The genus Atherimorpha White, 1915 is a Gondwanan relic, occurring in South America, Southern Africa and Australia. Females are rarely collected, and are not described for more than half of the known species. The female of Atherimorpha latipennis Stuckenberg, 1956 was collected for the first time in 2021 and is described here, along with a redescription of the male. We describe the differences from the male, with the reduced wings and poorly defined scutellum the most noteworthy. The female of A. latipennis represents the first recorded case of brachyptery in the family Rhagionidae. Possible drivers of brachyptery in Afrotropical Diptera are briefly discussed.

Aptery, Lesotho, snipe flies, taxonomy

The genus Atherimorpha White, 1915 (Diptera, Rhagionidae) is a Gondwanan relic (Kerr 2010; Kerr and Sinclair 2017) with 51 species recognised (Kerr and Sinclair 2017). Globally, the genus has received sporadic taxonomic attention, with most revisions only addressing regional faunas (Malloch 1932; Paramonov 1962; Nagatomi and Nagatomi 1990), though acknowledging the link between Australia, Africa and South America. Of the 50 extant species, the male is known in 40 cases and the female in 23. Both sexes are only known in 16 species and in three species, it is not clear which sex was described (see Philippi 1865; González et al. 2020). This pattern is also seen in the 12 Afrotropical species, both sexes are known in only four species, and the female is unknown for seven species.

Many Atherimorpha species are known from mountainous regions, usually near streams (Fig. 1), and emerge as adults for a limited time (Nagatomi and Nagatomi 1990; Kerr 2010). Mountain habitats often drive the evolution of specialised morphology, such as dwarfism in plants (Körner 2003), improved insulation and hypoxia resistance in mammals (Withers et al. 2016), macroptery in birds (Mayr 1963; Moore and Khan 2023) and both brachyptery and macroptery in insects (Leihy and Chown 2020; Moore and Khan 2023). Brachyptery and aptery are driven by both the increased cost of flight and the reduced benefit of flight (Leihy and Chown 2020). Factors increasing the cost of flight include high wind speed, habitat fragmentation, low temperature and low air pressure (Hackman 1964; Leihy and Chown 2020). These factors are all present in the alpine zone of the Lesotho highlands (Partridge et al. 2010; Badger et al. 2015). Predator or competitor release, increased habitat stability, or increased habitat complexity can also drive decreased benefit from flight. These factors can be harder to measure, but are generally not considered to play a role in alpine environments (Leihy and Chown 2020). In insects, the drivers of the evolution of brachyptery and macroptery are the same, with some species evolving to overcome the pressures of these environments (macroptery) while others evolve to avoid them (brachyptery).

Figure 1. 

Photograph of site where A. latipennis was collected. Afriski Mountain Lodge grounds (28°49.37'S, 28°43.68'E), with first author searching unsuccessfully for additional female specimens. Fifty-one males and single female were collected in 2021 and 68 males in 2022. Photo B. Muller.

We describe the female of Atherimorpha latipennis Stuckenberg, 1956 for the first time, redescribe the male to modern standards and provide colour photographs for the first time.

Specimens were collected using sweep nets at Afriski Mountain Lodge and Resort (Fig. 1; 28°49.37'S, 28°43.68'E) in December 2021 and November 2022 and the nearby tributary of the Malibamatso River (Fig. 2; 28°47.81'S, 28°41.26'E) in November 2022. Specimens were also collected at Afriski Mountain Lodge using a Malaise trap in November 2022. The resort falls within the alpine zone at 3032 m a.s.l., and the vegetation is classified as Drakensberg Afroalpine Heathland (Gd10), which is dominated by Fynbos shrubs and grass (Mucina and Rutherford 2006). The Malibamatso tributary is slightly lower at 2872 m a.s.l., but still falls within the Drakensberg Afroalpine Heathland vegetation type.

Figure 2. 

Photograph of site where A. latipennis was collected. Tributary of Malibamatso River (28°47.81'S, 28°41.26'E), a single male was collected in November 2022. Photo K. Jordaens, used with permission.

Specimens were examined using a Leica M80 microscope, photographed using a modified version of the system described by Brecko et al. (2014) and stacked using Helicon Focus 7. Male genitalia were dissected and macerated in lactic acid at 130 °C for 20 minutes, photographed using a Canon 400D and also stacked in Helicon Focus 7. Specimens were identified using the keys and descriptions in Nagatomi and Nagatomi (1990). Terminology follows Cumming and Wood (2017) and Kerr and Sinclair (2017).

Collection codens used in the text are as follows: BMSA – National Museum, Bloemfontein, South Africa; NMSA – KwaZulu-Natal Museum, Pietermaritzburg, South Africa.

The brachypterous female of A. latipennis is remarkable, being the first recorded case of brachyptery in the family Rhagionidae. Brachyptery has been recorded in 17 families of Diptera in the Afrotropics (Kirk-Spriggs and Sinclair 2017a), and the collection of the female of A. latipennis brings this to 18, slightly more than 15% of the families known from the region. Though the percentage of species showing this trait is much lower, the fact that it has evolved in parallel so many times warrants further discussion.

The evolution of brachyptery is often associated with habitat specialisation, though the degree to which this is driven by the increased costs of flight versus the decreased benefit varies between habitats (Hackman 1964; Leihy and Chown 2020). Alpine areas, coastal dunes and polar regions are associated with an increased cost of flight (Darlington 1943), while forests, caves and inquilines or parasitic lifestyles are associated with decreased benefit of flight (Southwood 1962; Roff 1990; Denno et al. 2001). Oceanic islands show attributes of both groups, but the influence of wind (and the associated cost of flight) is the major driver of brachyptery (Leihy and Chown 2020).

In the Afrotropics, both the decreased benefit and increased cost of flight appear to contribute to the evolution of brachyptery. Of the families in which it has been recorded, three include vertebrate inquilines or parasites, three invertebrate inquilines or parasites and six are known from forest habitats (Kirk-Spriggs and Sinclair 2017a, 2017b, 2021). As species of Sphaeroceridae occur in both ant nests and forests, there are 11 families where the lack of benefit is the driver of brachyptery. In contrast, one brachypterous family occurs in coastal dunes, four are recorded from oceanic islands and nine from mountains (now including the Rhagionidae), but as the Chloropidae, Limoniidae and Sphaeroceridae are recorded from both mountains and oceanic islands, 12 families show brachyptery driven by the increased cost of flight (Kirk-Spriggs and Sinclair 2017a, 2017b, 2021; van Zuijlen 2021). It is also worth noting that species of Chloropidae, Empididae, Limoniidae and Sphaeroceridae occur in both groups (Kirk-Spriggs and Sinclair 2017b, 2021).

Hackman (1964) mentioned that brachyptery occurred in one sex in some species but did not suggest possible mechanisms for this. While flight provides insects with evolutionary benefits —e.g., higher dispersal rates, predator avoidance and access to food or reproductive resources — there are undoubtedly costs associated as well —e.g., developmental costs of growing wings, limited use of confined habitats, exposure to severe environmental conditions (Leihy and Chown 2020). Under most conditions, the benefits outweigh the costs, but a shift in this balance drives the loss of flight (Hackman 1964; Leihy and Chown 2020). The primary difference in this regard between males and females is the access to reproductive resources. Increased mating events increases fitness in both male and female insects (Arnqvist and Nilsson 2000), though the increase is not equal in males and females. Females have a finite reproductive capacity and multiple mating events only increases fitness by 30–70% (Arnqvist and Nilsson 2000). Despite the advantage of multiple mating events in females, remaining close to suitable larval habitats is also evolutionarily advantageous. Males on the other hand have a higher theoretical maximum fitness which can only be achieved by locating many females, favouring the evolution of dispersal. Further specimens and studies are needed to confirm this in A. latipennis.

The Afrotropical region is large, about 20% of the world’s land surface and ecologically diverse, including eight of the world’s 35 terrestrial biodiversity hotspots (Marchese 2015), and largely underexplored biologically. The alpine zone in southern Africa, particularly Lesotho, has received limited attention to date. Biological surveys of the continent are likely to discover undescribed species, but even the addition of previously undescribed sexes can be remarkable, as shown here. This is particularly true of environments shown to drive atypical morphology. Atherimorpha have been collected from mountainous regions in Australia, Southern Africa and South America, yet comparatively few females have been described.

Given that alpine or mountainous environments can result in the evolution of brachyptery and that brachypterous Diptera present a collecting challenge, it is possible that other female Atherimorpha are also brachypterous. Future collecting efforts should include multiple techniques, as the usual techniques often rely on passive movement by the target individuals (e.g. Malaise traps) or active searching for flying adults. The inclusion of pitfall trapping, bush beating and other techniques usually used for walking insects may result in the discovery of more brachypterous females.

Peter Kerr is thanked for fruitful discussion on the preparation and identification of Afrotropical Atherimorpha. The Lesotho Ministry of Tourism, Environment and Culture, Department of Environment (MTEC-DoE) is thanked for the issuing the collecting permit. BSM thanks the National Museum, Bloemfontein, for its continued support.