Entomology Research

Revision of the Afrotropical species of Curtonotidae (Diptera: Ephydroidea) – systematics, biology, immature stages and biogeography

Ashley H. Kirk-Spriggs

Literature review

 

The acalyptrate fly family Curtonotidae, known by the vernacular name ‘hump-backed flies’, or ‘Quasimodo flies’ as I prefer, has an almost worldwide distribution, viz. 25 Afrotropical species (Wirth & Tsacas 1980); one Australasian/Oceanian species (Evenhuis 1996); one Nearctic species (Wirth 1965; Meier et al. 1997); 19 Neotropical species (Marshall et al. in press); 12 Oriental species (Delfinado 1969); and two Palaearctic species (Papp 1984). None of these species are currently known to occur in more than one zoogeographical region, although the genus Curtonotum Macquart, 1844, occurs in all regions in which the family is known (excepting the Australasian/Oceanian Region), and is the only genus known in the New World.

 

 

 

 

 

This group of species has been placed in the families Drosophilidae, Diastatidae, and Ephydridae, at various times, but contemporary workers appear unanimous in regarding it as having true family rank in its own right. Phylogenetically, the family is currently placed in the superfamily Ephydroidea sensu stricto (Camillidae, Campichoetidae, Crypytochetidae, Curtonotidae, Diastatidae, Drosophilidae, and Ephydridae) and the reasons for such a placement are discussed by McAlpine (1989) and Grimaldi (1990). This placement is supported by the preliminary studies of Meier et al. (1997), who studied and partially described the first-instar larva and puparium of the Nearctic species Curtonotum helvum (Loew, 1862). The number and arrangement of caudal tubules around the posterior end (anal division) of the puparium are indicative of putative homologies and are a groundplan feature of the Ephydroidea, as shared with other ephydroid families for which the immature stages are known, e.g. the Drosophildae, Ephydridae and Camillidae (Kirk-Spriggs et al. 2002). A molecular study to investigate the associations of the Curtonotidae with other families included within the Ephydroidea sensu stricto has not been undertaken, nor has the third-instar larva of any species of the family been described using stereoscan microscopy. The true relationships of the family cannot be ascertained until such time as these studies are undertaken.

 

 

The Afrotropical species were catalogued by Wirth & Tsacas (1980), who include species in three genera, namely: Axinota van der Wulp, 1886 (a single unnamed species from Madagascar), Curtonotum (20 species) and Cyrtona Séguy, 1938 (four species), which occur (collectively) in sub-Saharan Africa, Madagascar and Yemen in the Middle East. As the family was only partially revised in the mid–late 1970s (only the genus Curtonotum), many incorrect synonymies and errors in the generic placement of species have continued to be applied in the literature and have not been subsequently resolved. For this reason the species numbers, together with the country distributions of species listed by Wirth & Tsacas (1980) must be viewed with a high degree of scepticism.

 

Although regarded as a ‘small family’, initial studies by the writer of material from museums throughout the world has indicated (even with the application of traditional taxonomic methods alone), that the family is far more speciose in sub-Saharan Africa and Madagascar than was previously thought, and a recent prediction puts the probable number of undescribed species from the Afrotropical Region at 40+ species (Stuckenberg & Kirk-Spriggs in prep.). Recent and historical material examined during the initial phase of the project indicates that at least two new genera and 25+ species are new to science and await description.

 

The genus Curtonotum

 

While the genus Curtonotum appears to be most speciose in the arid and semi-arid savannas of sub-Saharan Africa, the genus Cyrtona is particularly speciose in the Guineo-Congolan Rainforest and Afromontane regions of sub-Saharan Africa, but in both cases, by no means exclusively so.

 

Tsacas (1974) dealt with the species of the genus Curtonotum occurring in Madagascar (seven species; all of which are endemic to the island) and later (Tsacas 1977), with Curtonotum species from the mainland Afrotropical Region and Yemen (12 species, seven of which were new). For both publications, notably the first, Tsacas dealt with limited material from Africa and the taxonomy and systematics of the genus have not been studied subsequently. Species of the genus exhibit a high degree of phenotypic uniformity, and for this reason most species are only separable by referral to characters of male and female genitalia, specifically the spermathecae and vaginal sclerites in the latter case, although female spermathecae require detailed evaluation to assess their usefulness in specific differentiation.

 

 

 

 

 

Tsacas (1977: 148) notes “les génitalia des Curtonotidae n’ont jamais été l’objet d’une etude morphologique, ainsi l’homologation de toutes les structures les composant n’est pas certaine.” Some studies of the structure and homologies of the genitalia of the three genera have subsequently been published by Pollock (2002), and Meier et al. (1997) investigated the female reproductive system of Curtonotum helvum and discussed the structure of the spermathecae of the three genera. Pollock (1996) studied the adaptations of Cyrtona species, the female reproductive system and seasonal changes. He found that the unnamed Cyrtona species he studied from Zimbabwe was larviparous. This appears to not be the case with the genus Curtonotum, and is uncertain for Axinota.

 

 

 

 

 

 

Some species of the genus, e.g. Curtonotum cuthbertsoni Duda, 1935, and C. quinquevittatum Curran, 1933, exhibit considerable variability in the shape of the aedeagal apodeme and aedeagus of the male genitalia, and in the case of C. cuthbertsoni, eight distinct phenotypes were recognised and illustrated by Tsacas (1977: 153). These ‘phenotypes’ require DNA analysis to explore the hypothesis that they in fact represent distinct species.

 

Initial study by the writer of most of the types of species in the genus has unveiled a number of nomenclatural problems, largely driven by incorrect lectotype designations by former workers or problems arising for the need for males to correctly define species and associate females. Such nomenclatural anomalies must be resolved before known nominate species can be re-described and new species described.

 

 

The genus ‘Cyrtona’

 

The genus Cyrtona is an ‘open book’ as regards our taxonomic and systematic knowledge. Only four species are known from the Afrotropical Regions, namely: C. albomaculata (Curran, 1933), C. capensis Hackman, 1960, C. consobrina Hackman, 1960, and C. pictipennis (Thomson, 1869). The genus has not been the subject of a taxonomic review; although such a review was initially planned by Tsacas, this project was later abandoned (L. Tsacas pers. comm.). Preliminary studies and examination of male genitalia has indicated that C. albomaculata sensu Wirth & Tsacas (1980) is in fact a complex of sibling species, while C. fuscipennis actually belongs to the genus Axinota and itself represents a complex of at least three species. This implies that Axinota may also be highly speciose in sub-Saharan Africa. Not all of the species currently ascribed to the genus Cyrtona are true Cyrtona.

 

 

 

 

Biology and immature stages

 

The biology of the species of Curtonotum was briefly reviewed by Tsacas (1977), based largely on information from specimen data labels and Meier et al. (1997) supplemented this information with field observations. Species of the genus appear to be crepuscular in habits (at least in Namibia – Kirk-Spriggs pers. obs.) and many species of the genus Curtonotum shelter in the burrows of aardvarks, warthogs and porcupines during hot periods of the day in various parts of Africa. There are additional records of species of the genus roosting in hollows in dry riverbanks, beneath shaded cliffs, and in hollow trees, etc. Further investigations of this behaviour are required to understand its significance. Species of Cyrtona have also been found in dry river banks (Pollock 2002).

 

 

 

 

 

Information on the biology of the Curtonotidae is scant, especially regarding the immature stages. The third-instar larva of Curtonotum simile Tsacas, 1977, (as Cyrtonotum cuthbertsoni) was described by Greathead (1958), who reared adults from damaged egg pods of the desert locust at two localities in Eritrea. Greathead regarded the flies to be general scavengers and notes that the damage they caused to locust eggs was minimal, as compared to insects causing primary attack. He briefly described the first- and second-instars, the third-instar and the puparium, and figured the cephaloskeleton, anterior and posterior spiracles, thoracic segments and pseudocephalon in lateral view, and the lateral and posterior views of the third-instar larva. His description was based on light microscopy, so many features regarded today as significant in the description of larvae and puparia could not be viewed using this method. The material on which these descriptions were based was lost for many years, but has recently come to light in the collection of the Natural History Museum, London (BMNH) and its identification as C. simile rather than C. saheliense as previously supposed can now be confirmed.

 

Meier et al. (1997) attempted the laboratory rearing of Curtonotum helvum using grasshopper egg pods and other rearing media, but was only partially successful, managing to describe only the egg and selected character states of the first-instar larva and puparium. The immature stages of both Cyrtona and Axinota remain entirely unknown and the true biology therefore remains a mystery.

 

Biogeography

 

Biogeographically speaking, a number of species exhibit a clear pattern of distribution. Curtonotum saheliensis, for example, is restricted the Sahel, and occurs from the Gambia to Sudan, apparently in all intervening countries which fall within that zone. Cyrtona appendiculata Séguy, 1938 (currently synonymised with C. albomaculata), is afromontane and C. pictipennis is restricted to the Kwa-Zulu Natal Drakensberg. Other species are more widely distributed in arid and semi-arid zones and savanna. Such distributions lend themselves to studies of biogeography and species radiation.

 

 

 

 

Project Motivation

 

Few groups of acalyprate flies have received as little attention as the Curtonotidae worldwide, and many species have been overlooked due to their phenotypic uniformity. There is, therefore, a substantial gap in our knowledge of almost all aspects of the family, including: systematics, phylogeny, biology, immature stages and biogeography. Initial investigations have revealed that the family is highly diverse in terms of the number of undescribed species, but is not too large to embark upon within the timeframe and timescale of the current study.

 

E.O. Wilson has recently outlined the vision of an ‘Encyclopædia of Life’, that devotes one page to all species on our planet, and many international organisations and treaties are devoted to this task (e.g. Global Biodiversity Initiative, All Species Foundation, Species 2000, US National Science Foundation, European Union’s ‘Fauna Europaea’, UN Convention on Biodiversity, Rio de Janeiro – to which South Africa is a signatory – and specifically related the Diptera, the BioSystematic Database of World Diptera, being compiled by the National Museum of Natural History, Smithsonian Institute, Washington D.C.).

 

With the ever-decreasing number in practising systematists in Africa as a whole, it is essential that systematic revisions of the kind proposed be undertaken on the African fauna, and specifically by systematists based in Africa. Knowledge of Africa’s biodiversity is essential to the initiatives listed above, assists in South Africa’s endeavours to meet her obligations as signatory to the Convention on Biodiversity, and further provides valuable information for bio-inventory initiatives instigated by other African countries in which the family occurs.

 

The need for such knowledge has broader implications in our understanding of higher taxa. The application of a combination of the traditional morphological taxonomic approach combined with a phylogenetic and molecular approach should prove a useful benchmark study which can be applied to other dipterous families in the future. Molecular studies at the familial and generic level would do much to improve our understanding of the evolution of the group and its relationship to other families within the Ephydroidea. Such a study has not been embarked upon before.

 

Studies of the immature stages of all three genera would be invaluable and lead to better interpretation of larval characters and the groundplan features of the Ephydroidea as a whole. As many species appear to exhibit clear distributional patterns, this makes the group ideal for biogeographical work and investigations of the radiation of species.

 

The Curtonotidae is a fascinating group of flies which has long deserved attention and reversionary work.

 

Scope of the project

 

       The project is primarily a systematic revision of a family of flies from one zoogeographical region of the world. The only statistics that shall be applied involve the respective lengths of the adult flies, their immature stages, or constituent structures.

       The project is limited to a revision of the species of Curtonotidae occurring in the Afrotropical Region, but shall deal with species in the Middle East, especially the Arabian Peninsula as such investigations of species occurring in this area are required to define the distributional limitations of species. Some material from other zoogeographic regions shall be consulted, but only to ensure that probable new taxa have not been described from elsewhere in the world.

       While biological observations shall be made on an opportunistic basis during periods of fieldwork, applied ecology is beyond the scope of the project and shall not be attempted.

       Rearing experiments shall be confined to the obtaining of immature stages for descriptive purposes and to investigations of periods of egg, larval instar and pupal development.

       DNA analysis shall be confined to an analysis of other ephydroid families (if available) and to the phenotypes of the Curtonotum cuthbertsoni complex, as correctly preserved and recently collected examples of all know species are not available for study.

 

Aims

 

       To access current taxonomic knowledge of the family Curtonotidae in the Afrotropical Region.

       To undertake typological studies of described nominate species. Resolution of issues of type designation and amendment of the nomenclature of the group in accordance with the International Code of Zoological Nomenclature (ICZN).

       To undertake fieldwork in various African countries to obtain specimens and note biology. Field investigations in Madagascar, East Africa (Kenya, Tanzania or Uganda), West Africa (Cameroon, Gabon or Ivory Coast) and Southern Africa (South Africa, Namibia, Malawi, Angola, or Mozambique).

       To undertake molecular investigation of the available families of Ephydroidea and within the Curtonotum cuthbertsoni complex.

       To undertake a comparative analysis of male genitalia of the three genera and the homologies of structures.

       To develop a phylogeny for the family.

       To describe new taxa

       To produce an identification key.

       To assess the validity of female genitalia in species differentiation and identification.

       To rear larvae and record their biology.

       To describe immature stages when available.

       To examine the biogeography of individual species and genera.

       To investigate species radiation in Africa and the Middle East.

 

Methods

 

The application of traditional taxonomic methods for the description of new taxa and the production of keys shall be applied, including line drawings using a camera lucida, colour photography, light microscopy and stereoscan microscopy. Standard methods include: maceration of male and female genitalia and dissection of respective parts for description and identification, collection of recent material in 96% alcohol for DNA analysis by use of Malaise traps, light traps and hand-collection, recording of biological observation in the field, laboratory rearing of larvae by exposure of living flies to breeding media, and the extraction of larvae for description using SEM, etc.

 

References

 

Curran, C. H. 1933. The African species of Curtonotum Macquart (Drosophilidae, Diptera). American Museum Novitates 675: 1–4.

Delfinado, M.D. 1969. The Oriental species of Curtonotidae (Diptera). Oriental Insects 3: 199–219.

Duda, O. 1935. Einide neue afrikanische akalyptrate Musciden (Dipt.) des British Museum. Stylops 4: 25–34.

Evenhuis, N. 1996. 97. Family Curtonotidae. Australasian/Oceanian Diptera Catalog – Web Version. Available at: http://hbs.bishopmuseum.org/aocat/curtonot.html

Greathead, D.J. 1958. Notes on the larva and life history of Cyrtonotum cuthbertsoni Duda (Dipt., Drosophilidae), a fly associated with the desert locust Schistocerca gregaria (Forskål). Entomologist’s Monthly Magazine 94: 36–37.

Grimaldi, D. 1990. A phylogenetic, revised classification of genera in the Drosophilidae (Diptera). Bulletin of the American Museum of Natural History 197: 1–139.

Hackman, W. 1960. Chapter XVIII. Diptera (Brachycera): Camillidae, Curtonotidae and Drosophilidae (pp. 381–389). In Hanström, B., Brinck, P. & Rudebeck, G. (eds). South African animal life. Results of the Lund University Expedition in 1950–1951. 7, Almqvest & Wilsell, Göteborg, Stockholm, Uppsalla [ix] + 10–488 pp.

Kirk-Spriggs, A.H., Barraclough, D.A. & Meier, R. 2002. The immature stages of Katacamilla cavernicola Papp, the first described for the Camillidae (Diptera: Schizophora), with comparison to other known Ephydroidea larvae, and notes on biology. Journal of Natural History 36: 1105–1128.

Loew, H. 1862. Diptera Americae septentrionalis indigena. Centuria secunda. Berliner entomologische Zeitschrift. 6: 185–232.

Macquart, J. 1844. Diptères exotiques nouveaux ou peu connus [2 (3).] Mémoires de la Société des Sciences, de l’Agriculture et des Arts de Lille 1842: 162–460.

Marshall, S.A., Kirk-Spriggs, A.H. & Klymko, J. (submitted). Curtonotidae (‘hump-backed flies’). Manual of Neotropical Diptera.

McAlpine, J.F. 1989. Phylogeny and classification of the Muscomorpha (pp. 1397–1518). In McAlpine, J.F. (ed.). Manual of Nearctic Diptera 3. Research Branch Agriculture Canada Monographs 28, Ministry of Supply and Services, Ottawa, Canada.

Meier, R., Kotrba, M. & Barber, K. 1997. A comparative study of the egg, first-instar larva, puparium and natural history of Curtonotum helvum (Curtonotidae; Ephydroidea: Diptera). American Museum Novitates 3219: 1–20.

Papp, L. 1984. Family Curtonotidae (pp. 221–22). In Soós, Á. & L. Papp (eds). Catalogue of Palaearctic Diptera. Volume 10. Clusiidae–Chloropidae. Akadémiai Kiadó, Budapest, 1–402 pp.

Pollock, J.N. 1996. Viviparous adaptations in the acalyptrate genera Pachylophus (Chloropidae) and Cyrtona (Curtonotidae) (Diptera: Schizophora). Annals of the Natal Museum 37: 183–189.

Pollock, J.N. 2002. Observations on the biology and anatomy of Curtonotidae (Diptera: Schizophora). Journal of Natural History 36: 1725–1745.

Séguy, E. 1938. Diptera I. Nematocera et Brachycera. Mission scientifique de l’Omo, 4 (Zool.). Mémoires du Muséum Nationale d’Histoire Naturelle. Paris (n. s.) 8: 319–380.

Stuckenberg, B.R. & Kirk-Spriggs, A.H. (in prep.). Diptera of the Afrotropical Region. In Bickel, D., Meier, R. & Pape, T. (eds.). Diptera diversity: status, challenges, and tools. Junk Publishers, Leiden.

Thomson, C. G. [1869]. Diptera Species novas descriptsit C. G. Thomson (pp. 443–614). In Kongliga svenska fregattan Eugenies resa omkring jorden under befäl af C. A. Virgin, åren 1851–1853. 2 (Zoologi), [section] I (Insecta), 617 pp. Stockholm ‘1868’.

Tsacas, L. 1974. Études préliminaire des Curtonotidae de Madagascar (Diptera). Annals de la Société Entomologique de France. Paris (n. s.) 10: 703–719.

Tsacas, L. 1977. Les Curtonotidae (Diptera) de l’Afrique: 1. Le genre Curtonotum Macquart. Annals of the Natal Museum 23: 145–171.

Wirth, W.W. & Tsacas, L. 1980. 73. Family Curtonotidae (pp. 671–672). In Crosskey, R.W. (ed.). Catalogue of the Diptera of the Afrotropical Region. British Museum (Natural History), London, [iv] + 5–1437 pp.

Wirth, W.W. 1965. Family Curtonotidae (p.759). In Stone, A., Sabrosky, C.W., Wirth, W.W., Foote, R.H. & Coulson, J.R. (eds.). A catalog of the Diptera of America north of Mexico. United States Department of Agriculture, Washington D.C., iv + 1–1696 pp.

Wulp, F. M. van der. 1886. Aanteekeningen betreffende javaansche Diptera. Tijdschrift Entomologie 30: 175–180.