Figure 1

Ovaries of sexual and asexual female pea aphids. A. Oviparous ovary from a sexual female showing large germaria at the distal tip of each ovariole, each filled with one or two oocytes, including older ones that are yolk-filled. B. Viviparous ovary from an asexual female, showing embryos at various stages of development. Scale as A, but germaria and oocytes at the distal tips are almost too small to see. C. Bright-field close-up of oviparous germarium and previtellogenic oocyte. Note large nucleoli and teardrop shape of trophocytes as reported in [6] (arrowheads). Somatic epithelial or follicle cells form a cuboidal epithelium surrounding oocyte [10] (arrows). The oocyte (nucleus indicated by asterisk) will continue to increase in size during later vitellogenesis. Nuclei stained with DAPI are shown below, with the oocyte nucleus barely visible over autofluorescence. D. Bright-field and DAPI close-up of a viviparous germarium and previtellogenic diploid oocyte (nucleus indicated by asterisk), about 1/6th size of C, which will soon commence embryonic mitoses. Also in contrast to C, germarial trophocytes are spherical [6] (arrowhead) and the somatic epithelial or sheath cells surrounding the oocyte are squamous [63, 64] (arrows). e, embryo; g, germarium; o, previtellogenic oocyte; sec/fc, somatic epithelial or follicle cells; sec/sc, somatic epithelial or sheath cells; tc, trophocytes. Scale bars are all 100 μm.