Late-successional biological soil crusts in a biodiversity hotspot: an example of congruency in species richness

Understanding the biodiversity of functionally important communities in Earth’s ecosystems is vital in the apportionment of limited ecosystem management funds and efforts. In southern California shrublands, which lie in a global biodiversity hotspot, biological soil crusts (BSCs) confer critical ecosystem services; however, their biodiversity remains unknown. In this study, six sites (n = 4 each, 25 m²) were established along a mediterranean shrubland environmental gradient in southern California. Here, the biodiversity of all BSC-forming lichens and bryophytes was evaluated, related to environmental traits along the gradient, and compared to species richness among North American ecosystems supporting BSCs (data from previous studies). In total, 59 BSC-forming lichens and bryophytes were observed, including the very rare Sarcogyne crustacea, a rare moss, and five endemic lichen species. Over half (61%) of the species observed were found at a single site. Along the gradient, species evenness of late-successional BSC was related to dew point and elevation, and both evenness and richness were related to distance to coast. Using an ordination analysis, five distinct late-successional BSC communities were identified: Riversidian, Spike moss, Casperian, Alisian, and Lagunian. Twenty-five lichens and 19 bryophytes are newly reported for North American BSC-forming organisms, now comprising ~1/2 of the North American total. BSCs in North American hot and cold deserts were approximately 4.0 and 2.4 times less species rich than BSCs found in southern California shrublands, respectively. Given the anthropogenic impacts on quality and distribution of California mediterranean shrublands, our results show that these sites represent important refugia of BSC species in this globally important region.     

Protein storage and root:shoot reallocation provide tolerance to damage in a hybrid willow system

To determine the mechanistic basis of tolerance, we evaluated six candidate traits for tolerance to damage using F₂ interspecific hybrids in a willow hybrid system. A distinction was made between reproductive tolerance and biomass tolerance; reproductive tolerance was designated as a plant’s proportional change in catkin production following damage, while biomass tolerance referred to a plant’s proportional change in biomass (i.e., regrowth) following damage. F₂ hybrids were generated to increase variation and independence among candidate traits. Using three clonally identical individuals, pre-damage candidate traits for tolerance to damage (root:shoot ratio, total nonstructural carbohydrate, and total available protein) and post-damage candidate traits (relative root:shoot ratio, phenolic ratio, and specific leaf area ratio) were measured. The range of variation for these six candidate traits was broad. Biomass was significantly increased two years after 50% shoot length removal, and catkin production was not significantly reduced when damaged, suggesting that F₂ hybrids had great biomass tolerance and reproductive tolerance. Based on multiple regression methods, increased reproductive tolerance was associated with increased protein storage and decreased relative root:shoot ratio (reduced root allocation after damage). In addition, a positive relationship between biomass tolerance and condensed tannins was detected, and both traits were associated with increased reproductive tolerance. These four factors explained 57% of the variance in the reproductive tolerance of F₂ hybrids, but biomass tolerance explained the majority of the variance in reproductive tolerance. Changes in plant architecture in response to plant damage may be the underlying mechanism that explains biomass tolerance.     

The use of specialisation indices to predict vulnerability of coral‐feeding butterflyfishes to environmental change

In the absence of detailed assessments of extinction risk, ecological specialisation is often used as a proxy of vulnerability to environmental disturbances and extinction risk. Numerous indices can be used to estimate specialisation; however, the utility of these different indices to predict vulnerability to future environmental change is unknown. Here we compare the performance of specialisation indices using coral‐feeding butterflyfishes as a model group. Our aims were to 1) quantify the dietary preferences of three butterflyfish species across habitats with differing levels of resource availability; 2) investigate how estimates of dietary specialisation vary with the use of different specialisation indices; 3) determine which specialisation indices best inform predictions of vulnerability to environmental change; and 4) assess the utility of resource selection functions to inform predictions of vulnerability to environmental change. The relative level of dietary specialisation estimated for all three species varied when different specialisation indices were used, indicating that the choice of index can have a considerable impact upon estimates of specialisation. Specialisation indices that do not consider resource abundance may fail to distinguish species that primarily use common resources from species that actively target resources disproportionately more than they are available. Resource selection functions provided the greatest insights into the potential response of species to changes in resource availability. Examination of resource selection functions, in addition to specialisation indices, indicated that Chaetodon trifascialis was the most specialised feeder, with highly conserved dietary preferences across all sites, suggesting that this species is highly vulnerable to the impacts of climate‐induced coral loss on reefs. Our results indicate that vulnerability assessments based on some specialisation indices may be misleading and the best estimates of dietary specialisation will be provided by indices which incorporate resource availability measures, as well as assessing responses of species to changes in resource availability.     

Multiple domains in MtENOD8 protein including the signal peptide target it to the symbiosome

Symbiotic nitrogen fixation occurs in nodules, specialized organs on the roots of legumes. Within nodules, host plant cells are infected with rhizobia that are encapsulated by a plant-derived membrane forming a novel organelle, the symbiosome. In Medicago truncatula, the symbiosome consists of the symbiosome membrane, a single rhizobium, and the soluble space between them, called the symbiosome space. The symbiosome space is enriched with plant-derived proteins, including the M. truncatula EARLY NODULIN8 (MtENOD8) protein. Here, we present evidence from green fluorescent protein (GFP) fusion experiments that the MtENOD8 protein contains at least three symbiosome targeting domains, including its N-terminal signal peptide (SP). When ectopically expressed in nonnodulated root tissue, the MtENOD8 SP delivers GFP to the vacuole. During the course of nodulation, there is a nodule-specific redirection of MtENOD8-SP-GFP from the vacuole to punctate intermediates and subsequently to symbiosomes, with redirection of MtENOD8-SP-GFP from the vacuole to punctate intermediates preceding intracellular rhizobial infection. Experiments with M. truncatula mutants having defects in rhizobial infection and symbiosome development demonstrated that the MtNIP/LATD gene is required for redirection of the MtENOD8-SP-GFP from the vacuoles to punctate intermediates in nodules. Our evidence shows that MtENOD8 has evolved redundant targeting sequences for symbiosome targeting and that intracellular localization of ectopically expressed MtENOD8-SP-GFP is useful as a marker for monitoring the extent of development in mutant nodules.     

MK-8825: a potent and selective CGRP receptor antagonist with good oral activity in rats

Rational modification of the clinically tested CGRP receptor antagonist MK-3207 (3) afforded an analogue with increased unbound fraction in rat plasma and enhanced aqueous solubility, 2-[(8R)-8-(3,5-difluorophenyl)-8-methyl-10-oxo-6,9-diazaspiro[4.5]dec-9-yl]-N-[(6S)-2'-oxo-1',2',5,7-tetrahydrospiro[cyclopenta[b]pyridine-6,3'-pyrrolo[2,3-b]pyridin]-3-yl]acetamide (MK-8825) (6). Compound 6 maintained similar affinity to 3 at the human and rat CGRP receptors but possessed significantly improved in vivo potency in a rat pharmacodynamic model. The overall profile of 6 indicates it should find utility as a rat tool to investigate effects of CGRP receptor blockade in vivo.     

A performance-based cost to honest signalling in male green anole lizards (Anolis carolinensis)

Sexual signals are considered costly to produce and maintain under the handicap paradigm, and the reliability of signals is in turn thought to be maintained by these costs. Although previous studies have investigated the costly nature of signal production, few have considered whether honesty might be maintained not by the costliness of the signal itself, but by the costs involved in producing the signalled trait. If such a trait is itself costly to produce, then the burden of energetic investment may fall disproportionately on that trait, in addition to any costs of signal maintenance that may also be operating. Under limited resource conditions, these costs may therefore be great enough to disrupt an otherwise reliable signal-to-trait relationship. We present experimental evidence showing that dietary restriction decouples the otherwise honest relationship between a signal (dewlap size) and a whole-organism performance trait (bite force) in young adult male Anolis carolinensis lizards. Specifically, while investment in dewlap size is sustained under low-resource condition relative to the high-resource treatment, investment in bite force is substantially lower. Disruption of the otherwise honest dewlap size to bite force relationship is therefore driven by costs associated with the expression of performance rather than the costs of signal production in A. carolinensis.     

Visual extrapolation under risk: human observers estimate and compensate for exogenous uncertainty

Humans commonly face choices between multiple options with uncertain outcomes. Such situations occur in many contexts, from purely financial decisions (which shares should I buy?) to perceptuo-motor decisions between different actions (where should I aim my shot at goal?). Regardless of context, successful decision-making requires that the uncertainty at the heart of the decision-making problem is taken into account. Here, we ask whether humans can recover an estimate of exogenous uncertainty and then use it to make good decisions. Observers viewed a small dot that moved erratically until it disappeared behind an occluder. We varied the size of the occluder and the unpredictability of the dot''s path. The observer attempted to capture the dot as it emerged from behind the occluded region by setting the location and extent of a ‘catcher’ along the edge of the occluder. The reward for successfully catching the dot was reduced as the size of the catcher increased. We compared human performance with that of an agent maximizing expected gain and found that observers consistently selected catcher size close to this theoretical solution. These results suggest that humans are finely tuned to exogenous uncertainty information and can exploit it to guide action.