Cytogenetics and reproductive biology

Both species are ovoviviparous; all stages of embryonic development occur inside the mother’s body. In view of the absence of any notes on ovisacs in other species of Aclerda in the coccidological literature, I suppose that the genus as a whole is ovoviviparous.

Both species have a spermatheca, attached medially between two lateral oviducts (Fig. 2).

Unexpectedly, the mode of reproduction is found to be absolutely different in these two species.

Aclerda pseudozoysiae has bisexual reproduction, with the presence of male stages of the life cycle in the analyzed population. The studied male ultimonymphs contained bundles of sperms in their testicles (Fig. 3). Specimens with meiotic divisions were not collected. Male larvae and nymphs, and about 50% of the embryos inside each of the four dissected adult females demonstrated a heterochromatinization of one haploid set of chromosomes (Fig. 4), that is common for the majority of cytogenetically studied groups of the superfamily Coccoidea (see, for example, the review of Gavrilov 2007). According to the special experimental studies, elaborated on different genera of Coccoidea (see Brown and Nelson-Rees 1961) the presence of heterochromatinized haploid set characterizes male developmental stages only and moreover, the heterochromatinized set is usually of the paternal origin. Based on this heterochromatinization, Aclerda pseudozoysiae is suggested to have either a Lecanoid or a Comstockioid genetic system, these systems being difficult to distinguish without special analysis of male meiosis (see, for example, Nur 1980). The diploid karyotype of Aclerda pseudozoysiae includes 16 chromosomes forming gradual size series (Fig. 5).

On the contrary, in the studied population of Aclerda takahashii, no male stages of the life cycle were found and adult females did not have sperms and their spermathecae and oviducts. So, the species demonstrates a parthenogenetic form of reproduction. The diploid chromosomal number of Aclerda takahashii was found to be 18 (Fig. 6, 7) with chromosomes forming more or less gradual size series. Some of the cells showed a nucleolus located at the end of one of the longer chromosomes (Fig. 7) (the localization of NORs in scale insects was discussed earlier by Gavrilov and Trapeznikova 2007). The heterochromatinization of one haploid set of chromosomes was not found in any of about 150 studied embryos from 4 females and, so, theoretically, all these embryos must be female embryos. However, only about 50 % of the embryos inside each studied female were diploid, and the others demonstrated haploid number (n=9) of chromosomes in each of the cells (Fig. 8). This sudden form of parthenogenesis seems to be unknown in scale insects. Usual haplo-diploidy is inherent in different species of Iceryini scale insects (superfamily Orthezioidea), but diploid progeny are characteristically produced by fertilized Iceryini females only (Hughes-Schrader 1948). In the superfamily Coccoidea, parthenogenesis with different ways of diploidy restoration is known in different families, but in all studied cases of deuterotoky and arrhenotoky, haploid embryos are not produced, diploidy is restored in all embryos and the heterochromatinization of one haploid set of chromosomes marks male embryos (Nur 1971, 1980). Probably, in Aclerda takahashii the parthenogenetic diploidy restoration takes place in a part of embryos only. The question whether haploid embryos are able to produce viable males/ females can not be answered without additional observations in the field and laboratory experiments.