Sex, drugs and recombination: the wild life of Aspergillus

Throughout the eukaryotes, sexual reproduction is an almost universal phenomenon. However, within the Kingdom Fungi, this relationship is not so clear‐cut. Fungi exhibit a spectrum of reproductive modes and life‐cycles; amongst the better known species, sexual reproduction is often facultative, can be rare, and in over half of the known Ascomycota (the moulds) is unknown ( Taylor et al. 1999 ). However, over the last decade, it has become apparent that many of these asexual mitosporic taxa undergo cryptic recombination via unobserved mechanisms and that wholly asexual fungi are, in fact, a rarity ( Taylor et al. 1999, 2001 ; Heitman 2010 ). This revolution in our understanding of fungal sexuality has come about in two ways: Firstly, sexual reproduction leaves an imprint on fungal genomes by maintaining genes required for mating and by generating patterns of mutation and recombination restricted to meiotic processes. Secondly, scientists have become better at catching fungi in flagrante delicto. The genus Aspergillus is one such fungus where a combination of population genetics, genomics and taxonomy has been able to intuit the existence of sex, then to catch the fungus in the act and formally describe their sexual stages. So, why are sexy moulds exciting? One species in particular, Aspergillus flavus, is notorious for its ability to produce a diverse array of secondary metabolites, of which the polyketide aflatoxins (AF) are carcinogenic and others (such as cyclopiazonic acid) are toxigenic. Because of the predilection of A. flavus to grow on crops, such as peanuts, corn and cotton, biocontrol is widely used to mitigate infection by pre‐applying nonaflatoxigenic (AF?) strains to competitively exclude the wild‐type AF+ strains. However, the eventual fate in nature of these biocontrol strains is not known. In this issue of Molecular Ecology, Olarte et al. (2012) make an important contribution by using laboratory crosses of A. flavus to show that not only is AF highly heritable, but AF? strains can become AF+ via crossing over during meiosis. This observation has raised the spectre of cross‐breeding and non‐mendelian inheritance of AF between native and biocontrol strains of the fungus, leading to an increase in the natural diversity of the fungus with perhaps unanticipated consequences.     

Frequency and inheritance of non‐male producing clones in Daphnia magna: evolution towards sex specialization in a cyclical parthenogen?

In Daphnia (Cladocera, Crustacea), parthenogenetic reproduction alternates with sexual reproduction. Individuals of both sexes that belong to the same parthenogenetic line are genetically identical, and their sex is determined by the environment. Previously, non-male producing (NMP) genotypes have been described in species of the Daphnia pulex group. Such genotypes can only persist through phases of sexual reproduction if they co-occur with normal (MP) genotypes that produce both males and females, and thus the breeding system polymorphism is similar to gynodioecy (coexistence of females with hermaphrodites), which is well known in plants. Here we show that the same breeding system polymorphism also occurs in Daphnia magna, a species that has diverged from D. pulex more than 100 MY ago. Depending on the population, between 0% and 40% of D. magna females do not produce males when experimentally exposed to a concentration of the putative sex hormone methyl farnesoate that normally leads to male-only clutches. Natural broods of these NMP females never contained males, contrasting with high proportions of male offspring in MP females from the same populations. The results from a series of crossing experiments suggest that NMP is determined by a dominant allele at a single nuclear locus (or a several closely linked loci): NMP × MP crosses always yielded 50% NMP and 50% MP offspring, whereas MP × MP crosses always yielded 100% MP offspring. Based on cytochrome c oxidase subunit I-sequences, we found that NMP genotypes from different populations belong to three highly divergent mitochondrial lineages, potentially representing three independent evolutionary origins of NMP in D. magna. Thus, the evolution of NMP genotypes in cyclical parthenogens may be more common than previously thought. Moreover, MP genotypes that coexist with NMP genotypes may have responded to the presence of the latter by partially specializing on male production. Hence, these populations of D. magna may be a model for an evolutionary transition from a purely environmental to a partially genetic sex determination system.     

Evolutionarily accelerated invasions: the rate of dispersal evolves upwards during the range advance of cane toads

Human activities are changing habitats and climates and causing species' ranges to shift. Range expansion brings into play a set of powerful evolutionary forces at the expanding range edge that act to increase dispersal rates. One likely consequence of these forces is accelerating rates of range advance because of evolved increases in dispersal on the range edge. In northern Australia, cane toads have increased their rate of spread fivefold in the last 70 years. Our breeding trials with toads from populations spanning the species' invasion history in Australia suggest a genetic basis to dispersal rates and interpopulation genetic variation in such rates. Toads whose parents were from the expanding range front dispersed faster than toads whose parents were from the core of the range. This difference reflects patterns found in their field-collected mothers and fathers and points to heritable variance in the traits that have accelerated the toads' rate of invasion across tropical Australia over recent decades. Taken together with demonstrated spatial assortment by dispersal ability occurring on the expanding front, these results point firmly to ongoing evolution as a driving force in the accelerated expansion of toads across northern Australia.     

Disease and colony establishment in the dampwood termite Zootermopsis angusticollis: survival and fitness consequences of infection in primary reproductives

Pathogens have likely infl uenced life-history evolution in social insects because their nesting ecology and sociality can exacerbate the risk of disease transmission and place demands on the immune system that ultimately can impact colony survival and growth. The costs of the maintenance and induction of immune function may be particularly significant in termites, which have a nitrogen-poor diet. We examined the effect of fungal exposure on survival and reproduction during colony foundation in the dampwood termite Zootermopsis angusticollis by experimentally pairing male and female primary reproductives and exposing them to single (‘acute’) and multiple (‘serial’) dosages of conidia of the fungus Metarhizium anisopliae and recording their survival and fitness over a 560 day period. The number of eggs laid 70 days post-pairing was significantly reduced relative to controls in the serial-exposure but not the acute-exposure treatment. Reproduction thus appeared to be more resilient to a single pathogen exposure than to serial challenge to the immune system. The impact of fungal exposure was transient: all surviving colonies had similar reproductive output after 300 days post-pairing. Our results suggest that disease can have significant survival and fitness costs during the critical phase of colony foundation but that infection at this time may not necessarily impact long-term colony growth. Received 25 February 2005; revised 27 September and 20 October 2005; accepted 20 December 2005.     

Predictive ecology: systems approaches

The world is experiencing significant, largely anthropogenically induced, environmental change. This will impact on the biological world and we need to be able to forecast its effects. In order to produce such forecasts, ecology needs to become more predictive--to develop the ability to understand how ecological systems will behave in future, changed, conditions. Further development of process-based models is required to allow such predictions to be made. Critical to the development of such models will be achieving a balance between the brute-force approach that naively attempts to include everything, and over simplification that throws out important heterogeneities at various levels. Central to this will be the recognition that individuals are the elementary particles of all ecological systems. As such it will be necessary to understand the effect of evolution on ecological systems, particularly when exposed to environmental change. However, insights from evolutionary biology will help the development of models even when data may be sparse. Process-based models are more common, and are used for forecasting, in other disciplines, e.g. climatology and molecular systems biology. Tools and techniques developed in these endeavours can be appropriated into ecological modelling, but it will also be necessary to develop the science of ecoinformatics along with approaches specific to ecological problems. The impetus for this effort should come from the demand coming from society to understand the effects of environmental change on the world and what might be performed to mitigate or adapt to them.     

Habitat quality ranking depends on habitat-independent environmental factors: a model and results from Callosobruchus maculatus

1. Survival and reproduction in different habitats of a heterogeneous environment are affected by intrinsic habitat properties as well as by habitat-independent extrinsic factors. It is argued that the ranking of habitats according to quality may depend on extrinsic environmental factors that act with the same intensity in all habitats. This can happen if, across habitats, high reproductive success in the absence of extrinsic mortality is coupled with late reproduction.
2. In a model of a semelparous organism with overlapping generations that uses two habitats, the effect of different patterns of extrinsic mortality on habitat quality are analysed, as measured by the reproductive value of an egg, which estimates its expected contribution to the future gene pool.
3. Measurements of fitness components in Callosobruchus maculatus (F.) (Coleoptera: Bruchidae) on four host species demonstrate that, across hosts, long development can be associated with high reproductive success in the absence of extrinsic mortality. As a result, the quality ranking of three out of the four hosts would be different in a stable population regulated by intraspecific competition and egg parasitoids than in a growing population or a stable population regulated by age-independent larval mortality.
4. It is suggested that habitat-independent mortality may play a role in the evolution of ecological niches.     

沿海榆毡蚧的生物学特性及防治

园林重要害虫沿海榆毡蚧Eriococcus costatus(Danzig)在山西太谷1年发生1代,以2龄若虫及预蛹越冬。雌虫经卵、1龄若虫、2龄若虫、成虫完成生活史。雄虫则经卵、1龄若虫、2龄若虫、预蛹、冬前蛹(无翅型)、无翅雄成虫和部分若虫到冬后化蛹(有翅型)、有翅雄成虫,完成其生活史。影响该虫种群动态的主要生态因子包括温度、湿度、食料、天敌等,其中湿度在初孵若虫期是最主要的影响因子。4月上中旬为该虫的最佳防治时期,杀虫剂宜采用内吸性、触杀型的,且脂溶性效果较好。     

The genomic and physiological basis of life history variation in a butterfly metapopulation

Unravelling the mechanisms underlying variation in life history traits is of fundamental importance for our understanding of adaptation by natural selection. While progress has been made in mapping fitness-related phenotypes to genotypes, mainly in a handful of model organisms, functional genomic studies of life history adaptations are still in their infancy. In particular, despite a few notable exceptions, the genomic basis of life history variation in natural populations remains poorly understood. This is especially true for the genetic underpinnings of life history phenotypes subject to diversifying selection driven by ecological dynamics in patchy environments--as opposed to adaptations involving strong directional selection owing to major environmental changes, such as latitudinal gradients, extreme climatic events or transitions from salt to freshwater. In this issue of Molecular Ecology,Wheat et al. (2011) now make a significant leap forward by applying the tools of functional genomics to dispersal-related life history variation in a butterfly metapopulation. Using a combination of microarrays, quantitative PCR and physiological measurements, the authors uncover several metabolic and endocrine factors that likely contribute to the observed life history phenotypes. By identifying molecular candidate mechanisms of fitness variation maintained by dispersal dynamics in a heterogeneous environment,they also begin to address fascinating interactions between the levels of physiology, ecology and evolution.     

Boechera, a model system for ecological genomics

The selection and development of a study system for evolutionary and ecological functional genomics (EEFG) depend on a variety of factors. Here, we present the genus Boechera as an exemplary system with which to address ecological and evolutionary questions. Our focus on Boechera is based on several characteristics as follows: (i) native populations in undisturbed habitats where current environments reflect historical conditions over several thousand years; (ii) functional genomics benefitting from its close relationship to Arabidopsis thaliana; (iii) inbreeding tolerance enabling development of recombinant inbred lines, near-isogenic lines and positional cloning; (iv) interspecific crosses permitting mapping for genetic analysis of speciation; (v) apomixis (asexual reproduction by seeds) in a genetically tractable diploid; and (vi) broad geographic distribution in North America, permitting ecological genetics for a large research community. These characteristics, along with the current sequencing of three Boechera species by the Joint Genome Institute, position Boechera as a rapidly advancing system for EEFG studies.     

Transgenerational and developmental plasticity at the molecular level: Lessons from Daphnia

Listen to the news and you are bound to hear that researchers are increasingly interested in the biological manifestations of trauma that reverberate through the generations. Research in this area can be controversial in the public realm, provoking societal issues about personal responsibility (are we really born free or are we born with the burden of our ancestors’ experience?). It is also a touchy subject within evolutionary biology because it provokes concerns about Lamarckianism and general scepticism about the importance of extra‐genetic inheritance (Laland et al., 2014 ). Part of why the research in this area has been controversial is because it is difficult to study. For one, there is the problem of how long it takes to track changes across generations, making long‐term, multi‐generational studies especially tricky in long‐lived species. Moreover, there are presently very few (if any) known molecular mechanisms by which environmental effects can be incorporated into the genome and persist for multiple successive generations, casting doubt on their evolutionary repercussions. Fortunately, you only have to look in your local pond to find the creatures that are teaching us a great deal about how and why the experiences of parents are passed down to their offspring. In this issue of Molecular Ecology, Hales et al. (Hales et al., 2017 ) illustrate the power of Daphnia (“water fleas”) for making headway in this field.