Queen-worker differences in spermatheca reservoir of phylogenetically basal ants

Morphology and ultrastructure of the colleterial glands in Myzinum flower wasps (Tiphiidae, Hymenoptera)

The strategies used by females to ensure the survival of their offspring are one of the key elements in insect reproductive biology. Ectoparasitoid hymenopterans, such as tiphiid wasps, use their ovipositor to deliver a single egg on the host body, where the larva develops. Here we describe the colleterial glands in females of two species of Myzinum and discuss the homology with other glands among Hymenoptera. The glands appear as two large opaque round sac-like structures that are connected to the oviduct. Histological sections revealed a compound gland, with a single layer of class-1 epithelial cells surrounded by a layer of class-3 gland cells, which is uncommon in Hymenoptera. Ultrastructure points to active protein synthesis, consistent with the role of colleterial glands. Despite the consensus that colleterial glands in Hymenoptera evolved with two distinct forms, the venom gland and Dufour's gland, the three glands were present in both Myzinum species. The few studies regarding the structure, function, and homology among the female accessory glands in Hymenoptera do not allow to make conclusive statements about the evolution of these glands. Therefore, the finding in Myzinum is probably the reflection of a lack of information, rather than an exception within Aculeata.

Advances in the understanding of Blattodea evolution: Insights from phylotranscriptomics and spermathecae

Cockroaches, an ancient and diverse group of insects on earth that originated in the Carboniferous, displays a wide array of morphology or biology diversity. The spermatheca is an organ of the insect reproductive system; the diversity of spermathecae might be the adaption to different mating and sperm storage strategies. Yet a consensus about the phylogenetic relationships among the main lineages of Blattodea and the evolution of spermatheca has not been reached until now. Here we added the transcriptome data of Anaplectidae for the first time and supplemented other family level groups (such as Blaberidae, Corydiidae) to address the pending issues. Our results showed that Blattoidea was recovered as sister to Corydioidea, which was strongly supported by molecular evidence. In Blattoidea, (Lamproblattidae + Anaplectidae) + (Cryptocercidae + Termitoidae) was strongly supported by our molecular data. In Blaberoidea, Pseudophyllodromiidae and Blaberidae were recovered to be monophyletic, while Blattellidae was found to be paraphyletic with respect to Malaccina. Ectobius sylvestris + Malaccina discoidalis formed the sister group to other Blaberoidea; Blattellidae (except Malaccina discoidalis) + Nyctiboridae was found as the sister of Blaberidae. Corydiidae was recovered to be non-monophyletic due to the embedding of Nocticola sp. Our ASR analysis of spermatheca suggested that primary spermathecae were present in the common ancestor, and it transformed at least six times during the evolutionary history of Blattodea. The evolution of spermatheca could be described as a unidirectional trend: the increased size to accommodate more sperm. Furthermore, major splits within the existing genera of cockroaches occurred in the Upper Paleogene to Neogene. Our study provides strong support for the relationship among three superfamilies and offers some new insights into the phylogeny of cockroaches. Meanwhile, this study also provides basic knowledge on the evolution of spermathecae and reproductive patterns.

Near-anoxia induces immobilization and sustains viability of sperm stored in ant queens

After copulation, insect females store sperm in a spermatheca for some duration until fertilization. At the beginning of their adult lives, ant queens can preserve numerous viable sperm cells from copulation for over ten years. However, the key factors influencing long-term sperm storage have not been identified. Here we show that the spermathecal environment is nearly anoxic, which induces sperm immobilization. Furthermore, mitochondrial respiratory inhibitors suppress sperm motility, suggesting that sperm immobilization may be caused by a shortage of ATP generated from only glycolysis under near-anoxic conditions. Sperm immobilization is not induced by acidification via glycolytic metabolism because the spermathecal fluid is not acidic. Finally, we show that artificial anoxic conditions rather than aerobic conditions sustain viable sperm cells. Therefore, near-anoxia is a key factor influencing long-term sperm storage in ant queens. The viability of sperm cells under artificial anoxia, however, is lower than that of those dissected immediately from queens. Moreover, the immotile sperm cells under more than 4 h of anoxia do not begin swimming after aerobic exposure, unlike those under anoxic conditions for less than 2 h. This finding indicates that factors other than anoxia are also necessary for long-term sperm preservation.

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.

e Silva J, Santos de Oliveira C, Moritz G. Investigation of the spermathecal morphology, reproductive strategy and fate of stored spermatozoa in three important thysanopteran species

In insects, females can keep sperm capable of fertilisation over a long period with the help of the spermatheca. The effectiveness of storing fertile sperm is expected to reflect in the reproductive strategy and, thus, the morphology of the involved organs. In this work, we focused on the relationship between reproduction and morphology in the haplodiploid Thysanoptera, especially if a loss of these traits occurs under thelytoky. The spermathecal morphology and the fate of stored spermatozoa were studied by microscopic techniques (high-resolution x-ray computed tomography and transmission electron microscopy) in three species with different reproductive modes and lifestyles (Suocerathrips linguis, Echinothrips americanus, Hercinothrips femoralis). Mating experiments were conducted to analyse the use of the transferred sperm in the thelytokous H. femoralis. Results show that the spermathecae are relatively simple, which can be explained by the availability of sperm and the short lifespan of the females. However, the spermatheca in H. femoralis seems to be vestigial compared to the arrhenotokous species and females do not use sperm for fertilisation. No substantial change was observed in the structure of spermatozoa, despite an enlargement of the sperm organelles being measured during storage in all three species. The results of this work demonstrate differences in the morphology of the spermatheca, especially concerning the reproduction mode, promoting the understanding of the complex interaction between morphology and behaviour.

Spermatheca of the scorpionfly Sinopanorpa tincta (Navás, 1931) (Mecoptera: Panorpidae)

The spermathecal structure of the scorpionfly Sinopanorpa tincta (Navás, 1931) was investigated using light microscopy, scanning, and transmission electron microscopy. The spermatheca consists of a bean-shaped spermathecal reservoir and an elongated spermathecal duct. The spermathecal reservoir can be subdivided into a distal portion with well-developed muscles and a proximal transitional portion connected to the spermathecal duct. The spermathecal duct is slender for its basal three-fourths and is greatly thicker for its distal one-fourth, which is mainly responsible for secretory function. A spermathecal pump formed from longitudinal muscle fibers was attached to the reservoir to control the transport of sperm. The lumen of the spermathecal reservoir is lined with a cuticle and filled with spermatozoa after copulation. The epithelium of the distal reservoir comprises a single type of epithelial cells, while the epithelium of the proximal reservoir and the spermathecal duct has three types of cells: secretory cells, duct-forming cells, and common epithelial cells. The secretory cells are rich in mitochondria, rough endoplasmic reticulum, and electron-dense secretory vesicles. The duct-forming cells form cuticular ducts, which connect the secretory cells to the lumen of the spermatheca. The spermathecal reservoir mainly serves as the storage of sperm, but the proximal reservoir as well as the spermathecal duct serves as secretory functions that maintain sperm viability.

Irreversible sterility of workers and high-volume egg production by queens in the stingless bee Tetragonula carbonaria

Social insects are characterised by a reproductive division of labour between queens and workers. However, in the majority of social insect species, the workers are only facultatively sterile. The Australian stingless bee Tetragonula carbonaria is noteworthy as workers never lay eggs. Here, we describe the reproductive anatomy of Tcarbonaria workers, virgin queens and mated queens. We then conduct the first experimental test of absolute worker sterility in the social insects. Using a controlled microcolony environment, we investigate whether the reproductive capacity of adult workers can be rescued by manipulating the workers' social environment and diet. The ovaries of T. carbonaria workers that are queenless and fed unrestricted, highly nutritious royal jelly remain non-functional, indicating they are irreversibly sterile and that ovary degeneration is fixed prior to adulthood. We suggest that Tcarbonaria might have evolved absolute worker sterility because colonies are unlikely to ever be queenless.

Morphology of the spermatheca of Triatoma lecticularia (Hemiptera: Reduviidae) (Stal, 1859)

Triatoma lecticularia (Hemiptera: Reduviidae) (Stal, 1859) is a potential vector of Chagas's disease and the comprehension of its reproductive biology is an important tool to control this insect. In the reproductive tract of female insects, the spermatheca plays a crucial role storing male spermatozoa after mating. Whithin insects the spermatheca shows a wide morphological diversity and the analysis of this characteristic can contribute to understand the reproductive biology of the species. This study describes the histology and histochemistry of the spermatheca of T. lecticularia. Females have a pair of elongated spermathecal reservoirs without associated accessory gland. The reservoir opens into the common oviduct via a narrow muscular duct. The reservoir epithelium has single layer of columnar secretory cells. The control of the release of spermatozoa from the spermatheca occurs via the muscular duct. The anatomical features of the spermatheca of T. lecticularia resemble those described of other Reduviidae. However, the histological and histochemical features of spermatheca observed in T. lecticularia were important to explain the maintenance of the viability of the spermatozoa stored.

Transcriptome profiling of the spermatheca identifies genes potentially involved in the long-term sperm storage of ant queens

Females of social Hymenoptera only mate at the beginning of their adult lives and produce offspring until their death. In most ant species, queens live for over a decade, indicating that ant queens can store large numbers of spermatozoa throughout their long lives. To reveal the prolonged sperm storage mechanisms, we identified enriched genes in the sperm-storage organ (spermatheca) relative to those in body samples in Crematogaster osakensis queens using the RNA-sequencing method. The genes encoding antioxidant enzymes, proteases, and extracellular matrix-related genes, and novel genes that have no similar sequences in the public databases were identified. We also performed differential expression analyses between the virgin and mated spermathecae or between the spermathecae at 1-week and 1-year after mating, to identify genes altered by the mating status or by the sperm storage period, respectively. Gene Ontology enrichment analyses suggested that antioxidant function is enhanced in the spermatheca at 1-week after mating compared with the virgin spermatheca and the spermatheca at 1-year after mating. In situ hybridization analyses of 128 selected contigs revealed that 12 contigs were particular to the spermatheca. These genes have never been reported in the reproductive organs of insect females, suggesting specialized roles in ant spermatheca.

Degeneration patterns of the worker spermatheca during morphogenesis in ants (Hymenoptera: Formicidae)

Reproductive division of labor is one of the crucial features in social insects, however, the developmental mechanisms leading to modifications in the reproductive apparatus of workers are still not very clear. Ants show a remarkable diversity in the morphological specialization of the worker's reproductive apparatus, that allows to distinguish four types, type 1: workers that have ovaries and a functional spermatheca, and that reproduce like queens, type 2: workers have ovaries and a vestigial spermatheca, type 3: workers have ovaries but no spermatheca, and type 4: workers lost both ovaries and spermatheca. We investigated morphogenesis of the worker spermatheca in 28 ant species by histological examination. In workers of type 1, the morphogenesis of the spermatheca is very similar to that in ant queens. In type 2, the spermathecal disc also differentiates, however, the development is interrupted and remains vestigial. In types 3 and 4, the absence of the spermatheca in the adult phase is caused by a degeneration after initial formation of the spermathecal disc or by a complete lack of the spermathecal discs. The timing of these interruption and degeneration events varies among species. The species exhibiting an earlier interrupting point of spermatheca formation in workers have a larger queen-worker dimorphism, that seems to be independent from ant phylogeny.

Protein and Peptide Composition of Male Accessory Glands of Apis mellifera Drones Investigated by Mass Spectrometry

In honeybees, reproductive females usually mate early in their life with more than 10 males in free flight, often within 10 minutes, and then store male gametes for up to five years. Because of the extreme polyandry and mating in free flight special adaptations in males are most likely. We present here the results of an investigation of the protein content of four types of male reproductive glands from the Western honeybee (Apis mellifera) drone, namely seminal vesicles (secretion in ejaculate), as well as bulbus, cornua and mucus glands (secretions for the mating plug). Using high resolution and accuracy mass spectrometry and a combination of database searching and de novo sequencing techniques it was possible to identify 50 different proteins in total, inside all mentioned glands, except in the mucus gland. Most of the proteins are unique for a specific gland type, only one of them (H9KEY1/ATP synthase subunit O) was found in three glands, and 7 proteins were found in two types of glands. The identified proteins represent a wide variety of biological functions and can be assigned to several physiological classes, such as protection, energy generation, maintaining optimal conditions, associated mainly with vesicula seminalis; signaling, cuticle proteins, icarpin and apolipoproteins located mainly in the bulbus and cornua glands; and some other classes. Most of the discovered proteins were not found earlier during investigation of semen, seminal fluid and tissue of reproductive glands of the bee drone. Moreover, we provide here the origin of each protein. Thus, the presented data might shed light on the role of each reproductive gland.

Ultrastructure of the female reproductive apparatus of the egg parasitoid Gryon pennsylvanicum (Ashmead) (Hymenoptera, Platygastridae)

The growing interest in Leptoglossus occidentalis, the conifer seed bug pest accidentally introduced into Europe in the 1990s, led us to investigate the female reproductive structures of the hymenopteran platygastrid Gryon pennsylvanicum, which is its candidate antagonist for biological control programmes. Our study revealed a genital apparatus with some characteristic features, such as an unusual length of the oviduct (divided into a long proximal and a short distal tract), the absence of accessory glands and the presence of a spermatheca provided with a small spermathecal gland. The ultrastructural investigation revealed that the shorter part of the common oviduct is involved in ion uptake whereas the longer part has two cell types with secretory function: the former with dense bodies and the latter with granular particles. The secretory contents of both are released into the oviduct lumen. The granular particles are formed in a complex of modified endoplasmic reticulum and appear as virus-like particles.

New insights into the roles of juvenile hormone and ecdysteroids in honey bee reproduction

In workers of the Western honeybee, Apis mellifera, juvenile hormone (JH) and ecdysteroids regulate many aspects of age polyphenism. Here we investigated whether these derived functions in workers have developed by an uncoupling of endocrine mechanisms in adult queens and workers, or whether parallels can be found between the roles of the two hormones in both castes. We looked at yolk protein metabolism as a process central to the physiology of both queens and workers, and at sperm storage as a feature of the queen alone. Queens of differing fertility status (virgin, virgin but CO2-treated, inseminated, freshly laying and 1-2 years-old) were compared regarding vitellogenin (Vg), JH and ecdysteroid-titers in their hemolymph, as well as ovarian yolk protein and spermathecal gland composition. Our results showed that hormone titres were unrelated to the composition of spermathecal glands. JH-concentrations in the hemolymph were low in the groups of queens characterized by yolk uptake into the ovaries, and high in pre-vitellogenic queens or animals that were forced to interrupt egg-laying by caging. Ecdysteroid-concentrations were higher in untreated virgins than after insemination or during egg-laying. They were not affected by the caging of queens. These patterns of hormone changes were parallel to those known from worker bees. Together, these findings suggest a conserved role for JH as repressor of vitellogenin uptake into tissues, and for ecdysteroids in preparing tissues for this process. An involvement of the two hormones in the regulation of sperm storage seems unlikely. Our results add to the view that JH and ecdysteroids act similarly on the yolk protein metabolism of both castes of A. mellifera. This may imply that it was the biochemical versatility of Vg rather than that of hormonal regulatory circuits that allowed for the functional separation of the two castes.

Morphological and morphometrical assessment of spermathecae of Aedes aegypti females

The vectorial capacity of Aedes aegypti is directly influenced by its high reproductive output. Nevertheless, females are restricted to a single mating event, sufficient to acquire enough sperm to fertilize a lifetime supply of eggs. How Ae. aegypti is able to maintain viable spermatozoa remains a mystery. Male spermatozoa are stored within either of two spermathecae that in Ae. aegypti consist of one large and two smaller organs each. In addition, each organ is divided into reservoir, duct and glandular portions. Many aspects of the morphology of the spermatheca in virgin and inseminated Ae. aegypti were investigated here using a combination of light, confocal, electron and scanning microscopes, as well as histochemistry. The abundance of mitochondria and microvilli in spermathecal gland cells is suggestive of a secretory role and results obtained from periodic acid Schiff assays of cell apexes and lumens indicate that gland cells produce and secrete neutral polysaccharides probably related to maintenance of spermatozoa. These new data contribute to our understanding of gamete maintenance in the spermathecae of Ae. aegypti and to an improved general understanding of mosquito reproductive biology.

Survey of the exocrine system in Protanilla wallacei (Hymenoptera, Formicidae)

We studied the exocrine system of both workers and ergatoid queens of Protanilla wallacei using light, scanning and transmission electron microscopy. Our survey revealed the presence of 26 glands, of which 6 had never been found before in ants. Five of these represent novel discoveries for social insects in general. The overall novel discoveries comprise an epithelial stipes gland, a pharyngeal wall gland, a central petiole gland, a lateral postpetiole gland and a foot-sole gland in the hindleg pretarsi. The intramandibular epithelial gland was already reported in some bees previously, but is now for the first time also reported in ants. The exocrine system of workers and ergatoid queens is very similar, with only the spermathecal gland showing an obvious difference. This is in line with the limited anatomical as well as behavioural difference between both castes in Protanilla compared to the situation in Leptanilla.

Evolution of novel mosaic castes in ants: modularity, phenotypic plasticity, and colonial buffering

Many ants have independently evolved castes with novel morphology as well as function, such as soldiers and permanently wingless (ergatoid) queens. We present a conceptual model, based on modularity in morphology and development, in which evolutionary innovation is facilitated by the ancestral ant polyphenism of winged queens and wingless workers. We suggest that novel castes evolved from rare intercastes, anomalous mosaics of winged queens and workers, erratically produced by colonies through environmental or genetic perturbations. The colonial environment is highly accommodating and buffers viable intercastes from individual selection. Their cost is limited because they are diluted by the large number of nestmates, yet some can bring disproportionate benefits to their colonies in the context of defense or reproduction (e.g., wingless intercastes able to mate). Useful intercastes will increase in frequency as their morphology is stabilized through genetic accommodation. We show that both soldiers and ergatoid queens are mosaics of winged queens and workers, and they are strikingly similar to some intercastes. Modularity and developmental plasticity together with winged/wingless polyphenism thus allow for the production of highly variable mosaic intercastes, and colonies incubate the advantageous mosaics.

Lifetime monogamy and the evolution of eusociality

All evidence currently available indicates that obligatory sterile eusocial castes only arose via the association of lifetime monogamous parents and offspring. This is consistent with Hamilton's rule (br(s) > r(o)c), but implies that relatedness cancels out of the equation because average relatedness to siblings (r(s)) and offspring (r(o)) are both predictably 0.5. This equality implies that any infinitesimally small benefit of helping at the maternal nest (b), relative to the cost in personal reproduction (c) that persists throughout the lifespan of entire cohorts of helpers suffices to establish permanent eusociality, so that group benefits can increase gradually during, but mostly after the transition. The monogamy window can be conceptualized as a singularity comparable with the single zygote commitment of gametes in eukaryotes. The increase of colony size in ants, bees, wasps and termites is thus analogous to the evolution of multicellularity. Focusing on lifetime monogamy as a universal precondition for the evolution of obligate eusociality simplifies the theory and may help to resolve controversies about levels of selection and targets of adaptation. The monogamy window underlines that cooperative breeding and eusociality are different domains of social evolution, characterized by different sectors of parameter space for Hamilton's rule.

Evolution of specialized spermatheca morphology in ant queens: insight from comparative developmental biology between ants and polistine wasps

In many ant species, the queens can keep spermatozoa alive in their spermatheca for several years, which goes along with unique morphological characteristics of the queen's spermatheca. The relative spermatheca size in ant queens is prominently larger than that in social wasps. Furthermore, the epithelium lining the spermatheca reservoir of ants consists of columnar cells in the hilar region and squamous cells in the distal region, whereas it is formed by columnar cells only in social wasps. To study the evolution of the unique spermatheca morphology in ant queens, we compared the various processes during spermatheca development between two ponerine ant species of the genus Pachycondyla (=Brachyponera) and three polistine wasp species of the genus Polistes. From histological observations, we can define four developmental events in the ant queens: (1) invagination of the spermatheca primordium, (2) the reservoir wall thickness becomes unequal, (3) the reservoir diameter doubles as the lining epithelial cells become flattened except for the hilar region, and (4) the increase in thickness of the reservoir epithelium is limited to the hilar region which doubles in thickness. In polistine wasps, the second and the third developmental events are absent and the entire epithelium of the spermatheca wall becomes thick in the final step. We therefore conclude that for ant queens the second and third steps are crucial for the enlargement of the spermatheca size, and that the second to the fourth steps are crucial for the specialization of the reservoir wall structure.

Prudent sperm use by leaf-cutter ant queens

In many species, females store sperm between copulation and egg fertilization, but the consequences of sperm storage and patterns of sperm use for female life history and reproductive success have not been investigated in great detail. In hymenopteran insect societies (ants, bees, wasps), reproduction is usually monopolized by one or relatively few queens, who mate only during a brief period early in life and store sperm for later use. The queens of some ants are particularly long-lived and have the potential to produce millions of offspring during their life. To do so, queens store many sperm cells, and this sperm must remain viable throughout the years of storage. Queens should also be under strong selection to use stored sperm prudently when fertilizing eggs. We used the leaf-cutter ant Atta colombica to investigate the dynamics of sperm use during egg fertilization. We show that queens are able to fertilize close to 100 per cent of the eggs and that the average sperm use per egg is very low, but increases with queen age. The robustness of stored sperm was found to decrease with years of storage, signifying that senescence affects sperm either directly or indirectly via the declining glandular secretions or deteriorating sperm-storage organs. We evaluate our findings with a heuristic model, which suggests that the average queen has sperm for almost 9 years of normal colony development. We discuss the extent to which leaf-cutter ant queens have been able to optimize their sperm expenditure and infer that our observed averages of sperm number, sperm robustness and sperm use are consistent with sperm depletion being a significant cause of mortality of mature colonies of Atta leaf-cutter ants.

Comparison of spermatheca morphology between reproductive and non-reproductive females in social wasps

Social wasps show an obvious evolution of the differentiation in behavior and external size between reproductive and non-reproductive females, with no clear differences in the Stenogastrinae, via overlap in the Polistinae, to clear differences in the Vespinae. In this study, we examined the morphological appearance of the spermatheca in representative species of these three subfamilies. The general anatomical organization of the spermatheca comprises a reservoir, a duct and two spermathecal glands, and is in line with its common structure in other social Hymenoptera. All examined wasp species have a spermathecal reservoir with uniform wall thickness, which is similar to the situation in the bees, but differentiates them from the ants. Within the wasps, the shape of the reservoir, the shape of the spermathecal glands and their attachment site to the spermatheca differs among the Stenogastrinae, Polistinae and Vespinae. The reservoir wall is thick in the Polistinae and Vespinae, while in the Stenogastrinae, it varies from thin in Parischnogaster to thick in Eustenogaster, with an intermediate situation in Liostenogaster. In all examined species, we found no differences in the spermathecal development between reproductive and non-reproductive wasps.

Dynamics of sperm transfer in the ant Leptothorax gredleri

Mating tactics differ remarkably between and within species of social Hymenoptera (bees, wasps, ants) concerning, e.g., mating frequencies, sperm competition, and the degree of male sperm limitation. Although social Hymenoptera might, therefore, potentially be ideal model systems for testing sexual selection theory, the dynamics of mating and sperm transfer have rarely been studied in species other than social bees, and basic information needed to draw conclusions about possible sperm competition and female choice is lacking. We investigated sperm transfer in the ant Leptothorax gredleri, a species in which female sexuals attract males by "female calling." The analysis of 38 female sexuals fixed immediately or up to 7 days after copulation with a single male each revealed that the sperm is transferred into the female bursa copulatrix embedded in a gelatinous mass, presumably a spermatophore. Sperm cells rapidly start to migrate from the tip of the spermatophore towards the spermatheca, but transfer is drastically slowed down by an extreme constriction of the spermathecal duct, through which sperm cells have to pass virtually one by one. This results in the spermatheca being filled only between one and several hours after mating. During this time, the posterior part of the spermatophore seals the junction between bursa copulatrix and spermathecal duct and prevents sperm loss. The prolonged duration of sperm transfer might allow female sexuals to chose between ejaculates and explain previously reported patterns of single paternity of the offspring of multiply mated queens.

Winged queens replaced by reproductives smaller than workers in Mystrium ants

In ants, winged queens that are specialized for independent colony foundation can be replaced by wingless reproductives better adapted for colony fission. We studied this shift in reproductive strategy by comparing two Mystrium species from Madagascar using morphometry, allometry and dissections. Mystrium rogeri has a single dealate queen in each colony with a larger thorax than workers and similar mandibles that allow these queens to hunt during non-claustral foundation. In contrast, Mystrium 'red' lacks winged queens and half of the female adults belong to a wingless 'intermorph' caste smaller and allometrically distinct from the workers. Intermorphs have functional ovaries and spermatheca while those of workers are degenerate. Intermorphs care for brood and a few mate and reproduce making them an all-purpose caste that takes charge of both work and reproduction. However, their mandibles are reduced and inappropriate for hunting centipedes, unlike the workers' mandibles. This together with their small thorax disallow them to perform independent colony foundation, and colonies reproduce by fission. M. rogeri workers have mandibles polymorphic in size and shape, which allow for all tasks from brood care to hunting. In M. 'red', colonial investment in reproduction has shifted from producing expensive winged queens to more numerous helpers. M. 'red' intermorphs are the first case of reproductives smaller than workers in ants and illustrate their potential to diversify their caste system for better colonial economy.