Tikuna atramentum (Traver) Savage & Flowers & Porras, 2005

Savage, Harry M., Flowers, R. Wills & Porras, Wendy, 2005, Rediscovery of Choroterpes atramentum in Costa Rica, type species of Tikuna new genus (Ephemeroptera: Leptophlebiidae: Atalophlebiinae), and its role in the " Great American Interchange ", Zootaxa 932 (1), pp. 1-14 : 4-11

Tikuna atramentum (Traver) new combination

( Figs. 1–22 )

Choroterpes atramentum Traver 1947:156

Male Imago (in alcohol). Length: body 7.8 mm; forewings, 6.7 mm. Head whitish yellow, antennae translucent. Thorax: nota whitish yellow, submedian longitudinal brownish black stripes extend from anterior margin of pronotum to posterior mesonotum, submedian stripes broken on metanotum; sterna and pleura whitish yellow. Forewings ( Fig. 1 ): stigmatic crossveins not anastomosed to very weakly anastomosed; costal brace yellow; longitudinal veins brownish yellow to hyaline, veins C, Sc and R 1 darker, posterior veins lighter, distal 1/3 of Sc washed with brownish black, basal portion of these cross­ veins brownish yellow, crossveins of R 1 cell washed with brownish black, wash darker and wider anteriorly, 2 crossveins at base of radial field and 1 median crossvein between R 4+5 and MA brownish black, remaining crossveins light yellow to hyaline; membrane of C cell with brownish black clouds surrounding anterior portion of crossveins as in Fig. 1 , posterior portion of costal crossveins basal to stigma with brownish yellow clouds, basal portion of stigma in C cell with a light reddish brown to brownish black wash; basal crossvein in cell R 2 with cloud distinctly wider anteriorly, median crossvein with a prominent, large, brownish black cloud, apical crossveins with narrow clouds that widen anteriorly; apex of wings with a light yellow band covering apical 1/3 of Sc cell and apex of R 1 cell, a brownish black to reddish brown band continues apically from near apex of vein Sc to apex of wing in radial field just posterior to R 2; remainder of membrane hyaline, translucent. Hind wings ( Fig. 2 ): longitudinal veins and crossveins hyaline, veins C and Sc darker, posterior veins lighter; membrane whitish hyaline, translucent. Forelegs light yellow, inner margin of femora with brownish black, distal, longitudinal streak and small dash near base; remainder of legs pale yellow. Abdomen ( Fig. 7 ): terga whitish yellow; tergum 1 with posterior submedian brownish black marks and narrow brownish black lines along anterior margin; terga 2–5 with anterior and posterior, submedian, and spiracular brownish black marks, brownish black wash continues anterolaterally from anterior margin of posterior marks; tergum 6 with anterior and posterior submedian marks, posterior marks absent on tergum 7; tergum 8 with prominent submedian brownish black marks that converge distally; tergum 9 with light, narrow brownish black submedian washes that converge distally; tracheae semihyaline; sterna whitish yellow. Genitalia ( Figs. 11, 12 ): styliger plate, forceps and penes light yellow. Caudal filaments whitish.

Female Imago (in alcohol). Length: body, 6.4–7.3 mm.; forewings, 6.6–6.9 mm. Head whitish yellow with heavy brownish black wash near compound eyes. Antennae whitish yellow. Thorax: color and marks as in M but with middle of mesonotum washed with tan. Wings: similar to male except C cell of forewings with three large brownish black clouds located basal to large median cloud in R1 cell; hind wings as in Fig. 2 . Legs: [broken off and missing]. Abdomen ( Fig. 8 ): terga washed with brownish yellow, darker medially; terga 1–5 with brownish black marks similar to male except marks larger; tergum 6 with large anterior and small posterior submedian marks; tergum 7 with anterior submedian marks and heavy brownish black wash continuing posteriorly from marks; color and marks on terga 8–9 as in male; tergum 8 with posterolateral spines; color of spiracles, tracheae and sterna as in male; caudal filaments whitish.

Nymph (in alcohol, Fig. 14 ). Body length 6.1–7.5 mm. Head brownish yellow to yellowish brown, lateral edges of genae darker. Antennae pale yellow. Mouthparts ( Figs. 19–23 ): labrum with maximum length slightly greater than 1/5 width; anteromedian emargination well developed with 6 very small, apically flattened denticles; segment 2 of labial palpi subequal to length of segment 1; segment 3 of palpi 7/10 length of segment 2. Thorax: yellowish brown, pleura whitish yellow with sclerites yellowish brown; sterna whitish yellow, meso­ and metanotum washed with pale brown laterally; brownish black marks as in male imago. Legs brownish yellow, forelegs slightly darker. Abdomen: terga and sterna light yellowish brown, with rear margins darker brown, terga 8–10 darker brown; terga 1– 6 and 8 with brownish black maculae as in male imago, terga 1–6 with small posterolateral brownish black diagonal streaks; tergum 10 with brownish­black wash laterally and a pale median area. Gill membrane translucent, tracheae washed lightly to heavily with brownish black. Caudal filaments whitish yellow.

Specimens examined: ♂ subimaginal holotype, COSTA RICA, Río Pedregoso , Feb. 1939, D.L. Rounds ; 1 ♀ subimaginal allotype and 1 male paratype (genitalia missing), same data as holotype. Other specimens examined: COSTA RICA: Guanacaste Prov. 1 ♂ imago ( INBio) Canton de Nandayure , San Pedro, at light, 8­XI­2002, W. Porras, R.W. Flowers, Y. Cardenas . 1 ♂ imago ( INBio) Reserva Monte Alto, Río Nosara , at light, 21­ VI­2002, W. Porras, R.W. Flowers . 1 immature nymph, same locality, 22­VI­2002, R.W. Flowers, W. Porras . 1 ♂ subimago, same locality and collectors, 18­VI­2002 . 11 ♂, 5 ♀ subimagos (5 ♂, 2 ♀: INBio; 6 ♂, 3 ♀: UCR), Finca Agua Fria, San Pablo de Nandayure , luces, 10­IV­2002, W. Porras. Area de Conservación Guanacaste: Sector Santa Elena : 1 ♀ imago, área serpentina, Malaise trap, 3­IX­2002, R.W. Flowers. 1 ♀ imago, same locality and method, 17­IX­2002 . 1 immature nymph, Río Cuajiniquil , 7­XII­2002, R.W. Flowers, M.M. Chavarría. Sector Santa Rosa : 3 immature nymphs, Río Cuajiniquil , 21­XII­2002, M.M. Chavarría . 3 immature nymphs, Río Cuajiniquil, Sendero Cafetal , 15­XII­2002. San José Prov . 6 immature nymphs ( UCR), El Rodeo, 850m . quebrada en las instalaciones de UPAZ, 4­10­98.

Distribution ( Fig. 24 ): Western Costa Rica, primarily on the peninsulas of Santa Elena and Nicoya.

Ecology: All specimens collected during 2002 came from seasonal streams in areas of Costa Rica that experience a four to six­month dry season. The first collection in April near Carmona was at light next to the Río Nandayure which has flowing water nine months of the year; from March to June flow becomes intermittent with some permanent pools and subterranean flow. The mayflies were collected next to the only permanent pool on that stretch of river. Adults and nymphs were found in the Río Nosara in and below the Reserva Monte Alto in June. This stream is small, with moderate to dense shade. Inside the reserve, T. atramentum was found in an area of riffles and small pools below a waterfall; the site below the reserve consisted of riffles and a large pool that contained a diverse population of large river shrimp. This area dries completely from the end of February to June.

The San Pedro site in Nicoya, where a single adult male was taken at UV light, is a sparsely populated mountainous area consisting of a mosaic of small farms and ranches and patches of second­growth forest. The light was set up next to a small stream that disappears in the dry season but has abundant water and is prone to spates the during the rainy season.

In the Santa Elena Peninsula, the area where adults of T. atramentum , where taken in a Malaise trap is on a ridge of serpentine rock in a mixture of grassland and fragments of dwarf forest. This serpentine area is the geologically oldest part of Costa Rica, and soil is unusually nutrient­poor. During the rainy season small streams drain the ridge into the Río Potrero Grande and the Río Cuajiniquil. In early December (a month after the start of the dry season) the Río Potrero Grande was still flowing, but few mayfly nymphs were found. These belonged to the typical flowing­water community ( Thraulodes, Baetodes, Leptohyphes ) found throughout Costa Rica and Panamá in clean to moderately clean water. By contrast, water flow in the Río Cuajiniquil had almost stopped, but water was still plentiful in numerous pools between rocks. In the place where we found nymphs of T. atramentum , nymphs of Caenis sp. , Choroterpes s.s. sp., and Callibaetis sp. were abundant. A short distance downstream in a large, waist­deep pool, nymphs of Ulmeritoides were collected. The entire mayfly community in the Río Cuajiniquil consisted of species rare or at least uncommon in other areas of Costa Rica.

El Rodeo is a forest fragment in the middle of large cleared agricultural area. The streams here are temporary.

No information other than the name of the river is known for the type locality. There are two "Río Pedregosos" and three "Quebrada Pedregosas" listed for Costa Rica. The best known of these is the Río Pedregoso which flows south from Cerro de la Muerte into the Río Terraba basin near the city of San Isidro de General. The other Río Pedregoso is nearby but flows northwest into the Río Pirrís, which empties into the Pacific Ocean between Punta Judas and Parque Nacional Manuel Antonio. Two of the "quebradas" are located not far away, but in areas that had not yet been colonized and were probably not accessible to travelers in 1939. Interestingly, the third Quebrada Pedregosa is in Nicoya near the town of Jicaral, which was an accessible area in the early 1900's.

Tikuna atramentum apparently has a long emergence period, or is multigenerational with adult emergence taking place throughout the period when water is found in the streams where they live. In Nicoya adults have been found in April, June, and November. In Santa Elena, nymphs found in late December had large wing pads with the wings inside just beginning to darken.

Figures

FIGURES 1–13. Tikuna atramentum, imago and subimago. 1, fore– and hind wings; 2, hind wing, enlarged; 3, head of ♂ imago, lateral view; 4, head of ♀ imago, dorsal view; 5, fore­ and hind wings of holotype subimago; 6, hind wing of holotype subimago, enlarged; 7, abdominal terga 1–9 of ♂ imago. 8, abdominal terga 1–9 of ♀ imago. 9, sterna 7–9 of ♀ imago; 10, claws of ♀ imago; 11, genital segments of ♂ imago; 12, penes, enlarged; 13, genital segments of holotype ♂ subimago.

FIGURES 14–18. Tikuna atramentum, nymph. 14, nymph (median caudal filament broken); 15, foreclaw. 16–18, abdominal gills on: 16, segment 1; 17, segment 5; 18, segment 7.

FIGURES 19–23. nymphal mouthparts. 19, labrum; 20, left mandible; 21, maxilla; 22, hypopharynx; 23, labium: left, dorsum; right, venter.

FIGURES 24–25. 24, Geological map of Costa Rica (redrawn from Abratis 1998) showing terranes of the Nicoya Complex (light grey), localities of recent collections of Tikuna atramentum (black squares), and two possible locations for the type locality (question marks). 25, Reconstruction of development of Lower Central America during the late Cretaceous (80 Ma) and early Tertiary (50 Ma) (redrawn from Meschede 1998). The black arrows point to the northern apex of the Costa Rica–Panamá island arc.