Competition,niche specialization and the evolution of brain size in the genus Peromyscus

Previous studies of relative brain size in mammals have suggested an association with complex habitats and with low reproductive rate. In order to examine the causal relationships more thoroughly, a detailed examination of relative brain size variation in the genus Peromyscus was undertaken. Endocranial volumes were used to estimate brain weight for 32 species including 161 subspecies, and relative brain size calculated as the species deviation from the allometric relationship between brain and body size. The intrageneric allometric coefficient was higher than most values previously reported from low taxonomic levels, but intraspecific coefficients were generally lower than this. Island species, and relict species isolated on mountain tops, which may be ecological ‘islands’, had consistently small relative brain sizes, but peninsular species were large brained. Among the remaining species there were significant correlations between litter size and relative brain size, and between the number of competitor species and relative brain size. Species with many competitor species have relatively large brains and small litters. It is concluded that the nature of the geographical distribution, the pattern of species formation and habitat complexity all influence relative brain size in existing forms.     

Competition, niche specialization and the evolution of brain size in the genus Peromyscus

Previous studies of relative brain size in mammals have suggested an association with complex habitats and with low reproductive rate. In order to examine the causal relationships more thoroughly, a detailed examination of relative brain size variation in the genus Peromyscus was undertaken. Endocranial volumes were used to estimate brain weight for 32 species including 161 subspecies, and relative brain size calculated as the species deviation from the allometric relationship between brain and body size. The intrageneric allometric coefficient was higher than most values previously reported from low taxonomic levels, but intraspecific coefficients were generally lower than this.
Island species, and relict species isolated on mountain tops, which may be ecological 'islands', had consistently small relative brain sizes, but peninsular species were large brained. Among the remaining species there were significant correlations between litter size and relative brain size, and between the number of competitor species and relative brain size. Species with many competitor species have relatively large brains and small litters. It is concluded that the nature of the geographical distribution, the pattern of species formation and habitat complexity all influence relative brain size in existing forms.     

Selection footprint in the FimH adhesin shows pathoadaptive niche differentiation in Escherichia coli

Spread of biological species from primary into novel habitats leads to within-species adaptive niche differentiation and is commonly driven by acquisition of point mutations in individual genes that increase fitness in the alternative environment. However, finding footprints of adaptive niche differentiation in specific genes remains a challenge. Here we describe a novel method to analyze the footprint of pathogenicity-adaptive, or pathoadaptive, mutations in the Escherichia coli gene encoding FimH-the major, mannose-sensitive adhesin. Analysis of distribution of mutations across the nodes and branches of the FimH phylogenetic network shows (1) zonal separation of evolutionary primary structural variants of FimH and recently derived ones, (2) dramatic differences in the ratio of synonymous and nonsynonymous changes between nodes from different zones, (3) evidence for replacement hot-spots in the FimH protein, (4) differential zonal distribution of FimH variants from commensal and uropathogenic E. coli, and (5) pathoadaptive functional changes in FimH brought by the mutations. The selective footprint in fimH indicates that the pathoadaptive niche differentiation of E. coli is either in its initial stages or undergoing an evolutionary "source/sink" dynamic.     

Competition and co-existence of Zoophthora radicans and Pandora blunckii, two co-occurring fungal pathogens of the diamondback moth, Plutella xylostella

The entomopathogenic fungi Zoophthora radicans and Pandora blunckii co-occur in field populations of Plutella xylostella and, therefore, are likely to interact during the infection process. We have investigated the possible outcomes of these interactions in the laboratory. Using four isolates, two of each fungal species, inter-specific interaction experiments were done in Petri dishes and on intact plants. In Petri dish experiments, larvae were inoculated directly using sporulating mats of mycelium, both species had the same opportunity to infect and only the relative concentration of conidia of each pathogen species applied was manipulated. In the intact plant experiments, larvae were placed onto fungus-contaminated plants, inoculation was passive and the probability of infection by either or both species of fungi depended on larval activity and proximity to inoculum. In the Petri dish experiment, the species with the largest concentration of conidia out-competed the other regardless of virulence, and results were similar in the intact plant experiment. The ecological implications for competition or co-existence of these two pathogens in the field are discussed.     

Uromyces umiamensis, a new rust species on Momordica cochinchinensis in India

Uromyces umiamensis is described as a new rust fungus (Basidiomycota, Uredinales) of Momordica cochinchinensis (Cucurbitaceae) from Meghalaya, in northeastern India. The species differs from the known Uromyces species on members of Cucurbitaceae in terms of the character of the teliospores and aeciospores and its apparently demicyclic life cycle. Besides U. yakushimensis and the present species, all Uromyces species known from cucurbits occur in the New World. A key to known Uromyces species on Cucurbitaceae is provided.     

Within-genotype epigenetic variation enables broad niche width in a flower living yeast

Niche theory is one of the central organizing concepts in ecology. Generally, this theory defines a given species niche as all of the factors that effect the persistence of the species as well as the impact of the species in a given location ( Hutchinson 1957 ; Chase 2011 ). Many studies have argued that phenotypic plasticity enhances niche width because plastic responses allow organisms to express advantageous phenotypes in a broader range of environments ( Bradshaw 1965 ; Van Valen 1965 ; Sultan 2001 ). Further, species that exploit habitats with fine‐grained variation, or that form metapopulations, are expected to develop broad niche widths through phenotypic plasticity ( Sultan & Spencer 2002 ; Baythavong 2011 ). Although a long history of laboratory, greenhouse and reciprocal transplant experiments have provided insight into how plasticity contributes to niche width ( Pigliucci 2001 ), recent advances in molecular approaches allow for a mechanistic understanding of plasticity at the molecular level ( Nicotra et al. 2010 ). In particular, variation in epigenetic effects is a potential source of the within‐genotype variation that underlies the phenotypic plasticity associated with broad niche widths. Epigenetic mechanisms can alter gene expression and function without altering DNA sequence ( Richards 2006 ) and may be stably transmitted across generations ( Jablonka & Raz 2009 ; Verhoeven et al. 2010 ). Also, epigenetic mechanisms may be an important component of an individual’s response to the environment ( Verhoeven et al. 2010 ). While these ideas are intriguing, few studies have made a clear connection between genome‐wide DNA methylation patterns and phenotypic plasticity (e.g. Bossdorf et al. 2010 ). In this issue of Molecular Ecology, Herrera et al. (2012) present a study that demonstrates epigenetic changes in genome‐wide DNA methylation are causally active in a species’ ability to exploit resources from a broad range of environments and are particularly important in harsh environments.     

Competition between the facultatively chemolithotrophic Thiobacillus A2, an obligately chemolithotrophic Thiobacillus and a heterotrophic spirillum for inorganic and organic substrates

Competition in a chemostat between the versatile Thiobacillus A2 and the specialized T. neapolitanus for thiosulfate as the sole growth-limiting substrate, led to dominance of the specialized over the versatile organism, at dilution rates 0.025 h^-1. Increasing concentrations of acetate or glycollate in the thiosulfate medium caused increased relative numbers of T. A2 in steady states at D=0.07 h^-1. Eventually, with 10–12 mmol of organic substrate per litre, complete dominance of T. A2 over T. neapolitanus occurred.Mixed cultures of T. A2 and a specialized spirillumshaped heterotroph, competing for acetate as sole growth-limiting substrate resulted in complete dominance of the heterotroph at dilution rates of 0.07 and 0.15 h^-1. In this case increasing concentrations of thiosulfate in the acetate medium, up to 10 mM, eventually led to the elimination of the heterotroph.These results have been interpreted as evidence that T. A2 was growing mixotrophically. As the concentration of the second substrate was raised, the number of T. A2 cells increased and as a result T. A2 consumed an increasing portion of the common substrate.In mixed chemostat cultures containing all three organisms, T. A2 could maintain itself with all tested ratios of acetate and thiosulfate in the inflowing medium. The heterotroph was excluded from the culture below a relatively low acetate to thiosulfate ratio, whilst above a relatively high acetate to thiosulfate ratio T. neapolitanus was completely eliminated.These results were discussed in relation to the ecological niche of Thiobacillus A2-type organisms.     

Nitrate-based niche differentiation by distinct sulfate-reducing bacteria involved in the anaerobic oxidation of methane

Diverse associations between methanotrophic archaea (ANME) and sulfate-reducing bacterial groups (SRB) often co-occur in marine methane seeps; however, the ecophysiology of these different symbiotic associations has not been examined. Here, we applied a combination of molecular, geochemical and Fluorescence in situ hybridization (FISH) coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS) analyses of in situ seep sediments and methane-amended sediment incubations from diverse locations (Eel River Basin, Hydrate Ridge and Costa Rican Margin seeps) to investigate the distribution and physiology of a newly identified subgroup of the Desulfobulbaceae (seepDBB) found in consortia with ANME-2c archaea, and compared these with the more commonly observed associations between the same ANME partner and the Desulfobacteraceae (DSS). FISH analyses revealed aggregates of seepDBB cells in association with ANME-2 from both environmental samples and laboratory incubations that are distinct in their structure relative to co-occurring ANME/DSS consortia. ANME/seepDBB aggregates were most abundant in shallow sediment depths below sulfide-oxidizing microbial mats. Depth profiles of ANME/seepDBB aggregate abundance revealed a positive correlation with elevated porewater nitrate relative to ANME/DSS aggregates in all seep sites examined. This relationship with nitrate was supported by sediment microcosm experiments, in which the abundance of ANME/seepDBB was greater in nitrate-amended incubations relative to the unamended control. FISH-NanoSIMS additionally revealed significantly higher ¹⁵N-nitrate incorporation levels in individual aggregates of ANME/seepDBB relative to ANME/DSS aggregates from the same incubation. These combined results suggest that nitrate is a geochemical effector of ANME/seepDBB aggregate distribution, and provides a unique niche for these consortia through their utilization of a greater range of nitrogen substrates than the ANME/DSS.     

Social intelligence, human intelligence and niche construction

This paper is about the evolution of hominin intelligence. I agree with defenders of the social intelligence hypothesis in thinking that externalist models of hominin intelligence are not plausible: such models cannot explain the unique cognition and cooperation explosion in our lineage, for changes in the external environment (e.g. increasing environmental unpredictability) affect many lineages. Both the social intelligence hypothesis and the social intelligence-ecological complexity hybrid I outline here are niche construction models. Hominin evolution is hominin response to selective environments that earlier hominins have made. In contrast to social intelligence models, I argue that hominins have both created and responded to a unique foraging mode; a mode that is both social in itself and which has further effects on hominin social environments. In contrast to some social intelligence models, on this view, hominin encounters with their ecological environments continue to have profound selective effects. However, though the ecological environment selects, it does not select on its own. Accidents and their consequences, differential success and failure, result from the combination of the ecological environment an agent faces and the social features that enhance some opportunities and suppress others and that exacerbate some dangers and lessen others. Individuals do not face the ecological filters on their environment alone, but with others, and with the technology, information and misinformation that their social world provides.     

Lineage diversification in a widespread species: roles for niche divergence and conservatism in the common kingsnake, Lampropeltis getula

Niche conservatism and niche divergence are both important ecological mechanisms associated with promoting allopatric speciation across geographical barriers. However, the potential for variable responses in widely distributed organisms has not been fully investigated. For allopatric sister lineages, three patterns for the interaction of ecological niche preference and geographical barriers are possible: (i) niche conservatism at a physical barrier; (ii) niche divergence at a physical barrier; and (iii) niche divergence in the absence of a physical barrier. We test for the presence of these patterns in a transcontinentally distributed snake species, the common kingsnake ( Lampropeltis getula ), to determine the relative frequency of niche conservatism or divergence in a single species complex inhabiting multiple distinct ecoregions. We infer the phylogeographic structure of the kingsnake using a range-wide data set sampled for the mitochondrial gene cytochrome b . We use coalescent simulation methods to test for the presence of structured lineage formation vs. fragmentation of a widespread ancestor. Finally, we use statistical techniques for creating and evaluating ecological niche models to test for conservatism of ecological niche preferences. Significant geographical structure is present in the kingsnake, for which coalescent tests indicate structured population division. Surprisingly, we find evidence for all three patterns of conservatism and divergence. This suggests that ecological niche preferences may be labile on recent phylogenetic timescales, and that lineage formation in widespread species can result from an interaction between inertial tendencies of niche conservatism and natural selection on populations in ecologically divergent habitats.     

Common resistance in red raspberry to Botrytis cinerea and Didymella applanata, two pathogens occupying the same ecological niche

Comparisons were made between Botrytis cinerea and Didymella applanata, which occupy the same ecological niche on canes of red raspberry. Isolates of B. cinerea from diverse localities within the British Isles were pathogenic to the SCRI selection M30 when internodal wounds on young canes were inoculated. A single inoculation frequently caused the buds at several nodes to fail the following spring. Differences in the lengths of the stem lesions that formed indicated differences in isolate pathogenicity, but these were not related to isolate origin. Bud suppression and lateral shoot failure also occurred when petioles of cvs Mailing Orion, Mailing Jewel and Glen Clova were wound inoculated with B. cinerea up to late August. The relative resistance of seven cultivars to three isolates of each pathogen was determined. Principal components analysis of data from five estimates of resistance to each pathogen showed that 40% of the variation described a common resistance to the two diseases. Further analysis showed that cvs Chilcotin and Meeker had the strongest common resistance and that cvs Glen Prosen and Mailing Jewel had the weakest. The remaining variation described cultivar differences in relative bud length after petiole inoculation with either pathogen, and differences in the relative importance of spring and autumn symptoms. Only 7% of the variation indicated independent resistance to the two pathogens and this was not influenced by cultivar differences.     

Phylogeny,niche conservatism and the latitudinal diversity gradient in mammals

Biologists have long searched for mechanisms responsible for the increase in species richness with decreasing latitude. The strong correlation between species richness and climate is frequently interpreted as reflecting a causal link via processes linked to energy or evolutionary rates. Here, we investigate how the aggregation of clades, as dictated by phylogeny, can give rise to significant climate–richness gradients without gradients in diversification or environmental carrying capacity. The relationship between climate and species richness varies considerably between clades, regions and time periods in a global-scale phylogenetically informed analysis of all terrestrial mammal species. Many young clades show negative richness–temperature slopes (more species at cooler temperatures), with the ages of these clades coinciding with the expansion of temperate climate zones in the late Eocene. In carnivores, we find steeply positive richness–temperature slopes in clades with restricted distributions and tropical origins (e.g. cat clade), whereas widespread, temperate clades exhibit shallow, negative slopes (e.g. dog–bear clade). We show that the slope of the global climate–richness gradient in mammals is driven by aggregating Chiroptera (bats) with their Eutherian sister group. Our findings indicate that the evolutionary history should be accounted for as part of any search for causal links between environment and species richness.     

Stream microhabitat selectivity,resource partitioning,and niche shifts in grazing caddisfly larvae

Microhabitat selectivity, resource partitioning, and niche shifts in five species of grazing caddisfly larvae (Glossosoma califica, G. penitum, Dicosmoecus gilvipes, Neophylax rickeri, and N. splendens) were quantified by underwater measurement of microhabitat availability and utilization in three northern California streams. The microhabitat parameters water depth and velocity and rock size, roughness, and slope were measured. Comparisons of habitat available to habitat used revealed significant selection for at least two microhabitat parameters by each population, with depth and velocity being the most important. Comparisons of habitat used by different species showed significant partitioning of at least two microhabitat parameters at each site, with depth being partitioned at all sites. Non-parametric discriminant analysis revealed significant microhabitat partitioning on a multivariate level at two sites. Comparisons of habitat used at different sites quantified a major niche shift by D. gilvipes in its preference for riffles versus pools. Size-selective predation by dippers (Cinclus mexicanus) and steelhead (Salmo gairdneri gairdneri) is proposed as a hypothesis to explain the observed resource partitioning and niche shift.     

Demographic constraints in evolution: Towards unifying the evolutionary theories of senescence and niche conservatism

Summary I suggest that there may be a fundamental conceptual unity between two seemingly disparate phenomena: (1) senescence (the progressive deterioration in physiological function and, thus, individual fitness with age) and (2) niche conservatism (the observation that species often seem rather fixed over evolutionary time in their basic niche properties). I argue that both phenomena arise from demographic asymmetries. The evolutionary theory of ageing rests on the observation that the force of selection declines with age, reflecting the basic demographic facts that in persistent populations there are always fewer individuals in old than in young age classes and these individuals tend to have lower reproductive value. A similar demographic asymmetry arises when populations inhabit environments with source habitats (i.e. where conditions are within the species' niche) and sink habitats (where conditions lie outside the niche): there tend to be more individuals in sources than in sinks and individuals in sources have relatively higher reproductive values. These demographic asymmetries should often imply that the force of selection is greater in sources than in sinks, leading automatically towards niche conservatism. I suggest that niche evolution is most likely in circumstances where these demographic asymmetries in space weaken or reverse.     

Diversity and endemism in deglaciated areas: ploidy,relative genome size and niche differentiation in the Galium pusillum complex (Rubiaceae) in Northern and Central Europe

Background and Aims

Plants endemic to areas covered by ice sheets during the last glaciation represent paradigmatic examples of rapid speciation in changing environments, yet very few systems outside the harsh arctic zone have been comprehensively investigated so far. The Galium pusillum aggregate (Rubiaceae) is a challenging species complex that exhibits a marked differentiation in boreal parts of Northern Europe. As a first step towards understanding its evolutionary history in deglaciated regions, this study assesses cytological variation and ecological preferences of the northern endemics and compares the results with corresponding data for species occurring in neighbouring unglaciated parts of Central and Western Europe.

Methods

DNA flow cytometry was used together with confirmatory chromosome counts to determine ploidy levels and relative genome sizes in 1158 individuals from 181 populations. A formalized analysis of habitat preferences was applied to explore niche differentiation among species and ploidy levels.

Key Results

The G. pusillum complex evolved at diploid and tetraploid levels in Northern Europe, in contrast to the high-polyploid evolution of most other northern endemics. A high level of eco-geographic segregation was observed between different species (particularly along gradients of soil pH and competition) which is unusual for plants in deglaciated areas and most probably contributes to maintaining species integrity. Relative monoploid DNA contents of the species from previously glaciated regions were significantly lower than those of their counterparts from mostly unglaciated Central Europe, suggesting independent evolutionary histories.

Conclusions

The aggregate of G. pusillum in Northern Europe represents an exceptional case with a geographically vicariant and ecologically distinct diploid/tetraploid species endemic to formerly glaciated areas. The high level of interspecific differentiation substantially widens our perception of the evolutionary dynamics and speciation rates in the dramatically changing environments of Northern Europe.     

Predictability, toxicity, and trophic niche breadth in fungus-feeding Drosophilidae (Diptera)

Abstract. 1. The mycophagous Drosophilidae flies in eastern North America display a range of ecological responses to their fungal trophic resources. Some ( Drosophilu duncani Sturtevant, and two species labelled as Mycodrosophila cluytonae Wheeler and Takada) specialize on the bracket fungi of the family Polyporaceae. Other species ( Drosophila falleni Wheeler, D.recens Wheeler, D.putridu Sturtevant and D.tripunctuta Loew) are broad generalists, non-selectively consuming a diverse array of Basidioniycete mushrooms. D.restaceu von Roser and D.ordinuria Coquillett utilize a broad subset of the Basidio-mycetes, while M.dimidiata hew feeds on some Basidioniycetes, including a variety of Clavariaceae (coral fungi) and Heterobasidiomycetes (jelly fungi) not commonly used by other flies, and Ascomycetes (cup fungi).
2. Unlike some phytophagous insects, host chemistry seems to have little effect on host preferences. The mycophagous drosophilids do not avoid fungi thought to be toxic or undigestible to other Diptera.
3. Resource predictability appears to delimit trophic niches in the mycophagous guild. The average duration of individual host mushroom caps is negatively correlated with three measures of trophic niche breadth. Specialist fly species utilize long-lasting resources, while more generalized mycophagous species include progressively ephemeral fungi in their diets.     

Performance of seedlings of Mediterranean woody species under experimental gradients of irradiance and water availability: trade-offs and evidence for niche differentiation

The aim of the study was to assess the potential importance for Mediterranean plants of trade-offs in the response to irradiance and water availability at the regeneration stage. Survival and growth patterns across an experimentally imposed irradiance gradient (1, 6, 20 and 100% sunlight) were studied in seedlings of eight Mediterranean woody species, together with the impact of a simulated summer drought. We found evidence of some of the trade-offs previously reported for non-Mediterranean plant communities, such as between survival in the shade and relative growth rate (RGR) at high light, but no evidence for others, such as between shade and drought tolerances. The impact of drought on survival and RGR was stronger in high light than in deep shade. The observed species-specific differences in performance provide a mechanistic basis for niche differentiation at the regeneration stage, contributing to possible explanations of species coexistence in Mediterranean ecosystems.     

桃园山楂叶螨、桃一点斑叶蝉及其主要天敌生态位

对山东桃园山楂叶螨、桃一点斑叶蝉及其主要天敌的时间、空间和时间一空间二维生态位宽度和生态位重叠进行了研究。结果表明,主要天敌异色瓢虫、七星瓢虫、龟纹瓢虫、大草蛉和蜘蛛与该2种害虫在时间上的同步性和空间上的同域性均较强,为保护利用天敌控制该2种害虫提供了依据。