Impact of inter‐ and intra‐specific competition among larvae on larval,adult, and life‐table traits of Aedes aegypti and Aedes albopictus females

1. Few studies have taken a comprehensive approach of measuring the impact of inter‐ and intra‐specific larval competition on adult mosquito traits. In this study, the impact of competition among Aedes aegypti (L.) and A. albopictus (Skuse) was quantified over the entire life of a cohort. 2. Competitive treatments affected hatch‐to‐adult survivorship and the development time to adulthood of females for both species but affected the median wing length of females only for A. albopictus. Competitive treatments had no significant effect on the median adult female longevity nor were there any effects on other individual traits related to blood feeding and reproductive success. 3. Analysis of life table traits revealed no effect of competitive treatment on the net reproductive rate (R₀) but there were significant effects on the cohort generation time (T_c) and the cohort rate of increase (r) for both species. 4. Inter‐ and intra‐specific competition among Aedes larvae may produce individual and population‐level effects that are manifest in adults; however, benign conditions may enable resulting adults to compensate for some impacts of competition, particularly those affecting blood‐feeding success, fecundity, and the net reproductive rate, R₀. The effect of competition, therefore, affects primarily larva‐to‐adult survivorship and the larval development time, which in turn impacts the cohort generation time, T_c, and ultimately the cohort rate of increase, r. 5. The lack of effects of the larval rearing environment on adult longevity suggests that effects on vectorial capacity owing to longevity may be limited if adults have easy access to sugar and bloodmeals.     

Size variation and reproductive success in the mosquito Aedes cantans

Abstract. A link between density-dependent larval competition and adult size of the mosquito Aedes cantans was demonstrated in northern England. Ponds containing high larval densities produced smaller larvae which, in turn, resulted in smaller adults at emergence.
In both 1989 and 1990, parous mosquitoes caught at human bait were larger than nulliparous ones, suggesting that larger mosquitoes are more successful at host location and egg-laying and also that they may be longer lived.
Larger mosquitoes produced larger egg clutches than smaller females: however, there was no difference in the size of eggs laid by large and small females.     

Effects of intraspecific larval competition on adult longevity in the mosquitoes Aedes aegypti and Aedes albopictus

Abstract Larval competition is common in container‐breeding mosquitoes. The impact of competition on larval growth has been thoroughly examined and findings that larval competition can lead to density‐dependent effects on adult body size have been documented. The effects of larval competition on adult longevity have been less well explored. The effects of intraspecific larval densities on the longevity of adults maintained under relatively harsh environmental conditions were tested in the laboratory by measuring the longevity of adult Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) that had been reared under a range of larval densities and subsequently maintained in high‐ or low‐humidity regimes (85% or 35% relative humidity [RH], respectively) as adults. We found significant negative effects of competition on adult longevity in Ae. aegypti, but not in Ae. albopictus. Multivariate analysis of variance suggested that the negative effect of the larval environment on the longevity of Ae. aegypti adults was most strongly associated with increased development time and decreased wing length as adults. Understanding how larval competition affects adult longevity under a range of environmental conditions is important in establishing the relationship between models of mosquito population regulation and epidemiological models of vector‐borne disease transmission.     

Wolbachia modulates Chikungunya replication in Aedes albopictus

The Aedes albopictus mosquito has been involved as the principal vector of recent major outbreaks due to the chikungunya virus (CHIKV). The species is naturally infected by two strains of Wolbachia (wAlbA and wAlbB). Wolbachia infections are thought to have spread by manipulating the reproduction of their hosts; cytoplasmic incompatibility is the mechanism used by Wolbachia to invade natural populations of many insects including Ae. albopictus. Here, we report a study on the effects of removing Wolbachia from Ae. albopictus on CHIKV replication and examine the consequences of CHIKV infection on some life‐history traits (survival and reproduction) of Wolbachia‐free Ae. albopictus. We found that Wolbachia‐free mosquitoes maintained a highly heterogeneous CHIKV replication compared to Wolbachia‐infected individuals. In Wolbachia‐infected Ae. albopictus, the regular increase of CHIKV followed by a steady viral load from day 4 post‐infection onwards was concomitant with a decline in Wolbachia density. This profile was also detected when examining the two key organs for viral transmission, the midgut and the salivary glands. Moreover, Wolbachia‐free Ae. albopictus was not altered in life‐history traits such as survival, oviposition and hatching characteristics whether infected or not with CHIKV. We found that Wolbachia is not essential for viral replication, its presence could lead to optimize replication from day 4 post‐infection onwards, coinciding with a decrease in Wolbachia density. Wolbachia may regulate viral replication in Ae. albopictus, with consequences on survival and reproduction.     

Genome analyses substantiate male mutation bias in many species

In many species the mutation rate is higher in males than in females, a phenomenon denoted as male mutation bias. This is often observed in animals where males produce many more sperm than females produce eggs, and is thought to result from differences in the number of replication-associated mutations accumulated in each sex. Thus, studies of male mutation bias have the capacity to reveal information about the replication-dependent or replication-independent nature of different mutations. The availability of whole genome sequences for many species, as well as for multiple individuals within a species, has opened the door to studying factors, both sequence-specific and those acting on the genome globally, that affect differences in mutation rates between males and females. Here, we assess the advantages that genomic sequences provide for studies of male mutation bias and general mutation mechanisms, discuss major challenges left unresolved, and speculate about the direction of future studies.     

Competitive ability depends on mating system and ploidy level across Capsella species

Background and AimsSelf-fertilization is often associated with ecological traits corresponding to the ruderal strategy, and selfers are expected to be less competitive than outcrossers, either because of a colonization/competition trade-off or because of the deleterious genetic effects of selfing. Range expansion could reduce further competitive ability while polyploidy could mitigate the effects of selfing. If pollinators are not limited, individual fitness is thus expected to be higher in outcrossers than in selfers and, within selfers, in polyploids than in diploids. Although often proposed in the botanical literature and also suggested by meta-analyses, these predictions have not been directly tested yet.MethodsIn order to compare fitness and the competitive ability of four Capsella species with a different mating system and ploidy level, we combined two complementary experiments. First, we carried out an experiment outdoors in north-west Greece, i.e. within the range of the obligate outcrossing species, C. grandiflora, where several life history traits were measured under two different disturbance treatments, weeded plots vs. unweeded plots. To better control competition and to remove potential effects of local adaptation of the outcrosser, we also performed a similar competition experiment but under growth chamber conditions.Key ResultsIn the outdoor experiment, disturbance of the environment did not affect the phenotype in any of the four species. For most traits, the obligate outcrossing species performed better than all selfing species. In contrast, polyploids did not survive or reproduce better than diploids. Under controlled conditions, as in the field experiment, the outcrosser had a higher fitness than selfing species and was less affected by competition. Finally, contrary to the outdoor experiment where the two behaved identically, polyploid selfers were less affected by competition than diploid selfes.ConclusionsIn the Capsella genus, selfing induces lower fitness than outcrossing and can also reduce competitive ability. The effect of polyploidy is, however, unclear. These results highlight the possible roles of ecological context in the evolution of selfing species.     

Ecological correlates of the distribution limits of two poeciliid species along a salinity gradient

Identifying the environmental factors responsible for the formation of a species' distribution limit is challenging because organisms interact in complex ways with their environments. However, the use of statistical niche models in combination with the analysis of phenotypic variation along environmental gradients can help to reduce such complexity and identify a subset of candidate factors. In the present study, we used such approaches to describe and identify factors responsible for the parapatric distribution of two closely‐related livebearer fish species along a salinity gradient in the lowlands of Trinidad, West Indies. The downstream distribution limits of Poecilia reticulata were strongly correlated with the brackish–freshwater interface. We did not observe significant phenotypic variation in life‐history traits for this species when comparing marginal with more central populations, suggesting that abrupt changes in conditions at the brackish–freshwater interface limit its distribution. By contrast, Poecilia picta was present across a wide range of salinities, although it gradually disappeared from upstream freshwater localities. In addition, P. picta populations exhibited an increase in offspring size in localities where they coexist with P. reticulata, suggesting a role for interspecific competition. The parapatric distribution of these two species, suggests that P. reticulata distributions are limited by an abiotic factor (salinity), whereas P. picta is limited by a biotic factor (interspecific competition). Similar parapatric patterns have been previously described in other systems, suggesting they might be a common pattern in nature. © 2013 The Linnean Society of London     

Fragmentation and comparative genetic structure of four mediterranean woody species: complex interactions between life history traits and the landscape context

Aim The effect of habitat fragmentation on population genetic structure results from the interaction between species’ life history traits and the particular landscape context, and both components are inherently difficult to tease apart. Here, we compare the genetic (allozyme) structure of four co‐occurring woody species with contrasting life histories to explore how well their response to the same fragmentation process can be predicted from their functional traits. Location A highly fragmented forest landscape located in the lower Guadalquivir catchment, south‐western Spain. Methods We sampled four species (Cistus salviifolius, Myrtus communis, Pistacia lentiscus and Quercus coccifera) from the same 23 forest fragments known to form a representative array of habitat characteristics in the region. We assessed genetic diversity (A, H_e and N_g) and differentiation (F_IS and F_ST) for each species and explored their potential drivers using a model‐selection approach with four fragment features (size, historical and current connectivity, and stability) as predictor variables. Results Regional‐scale genetic diversity increased from the shortest‐lived to the longest‐lived species, while population differentiation of the self‐compatible species was roughly double that of the three self‐incompatible species. Fragment size was the only feature that did not consistently affect the genetic diversity of local populations across all species. Three species showed signs of being affected by fragmentation, yet each responded differently to the set of fragment features considered. We observed several trends that were at odds with simple life history‐based predictions but could arise from patterns of gene flow and/or local‐scale demographic processes. Main conclusions Our comparative study of various landscape features and species underscores that the same fragmentation process can have very different, and complex, consequences for the population genetic structure of plants. This idiosyncrasy renders generalizations across natural systems very difficult and highlights the need of context‐oriented guidelines for an efficient conservation management of species‐rich landscapes.     

Assessing the impact of density dependence in field populations of Aedes aegypti

Although many laboratory studies of intra-specific competition have been conducted with Ae. aegypti, there have been few studies in natural environments and none that examined density dependence in natural containers at normal field densities. Additionally, current mathematical models that predict Ae. aegypti population dynamics lack empirically-based functions for density-dependence. We performed field experiments in Tapachula, Mexico, where dengue is a significant public health concern. Twenty-one containers with natural food and water that already contained larvae were collected from local houses. Each container was divided in half and the naturally occurring larvae were apportioned in a manner that resulted in one side of the container (high density) having four times the density of the second side (low density). Larvae were counted and pupae were removed daily. Once adults emerged, wing span was measured to estimate body size. Density had a significant impact on larval survival, adult body size, and the time taken to transition from 4(th) instar to pupation. Increased density decreased larval survival by 20% and decreased wing length by an average of 0.19 mm. These results provide a starting point for a better understanding of density dependence in field populations of Ae. aegypti.     

Maternal effects and their consequences for offspring fitness in the Yellow Dung Fly

1. Maternal adult diet and body size influence the fecundity of a female and possibly the quality and the performance of her offspring via egg size or egg quality. In laboratory experiments, negative effects in the offspring generation have often been obscured by optimal rearing conditions.
2. To estimate these effects in the Yellow Dung Fly, Scathophaga stercoraria , how maternal body size and adult nutritional status affected her fecundity, longevity and egg size were first investigated.
3. Second, it was investigated how female age and adult nutritional experience, mediated through the effects of egg size or egg quality, influenced the performance of offspring at different larval densities.
4. Maternal size was less important than maternal adult feeding in increasing reproductive output. Without food restriction, large females had larger clutch sizes and higher oviposition rates, whereas under food restriction this advantage was reversed in favour of small females.
5. Offspring from mothers reared under nutritional stress experienced reduced fitness in terms of egg mortality and survival to adult emergence. If the offspring from low-quality eggs survived, the transmitted maternal food deficiency only affected adult male body size under stressful larval environments.
6. Smaller egg sizes due to maternal age only slightly affected the performance of the offspring under all larval conditions.     

斑痣悬茧蜂在黏虫寄主体内与中红侧沟茧蜂竞争下的存活和发育表现

【目的】不同种寄生蜂在同一小生境中可能寄生同一共享寄主。本研究旨在为认识寄生蜂种间互作关系,并为科学评价寄生性天敌控害效应提供依据。【方法】在室内以单寄生性斑痣悬茧蜂Meteorus pulchricornis(Wesmael)和中红侧沟茧蜂Microplitis mediator(Halidy)及其寄主黏虫Mythimna separata(Walker)低龄幼虫为材料,以寄生顺序和间隔时间为因素进行种间寄生竞争效应实验,观察比较两种蜂的存活和斑痣悬茧蜂子代的发育历期、体型大小和寿命等发育参数。【结果】不同寄生顺序和间隔时间组合处理下斑痣悬茧蜂子代蜂存活率始终高于中红侧沟茧蜂,且先寄生的斑痣悬茧蜂子代存活率高于后寄生的蜂,提前24 h寄生的斑痣悬茧蜂子代存活率可高达96.7%。当斑痣悬茧蜂先于中红侧沟茧蜂寄生时,其子代幼虫发育历期比单独寄生(对照)时显著延长;当后于中红侧沟茧蜂寄生时,其子代幼虫发育历期与单独寄生时无显著差异。各竞争处理下,斑痣悬茧蜂子代成虫寿命均长于单独寄生的子代成虫;子代成虫后足胫节长度与单独寄生相比明显缩短。【结论】结果说明,斑痣悬茧蜂在黏虫低龄幼虫体内与中红侧沟茧蜂的竞争中占有优势,但竞争对斑痣悬茧蜂子代生长发育具有负面影响。     

Aedes albopictus, vector of chikungunya and dengue viruses in Reunion Island: biology and control

Chikungunya virus (CHIKV) and dengue virus (DENV) are mosquito-borne viruses transmitted by the Aedes genus. Dengue is considered as the most important arbovirus disease throughout the World. Chikungunya, known from epidemics in continental Africa and Asia, has up to now been poorly studied. It has been recently responsible for the severe 2004-2007 epidemic reported in the Indian Ocean (IO), which has caused several serious health and economic problems. This unprecedented epidemic of the IO has shown severe health troubles with morbidity and death associated, which had never been observed before. The two major vectors of those arboviruses in the IO area are Aedes aegypti and Aedes albopictus. The latest is considered as the main vector in most of the islands of the area, especially in Reunion Island. Ae. albopictus showed strong ecological plasticity. Small disposable containers were the principal urban breeding sites, and preferred natural developmental sites were bamboo stumps and rock holes in peri-urban and gully areas. The virus has been isolated from field collected Ae. albopictus females, and in two out of 500 pools of larvae, demonstrating vertical transmission. Experimental works showed that both Ae. albopictus and Ae. aegypti from west IO islands are efficient vectors of dengue and chikungunya viruses. Since 2006 and all along the epidemic of CHIKV, measures for the control of larvae (temephos then Bacillus thuringiensis) and adults (fenitrothion, then deltamethrine) of Ae. albopictus where applied along with individual and collective actions (by the use of repellents, and removal of breeding sites around houses) in Reunion Island. In order to prevent such epidemics, a preventive plan for arboviruses upsurge is ongoing processed. This plan would allow a quicker response to the threat and adapt it according to the virus and its specific vector.     

Age and growth of the bull shark (Carcharhinus leucas) around Reunion Island,South West Indian Ocean

Sharks exhibit varied demographic strategies depending on both the species and the population location, which make them more or less vulnerable to fishing. Accurate evaluation of local age and growth parameters is therefore fundamental for the sustainable management of their stocks. Although demographic parameters have been assessed for bull shark (Carcharhinus leucas) populations in several locations of the world, this information is missing so far around Reunion Island, in the south-west Indian Ocean. To fill this gap of knowledge, age and growth data were gathered from the vertebrae of 140 individuals of C. leucas (77 females and 63 males, mostly adults) fished around the island between 2012 and 2019. After verification of the annual deposition of growth band pairs on these structures using relative marginal increment analysis on 40 individuals, band pairs were counted along the vertebral centrum for each individual. Thanks to this approach, growth was shown to significantly differ between male and female C. leucas around Reunion Island, with respective von Bertalanffy growth model equations of L_t =  and L_t = . Indeed, the females of the species fished in this area were significantly (P < 0.001) larger than local males, with an estimated difference in size of ~16.1 cm at 20 years old. They also apparently reach older ages, with an estimated maximum age of 33.50 years, against 29.75 years only for the males. The estimated size at birth around the island is larger than elsewhere in the world, varying from 92.30 to 100.00 cm depending on the method used. These results confirm that the population of C. leucas around Reunion Island exhibits a K-selected strategy, which makes it highly vulnerable to fishing pressure.     

Impact of variable pelagic environments on natural larval growth and recruitment of the reef fish Thalassoma bifasciatum

New recruits of the bluehead wrasse Thalassoma bifasciatum were censused and collected from nearshore reefs of Barbados, West Indies, every 2 weeks for 20 months. Their temporal coincidence with low salinity (<34·5) water during their pelagic larval stage was determined by comparing the otolith records of new recruits with conductivity and temperature records from a current meter moored 2 km off the west coast of the island. Larval residence in a low salinity North Brazil Current (NBC) ring appeared to have a negative impact on growth. Larvae that encountered a NBC ring for at least 7 days during either the first half of the larval period exhibited slower larval growth than those that did not encounter a ring for 7 days during any part of their larval period. As a result of this slower growth, larvae that encountered low salinity waters had a longer pelagic larval duration and were larger at the time of settlement. The magnitude of settlement was not distinctly related to the presence or absence of a NBC ring, but the largest settlement event occurred at the end of the longest ring event. Early juvenile growth did not vary between fish that had encountered a ring and those that did not, so size differences at settlement were propagated through the first week of life on the reef. The potentially opposing attributes of fast and slow‐growing larvae ( e.g . fast growing larvae with shorter larval stage duration but smaller size at settlement and higher susceptibility to reef predation), and the resulting differential mortality on the reef may promote the persistence of individuals in the population with contrasting life history traits, and contribute to the lack of a relationship between larval growth and recruitment success. Positive transport related effects of rings ( i.e . enhanced retention during some ring events) may further complicate matters by outweighing the negative impact of rings on larval growth.     

The effect of multi‐species host density on superparasitism and sex ratio in a gregarious parasitoid

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Effects of Different Photoperiods and Chilling Treatments on Growth and Reproduction of Cardamine flexuosa With. and Its Ecological Implications

Abstract Phenotypic variability of Cardamine flexuosa (Cruciferae) was examined in response to different lengths of exposure to low temperature (5°C) at the juvenile stage, and to two photoperiod regimes (8 and 16 hrs day-lengths) in the subsequent growth period. The results indicated that this species had a facultative chilling or long-day requirement for flowering. The long-day and chilling treatments both caused an earlier onset of stem internode elongation. Longer chilling treatments reduced the number of nodes and increased internode length under both long and short photoperiod regimes. Prolonged chilling treatments followed by long-day photoperiod remarkably induced more numerous basal branches and inflorescences, as a result producing more siliques. Remarkable rosette leaves Were formed at the base of the main stem when partial chilling and the short-day treatment suppressed stem internode elongation. The responses to chilling and long-day treatment closely resembled the synchronized flowering of this species in spring in the field. Delayed flowering under the short-day treatment resembled size- or age-dependent flowering in late summer to autumn in the field populations.     

Interannual variability in seasonal dynamics and species composition of drifting young-of-the-year fishes in two European lowland rivers

st young-of-the-year (YOY) fishes in two lowland rivers in the Czech Republic (Danube Basin) drifted from mid-May to mid-July and almost exclusively at night. The peak of drift density lasted c . 3 weeks and depended on water temperature (by its effect on fish spawning), but not on discharge. Peak drift densities varied between years and rivers from 80 to 1354 fish 1000 m⁻³. More than 98% of drifting fish were cyprinids. Rutilus rutilus, Rhodeus sericeus, Gobio spp., Alburnus alburnus and Abramis brama were dominate in the 22 species encountered in the River Morava. Carassius auratus gibelio and R. sericeus were the most common of 17 species in the River Kyjovka. Species composition of drifting fishes was similar among years in the Morava but varied in the Kyjovka. The species composition of drifting fishes did not differ from those of the YOY fish assemblage in nursery areas during the drift season. Relative abundances in nursery areas decreased after the drift season in species that dominated in the drift, but increased in those that avoided drift. It is suggested that drift is a regular part of the life history of many cyprinid fishes and interannual variability in density and species composition of drifting YOY fish can be explained by variable spawning success among years. Differences in the relative abundances of the YOY fish assemblage in nurseries during and after the drift season suggests that drift may cause significant mortality.     

Life‐History Data in Bioindication Procedures,Using the Example of Hoverflies (Diptera,Syrphidae) in the Elbe Floodplain

This is the first study to relate syrphid life history traits to environmental variables with a multi‐trait approach. We aimed to answer two questions: 1. Do syrphid species respond to small scale changes in environmental variables in seasonally flooded grasslands in a Central European floodplain (Elbe)? 2. Can species response to environmental variables be explained by the biological characteristics of the species expressed by their life history traits? Despite their large mobility, syrphids did respond significantly to small scale changes in environmental variables (groundwater (GW) depth, cation exchange capacity, amplitude of variation of the GW‐depth). On the other hand, the biological traits of the syrphids did not sufficiently explain syrphid occurrence at the sites. Possible explanations are discussed and an outlook for further studies is given. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)