Lack of intermediate-scale disturbance data prevents robust extrapolation of plot-level tree mortality rates for old-growth tropical forests

Lloyd et al. (2009) question the methods, concepts and conclusions of Fisher et al. (2008) . We address these assertions, and place our work into a broader context. We demonstrate the veracity of Fisher et al. , and further show that lack of data for intermediate-scale tree mortality disturbance events for old-growth tropical forests might prevent robust extrapolation of forest plot biomass accumulation data, and accurate estimates of distribution parameters such as power-law exponents ( α ).     

Intergenerational reproductive parasitism in a stingless bee

Insect colonies have been traditionally regarded as closed societies comprised of completely sterile workers ruled over by a single once-mated queen. However, over the past 15 years, microsatellite studies of parentage have revealed that this perception is far from the truth ( Beekman & Oldroyd 2008 ). First, we learned that honey bee queens are far more promiscuous than we had previously imagined ( Estoup et al. 1994 ), with one Apis dorsata queen clocked at over 100 mates ( Wattanachaiyingcharoen et al. 2003 ). Then Oldroyd et al. (1994) reported a honey bee colony from Queensland, where virtually all the males were sons of a single patriline of workers – a clear case of a cheater mutant that promoted intra-colonial reproductive parasitism. Then we learned that both bumble bee colonies ( Lopez-Vaamonde et al. 2004 ) and queenless honey bee colonies ( Nanork et al. 2005, 2007 ) are routinely parasitized by workers from other nests that fly in and lay male-producing eggs that are then reared by the victim colony. There is even evidence that in a thelytokous honey bee population, workers lay female-destined eggs directly into queen cells, thus reincarnating themselves as a queen ( Jordan et al. 2008 ). And let us not forget ants, where microsatellite studies have revealed equally bizarre and totally unexpected phenomena (e.g. Cahan & Keller 2003 ; Pearcy et al. 2004 ; Fournier et al. 2005 ). Now, in this issue, Alves et al. (2009) use microsatellites to provide yet another shocking and completely unexpected revelation about the nefarious goings-on in insect colonies: intergenerational reproductive parasitism by stingless bee workers.     

Rewiring bacteria, two components at a time

In this issue, Skerker et al. (2008) present a rational method for rewiring the protein-protein interactions and output responses of prokaryotic two-component signal transduction systems. This work has important implications for understanding the specificity of protein interactions and for designing protein-based synthetic signaling cascades.     

New insight into the molecular pathways of metallothionein-mediated neuroprotection and regeneration

There is a large body of evidence demonstrating that metallothioneins (MTs) expressed in astrocytes following CNS injury, exhibit both neuroprotective and neuroregenerative properties and are critical for recovery outcomes. As these proteins lack signal peptides, and have well characterized free radical scavenging and heavy metal binding properties, the neuroprotective functions of MTs have been attributed to these intracellular roles. However, there is an increasing realization that the neuroprotective functions of MTs may also involve an extracellular component. In this issue of Journal of Neurochemistry , Ambjørn et al. reveal considerable insight into this novel function of MTs. In this review, we examine the seminal work of Ambjørn et al. in the context of our current understanding of the role of MT in astrocyte-neuron interactions in the injured brain, and also discuss the significant therapeutic potential of their work.     

Speciation genetics of biological invasions with hybridization

The negative effects of human‐induced habitat disturbance and modification on multiple dimensions of biological diversity are well chronicled ( Turner 1996 ; Harding et al. 1998 ; Lawton et al. 1998 ; Sakai et al. 2001 ). Among the more insidious consequences is secondary contact between formerly allopatric taxa ( Anderson & Hubricht 1938 ; Perry et al. 2002 ; Seehausen 2006 ). How the secondary contact will play out is unpredictable ( Ellstrand et al. 2010 ), but if the taxa are not fully reproductively isolated, hybridization is likely, and if the resulting progeny are fertile, the eventual outcome is often devastating from a conservation perspective ( Rhymer & Simberloff 1996 ; Wolf et al. 2001 ; McDonald et al. 2008 ). In this issue of Molecular Ecology, Steeves et al. (2010) present an analysis of hybridization between two avian species, one of which is critically endangered and the other of which is invasive. Their discovery that the endangered species has not yet been hybridized to extinction is promising and not what one would necessarily expect from theory.     

Tracing the recombination and colonization history of hybrid species in space and time

Hybrid speciation has long fascinated evolutionary biologists and laymen alike, presumably because it challenges our classical view of evolution as a ‘one‐way street’ leading to strictly tree‐like patterns of ancestry and descent. Homoploid hybrid speciation (HHS) has been a particularly interesting puzzle, as it appears to occur extremely rapidly, perhaps within less than 50 generations ( McCarthy et al. 1995 ; Buerkle et al. 2000 ). Nevertheless, HHS may sometimes involve extended or repeated periods of recombination and gene exchange between populations subject to strong divergent natural selection ( Buerkle & Rieseberg 2008 ). Thus, HHS provides a highly interesting setting for understanding the drivers and tempo of adaptive divergence and speciation in the face of gene flow ( Arnold 2006 ; Rieseberg & Willis 2007 ; Nolte & Tautz 2009). In the present issue of Molecular Ecology, Wang et al. (2011) explore a particularly challenging issue connected to HHS: they attempt to trace the colonization and recombination history of an ancient (several MYA) hybrid species, from admixture and recombination in the ancestral hybrid zone to subsequent range shifts triggered by tectonic events (uplift of the Tibetan plateau) and climatic shifts (Pleistocene ice ages). This work is important because it addresses key issues related to the origin of the standing genetic variation available for adaptive responses (e.g. to climate change) and speciation in temperate species, which are topics of great current interest ( Rieseberg et al. 2003 ; Barrett & Schluter 2008 ; de Carvalho et al. 2010 ).     

Searching for sex‐reversals to explain population demography and the evolution of sex chromosomes

Sex determination can be purely genetic (as in mammals and birds), purely environmental (as in many reptiles), or genetic but reversible by environmental factors during a sensitive period in life, as in many fish and amphibians ( Wallace et al. 1999 ; Baroiller et al. 2009a ; Stelkens & Wedekind 2010 ). Such environmental sex reversal (ESR) can be induced, for example, by temperature changes or by exposure to hormone‐active substances. ESR has long been recognized as a means to produce more profitable single‐sex cultures in fish farms ( Cnaani & Levavi‐Sivan 2009 ), but we know very little about its prevalence in the wild. Obviously, induced feminization or masculinization may immediately distort population sex ratios, and distorted sex ratios are indeed reported from some amphibian and fish populations ( Olsen et al. 2006 ; Alho et al. 2008 ; Brykov et al. 2008 ). However, sex ratios can also be skewed by, for example, segregation distorters or sex‐specific mortality. Demonstrating ESR in the wild therefore requires the identification of sex‐linked genetic markers (in the absence of heteromorphic sex chromosomes) followed by comparison of genotypes and phenotypes, or experimental crosses with individuals who seem sex reversed, followed by sexing of offspring after rearing under non‐ESR conditions and at low mortality. In this issue, Alho et al. (2010) investigate the role of ESR in the common frog (Rana temporaria) and a population that has a distorted adult sex ratio. They developed new sex‐linked microsatellite markers and tested wild‐caught male and female adults for potential mismatches between phenotype and genotype. They found a significant proportion of phenotypic males with a female genotype. This suggests environmental masculinization, here with a prevalence of 9%. The authors then tested whether XX males naturally reproduce with XX females. They collected egg clutches and found that some had indeed a primary sex ratio of 100% daughters. Other clutches seemed to result from multi‐male fertilizations of which at least one male had the female genotype. These results suggest that sex‐reversed individuals affect the sex ratio in the following generation. But how relevant is ESR if its prevalence is rather low, and what are the implications of successful reproduction of sex‐reversed individuals in the wild?     

Genetics of personalities: no simple answers for complex traits

Identifying the genes that underlie phenotypic variation in natural populations, and assessing the consequences of polymorphisms at these loci for individual fitness are major objectives in evolutionary biology. Yet, with the exception of a few success stories, little progress has been made, and our understanding of the link between genotype and phenotype is still in its infancy. For example, although body length in humans is largely genetically determined, with heritability estimates greater than 0.8, massive genome‐wide association studies (GWAS) have only been able to account for a very small proportion of this variation ( Gudbjartsson et al. 2008 ). If it is so difficult to explain the genetics behind relatively ‘simple’ traits, can we envision that it will at all be possible to find genes underlying complex behavioural traits in wild non‐model organisms? Some notable examples suggest that this can indeed be a worthwhile endeavour. Recently, the circadian rhythm gene Clock has been associated with timing of breeding in a wild blue tit population ( Johnsen et al. 2007 ; Liedvogel et al. 2009 ) and the Pgi gene to variation in dispersal and flight endurance in Glanville fritillary butterflies ( Niitepold et al. 2009 ). A promising candidate gene for influencing complex animal personality traits, also known as behavioural syndromes ( Sih et al. 2004 ), is the dopamine receptor D4 (DRD4) gene. Within the last decade, polymorphisms in this gene have been associated with variation in novelty seeking and exploration behaviour in a range of species, from humans to great tits ( Schinka et al. 2002 ; Fidler et al. 2007 ). In this issue, Korsten et al. (2010) attempt to replicate this previously observed association in wild‐living birds, and test for the generality of the association between DRD4 and personality across a number of European great tit populations.     

Sensitivity and specificity amplification in signal transduction

Intracellular signal transduction pathways transmit signals from the cell surface to various intracellular destinations, such as cytoskeleton and nucleus through a cascade of protein-protein interactions and activation events, leading to phenotypic changes such as cell proliferation, differentiation, and death. Over the past two decades, numerous signaling proteins and signal transduction pathways have been discovered and characterized. There are two major classes of signaling proteins: phosphoproteins (e.g., mitogen-activated protein kinases) and guanosine triphosphatases (GTPases; e.g., Ras and G proteins). They both function as molecular switches by addition and removal of one or more high-energy phosphate groups. This review discusses developments that seek to quantify the signal transduction processes with kinetic analysis and mathematical modeling of the signaling phosphoproteins and GTPases. These studies have provided insights into the sensitivity and specificity amplification of biological signals in integrated systems.     

Signal integration during development: mechanisms of EGFR and Notch pathway function and cross-talk

Metazoan development relies on a highly regulated network of interactions between conserved signal transduction pathways to coordinate all aspects of cell fate specification, differentiation, and growth. In this review, we discuss the intricate interplay between the epidermal growth factor receptor (EGFR; Drosophila EGFR/DER) and the Notch signaling pathways as a paradigm for signal integration during development. First, we describe the current state of understanding of the molecular architecture of the EGFR and Notch signaling pathways that has resulted from synergistic studies in vertebrate, invertebrate, and cultured cell model systems. Then, focusing specifically on the Drosophila eye, we discuss how cooperative, sequential, and antagonistic relationships between these pathways mediate the spatially and temporally regulated processes that generate this sensory organ. The common themes underlying the coordination of the EGFR and Notch pathways appear to be broadly conserved and should, therefore, be directly applicable to elucidating mechanisms of information integration and signaling specificity in vertebrate systems.     

Signal Integration During Development: Mechanisms of EGFR and Notch Pathway Function and Cross-Talk

ABSTRACT

Metazoan development relies on a highly regulated network of interactions between conserved signal transduction pathways to coordinate all aspects of cell fate specification, differentiation, and growth. In this review, we discuss the intricate interplay between the epidermal growth factor receptor (EGFR; Drosophila EGFR/DER) and the Notch signaling pathways as a paradigm for signal integration during development. First, we describe the current state of understanding of the molecular architecture of the EGFR and Notch signaling pathways that has resulted from synergistic studies in vertebrate, invertebrate, and cultured cell model systems. Then, focusing specifically on the Drosophila eye, we discuss how cooperative, sequential, and antagonistic relationships between these pathways mediate the spatially and temporally regulated processes that generate this sensory organ. The common themes underlying the coordination of the EGFR and Notch pathways appear to be broadly conserved and should, therefore, be directly applicable to elucidating mechanisms of information integration and signaling specificity in vertebrate systems.     

Carbonylated proteins are eliminated during reproduction in C. elegans

Oxidatively damaged proteins accumulate with age in many species (Stadtman (1992) Science 257 , 1220–1224). This means that damage must be reset at the time of reproduction. To visualize this resetting in the roundworm Caenorhabditis elegans, a novel immunofluorescence technique that allows the detection of carbonylated proteins in situ was developed. The application of this technique revealed that carbonylated proteins are eliminated during C. elegans reproduction. This purging occurs abruptly within the germline at the time of oocyte maturation. Surprisingly, the germline was markedly more oxidized than the surrounding somatic tissues. Because distinct mechanisms have been proposed to explain damage elimination in yeast and mice (Aguilaniu et al. (2003) Science 299 , 1751–1753; Hernebring et al. (2006) Proc Natl Acad Sci USA 103 , 7700–7705), possible common mechanisms between worms and one of these systems were tested. The results show that, unlike in yeast (Aguilaniu et al. (2003) Science 299 , 1751–1753; Erjavec et al. (2008) Proc Natl Acad Sci USA 105 , 18764–18769), the elimination of carbonylated proteins in worms does not require the presence of the longevity‐ensuring gene, SIR‐2.1. However, similar to findings in mice (Hernebring et al. (2006) Proc Natl Acad Sci USA 103 , 7700–7705), proteasome activity in the germline is required for the resetting of carbonylated proteins during reproduction in C. elegans. Thus, oxidatively damaged proteins are eliminated during reproduction in worms through the proteasome. This finding suggests that the resetting of damaged proteins during reproduction is conserved, therefore validating the use of C. elegans as a model to study the molecular basis of damage elimination.     

The biogeography of avian extinctions on oceanic islands revisited

A recent paper by Karels et al ., 'The biogeography of avian extinctions on oceanic islands' ( Journal of Biogeography , 2008, 35 , 1106–1111), uses structural equation modelling to assess the causes of the number of island bird species driven extinct in the historical period. Here, we critically assess the conclusions of the paper and argue that it does not provide the new insights into the causes of extinction in island birds that its authors claim.     

Modelling contemporary evolution in stickleback

During the past decade, two lines of research have advanced our understanding of micro‐evolution. On the one hand, a number of studies have generated evidence for strong selection on phenotypes ( Kingsolver et al. 2001 ) and the contemporary (sometimes deemed ‘rapid’) evolution of phenotypic traits ( Hendry & Kinnison 1999 ). On the other hand, other studies have sought to identify the genes that underlie ecologically important traits ( Ungerer et al. 2008 ). Over the next decade, micro‐evolutionists might expect considerable progress from the study of contemporary evolution at both the phenotypic and genetic level simultaneously. In this issue of Molecular Ecology, Le Rouzic et al. (2011) present a teaser for this approach. They examined contemporary evolution of an adaptive trait with a well‐studied genetic basis, the number of lateral plates, in threespine stickleback (Gasterosteus aculeatus L.). A time series of 20 years of change for this trait after introduction into a pond in Norway was compared with a similar time series of 12 years following the invasion of a lake in Alaska. Using a modelling approach, the authors then teased apart selection acting upon the phenotype and selection acting on a major effect gene. In both time series, selection was strong and consistent. The models suggested that selection could act directly on the phenotype, or through the gene’s pleiotropic effects.     

Rewiring the specificity of two-component signal transduction systems

Two-component signal transduction systems are the predominant means by which bacteria sense and respond to environmental stimuli. Bacteria often employ tens or hundreds of these paralogous signaling systems, comprised of histidine kinases (HKs) and their cognate response regulators (RRs). Faithful transmission of information through these signaling pathways and avoidance of detrimental crosstalk demand exquisite specificity of HK-RR interactions. To identify the determinants of two-component signaling specificity, we examined patterns of amino acid coevolution in large, multiple sequence alignments of cognate kinase-regulator pairs. Guided by these results, we demonstrate that a subset of the coevolving residues is sufficient, when mutated, to completely switch the substrate specificity of the kinase EnvZ. Our results shed light on the basis of molecular discrimination in two-component signaling pathways, provide a general approach for the rational rewiring of these pathways, and suggest that analyses of coevolution may facilitate the reprogramming of other signaling systems and protein-protein interactions.     

Bacterial biofilms in a 'genes-to-ecosystems' context

In ecology, there is an increasing amount of research dedicated to understanding how intraspecific genetic diversity can extend beyond the population level to influence the assembly of communities and the functioning of ecosystems. In this issue of Molecular Ecology, Koh et al. (2012) take this exploration to a new level using bacterial biofilms and protozoan grazers. They show that there is heritable variation in the phenotypes of different variants of biofilms of Serratia marcescens and that these strains display complementarity when combined in a diverse assemblage. Mixtures of variants were significantly more resistant to protozoan grazing than either wild‐type or variant biofilms grown in monocultures. While similar biodiversity effects of genotype mixtures have been observed in other systems, Koh et al. (2012) link phenotype variation of the biofilms to a single nucleotide polymorphism in one regulatory gene. Importantly, the authors demonstrate that minimal changes in a genotype can result in substantial shifts in interspecific ecological interactions.     

Immune correlates of protection against anthrax

Bacillus anthracis protective antigen (PA) has been produced from a recombinant B. subtilis and its efficacy, when combined with the Ribi adjuvant (MPL-TDW-CWS) or alhydrogel, has been compared with that of the licensed UK human vaccine, in guinea pigs challenged with aerosolized Ames strain spores. Recombinant PA combined with the Ribi adjuvant performed as well as PA from B. anthracis cultures in previous reports ( Ivins & Welkos 1986 ; Ivins et al . 1990 ; Turnbull et al . 1991 ; Jones et al . 1996 ; McBride et al . 1998 ) giving protection in 100% of animals exposed to the highest challenge dose of the Ames strain of B. anthracis that can be administered practically (retained lung doses of approximately 10⁶ spores).
In attempts at identifying markers of protection in immunized individuals, rPA in combination with the Ribi adjuvant induced a marker IgG₂ response in guinea pigs with no significant differences in IgG₁ levels when compared with other vaccine formulations ( McBride et al . 1998 ). In BALBc mice, rPA with the Ribi adjuvant induced a higher IgG_2a response compared with rPA with anhydrogel and the human vaccine.
To examine the role of anti-PA-specific antibodies in protection, guinea pig sera is being passively transferred into guinea pigs and SCID mice, followed by protection.
Similarly, B- and T-lymphocytes from immunized BALB/c mice are being separately and passively transferred into SCID mice with subsequent challenge. The neutralizing ability of the PA-specific antibodies is being studied using an in vitro macrophage lysis assay.