Testing male immunocompetence in two hymenopterans with different levels of social organization: ‘live hard,die young?’

Males are under different selective pressures than females, which results in differences in the physiology of the two sexes to maximize their fitness. In terms of immunity, males are typically considered as the ‘sicker sex’, where immunocompetence is reduced to favour increased reproductive output. However, male social Hymenoptera are also haploid and therefore lack allelic variation at the individual level, which can also lead to reduced immunocompetence. Over the last decade, several studies have provided evidence for a higher susceptibility to disease in males of social Hymenoptera, without clarifying whether this susceptibility was a direct consequence of their haploid condition or the result of a ‘live hard, die young’ overall evolutionary strategy. In the present study, we used an experimental approach of bacterial challenge to test the immune response of males and females in two species of social Hymenoptera (honey bees, Apis mellifera; paper wasps, Polistes dominula), where males show very different life‐history traits. Drones benefit from colony protection for most of their life, whereas P. dominula males leave their colonies and have to survive for weeks at leks. If the haploid condition is responsible for a higher susceptibility in males, we should expect a lower immune response in males of both species compared to females. Conversely, if the immunocompetence depends on the life‐history traits of males, an opposite trend is expected in males of the two species. Our results do not support the ‘haploid susceptibility hypothesis’ but are in accordance with the different life history of males from the two species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 274–278.     

Genetics and biology of the sawfly,Athalia rosae (Hymenoptera)

Hymenopteran insects are a unique group of animals in which arrhenotokous reproduction (haploid males develop from unfertilized eggs) is a rule. Males produce sperm through a non-reductional maturation division. A sawfly species,Athalia rosae ruficornis Jakovlev (Tenthredinidae, Symphyta, Hymenoptera), has been introduced as a new experimental material for studies on genetics and developmental biology. Basic features relating to the potential usefulness of the species in elucidating some of the important genetic and developmental biological problems are described.     

Insemination potential of male Trichogramma evanescens

Reproduction strategies of male parasitoids have received less attention than those of the females. In hymenopteran parasitoids that reproduce by arrhenotokous parthenogenesis, virgin females are able to reproduce, but they are constrained to produce only males. In such species, the number of sperm transferred to females is of prime importance for female reproductive success. In this study, we measured the insemination potential of male Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). Independent of their age and their sperm‐depletion status, males continued to mate with females until the end of their life. They quickly depleted their sperm supply by fertilizing 18 females during their lifetime, among which 80% were inseminated during the first 24 h. They fathered around 400 daughters over their lifetime. Our results suggest an absence of imaginal spermatogenesis in T. evanescens males that can be designated as prospermatogenic. Sperm is thus a limited resource in this species and females might encounter males with varying amounts of sperm.     

Semicystic spermatogenesis and reproductive strategy in Ophidion barbatum (Pisces, Ophidiidae)

In this paper the testicular structure and spermatogenesis of Ophidion barbatum are studied and the reproductive strategy of this species is analysed. The species has a rare type of spermatogenesis, called semicystic, in which the cyst ruptures in a stage prior to the spermatozoon stage. The most peculiar feature of the spermatozoon is its elongated shape, not typical of an oviparous species. Taking into account our results, the type of ovary and the spawning method, this species shows specialized characteristics which are fairly uncommon among oviparous species. The analysis of other biological aspects of the species, such as the capacity of the males to produce sounds, the low population density, the habit of individual members of burying themselves and the crepuscular habits, combined with our observations concerning their reproductive strategies, lead us to suggest a unique mating behaviour.     

Do army ant queens re-mate later in life?

Queens of eusocial Hymenoptera are inseminated only during a brief period before they start to lay eggs. This has probably been kin-selected because repeated insemination of old queens would normally be against the inclusive fitness interest of their daughter workers. Army ants have been considered to be the only possible exception to this rule due to their idiosyncratic life-history. We studied two distantly related species of army ants, the African Dorylus (Anomma) molestus and the Neotropical Eciton burchellii and present data from microsatellite genotyping, behavioural observations and sperm counts.We also describe the copulation behaviour of African army ants for the first time. Our results strongly suggest that, contradictory to earlier contentions, army ant queens do not mate repeatedly throughout their life and thus do not constitute an exception among the eusocial Hymenoptera in this respect. Sperm counts for males and queens of both species show that army ant queens have to mate with several males to become fully inseminated. However, sperm limitation by queens is unlikely to have been the prime reason for the evolution of high queen-mating frequencies in this group. Received 5 July 2006; revised 26 September 2006; accepted 11 October 2006.     

Cytogenetics of two species of Euceraphis (Homoptera,Aphididae)

Somatic cell divisions, spermatogenesis, and the prophase stages of primary oocytes, are described for two species of birch aphid, Euceraphis betulae (Koch) and E. punctipennis (Zetterstedt). Females of E. betulae have two autosome pairs, two pairs of X-chromosomes of different lengths, and two B-chromosomes. Females of E. punctipennis have the same number of X-chromosomes and B-chromosomes as E. betulae, but only a single pair of autosomes. The sex determination system is X₁X₂0. E. punctipennis males sometimes have only one B-chromosome. In the spermatogenesis of E. betulae, pairing of homologous autosomes occurs in early prophase I, but no evidence was found of chiasmata or end-to-end alignment of homologues. Instead, homologues remain closely aligned in parallel as they condense into metaphase, and anaphase I separates the products of pairing in a strictly reductional manner. The two unpaired X-chromosomes and both B-chromosomes are stretched on the anaphase I spindle and all four pass into the larger secondary spermatocyte. The second division is equational. The B-chromosomes thus show accumulation in spermatogenesis, which must be compensated in some way by an elimination mechanism in oogenesis. Meiosis of E. punctipennis is highly anomalous. The two autosomes pair but separate again in early prophase I, then one homologue becomes heterochromatic and is apparently rejected from the late prophase nucleus. A single, equational maturation division follows. In female meiosis I, both species show highly characteristic diplotene figures with multiple chiasmata, the B-chromosomes remaining unpaired. These results are discussed in relation to previous work on aphid cytogenetics.     

A new type of male dimorphism with ergatoid and short-winged males in Cardiocondyla cf. kagutsuchi

Summary. A new type of ant male dimorphism, consisting of wingless (ergatoid) and short-winged (brachypterous) males, was found in a species of the “Cardiocondyla kagutsuchi”- complex from Malaysia. The ergatoid males show the typical morphological and behavioral characteristics of those of many other Cardiocondyla species. The brachypterous males are morphologically intermediate between ergatoid males and typical winged males of other taxa in this genus. On one hand, they share a number of morphological and behavioral features with ergatoid males that might be adaptations to the loss of flight and intranidal mating: aggressive behavior towards rival males, a prolonged spermatogenesis, which is unique in winged males, paler body coloration, smaller compound eyes, shorter antennal funiculi, more rounded heads – perhaps due to the increased development of mandibular muscles, and an angular pronotum, probably for neck protection. Their short wings appear to protect the petiolar joints during fighting. On the other hand, the brachypterous males have not become as specialized as the ergatoids and to some extent keep the nature of the winged males of other species, i.e., they escape from the nest with a higher probability and with less injuries and do not show a reduction of the ocelli. In the sexual production season, the ergatoid males emerged first in small numbers and then both male morphs emerged in large numbers. The sex ratio was extremely female-biased in the earlier stage of sexual production, probably due to local mate competition.Received 13 December 2004; revised 17 February 2005; accepted 22 February 2005.     

Diatom life cycles and ecology in the Cretaceous

The earliest known diatom fossils with well‐preserved siliceous frustules are from Lower Cretaceous neritic marine deposits in Antarctica. In this study, we analyzed the cell wall structure to establish whether their cell and life cycles were similar to modern forms. At least two filamentous species (Basilicostephanus ornatus and Archepyrgus melosiroides) had girdle band structures that functioned during cell division in a similar way to present day Aulacoseira species. Also, size analyses of cell diameter indicated that the cyclic process of size decline and size restoration used to time modern diatom life cycles was present in five species from the Lower Cretaceous (B. ornatus, A. melosiroides, Gladius antiquus, Ancylopyrgus reticulatus, Kreagra forfex) as well as two species from Upper Cretaceous deposits (Trinacria anissimowii and Eunotogramma fueloepi) from the Southwest Pacific. The results indicate that the “Diatom Sex Clock” was present from an early evolutionary stage. Other ecological adaptations included changes in mantle height and coiling. Overall, the results suggest that at least some of the species in these early assemblages are on a direct ancestral line to modern forms.     

Aberrant spermatogenesis and the peculiar mechanism of sex determination in Symphypleonan Collembola (Insecta)

Light and electron microscopy evidence have been obtained to describe the peculiar spermatogenesis in the collembolan species Sminthurus viridis and Allacma fusca (Sminthuridae). In these two species, the two sexes differ for the lack of two chromosomes (the sex chromosomes) in males (males, 2n = 10; females, 2n = 12). While oogenesis seems to proceed normally, spermatogenesis is peculiar because the two daughter cells of the first meiotic division have different chromosome numbers (six and four). The cell receiving four chromosomes degenerates, while the cell receiving six chromosomes completes meiosis and produces identical spermatozoa (n = 6). At fertilization, pronuclei with six chromosomes fuse together to form zygotes with 2n = 12. Male embryos must lose two sex chromosomes during the first zygotic mitosis, as all male cells have 2n = 10 chromosomes. The sex chromosome system of these species can be identified as X1X1X2X2:X1X20. Electron microscopy observations show that the same peculiar spermatogenesis occurs also in two others species of the same family, Caprainea marginata and Lipothrix lubbocki. The peculiar sex determination system described is similar but not identical to what is observed in other insect orders, and it may represent an evolutionary step toward parthenogenesis. It is suggested that this peculiar spermatogenesis is common to all Symphypleona.     

Spermatogenesis in some Antarctic teleosts from the Ross Sea: histological organisation of the testis and localisation of bFGF

Testis structure and spermatogenetic activity were studied in two Antarctic teleostean species, Chionodraco hamatus and Trematomus bernacchii, captured during the austral summer in the Ross Sea. The specimens of C. hamatus showed full reproductive activity but, the spermatogenetic cycle being over, only spermatogonia and Sertoli cells were present in the seminiferous tubules whereas the lumina were full of sperm. By contrast, the specimens of T. bernacchii were in the stage of spermatogenetical recrudescence, having not yet entered the reproductive period. In this species, the seminiferous tubules were devoid of lumen and full of spermatogonial cysts, showing some mitoses. Many tubules contained cysts of meiotic spermatocytes I and, in one case only, small cysts of spermatocytes II. The final stages of spermatogenesis were lacking, presumably occurring later, in autumn/winter. The immunocytochemical tests aimed at identifying bFGF and FGFR1 revealed a positive reaction both in Sertoli cells and spermatogonia in the C. hamatus specimens, indicating that this species was ready to start a new spermatogenetic cycle. The weak reaction in the specimens of T. bernacchii suggests that, in this species, the stage of cell division was over and that of meiosis and differentiation was starting. These data indicate that Antarctic fish have an opportunistic spermatogenetic cycle. Accepted: 24 October 1999     

Cytogenetics of the parthenogenetic grasshopper Warramaba (formerly Moraba) virgo and its bisexual relatives

Hybrids of both sexes were obtained from the reciprocal crosses, carried out in the laboratory, between the species believed to have given rise, by hybridization some thousands of years ago, to the parthenogenetic species W. virgo. All males with a Y-chromosome derived from P196 died before reaching the adult stage, but two males from the reciprocal cross (i.e., with a Y from P169) survived up to the adult stage. Their testes were small but normal in structure and histology. At the first meiotic division almost all the chromosomes were univalents, 0–2 bivalents being formed. Some chiasmata between non-homologous chromosomes were present. Segregation at first anaphase is irregular so that sperms with 3–15 chromosomes are formed. Such hybrids appear to be entirely sterile.     

The need for sperm selection may explain why termite colonies have kings and queens,whereas those of ants,wasps and bees have only queens

Hymenoptera have haploid males, which produce sperm by cloning. Sperm selection theory predicts that because termites have diploid males that produce genetically diverse sperm, they may profit from a high sperm surplus (large K), whereas Hymenoptera (ants, bees and wasps) should produce few sperm per fertilization (low Κ). Male reproductive “kings”, which continuously provide spermatozoa during the whole life of the queen, allow for a large K. Available empirical evidence confirms the existence of a large difference in K between diploid insects, especially Blattodea (Isoptera) (K > 1,000), and haplo-diploids such as Hymenoptera (K < 10). The available data suggest that sperm selection may be an important evolutionary force for species with diploid, but not haploid males.     

Behavioural and ecological adaptations to the high mountain environment of Polistes biglumis bimaculatus

ABSTRACT.

• 1 Polistes biglumis bimaculatus (G. in Furcroy) (Hymenoptera: Vespidae), a high mountain species, was studied in the Alps. Adaptations of this species to the severe climate and reduced nesting season include nesting characteristics, social organization and division of labour, and caste succession.
• 2 Foundress association occurs only in the late pre-emergence period and is not the same as that seen in low altitude species.
• 3 The foundress females continue to forage even in the post-emergence period and workers and reproductive (males and females) emerge almost contemporaneously.

     

Sexual dimorphism in nuclear DNA content and floral morphology in populations of Silene latifolia (Caryophyllaceae)

The evolution of flower size has become a major focus of plant population biology. In order to gain insight into the causal basis for flower-size variation, we have explored the relationship between nuclear DNA content, flower size, and cell size within and among populations of the dioecious plant Silene latifolia. We found significant variation among populations for both DNA content and flower size, with a consistent sexual dimorphism within all populations (males have a bigger genome, but smaller flowers). The overall correlation between DNA content and flower size was negative, especially within males. The cell dimensions of calyx and petal cells were not significantly different between the sexes, indicating that females have bigger flowers because they contain more cells. These findings are discussed in the context of nucleotype theory, which predicts a slower growth rate (division rate) for cells with greater DNA content. This leads to the suggestion that males have smaller flowers because of the relatively slow rate of cell division due to their larger genome. It would be of great interest to know whether associated effects on flower size of changes in genome size of the type investigated in the present study can be generalized to other species.     

Confirmation of the existence of alloparasitoids in nature – host relationships of an Australian Coccophagus species that parasitizes mealy bugs

Heteronomous hyperparasitoids are parasitic wasps with sex‐related host relationships that are unique to a group of genera in the chalcidoid family Aphelinidae. Females are primary parasitoids of various sedentary bugs (mainly, scale insects, mealy bugs, and whiteflies). Males, in contrast, are hyperparasitic, and they frequently develop at the expense of female conspecifics. Alloparasitoids constitute a special category of heteronomous hyperparasitoids, for their males never develop through female conspecifics. The existence of alloparasitic host relationships and the utility of the category ‘alloparasitoid’ have both been questioned. Here, we present results that confirm the existence of the alloparasitic way of life among heteronomous aphelinids. We investigated an undescribed species of Coccophagus (Hymenoptera: Aphelinidae), an Australian parasitoid that attacks the introduced lantana mealy bug, Phenacoccus parvus Morrison (Homoptera: Pseudococcidae), in Queensland. A year‐long field survey regularly returned large numbers of female Coccophagus spec. near gurneyi individuals from P. parvus (total n = 4212), but only few males (n = 11). Males emerged from samples only when the encyrtid parasitoid Anagyrus diversicornis (Howard) (Hymenoptera: Encyrtidae) was present in samples in relatively high numbers. Laboratory oviposition tests confirmed that A. diversicornis is a male host and showed that males do not develop at the expense of conspecific females. Other studies show that males are attracted in numbers to virgin females held in cages above mealy bug‐infested Lantana montevidensis (Spreng.) Briq. (Verbenaceae) in the field, demonstrating that they are common in the population as a whole. This confirms that the males need hosts other than conspecific females and that their usual hosts are present outside of the lantana/P. parvus system. The implications of these results for developing a realistic classification of heteronomous host relationships are discussed.     

Timing of formation of Tetrahymena contractile ring microfilaments investigated by inhibition with skeletal muscle actin

Understanding the mechanism that determines the cell division plane is one of the most important problems in the fields of cell and developmental biology. Studying the timing and site of formation of contractile ring (CR) micro-filaments provides key information for solving the problem. We tried to create a nonfunctional CR in Tetrahymena by microinjecting rabbit skeletal muscle actin, which can copolymerize with Tetrahymena actin but has properties different from those of Tetrahymena actin. When skeletal muscle actin was injected in a predivision stage, before the onset of furrow constriction, long-term arrest of cell division was observed. Muscle actin did not cause any delay in cell division when the actin was injected at any stage other than the predivision stage. In all cases, muscle actin had little affect on other actin-related functions. Injected skeletal muscle actin polymerized near the equatorial division plane in cases of cell division arrest; it polymerized at other nonspecific locations when cell division was observed. Arrest occurred when the microinjection took place in the 17-min period just before the start of furrowing. This period coincides with the occurrence of equatorial deposits of p85, which is also suggested to be required for the determination of the division plane. The present experimental results are consistent with the idea that p85 is a crucial factor for determining the cell division plane and also functions as a polymerization nucleus for CR microfilaments. © 1992 Wiley-Liss, Inc.     

Chromosome systems in the eriococcidae (Coccoidea Homoptera)

Spermatogenesis is described in two eriococcid species and the observations are compared to those previously reported. In Gossyparia spuria the diploid chromosome number is 28 in both males and females. In the female all the chromosomes are euchromatic. In most male tissues 14 of the chromosomes are euchromatic (E) and 14 are heterochromatic (H). Prior to the first meiotic division in males the number of H chromosomes was reduced. During prophase I all the cells showed 14 E chromosomes and from 1 to over 9 H chromosomes. The range of chromosome numbers in metaphase I was similar to that in prophase I. All the chromosomes divided in anaphase I, and, following differential uncoiling at interkinesis, the E and H groups of chromosomes segregated from each other at anaphase II. Only the E groups formed sperm. The presence of a variable number of H chromosomes and a haploid number of E chromosomes in spermatogenesis suggested the presence of the multiple-D variant of the Comstockiella chromosome system. In this system some of the H chromosomes become euchromatic prior to prophase I of spermatogenesis and pair with their E homologues. All the remaining H chromosomes are thus univalents, while among the E elements, some are univalents and the rest are bivalents. The observed reduction in the number of H chromosomes in the first meiotic division which was previously attributed to pairing among the H chromosomes, is now interpreted to be the result of the return of some of the H chromosomes to a euchromatic state and to their subsequent pairing with their E homologues. Spermatogenesis in Eriococcus araucariae was similar to that of G. spuria except that the reduction in the number of H chromosomes was not as extensive. The chromosome systems of the two species are compared to those of other eriococcids and the differences are briefly discussed.Supported by grant GB1585 from the National Science Foundation, Washington, D. C.