First fossil horsefly (Diptera: Tabanidae) in Miocene Mexican amber
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- Strelow, J., Solórzano Kraemer, M.M., Ibáñez-Bernal, S. et al. Paläontol Z (2013) 87: 437. doi:10.1007/s12542-013-0171-7
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The fossil record of the Tabanidae is sparse when compared with other families of Diptera. Even in amber they are rare, probably because of their size and specific flight behavior. Horseflies from amber are only known from Cretaceous age New Jersey amber as well as from the Tertiary age Baltic and Dominican amber, but are herein described for the first time, with Stenotabanus oleariorum sp. n., from Mexican amber. The new species is compared to the fossil horseflies of the same genus S.brodzinskyi Lane, Poinar and Fairchild 1988 and S.woodruffi Lane and Fairchild 1989 from Dominican amber.
Der Fossilbericht der Tabaniden ist, im Vergleich zu anderen Dipterenfamilien insgesamt noch sehr spärlich. Auch in Bernsteinvorkommen sind Tabaniden selten, vermutlich wegen ihrer Größe und ihrem speziellen Flugverhalten. Tabaniden in Bernstein sind bis jetzt nur aus dem kreidezeitlichen Bernstein von New Jersey sowie dem tertiären Baltischen und Dominikanischen Bernstein bekannt. In der vorliegenden Untersuchung wird die erste Tabanide aus dem Mexikanischen Bernstein, Stenotabanus oleariorum sp. n, beschrieben. Die neue Art wird mit den beiden bis heute einzigen bekannten fossilen Tabaniden der gleichen Gattungen (S. brodzinskyi Lane, Poinar and Fairchild 1988 und S. woodruffi Lane and Fairchild 1989) des Dominikanischen Bernsteins verglichen.
The Tabanidae or horseflies are a very large and widely distributed family of brachycerous Diptera. Males and females of extant species feed on nectar and other plant sugars, while the females of some species are blood feeders from a variety of vertebrate hosts in order to improve ovogenesis and vitelogenesis. Some species occur across a range of open and forested habitats (Burger 2009), while others are confined to coastal zones. Horseflies usually rest on foliage or on tree trunks. The females oviposit on vegetation, commonly near aquatic or semi-aquatic habitats, and most larvae are found in a variety of aquatic and semi-aquatic habitats, usually in sand or soil of varying wetness (e.g., freshwater, ponds and streams) where they apparently prey on small invertebrates (Burger 2009). Adult tabanids are, therefore, restricted to habitats with a wet breeding site nearby. Additionally, most species of Tabanidae are crepuscular and only active during the warmer period of the year on sunny days. The adult flight activity decreases when it is cool and breezy. Indeed, in central Amazonia the occurrence of species is almost always restricted to the dry season (i.e., low humidity and high temperatures) when water levels in rivers and lakes are low (Ferreira et al. 2002). As a result of the dependency of the Tabanidae on specific ecological conditions, it is possible to compare living species with the fossil from Mexican amber and to draw conclusions as to the former amber forest ecosystem.
Eotabanoid lordi Mostovski, Jarzembowski and Coram 2003 (England)
Cratotabanus stenomyomorphus Martins-Neto and Santos 1994 (Brazil, South America); Cratotabanus sp. n. Grimaldi 2011 (Brazil, South America); Cratotabanus newjerseyensis Grimaldi 2011 (New Jersey amber, USA)
Mesomyia hoffeinsorum Trojan 2002; Mesomyia stigmatica Trojan 2002; Mesomyia cuprea Trojan 2002; Mesomyia yantarophila Trojan 2002; Sznablomyia parvula Trojan 2002; Tabanosoma tabaniforme Trojan 2002; Pseudotabanus dereckii Trojan 2002 (all Baltic amber)
Tabanus vectensis Cockerell 1921 (England); Tabanus statzi Moucha 1972 (Germany); Aemodipsus bornensis Maneval 1936 (France); Chyrosops seguyi Piton 1940 (France); Hexatoma oeningensis (Heer 1864) Evenhuis 1994 (Switzerland)
Silvius merychippi Melander 1947 (USA); Tabanus parahippi Cockerell 1909 (Colorado, USA); Tabanus hipparionis Cockerell 1909 (Colorado, USA); Tabanus merychippi Cockerell 1916 (Colorado, USA); Tabanus tremembeensis Martins-Neto Martins-Neto 2003 (Brazil, South America)
Stenotabanus brodinzkyi Lane, Poinar, and Fairchild 1988 (Dominican amber); Stenotabanus woodruffi Fairchild and Lane 1989 (Dominican amber); Stenotabanus oleariorum Strelow, Solórzano Kraemer, Ibáñez-Bernal, and Rust 2012 (Mexican amber)
Tabanus sudeticus Zeller 1842 (Germany and Poland); Tabanus fossilis Grabenhorst 1985 (Germany)
Tabanus sudeticus Zeller 1842 (Morocco)
Haematopota pinicola Stuckenberg 1975 (Copal inclusion)
In the present study, a specimen of Tabanidae from Miocene age Mexican amber is described. The specimen was compared to the two previously described fossil tabanids from the Dominican amber (Stenotabanus brodzinskyi Lane, Poinar and Fairchild 1988 and Stenotabanus woodruffi Lane and Fairchild 1994) as well as with extant species of the genus from the Neotropical region.
The comparison of the Neogene age tabanid faunae of the Caribbean Islands with those of Central America is of particular interest in terms of understanding the biogeographic relationships between Mexico and Hispaniola. The Mexican amber is mined in the vicinity of Simojovel de Allende in the state of Chiapas, Mexico. It is dated to be of Middle Miocene age (about 20 Ma) and can, therefore, be correlated with the Dominican amber deposits (Solórzano Kraemer 2007). Southern Mexico is considered to be a megadiversity region in the present day (Myers et al. 2000), and the analysis of recent and fossil insect taxa is significant in terms of ecological, paleobiogeographical and taphonomic studies.
Materials and methods
The horsefly is embedded in a piece of amber approximately 11 mm × 9.5 mm × 8 mm in size. The differentiation of species of tabanids is based on male genital differences, pronounced morphological differences of the head and its appendages, thoracic and abdominal patterns and coloration, and distinctive wing patterns. Because body colors and pubescent coloration of the living horseflies are important distinguishing features, it should be mentioned that the colors of the fossil tabanids may not reflect those of the living tabanids, but the color patterning is still preserved (as is the case in specimens preserved in other amber inclusions). The morphological terminology used below follows McAlpine (1981) and Burger (2009). For the taxonomic identification and investigation, a Leica Mz 95 and a Leica MZ 125 were used. Drawings were rendered with the aid of a drawing tube, and measurements are given in millimeters. Photographs of the amber inclusion were made with a Leica MZ 16 Stereomicroscope with a JVC ky-F70B Digital Camera. Compound photographs merging different focus levels to a single image were performed with using Discus software equipped with a stacking function.
Family Tabanidae Latreille 1802.
Subfamily Tabaninae Loew 1860.
Tribe Diachlorini Lutz 1909.
Diachlorinae Lutz 1909, 29 (= Diachlorini, according with Sabrosky 1999). Additional references: Enderlein 1922, 349 (as Diachlorini); Kröber 1932, 197; Philip 1941, 5, 10; Fairchild 1942, 297; Philip 1947, 284; Mackerras 1954, 431, 439 (diagnosis); Stone 1965 (reprint 1983, 328) (Nearctic catalog); Fairchild 1969, 207 (Classification); Fairchild 1971, 36 (Neotropical catalog); Fairchild and Burger 1994, 62 (Neotropical catalog); Sabrosky 1999, 111 (Family-group name).
Genus Stenotabanus Lutz 1913.
Stenotabanus Lutz 1913, 487; Lutz 1914, 167 (reprinted). Type-species: Tabanus taeniotes Wiedemann (Bequaert 1924, 30). Additional references: Enderlein 1925, 354; Kröber 1929, 113 (in part); Stone 1938, 31; Philip 1941, 11; Fairchild 1942, 297; Philip 1947, 285 (Nearctic catalog); Fairchild 1969, 214 (classification); Fairchild 1971, 44 (Neotropical catalog); Fairchild 1986 46 (Panama species); Fairchild and Burger 1994, 72 (Neotropical catalog); Chainey et al. 1999, 75 (South American species); Burger 2009, 502, 506 (key, Central America).
Leptotabanus Lutz and Neiva 1914, 72 (nomen nudum).
Styposelaga Enderlein 1922, 348. Type-species: Styposelaga sexannulata Enderlein (orig. des. = Tabanus incipiens Walker 1860).
Fossil species of Stenotabanus.
Stenotabanus brodzinskyi Lane, Poinar and Fairchild 1988, 594, Holotype female. Type-locality: Dominican Republic, Santo Domingo, unspecified amber mine in the Cordillera Septentrional mountain range, 15–20 Ma (late Early-early Middle Miocene).
Stenotabanus woodruffi Fairchild and Lane 1989, 630, Holotype female. Type-locality: Dominican Republic, 15–20 Ma (late Early-early Middle Miocene).
Stenotabanus oleariorum Strelow, Solórzano Kraemer, Ibáñez-Bernal and Rust new species.
Holotype female from the collection of the Staatliches Museum für Naturkunde, Schloss Rosenstein, Stuttgart, Germany (SMNS) with inventory number Mx 245. The specimen is embedded in early Middle Miocene amber from Simojovel de Allende, Chiapas, Mexico.
A small species with clear wings, appendix at base of vein R4, with frons slightly convergent-sided below, antennae nearly uniform colored, with basal flagellomere obtuse angled, mesonotum unstriped and abdomen unicolor.
The specific epithet is dedicated to Hans J. Olearius and Dr. Christian Olearius for their interest and support of science.
Thorax: Mesonotum orange-brown without longitudinal stripes, moderately beset with short, dark, scattered hairs medially and longer dark hairs anteriorly. Scutellum and notopleuron thinly clothed with long, scattered hairs. Katatergite heavily clothed with long dark hairs. Wings hyaline, pterostigma brown, basicosta sharply pointed without macrosetae. Costa (C), subcosta (Sc) and R1 covered with tiny short setae (Fig. 2c). Appendix present at base of R4, wings without distinct clouds or streaks. Legs slender, the tibia not flattened or inflated. Tibiae dark brown covered with short, dark hairs. Hind and fore tibiae without spurs, mid tibiae with two strong spurs. Tarsal claws sub-equal in size, paired on the legs where the tarsi are preserved, tarsi missing on both mid tibiae.
Abdomen: 5.1 mm long and 1.3 mm broad with seven segments visible, yellowish dark brown, covered with dark setae, no color pattern preserved. Seventh tergum dark brown, clothed with dark hairs. Terminalia of female inconspicuous.
The fossil horse fly described here from Mexican amber can be assigned to the subfamily Tabaninae by the absence of functional ocelli and also of hind tibial spurs, and to the tribe Diachlorini by the nude basicosta, wings without infuscate patterns, antennal flagellum with 4 annuli, and frons slightly widened below. The inclusion in amber does not facilitate seeing the divided condition of the ninth tergum or the color pattern of the eyes. We have assigned this species to the genus Stenotabanus Lutz on the basis of the bare eyes, the width of the frons, the form of the frontal callus, the clear wing membrane, unicolor pleura, unstripped mesonotum, and the antennal flagellum with obtuse angle and four annuli (Fairchild 1969).
Stenotabanus oleariorum sp. n differs from Stenotabanus brodzinskyi, by the presence of long erect dark setae anterolaterally and laterally on the mesonotum, and the lack in the latter of the appendix of R4. S. woodruffi also lacks the appendix at the fork of R4 and differs from the other two species by having the apical third of the wing infuscated, the frons considerably narrower and a sharp dorsal angle of the basal plate (Fig. 2a). S. oleariorum sp. n. is more similar to S. brodzinskyi by the form of the flagellar basal plate, differing by the wider frons and antenna coloration, whereas it is more similar to S. woodruffi because the frons is slender and has dull-edged angles of the basal plate. S. woodruffi and S. oleariorum sp. n. differ from S. brodzinskyi by being much paler in color of the integument with only parts of mesonotum, tarsi, and annulated part of antennae flagellum being black.
Currently, 99 species (divided into 7 subgenera) of the genus Stenotabanus are recognized (Burger 2009). The subgenera include: Stenotabanus Lutz 1913, Aegialomyia Philip 1941, Brachytabanus Fairchild 1942, Cretotabanus Faichild 1969, Melanotabanus Lutz and Neiva 1914, Phorcotabanus Fairchild 1961, and Stenochlorops Fairchild 1969. Of these, only Aegialomyia Philip 1941, Brachytabanus Fairchild 1942 and Stenotabanus Lutz 1913 occur in Central America (Fairchild 1969).
Fairchild (1980) erected two groups of Stenotabanus (Stenotabanus) based on his study on the Caribbean Island tabanid fauna, the brunettii species group with S. parvulus Williston 1887, S. alticolus Fairchild 1980, S. batesi Bequaert 1940, and the fenestra group, which contains S. fenestra Williston 1987, S. marcanoi Fairchild 1980, and S. hispaniolae Bequaert 1940. Fairchild (1988) placed the fossil horsefly S. brodzinskyi of the Dominican amber in the fenestra group based on the following characteristics: frons noticeably narrowed below and more than 4.0× as high as basal width, hyaline wings, and the lack of conspicuous abdominal color patterns. In the key provided by Fairchild (1980), S. oleariorum sp. n. resembles Stenotabanus marconoi Fairchild 1980 based on the narrow frons, the entirely clear wing, and the appendix at vein R4. However, it is smaller in size (9.1 mm compared to 11 mm in S. marconoi) and also has palpi and proboscis sub-equal in length (whereas S. marconoi having a proboscis about twice the length of the palpi). S. oleariorum sp. n. can be easily distinguished from S. fenestra Williston 1987 and S. hispaniolae Bequaert 1940 because of the blackish appearance and black wings that the latter two species share. In addition, S. fenestra Williston 1987 has the tibiae and basitarsi white pillose and the basicosta and antennae black, while S. hispaniolae has a parallel sided frons and narrow pale sutural bands on the abdomen (Fairchild 1980).
To date only one specimen of the genus Stenotabanus has been described from Mexican amber, the herein described S. oleariorum n. sp. This is the sole representative of the family from these deposits, clearly illustrating both the scarcity of tabanids as inclusions but also the variable preservation potential of different insect groups. In general, small-sized insects are more likely to become trapped in resin, while larger and stronger insects have better chances of escaping from fresh resin flows. Therefore, size is probably not the important taphonomic selection factor in the Tabanidae, because most of them are of considerable medium to large size, (e.g., S. oleariorum n. sp.). Seasonal factors and the extent of resin production, flight activity, as well as other behavioral characteristics or specific preferences are probably more important factors in explaining the poor record of horseflies in amber. This is exemplified by a study of Bickel and Asker (2004) who collected tree trunk invertebrate fauna in an Australian forest using sticky traps. Not a single Tabanidae was trapped from a total of 103,504 collected insects. Even though tabanids are not tree inhabitants they are active flyers and have, at least sometimes, the potential to get trapped in various types of triangle-shaped tent and cloth traps (emergence, malaise, and canopy traps) as well as in attractant traps (carbon dioxide and octenol).
A comprehensive revision of the fossil record of the Tabanidae has already been suggested by Martins-Neto (2003), but is outside the focus of the present study (Table 1). However, S. oleariorum n. sp. represents the third fossil member of the tribe Diachlorini and of the genus Stenotabanus reported in the literature. The similarities in the tabanid faunas of Mexican and Dominican amber deposits suggest a possible faunal interchange between both regions in pre-Miocene times. Fairchild (1969) notes that of the three tribes recognized in Tabaninae, Diachlorini contains the most primitive members. Furthermore, he divides the tribe into two groups: a primitive group including Stenotabanus Lutz that is probably derived from Dasybasis and in turn may have given rise to the more specialized groups such as Diachlorus. This is important, since in Mexico there are more endemic species known from the genus Stenotabanus than species from the genus Diachlorus (Ibáñez-Bernal and Coscarón 2000), but the phylogenetic relationships of the tribe and the Neotropical tabanids in general require clarification.
The extant distribution of Stenotabanus is restricted to the Neotropical region with reports from the southern parts of North America, the Caribbean Islands, Central America, and South America. The presently known Stenotabanus fauna of Mexico consist of ten endemic species and ten widespread species. The species of S. (Stenotabanus) that are geographically restricted include S. abacus Philip 1954, S. apaches Philip 1977, S. cribellum Osten Sacken 1886, S. litotes Fairchild 1953, S. mexicanus Philip 1977, S. pumiloides Williston 1901, S. stonei Philip 1958, and S. subtilis Bellardi 1862, and for S. (Aegialomyia) are S. chiapasensis Fairchild 1953, S. indotatus Ibáñez-Bernal 1991, S. occidentalis Philip 1976, and S. yaquii Philip 1976. The widespread species of S. (Stenotabanus) include S. flavidus Hine 1904, S. fulvistriatus Hine 1912, and S. minusculus Krober 1930, and for S. (Aegialomyia) are S. guttatulus Townsend 1893, S. jamaicenis Newstead 1909, S. littoreus Hine 1907, S. magnicallus Stone 1935, and S. pechumani Philip 1966.These species generally inhabit lentic habitats. On that account, the fossil Stenotabanus therefore indicates the existence of (temporary) water ponds in the plain regions within the former amber forest. As already mentioned in the introduction, female tabanids lay their eggs on vegetation near or above aquatic or semi-aquatic habitats, and most larvae inhabit marshes or streams, but some larvae inhabit even dry soil such as the immature stages of S. (Stenotabanus) incipiens Walker, which have been found in soil near an old log (Burger 2009). If the oviposition behavior did not change, adult species inhabited regions comparable to these environments probably within the woodlands, which would make entrapment in resin possible.
This research was possible with a postdoctoral fellowship to M.M.S.K, no. SO894/3-1, from the German Research Foundation (DFG). The authors would like to thank Dr. Günter Bechly from the Staatliches Museum für Naturkunde Stuttgart for the loan of the specimen. Special thanks are due to PD Dr. Torsten Wappler (Bonn) for valuable comments and helpful discussion and Prof. Dr. McCann (Bonn) for reading and correcting the manuscript.