HERMAPHRODITISM IN AN AFRICAN COCCID, WITH NOTES ON OTHER MARGARODIDS (COCCOUIDEA--HOMOPTERA)

Sex, males, and hermaphrodites in the scale insect Icerya purchasi

Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Here, we investigate the cottony cushion scale, Icerya purchasi, one of only three reported cases of androdioecy in insects. In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, males are ocassionally observed as well. In a large genetic analysis, we show for the first time that, although self-fertilization appears to be the primary mode of reproduction, rare outbreeding events do occur in natural populations, supporting the hypothesis that hermaphrodites mate with males and hence androdioecy is the mating system of I. purchasi. Thus, this globally invasive pest insect appears to enjoy the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males.

Chromosomal and reproductive features of some Oriental and Australasian scale insects (Homoptera, Coccinea)

Fourteen species of scale insects from the families Margarodidae s.l., Pseudococcidae, Eriococcidae, and Coccidae were investigated for the first time in respect to karyotypes, genetic systems, modes of reproduction and general anatomy of the female reproductive system. One of the studied species, Steatococcus samaraius Morrison, 1927, showed hermaphroditic reproduction of the female-like specimens, the other species demonstrated bisexual reproduction with a peculiar "Lecanoid" heterochromatinization of the paternal set of chromosomes in male embryos or thelytocous parthenogenesis. Antonina parazonata Williams, 2004 and Saccharolecanium krugeri (Zehntner, 1897) are recorded here for the first time from Thailand, Antonina vietnamensis Williams, 2004 and Geococcus satellitum Williams, 2004 - for the first time from Laos.

Contribution to the cytogenetics of Kuwaniini scale insects (Homoptera, Coccinea, Margarodidae s.l.)

Jansenus burgeri Foldi, 1997 (Margarodidae s.l., Xylococcinae, Kuwaniini) was studied cytogenetically for the first time. It was shown that the species reproduces bisexually, displays XX/X(0) sex chromosome system and 2n=6/5 (female/male) including two pairs of long autosomes and a pair of shorter X-chromosomes in female. The chromosome complement, adult female morphology and the life cycle of J. burgeri are illustrated. The cytogenetic data are in fact the first ones for Kuwaniini scale insects, because Kuwania oligostigma De Lotto, 1959 briefly cytogenetically studied by Hughes-Schrader (1963), in my opinion, may be excluded from the genus Kuwania Cockerell, 1903 and the tribe Kuwaniini, since this species shows aberrant morphological characters, specifically the total absence of abdominal spiracles and the presence of tubular ducts.

General trends of chromosomal evolution in Aphidococca (Insecta, Homoptera, Aphidinea + Coccinea)

Parallel trends of chromosomal evolution in Aphidococca are discussed, based on the catalogue of chromosomal numbers and genetic systems of scale insects by Gavrilov (2007) and the new catalogue for aphids provided in the present paper. To date chromosome numbers have been reported for 482 species of scale insects and for 1039 species of aphids, thus respectively comprising about 6% and 24% of the total number of species. Such characters as low modal numbers of chromosomes, heterochromatinization of part of chromosomes, production of only two sperm instead of four from each primary spermatocyte, physiological sex determination, "larval" meiosis, wide distribution of parthenogenesis and chromosomal races are considered as a result of homologous parallel changes of the initial genotype of Aphidococca ancestors. From a cytogenetic point of view, these characters separate Aphidococca from all other groups of Paraneoptera insects and in this sense can be considered as additional taxonomic characters. In contrast to available paleontological data the authors doubt that Coccinea with their very diverse (and partly primitive) genetic systems may have originated later then Aphidinea with their very specialised and unified genetic system.

The role of androdioecy and gynodioecy in mediating evolutionary transitions between dioecy and hermaphroditism in the animalia

Dioecy (gonochorism) is dominant within the Animalia, although a recent review suggests hermaphroditism is also common. Evolutionary transitions from dioecy to hermaphroditism (or vice versa) have occurred frequently in animals, but few studies suggest the advantage of such transitions. In particular, few studies assess how hermaphroditism evolves from dioecy or whether androdioecy or gynodioecy should be an "intermediate" stage, as noted in plants. Herein, these transitions are assessed by documenting the numbers of androdioecious and gynodioecious animals and inferring their ancestral reproductive mode. Both systems are rare, but androdioecy was an order of magnitude more common than gynodioecy. Transitions from dioecious ancestors were commonly to androdioecy rather than gynodioecy. Hermaphrodites evolving from sexually dimorphic dioecious ancestors appear to be constrained to those with female-biased sex allocation; such hermaphrodites replace females to coexist with males. Hermaphrodites evolving from sexually monomorphic dioecious ancestors were not similarly constrained. Species transitioning from hermaphroditic ancestors were more commonly androdioecious than gynodioecious, contrasting with similar transitions in plants. In animals, such transitions were associated with size specialization between the sexes, whereas in plants these transitions were to avoid inbreeding depression. Further research should frame these reproductive transitions in a theoretical context, similar to botanical studies.

The evolution of hermaphroditism by an infectious male-derived cell lineage: an inclusive-fitness analysis

There has been much recent interest in the role for genetic conflicts to drive the evolution of genetic systems. Here we consider the evolution of hermaphroditism in the scale insect tribe Iceryini and the suggestion that this has been driven by conflict between a female and an infectious male tissue derived from her father. We perform an inclusive-fitness analysis to show that, owing to genetic relatedness between father and daughter, there is scope for collaboration as well as conflict over the establishment of the infectious tissue. We also consider the evolutionary interests of a maternally inherited bacterial symbiont that has been implicated in mediating the tissue's establishment. More generally, our analysis reveals that genetic conflicts can drive the evolution of hermaphroditism.

Mitochondrial phylogeny certified PGL (Paternal Genome Loss) is of single origin and haplodiploidy sensu stricto (arrhenotoky) did not evolve from PGL in the scale insects (Hemiptera: Coccoidea)

In some arthropods, paternal chromosomes are inactivated or eliminated in adult males and are not transmitted to offspring by sperm. This unique chromosome system is called paternal genome loss (PGL). In scale insects (Hemiptera; superfamily Coccoidea), PGL is widespread and three types of PGL have been identified. The questions as to whether PGL is of single origin or of multiple origins, and whether PGL is evolved to haplodiploidy or derived from diplodiploidy such as XX-XO have remained areas of controversy. Preliminary phylogenetic analyses using nuclear ribosomal DNA of 495 nucleotide sites failed to provide conclusive answers to these questions. Here we report a highly-resolved phylogeny of scale insects based on 1,229 nucleotide sites from the mitochondrial genes (COI and COII). The paraphyly of Archaeococcoidea and the monophyly of Neococcoidea are strongly supported by Bayesian posterior probabilities p=0.99 and 1.00, respectively. These two hypotheses are supported also by maximum likelihood bootstrap probabilities BP=79.9 and 99.4%, respectively. The relationships among families of Neococcoidea are resolved, being supported by p=0.90-1.00 and BP=58.7-100%. Thus, the phylogenetic tree provides us a sound basis for reconstructing the evolutionary history of PGL in scale insects. Such results have demonstrated that (1) the common ancestor of scale insects was diplodiploidy of the XX-XO sex determination, (2) PGL has a single origin from XX-XO in the common ancestor of Neococcoidea, and (3) haplodiploidy was derived from XX-XO, but not from PGL. These results support the theories arguing that PGL is an evolutionary stable state.

Absence asymmetry: the evolution of monorchid beetles (Insecta: Coleoptera: Carabidae)

Asymmetrical monorchy, or the complete absence of one testis coupled with the presence of its bilateral counterpart, is reported for 174 species of the carabid beetle tribes Abacetini, Harpalini, and Platynini (Insecta: Coleoptera: Carabidae) based on a survey of over 820 species from throughout the family. This condition was not found in examined individuals of any other carabid beetle tribes, or of other adephagan beetle families. One monorchid taxon within Platynini exhibits symmetrical vasa deferentia at the beginning of the pupal stadium, suggesting that developmental arrest of the underdeveloped vas deferens takes place in pupation. The point at which development of the testis is interrupted is unknown. Complete absence of one organ of a bilateral pair--absence asymmetry--is rarely found in any animal clade and among insects is otherwise only known for testes in the minute-sized beetles of the family Ptiliidae, ovaries in Scarabaeinae dung beetles, and ovaries of some aphids. Based on current phylogenetic hypotheses for Carabidae, testis loss has occurred independently at least three times, and up to five origins are possible, given the variation within Abacetini. Clear phylogenetic evidence for multiple independent origins suggests an adaptive or functional cause for this asymmetry. A previously posited taxon-specific hypothesis wherein herbivory in the tribe Harpalini led to testis loss is rejected. Optimal visceral packing of the beetle abdomen is suggested as a general explanation. Specifically, based on the function of various organ systems, we hypothesize that interaction of internal organs and pressure to optimize organ size and space usage in each system led to the multiple origins and maintenance of the monorchid condition. Testes are the only redundant and symmetrically paired structures not thought to be developmentally linked to other symmetrical structures in the abdomen. Among all possible organs, they are the most likely--although the observed frequency is very small--to bypass constraints that maintain bilateral symmetry, resulting in absence asymmetry. However, based solely on our observations of gross morphology of internal organs, no function conclusively explains the ontogenetic loss of one testis in these taxa. Unlike the analogous absence asymmetry of organs in other animal groups, no dramatic body-form constraint--e.g., snakes and lung loss, ptiliid beetles' small body-size and relatively giant sperm--or adaptive scenario of improved locomotory performance--e.g., birds and ovary loss due to flight constraints-applies to these carabid beetles. We tentatively suggest that testis loss is driven wholly by an interaction among the internal organs of these beetles, possibly due to selective pressure to maximize the comparatively large accessory glands found in these taxa. However, as the ordering of these evolutionary events of testis loss and accessory gland size increase is not known, large accessory glands might have secondarily evolved to compensate for a decreased testicular output.

TELOMERIC ASSOCIATIONS OF GAMETIC AND SOMATIC CHROMOSOMES IN DIPLOID AND AUTOTETRAPLOID ORNITHOGALUM VIRENS

In acetocarmine root-tip squashes, diploid cells of Ornithogalum virens in prophase exhibit configurations resulting from end-to-end associations of the six chromosomes. Homologues lie opposite one another in a ring. Prophase chromosomes of the autotretraploid cells likewise associate end-to-end; however, four homogues instead of two generally lie adjacent to one another and four (or eight) ends are often connected instead of the two (or four) found in diploid cells. Prophase chromosomes in a haploid pollen grain of a diploid form an open chain of three chromosomes, whereas in pollen from the autotetraploid balanced gametes form a configuration in which homologous pairs lie adjacent to one another and are attached end-to-end to other homologous pairs of nonhomologous chromosomes to form a chain. These observations are discussed in terms of the role telomeric associations may play in recognition and pairing of homologous chromosomes during meiotic prophase. This recognition of homologues may occur as early as syngamy.

Identical linear order of chromosomes in both gametes of the acoel turbellarian Polychoerus carmelensis: a preliminary note

In an exceptionally well-defined first cleavage metaphase in a sectioned egg of Polychoerus carmelensis all 34 (2n) chromosomes were present in a single 8-micron section, and it was possible to identify the homologous chromosomes derived from the two parent gametes. Three groups of chromosomes from one parent, containing 7, 7, and 3 chromosomes, respectively, could be exactly matched by corresponding groups of homologues derived from the other gamete. The probability of such an ordered pattern occurring by chance is somewhat less than 1 in 2(48). The simplest explanation of this arrangement is that the 17 chromosomes contributed by the egg were in precisely the same linear order as those contributed by the spermatozoon. This suggests that during certain stages preceding first cleavage metaphase, the 17 members of each haploid set of chromosomes may have been attached, end-to-end, in a linear fashion, by highly specific bonds.