Themira lohmanus Ang

Ang, Yuchen, Rajaratnam, Gowri, Su, Kathy FY & Meier, Rudolf, 2017, Hidden in the urban parks of New York City: Themiralohmanus, a new species of Sepsidae described based on morphology, DNA sequences, mating behavior, and reproductive isolation (Sepsidae, Diptera), ZooKeys 698, pp. 95-111 : 100-105

Themira lohmanus Ang sp. n. Figures 2, 3

Material.

Holotype. ♂ [Lee Kong Chian Natural History Museum, Singapore (ZRC): ZRC_ENT_00001001], from ex-culture based on female collected June 2006 (Meier, R) in USA, New York, Brooklyn, Prospect Park [40.6563°N, 73.9686°W, elevation 20m ASL]. Paratypes. 2♂2♀ [ZRC: consecutive numbers running from ZRC_ENT_00001002 to ZRC_ENT_00001005], 3♂1♀ [American Museum of Natural History, New York, New York, USA (AMNH)], 1♂1♀ [National Museum of Natural History, Washington D.C., USA (USNM): USNMENT01384142, USNMENT01384143].

Etymology.

The new species is named after David J. Lohman, for his generous contributions of specimens to sepsid taxonomy.

Diagnosis.

Themira lohmanus is a relatively large, robust-looking sepsid species that resembles T. biloba . However, adult T. lohmanus males can be readily differentiated from the latter by their uniquely shaped, asymmetrical surstyli, which is symmetrical in T. biloba (Fig. 1A, see Morphological analysis section). While females of these two species do not have distinct structural differences, they can potentially be distinguished based on the color of the sclerous cuticle: in T. biloba , it tends to be glossy black while T. lohmanus tends to have a cupreous tinge. However, these characters may not be easily differentiated in faded specimens.

Description.

Males and females.Color (Figures 2, 3). Adults are black-colored flies. Sclerites mostly black with a cupreous shiny tinge, while membranous cuticle with a variegated orange hue. Gena and face light brown. Trochanters, as well as posterior region of fore coxae yellow to light brown. Eyes red. Antennae all black with Wings clear, without pterostigma. Halteres and calypter white.

Head ( A–D for Figures 2, 3). Chaetotaxy. Ocellar and postocellar setae divergent. Inner vertical setae convergent. 1 pair orbital setae, divergent. Posterior region of head capsule pruinose. Vibrissal angle with 2 larger vibrissae (dorsal longer than ventral), both smoothly medioclinate. Palps sclerotized and populated with multiple setae.

Thorax (A, B for Figures 2, 3). Chaetotaxy. Scutum with 1 pair discocentral setae on prescutum and 2 pairs on postscutum; anterior pair less than half as long as posterior pair. One postpronotal pair, 2 notopleural pairs; anterior pair half as long as posterior pair. One pair postalar setae. 1 pair apical scutellar setae. Anepisternum with short setulae on posterior region with 1 posteriad anepisternal seta. Pruinosity pattern . Scutum fully pruinose. Pleural thorax fully pruinose except for anepisternum, which is glossy.

Wing (Figures 2A, 3A). Veins bare. Cells entirely covered with microtrichiae except for basal costal cell. Section of costal vein between humeral vein and Radial 1 vein equally bisected by subcostal vein. Wing length 3.0-3.3 mm (♀), 3.2-3.8 (♂).

Males.Legs (Figure 2 E–G). Figure 2E: Forefemur on ventral surface with 2-3 spines submedially, one large (yellowish, translucent) cuticular protrusion medially and one thick, blunt bristle postmedially. Foretibia on ventral surface with clasp-like cuticular protrusions medially, with 3-4 spines on anterior region of protrusions. Figure 2F: Mid-femur with 3 anterior spines medially, mid-tibia without distinct spines. Figure 2G: Rear-femur slightly curved, with 2-3 dorsal spines. Rear-tibia expanded medially to accommodate large, osmoteria that covers 2/3 of anterior side. All tarsi normal, with tarsomeres 1-4 proceedingly shorter.

Abdomen (Figures 2A, B, H). Figure 2B: Glossy tergites, with small short setulae until tergite 4; 5th and 6th tergites with stouter setae. Figure 2A: Abdominal spiracles with well sclerotized margins; spiracles 1-4 in membrane, 5 on margin of and 6 and 7 within tergite. Figure 2H: Sternite 4 as bi-lobed arms terminating in two tufts of long bristles each; desclerotized in the middle. Sternite 5 as a triangular keel that subducts under sternite 4 anteriorly.

Hypopygium (Figure 2 I–L). Cerci a slight bump with one bristle each. Base of surstyli yellowish. Surstyli themselves asymmetrical; left surstylus as an enlarged lamina with a wide base, right surstylus as a shortened process.

Females.Legs (Figures 3 E–G). Forefemur (Figure 3E) on ventral surface with 2-3 spines postmedially. Other legs unmodified. Abdomen (Figure 3A, H). Abdominal spiracles with well sclerotized margins; spiracles 1-4 in membrane, 5 on margin of, and 6 and 7 within tergite.

Distribution.

Nearctic. Thus far only found in New York City (Central Park and Prospect Park); likely to be found in more localities in the future, especially where waterfowl congregate.

Biology.

Similar to T. biloba , adults have only been found near water bodies, due to the association with waterfowl dung which they use for breeding. Under laboratory conditions they can breed in cow dung, but preferentially lay eggs in waterfowl dung. Eggs take 2-3 days to hatch, and feed as larvae for approximately 6-7 days before entering the pupal stage. Adult eclosion usually occurs after about another 7-8 days. Specimen longevity under laboratory conditions range from 1-3 months.

Mating behavior profile.

The mating behavior can be categorized into three sections: (1) approach and mount, (2) mounted courtship and copulation, and finally (3) separation. All described behaviors are shown in Video 1 (time given as mm:ss; YouTube link https://youtu.be/ZrtxN02zXLY). Our description is part of a larger series of papers describing and investigating the mating behavior of sepsids (e.g. Ang et al. 2008, 2013; Puniamoorthy et al. 2008, 2009; Tan et al. 2011, 2010). However, this is the first case in which a species that lacks species-specific behavioral elements.

(1) Approach and mount.

When a male detects and shows interest in a female, it immediately gives chase and will attempt to mount the female from the rear (Behavior A1: Male Approach and Mount - 00:02). This can happen almost immediately when the male is introduced into the female (e.g., pairs 5 and 10), or only after a period of time (e.g., pairs 4, 8, and 11).

(2) Mounted courtship and copulation.

The behavior varies between pairs. Some females (e.g., pairs 5, 8 and 10) may immediately accept genital contact with the male upon his mounting, and proceed directly to copulation. Other females may be more resistant to the male (e.g., pairs 4 and 11), and only accept genital contact after an average of ~ 20 minutes ( ± ~ 7m). Copulation time itself is ~ 1h 38m ( ± 18m). While mounted, the male will attempt to display nine types of courtship behaviors, as described in detail in Table 4. The first behavior is M1 (Male Foreleg-Female Wingbase Grasp - 00:11), but the grasp is released soon after. Behavior M2 (Male Dragging - 00:24) tends to occur in the earlier parts of courtship, especially when the male has just mounted the female. Behaviors M3 (Male Midleg Tarsal Curl - 00:32) and M4 (Male Wing Flutter - 00:43) are observed early in this section, but can also occur later prior to separation. The most prominent behavior set is M5-M8: The male will start with M5 (Male Midleg-Rearleg Rub - 00:51), which is likely used for transferring substances from its hind leg osmeterium to its mid legs ( Araujo et al. 2014). The male will then directly proceed with either behavior M6 (Male Midleg-Female Wing Rub - 00:58), M7 (Male Midleg-Female Thorax Rub - 01:04) or M8 (Male Midleg-Female Head Rub - 01:10). Behavior M9 (Male Hind leg-Female Wing Rub - 01:16) was also observed in between the M5-8 behavior sets, and is also likely to be involved in the transfer of substances from hind leg osmeterium to wing ( Araujo et al. 2014). These leg-rubbing behaviors are the most common actions performed by the male. Finally, the male will also perform M10 (Male Sternite Brushing - 01:25), which is always observed in the later part of this period, usually closer to the separation phase.

Females also display several behavioral elements, often in response to male behaviors. They are described in detail in Table 5: consistent is F1 (Female Body Shake - 01:51) when the male mounts her. This shaking may last for only a few seconds or is protracted; sometimes it is so violent that the couple will flip over. After her initial shake, the female tends to start walking around carrying the mounted male while the male may attempt to anchor his feet on the substrate (M2: Male Dragging; see above) resulting in the female dragging the male. The female is also observed to rub those parts of her body with her fore-, mid- and hind legs that the male has contacted (see behaviors M5 to M9) (F2: Female Self-rubbing - 02:04). Finally, the female may occasionally evert her ovipositor (F3: Female Ovipositor Eversion - 02:14). This only occurs during courtship, before the male is copulating with her.

(3) Separation.

Separation is always preceded by a significant amount of female shaking (Behavior F1). The male will then start to turn around (180°) facing directly away from the female. Both parties will start pulling (behavior S1 - 02:32) and after some amount of ‘straining’ (an average time of 26.5 ± 6.41s), the pair will be able to disengage. This difficulty in separation is also known for Themira biloba and females have been observed to be dragging dead, intromittent males that have failed to disengage from the female (pers. obs. Mindy Tuan).