Tachytrechus alatus

Brooks, Scott E. & Cumming, Jeffrey M., 2008, The Tachytrechus alatus species group (= Syntomoneurum Becker) revisited: new species and revised species group limits (Diptera: Dolichopodidae), Zootaxa 1676, pp. 1-27 : 2-3

Tachytrechus alatus species group

Diagnosis. Vertical bristles strongly reduced in males; face broad; clypeus projected below lower margin of eyes; palpus large; scape setose dorsally and ventrally; males (and females of some species) with white-tipped arista-like stylus; 1–2 notopleural bristles; fore femur (Fig. 10C) and hind basitarsus with strong basiventral bristle; male mid femur with ventral tubercle before middle; pulvilli of mid- and hindlegs very reduced; basiventral surface of fore femur (Fig. 10C) and anterior surface of mid coxa with cluster of 2–3 strong bristles; mid femur with 1 strong anterior preapical bristle; hind femur with 1–3 anterior preapical bristles; male abdominal sternite 5 emarginate and membranous posteriorly with eversible glandular structure usually present; male abdominal tergite 6 bare; male segment 7 pedunculate, bare; hypopygium large; apicoventral epandrial lobe with branched seta; apex of postgonite distally upturned at a right angle and flared laterally, bifurcate with well-developed apicoventral arms; ejaculatory apodeme with basal projection elongate and flexed ventrally; female abdominal tergites 6 and 7 divided medially, tergite 10 of female divided into subtriangular hemitergites, each with inner medial spine.

Remarks. The diagnostic features listed above include at least five character states that can be considered synapomorphic for the T. alatus species group, namely the reduced vertical bristles in males (state 1.1), strong basiventral bristle on the fore femur (state 4.1), reduced pulvilli on the mid- and hindlegs (state 9.1), and ventral cluster of 2–3 strong bristles on the fore femur (state 5.1) and mid coxa (state 7.1) of males (see “Phylogeny and Zoogeographic Considerations”).

In the T. alatus species group the vertical bristles of males are dramatically reduced, such that they are subequal to the uppermost postocular seta in most species. Brooks (2005) noted reduction of vertical setae in some additional species of Tachytrechus including T. laevigatus (Becker) , T. flabellifer (Osten Sacken) and T. seriatus (Robinson) . In some other species of Tachytrechus the vertical bristles of males are somewhat weaker than those of females, but they are strong compared to the condition in males of the T. alatus species group.

Some undescribed species of the closely related T. castus species group (see “Phylogeny and Zoogeographic Considerations”) from Mexico and Costa Rica (USNM, CNC) also possess several long setae on the ventral surface of the fore femur and on the anterior surface of the mid coxa; however, these setae are not consolidated into a distinct cluster as in males of the T. alatus species group. One of these undescribed species, which is known from a single male labelled “Mex.” (USNM), also possesses a very weak, hair-like basiventral seta on the fore femur, which is possibly homologous with the strong basiventral bristle observed in the T. alatus species group. However, this species possesses strong, straight, parallel vertical setae on the head, indicating it belongs to the T. castus group (see “Phylogeny and Zoogeographic Considerations” below).

The large membraneous region on abdominal tergite 5, which was listed as a synapomorphy of the entire T. alatus species group in Brooks (2005, character 35), is more difficult to discern when some of the new species and T. transversus are taken into account. This character, which is difficult to code into discrete states, is described under each species treatment, but is not included in the group diagnosis and present analysis (see “Phylogeny and Zoogeographic Considerations”). In addition, because the white-tipped arista-like stylus of males of the T. alatus species group occurs in males of some species of the T. flabellifer species group and in some apparently undescribed species of the T. castus species group (EMUS, USNM) (but not T. dilaticosta or T. castus ), it is also excluded from the present analysis.

At present, very little is known about the ecology and habitats of the T. alatus species group. Detailed habitat information has only been noted for the type series of T. giganteus (Brooks) . This species was collected in a wet forest near a pair of narrow (about 30 cm wide) streams a few centimeters deep with overhanging vegetation and streambeds comprising bedrock, boulders, gravel and sand ( Brooks & Wheeler, 2002). The T. alatus species group has been collected within an elevational range of 150–2000 m.