Bioacoustics of Tangana asymmetrica

REMARKS The female spermathecae ( Fig. 12 ) of Tangana and Rowellacris Ritchie & Hemp n. gen. , not previously studied, are here shown to be radically different from those of Ixalidium species, as here defined, or of any other acridoid, and the status of Tangana as a valid genus is confirmed, based both on molecular evidence and on striking divergence in characters of the genitalia in both sexes from those in Ixalidium . This account of the morphology of Tangana is based on the only described species, Tangana asymmetrica Ramme ( paratype male, Fig. 16 ). The crumpled appearance of the tip of the aedeagus of this paratype , shown in dorsal view in Figure 16B may be a result of trauma sustained by the living insect. Other specimens seen, from a wide range of localities ( Fig. 17 ), do not show this wrinkled effect. The male terminalia in Tangana are the most heavily modified and specialised in the family Ixalidiidae Hemp, Song & Ritchie n. fam. In addition to the unique asymmetry of the external terminalia, the most striking features of the male genital complex in T. asymmetrica are its overall size in relation to body length (up to 5.6 mm out of around 23 mm ), the inflated and fused distal endophallic sclerites (apical valves of endophallus), the epiphallic apodemes and the finger-like paired arms of the ventral lobe. The homology of the modified ventral lobe in Tangana with the same paired sclerite in Ixalidium and all other members of the family is largely proven by the consistent presence of the ventral lobe apodeme, representing the reduced ventral infold which arises from the anterior ventro-internal margin of the lobe. The anterior dorsal positioning of the genital pore at the base of the inflated aedeagus, rather than at its tip, is an autapomorphy of the genus Tangana . The epiphallus with its long asymmetrically placed apodemes, differs from that of all other Acridoidea, including its nearest relatives in Ixalidiidae Hemp, Song & Ritchie n. fam. Males typically adopt a dorsal mating position and copulate from the left side of the female. Since the male abdominal apex is turned upwards and forwards to connect with the underside of the female abdominal tip at a slight angle, the asymmetric form and alignment of the epiphallus allows the male to achieve the correct alignment to grip the female subgenital plate and egg-guide from the left side. During mating, when the epiphallus grasps the female subgenital plate, the egg guide probably slides over the sensory cushion on the posterior surface of the epiphallic bridge and docks within the dorsal epiphallic pouch. Fusion of the normally separate lateral sclerites of the epiphallus with the lateral plate ( Fig. 17 P-S) presumably gives the epiphallus greater rigidity to resist bending when the lophi are under tension, grasping the female subgenital plate. Given the considerable force with which the lophi would be inserted into the female genital cavity, their flattened button-like tips ( Fig. 16A ) may be an adaptation to prevent damage to the internal surface of the female subgenital plate. Although the hinged endophallus seems quite rigid in alcohol-preserved specimens, it appears that in life considerable mobility is possible. In lateral view the long axis of the aedeagus (apical endophallic sclerites) may form an obtuse angle of about 135° to the basal valves, such that the aedeagus is depressed to lie close to the ventral lobe ( Fig. 17I ). However in some cases the aedeagus is found to have become flexed upwards and forwards (capitad) to an acute angle of between 80° and 60° with the endophallic apodemes ( Fig. 17G ). When the fused apical sclerites are flexed upwards, a large space is created between the aedeagus and the two upcurved arms of the ventral lobe. Membranes folded below the inflated tip of the aedeagus in its lowered position ( Fig. 17I ) are unfurled and drawn taut when it is fully raised ( Fig. 17G ). In dead specimens this variation in relative angle between cingulum and aedeagus and in the angle of flexion of the endophallus at its hinged break can present a strikingly different appearance. This may give a false impression of taxonomically significant character differences, where in reality none exist. During mating it is likely that the tips of the ventral lobe arms are thrust upwards and forwards between the ventral ovipositor valves of the female as the epiphallic lophi pull downwards and backwards against the tip of the subgenital plate and egg guide, opening up the female genital chamber between the lower surface of the ventral ovipositor valves and the dorsal surface of the subgenital plate; the domed aedeagus could then be driven forward into the genital chamber; vertical rotation of the genitalia would mean that the spermatophore would be extruded ventrally onto the floor of the female genital chamber. It would then need to move upwards and forwards to reach the vestibule of the spermatheca. The presence of the asymmetric prong arising from the right side of the massively reinforced supra-anal plate ( Fig. 5H ) narrows the space available for the aedeagus and ventral lobe arms to be everted for copulation. It is unclear whether during mating the prong ends up pointing vertically upwards or forwards over the male abdomen. If it was near vertical, it could perhaps be inserted upwards between the ovipositor ventral valves, or even between both ventral and dorsal valves, to keep the male and female locked together during mating. If it can be deployed horizontally it could perhaps enter the genital chamber. Whichever is the case, the genitalia must be everted past it and rotated upwards and forwards over the male abdomen to perform spermatophore transfer to the female genital chamber. GENITAL ASYMMETRY IN TANGANA Bilateral asymmetry is common in the male genitalia of insects ( Huber et al. 2007 ) and a few striking examples of internal genital asymmetry occur in Acridoidea, most notably in the aedeagus of the Central American acridid genus Rhachicreagra Rehn, 1905 ( Ommatolampidinae Brunner von Wattenwyl, 1893 ) ( Jago & Rowell 1981 ) and the epiphallus of the genus Stolzia Willemse, 1930 ( Oxyinae Brunner von Wattenwyl, 1893 ) ( Hollis 1975: 212 ). However, pronounced external asymmetry within the Acridoidea appears to be restricted to the genus Tangana . Huber et al. (2007) proposed that one major evolutionary driver of asymmetry is sexual selection in males for the capacity to adopt a dorsal mating position which requires asymmetric contact between male and female genitalia. In Tangana , the development of novel structures is predominantly to the right side of the male (dextral), corresponding to a leftsided approach to the female genitalia. Only one example is known of a Tangana asymmetrica male with sinistrally asymmetric terminalia. This is a paratype specimen in the Museum für Naturkunde Berlin , mentioned by Ramme (1929) in his original description of T. asymmetrica . This sinistral paratype male has a prong on the left side, but it is not a mirror-image of the dextral morphotype since it also has traces of a short process at the corresponding point on the right side of the abdomen ( Fig. 16E ). The extreme rarity of sinistral variants in Tangana suggests that either the morphological change itself or a concomitant change in mating position are highly disadvantageous for mating success. The condition of the internal genitalia in this sinistral specimen is unknown. The functional morphology of the male and female genitalia in Tangana asymmetrica in relation to mating and spermatophore formation and transfer requires further research using the methodology employed by Woller & Song (2017) .