Evolutionary Morphology of the External Insect Genitalia. 2. Hymenoptera

Publisher Website
Google Scholar
Abstract
The Hymenoptera have the least sexually dimorphic combined with the least specialized genitalia among the Pterygota. The only major female modifications are: (1) a shift in the articulation of gonocoxite IX to gonocoxite VIII; and (2) reduction (and elimination in Apocrita) of (coxo) sternites V11I and IX. Subsequent changes have tended toward: (1) secondary flexion between abdominal segments I and II of Apocrita to facilitate use of long gonapophyses (ovipositor), and (secondarily) to sting; (2) withdrawal of the gonapophyses beneath the abdomen into a fold resulting from the desclerotization of the genital coxostcrnites (Symphyta), and ultimately, invagination with the terminal abdominal somites together with a mesal division of their tergites (Apocrita); (3) shortening and reduction of the gonostyli to (usually) 1 segment; (4) dimorphism in the 2 pairs of gonapophyses and modification of simple segmented tubes to laterally compressed, toothed blades; (5) enlargement and subdivision of the teeth on the gonapophyses in Symphyta, and development of patterns in proprioceptive sensilla on them, reflecting that; (6) penetration of the substrate by the gonapophyses (of many sawflies, at least) is through their spring-loaded rami, teeth and annuli acting as a vibratory wedge; and (7) modification of the colleterial glands into producers of gall-inciting substances (some Symphyta–Tenthredinidae), or toxic materials (Aculeata); the ovipositor has lost its egg-laying function in the latter and becomes the sting. Major modifications in the male have been: (1) disarticulation of gonocoxite IX from tergite IX and reattachment to sternite IX; (2) mesal fusion of parts of the 2 gonocoxites, and transverse separation of some of the compound sections; (3) mesal fusion of the olistheter components of gonapophyses IX (rhachies) ventrally to form a tube out of the appendages; and (4) development of pincers on the distal portions of Section 3 of the gonocoxites. Subsequent evolution in the male has included: (1) redivision of gonapophyses IX ventrally, restoring the separate identities of the appendages from the derived tubular structure; splitting was by a separation between the ventral rami laterally and the mesal fused rhachies rather than through redivision of the rhachies; the resultant detached, united rhachies appear as a separate sclerite in primitive Symphyta, lower Apocrita, and males of some other Holometabola; (2) the fused dorsal rami (notum) of gonapophyses IX of Tenthredinoidea have become desclerotized, allowing independent motion of the appendages; (3) the projections on Section 3 of either gonocoxite have become opposable pincers (volsellae), but degenerated or became otherwise modified in many higher Aculeata; and (4) the gonostyli of Aculeata have tended to lose their musculature, and have become closely attached to the gonocoxites.

This publication has 0 references indexed in Scilit: