Genetic differentiation among sympatric cuckoo host races: males matter

Generalist parasites regularly evolve host-specific races that each specialize on one particular host species. Many host-specific races originate from geographically structured populations where local adaptations to different host species drive the differentiation of distinct races. However, in sympatric populations where several host races coexist, gene flow could potentially disrupt such host-specific adaptations. Here, we analyse genetic differentiation among three sympatrically breeding host races of the brood-parasitic common cuckoo, Cuculus canorus. In this species, host-specific adaptations are assumed to be controlled by females only, possibly via the female-specific W-chromosome, thereby avoiding that gene flow via males disrupts local adaptations. Although males were more likely to have offspring in two different host species (43% versus 7%), they did not have significantly more descendants being raised outside their putative foster species than females (9% versus 2%). We found significant genetic differentiation for both biparentally inherited microsatellite DNA markers and maternally inherited mitochondrial DNA markers. To our knowledge, this is the first study that finds significant genetic differentiation in biparentally inherited markers among cuckoo host-specific races. Our results imply that males also may contribute to the evolution and maintenance of the different races, and hence that the genes responsible for egg phenotype may be found on autosomal chromosomes rather than the female-specific W-chromosome as previously assumed.     

Disappearance of eggs from nonparasitized nests of brood parasite hosts: the evolutionary equilibrium hypothesis revisited

The evolutionary equilibrium hypothesis was proposed to explain variation in egg rejection rates among individual hosts (intra‐ and interspecific) of avian brood parasites. Hosts may sometimes mistakenly reject own eggs when they are not parasitized (i.e. make recognition errors). Such errors would incur fitness costs and could counter the evolution of host defences driven by costs of parasitism (i.e. creating equilibrium between acceptors and rejecters within particular host populations). In the present study, we report the disappearance of host eggs from nonparasitized nests in populations of seven actual and potential hosts of the common cuckoo Cuculus canorus. Based on these data, we calculate the magnitude of the balancing parasitism rate provided that all eggs lost are a result of recognition errors. Importantly, because eggs are known to disappear from nests for reasons other than erroneous host rejection, our data represent the maximum estimates of such costs. Nonetheless, the disappearance of eggs was a rare event and therefore incurred low costs compared to the high costs of parasitism. Hence, costs as a result of recognition errors are probably of minor importance with respect to opposing selective pressure for the evolution of egg rejection in these hosts. We cannot exclude the possibility that low or intermediate egg rejection rates in some host populations may be caused by spatiotemporal variation in the occurrence of parasitism and gene flow, creating a variable influence of opposing costs as a result of recognition errors and the costs of parasitism.     

Engagement,Retention, and Progression to Type 2 Diabetes: A Retrospective Analysis of the Cluster-Randomised "Let's Prevent Diabetes" Trial

BackgroundPrevention of type 2 diabetes mellitus (T2DM) is a global priority. Let’s Prevent Diabetes is a group-based diabetes prevention programme; it was evaluated in a cluster-randomised trial, in which the primary analysis showed a reduction in T2DM (hazard ratio [HR] 0.74, 95% CI 0.48–1.14, p = 0.18). We examined the association of engagement and retention with the Let’s Prevent Diabetes prevention programme and T2DM incidence.ConclusionsThis study suggests that being retained/engaged in a relatively low-resource, pragmatic diabetes prevention programme for those at high risk is associated with reductions in the progression to T2DM in comparison to those who receive standard care. Nonengagers and nonretainers share similar high-risk traits. Service providers of programmes should focus on reaching these hard-to-reach groups.

Trial Registration

ClinicalTrials.gov ISRCTN80605705     

Life history theory and dental development in four species of catarrhine primates

Dental development was reconstructed in several individuals representing four species of catarrhine primates--Symphalangus syndactylus, Hylobates lar, Semnopithecus entellus priam, and Papio hamadryas--using the techniques of dental histology. Bar charts assumed to represent species-typical dental development were constructed from these data and estimated ages at first and third molar emergence were plotted on them along with ages at weaning, menarche, and first reproduction from the literature. The estimated age at first molar emergence appears to occur at weaning in the siamang, lar gibbon, and langur, and just after weaning in the baboon. Age at menarche and first reproduction occur earlier relative to dental development in both cercopithecoids than in the hylobatids, suggesting that early reproduction may be a derived trait in cercopithecoids. The results are examined in the context of life history theory.     

Female inheritance of malarial lap genes is essential for mosquito transmission

Members of the LCCL/lectin adhesive-like protein (LAP) family, a family of six putative secreted proteins with predicted adhesive extracellular domains, have all been detected in the sexual and sporogonic stages of Plasmodium and have previously been predicted to play a role in parasite-mosquito interactions and/or immunomodulation. In this study we have investigated the function of PbLAP1, 2, 4, and 6. Through phenotypic analysis of Plasmodium berghei loss-of-function mutants, we have demonstrated that PbLAP2, 4, and 6, as previously shown for PbLAP1, are critical for oocyst maturation and sporozoite formation, and essential for transmission from mosquitoes to mice. Sporozoite formation was rescued by a genetic cross with wild-type parasites, which results in the production of heterokaryotic polyploid ookinetes and oocysts, and ultimately infective Deltapblap sporozoites, but not if the individual Deltapblap parasite lines were crossed amongst each other. Genetic crosses with female-deficient (Deltapbs47) and male-deficient (Deltapbs48/45) parasites show that the lethal phenotype is only rescued when the wild-type pblap gene is inherited from a female gametocyte, thus explaining the failure to rescue in the crosses between different Deltapblap parasite lines. We conclude that the functions of PbLAPs1, 2, 4, and 6 are critical prior to the expression of the male-derived gene after microgametogenesis, fertilization, and meiosis, possibly in the gametocyte-to-ookinete period of differentiation. The phenotypes detectable by cytological methods in the oocyst some 10 d after the critical period of activity suggests key roles of the LAPs or LAP-dependent processes in the regulation of the cell cycle, possibly in the regulation of cytoplasm-to-nuclear ratio, and, importantly, in the events of cytokinesis at sporozoite formation. This phenotype is not seen in the other dividing forms of the mutant parasite lines in the liver and blood stages.     

My favorite cell: Giardia

The gut protozoan parasite, Giardia duodenalis, is the best characterized example of the most ancient eukaryotes, which are anaerobic and appear to be primitively amitochondrial. Apart from its obvious medical importance, Giardia is fascinating in its own right. Its prokaryotic-like anaerobic metabolism renders it selectively sensitive to some bacterial drugs, especially the nitroimidazoles, which are activated to form toxic radicals. Other features, including an enzyme that reduces oxygen directly to water, cysteine as the keeper of redox balance, a plasmid, and toxin-like genes are also distinctly prokaryotic-like. But, unlike prokaryotes, Giardia has a sophisticated, highly developed cytoskeleton, bounded nuclei, linear chromosomes capped with telomeric repeats, and telomere positional regulation of gene expression. BioEssays 20 :256–263, 1998.© 1998 John Wiley & Sons, Inc.     

Impact of color-coded and warning nutrition labelling schemes: A systematic review and network meta-analysis

BackgroundSuboptimal diets are a leading risk factor for death and disability. Nutrition labelling is a potential method to encourage consumers to improve dietary behaviour. This systematic review and network meta-analysis (NMA) summarises evidence on the impact of colour-coded interpretive labels and warning labels on changing consumers’ purchasing behaviour.Methods and findingsWe conducted a literature review of peer-reviewed articles published between 1 January 1990 and 24 May 2021 in PubMed, Embase via Ovid, Cochrane Central Register of Controlled Trials, and SCOPUS. Randomised controlled trials (RCTs) and quasi-experimental studies were included for the primary outcomes (measures of changes in consumers’ purchasing and consuming behaviour). A frequentist NMA method was applied to pool the results. A total of 156 studies (including 101 RCTs and 55 non-RCTs) nested in 138 articles were incorporated into the systematic review, of which 134 studies in 120 articles were eligible for meta-analysis. We found that the traffic light labelling system (TLS), nutrient warning (NW), and health warning (HW) were associated with an increased probability of selecting more healthful products (odds ratios [ORs] and 95% confidence intervals [CIs]: TLS, 1.5 [1.2, 1.87]; NW, 3.61 [2.82, 4.63]; HW, 1.65 [1.32, 2.06]). Nutri-Score (NS) and warning labels appeared effective in reducing consumers’ probability of selecting less healthful products (NS, 0.66 [0.53, 0.82]; NW,0.65 [0.54, 0.77]; HW,0.64 [0.53, 0.76]). NS and NW were associated with an increased overall healthfulness (healthfulness ratings of products purchased using models such as FSAm-NPS/HCSP) by 7.9% and 26%, respectively. TLS, NS, and NW were associated with a reduced energy (total energy: TLS, −6.5%; NS, −6%; NW, −12.9%; energy per 100 g/ml: TLS, −3%; NS, −3.5%; NW, −3.8%), sodium (total sodium/salt: TLS, −6.4%; sodium/salt per 100 g/ml: NS: −7.8%), fat (total fat: NS, −15.7%; fat per 100 g/ml: TLS: −2.6%; NS: −3.2%), and total saturated fat (TLS, −12.9%; NS: −17.1%; NW: −16.3%) content of purchases. The impact of TLS, NS, and NW on purchasing behaviour could be explained by improved understanding of the nutrition information, which further elicits negative perception towards unhealthful products or positive attitudes towards healthful foods. Comparisons across label types suggested that colour-coded labels performed better in nudging consumers towards the purchase of more healthful products (NS versus NW: 1.51 [1.08, 2.11]), while warning labels have the advantage in discouraging unhealthful purchasing behaviour (NW versus TLS: 0.81 [0.67, 0.98]; HW versus TLS: 0.8 [0.63, 1]). Study limitations included high heterogeneity and inconsistency in the comparisons across different label types, limited number of real-world studies (95% were laboratory studies), and lack of long-term impact assessments.ConclusionsOur systematic review provided comprehensive evidence for the impact of colour-coded labels and warnings in nudging consumers’ purchasing behaviour towards more healthful products and the underlying psychological mechanism of behavioural change. Each type of label had different attributes, which should be taken into consideration when making front-of-package nutrition labelling (FOPL) policies according to local contexts. Our study supported mandatory front-of-pack labelling policies in directing consumers’ choice and encouraging the food industry to reformulate their products.Protocol registryPROSPERO (CRD42020161877).

Jing Song and co-workers report a systematic review and network meta-analysis assessing evidence on food labeling and purchasing decisions.     

Parasites delay worker reproduction in bumblebees: consequences for eusociality

Workers in eusocial insects usually tend the brood of the queenand so achieve representation in the next generation throughaiding relatives to reproduce. However, workers of some eusocialspecies, such as bumblebees, are capable of reproductive activityeven in the presence of the queen (in queen-right colonies),and worker reproduction is associated with aggressive behaviorsand egg cannibalism, both of which reduce colony efficiency.Thus, factors that affect worker ovariandevelopment, a preconditionfor reproduction, can influence social harmony and colony productivity.Parasites are a ubiquitous and important part of the bioticenvironment of all organisms. Here we show that parasites playan important role in the reproductive physiology of worker bumblebeesin queen-right colonies of Bombus terrestris, affecting thepattern and timing of ovarian development and oviposition. Workersfrom colonies parasitized with the intestinal trypanosome Crithidiabombi had less developed ovaries than workers of the same agefrom unparasitized colonies. In addition, parasitized colonieswere smaller than unparasitized colonies for about the firsthalf of colony development. This generated further demographiceffects such that workers were on average younger in parasitizedthan in unparasitized colonies around the time of the onsetof worker oviposition, and worker oviposition occurred significantlylater in parasitized colonies. Workers in parasitized coloniestherefore had lower individual reproductive potential and werecooperative for a larger proportion of the colony cycle thanthose in unparasitized colonies. In this system, where transmissionof the parasite between years probably occurs only in infested,young queens, this effect may represent an adaptation on thepart of the parasite to ensure its successful passage throughthe winter. Parasites, by reducing the cost of worker cooperation,may facilitate queen control over her worker force and playan important role in moderating the social organization of eusocialinsect colonies.     

Cophylogeny of the anther smut fungi and their caryophyllaceous hosts: Prevalence of host shifts and importance of delimiting parasite species for inferring cospeciation

Background  

Using phylogenetic approaches, the expectation that parallel cladogenesis should occur between parasites and hosts has been validated in some studies, but most others provided evidence for frequent host shifts. Here we examine the evolutionary history of the association between Microbotryum fungi that cause anther smut disease and their Caryophyllaceous hosts. We investigated the congruence between host and parasite phylogenies, inferred cospeciation events and host shifts, and assessed whether geography or plant ecology could have facilitated the putative host shifts identified.