Abstract
So far, available cytogenetic data on 24 species of Rhopalidae reveal a male diploid chromosome number of 13, with a pair of m chromosomes and an X0/XX (male/female) sex chromosome determining system. As a rule Heteroptera have holokinetic chromosomes and a pre-reductional type of meiosis: the autosomal bivalents and the m pseudobivalent segregate reductionally at first meiotic division, while the X chromosome segregates equationally. In the present study, the meiotic chromosome behaviour was analyzed in males from different Argentinean populations of Jadera haematoloma and J. sanguinolenta. Our results corroborate the diploid chromosome number and general patterns of male meiosis previously reported by other authors in samples from Brazil and Texas (USA). Among bivalents, one is remarkably larger and may present one or two terminal chiasmata. Comparison of mean chi- asma frequency between Jadera haematoloma (5.63) and J. sanguinolenta (5.14) revealed that differences are significant. In most individuals of both species the largest pair appears as univalents in a variable number of cells and shows a regular meiotic segrega- tion. Autosomal univalents orientate axially at metaphase I (with their long axis parallel to the spindle axis) and segregate equation- ally at anaphase I. At metaphase II they associate end-to-end forming a pseudobivalent that segregates reductionally at anaphase II. An hypothesis is suggested to explain the appearance of the largest pair, either as a ring/rod bivalent or as univalents within the same individual, although an asynaptic or desynaptic origin of the univalents cannot be ascertained. The highly regular meiotic behaviour of this autosomal pair could ensure a high fertility of the individuals, and could be considered a selectively neutral condition or, at least, not detrimental.
Highlights
Members of the family Rhopalidae are frequently called scentless plant bugs
As the rule for the order Heteroptera, the family is cytologically charac terised by the possession of holokinetic chromosomes and a pre-reductional type of meiosis: while the autosomal bivalents and the m chromosomes segregate reductionally at anaphase I, the sex chromosomes are achiasmatic and segregate equationally
The material included in the pre sent study comprises 11 adult males of Jadera haematoloma collected from the Natural Preserve Martín García Island (Buenos Aires Province, 9 specimens captured in November 1995 and 1996) and Gualeguaychú (Entre Ríos Province, 2 specimens captured in February 1997), and 32 adult males of Jadera sanguinolenta obtained from the Natural Preserve Martín García Island (Buenos Aires Province, 11 specimens captured in November 1995), Gualeguaychú (Entre Ríos Prov ince, 11 specimens captured in February 1997) and Iguazú National Park
Summary
Members of the family Rhopalidae are frequently called scentless plant bugs. The taxon was first recognised as a higher group by Amyot and Serville in 1853 as the “Rhopalides” and later considered as a subfamily of the Coreidae, it is currently treated as a distinct family (Schaefer, 1964; Schuh & Slater, 1995). Two subfamilies (Rhopalinae and Serinethinae) comprising 18 genera and 209 recognised species are distributed in all major faunal regions in both the Old and the New Worlds (Schuh & Slater, 1995). Wilson (1905) introduced the term m chromosomes to describe the smallest chromosome pair in Hemiptera which behaves differently from both the autosomes and the sex chromosomes during meiosis. The m chromo somes segregate equationally at the second meiotic divi sion, resembling the autosomal bivalents. As the rule for the order Heteroptera, the family is cytologically charac terised by the possession of holokinetic chromosomes and a pre-reductional type of meiosis: while the autosomal bivalents and the m chromosomes segregate reductionally at anaphase I, the sex chromosomes are achiasmatic and segregate equationally
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