snow packs in certain cold regions of the world.     

Snow and Glacial Algae: A Review1

Snow or glacial algae are found on all continents, and most species are in the Chlamydomonadales (Chlorophyta) and Zygnematales (Streptophyta). Other algal groups include euglenoids, cryptomonads, chrysophytes, dinoflagellates, and cyanobacteria. They may live under extreme conditions of temperatures near 0°C, high irradiance levels in open exposures, low irradiance levels under tree canopies or deep in snow, acidic pH, low conductivity, and desiccation after snow melt. These primary producers may color snow green, golden-brown, red, pink, orange, or purple-grey, and they are part of communities that include other eukaryotes, bacteria, archaea, viruses, and fungi. They are an important component of the global biosphere and carbon and water cycles. Life cycles in the Chlamydomonas–Chloromonas–Chlainomonas complex include migration of flagellates in liquid water and formation of resistant cysts, many of which were identified previously as other algae. Species differentiation has been updated through the use of metagenomics, lipidomics, high-throughput sequencing (HTS), multi-gene analysis, and ITS. Secondary metabolites (astaxanthin in snow algae and purpurogallin in glacial algae) protect chloroplasts and nuclei from damaging PAR and UV, and ice binding proteins (IBPs) and polyunsaturated fatty acids (PUFAs) reduce cell damage in subfreezing temperatures. Molecular phylogenies reveal that snow algae in the Chlamydomonas–Chloromonas complex have invaded the snow habitat at least twice, and some species are polyphyletic. Snow and glacial algae reduce albedo, accelerate the melt of snowpacks and glaciers, and are used to monitor climate change. Selected strains of these algae have potential for producing food or fuel products.     

Marine biogeography of southern Australia: phylogeographical structure in a temperate sea-star

Aim To test whether marine biogeographical patterns observed at the community level are also important within species. It is postulated that historical hydrogeographic barriers have driven in situ diversification. Location The intertidal and shallow subtidal zones of southern Australia, New Zealand and nearby islands. Australia's temperate marine communities are characterized by a high degree of endemism and show strong biogeographical structure along an east–west axis. Methods Phylogeographical analysis of the widespread asteriid sea‐star Coscinasterias muricata Verrill across southern Australia and New Zealand. Forty‐two samples from 27 locations were included in phylogenetic analyses of mitochondrial (CO1; control region) and nuclear (ITS2) DNA sequences. Results Analysis of mtDNA revealed a deep phylogenetic split within Australian C. muricata, strongly correlated with latitude. ‘Northern’ haplotypes (latitude ≤ 37.6° S, nine sites, 15 samples) were 7.3–9.4% divergent from ‘southern’ haplotypes (latitude ≥ 37.6° S, 19 sites, 27 samples), consistent with late Pliocene separation. Eastern and western representatives of the ‘northern’ clade were 0.5–1.0% divergent, probably reflecting Pleistocene isolation. The ‘southern’ clade of Australia is also represented in New Zealand, indicating Pleistocene oceanic dispersal. Nuclear DNA (ITS2) sequences yielded relatively little phylogenetic resolution, but were generally congruent with mtDNA‐based groupings. Main conclusions The phylogeographical pattern detected within Australian C. muricata closely resembles marine biogeographical groupings proposed on the basis of community and species distributions. Recurring evolutionary patterns may have been driven by the hydrographic history of southern Australia. Specifically, we suggest that Plio‐Pleistocene temperature change and the repeated opening and closure of Bass Strait promoted allopatric divergence and perhaps cryptic speciation in C. muricata.     

An assessment of the status of Polycirridae genera (Annelida: Terebelliformia) and evolutionary transformation series of characters within the family

A phylogenetic analysis was performed to determine the monophyly of non‐monotypic genera of the terebelliform family Polycirridae, i.e. Polycirrus, Amaeana, Lysilla, and Hauchiella, and the evolution of characters among members of this clade. The monotypic genera, Enoplobranchus and Biremis, were also included, together with members of both known species in Hauchiella. Representative species were included for remaining genera: 14 species of Polycirrus, six species of Amaeana, and six species of Lysilla. Out‐groups consisted of representatives of Spionidae, Cirratulidae, and Sabellariidae, as well as several species of Telothelepodidae. A total of 40 in‐ and out‐group species were coded for 50 subjects (‘characters’) and 117 subject–predicate relationships (‘states’). Although results are consistent with recent phylogenetic studies within Terebelliformia that suggest Polycirridae monophyly, only Hauchiella was found to be monophyletic, albeit part of the more inclusive clade comprising remaining polycirrid genera. Evolutionary transformation series are discussed for selected characters in relation to the non‐monophyly of Polycirrus, Lysilla, and Amaeana. Implications for the use of supraspecific taxa as ‘taxonomic surrogates’ are highlighted. The definition of Polycirridae is emended. © 2015 The Linnean Society of London     

Systematics and evolution of the cutworm moths (Lepidoptera: Noctuidae): evidence from two protein-coding nuclear genes

Abstract. A broad molecular systematic survey of Noctuidae was undertaken to test recent hypotheses on the problematic definitions and relationships of the subfamilies, with special emphasis on the ‘trifines.’ An initial hypothesis of noctuid classification to the subtribal level was synthesized from recent reviews, and then sampled as broadly as possible. Concatenated sequences for the nuclear genes elongation factor‐1α (EF‐1α; 1200 bp) and dopa decarboxylase (DDC; 700–1100 bp) were analysed for a total of 146 exemplar species, twice that of a previous study. Trees were estimated using likelihood, distance, and both equally weighted and ‘six‐parameter’ parsimony. Of the 144 possible nodes, bootstrap support (BP) was ≥ 50% for ～80, and ≥ 80% for ～60. There was very strong support (BP ≥ 90%) for an ‘L.A.Q.’ clade encompassing nearly all quadrifine noctuids plus Arctiidae and Lymantriidae, decisively rendering Noctuidae paraphyletic. We present a new classification for Noctuoidea in which Noctuidae sensu stricto is restricted to trifines; most quadrifine subfamilies are raised to full families. Within the ‘L.A.Q.’ clade, Aganainae and Herminiinae were strongly grouped, but other relationships were weakly supported, probably due to limited taxon sampling. Nolidae and Euteliinae + Stictopterinae are generally grouped with the ‘L.A.Q.’ clade, but with weak support. All analyses favour the broadest definitions proposed for the trifine clade (our Noctuidae sensu stricto) although support is not strong, except that the exemplar of Eustrotiinae: Eublemmini is placed securely in the ‘L.A.Q.’ clade. Numerous recent proposals for dismantling and recombining the ‘Hampsonian’ traditional trifine subfamilies are strongly supported, most notably a broadly defined ‘true cutworm’ clade (Noctuinae s.l.), encompassing the greater part of the traditional subfamilies Amphipyrinae, Cuculliinae, Hadeninae and Noctuinae s.s. (BP ≥ 95%). Within this clade there is strong support for Apameini s.s.+ Xylenini s.l. and for Noctuinae s.s. and divisions thereof, but little support for monophyly or subdivision of Hadeninae. Noctuinae s.l. invariably are allied with Heliothinae, scattered remnants of the traditional Amphipyrinae, and several smaller groups in a broader ‘pest clade’, albeit with weak support. Relationships among the remaining ‘lower’ trifines are not strongly resolved. Mapping of a preliminary synopsis of species diversities, host use patterns and latitudinal distributions on the phylogeny suggests that the diversification of trifines may have been promoted, to a degree unique among Macrolepidoptera, by the Tertiary expansion of seasonal, open habitats and their associated herbaceous floras.     

The phylogenetic placement of Psechridae within Entelegynae and the convergent origin of orb‐like spider webs

Evolutionary convergence of phenotypic traits provides evidence for their functional success. The origin of the orb web was a critical event in the diversification of spiders that facilitated a spectacular radiation of approximately 12 000 species and promoted the evolution of novel web types. How the orb web evolved from ancestral web types, and how many times orb‐like architectures evolved in spiders, has been debated for a long time. The little known spider genus Fecenia (Psechridae) constructs a web that resembles the archetypical orb web, but morphological data suggest that Psechridae (Psechrus + Fecenia) does not belong in Orbiculariae, the ‘true orb weavers’, but to the ‘retrolateral tibial apophysis (RTA) clade’ consisting mostly of wandering spiders, but also including spiders building less regular webs. Yet, the data are sparse and no molecular phylogenetic study has estimated Fecenia's exact position in the tree of life. Adding new data to sequences pulled from GenBank, we reconstruct a phylogeny of Entelegynae and phylogenetically test the monophyly and placement of Psechridae, and in doing so, the alternative hypotheses of monophyletic origin of the orb web and the pseudo‐orb versus their independent origins, a potentially spectacular case of behavioural convergence. We also discuss the implications of our results for Entelegynae systematics. Our results firmly place a monophyletic Psechridae within the RTA clade, phylogenetically distant from true orb weavers. The architectural similarities of the orb and the pseudo‐orb are therefore clearly convergent, as also suggested by detailed comparisons of these two web types, as well as the spiders' web‐building behaviours and ontogenetic development. The convergence of Fecenia webs with true orbs provides a remarkable opportunity to investigate how these complex sets of traits may have interacted during the evolution of the orb.     

Brandtia ciliaticola gen. et sp. nov. (Chlorellaceae,Trebouxiophyceae) a common symbiotic green coccoid of various ciliate species

Many freshwater protists harbor unicellular green algae within their cells and these host‐symbiont relationships slowly are becoming better understood. Recently, we reported that several ciliate species shared a single species of symbiotic algae. Nonetheless, the algae from different host ciliates were each distinguishable by their different genotypes, and these host‐algal genotype combinations remained unchanged throughout a 15‐month period of sampling from natural populations. The same algal species had been reported as the shared symbiont of several ciliates from a remote lake. Consequently, this alga appears to play a key role in ciliate‐algae symbioses. In the present study, we successfully isolated the algae from ciliate cells and established unialgal cultures. This species is herein named Brandtia ciliaticola gen. et sp. nov. and has typical ‘Chlorella‐like’ morphology, being a spherical autosporic coccoid with a single chloroplast containing a pyrenoid. The alga belongs to the Chlorella‐clade in Chlorellaceae (Trebouxiophyceae), but it is not strongly connected to any of the other genera in this group. In addition to this phylogenetic distinctiveness, a unique compensatory base change in the SSU rRNA gene is decisive in distinguishing this genus. Sequences of SSU‐ITS (internal transcribed spacer) rDNA for each isolate were compared to those obtained previously from the same host ciliate. Consistent algal genotypes were recovered from each host, which strongly suggests that B. ciliaticola has established a persistent symbiosis in each ciliate species.     

Craniid brachiopods: aspects of clade structure and distribution reflect continental drift (Brachiopoda: Craniiformea)

We present maximum likelihood and Bayesian inference relative time‐tree analyses of aligned gene sequences from a worldwide collection of craniiform brachiopods belonging to two genera, Novocrania and Neoancistrocrania. Sequences were obtained from one mitochondrial and three nuclear‐encoded ribosomal RNA genes from varying numbers of specimens. Data‐exploration by network (splits) analyses indicates that each gene identifies the same divergent clades and (with one minor exception) the same inter‐clade relationships. Neoancistrocrania specimens were found only in the Pacific Ocean, near Japan, on the Norfolk and Chesterfield Ridges, and near the Solomon Islands. The Novocrania clades, in approximate order of increasing distance from the root comprise 1. a ‘Northern’ clade of animals collected in the NE. Atlantic, W. Mediterranean and Adriatic; 2. a ‘Tethyan’ clade comprising animals from the E. Mediterranean, Cape Verde islands and the Caribbean (Belize and Jamaica); 3. a ‘NE. Pacific’ clade containing animals from Vancouver Island and from localities near Japan and south of Taiwan; 4. a ‘Southern’ clade that contains two widely separated subclades, one from New Zealand and the other with an extraordinarily wide distribution, ranging from near Japan in the north to the Chesterfield Ridge and Solomon Islands in the West, and in the East to the Galapagos Islands, the coast of South America (Chile) and Richardson seamount (off South Africa) in the South Atlantic. To the South, members of this clade were found in the Weddell, Scotia and Bellinghausen Antarctic Seas. The root of the extant craniid radiation was previously found (by relaxed‐clock analysis) to lie on the branch connecting the two genera so that, in effect, the one clade of Neoancistrocrania serves to polarise evolutionary relationships within the several clades of Novocrania. As previously suggested, all results confirm that Neoancistrocrania is sister to the ‘Northern’ Novocrania clade, and this leads to a proposal that Neoancistrocrania represents one extreme of a wide range of variation in ancestral ventral valve mineralisation, speciation (～90 Ma) resulting from competitive exclusion in rapidly‐growing reef environments. To the extent possible, the identified molecular clades are correlated with named species of Novocrania. The reproductive and population biology of craniid brachiopods is not well known, but from available evidence they are considered to have low‐dispersal potential and, except in enclosed localities such as cold‐water fjords, to have small effective population sizes, features which are consistent with the observed divergent populations in well‐separated localities. Exceptionally slow craniid molecular (rDNA) evolution is suggested by the short branch of Novocrania where it has been used as an outgroup for large‐scale analyses of metazoans. Slow molecular evolution is also indicated by the existence of a distinct Tethyan clade, reflecting restricted dispersal at former times, and by the uniform, short, genetic distances and exceptionally wide geographical distribution of the Southern clade. Thus, the geographical distribution and phylogenetic divergence of craniid brachiopods is an example of phylotectonics, in which relationships revealed by phylogenetic analyses reflect opportunities for dispersal and settlement that were created by tectonic plate movements associated, in this case, with opening and closure of Tethys and the breakup of Gondwana. Molecular dating of craniid divergences and radiochemical dating of tectonic events thus illuminate one another. © 2014 The Linnean Society of London     

Effects of snow removal and algal photoacclimation on growth and export of ice algae

Net growth of ice algae in response to changes in overlying snow cover was studied after manipulating snow thickness on land-fast, Arctic sea ice. Parallel laboratory experiments measured the effect of changing irradiance on growth rate of the ice diatom, Nitzschia frigida. After complete removal of thick snow (≥9 cm), in situ ice algae biomass declined (over 7–12 days), while removal of thin snow layers (4–5 cm), or partial snow removal, increased net algal growth. Ice bottom ablation sometimes followed snow removal, but did not always result in net loss of algae. Similarly, in laboratory experiments, small increases in irradiance increased algal growth rate, while greater light shifts suppressed growth for 3–6 days. However, N. frigida could acclimate to relatively high irradiance (110 μmol photons m² s⁻¹). The results suggest that algal loss following removal of a thick snow layer was due to the combination of photoinhibition and bottom ablation. The smaller relative increase in irradiance after removal of thin or partial snow layers allowed algae to maintain high specific-growth rates that compensated for loss from physical mechanisms. Thus, the response of ice algae to snow loss depends both on the amount of change in snow depth and algal photophysiology. The complex response of ice algae growth and export loss to frequently changing snow fields may contribute to horizontal and temporal patchiness of ecologically and biogeochemically important variables in sea ice and should be considered in predictions of how climate change will affect Arctic marine ecosystems.     

Functional effects of parasites on food web properties during the spring diatom bloom in Lake Pavin: a linear inverse modeling analysis

This study is the first assessment of the quantitative impact of parasitic chytrids on a planktonic food web. We used a carbon-based food web model of Lake Pavin (Massif Central, France) to investigate the effects of chytrids during the spring diatom bloom by developing models with and without chytrids. Linear inverse modelling procedures were employed to estimate undetermined flows in the lake. The Monte Carlo Markov chain linear inverse modelling procedure provided estimates of the ranges of model-derived fluxes. Model results support recent theories on the probable impact of parasites on food web function. In the lake, during spring, when 'inedible' algae (unexploited by planktonic herbivores) were the dominant primary producers, the epidemic growth of chytrids significantly reduced the sedimentation loss of algal carbon to the detritus pool through the production of grazer-exploitable zoospores. We also review some theories about the potential influence of parasites on ecological network properties and argue that parasitism contributes to longer carbon path lengths, higher levels of activity and specialization, and lower recycling. Considering the "structural asymmetry" hypothesis as a stabilizing pattern, chytrids should contribute to the stability of aquatic food webs.