Microclimate and limits to photosynthesis in a diverse community of hypolithic cyanobacteria in northern Australia

Hypolithic microbes, primarily cyanobacteria, inhabit the highly specialized microhabitats under translucent rocks in extreme environments. Here we report findings from hypolithic cyanobacteria found under three types of translucent rocks (quartz, prehnite, agate) in a semiarid region of tropical Australia. We investigated the photosynthetic responses of the cyanobacterial communities to light, temperature and moisture in the laboratory, and we measured the microclimatic variables of temperature and soil moisture under rocks in the field over an annual cycle. We also used molecular techniques to explore the diversity of hypolithic cyanobacteria in this community and their phylogenetic relationships within the context of hypolithic cyanobacteria from other continents. Based on the laboratory experiments, photosynthetic activity required a minimum soil moisture of 15% (by mass). Peak photosynthetic activity occurred between approximately 8°C and 42°C, though some photosynthesis occurred between ?1°C and 51°C. Maximum photosynthesis rates also occurred at light levels of approximately 150–550 μmol m^?2 s^?1. We used the field microclimatic data in conjunction with these measurements of photosynthetic efficiency to estimate the amount of time the hypolithic cyanobacteria could be photosynthetically active in the field. Based on these data, we estimated that conditions were appropriate for photosynthetic activity for approximately 942 h (～75 days) during the year. The hypolithic cyanobacteria community under quartz, prehnite and agate rocks was quite diverse both within and between rock types. We identified 115 operational taxonomic units (OTUs), with each rock hosting 8–24 OTUs. A third of the cyanobacteria OTUs from northern Australia grouped with Chroococcidiopsis, a genus that has been identified from hypolithic and endolithic communities from the Gobi, Mojave, Atacama and Antarctic deserts. Several OTUs identified from northern Australia have not been reported to be associated with hypolithic communities previously.     

Homogeneous detection of cyanobacterial DNA via polymerase chain reaction

Aims: To design a primer set enabling the identification through PCR of high‐quality DNA for routine and high‐throughput genomic screening of a diverse range of cyanobacteria. Methods and Results: A codon‐equivalent multiple alignment of the phycocyanin alpha‐subunit coding sequence (cpcA) of 22 cyanobacteria was generated and analysed to produce a single degeneracy primer set with virtually uniform product size. Also, an 18S ribosomal RNA detection set is proposed for rejecting false positives. The primer sets were tested against five diverse cyanobacteria, Chlorella vulgaris, Saccharomyces cerevisiae, and Escherichia coli. All five cyanobacteria showed positive amplification of cpcA product with homogeneous fragment length, and no products were observed for any other organism. Additionally, the only product formation observed for the 18S rRNA set was in C. vulgaris and S. cerevisiae. Conclusions: The newly proposed primer set served as effective check primers for cyanobacteria. Cyanobacteria gDNA had a positive, homogenous result, while other bacteria, eukaryotes and alga tested were negative. Significance and Impact of the Study: These novel, broad‐spectrum primers will greatly increase the utility of PCR on newly discovered cyanobacterial species.     

Scale‐dependent spatial patterns in benthic communities around a tropical island seascape

Understanding and predicting patterns of spatial organization across ecological communities is central to the field of landscape ecology, and a similar line of inquiry has begun to evolve sub‐tidally among seascape ecologists. Much of our current understanding of the processes driving marine community patterns, particularly in the tropics, has come from small‐scale, spatially‐discrete data that are often not representative of the broader seascape. Here we expand the spatial extent of seascape ecology studies and combine spatially‐expansive in situ digital imagery, oceanographic measurements, spatial statistics, and predictive modeling to test whether predictable patterns emerge between coral reef benthic competitors across scales in response to intra‐island gradients in physical drivers. We do this around the entire circumference of a remote, uninhabited island in the central Pacific (Jarvis Island) that lacks the confounding effects of direct human impacts. We show, for the first time, that competing benthic groups demonstrate predictable scaling patterns of organization, with positive autocorrelation in the cover of each group at scales < ~1 km. Moreover, we show how gradients in subsurface temperature and surface wave power drive spatially‐abrupt transition points in group dominance, explaining 48–84% of the overall variation in benthic cover around the island. Along the western coast, we documented ten times more sub‐surface cooling‐hours than any other part of the coastline, with events typically resulting in a drop of 1–4°C over a period of < 5 h. These high frequency temperature fluctuations are indicative of upwelling induced by internal waves and here result in localized nitrogen enrichment (NO₂ + NO₃) that promotes hard coral dominance around 44% of the island's perimeter. Our findings show that, in the absence of confounding direct human impacts, the spatial organization of coral reef benthic competitors are predictable and somewhat bounded across the seascape by concurrent gradients in physical drivers.     

Age‐dependent trajectories differ between within‐pair and extra‐pair paternity success

Reproductive success is associated with age in many taxa, increasing in early life followed by reproductive senescence. In socially monogamous but genetically polygamous species, this generates the interesting possibility of differential trajectories of within‐pair and extra‐pair siring success with age in males. We investigate these relationships simultaneously using within‐individual analyses with 13 years of data from an insular house sparrow (Passer domesticus) population. As expected, we found that both within‐ and extra‐pair paternity success increased with age, followed by a senescence‐like decline. However, the age trajectories of within‐ and extra‐pair paternity successes differed significantly, with the extra‐pair paternity success increasing faster, although not significantly, in early life, and showing a delayed decline by 1.5 years on average later in life compared to within‐pair paternity success. These different trajectories indicate that the two alternative mating tactics should have age‐dependent pay‐offs. Males may partition their reproductive effort between within‐ and extra‐pair matings depending on their current age to reap the maximal combined benefit from both strategies. The interplay between these mating strategies and age‐specific mortality may explain the variation in rates of extra‐pair paternity observed within and between species.     

Inhibition of mitochondrial complex I improves glucose metabolism independently of AMPK activation

Accumulating evidences showed metformin and berberine, well‐known glucose‐lowering agents, were able to inhibit mitochondrial electron transport chain at complex I. In this study, we aimed to explore the antihyperglycaemic effect of complex I inhibition. Rotenone, amobarbital and gene silence of NDUFA13 were used to inhibit complex I. Intraperitoneal glucose tolerance test and insulin tolerance test were performed in db/db mice. Lactate release and glucose consumption were measured to investigate glucose metabolism in HepG2 hepatocytes and C2C12 myotubes. Glucose output was measured in primary hepatocytes. Compound C and adenoviruses expressing dominant negative AMP‐activated protein kinase (AMPK) α1/2 were exploited to inactivate AMPK pathway. Cellular NAD⁺/NADH ratio was assayed to evaluate energy transforming and redox state. Rotenone ameliorated hyperglycaemia and insulin resistance in db/db mice. It induced glucose consumption and glycolysis and reduced hepatic glucose output. Rotenone also activated AMPK. Furthermore, it remained effective with AMPK inactivation. The enhanced glycolysis and repressed gluconeogenesis correlated with a reduction in cellular NAD⁺/NADH ratio, which resulted from complex I suppression. Amobarbital, another representative complex I inhibitor, stimulated glucose consumption and decreased hepatic glucose output in vitro, too. Similar changes were observed while expression of NDUFA13, a subunit of complex I, was knocked down with gene silencing. These findings reveal mitochondrial complex I emerges as a key drug target for diabetes treatment. Inhibition of complex I improves glucose homoeostasis via non‐AMPK pathway, which may relate to the suppression of the cellular NAD⁺/NADH ratio.     

Common and rare species respond to similar niche processes in macroinvertebrate metacommunities

Ecologists have long investigated why communities are composed of a few common species and many rare species. Most studies relate rarity to either niche differentiation among species or spatial processes. There is a parallel between these processes and the processes proposed to explain the structure of metacommunities. Based on a metacommunity perspective and on data on stream macroinvertebrates from different regions of Brazil, we answer two questions. 1) Are sets of common and rare species affected by similar niche and spatial processes? 2) How does the community composition of common and of rare species differ? The main hypothesis we test is that common species are mainly affected by environmental factors, whereas rare species are mostly influenced by dispersal limitation. We used variation partitioning to determine the proportion of variation explained by the environment and space in common and rare species matrices. Contrary to our expectations, evidence supported the idea that both common and rare species are affected mainly by environmental factors, even after controlling for the differing information content between common and rare species matrices. Moreover, the abundance of some common species is also a good predictor of variation in rare species matrices. Niche differences are unlikely to be the sole cause of patterns of rarity in these metacommunities. We suggest that sets of common and rare species react to similar major environmental gradients and that rare species also respond to processes that operate at a more fine‐grained spatial scale, particularly biotic interactions. We extend the view that species sorting is the dominant process structuring metacommunities and argue that future studies focusing on rarity would benefit from a metacommunity perspective.