Unfertilized Eggs Research Articles

MobileOne-YOLO: Improving the YOLOv7 network for the detection of unfertilized duck eggs and early duck embryo development - a novel approach

Unfertilized duck eggs and early dead embryo eggs can significantly harm normally developing embryo eggs if not detected and removed in a timely manner. The traditional light-illumination technique currently used for this purpose is inefficient, time-consuming, and labor-intensive, making it unsuitable for modern farms and hatcheries. To address this issue, this study focuses on duck eggs incubated for a period of 10 days. This paper introduces a newly developed duck egg image acquisition device that incorporates a duck egg suction lifter with a built-in light source. The device is designed based on the incubation process and has the potential for rapid implementation in actual production. Furthermore, this study describes an improved algorithm for identifying unfertilized duck eggs and early dead embryo eggs based on the YOLOv7 network. The algorithm incorporates the use of MobileOne as a replacement for YOLOv7′s backbone network and lightweight operations applied to the YOLO head. The test results demonstrate that the MobileOne-YOLO achieves 98.10% detection accuracy, 98.55% recall, 97.79% mAP50, 98.55% precision, and 142.8 FPS in the test set images. In comparison, the original YOLOV7 also achieves 98.10% detection accuracy, 97.10% recall, 97.86% mAP50, 100.00% precision, and 101.2 FPS. The MobileOne-YOLO network maintains the same level of detection accuracy as the YOLOV7 network while achieving significantly improved detection speed. The technical method proposed in this study meets the actual production requirements in terms of detection accuracy and speed. Moreover, the image acquisition method adopted in this study is based on the incubation process, making it readily applicable to production practice. This study provides a new foundation for the subsequent development of intelligent detection equipment for identifying unfertilized duck eggs and early dead embryo eggs.

Effects of Polyploidization on Locomotor and Flight Activity, and Body Size of Males in Japanese Bumblebee, Bombus ignitus

Polyploid animals are seen in the wild in only a few groups such as planaria, weevils, ants, wasps, and bees. The sex of bumblebees is determined by the single-locus complementary sex determination (sl-CSD) system resulting in females emerging from fertilized eggs and males (normal males, haploid) emerging from unfertilized eggs. However, diploid males (polyploids) emerged from fertilized eggs when the sex-determining locus become homozygous caused by inbreeding due to population contraction. To examine the effects of polyploidization on behavioral characteristics in bumblebee males, Bombus ignitus, haploid and diploid males were compared in locomotor activity, ease of staying inside the hive, and flight activity in a laboratory experiment. The results showed that diploid males had higher locomotor activity levels, were less likely to stay inside the hive, and had lower flight activity levels than haploid males. The reduced flight activity levels may lead to lower mating rates in the field. Furthermore, the body size of diploid males was smaller than that of haploid males. Diploid males of bumblebees have a low reproductive and produce diploid sperms to emerge sterile triploids, thus creating a considerable genetic load on the population. The behavioral and morphological characteristics of diploid males may unintentionally serve as a mechanism to prevent the emergence of sterile triploids.

Dichotomous sperm in Lepidopteran insects: a biorational target for pest management.

Lepidoptera are unusual in possessing two distinct kinds of sperm, regular nucleated (eupyrene) sperm and anucleate (apyrene) sperm ('parasperm'). Sperm of both types are transferred to the female and are required for male fertility. Apyrene sperm play 'helper' roles, assisting eupyrene sperm to gain access to unfertilized eggs and influencing the reproductive behavior of mated female moths. Sperm development and behavior are promising targets for environmentally safer, target-specific biorational control strategies in lepidopteran pest insects. Sperm dimorphism provides a wide window in which to manipulate sperm functionality and dynamics, thereby impairing the reproductive fitness of pest species. Opportunities to interfere with spermatozoa are available not only while sperm are still in the male (before copulation), but also in the female (after copulation, when sperm are still in the male-provided spermatophore, or during storage in the female's spermatheca). Biomolecular technologies like RNAi, miRNAs and CRISPR-Cas9 are promising strategies to achieve lepidopteran pest control by targeting genes directly or indirectly involved in dichotomous sperm production, function, or persistence.

Masculinizer gene controls male sex determination in the codling moth, Cydia pomonella

The molecular mechanisms of sex determination in moths and butterflies (Lepidoptera) with female heterogamety (WZ/ZZ) are poorly understood, except in the silkworm Bombyx mori. However, the Masculinizer (Masc) gene that controls male development and dosage compensation in B. mori, appears to be conserved in Lepidoptera, as its masculinizing function was recently confirmed in several moth species. In this work, we investigated the role of the Masc gene in sex determination of the codling moth Cydia pomonella (Tortricidae), a globally important pest of pome fruits and walnuts. The gene structure of the C. pomonella Masc ortholog, CpMasc, is similar to B. mori Masc. However, unlike B. mori, we identified 14 splice variants of CpMasc in the available transcriptomes. Subsequent screening for sex specificity and genetic variation using publicly available data and RT-PCR revealed three male-specific splice variants. Then qPCR analysis of these variants revealed sex-biased expression showing a peak only in early male embryos. Knockdown of CpMasc by RNAi during early embryogenesis resulted in a shift from male-to female-specific splicing of the C. pomonella doublesex (Cpdsx) gene, its downstream effector, in ZZ embryos, leading to a strongly female-biased sex ratio. These data clearly demonstrate that CpMasc functions as a masculinizing gene in the sex-determining cascade of C. pomonella. Our study also showed that CpMasc transcripts are provided maternally, as they were detected in unfertilized eggs after oviposition and in mature eggs dissected from virgin females. This finding is unique, as maternal provision of mRNA has rarely been studied in Lepidoptera.

Worker Reproduction in the Highly Polygynous Ant Crematogaster pygmaea Forel, 1904 (Hymenoptera: Formicidae)

In most ant species, workers have retained functional ovaries, allowing them to potentially lay viable unfertilized eggs that develop into males. Mechanisms (ex.: queen and/or worker policing) have nevertheless evolved to control worker reproduction when the queen is present. In many species with a high degree of polygyny, especially in tramp species, complete sterility of workers has evolved, presumably to “trap” them within their “worker phenotype”. Our study showed for the first time that in the highly polygynous and polydomous ant Crematogaster pygmaea, workers retained the full capacity to produce reproductive eggs in queenless colonies, with at least some of them developing in adult males. We provide evidence that worker-produced males are reproductively functional. Although most queenless colonies produced eggs, few larvae developed into pupae and adult males. We conclude that workers strongly police the worker-produced offspring, even in the queen's absence. Probable high relatedness between queens of C. pygmaea colonies and strong genetic proximity between brood and workers could force the workers in their helper, non-reproductive function even if they keep the ability to reproduce. Our observations indicate that the production of adult males and gynes in C. pygmaea is controlled by seasonal factors related to the rainy season.

Embryonic Development of Parthenogenetic and Sexual Eggs in Lower Termites.

Worldwide, termites are one of few social insects. In this research, the stages of embryonic development in the parthenogenetic and sexual eggs of Reticulitermes aculabialis and R. flaviceps were observed and described. In R. flaviceps, the egg development of the FF and FM groups happened during the early phases of development, whereas in R. aculabialis, this appeared mainly during the late phase of development. The variance in the number of micropyles between the R. flaviceps FF colony type and the R. aculabialis FF colony type was statistically significant. Five stages of egg development were found in both types of R. aculabialis but only the sexual eggs of R. flaviceps. In R. flaviceps, 86% of the parthenogenetic eggs stopped growing during the blastoderm development, with the yolk cell assembling frequently in the center of the egg. According to the results of the single-cell transcriptome sequencing, we investigated the egg-to-larval expression level of genes (pka, map2k1, mapk1/3, hgk, mkp, and pax6) and indicated that the levels of essential gene expression in RaFF were considerably higher than in RfFF (p < 0.05). We also discovered that the oocyte cleavage rate in the FF colony type was considerably lower in R. flaviceps compared to R. aculabialis, which gave rise to a smaller number of mature oocytes in R. flaviceps. During ovulation in both species, oocytes underwent activation and one or two cleavage events, but the development of unfertilized eggs ceased in R. flaviceps. It was shown that termite oocyte and embryonic development were heavily influenced by genes with significant expressions. Results from the databases KEGG, COG, and GO unigenes revealed the control of numerous biological processes. This study is the first to complete a database of parthenogenetic and sexual eggs of R. flaviceps and R. aculabialis.

Possible role of translation in unfertilized sea urchin eggs.

Unfertilized eggs of animals contain maternal messenger RNAs (mRNAs) and proteins, which are required for the maintenance of metabolism and regulation of development during the initial stages of embryogenesis. Unfertilized eggs are transcriptionally and translationally quiescent. After fertilization, activated translation of maternal mRNAs is one of the major forces that direct the early stages of embryogenesis before activation of the zygotic genome. However, a low rate and level of protein synthesis have been detected in unfertilized sea urchin eggs indicating that translation is not completely inhibited. Analysis of translatomes of unfertilized eggs and early embryos detected three sets of maternal mRNAs translated either before or after fertilization, or both before and after fertilization. Proteins encoded by maternal mRNAs, which are translated in unfertilized eggs, perform many different functions required for homeostasis, fertilization, egg activation, and early development. This suggests that translation in unfertilized sea urchin eggs may be required to renew the pool of proteins involved in these processes. Thus, translation may be necessary to maintain the fertility and developmental potential of sea urchin eggs during the long-term storage of eggs in ovaries until spawning begins.

Egg-mediated maternal effects in a cooperatively breeding cichlid fish

Mothers can influence offspring phenotype through egg-mediated maternal effects, which can be influenced by cues mothers obtain from their environment during offspring production. Developing embryos use these components but have mechanisms to alter maternal signals. Here we aimed to understand the role of mothers and embryos in how maternal effects might shape offspring social phenotype. In the cooperatively breeding fish Neolamprologus pulcher different social phenotypes develop in large and small social groups differing in predation risk and social complexity. We manipulated the maternal social environment of N. pulcher females during egg laying by allocating them either to a small or a large social group. We compared egg mass and clutch size and the concentration of corticosteroid metabolites between social environments, and between fertilized and unfertilized eggs to investigate how embryos deal with maternal signalling. Mothers in small groups produced larger clutches but neither laid smaller eggs nor bestowed eggs differently with corticosteroids. Fertilized eggs scored lower on a principal component representing three corticosteroid metabolites, namely 11-deoxycortisol, cortisone, and 11-deoxycorticosterone. We did not detect egg-mediated maternal effects induced by the maternal social environment. We discuss that divergent social phenotypes induced by different group sizes may be triggered by own offspring experience.

Natural spawning of the leopard grouper (Mycteroperca rosacea) in captivity in La Paz, Mexico

Natural spawning of the leopard grouper (Mycteroperca rosacea) was studied in captivity from 2004 to 2008 under natural photoperiod conditions. Fish spawned naturally in 2006, but only 90,000 unfertilized eggs were collected. A total of 43 and 27 spawning days were observed in 2007 and 2008, respectively. Spawning season began in March and lasted until May–June and was related to an increase in water temperature from 21.1 to 23.8 °C. The mean (SE) number of eggs released each day was 101,705 (13,876) in 2007 and 40,510 (7,874) in 2008, and the total number of eggs collected in 2007 and 2008 was 4.37 × 106 and 1.07 × 106, respectively. The number of eggs collected per month was not significantly different within each year (P &gt; 0.05), although a significant difference was observed between 2007 and 2008 (P &lt; 0.05). The annual relative number of eggs released was 288,750 eggs·kg–1 in 2007 and 72,919 eggs·kg–1 in 2008, and viable egg production was 184,800 eggs kg–1 in 2007 and 25,375 eggs kg–1 in 2008. The fertilization rate (%) of the eggs collected daily differed significantly throughout the spawning season of 2007 (P &lt; 0.05). The fertilization rate also differed (P &lt; 0.05) between 2007 (61.10%) and 2008 (32.30%). Statistical analysis of the 2 consecutive spawning seasons indicated no correlation between the fertilization rate and fecundity. The effect of the moon phase on spawning was also considered. The fish spawned at dusk before total darkness. Mean (SD) egg diameter was 864.0 ± 22.0 μm.

Evaluation of carboxylated poly-l-lysine for cryopreservation of Labeo rohita sperm.

Carboxylated poly-l-lysine (CPLL) is an anti-freeze agent having pronounced non-permeating yet membrane stabilizing cryoprotective capabilities. The objective was to evaluate the CPLL supplementation in extender in terms of post-thaw quality (sperm), total anti-oxidant activity (milt) and fertilization potential of cryopreserved Labeo rohita sperm. For this purpose, male brood fish reared at a fish seed hatchery, Rawal Town Islamabad, Pakistan were captured from different rearing ponds and acclimatized in hatchery ponds for 6 h. The brooder was injected with Ovaprim (0.2 mL/kg), and milt was collected after 8 h in cooled sterilized falcon tubes, maintained at 4°C and evaluated for sperm motility. The milt collected from three brooders (n = 3) was diluted in extenders viz., modified Kurokura-2 extender having 10% methanol (control); experimental extenders with CPLL supplementation at the rate of 0.5%, 1% and 1.5%. Diluted milt was filled in 0.5 mL straws, exposed to liquid nitrogen vapours and cryopreserved. Cryopreserved milt was thawed at 25°C and assessed for post-thaw sperm quality. Sperm motility, motility duration, viability, total anti-oxidant capacity and DNA integrity was significantly higher (p < 0.05) in the extender having 1.5% CPLL than control. To evaluate the fertilization rates, male and female brooders were injected with Ovaprim at 0.2 mL/Kg and 0.5 mL/Kg body weight respectively. Fresh eggs and milt were collected through abdominal stripping. Batches of 10 g of eggs from each female (n = 2) were fertilized with one straw, each from frozen sperm with KE + methanol (control), KE + methanol + 1.5% CPLL and 50 μL fresh milt (negative control). After 1.5 h of fertilization, eggs were collected from all jars and a total of 200 eggs were counted. The fertilized eggs appeared clear and transparent while unfertilized eggs looked opaque with disintegrated nuclei. Sperm fertilization rate (%) was higher (p < 0.05) in extender KE + methanol + 1.5% CPLL (78.7 ± 0.5) compared to control (KE + methanol) (52.0 ± 0.4) however, it was lower compared to that of negative control, the fresh milt (85.2 ± 0.6). In conclusion, supplementation of carboxylated poly-l-lysine (1.5%) to modified Kurokura-2 extender having 10% methanol improves post-thaw motility, motility duration, viability, DNA integrity, anti-oxidant capacity (milt) and fertilizing ability of cryopreserved L. rohita sperm.

An optimization strategy for detection of fertile pigeon egg based on NIR spectroscopy analysis

During the incubation of pigeon eggs, unfertilized eggs not only cause a waste of hatching resources but may also cause contamination from exploder eggs for other eggs. The fertilization status of pigeon eggs can be determined using the visible near-infrared (Vis-NIR) spectroscopy technique, allowing for the removal of unfertilized eggs. We have constructed a strategy for the individual and combined use of mean centralization, multivariate scatter correction, and standardized spectral preprocessing methods. The effect of the individual and combined preprocessing methods on the performance of the classification model under this strategy is explored using the mobile window partial least squares discriminant analysis (MWPLS-DA) model combined with grid search technology to find the optimal discriminant model. Experimental results have shown that the model effort of the MWPLS-DA model combined with the combined preprocessing method is generally better than the model with the individual preprocessing method. The model based on the combination of standardized and multi-scattering correction preprocessing methods (STD-MC) achieved higher classification accuracy than the model based on other preprocessing methods. The classification accuracy (ACC) of the model performed on the test set is 98.60%, which meets the requirements for fertilization identification of pigeon eggs.

Evolution of acoustic signals associated with cooperative parental behavior in a poison frog

The emergence of complex social interactions is predicted to be an important selective force in the diversification of communication systems. Parental care presents a key social context in which to study the evolution of novel signals, as care often requires communication and behavioral coordination between parents and is an evolutionary stepping-stone toward increasingly complex social systems. Anuran amphibians (frogs and toads) are a classic model of acoustic communication and the vocal repertoires of many species have been characterized in the contexts of advertisement, courtship, and aggression, yet quantitative descriptions of calls elicited in the context of parental care are lacking. The biparental poison frog, Ranitomeya imitator, exhibits a remarkable parenting behavior in which females, cued by the calls of their male partners, feed tadpoles unfertilized eggs. Here, we characterized and compared calls across three social contexts, for the first time including a parental care context. We found that egg-feeding calls share some properties with both advertisement and courtship calls but also had unique properties. Multivariate analysis revealed high classification success for advertisement and courtship calls but misclassified nearly half of egg feeding calls as either advertisement or courtship calls. Egg feeding and courtship calls both contained less identity information than advertisement calls, as expected for signals used in close-range communication where uncertainty about identity is low and additional signal modalities may be used. Taken together, egg-feeding calls likely borrowed and recombined elements of both ancestral call types to solicit a novel, context-dependent parenting response.

AmelHap: Leveraging drone whole-genome sequence data to create a honey bee HapMap

Honey bee, Apis mellifera, drones are typically haploid, developing from an unfertilized egg, inheriting only their queen’s alleles and none from the many drones she mated with. Thus the ordered combination or ‘phase’ of alleles is known, making drones a valuable haplotype resource. We collated whole-genome sequence data for 1,407 drones, including 45 newly sequenced Scottish drones, collectively representing 19 countries, 8 subspecies and various hybrids. Following alignment to Amel_HAv3.1, variant calling and quality filtering, we retained 17.4 M high quality variants across 1,328 samples with a genotyping rate of 98.7%. We demonstrate the utility of this haplotype resource, AmelHap, for genotype imputation, returning >95% concordance when up to 61% of data is missing in haploids and up to 12% of data is missing in diploids. AmelHap will serve as a useful resource for the community for imputation from low-depth sequencing or SNP chip data, accurate phasing of diploids for association studies, and as a comprehensive reference panel for population genetic and evolutionary analyses.

Alternative signal pathways underly fertilization and egg activation in a fish with contrasting modes of spawning

BackgroundThe processes of fertilization and egg activation are vital for early embryogenesis. However, while the mechanisms associated with key events during these processes differ among species and modes of spawning, the signal pathways underlying these processes are opaque for many fishes, including economically important species.ResultsWe investigated phenotypic traits, ultrastructure and protein expression levels in the eggs of the topmouth culter (Culter alburnus), a protected and economically important freshwater fish that exhibits two spawning modes, producing semi-buoyant eggs and adhesive eggs. Unfertilized eggs of C. alburnus were examined, as well as eggs at fertilization and 30 min post fertilization. Our results showed that in semi-buoyant eggs, energy metabolism was activated at fertilization, followed by elevated protein expression of cytoskeleton and extracellular matrix (ECM)-receptor interactions that resulted in rapid egg swelling; a recognized adaptation for lotic habitats. In contrast, in adhesive eggs fertilization initiated the process of sperm-egg fusion and blocking of polyspermy, followed by enhanced protein expression of lipid metabolism and the formation of egg envelope adhesion and hardening, which are adaptive in lentic habitats.ConclusionOur findings indicate that alternative signal pathways differ between modes of spawning and timing during the key processes of fertilization and egg activation, providing new insights into the molecular mechanisms involved in adaptive early embryonic development in teleost fishes.

Lipid-related thiamine deficiency cause mortality of river lampreys (Lampetra fluviatilis) during pre-spawning fasting

River lampreys (Lampetra fluviatilis) were caught in the fall 2014 on entering the River Perhonjoki for spawning and kept at a hatchery until spawning in late spring 2015 to produce larvae for compensatory stockings. Since the lampreys died massively from early February onwards, they were investigated in March and May to clarify the cause of the deaths. The symptoms in lampreys resembled those of lipid-related thiamine (vitamin B1) deficiency of salmonines, called the M74 syndrome in the Baltic Sea area. Because the lipid content of lampreys was known to be high, thiamine concentrations were analyzed in the liver and ovulated unfertilized eggs, and the mass, length, and whole-body lipid content were also measured. The hepatic total thiamine (TotTh) concentration was significantly negatively correlated with the body lipid content and fatness index (mass to length ratio) in both females and males. In females, the hepatic TotTh concentration was less than half that in males, and the most moribund lampreys were the largest and fattiest females. Females that survived until artificial stripping of the eggs were smaller, and their hepatic thiamine concentration was higher, and the fatness index lower, than in females in March. The concentration of free thiamine in the eggs had a stronger positive correlation with the hepatic TotTh concentration than the phosphorylated thiamine derivatives and was also significantly and negatively correlated with the fatness index and mass. It was concluded that increased lipid peroxidation due to the mobilization of polyunsaturated fatty acids from lipids in exogenous vitellogenesis consumed thiamine as an antioxidant during pre-spawning fasting—especially in the fattiest females—and thus caused their death. It is suggested that to ensure compensatory stockings, the largest lampreys could be thiamine-injected at the hatchery to improve their survival until stripping of the eggs and to improve the eggs’ thiamine status.

Nondestructive prediction of fertilization status and growth indicators of hatching eggs based on respiration

Respiration continues throughout the incubation of eggs and is closely related to fertilization status and changes in chick embryo growth. Here, we explored the relationship between egg respiration, fertilization status, and growth indicators during incubation. First, we studied the changes in respiration of eggs during incubation and found that O2 consumption and CO2 emission were increased gradually during incubation and reached a maximum value when the shells were broken by the chick (21 days). Next, we established models to classify eggs according to the difference in respiration between fertilized and unfertilized eggs early during incubation using random forest (RF), logical regression, and support vector machine (SVM). The accuracy rates of RF and SVM on the third day of incubation were 99.32% and 98.63%, respectively, and reached 100% on the fifth day. Finally, a linear model was used to establish the relationship between chicken embryo respiration and yolk free body mass (YFBM) (R2 values of 0.99 and 0.98 for the early and late incubation periods, respectively), heart mass (R2 = 0.94), liver mass (R2 = 0.97), and the digestive system (DS) mass (R2 = 0.98). The R2 values for the relationships between the real and the predicted YFBM values and heart, liver, and DS masses were 0.98, 0.89, 0.87 and 0.88, respectively, indicating the good fit of the model. This study provides a theoretical basis for the detection of sterile eggs and dead-embryo eggs during incubation.

Egg viability and egg mass underlie immune tradeoffs and differences between urban and rural lizard egg yolk physiology

Urbanization can cause innumerable abiotic and biotic changes that have the potential to influence the ecology, behavior, and physiology of native resident organisms. Relative to their rural conspecifics, urban Side-blotched Lizard (Uta stansburiana) populations in southern Utah have lower survival prospects and maximize reproductive investment via producing larger eggs and larger clutch sizes. While egg size is an important predictor of offspring quality, physiological factors within the egg yolk are reflective of the maternal environment and can alter offspring traits, especially during energetically costly processes, such as reproduction or immunity. Therefore, maternal effects may represent an adaptive mechanism by which urban-dwelling species can persist within a variable landscape. In this study, we assess urban and rural differences in egg yolk bacterial killing ability (BKA), corticosterone (CORT), oxidative status (d-ROMs), and energy metabolites (free glycerol and triglycerides), and their association with female immune status and egg quality. Within a laboratory setting, we immune challenged urban lizards via lipopolysaccharide injection (LPS) to test whether physiological changes associated with immune system activity impacted egg yolk investment. We found urban females had higher mite loads than rural females, however mite burden was related to yolk BKA in rural eggs, but not urban eggs. While yolk BKA differed between urban and rural sites, egg mass and egg viability (fertilized vs. unfertilized) were strong predictors of yolk physiology and may imply tradeoffs exist between maintenance and reproduction. LPS treatment caused a decrease in egg yolk d-ROMs relative to the control treatments, supporting results from previous research. Finally, urban lizards laid a higher proportion of unfertilized eggs, which differed in egg yolk BKA, CORT, and triglycerides in comparison to fertilized eggs. Because rural lizards laid only viable eggs during this study, these results suggest that reduced egg viability is a potential cost of living in an urban environment. Furthermore, these results help us better understand potential downstream impacts of urbanization on offspring survival, fitness, and overall population health.

Host size selection and progeny sex determination in Hymenoepimecis bicolor (Hymenoptera, Ichneumonidae, Pimplinae)

AbstractSome hymenopteran parasitoids induce intricate behavioral alterations in their spider hosts. Despite these refined adaptations, the success of their attacks and larval development relies on careful host selection. Large hosts will certainly assure the biomass required for the parasitoid larva to pupate, but the selection of large hosts is constrained by the risks involved in the process of host subduing and immobilization. Temporal oscillations in the availability of hosts within the optimal size range may compose another important component of selection. To investigate these issues, we tested the hypothesis that Hymenoepimecis bicolor consistently attacks, and has the reproduction period synchronized with medium‐sized individuals of its host, the spider Trichonephila clavipes. We observed that (i) medium–small hosts are preferential victims, (ii) the period of oviposition of H. bicolor is synchronized with the availability of host individuals within these size classes, and (iii) these preferences can be strong enough to remain stable, regarding the temporal variation in the availability of the most suitable hosts. We also reported that (iv) parasitoid females destinate unfertilized eggs to small hosts, which produce male larvae. Data on these aspects allowed us to discuss why there is a preference for specific host sizes. The factors involved include the larval demands, the relative size between the adult wasps and spiders, and the capacity of the hosts to acquire food during larval development.

Genetic evidence for parthenogenesis in the small carpenter bee Ceratina dallatoreana (Apidae, Ceratinini) in its native distribution range

Arrhenotoky is the typical mode of reproduction in Hymenoptera. Diploid females develop from fertilized eggs, whereas haploid males originate from unfertilized eggs. However, some taxa of Hymenoptera have evolved thelytoky, in which diploid females originate parthenogenetically from unfertilized diploid eggs. In contrast to some other hymenopteran lineages, like ants and parasitic wasps, thelytoky is generally very rare in bees. Here, we evaluated the frequency of thelytoky in the small carpenter bee Ceratina dallatoreana, which was previously assumed to be thelytokous. By comparing genotypes of microsatellite loci between mothers and their offspring, we found that all female offspring were genetically identical to their mothers. We conclude that parthenogenesis is the prevailing and perhaps obligate mode of reproduction in C. dallatoreana. We also classify the cytological mode of this parthenogenesis as apomixis, or automictic parthenogenesis with central fusion and extremely reduced or non-existing recombination, because offspring showed no decrease of heterozygosity. Because sociality is influenced by relatedness and Ceratina are ancestrally facultatively social, the high relatedness afforded by parthenogenesis should associate with social living in the nest. In accordance with previous work, however, we found no social nests of C. dallatoreana.

Parthenogenetic Reproduction in Strumigenys Ants: An Update

Parthenogenetic reproduction is a common feature for social Hymenoptera, as males typically develop from unfertilized eggs (arrhenotoky). Production of female offspring without the involvement of sperm (thelytoky) also exists but is rather exceptional as it has been reported for only 16 ant species so far. Three of these belong to the genus Strumigenys: S. hexamera, S. membranifera and S. rogeri. Our observations on the reproductive biology in various Oriental Strumigenys species extends this list of thelytokous ants with three more species: S. emmae, S. liukueiensis and S. solifontis. Of these six thelotykous species, S. emmae, S. membranifera and S. rogeri are known as tramp species. Reproduction without the need to fertilize eggs no doubt offers these species a considerable advantage when establishing colonies in new environments. Published histological data on S. hexamera and S. membranifera already showed that the queens possess a functional spermatheca. We now provide evidence that this is also the case for the four other thelytokous Strumigenys species. Retaining a functional spermatheca and reproductive system may keep the queens ready for the exceptional event of mating and hence increase genetic variability, as males do occur very rarely.