A new species of Aulacigaster from Zurquí de Moravia , a Costa Rican cloud forest ( Diptera : Aulacigastridae )

A new species of Aulacigaster Macquart, 1835 A. zurqui sp. nov., is described from Costa Rica. The new species, which is classified in the plesiomorphica species group following a cladistics analysis, can be separated from all congeners by having a triangular 1st flagellomere and stout body that is uniformly dark-brown to black. An expanded diagnosis of the plesiomorphica group and a modified key to the Neotropical Aulacigaster are provided to accommodate the new species.


INTRODUCTION
Two species of the dipteran family Aulacigastridae were collected as part of the ZADBI project (Borkent and Brown 2015), a 3-year grant funded by the National Science Foundation (NSF) to estimate fly diversity within a Costa Rican cloud forest, Zurquí de Moravia (hereafter referred to only as Zurquí).One is Aulacigaster melanoleuca (Hennig, 1956), originally described from Costa Rica and widespread in that country.The other is described here as new.
Aulacigastridae are a small family of acalyptrate flies with two extant genera, Aulacigaster Macquart, 1835, distributed worldwide, and Curiosimusca Rung et al. (Rung et al. 2005) from the Oriental Region.Aulacigaster, now numbering 56 species (Rung and Mathis 2011; this contribution), have been observed associated with slime fluxes of deciduous trees (Robinson 1953, Cole and Streams 1970, Davis and Zack 1978, Ferrar 1987, Mathis and Freidberg 1994, Hilger and Kassebeer 2000, Papp 2008, Rung and Mathis 2011) or with the phytotelmata of bromeliads (Rung and Mathis 2011).In the Neotropical Region, 38 species are known to occur, divided among six species groups (Rung and Mathis 2011; this contribution): the leucopeza group, also with species in the Nearctic Region and Old World, and the bromeliae, ecuadoriensis, femorata, grimaldii, and plesimorphica groups, which are exclusively Neotropical.
In this paper, I describe a new species of Aulacigaster from Zurquí.Since the genus has already been revised (Rung and Mathis 2011) and no additional species have been described since, a comprehensive revision is not necessary.The new species can be separated from all congeners by the triangular shape of the 1 st flagellomere and by having a stout body that is uniformly dark-brown to black.In addition to the species' description, I present evidence that it belongs to the plesimorphica group, provide an expanded diagnosis of the group, and indicate where the new species fits in the "Key to the Neotropical Species Groups and Species of Aulacigaster Macquart" (Rung and Mathis 2011: 6-9).

MATERIAL AND METHODS
The descriptive terminology is from McAlpine (1981), except that the nomenclature for the structures of the male terminalia follows Cumming et al. (1995).
The following ratios are used in the new species' description and appended key: 1) scutal ratio: the greatest length of scutum divided by the greatest width of scutum; 2) head ratio: the greatest length of head divided by the greatest height of head.
Specimens are small and study and illustration of the male terminalia required the use of a compound microscope.Photographs were taken with a Nikon Coolpix Ds-Fi1 digital camera through a Nikon SMZ1500 dissecting scope and were assembled using Combine Z.The photographs were enhanced, formatted, and arranged in Adobe Photoshop 7.
Drawings of the male terminalia were traced over pictures assembled using Combine Z, taken using a Nikon Coolpix Ds-Fi1 digital camera through a Nikon Eclipse 600 compound microscope.
The consensus cladogram was drawn in Adobe Illustrator CS6.A phylogenetic analysis was performed to ascertain where the new species fits the phylogeny provided by Rung and Mathis (2011).To this end, the character matrix in Rung and Mathis (2011: appendix) was expanded to include the new species, with the following character states added to the last row "11111111113311-121121311." Analyses were done using PAUP 4.0 (Swofford 2002).The matrix was analyzed with a branchand-bound search, with all characters unordered and equally weighed, followed by three iterations of successive weighting (Farris 1969).For more information about the choice of ingroup and outgroup taxa, consult Rung and Mathis (2011).

RESULTS
Phylogenetic position of A. zurqui sp.nov.
Adding A. zurqui sp.nov., to the matrix of Rung and Mathis (2011: appendix) (see Materials and Methods), and performing an exhaustive search, resulted in 17 optimal trees with 41 steps, a consistency-index of 0.78, and a retention index of 0.91.The competing topologies differ in the the relationships among the species of the leucopeza group.In all reconstructions the relationships among the bromeliae and the plesiomorphica (now including A. zurqui sp.nov.) groups and the remaining species of Neotropical Aulacigaster (a clade composed of the grimadii, the ecuadoriensis, the minuta and the femorata groups) resulted in a trichotomy (Fig. 1).
The strict consensus cladogram of the 17 trees obtained in this analysis (Fig. 1) does not differ from one obtained by Rung and Mathis (2011: 118, fig. 202), except for the addition of the new species.In the present work, the new species clustered with the plesiomorphica group, sharing with it one homoplasious, yet unambiguous, synapomorphy, the presence of a group of long, strong setae on one of the posterior processes of the gonopod (character 22, state 3 in Rung and Mathis 2011: 116;Fig. 8).This process is also present in two species of the ecuadoriensis group present in the analysis, A. ecuadoriensis (Hennig, 1969) and A.
Figure 1.Strict consensus cladogram obtained from 17 optimum trees, summarizing a cladistics analysis of Aulacigaster.The optimum trees were obtained with a branch-and-bound search, characters unordered and equally weighted, and have 41 steps, consistency-index (CI) 0.78 and retention index (RI) 0.91.The number on the nodes indicate the species-groups as follows: 1.The leucopeza group; 2. The plesiomorphica group; 3. The bromeliae group; 4. The grimaldii group; 5.The femorata group; 6.The minuta group; 7. The ecuadoriensis group.melanoleuca (Hennig, 1956).Aulacigaster zurqui sp.nov., also shares with those two species, the triangular shape of the first flagellomere (character11, state 3 in Rung and Mathis 2011:116; Figs 2-5).However, it lacks a uniquely derived character of that group, the pleural region white on the lower half.It also lacks the elongated body, a synapomorphy that unites the ecuadoriensis and the minuta groups.
Given the results of the cladistics analysis, I have decided to place the new species in the plesiomorphica group, despite some taxonomic ambiguity.Aulacigaster zurqui sp.nov., lacks some of the striking characters that are used to diagnose the plesiomorphica group, such as the lunate silver stripe on the frons, and the characteristic shape of the face, which often bears a facial band.It is possible that, in the future, as new taxa are collected and new character systems are explored, a better placement for A. zurqui sp.nov.will be found.

Modified key to species
The new species keys out to couplet 6 in the "Key to the Neotropical Species Groups and Species of Aulacigaster Macquart" (Rung and Mathis 2011: 6-9).In couplet 6, the plesiomorphica group is separated.Couplet 6 is herein modified as follows, to accommodate for this new species (changes to previous key in boldface):  Diagnosis.The plesiomorphica group is distinguished from other species groups by the following combination of characters: Stout, medium-sized flies, body length 2.4-3.5 mm.Coloration and vestiture: Frons often with anterior1/3-1/2 yellowish in ground color, rarely completely black; anterior portion of frons densely microtomentose, often with microtomentum forming a wide, lunate, silvery stripe; facial band often present.Anepisternum mostly dull microtomentose.Abdomen in a few cases with a large, white to yellowish region on syntergite 1+2.Morphology: Head: Head higher than long (head ratio less than 0.9); 1st flagellomere often rounded, rarely triangular; face strongly convex on ventral 2/3, easily visible in lateral view; ocellar seta minute; fronto-orbital setae with posterior seta slightly internal to and almost transversely aligned with anterior seta.Thorax: Subcosta partially fused with vein R1 apically but terminated at costa.Male abdomen and terminalia: Surstylus a short, posteroventral lobe in lateral view; cerci often partially fused; subepandrial sclerite typically forming a single, platelike structure; gonopods often with 2 posterior processes; one bearing 4-5 strong, stout setae.
Biology.There is sparse biological information on species of this group.Exemplars that were hand collected in the rainforest were captured on tree trunks and other aerial portions of large Ceiba trees with no visible, wound-exuding sapfluxes (Rung and Mathis 2011).
Discussion.Species of the plesiomorphica group are distinguished by the presence/absence of a facial band, the shape of the face, and coloration of the legs.In some cases, species can only be identified with certainty by referring to the shape of the surstylus and other structural characters of the male, such as the shape of sternite 5, presence/absence of setae on the hind trochanter and hind tibia.
With the addition of the species described herein, the plesiomorphica group includes 11 species.The group is exclusively Neotropical.
Diagnosis.This species can be separated from all congeners by having a triangular 1 st flagellomere and body stout, uniformly dark-brown to black.
Thorax.Acrostichal setae in 2 rows; scutellum strongly raised (angle with scutum less than 135°), approximately triangular, apex rounded, disk of scutellum convex; basal scutellar seta a little less than 1/2 length of posterior seta; wings with one row of stronger setae on Coastal vein.
Male abdomen and terminalia: Surstylus inconspicuous in lateral view in unprepared specimens, folded beneath the epandrium and appearing as a strongly setose postero-ventral region.After preparation, an approximately triangular sheath can be observed in lateral view, bearing 2 long setae, one pre-apical Figure 10.Aulacigaster zurqui sp.nov.: digital photographs of the labels pinned with the male holotype.and one apical; subepandrial sclerite with 2 lateral arms on each end, nearly parallel, well sclerotized; anterior dorsal process of gonopod subequal in size to anterior dorsal process; gonopod subrectangular, wider than high in profile, with posteriormost ventral process pointed, at base as wide as base of anterior dorsal process; anteriormost ventral process bearing 5 strong, strong setae; cerci lost during preparation.
Etymology.The specific epithet, zurqui, is the cloud forest where the species was collected.The name is a noun in apposition.
Ecology.Nothing is known about the habits and biology of this new species.

FINAL REMARKS
Including this contribution, 14 species of Aulacigaster are known from Costa Rica.The new species, A. zurqui, belongs to the plesiomorphica species-group according to a cladistic analysis and is united with the other species of that group by one homoplasious synapomorphy: the presence of a process on the posterior portion of the gonopod bearing long, strong setae.