Planinasus Cresson

Mathis, Wayne N., Rung, Alessandra & Kotrba, Marion, 2012, A revision of the genus Planinasus Cresson (Diptera, Periscelididae), ZooKeys 225, pp. 1-83 : 6-11

Genus Planinasus Cresson

Planinasus Cresson 1914: 245 [in the family Ephydridae ; type species: Planinasus ambiguus Cresson, by original designation]; Cresson 1918: 65 [discussion, genus probably not in Ephydridae ]. Malloch 1934: 52 [generic key, in family Perisceli[di]dae]. Curran 1934: 327 [generic key, in family Drosophilidae ]. Hennig 1969: 614-616 [revision, in family Aulacigastridae ]. McAlpine 1983: 56 [discussion, assigned to family Periscelididae ]. Mathis and Rung 2011: 363 [world catalog].

Schizochaeta Malloch 1934: 52 [type species: Schizochaeta shannoni Malloch, by original designation]. Hennig 1969: 614 [synonymy].

Diagnosis.

Head: Frons with 1 pair of interfrontal setae; reclinate fronto-orbital seta usually smaller than and inserted behind proclinate seta; both medial and lateral vert ical setae well developed; postvertical setae absent. Interantennal space at least equal to antennal length, much greater in some species; basal flagellomere arising from anterior surface of pedicel; arista bipectinate. Face uniformly sclerotized and usually arched, bearing a prominent, dorsoclinate, sometimes convergent to cruciate pair of setae near or on transverse facial carina, usually with several other facial setae, these usually ventroclinate and sometimes arranged in a transverse row. Eye bare of interfacetal microsetulae. Genal height less than width of pedicel, lacking a genal seta.

Thorax: Dorsocentral setae 2, both postsutural ( Planinasus ambiguus with a 3rd small, anterior, dorsocentral seta, less than 1/3 length of either posterior 2); supra-alar seta 1; postalar seta 1; postpronotum shiny, lacking a well-developed seta; notopleural setae 2; lateral scutellar setae 1 pair, apical, basal seta lacking; scutellar disc bare; anepisternal setae usually 2, inserted along posterior margin; katepisternal setae 2, anterior seta slightly weaker. Wing: no costal breaks (a weakness in the costa just apicad of the humeral crossvein); costa extended to vein M; subcosta rudimentary, neither reaching costal margin nor fused apically with vein R1; vein R2+3 minutely but densely trichose on ventral surface; crossvein bm-cu present, with distinct discal cell and cell bm; cell cup present; discal cell with a fold running entire length; vein CuA2 well developed. Legs: forefemur with 1-2 posteroventral setae at apical 1/3; midtibia with apicoventral spine-like seta; hindfemur with anterodorsal preapical seta; all tibiae with subapical dorsal seta.

Abdomen: Male: Segments 1-6 with tergites and sternites separate and spiracles 1-6 in membrane; tergite 6 well developed, sternite 6 short and slightly asymmetrical; pregenital segment (sternites 7, 8?) short, immediately adjacent to epandrium, with spiracle 7 within sclerotized portion. Male terminalia as follows: Largely symmetrical; epandrium well developed, bearing numerous setulae; cerci poorly developed, largely unsclerotized, bearing sparse setulae; surstylus usually a long process fused with epandrium, generally, surstyli generally separated from each other (fused medially in Planinasus ambiguus ); gonostylus relatively simple to complex, often with elaborate processes; pregonite articulated with apex of lateral hypandrial arm; postgonite long, bearing processes and a ventral lobe with setae; subepandrial sclerite rod-like, connecting surstylus with apex of hypandrial arm; aedeagus short; phallapodeme long, narrow; ejaculatory apodeme varying, sometimes dramatically, very large to tiny; hypandrium U or V shaped, often widely so. Female: Spiracle 7 ( “stigma”) not free in female postabdomen. Spermathecae 2; ventral receptacle one-chambered.

Distribution.

Known only from the New World tropics.

Natural History.

Specimens of Planinasus are generally rare in collections, and nothing is known about their immature stages, life cycle, or ecology. Their rarity in collections, however, is not necessarily a reflection of their diversity and/or abundance in nature. Specimens are comparatively small, obscure, and could easily be overlooked. We have collected hundreds of specimens of numerous species in the countries of Bolivia, Ecuador, Guyana, Mexico (Chiapas), Peru ( Huánuco, Cuzco, Madre de Dios), and on some islands of the Caribbean (Cuba, Dominica, Dominican Republic, Jamaica, and Tobago). In all areas, specimens were collected by sweeping dense, understory vegetation- -some bearing flowers--that was associated with shaded, damp, habitats. In Ecuador, we found specimens to be relatively common on the exposed sand or mud substrates in shaded, riparian habitats. Here we observed specimens exposed on the surface of stones or large fallen leaves, perhaps posturing to be seen by conspecifics. We captured numerous specimens alive by simply and carefully lowering a vial over them.

Our field work and sampling, regardless of the collecting technique, also indicates that two to four species frequently occur sympatrically at the same microhabitat. We observed that one species at these sites usually predominates in numbers of individuals. How the various species partition the habitat and what their population structure is are basic questions that remain unanswered.

Grimaldi and Fenster (1989) noted certain preconditions associated with male hypercephaly. Although their list primarily pertains to Drosophilidae , they may also apply elsewhere in Diptera , including species of Planinasus that demonstrate hypercephaly. These preconditions, which were manifested at least partially in the few observations we made (see "Mating behavior" under Planinasus kotrbae ), are: territoriality, face-to-face confrontations, head butting and jousting. Perhaps, like Drosophilidae , there is more aggressiveness among species with hypercephaly than their unmodified relatives. Further observation and comparison are obviously needed, and we hope that this revision will foster such.

Discussion.

Several species exhibit considerable sexual dimorphism, especially in the width and coloration of the face. Males in these species tend to have wider faces (hypercephaly), i.e., larger facial ratios, and frequently there is a distinctive colorational pattern. The facial pattern usually also involves microtomentum or its absence in additional to color. These details are included in descriptions of appropriate species.

Within the subfamily Stenomicrinae the sister group of Planinasus is apparently either Cyamops or Stenomicra ( Winkler et al. 2010, Mathis and Rung 2011) or perhaps both. The relationship with Cyamops is based on the following putative synapomorphies:

1. Midtibia with an apical, anteroventral spine-like seta.

2. Arista bipectinate ( McAlpine 1983: 56).

3. Face bearing a dorsoclinate pair of setae, these usually inserted above other facial setae.

Planinasus is distinct from other genera of Periscelididae and its monophyly is established by the following putative synapomorphies:

1. Frons bearing a pair of interfrontal setae that are usually slightly reclinate to dorsoclinate. The interfrontal setae, as described, are unique to Planinasus .

2. Forefemur with 1-3 posteroventral setae on apical half.

3. Scutellum bearing a single pair of marginal setae, these apical (also in some species of Cyamops ).

4. Reclinate fronto-orbital seta inserted behind proclinate fronto-orbital seta.

5. Each tibia with a dorsoapical seta.

6. Hindfemur with a subapical dorsal seta.

7. Anepisternum with 1-2 setae along posterior margin (relatively common in other taxa of Asteioinea).

8. Several characters of the male terminalia.

Key to extant species of Planinasus Cresson

The ambiguus group

Included species. Planinasus aenigmaticus sp. n., Planinasus ambiguus Cresson, and Planinasus neotropicus sp. n.

Diagnosis. This species group is distinguished by the following combination of characters: Head: Interfrontal seta short, about half length of lateral vertical seta. Antennal coloration variable; pedicel with short ventral projection; basal flagellomere short, about as high as long. Large facial setae arranged in 2-3 transverse rows; face of males and females similar in shape and color. Thorax: Anepisternum with 1 large seta along posterior margin. Wing hyaline to faintly infumate. Forefemur of male lacking subapical, irregular, pale-colored annulus, bearing 2 large seta at apical 1/3 along posteroventral surface. Abdomen: Surstylus generally thumb-like, without posterior processes or lobes, in nearly vertical alignment with anterior margin of epandrium; postgonite with robustly developed lobe bearing numerous setulae apically; phallus mostly sclerotized, large, convoluted; ejaculatory apodeme generally well developed, at least as long as phallapodeme, with expanded apex.

Discussion. There is little if any dimensional or colorational sexual dimorphism in specimens of this species group. Dimensions and ratios of the heads of both males and females are essentially the same or with broad overlap. Species of this group share with species of the nigritarsus group, and only with them, a postgonite with a robustly developed lobe that bears numerous setulae. In other species of Planinasus , the lobe of the postgonite, which is generally less developed, bears fewer than four apical setulae, and fewer than six setulae overall. The ambiguus and nigritarsus groups also share a well-developed ejaculatory apodeme that is at least as long as the phallapodeme (this character state is also present in Planinasus mcalpineorum sp. n. of the nigrifacies group).