Body‐colour variation in an orb‐web spider and its effect on predation success

Animal body coloration serves several functions such as thermoregulation, camouflage, aposematism, and intraspecific communication. In some orb‐web spiders, bright and conspicuous body colours are used to attract prey. On the other hand, there are other species whose body colour does not attract prey. Using a spider species showing individual body‐colour variation, the present study aimed to determine whether or not the variation in body colour shows a correlation with predation rates. We studied the orb‐web spider (Cyclosa argenteoalba) using both field observations and T‐maze experiments, in which the prey were exposed to differently coloured spiders. Cyclosa argenteoalba has silver‐ and black‐coloured areas on its dorsal abdomen, with the ratio of these two colours varying continuously among individuals. The bright and conspicuous silver area reflects ultraviolet light. Results of both field observations and colour choice experiments using Drosophila flies as prey showed that darker spiders have a greater chance of capturing prey than silver spiders. This indicates that body‐colour variation affects predation success among individuals and that the bright silver colour does not function to attract prey in C. argenteoalba.     

Lipids and trophic interactions of ice fauna and pelagic zooplankton in the marginal ice zone of the Barents Sea

Gammarus wilkitzkii, Apherusa glacialis, Onismus nanseni, Onismus glacialis, Boreogadus saida, Parathemisto libellula and Calanus hyperboreus, collected in late June in the Barents Sea marginal ice zone, contained substantial levels (28–51% of the dry mass) of total lipid, the highest levels (51% and 41% respectively) being in  A. glacialis and  C. hyperboreus. Neutral lipids were present in greater amounts than polar lipids in all species. Triacylglycerols were major neutral lipids in A. glacialis, G. wilkitzkii and O. nanseni; triacylglycerols and wax esters were present in similar amounts in O. glacialis; higher levels of wax esters than triacylglycerols occurred in P. libellula; wax esters greatly exceeded triacylglycerols in C. hyperboreus, the opposite being true for B. saida. Diatom fatty acid markers were prominent in the triacylglycerols of G. wilkitzkii, O. nanseni, O. glacialis and, particularly, of  A. glacialis; 20:1(n-9) and 22:1(n-11) moieties were abundant in wax esters of G. wilkitzkii, O. nanseni, O. glacialis, P. libellula and  C. hyperboreus, and in triacylglycerols of B. saida. We deduce that  A. glacialis feeds mainly on ice algae and phytodetritus, G. wilkitzkii and the Onismus spp. feed on calanoid copepods as well as ice algae, whereas P. libellula and especially B. saida feed extensively on calanoid copepods. Accepted: 17 May 1998     

Changes in structure of over‐ and midstory tree species in a Mediterranean‐type forest after an extreme drought‐associated heatwave

Worldwide, extreme climatic events such as drought and heatwaves are associated with forest mortality. However, the precise drivers of tree mortality at individual and stand levels vary considerably, with substantial gaps in knowledge across studies in biomes and continents. In 2010–2011, a drought‐associated heatwave occurred in south‐western Australia and drove sudden and rapid forest canopy collapse. Working in the Northern Jarrah (Eucalyptus marginata) Forest, we quantified the response of key overstory (E. marginata, Corymbia calophylla) and midstory (Banksia grandis, Allocasuarina fraseriana) tree species to the extreme climate event. Using transects spanning a gradient of drought impacts (minimal (50–100 m), transitional (100–150 m) and severe (30–60 m)), tree species mortality in relation to stand characteristics (stand basal area and stem density) and edaphic factors (soil depth) was determined. We show differential mortality between the two overstory species and the two midstory species corresponding to the drought‐associated heatwave. The dominant overstory species, E. marginata, had significantly higher mortality (~19%) than C. calophylla (~7%) in the severe zone. The midstory species, B. grandis, demonstrated substantially higher mortality (~59%) than A. fraseriana (~4%) in the transitional zone. Banksia grandis exhibited a substantial shift in structure in response to the drought‐associated heatwave in relation to tree size, basal area and soil depth. This study illustrates the role of climate extremes in driving ecosystem change and highlights the critical need to identify and quantify the resulting impact to help predict future forest die‐off events and to underpin forest management and conservation.     

Comparative intra‐ and interspecific sexual organ reciprocity in four distylous Primula species in the Himalaya‐Hengduan Mountains

• Distyly is a mechanism promoting cross‐pollination within a balanced polymorphism. Numerous studies show that the degree of inter‐morph sexual organ reciprocity (SOR) within species relates to its pollen‐mediated gene flow. Similarly, a lower interspecific SOR should promote interspecific isolation when congeners are sympatric, co‐blooming and share pollinators. In this comparative study, we address the significance of SOR at both intra‐ and interspecific levels.
• Seventeen allopatric and eight sympatric populations representing four Primula species (P. anisodora, P. beesiana, P. bulleyana and P. poissonii) native to the Himalaya‐Hengduan Mountains were measured for eight floral traits in both long‐ and short‐styled morphs. GLMM and spatial overlap methods were used to compare intra‐ and interspecific SOR.
• While floral morphology differed among four Primula species, SOR within species was generally higher than between species, but in species pairs P. poissonii/P. anisodora and P. beesiana/P. bulleyana, the SOR was high at both intra‐ and interspecific levels. We did not detect a significant variation in intraspecific SOR or interspecific SOR when comparing allopatric versus sympatric populations for all species studied.
• As intraspecific SOR increased, disassortative mating may be promoted. As interspecific SOR decreased, interspecific isolation between co‐flowering species pairs also may increase. Hybridisation between congeners occurred when interspecific SOR increased in sympatric populations, as confirmed in two species pairs, P. poissonii/P. anisodora and P. beesiana/P. bulleyana.

     

Host‐specific thermal profiles affect fitness of a widespread pathogen

Host behavior can interact with environmental context to influence outcomes of pathogen exposure and the impact of disease on species and populations. Determining whether the thermal behaviors of individual species influence susceptibility to disease can help enhance our ability to explain and predict how and when disease outbreaks are likely to occur. The widespread disease chytridiomycosis (caused by the fungal pathogen Batrachochytrium dendrobatidis, Bd) often has species‐specific impacts on amphibian communities; some host species are asymptomatic, whereas others experience mass mortalities and population extirpation. We determined whether the average natural thermal regimes experienced by sympatric frog species in nature, in and of themselves, can account for differences in vulnerability to disease. We did this by growing Bd under temperatures mimicking those experienced by frogs in the wild. At low and high elevations, the rainforest frogs Litoria nannotis, L. rheocola, and L. serrata maintained mean thermal regimes within the optimal range for pathogen growth (15–25°C). Thermal regimes for L. serrata, which has recovered from Bd‐related declines, resulted in slower pathogen growth than the cooler and less variable thermal regimes for the other two species, which have experienced more long‐lasting declines. For L. rheocola and L. serrata, pathogen growth was faster in thermal regimes corresponding to high elevations than in those corresponding to low elevations, where temperatures were warmer. For L. nannotis, which prefers moist and thermally stable microenvironments, pathogen growth was fastest for low‐elevation thermal regimes. All of the thermal regimes we tested resulted in pathogen growth rates equivalent to, or significantly faster than, rates expected from constant‐temperature experiments. The effects of host body temperature on Bd can explain many of the broad ecological patterns of population declines in our focal species, via direct effects on pathogen fitness. Understanding the functional response of pathogens to conditions experienced by the host is important for determining the ecological drivers of disease outbreaks.     

Landscape‐scale life‐history gradients in New Zealand freshwater fish

相似文献   

Sequence capture and next‐generation sequencing of ultraconserved elements in a large‐genome salamander

Amidst the rapid advancement in next‐generation sequencing (NGS) technology over the last few years, salamanders have been left behind. Salamanders have enormous genomes—up to 40 times the size of the human genome—and this poses challenges to generating NGS data sets of quality and quantity similar to those of other vertebrates. However, optimization of laboratory protocols is time‐consuming and often cost prohibitive, and continued omission of salamanders from novel phylogeographic research is detrimental to species facing decline. Here, we use a salamander endemic to the southeastern United States, Plethodon serratus, to test the utility of an established protocol for sequence capture of ultraconserved elements (UCEs) in resolving intraspecific phylogeographic relationships and delimiting cryptic species. Without modifying the standard laboratory protocol, we generated a data set consisting of over 600 million reads for 85 P. serratus samples. Species delimitation analyses support recognition of seven species within P. serratus sensu lato, and all phylogenetic relationships among the seven species are fully resolved under a coalescent model. Results also corroborate previous data suggesting nonmonophyly of the Ouachita and Louisiana regions. Our results demonstrate that established UCE protocols can successfully be used in phylogeographic studies of salamander species, providing a powerful tool for future research on evolutionary history of amphibians and other organisms with large genomes.     

Diploidization and genome size change in allopolyploids is associated with differential dynamics of low‐ and high‐copy sequences

Recent advances have highlighted the ubiquity of whole‐genome duplication (polyploidy) in angiosperms, although subsequent genome size change and diploidization (returning to a diploid‐like condition) are poorly understood. An excellent system to assess these processes is provided by Nicotiana section Repandae, which arose via allopolyploidy (approximately 5 million years ago) involving relatives of Nicotiana sylvestris and Nicotiana obtusifolia. Subsequent speciation in Repandae has resulted in allotetraploids with divergent genome sizes, including Nicotiana repanda and Nicotiana nudicaulis studied here, which have an estimated 23.6% genome expansion and 19.2% genome contraction from the early polyploid, respectively. Graph‐based clustering of next‐generation sequence data enabled assessment of the global genome composition of these allotetraploids and their diploid progenitors. Unexpectedly, in both allotetraploids, over 85% of sequence clusters (repetitive DNA families) had a lower abundance than predicted from their diploid relatives; a trend seen particularly in low‐copy repeats. The loss of high‐copy sequences predominantly accounts for the genome downsizing in N. nudicaulis. In contrast, N. repanda shows expansion of clusters already inherited in high copy number (mostly chromovirus‐like Ty3/Gypsy retroelements and some low‐complexity sequences), leading to much of the genome upsizing predicted. We suggest that the differential dynamics of low‐ and high‐copy sequences reveal two genomic processes that occur subsequent to allopolyploidy. The loss of low‐copy sequences, common to both allopolyploids, may reflect genome diploidization, a process that also involves loss of duplicate copies of genes and upstream regulators. In contrast, genome size divergence between allopolyploids is manifested through differential accumulation and/or deletion of high‐copy‐number sequences.     

Elevational partitioning in species distribution,abundance and body size of Australian alpine grasshoppers (Kosciuscola)

Changes in the physical environment with elevation can influence species distributions and their morphological traits. In mountainous regions, steep temperature gradients can result in patterns of ecological partitioning among species that potentially increases their vulnerability to climate change. We collected data on species distributions, relative abundance and body size for three grasshopper species of the genus Kosciuscola (K. usitatus, K. tristis and K. cognatus) at three locations within the mountainous Kosciuszko National Park in Australia (Thredbo, Guthega and Jagungal). All three species showed differences in their distributions according to elevation, with K. usitatus ranging from 1400 to 2000 m asl, K. tristis from 1600 to 2000 m asl and K. cognatus from 1550 to 1900 m asl. Decreasing relative abundance with increasing elevation was found for K. usitatus, but the opposite pattern was found for K. tristis. The relative abundance of K. cognatus did not change with elevation but was negatively correlated with foliage cover. Body size decreased with elevation in both male and female K. usitatus, which was similarly observed in female K. tristis and male K. cognatus. Our results demonstrate spatial partitioning of species distributions and clines in body size in relation to elevational gradients. Species‐specific sensitivities to climatic gradients may help to predict the persistence of this grasshopper assemblage under climate change.     

Change in nuclear DNA content and pollen size with polyploidisation in the sweet potato (Ipomoea batatas,Convolvulaceae) complex

• Genome size evolution and its relationship with pollen grain size has been investigated in sweet potato (Ipomoea batatas), an economically important crop which is closely related to diploid and tetraploid species, assessing the nuclear DNA content of 22 accessions from five Ipomoea species, ten sweet potato varieties and two outgroup taxa.
• Nuclear DNA amounts were determined using flow cytometry. Pollen grains were studied using scanning and transmission electron microscopy.
• 2C DNA content of hexaploid I. batatas ranged between 3.12–3.29 pg; the mean monoploid genome size being 0.539 pg (527 Mbp), similar to the related diploid accessions. In tetraploid species I. trifida and I. tabascana, 2C DNA content was, respectively, 2.07 and 2.03 pg. In the diploid species closely related to sweet potato e.g. I. ×leucantha, I. tiliacea, I. trifida and I. triloba, 2C DNA content was 1.01–1.12 pg. However, two diploid outgroup species, I. setosa and I. purpurea, were clearly different from the other diploid species, with 2C of 1.47–1.49 pg; they also have larger chromosomes. The I. batatas genome presents 60.0% AT bases.
• DNA content and ploidy level were positively correlated within this complex. In I. batatas and the more closely related species I. trifida, the genome size and ploidy levels were correlated with pollen size. Our results allow us to propose alternative or complementary hypotheses to that currently proposed for the formation of hexaploid Ipomoea batatas.

     

Genomic analyses of a “living fossil”: The endangered dove‐tree

Davidia involucrata Baill, also known as the dove‐tree, is a living fossil and an endangered species currently restricted to the mountains of southwestern and central China. It has a beautiful and innovative trait of high horticultural value: two white bracts covering the flower caputila. Here, we report on the chromosome‐scale genome of this species using single‐molecule real‐time long reads and chromosome conformation capture (Hi‐C) techniques. This species has a larger genome size of 1,169 Mb and contains relatively more genes (42,554) than the closely related species Camptotheca acuminata (397 Mb and 31,825 genes). Both species shared one recent whole genome duplication before their divergence. The expansion of the repetitive elements after their divergence contributed greatly to the increase in the genome size of the dove‐tree. Photosynthesis‐related genes were almost absent or showed reduced expression in the bracts of the dove‐tree, while defence‐ and chemical‐related genes increased greatly, highlighting the important roles of the bracts in protecting flowers and attracting pollinators. The effective population size of the dove‐tree continuously decreased during the climate changes of the Quaternary. Such climate sensitivity should be fully considered in conservation efforts for this relict endangered species in the context of continuous climate warming in the future.     

Chick diet of dovekies Alle alle in Northwest Greenland

This paper reports the results of an investigation of dovekies (Alle alle) breeding at Hakluyt Island in the Thule District, Northwest Greenland. The paper presents a comprehensive examination of the chick diet of dovekies in the species' most important breeding area. Food delivered to nestlings consisted primarily of copepods Calanus hyperboreus and C. glacialis in the copepodite stages IV and V. Themisto libellula, other amphipods, decapods and fish larvae in small numbers were found in the chick diet. The zooplankton in the chick diet is presented both in terms of numbers and dry weight. The characteristic copepod of high-arctic waters, C. hyperboreus, was found to be the single most important species in the chick diet, contributing approximately 54% of the dry food weight. The food samples revealed low diversity, and the three species C. hyperboreus, C. glacialis and T. libellula made up 91.5% of the total zooplankton dry weight. The results from this paper are compared with previous dovekie-chick diet studies. Accepted: 14 June 2000     

Lipids and life strategies of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in late autumn, Kongsfjorden, Svalbard

Stage IV and V copepodites were the dominant forms of Calanus finmarchicus, C. glacialis and C. hyperboreus in Kongsfjorden in late September 1997. Stage IV and V copepodites of C. glacialis and C. hyperboreus were rich in lipid, largely wax esters, and were well fitted to overwinter. Stage IV copepodites of C. finmarchicus were also rich in wax esters, but stage V copepodites of C. finmarchicus were less wax ester-rich. Large size increments between stage IV and V copepodites and between stage V copepodites and females were noted in C. finmarchicus. A very large increment between stage IV and V copepodites was noted for C. glacialis but the size difference between stage V copepodites and females was very small in this species. Particularly large increments were noted between stage IV and V copepodites of C. hyperboreus and also between stage V copepodites and females of this species. The very large, wax ester-rich C. hyperboreus is well adapted to survive the most extreme variations in the Arctic, in Arctic basin waters, whereas the smaller, wax ester-rich C. glacialis is adapted to survive less extreme Arctic variations, as in Arctic shelf waters. The smallest of the three, C. finmarchicus, is best adapted to survive the more predictable waters of the North Atlantic and the Barents Sea. Accepted: 3 January 2000     

Cold weather events provoke egg ejection behaviour in open‐nesting passerines

We analysed 25 conspecific egg ejection events from a large sample of nests (n = 762) of three passerine species. In two species, most of the events could not be explained by intraspecific brood parasitism or nest sanitation behaviour. At least some of these cases were behavioural responses to unfavourable weather conditions in the spring of 2017. We conclude that clutch size adjustment through egg ejection may be more widespread among passerines than previously thought.     

Relationships between intra‐specific variation in seed size and recruitment in four species in two contrasting habitats

Large seeds contain more stored resources, and seedlings germinating from large seeds generally cope better with environmental stresses such as shading, competition and thick litter layers, than seedlings germinating from small seeds. A pattern with small‐seeded species being associated with open habitats and large‐seeded species being associated with closed (shaded) habitats has been suggested and supported by comparative studies. However, few studies have assessed the intra‐specific relationship between seed size and recruitment, comparing plant communities differing in canopy cover. Here, seeds from four plant species commonly occurring in ecotones between open and closed habitats (Convallaria majalis, Frangula alnus, Prunus padus and Prunus spinosa) were weighed and sown individually (3200 seeds per species) in open and closed‐canopy sites, and seedling emergence and survival recorded over 3 years. Our results show a generally positive, albeit weak, relationship between seed size and recruitment. In only one of the species, C. majalis, was there an association between closed canopy habitat and a positive seed size effect on recruitment. We conclude that there is a weak selection gradient favouring larger seeds, but that this selection gradient is not clearly related to habitat.     

Ticks on snakes: The ecological correlates of ectoparasite infection in free‐ranging snakes in tropical Australia

Parasites profoundly influence the lives of their hosts, yet the dynamics of host–parasite interactions are poorly understood – especially in reptiles. We examined the ecological correlates of parasitism by ixodid ticks in an assemblage of 10 snake species in tropical Australia. In total, we recorded 3803 ticks on 1841 individual snakes of six species (no ticks were found on the other species). Molecular analyses confirmed the tropical reptile tick (Amblyomma fimbriatum: Ixodidae) to be the most common snake tick at our study site, with inter‐ and intraspecific variation in tick prevalence and intensity. Tick attachment sites were random on most snake species, but both male and female ticks congregated on the heads of the colubrid snake Boiga irregularis and the python Simalia amethistina. In these same species, tick loads were higher on snakes captured in woodland than in rainforest. Females of two python species (Aspidites melanocephalus and S. amethistina) had higher tick loads than did males. In B. irregularis, individuals captured in the dry season had higher tick loads than those captured in the wet season. In most parasitized snake species, larger individuals had greater tick loads. Data from snake recaptures confirmed individual tick burdens frequently varied, with little correlation between tick loads on the same snake at successive captures (except for B. irregularis). Finally, tick intensity was not correlated with (and thus, presumably did not influence) the body condition of any snake species in our study. Use of specific types of refuge sites may strongly influence tick loads on snakes in this system.     

Whole‐genome resequencing reveals the pleistocene temporal dynamics of Branchiostoma belcheri and Branchiostoma floridae populations

Global climatic fluctuations governed the ancestral demographic histories of species and contributed to place the current population status into a more extensive ecological and evolutionary context. Genetic variations will leave unambiguous signatures in the patterns of intraspecific genetic variation in extant species since the genome of each individual is an imperfect mosaic of the ancestral genomes. Here, we report the genome sequences of 20 Branchiostoma individuals by whole‐genome resequencing strategy. We detected over 140 million genomic variations for each Branchiostoma individual. In particular, we applied the pairwise sequentially Markovian coalescent (PSMC) method to estimate the trajectories of changes in the effective population size (N_e) of Branchiostoma population during the Pleistocene. We evaluated the threshold of sequencing depth for proper inference of demographic histories using PSMC was ≥25×. The PSMC results highlight the role of historical global climatic fluctuations in the long‐term population dynamics of Branchiostoma. The inferred ancestral N_e of the Branchiostoma belcheri populations from Zhanjiang and Xiamen (China) seawaters was different in amplitude before the first (mutation rate = 3 × 10^?9) or third glaciation (mutation rate = 9 × 10^?9) of the Pleistocene, indicating that the two populations most probably started to evolve in isolation in their respective seas after the first or third glaciation of the Pleistocene. A pronounced population bottleneck coinciding with the last glacial maximum was observed in all Branchiostoma individuals, followed by a population expansion occurred during the late Pleistocene. Species that have experienced long‐term declines may be especially vulnerable to recent anthropogenic activities. Recently, the industrial pollution and the exploitation of sea sand have destroyed the harmonious living environment of amphioxus species. In the future, we need to protect the habitat of Branchiostoma and make full use of these detected genetic variations to facilitate the functional study of Branchiostoma for adaptation to local environments.