Leptogenys processionalis distinguenda

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Brunei Darussalam, Indonesia, Malaysia.

Association with Other Organisms
Ott et al. 2015 - is one of the best-studied myrmecophilous spiders. It inhabits colonies of the Southeast Asian army ant Leptogenys distinguenda (Witte et al., 1999; Witte, 2001; Witte et al., 2009; von Beeren et al., 2012a) with a high prevalence (46 colonies colonized out of 50) at the Ulu Gombak study site (Malaysia, Selangor. Gombak valley, near Kuala Lumpur; secondary rain forest,). Its host spectrum is unknown as host records have not been studied systematically. Even though it shows a high prevalence with L. distinguenda, these spiders presumably have only a low negative impact on the host population, which seems to be a common phenomenon in ant-nest inhabiting spiders such as Cosmophasis itaeniata Keyserling and Attacobius attarum Roewer (Cushing 2012). In S. maschwitzi, this is indicated by the spider’s kleptoparasitic habit by feeding on dead host prey items (Witte et al., 2008; Witte et al., 2009) and the low number of individuals per colony (range = 0–30 spiders per colony, median = 4 spiders per colony, Nhost colonies = 50). In contrast to C. bitaeniata and A. attarum, S. maschwitzi does not prey on immatures of the host and has instead lost its predatory behavior, a plesiomorphic trait in spiders (Riechert and Luczak, 1982). In species-rich host-myrmecophile communities, low-cost parasites like S. maschwitzi are supposedly more likely to achieve high levels of integration due to lower selection pressure on the host to evolve counterdefenses (Witte et al., 2008; von Beeren et al., 2011). Indeed, S. maschwitzi is very well integrated into the social system of its predatory host L. distinguenda (“integrated species” sensu Kistner, 1979). Most interactions between spiders and workers are peaceful in nature and spiders are even sometimes groomed by host ants (von Beeren et al., 2012a). This might be in part due to the fact that S. maschwitzi acquires nestmate recognition cues from ant workers (“acquired chemical mimicry” sensu von Beeren et al., 2012b), thus duping workers to be colony members (von Beeren et al., 2012a). A chemical mimicry strategy was also found in the salticid spider C. bitaeniata, a guest of the weaver ant Oecophylla smaragdina Fabricius (Allan et al., 2002), and might generally constitute a good strategy to avoid ant attacks in nest-inhabiting myrmecophiles (Lenoir et al., 2001). Interestingly, the nestmate-recognition cues were acquired differently: S. maschwitzi acquired them from host workers, while C. bitaeniata acquired them by feeding on host larvae (Elgar and Allan, 2004). It should not be forgotten, though, that additional behavioral and morphological adaptations might play important roles in interspecific interactions between spiders and ants. A detailed experimental study revealed, for example, that S. maschwitzi does not entirely depend on chemical mimicry for social integration (von Beeren et al., 2012a). In laboratory nests they primarily rested on top of ants, which might help to avoid constant confrontations with ant workers (see video footage at http://www.evolution-of-life.com/en/observe/video/fiche/an-evolutionary-arms-race.html). Adaptations to the nomadic life style of its army ant host are apparent. Sicariomorpha maschwitzi participates in the frequent host emigrations to new nest sites by using a combination of tactile and chemical stimuli (Witte et al., 1999). Spiders were found primarily when ant traffic flow on trails was high (see fig. 2). Very little is known about the reproduction of S. maschwitzi. Spiders were regularly observed to mate in laboratory nests among ant workers (sex ratio is 1:1, Nspiders = 95). Unfortunately, egg-laying was never observed. Histological sections of female opisthosomas revealed unusually large eggs indicating high investment in offspring (Witte et al., 1999; Witte, 2001). This requires further investigation, but we speculate that spiderlings hatch shortly after egglayingin order to avoid a free-living phase and immediately track the frequent colony migrations. In summary, S. maschwitzi shows several characteristics that seem to be specific adaptations to the life with its army ant host, a life style that is generally assumed to be a favorable niche by providing a predator-free space and richly laden tables of high-quality food (Holldobler and Wilson 1990).



Nomenclature

 *  distinguenda. Lobopelta distinguenda Emery, 1887b: 430, pl. 1, fig. 4 (w.) BORNEO. Combination in Leptogenys: Emery, 1895k: 461. Subspecies of ocellifera: Emery, 1893f: 243; Forel, 1901h: 46. Currently subspecies of processionalis: Emery, 1911d: 105.