Description of the karyotype of Sphyracephala detrahens (Diptera, Diopsidae)
expand article infoAyumi Kudo
‡ Tokyo Metropolitan University, Tokyo, Japan
Open Access


The eye stalks in Diopsidae (Bilberg, 1820) have been widely examined, but the evolutionary origin of this unique trait remains unclear. Thus, further studies of Sphiracephala (Say, 1828), the extant genus forming a basal branch of Diopsinae, are needed. The present study aimed to identify the karyotype of Sphyracephala detrahens (Walker, 1860) with conventional Giemsa staining. Cytogenetic analysis revealed a diploid number of 2n = 10 including two pairs of metacentric chromosomes, a pair of telocentric chromosomes, a pair of dot-like chromosomes, and a pair of sex chromosomes in S. detrahens. The congener Sphyracephala brevicornis (Say, 1817) has been reported to have the same diploid number, 2n = 10, but different chromosome formula. These results demonstrate that chromosome rearrangements often occur in the genus Sphyracephala.


Cytogenetics, chromosomes, karyology


Nearly all species of Diopsidae (Bilberg, 1820) are well-known for their exaggerated eye stalks (Shillito 1971). There are approximately 160–8000 species and 10–15 genera containing stalk-eyed flies in the family Diopsidae (Shillito 1971; Steyskal 1972; Carr et al. 2006; Ovtshinnikova and Galinskaya 2016; Roskov et al. 2019). Although both males and females in Diopsinae have eyes that are laterally displaced from the central head, the level of sexual dimorphism varies between and within species (Burkhardt and de la Motte 1985; Wilkinson and Dodson 1997; Meier and Hilger 2000). Some species of stalk-eyed flies with extreme sexual dimorphism are used as model organisms to study the evolution of sexually selected traits (Wilkinson et al. 1998; Carr et al. 2005; Husak and Swallow 2011; Knell et al. 2013). For example, in Teleopsisdalmanni (Wiedemann, 1830), morphology, sexual behavior, development, and cytology has been widely studied (Wilkinson and Reillo 1994; Presgraves et al. 1997; Hurley et al. 2002; Egge et al. 2011; Worthington et al. 2012; Cotton et al. 2015; Meade et al. 2019). However, limited information regarding the ecology, biology, and cytology of most stalk-eyed fly species is available, particularly for monomorphic species and primitive groups such as Sphyracepalini.

Sphyracephala shows the most likely ancestral state of extant Diopsinae (Kotrba 2004). Sphyracephala detrahens (Walker, 1860) is distributed in Taiwan, China, the Philippines, Indonesia, Papua New Guinea, and the southern islands of Japan (Ohara 1993). A few studies have examined the ecology and morphology of Japanese populations, and found the length of eye stalks less or not sexually dimorphic (Ohara 1993, 1997).

Although Baker and Wilkinson (2001) suggested that ancestral species in Diopsinae share monomorphic eye stalks, Kotrba (2004) used cladistics analysis that included the extinct species of Prosphyracephala to predict that sexual dimorphic eye stalks evolved in early Diopsinae. To reveal the origin of eye stalks in Diopsinae, basic studies including cytogenetic analysis of the species in Sphyracephalini need to be performed. The current study aimed to describe the karyotype of S. detrahens using standard chromosome staining.

Material and methods

S. detrahens was collected from Iriomote Island, Okinawa, Japan in April 2019 by A. Kudo (Fig. 1).All flies were maintained on organic media with yeast at 25 °C in a 14-h light:10-h dark cycle.

Metaphase chromosomes were obtained from cerebral ganglia of 3rd instar larvae as described by Imai et al. (1988) without colchicine treatment. The chromosome preparations were stained with 5% Giemsa solution. The preparations were observed under a Keyence BZ-X700 fluorescence microscope (Osaka, Japan) equipped with a Nikon Plan Apo100×/1.45 oil objective and Nikon immersion Oil Type NF (Tokyo, Japan). Twenty metaphase cells with well-spread chromosomes were selected and photographed using Keyence BZ-X Analyzer software, and then processed in GIMP ver. 2. 10. 12. Fifteen individuals including 10 females and 5 males were successfully karyotyped. The length of the long and short chromosome arm was measured with Image J software ver. 1.52a (NIH, Bethesda, MD, USA). These data were used to calculate the chromosome index and arm ratio, following which chromosome classification and idiogram construction were performed as described by Levan et al. (1964).

Figure 1.

Stalk-eyed flies Sphyracephala detrahens.

Morphometric parameters of Sphyracephala detrahens chromosomes from mitotic metaphase plates.

Chromosome Length of short arm (mean ± SE µm) Length of long arm (mean ± SE µm) Total length of Chromosome (mean ± SE µm) Arm ratio Centromeric index Chromosome classification §
1 4.11 ± 0.15 4.45 ± 0.15 8.56 ± 0.29 1.08 48.0 m
2 2.49 ± 0.09 2.94 ± 0.10 5.43 ± 0.18 1.18 45.9 m
3 3.95 ± 0.14 t
4 0.66 ± 0.02 d
X 1.63 ± 0.06 3.56 ± 0.11 5.19 ± 0.17 2.18 31.5 sm
Y 1.80 ± 0.18 2.13 ± 0.24 3.93 ± 0.41 1.18 45.9 m

Results and discussion

This is the first study to reveal that the chromosome number of S. detrahens was 2n = 10 (Fig. 2). The karyotype of S. detrahens consisted of two pairs of metacentric chromosomes, a pair of rod-shaped telocentric chromosomes, a pair of dot-like microchromosomes, and a pair of sex chromosomes (Figs 2, 3). In the female cerebral ganglia cells, a homomorphic sex chromosome pair was formed by the two submetacentric X-chromosomes (Fig. 2A). In the male cerebral ganglia cells, a heteromorphic pair of sex chromosomes was formed by the X-chromosome and metacentric Y-chromosome (Fig. 2B). The Y-chromosome was slightly stained and was shorter than the X-chromosome (Fig. 2).

Figure 2.

Mitotic metaphase of Sphyracephala detrahens with 2n = 10 chromosomes A female B male. Scale bars: 5µm.

Although a congener, S. brevicornis, had the same diploid chromosome number 2n = 10, the karyograms of S. brevicornis differed from that of S. detrahens (Fig. 3); the karyotype of S. brevicornis consisted of two pairs of metacentric chromosomes, two pairs of telocentric chromosomes, and a pair of small telocentric XY pair (Jan 1966). The sex chromosomes showed the greatest differences between the two species. Both the X and Y chromosomes in S. detrahens were bi-armed and larger compared to those in S. brevicornis. Thus, chromosomal rearrangements occurred in these two species and their relatives. Information about the phylogenetic relationships between S. detrahens and its congeners has been never analyzed. Further investigations into phylogenetic relationships will aid in the understanding of differences in karyograms between S. detrahens and S. brevicornis. Despite the lack of karyological information in Diopsinae, comparative cytogenetic analyses using related species will lead to a greater understanding of chromosomal evolution in stalk-eyed flies.

Figure 3.

Idiograms of Sphyracephala detrahens and Sphyracephala brevicornis. The numbers above each bar indicate chromosome numbers. The light and dark regions represent short arms and long arms, respectively. Idiograms of S. brevicornis were modified and redrawn from Idiogram 1 of S. brevicornis (Jan 1966).


I would like to thank Haruna Fujioka, Wataru Kojima and Yasukazu Okada for collecting flies; Keiko Sakiyama for fly maintenance; Kazuyuki Hirai for his technical advice on chromosomal preparation; and Masafumi Nozawa for comments on karyotyping. I also thank Igor Sharakhov for comments on this manuscript.


  • Burkhardt D, de la Motte I (1985) Selective pressures, variability, and sexual dimorphism in stalk-eyed flies (Diopsidae). Naturwissenschaften 72: 204–206.
  • Carr M, Cotton S, Foldvari M, Kotrba M (2006) A description of a new species of Diasemopsis (Diptera, Diopsidae) from the Comoro Islands with morphological, molecular and allometric data. Zootaxa 1211: 1–19.
  • Carr M, Hurley I, Fowler K, Pomiankowski A, Smith HK (2005) Expression of defective proventriculus during head capsule development is conserved in Drosophila and stalk-eyed flies (Diopsidae). Development Genes and Evolution 215: 402–409.
  • Cotton AJ, Cotton S, Small J (2015) Male mate preference for female eyespan and fecundity in the stalk-eyed fly, Teleopsisdalmanni. Behavioral Ecology 26: 376–385.
  • Egge AR, Brandt Y, Swallow JG (2011) Sequential analysis of aggressive interactions in the stalk-eyed flyTeleopsisdalmanni. Behavioral Ecology and Sociobiology 65: 369–379.
  • Hurley I, Pomiankowski A, Fowler K, Smith H (2002) Fate map of the eye-antennal imaginal disc in the stalk-eyed fly Cyrtodiopsis dalmanni. Development Genes and Evolution 212: 38–42.
  • Imai HT, Taylor RW, Crosland MWJ, Crozier RH (1988) Modes of spontaneous chromosomal mutation and karyotype evolution in ants with reference to the minimum interaction hypothesis. Japanese Journal of Genetics 63: 159–185.
  • Kotrba M (2004) Baltic amber fossils reveal early evolution of sexual dimorphism in stalk-eyed flies (Diptera: Diopsidae). Organisms, Diversity & Evolution 4: 265–275.
  • Meade LC, Dinneen D, Kad R, Lynch DM, Fowler K, Pomiankowski A (2019) Ejaculate sperm number compensation in stalk-eyed flies carrying a selfish meiotic drive element. Heredity 122: 916–926.
  • Ohara K (1993) First record of the family Diopsidae from Japan (Diptera, Brachycera). Bulletin of the Tokushima Prefectural Museum 3: 39–47. [In Japanese]
  • Ohara K (1997) Sphyracephala detrahens (Diptera, Diopsidae) in the Yaeyama Islands, Okinawa, Japan. Bulletin of the Tokushima Prefectural Museum 7: 25–37. [In Japanese]
  • Presgraves DC, Severance E, Wilkinson GS (1997) Sex chromosome meiotic drive in stalk-eyed flies. Genetics 147: 1169–1180.
  • Roskov Y, Ower G, Orrell T, Nicolson D, Bailly N, Kirk PM, Bourgoin T, DeWalt RE, Decock W, van Nieukerken E, Zarucchi J, Penev L (Eds) (2019) Species 2000 & ITIS Catalogue of Life, 2019 Annual Checklist. Digital resource at Species 2000: Naturalis, Leiden, the Netherlands. ISSN 2405-884X.
  • Wilkinson GS, Dodson GN (1997) Function and Evolution of Antlers and Eye Stalks in Flies. The Evolution of Mating Systems in Insects and Arachnids. Cambridge University Press, Cambridge, 310–328.
  • Wilkinson GS, Presgraves DC, Crymes L (1998) Male eye span in stalk-eyed flies indicates genetic quality by meiotic drive suppression. Nature 391: 276–279.
  • Wilkinson GS, Reillo PR (1994) Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly. Proceedings of the Royal Society B: Biological Sciences 255: 1–6.
  • Worthington AM, Berns CM, Swallow JG (2012) Size matters, but so does shape: quantifying complex shape changes in a sexually selected trait in stalk-eyed flies (Diptera: Diopsidae). Biological Journal of the Linnean Society 106: 104–113.