Staminodeus

Nico M. Franz, 2003, Mating behaviour of Staminodeus vectoris (Coleoptera: Curculionidae), and the value of systematics in behavioural studies, Journal of Natural History 37 (14), pp. 1727-1750 : 1738-1740

Natural history of Staminodeus

At La Selva, the adults of S. vectoris have been collected on species of cyclanths throughout the year, including A. euryspatha Harling, A. sleeperae Grayum & Hammel, A. uncinata, A. utilis (Oerst.) Harling, A. vagans Harling, Carludovica rotundifolia H. Wendl. ex Hook. fil., C. sulcata Hammel, Chorigyne pendula (Hammel) R. Erkisson, Dicranopygium umbrophilum Hammel, D. wedelii Harling, and Evodianthus funifer (Poit.) Lindman (Franz, 1999). Apparently, Cyclanthus bipartitus Poit. is the only cyclanth species from which S. vectoris is absent; it is sister to all remaining cyclanths and lacks their characteristic staminodes (Harling, 1958). However, according to the observations presented here, the mating behaviour of S. vectoris at La Selva is restricted to Asplundia and Evodianthus . The adults visit other cyclanth species, feeding on the staminodes without detaching them. Typically, there are up to 100 individuals of S. vectoris on the inflorescences of Asplundia and Evodianthus , but fewer than ten individuals on those of Carludovica , Chorigyne and Dicranopygium (n =3–40 inflorescences per species of cyclanth, according to Franz, 1999). Therefore, although the adults of S. vectoris visit many cyclanth species at La Selva, they concentrate on those species used for feeding and mating.

The eggs of S. vectoris appear to hatch shortly after oviposition, because third instar larvae are present in the leaf litter as soon as five days after anthesis. Presumably, they begin to feed along the deteriorating staminode, before moving into the detritus and completing their development under humid conditions in the leaf litter. They are detritivorous and display fast negative phototaxis when disturbed. Pupation occurs in the top 1.0 cm layer of the ground. The entire life cycle lasts 12–20 days (n #25, according to Franz, 1999).

Brief notes on the natural history of two additional species of Staminodeus are available (Franz, 2001). Staminodeus curvitibialis is associated with Sphaeradenia hamata Harling in La Planada, Nariño, Colombia, and with Asplundia caput-medusae (Hook. fil.) Harling in Portachuelo and Rancho Grande, Aragua, Venezuela. Staminodeus denticulatus is associated with Carludovica palmata Ruíz & Pavón, with E. funifer in San Vito, Puntarenas, Costa Rica, and with Asplundia sp. in Chiriquí Grande, Bocas del Toro, Panama. Therefore, all Staminodeus species for which hosts are known have been collected on cyclanths.

Morphology and phylogeny of Staminodeus

The male prothoracic legs display considerable morphological variation among the seven described species of Staminodeus , providing external diagnostic characters for the recognition of species (Franz, in press). Staminodeus inermis Franz lacks the row of teeth along the anteroventral margin of its mucronate protibia. Staminodeus curvitibialis Franz and S. denticulatus Franz have 12–18 small teeth along an apically inermous protibia; whereas S. bispinosus Franz, S. forcipis Franz, S. dilatatus Franz, and S. vectoris have 3–10 large teeth along an apically mucronate protibia (figure 7). The male protibia of S. curvitibialis is curved. The male profemur of S. forcipis is curved, and has larger ventral teeth, e.g. in comparison to S. vectoris. Finally, the males of S. denticulatus, S. bispinosus and S. forcipis have a small, curved spine on the frons, resembling that of the females, except for its smaller size.

The female frontal spines are similar among all seven species of Staminodeus . The only notable exception is S. denticulatus, which has a slightly larger spine (Franz, 2001). The female prothoracic legs lack the row of teeth, and the protibia is inermous at the apex.

A phylogeny of the species of Staminodeus has been proposed by Franz (2001), using Notolomus basalis LeConte, Perrelleschus carludovicae (Günther) and Systenotelus costaricensis Anderson & Gómez as outgroup taxa (figure 8). The cladistic analysis for ten taxa and 18 characters yielded a single most parsimonious cladogram (L=22, CI=86, RI=90). Those characters with apparent relevance for the mating behaviour of Staminodeus are mapped according to fast optimization (for explanation see table 2 ). Most remaining characters are generated from the male genitalia. The cladogram optimises the presence of the female frontal spine as a synapomorphy for Staminodeus . As the result of a reversal, the promucron in males is absent in S. curvitibialis + S. denticulatus. The synapomorphies of the clade inside of S. inermis are the ventrally toothed profemur and protibia in males. The size, shape, and number of teeth along the anteroventral protibial margin support S. curvitibialis + S. denticulatus and its sister taxon, the clade of S. bispinosus to S. vectoris. Finally, the small frontal spine in males is convergent in S. denticulatus and S. bispinosus + S. forcipis.