ABSTRACT
Pronounced non‐genetic polymorphisms, or polyphenisms, occur in some monogonont rotifers reproducing by diploid, female parthenogenesis. In many brachionids, there is great variation in ...spine length. In trimorphic species of Asplanchna, females can vary in size and shape, from a small saccate morph to giant cruciform and campanulate morphs. In species that also reproduce sexually, diploid eggs can develop into two types of females. Amictic females produce diploid eggs that develop parthenogenetically into females; mictic females produce haploid eggs that develop parthenogenetically into males or, if fertilized, into resting eggs. In a species of Synchaeta, amictic females produce diploid eggs that can be either thin‐shelled and subitaneous or thicker‐shelled and diapausing. In all cases, morph determination occurs during the oogenesis or embryological development of diploid eggs in the maternal body cavity. For the first time, these polymorphisms are reviewed together and compared regarding a number of features associated with transitions from default to induced morphs: (i) type of variation (morphological, physiological, or both; continuous or discrete); (ii) inducing signal (environmental, endogenous, or both); (iii) universality of response to that signal (all or only some individuals); (iv) fitness cost; (v) reversibility; and (vi) ecological significance. Most of the polymorphisms fall into two major categories regarding these features. Transitions suitable for predictable environments involve: universal responses to environmental signals; continuous morphological variation; low reproductive cost; rapid reversibility; and adaptations for defence, hydrodynamics or prey ingestion. Transitions suitable for unpredictable environments are bet‐hedging strategies and usually involve: partial (stochastic) responses to environmental or endogenous signals; discontinuous physiological variation; initiation of diapause, and thus high reproductive cost and slow reversibility. Two cases of morphological variation also involve the simultaneous production of different morphs and likely are adaptations for an uncertain future: continuous spine‐length variation due to maternal age in Brachionus calyciflorus, and production of discrete cruciform and campanulate females in Asplanchna spp.
Abstract
The rotifer
Epiphanes brachionus spinos
a occurs in shallow temporary waters with hydroperiods up to several months in the Chihuahuan Desert (U.S.A. and Mexico). Clonal populations from one ...such habitat were initiated from stem females hatched from fertilised resting eggs in flooded dried sediment, and cultured with the alga
Cryptomonas erosa
at 19°C in a photoperiod (L:D 16:8). Experiments show that the rotifer has: (1) a morphological response to the predatory rotifer
Asplanchna
, with which it can co‐occur; and (2) an early and constant propensity for sex and resting‐egg production during population development.
Stem females, and females from later generations, have two posterior spines. Measurements of live juveniles and adults indicate that spine length increases isometrically during postnatal growth.
Presence of live
Asplanchna brightwellii
, or its kairomone in
Asplanchna
‐conditioned medium, significantly increase spine length. In one clone, spine lengths of juvenile
Epiphanes
from cultures with or without live
Asplanchna
were, respectively,
c.
40 and
c.
27 μm. In that clone, spine lengths of adult
Epiphanes
in cultures with or without
Asplanchna
kairomone were, respectively,
c.
54 and
c.
37 μm. In another clone, these spine lengths were, respectively,
c.
44 and
c.
36 μm.
Asplanchna
‐induced spine elongation may act as a mechanical defence against capture and ingestion by the predator.
Sexual reproduction in
E. brachionus spinosa
populations is initiated soon after populations develop from stem females and then continues at a rate allowing both population growth by female parthenogenesis and production of resting eggs. Resting eggs hatched after 6–12 days at 19°C. Stem females were amictic (producing daughters parthenogenetically) but produced some daughters that were mictic (producing haploid males parthenogenetically or fertilised resting eggs). In subsequent generations tested 2–7 weeks after hatching of stem females, amictic females from three clonal populations produced similar proportions of mictic daughters (mean
c.
0.25) when cultured singly in large volumes (15 and 40 ml) or a small one (1.5 ml).
Mictic‐female production is probably automatic and controlled by an endogenous mechanism, rather than specifically induced by crowding or some other environmental factor. Early and continuous sexual reproduction assures production of resting eggs throughout short and unpredictable hydroperiods.
A review of research on life‐cycle events in field and laboratory populations of monogonont rotifers shows that there is great variation at multiple levels: (1) degree of sexual dimorphism; (2) ...occurrence and timing of sex; (3) propensity for sex during sexual periods; (4) factors controlling initiation of sex; and (5) timing and extent of emergence from diapause. There is no regular pattern where: (1) fertilised resting eggs hatch to start the growing season; (2) populations develop via female parthenogenesis during favourable conditions; and then (3) bisexual reproduction with resting‐egg production occurs during later, unfavourable conditions.
Sexual reproduction in natural populations can occur throughout much of the growing season, be restricted to some period(s) during the growing season, or be completely absent. During sexual reproduction in both natural and laboratory populations, only some fraction of females produces males or resting eggs. This bet‐hedging strategy can prevent a population crash and permits future population growth via female parthenogenesis. Selection against sexual reproduction, and rapid loss of sex, can occur.
Laboratory experiments with pond‐dwelling species have identified specific environmental factors that induce sex in different species: (1) increasing population density; (2) dietary tocopherol (vitamin E) and (3) long photoperiods. These factors generally are associated with favourable conditions for population growth and production of energy‐rich resting eggs: (1) large population size; (2) high probability of contacts between males and fertilisable females; and (3) nutritious diets. Endogenous factors can inhibit responses to these environmental inducers, and thus favour female parthenogenesis.
The timing of resting‐egg hatching depends on: (1) occurrence of specific environmental conditions; (2) the minimum duration of obligate diapause; and (3) the genotype and physiology of females producing resting eggs. Hatching may occur shortly after oviposition, after a long diapause before or at the start of a new growing season, or throughout the growing season. Hatching can be massive and contribute substantially to population growth and genetic diversity.
Areas for future research include: (1) determining the timing and extent of sex and resting‐egg hatching in more natural populations, especially those that are marine, benthic, sessile, and interstitial; and (2) identifying environmental and physiological factors controlling these events.
Experiments with two strains of the facultative epibiont,
Brachionus rubens
, tested the ability of this rotifer to avoid predation by the rotifer
Asplanchna
, and its propensity for sexual ...reproduction and consequent diapause at different population densities. Unlike some congeners,
B. rubens
did not have a morphological response to
Asplanchna
by developing longer spines or a larger body. However, it responded to this predator, and its kairomone, with a behavioral defense: a higher propensity to transition from free-swimming to attachment, typically in dense aggregations. Attached individuals were less likely to be captured and ingested, so that
B. rubens
outlived
Asplanchna
in some mixed-species cultures. Although crowding induces sex in some congeners, it did not do so in
B. rubens
. Instead, the proportion of sexual (mictic) daughters produced by females cultured in different volumes (0.5–60 ml) was density-independent: ~ 0.2 for the Argentina strain and ~ 0.6 for the Australia strain. Such fixed levels of sex have rarely been detected in rotifers. In
B. rubens
, they may be a strategy to ensure some sex with diapause at all times, but permit continued population growth via female parthenogenesis at the very high densities that normally occur on hosts and other surfaces.
Some of the most pressing problems currently facing chemical education throughout the world are rehearsed. It is suggested that if the notion of "context" is to be used as the basis for an address to ...these problems, it must enable a number of challenges to be met. Four generic models of "context" are identified that are currently used or that may be used in some form within chemical education as the basis for curriculum design. It is suggested that a model based on physical settings, together with their cultural justifications, and taught with a socio-cultural perspective on learning, is likely to meet those challenges most fully. A number of reasons why the relative efficacies of these four models of approaches cannot be evaluated from the existing research literature are suggested. Finally, an established model for the representation of the development of curricula is used to discuss the development and evaluation of context-based chemical curricula.
A professional's guide to solving complex problems while designing modern softwareKey FeaturesLearn best practices for designing an enterprise-grade software structureUnderstand the importance of ...building reliable, maintainable, and scalable systemsBecome a professional software architect by learning the most effective patterns and architectural conceptsBook DescriptionAs businesses are undergoing a digital transformation to keep up with competition, it is now more important than ever for IT professionals to design systems to keep up with the rate of change and maintain the stability of their systems.This book takes you through the architectural patterns that power cloud software systems and the key forces driving architectural decisions such as events, serverless, and micro-frontends, along with demonstrating how to implement and operate anti-fragile systems. You'll understand how to divide up a system and define boundaries so that teams can work on implementation of the system within their areas of remit. The book also covers low-level event and data patterns that support the entire architecture, while getting you up and running with the different autonomous service patterns. As you progress, you'll focus on best practices for security, reliability, testability, observability, and performance. Finally, the book combines all that you've learned, explaining the methodology for continuous experimentation, deployment, and delivery before providing you with some final thoughts on how to start making progress.By the end of this book, you'll be able to architect your own event-driven, serverless systems that are ready to adapt and change so that you can deliver value at the pace needed by your business.What you will learnExplore architectural patterns for creating anti-fragile systems that thrive with changeFocus on DevOps practices that empower self-sufficient, full-stack teamsBuild enterprise-scale serverless systemsApply microservices principles to the frontendDiscover how SOLID principles apply to event-driven systemsCreate fault-tolerant processing with the stream circuit breaker pattern and fault eventsDeploy a multi-regional system, including regional health checks, latency based routing, and replicationExplore the Strangler pattern for migrating legacy systems Who This Book Is ForThis book is for software architects and aspiring software architects who want to learn about different patterns and best practices to design better software. Intermediate-level experience in software development and design is required. Beginner-level knowledge of the cloud will also be beneficial.
The planktonic rotifer, Brachionus calyciflorus, displays extensive variation in the length of its anterior and posterior spines. Notably, posterolateral spines may be absent or near body length. ...Studies of laboratory and natural populations have identified the different factors controlling this variation and have investigated the trade-offs associated with increased spine development. Low temperature and low food availability can induce modest spine elongation that may reduce sinking rate. A kairomone released by the carnivorous rotifer Asplanchna induces pronounced spine elongation, without detectable reproductive cost, that can provide an effective defense against this predator. Endogenous mechanisms also operate: Spine development is inhibited in females hatched from fertilized resting eggs and can be promoted by increasing maternal age. Genetic variation for the length of spines in both noninduced (default) and induced phenotypes occurs among and within populations. Asplanchna in natural communities likely leads to seasonal selection for genotypes that can develop increasingly long spines.
Abstract
The planktonic rotifer Brachionus calyciflorus was reported to have a behavioral response to the predatory rotifer Asplanchna, where individuals move up to a surface-film refuge. Here, I ...re-examine this response and also test the hypothesis that Asplanchna affects the propensity of B. calyciflorus to attach to glass surfaces. In eight experiments where B. calyciflorus was exposed to a strong Asplanchna stimulus for periods varying from 3 to 65 h, adults and juveniles showed no increase in propensity to settle at the surface film or to attach to glass surfaces. In treatments with and without Asplanchna, percentages of Brachionus free-swimming, attached to glass or settled at the surface film were 81–100%, 0–18% and 0–3%, respectively. Three types of defensive responses in planktonic rotifers are reviewed: (1) transgenerational, spine-development responses to the Asplanchna kairomone in many brachionids; (2) slow-onset (4–48 h) increases in attachment propensity due to Asplanchna, or just its kairomone, in the facultatively epizoic Brachionus rubens and Brachionus variabilis and in an attachment-prone clone of Brachionus dorcas (B. calyciflorus species complex) and (3) brief escape movements caused by disturbance immediately after contact or near-contact with various predators (Asplanchna, Daphnia, copepods) in Filinia, Keratella, Hexarthra and Polyarthra.
This paper presents a scalable high-performance software library to be used for graph analysis and data mining. Large combinatorial graphs appear in many applications of high-performance computing, ...including computational biology, informatics, analytics, web search, dynamical systems, and sparse matrix methods. Graph computations are difficult to parallelize using traditional approaches due to their irregular nature and low operational intensity. Many graph computations, however, contain sufficient coarse-grained parallelism for thousands of processors, which can be uncovered by using the right primitives. We describe the parallel Combinatorial BLAS, which consists of a small but powerful set of linear algebra primitives specifically targeting graph and data mining applications. We provide an extensible library interface and some guiding principles for future development. The library is evaluated using two important graph algorithms, in terms of both performance and ease-of-use. The scalability and raw performance of the example applications, using the Combinatorial BLAS, are unprecedented on distributed memory clusters.
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