Assembly rules of reef corals are flexible along a steep climatic gradient

Coral reefs, one of the world's most complex and vulnerable ecosystems, face an uncertain future in coming decades as they continue to respond to anthropogenic climate change, overfishing, pollution, and other human impacts [1, 2]. Traditionally, marine macroecology is based on presence/absence data from taxonomic checklists or geographic ranges, providing a qualitative overview of spatial shifts in species richness that treats rare and common species equally [3, 4]. As a consequence, regional and long-term shifts in relative abundances of individual taxa are poorly understood. Here we apply a more rigorous quantitative approach to examine large-scale spatial variation in the species composition and abundance of corals on midshelf reefs along the length of Australia's Great Barrier Reef, a biogeographic region where species richness is high and relatively homogeneous [5]. We demonstrate that important functional components of coral assemblages "sample" space differently at 132 sites separated by up to 1740 km, leading to complex latitudinal shifts in patterns of absolute and relative abundance. The flexibility in community composition that we document along latitudinal environmental gradients indicates that climate change is likely to result in a reassortment of coral reef taxa rather than wholesale loss of entire reef ecosystems.     

Mapping of ionomic traits in Mimulus guttatus reveals Mo and Cd QTLs that colocalize with MOT1 homologues

Natural variation in the regulation of the accumulation of mineral nutrients and trace elements in plant tissues is crucial to plant metabolism, development, and survival across different habitats. Studies of the genetic basis of natural variation in nutrient metabolism have been facilitated by the development of ionomics. Ionomics is a functional genomic approach for the identification of the genes and gene networks that regulate the elemental composition, or ionome, of an organism. In this study, we evaluated the genetic basis of divergence in elemental composition between an inland annual and a coastal perennial accession of Mimulus guttatus using a recombinant inbred line (RIL) mapping population. Out of 20 elements evaluated, Mo and Cd were the most divergent in accumulation between the two accessions and were highly genetically correlated in the RILs across two replicated experiments. We discovered two major quantitative trait loci (QTL) for Mo accumulation, the largest of which consistently colocalized with a QTL for Cd accumulation. Interestingly, both Mo QTLs also colocalized with the two M. guttatus homologues of MOT1, the only known plant transporter to be involved in natural variation in molybdate uptake.     

An indirect cue of predation risk counteracts female preference for conspecifics in a naturally hybridizing fish Xiphophorus birchmanni

Mate choice is context dependent, but the importance of current context to interspecific mating and hybridization is largely unexplored. An important influence on mate choice is predation risk. We investigated how variation in an indirect cue of predation risk, distance to shelter, influences mate choice in the swordtail Xiphophorus birchmanni, a species which sometimes hybridizes with X. malinche in the wild. We conducted mate choice experiments to determine whether females attend to the distance to shelter and whether this cue of predation risk can counteract female preference for conspecifics. Females were sensitive to shelter distance independent of male presence. When conspecific and heterospecific X. malinche males were in equally risky habitats (i.e., equally distant from shelter), females associated primarily with conspecifics, suggesting an innate preference for conspecifics. However, when heterospecific males were in less risky habitat (i.e., closer to shelter) than conspecific males, females no longer exhibited a preference, suggesting that females calibrate their mate choices in response to predation risk. Our findings illustrate the potential for hybridization to arise, not necessarily through reproductive "mistakes", but as one of many potential outcomes of a context-dependent mate choice strategy.     

Novel scabies mite serpins inhibit the three pathways of the human complement system

Scabies is a parasitic infestation of the skin by the mite Sarcoptes scabiei that causes significant morbidity worldwide, in particular within socially disadvantaged populations. In order to identify mechanisms that enable the scabies mite to evade human immune defenses, we have studied molecules associated with proteolytic systems in the mite, including two novel scabies mite serine protease inhibitors (SMSs) of the serpin superfamily. Immunohistochemical studies revealed that within mite-infected human skin SMSB4 (54 kDa) and SMSB3 (47 kDa) were both localized in the mite gut and feces. Recombinant purified SMSB3 and SMSB4 did not inhibit mite serine and cysteine proteases, but did inhibit mammalian serine proteases, such as chymotrypsin, albeit inefficiently. Detailed functional analysis revealed that both serpins interfered with all three pathways of the human complement system at different stages of their activation. SMSB4 inhibited mostly the initial and progressing steps of the cascades, while SMSB3 showed the strongest effects at the C9 level in the terminal pathway. Additive effects of both serpins were shown at the C9 level in the lectin pathway. Both SMSs were able to interfere with complement factors without protease function. A range of binding assays showed direct binding between SMSB4 and seven complement proteins (C1, properdin, MBL, C4, C3, C6 and C8), while significant binding of SMSB3 occurred exclusively to complement factors without protease function (C4, C3, C8). Direct binding was observed between SMSB4 and the complement proteases C1s and C1r. However no complex formation was observed between either mite serpin and the complement serine proteases C1r, C1s, MASP-1, MASP-2 and MASP-3. No catalytic inhibition by either serpin was observed for any of these enzymes. In summary, the SMSs were acting at several levels mediating overall inhibition of the complement system and thus we propose that they may protect scabies mites from complement-mediated gut damage.     

Pollen limitation and natural selection on floral characters in the yellow monkeyflower, Mimulus guttatus

In flowering plants, pollen limitation has been proposed to intensify selection on floral characters important in pollinator attraction, but may also select for traits that increase seed set through autonomous selfing. Here, a factorial design (+/- pollen addition, +/- pollinator removal) was used to investigate how the pollination environment affects selection on floral morphology via female fitness in a mixed-mating population of the yellow monkeyflower, Mimulus guttatus (Phrymaceae). Female fitness was strongly pollen-limited, with supplementally pollinated plants setting 37% more seeds than open-pollinated individuals. Strong positive selection was found on flower length, weak positive selection on flower width : length ratio and no selection on stigma-anther distance in both open-pollinated and supplementally pollinated treatments. By contrast, flowers with relatively narrow corollas and low stigma-anther distances were favored in the pollinator exclusion treatment. These results provide mixed support for the idea that pollen limitation intensifies selection on floral characters. Despite strong phenotypic selection, natural pollen limitation did not mediate selection on characters associated with either pollinator attraction or self-fertilization. However, the novel pattern of selection on severely pollen-limited plants suggests that reproductive assurance against pollinator loss may have been directly involved in the floral evolution of closely related selfing taxa.     

Localization of the delta-like-1-binding site in human Notch-1 and its modulation by calcium affinity

The Notch signaling pathway plays a key role in a myriad of cellular processes, including cell fate determination. Despite extensive study of the downstream consequences of receptor activation, very little molecular data are available for the initial binding event between the Notch receptor and its ligands. In this study, we have expressed and purified a natively folded wild-type epidermal growth factor-like domain (EGF) 11-14 construct from human Notch-1 and have used flow cytometry and surface plasmon resonance analysis to demonstrate a calcium-dependent interaction with the human ligand Delta-like-1. Site-directed mutagenesis of three of the calcium-binding sites within the Notch-(11-14) fragment indicated that only loss of calcium binding to EGF12, and not EGF11 or EGF13, abrogates ligand binding. Further mapping of the ligand-binding site within this region by limited proteolysis of Notch wild-type and mutant fragments suggested that EGF12 rather than EGF11 contains the major Delta-like-1-binding site. Analysis of an extended fragment EGF-(10-14), where EGF11 is placed in a native context, surprisingly demonstrated a reduction in ligand binding, suggesting that EGF10 modulates binding by limiting access of ligand. This inhibition could be overcome by the introduction of a calcium binding mutation in EGF11, which decouples the EGF-(10-11) module interface. This study therefore demonstrates that long range calcium-dependent structural perturbations can influence the affinity of Notch for its ligand, in the absence of any post-translational modifications.     

Identification of a ciliate (Oligohymenophorea: Scuticociliatia) associated with brown band disease on corals of the Great Barrier Reef

A ciliate associated with the coral disease brown band (BrB) was identified as a new species belonging to the class Oligohymenophorea, subclass Scuticociliatia. The ciliates were characterized by the presence of large numbers of intracellular dinoflagellates and displayed an elongated, tube-shaped body structure. They had uniform ciliature, except for three distinct cilia in the caudal region, and were typically 200 to 400 microm in length and 20 to 50 microm in width.