|Chamorro-Lacayo, Maria Lourdes - UNIVERSITY OF MINNESOT|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 24, 2004
Publication Date: October 1, 2004
Citation: Chamorro-Lacayo, M., Konstantinov, A.S. 2004. Comparative morphology of the prothorax and procoxa in the new world Cryptocephalini (Coleoptera: Chrysomelidae: Cryptocephalinae) and hypothesis on possible movements of the trochanter. Meeting Abstract. 1:150-152 Interpretive Summary: not applicable
Technical Abstract: Cryptocephalini, also known as case-bearing leaf beetles, are robust, cylindrical and compact beetles, measuring between 2-7 mm long. Thirteen valid genera in three subtribes are presently recorded in New World Cryptocephalini: Mastacanthus Suffrian, Sternoglossus Suffrian, Griburius Haldeman, Metallactus Suffrian, Pachybrachis Chevrolat, and Ambrotodes Suffrian in Pachybrachina; Heptarthrius Suffrian, Lexiphanes Gistl, and Stegnocephala Baly in Monachulina; and Cryptocephalus Geoffroy, Diachus LeConte, Bassareus Haldeman, and Triachus LeConte in Cryptocephalina (Seeno & Wilcox 1982). The comparative morphology of Cryptocephalinae, as well as other leaf beetles, is not well studied. This paper describes the diversity of prothoracic features, including internal ridges of the prosternum, proendosternites, coxae, trochanters and trochantines. aforementioned structures in all but two (Mastacanthus and Sternoglossus, both belonging to Pachybrachina) valid New World Cryptocephalini genera. A number of useful morphological characters that may aid in identification, supplement phylogenetic studies of the group and further clarify relationships at the generic level and beyond have been revealed. Distribution of the main characters generally supports current generic classification of New World Cryptocephalini, but favors two family level taxa instead of three currently recognized. Two main types of prothorax were found among Cryptocephalini. The first type occurs in the Cryptocephalina and Monachulina. They share the following main character states: cylindrical hypomeron projection; posterior margin of the intercoxal prosternal process not extending beyond hypomeron projection; 'three dimensional' intercoxal prosternal process and totally different internal structures of the prosternum (including the internal ridge on the margin of the intercoxal prosternal process and some previously poorly described openings). They also have strongly dentate basal margin, with the exception of Diachus and Triachus, which we view as secondary loss due to small body size. In Pachybrachina the hypomeron projection is flat; posterior margin of the intercoxal prosternal process extending beyond hypomeron projection; flat intercoxal prosternal process and a number of unique features in the internal structures of prosternum; and in some genera a very distinct trochanter. At this time, without rigorous analysis of a variety of morphological structures, we do not propose any formal changes in the higher classification of Cryptocephalini. Previously undescribed for Polyphaga (Lawrence and Britton 1994), a monocondylic joint between the coxa and trochantin is found in all studied genera. The main movement of the trochanter is rotation along its axis inside the cavity of the coxa. This rotation allows the distal portion of the profemora and the rest of the leg to move at great amplitude. Rotation of the trochanter is caused by contraction of a muscle attached to the trochanter tendon. If the tendon is attached to the trochanter longitudinally, it pulls the trochanter inside the coxal cavity and its spiral ridge slides along the coxal groove and the posterior projection of the coxa, which forces the trochanter to rotate. We did not observe these movements and described transfer of advance movements into rotation as a hypotheses based on morphological observations. We also did not find a tendon which would pull the trochanter in the opposite direction in order for it to return to its original position. However, the coxal cuticle may function as a spring pushing the trochanter back after it was squeezed by vertical movements of the trochanter. If the tendon is attached to the trochanter transversely then the muscle will rotate it and the associated vertical movement (due to the oblique position of the spiral ridge) would squeeze the coxal cuticle so it would return the trochanter to its original position when the muscle relaxes. In this last scenario circular movement is transferred to advancing. In both cases the vertical (advance) movement of the trochanter inside the coxa is responsible for squeezing the coxa and eventually returning the trochanter to its original position. Therefore, the trochanter and coxa represent a device which transfers one kind of movements into another. However whether the advancing movements are being transferred into rotation or rotation to advancing remains unclear.