How to compute the effective size of spatiotemporally structured populations using separation of time scales

Calculations to derive effective population size become highly complicated when complex population structure is considered. We provide an easy method of computing the effective size of a subdivided population with overlapping generations (a spatiotemporally structured population) using an approximation based on separation of time scales. We also numerically compute the effective size to verify the accuracy of the derived formula. Various interesting quantities, including moments of coalescent time, are readily derived using this approach.     

Sustained oscillations via coherence resonance in SIR

Sustained oscillations in a stochastic SIR model are studied using a new multiple scale analysis. It captures the interaction of the deterministic and stochastic elements together with the separation of time scales inherent in the appearance of these dynamics. The nearly regular fluctuations in the infected and susceptible populations are described via an explicit construction of a stochastic amplitude equation. The agreement between the power spectral densities of the full model and the approximation verifies that coherence resonance is driving the behavior. The validity criteria for this asymptotic approximation give explicit expressions for the parameter ranges in which one expects to observe this phenomenon.     

Molecular phylogeny, scale evolution and taxonomy of centrohelid heliozoa

Heliozoa are ubiquitous, unicellular phagotrophs with slender radiating axopodia for trapping prey. We sequenced 18S rRNA genes from 35 cultured centrohelid heliozoa (18 studied by electron microscopy) and 28 environmental libraries (18 freshwater, 10 marine), yielding 97 new sequences, this exceeding described species. Phylogenetic analyses show two major groups and that ancestral centrohelids probably had inner plate-like tangential and distinct outer radial silica scales, the latter diverging early into contrasting scale types seen in extant Pterocystis/Choanocystis and Acanthocystis/Raphidiophryidae. Scales were lost at least thrice. Pterocystis is paraphyletic, as was the classical family Acanthocystidae; Heterophrys was polyphyletic. Using scale morphology and rRNA sequences, we establish new families Pterocystidae (Pterocystis, Raineriophrys, Chlamydaster), Marophryidae (type Marophrys (Heterophrys) marina gen. et comb. nov.) and Choanocystidae, new suborders Pterocystina (Pterocystidae, Choanocystidae, Heterophryidae) and Acanthocystina (Acanthocystidae, Raphidiophryidae, Marophryidae), and ten new Pterocystis, Acanthocystis and Choanocystis species. Most clades are exclusively freshwater or exclusively marine; evolutionary transitions between these habitats have been rare.     

Predation Hot Spots: Large Scale Impact of Local Aggregations

Abstract   Broad scale survey distributions of fish are dominated by some extremely high catches. With a novel survey design we resolved the small-scale fish distribution in the spatio-temporal vicinity of these extreme hauls and showed that in the North Sea they generally do not occur in isolation. An additional case study where stomach contents of fish predators were analyzed revealed that they actually indicate aggregations of piscivorous fish predators on prey aggregations. We show that the predation impact can reach immense dimensions, an aggregation of more than 50 million juvenile cod (Gadus morhua) was entirely wiped out in 5 days by predatory whiting (Merlangius merlangus), aggregating on these juveniles in an area of approximately 18 km². The consumption of only 32 hot spots of similar magnitude as observed in our study adds up to the average size of an incoming North Sea cod year class. These findings support the hypothesis of predation as the major source of mortality in young-of-the-year demersal fish species and questions the generality of fish aggregation as an effective anti-predator strategy. This study highlights the system-wide structuring force of small-scale predation hot spots and further points to the importance of a more realistic implementation of local high-intensity predation events in food web models. Electronic supplementary material:   The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

Background and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan.Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively.Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species.Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.     

Limited influence of local and landscape factors on finescale gene flow in two pond‐breeding amphibians

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis between the ponds. We found overall high genetic connectivity across distances up to 17 km for both species and a limited effect of natural and anthropogenic factors on gene flow. We found the null models best explained patterns of genetic differentiation at a local level and found several factors at the landscape level that weakly influenced gene flow. This research indicates multiscale investigations that incorporate local and landscape factors are valuable for understanding patterns of gene flow. Our findings suggest that dispersal rates in this system are high enough to minimize genetic structuring and that current forestry practices do not significantly impede dispersal.     

KELP PATCH DYNAMICS IN THE FACE OF INTENSE HERBIVORY: STABILITY OF AGARUM CLATHRATUM (PHAEOPHYTA) STANDS AND ASSOCIATED FLORA ON URCHIN BARRENS1

The brown alga Agarum clathratum (Dumortier) is the only large, perennial, fleshy macrophyte commonly found on urchin‐dominated barrens in the northwestern North Atlantic. We examined the spatial and temporal stability of A. clathratum stands and their impact on algal recruitment in the Mingan Islands, northern Gulf of St. Lawrence. The stands were highly stable in space and time, with only small intersite variations. The percent cover of A. clathratum in 144‐m² areas increased by 6.5%–11.4% over a 2‐year period, and most changes in abundance occurred at the edge of the stands. The surface area of small (<13 m²) single stands of A. clathratum increased by approximately 1.8%·month^?1, although marked increases (>95%) occurred during winter, largely because adjacent stands merged into larger single stands. Mature stands of A. clathratum appear to enhance algal recruitment, as juvenile A. clathratum and the understory red alga Ptilota serrata (Kützing) were orders of magnitude more abundant inside than outside the stands. The experimental removal of the A. clathratum canopy (1‐m² portions) had no long‐term effect on the abundance of A. clathratum, which within 14 months had recolonized most of the cleared areas. In contrast to juvenile A. clathratum, the abundance of P. serrata rapidly decreased after canopy removal. Our results demonstrate that A. clathratum stands are a stable component of urchin barrens in spite of the heavy grazing that typically occurs there. Maintenance and expansion of A. clathratum stands and associated flora appear to depend on positive interactions with self‐defended adult A. clathratum.     

Distribution and characterization of proteins associated with cornification in the epidermis of gecko lizard

The distribution and molecular weight of epidermal proteins of gecko lizards have been studied by ultrastructural, autoradiographic, and immunological methods. Setae of the climbing digital pads are cross-reactive to antibodies directed against a chick scutate scale beta-keratin but not against feather beta-keratin. Cross-reactivity for mammalian loricrin, sciellin, filaggrin, and transglutaminase are present in alpha-keratogenic layers of gecko epidermis. Alpha-keratins have a molecular weight in the range 40-58 kDa. Loricrin cross-reactive bands have molecular weights of 42, 50, and 58 kDa. Bands for filaggrin-like protein are found at 35 and 42 kDa, bands for sciellin are found at 40-45 and 50-55 kDa, and bands for transglutaminase are seen at 48-50 and 60 kDa. The specific role of these proteins remains to be elucidated. After injection of tritiated histidine, the tracer is incorporated into keratin and in setae. Tritiated proline labels the developing setae of the oberhautchen and beta layers, and proline-labeled proteins (beta-keratins) of 10-14, 16-18, 22-24 and 32-35 kDa are extracted from the epidermis. In whole epidermal extract (that includes the epidermis with corneous layer and the setae of digital pads), beta-keratins of low-molecular weight (10, 14-16, and 18-19 kDa) are prevalent over those at higher molecular weight (34 and 38 kDa). In contrast, in shed epidermis of body scales (made of corneous layer only while setae were not collected), higher molecular weight beta-keratins are present (25-27 and 30-34 kDa). This suggests that a proportion of the small beta-keratins present in the epidermis of geckos derive from the differentiating beta layer of scales and from the setae of digital pads. Neither small nor large beta-keratins of gecko epidermis cross-react with an antibody specifically directed against the feather beta-keratin of 10-12 kDa. This result shows that the 10 and 14-16 kDa beta-keratins of gecko (lepidosaurian) have a different composition than the 10-12 kDa beta-keratin of feather (archosaurian). It is suggested that the smaller beta-keratins in both lineages of sauropsids were selected during evolution in order to build elongated bundles of keratin filaments to make elongated cells. Larger beta-keratins in reptilian scales produce keratin aggregations with no orientation, used for mechanical protection.     

Coupling ecology and evolution: malaria and the S-gene across time scales

Malaria has long been a scourge to humans. The exceptionally high mortality in some regions has led to strong selection for resistance, even at the cost of increased risk of potentially fatal red blood cell deformities in some offspring. In particular, genes that confers resistance to malaria when they appear in heterozygous individuals are known to lead to sickle-cell anemia, or other blood diseases, when they appear in homozygous form. Thus, there is balancing selection against the evolution of resistance, with the strength of that selection dependent upon malaria prevalence. Over longer time scales, the increased frequency of resistance in a population might be expected to decrease the frequency of malaria and reduce selection for resistance. However, possession of the sickle-cell gene leads to longer-lasting parasitaemia in heterozygote individuals, and therefore the presence of resistance may actually increase infection prevalence. In this paper, we explore the interplay among these processes, operating over very different time scales. In particular, we show that on the fast time scale of malarial dynamics, the disease level reaches an equilibrium; on the slower, evolutionary time scale, this equilibrium tracks gene frequency. We analyze the slow time scale dynamics to investigate the impact of malaria on the evolution of resistance.     

薇甘菊入侵扩散机制研究进展与改进思考

从薇甘菊(Mikania micrantha H B.k)的入侵分布、入侵能力以及群落可侵入性等方面对其入侵机制研究进展进行了分析和总结.以往的研究工作没有重视对薇甘菊入侵过程的整体性研究、对入侵扩散影响因素分析、空间尺度约束影响分析,以及分析方法和技术手段的缺陷.因此,未来应重点开展薇甘菊入侵扩散过程重建及潜在危害区域预测、景观结构对薇甘菊入侵危害的影响等研究,并完善薇甘菊入侵扩散的动态监测网络及风险评估体系.