Helochares (Hydrobaticus) nexus Short & Girón 2018, n. sp.
Creators: name: Short, Andrew Edward Z.
name: Girón, Jennifer C.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Helochares
Helochares nexus

description: Helochares (Hydrobaticus) nexus n. sp.
Figs. 2C, 5D, 6 C–D, 7F–H, 9C, 10B.
Type material. Holotype (male): “PANAMA: Cocle Province / 8 39’05.2”N, 80 35’18.7”W / 8.vi.2008, leg. A.E.Z. Short / AS-08-015; detrital pools/ in stream that crosses road”. (SEMC). Paratypes (41): ECUADOR: Manabi Province: 1.4 km E. of Pyampe, Puerto Lopez, Machalilla National Park, 25.x.1978, leg. J. Anderson (2, USNM); Guayas Province: 5.5 km N. of Noboi, 12.i.1978, leg. P.J. Spangler & J. Anderson (5, SEMC, USNM). PANAMA: Cocle Province: Same data as holotype (15, SEMC, including DNA voucher SLE1206); Colon Province: Parque Nacional Soberania, Pipeline Rd, Km 6.1, 7-21.vi.1995, leg. J. Ashe & R. Brooks #265 (1, SEMC); Panama Province: Paraiso, CZ [Canal Zone], 29.i.1911, leg. E.A. Schwarz (2, USNM); Las Cruces, CZ [Canal Zone], 23.iii.1911, leg. A.H. Jennings (1, USNM); Gamboa, Old Gamboa Road, 10.vi.1983, leg. C. Michalski, flight intercept trap (2, SEMC). VENEZUELA: Zulia State: Perija National Park, Toromo, 10° 3' 3.4806" N, 72° 42' 58.4352" W, 28.i.2009, detrital pool; leg. A. Short, VZ09-0128-01A (6, MIZA, MALUZ, SEMC); same data but seepage; VZ09-0128-01B (1, SEMC, DNA Voucher SLE1195); Perija National Park, Tukuko, 9° 50' 29.3994"N, 72° 49' 18.5916"W, 270 m, 22.ix.2007, rock pools/margin, leg. A.E.Z. Short, AS-07- 020b (1, SEMC); Perija National Park, Tukuko, Rio Manantial, 16.vii.2008, margins and pools, leg. A. Short, AS- 08-27 (2, SEMC); same locality but 29.i.2009, gravel margin, leg. Short, García, & Camacho, VZ 09-0129-01A (2, SEMC); same locality but 29.i.2009, detrital pool, leg. Short, García, & Camacho, VZ 09-0129-01B (1, SEMC).
Other Material examined (1): ECUADOR: Esmeraldas Province: La Chiquita, 11 km SE of San Lorenzo, 19.viii.1971, pond, leg. J. Cohen (1, USNM).
Differential diagnosis. Body size 4.3–5.0 mm. Clypeus uniformly pale in color (Fig. 5D). Elytra with ten rows of serial punctures, rows 1–4 weakly impressed into striae (Fig. 2C). Abdominal ventrites pale yellow either entirely or with medial half slightly darkened to light to medium brown (Figs. 6 C–D); pubescence dense and evenly distributed, the longest hairs shorter than those on the metaventrite. Aedeagus (Figs. 7 F–H) 2.2 to 2.3-times longer than its greatest width; apex of parameres truncate, with outer corners widely rounded; inner corners of apex of parameres forming an acute angle; lateral outer margins of parameres diverging on apical third; median lobe with apex narrowly tapering to a blunt point.
Description. In addition to differential diagnosis: Dorsal body coloration yellow to medium brown, with pronotal disc moderately darker.
Variation. While all specimens examined have pale markings on the abdomen (which is so far unique to this species among those included in this review), there is considerable variation in this character. In some specimens, the abdomen is entirely pale without any trace of darkening medially, while others have at least some portion of the central third to half distinctly darkened. This variation is observed even within specimens from the same series and does not appear related to differences in sclerotization. The single specimen from Esmeraldas Province, Ecuador is a male, and the aedeagus matches this species very well; however, it had been preserved in medium-grade ethanol for more than 45 years and consequently is very darkly colored, almost black throughout. Due to its preservation, we choose not to designate it as a paratype.
Distribution. Ecuador, Panama, Venezuela (Zulia) (Fig. 10B).
Etymology. Nexus (L), meaning connection, in reference to the species spanning the connection between Central America and South America.
Biology. Most collecting events have been associated with streams and creeks, with specimens typically being found along the margins or in associated side pools with abundant decaying organic matter (e.g. Fig 9C). A few specimens have been collected by flight intercept traps. This species has been observed to carry its egg case.
Remarks. This species straddles the junction between Central and South America, being found in mountainous areas in both central Panama, northwestern Venezuela, and coastal regions of Ecuador. The Cordillera de Perijá, which forms the northern border between Colombia and Venezuela, has been found to harbor Central American elements before, including several species of Oocyclus that were otherwise only known in Costa Rica and Panama (Short & García 2010). There is rather substantial genetic divergence between the Venezuelan and Panamanian populations, which exhibit a raw genetic distance of 7.2% between them. No recent collections from Ecuador populations were available for DNA extraction.
description: Published as part of Short, Andrew Edward Z. & Girón, Jennifer C., 2018, Review of the Helochares (Hydrobaticus) MacLeay of the New World (Coleoptera: Hydrophilidae: Acidocerinae), pp. 29-50 in Zootaxa 4407 (1) on pages 39-42, DOI: 10.11646/zootaxa.4407.1.2, http://zenodo.org/record/3766290