Sally Hughes-Schrader

The kinetochore of the hemiptera

Summary(1)Breakage of chromosomes was induced by X-rays in adult and nymphal males of Euschistus servus, E. tristigmus and Solubea pugnax (Pentatomidae; Hemiptera-Heteroptera).(2)The diffuse nature of the kinetochore is demonstrated by the ability of chromosome fragments to perpetuate themselves mitotically through many cell generations of spermatogonia.(3)Free fragments, when not immobilized by the effects of radiation, are also capable of meiotic mitosis. A holokinetic, rather than a telomeric, nature is thus demonstrated for the meiotic restriction of kinetochore activity to chromosome ends, normal for Heteroptera and certain other Hemiptera.(4)Simple fragmentation as a factor in the evolution of compound sex chromosomes is supported by the observation that fragments of the X chromosome co-orient with the Y in a typical “touch and go” pairing.(5)The results are discussed with relation to problems of kinetochore structure and mitosis.

Distance segregation and compound sex chromosomes in mantispids (Neuroptera: Mantispidae)

The sex chromosomes segregate precociously in prometaphase I of male meiosis, without prior synapsis or any physical connection, in 4 species of American mantispids (Neuroptera: Mantispidae). Segregational movements are interpolar, and are implemented through chromosomal fibers. Univalent autosomes, present from diakinesis on in several species, are capable of a similar distance segregation in prometaphase. The sex chromosomes are XX ♀ —XY ♂, as is characteristic of the Order, with the exception of Entanoneura phthisica in which both elements are compound —X1X2X3Y1Y2Y3in the male, and X1X1X2X2X3X3 in the female. In tetraploid sectors of gonial origin in testes of this species no sex bivalents are formed; a distance segregation of 6 sex univalents to each pole is effected, but — as observed in the one individually identifiable pair — segregation separates complete homologues, Y1 from Y1, X1 from X1, etc. In all species the male meiotic spindle is formed by the collocation of individual chromosomal spindle units within which bivalents become deformed; the timing and degree of deformation vary with the species. In karyotype the American species conform to a common pattern with the known Japanese and European species; diploid numbers range only from 18 to 22, and each complement carries the family insigné of one pair of disproportionately large autosomes in a set of small and rather uniformly sized chromosomes.

Hermaphroditism in icerya zeteki cockerell, and the mechanism of gonial reduction in iceryine coccids (coccoidea: Margarodidae morrison)

In the Panamanian iceryine coccid Icerya zetekiCockerell (Family MargarodidaeMorrison) all females become hermaphroditic early in the first instar; occasional males arise from unfertilized eggs, but self-fertilization is assured by the protandry of the hermaphrodite. In the development of the ovotestis, initiation of the male phase is brought about by haploidization of those germ cells destined for spermatogenesis. In both Icerya zeteki and Icerya purchasi this gonial reduction results from the degeneration and elimination of one genome during prophase. Except for minor variations in the coiling cycle of spermatocytes, the chromosomes (n=2) of I. zeteki correspond closely to those of all other haplo-diploid iceryines known. The present status of the species Icerya zetekiCockerell is reviewed, and on both taxonomicand cytological grounds is judged to be uncertain.

Gueriniella and the cytotaxonomy of iceryine coccids (Coccoidea:Margarodidae)

The chromosome complement of Gueriniella serratulae (F.) Fernald, Tribe Iceryini, Subfamily Monophlebinae of the primitive coccid Family Margarodidae, is 2 n ♀=6; males are unknown. Reproduction is by thelytokous parthenogenesis. Meiosis is normal; polar bodies do not contribute to the formation of a zygote-substitute nucleus; and development is initiated by a haploid cleavage of the female pronucleus. Diploidy is restored by the fusion of the 2 nuclei resulting from this division. With the exception of Gueriniella, all cytologically known Iceryini are haplo-diploids, with a chromosome complement of n=2. The hypothesis is proposed that Gueriniella is a persistent primitive stemming from the ancestral iceryine stock prior to the loss of the sex chromosomes and the evolution of haplo-diploidy within the tribe. A review of the available evidence from cytology, taxonomy, endosymbiosis, behavior and distribution shows good agreement with this interpretation.

On the cytotaxonomy of phasmids (Phasmatodea)

SummaryA wide diversity in chromosome complement is found in two species of phasmids of the primitive group Prisopini—Prisopus ariadneHebard and Prisopus berosusWestwood. P. ariadne has a diploid male complement of 28, comprising 13 pairs of relatively large mediokinetic autosomes and Neo XY sex chromosomes. P. berosus, 2n ♂=49, has relatively small autosomes most of which are mediokinetic, and retains the XO—XX sex mechanism. Chromosomal polymorphism in this species is suggested by the presence of an unequal pair of autosomes and a structural differentiation in the X in one of two males studied.The relative amount of DNA per nucleus in male germ cells (Peulgen cytophotometry) shows a significant difference in total chromosomal content between the complements of the two species.These data are discussed with reference to the cytotaxonomy of phasmids.

Diversity of chromosomal segregational mechanisms in Mantispids (Neuroptera: Mantispidae)

The asymmetry of karyotype previously regarded as a Family character of the Mantispidae is absent in 4 species representative of one of the species-groups tyxonomically distinguishable in the Mantispas of the Western Hemisphere. Further diversity is evident in the evolutionary loss of the Y chromosome in Plega dactylota Rehn and the substitution of a Neo-XY system for distance segregation in P. signata (Hagen). In the Mantispas pseudo- or “sticky” sex-bivalents are present at diakinesis with a maximum frequency of 50% in M. fuscicornis Banks. By final metaphase this is reduced to 2% or less except in M. uhleri Banks in which 6% of the spermatocytes retain sex-bivalents. Univalent autosomes, observed in all but one of the species studied, occur in less than 1% of the cells at first metaphase except in M. interrupta Say and Plega dactylota in which their frequency approaches 8%. The precocious segregation of these unconjoined autosomes shows that univalency, rather than any sex-related attribute, underlies distance segregation.

Segregational mechanisms of sex chromosomes in Spongilla-flies (Neuroptera: Sisyridae)

Evolutionary loss of the Y chromosome has occurred in Climacia areolaris (Hagen) of the neuropteran family Sisyridae. The diploid set comprises 6 pairs of autosomes, plus 2 X chromosomes in the female and 1 X in the male. The Y is retained in Sisyra vicaria (Walker) of the same family: its chromosome number is 14 in both sexes including 2 X chromosomes in the female and 1 X plus Y in the male. Two alternative pathways for the segregation of the sex chromosomes — distance segregation and sex bivalent formation — co-exist in the latter species in a ratio of approximately 1 to 6; the possible phylogenetic significance of this feature is discussed.

Male Meiosis in Camel-flies (Raphidioptera; Neuropteroidea)

Male meiosis in 3 species of the raphidiopteran genus Agulla — A. bicolor Banks, A. astuta (Banks), and A. bractea Carpenter — closely parallels that of Neuroptera. The diploid complement in each comprises 12 pairs of autosomes plus X and Y; all are mediokinetic. One male of A. bicolor carried an extra pair of autosomes indistinguishable from the shortest member of the usual set: these formed a normal bivalent and segregated synchronously with the other autosomes. The spindle is formed by the collocation of individual units which envelope each chromosomal mass. The sex chromosomes are spatially separate on emergence from the joint vesicle of early prophase; oriented toward opposite poles they move into the interpolar axis and a central spindle unit forms about them. This unit elongates disproportionately in early premetaphase, and its subsequent contraction is not synchronous with that of the other units. Distance segregation of X and Y is completed in early premetaphase. Autosomal bivalents are chiasmate; their congressional maneuvers involve, in addition to the usual interpolar oscillations, a lateral movement to the periphery of the spindle to form a variably complete ring at the equator. Autosomal univalents occur with a frequency of 13% in A. bicolor, 2% in A. astuta, and 1% in A. bractea; they undergo distance segregation with the sex chromosomes in the central spindle unit. The phylogenetic significance of the data is considered.

Chromosomal segregational mechanisms in ant-lions (Myrmeleontidae, Neuroptera)

In a single male specimen of Myrmeleon mexicanum Banks the sex chromosomes, normally X and Y, were replaced by what appeared to be X1X2 and Y. These segregated as expected on that interpretation in only half of the spermatocytes — in the other half, one X and the Y segregated from the other X. This atypical segregation is explicable on the assumption that one of the supposed Xs is a supernumerary, not a sex chromosome, and the diploid complement of the male comprises six pairs of autosomes plus a supernumerary and the X and Y sex chromosomes. The orientation of the X chromosomes at first metaphase was variable: kinetochoric activity may be localized midway the length of the chromosome, as in gonial mitosis, or terminally. Comparative study of three congeneric species, seven of Brachynemurus, one of Psammoleon, and one of Vella showed normal segregation in all, and no evidence for secondary kinetochoric activity. In nine of the species studied one pair of autosomes was unconjoined at first metaphase in 0.3%–1.2% of primary spermatocytes. These autosomes segregated precociously with the sex chromosomes in the central unit of the spindle. In one exceptional male of Brachynemurus hubbardi Currie all first meiotic metaphases showed this behavior, and a compound X1X2/Y1Y2 system was thus simulated. Bivalent formation replaced distance segregation of sex chromosomes in 0.4%–3.2% of the spermatocytes in seven of the thirteen species studied. These sex-bivalents frequently displayed partial or complete failure in congression.

Segregational mechanisms of sex chromosomes in megaloptera (Neuropteroidea)

In male meiocytes of 2 species of the megalopteran family Corydalidae, Corydalus cornutus (L.) (2n=24, comprising 11 pairs of autosomes plus X and Y in the male and 2 Xes in the female) and Neohermes filicornis (Banks) (2n=22, comprising 10 pairs of autosomes plus X and Y in the male and 2 Xes in the female), the sex chromosomes invariably form a bivalent and segregate synchronously with the autosomes. In Neohermes this sex-bivalent is of the parachute type. Absence of autosomal univalents and of the straight-jacket deformation of chromosomes in individual spindle units further distinguishes these megalopteran meiocytes from those of Neuroptera and Raphidioptera previously described. The bearing of these findings on phylogenetic relationships of the recent Orders of the Neuropteroidea is briefly considered.