Artabrus aurantipilosus, Hurni-Cranston & Hill, 2020

Hurni-Cranston, Tiziano & Hill, David E., 2020, Description of a new jumping spider, Artabrus aurantipilosus sp. nov. (Araneae: Salticidae: Plexippina), from Banda Neira, Indonesia, Peckhamia 222 (1), pp. 1-19 : 7-16

Artabrus aurantipilosus sp. nov.

Figures 8-11

Type material. The holotype ♂ ( HC-BN 2m) and paratype ♀ ( HC-BN2 f) were collected by the senior author ( THC) on a Banyan tree ( Ficus sp. ) in the middle of an intersection near the Cilu Bintang Estate, Banda Neira (4.527642°S, 129.898610°E, FEB 2016; Figures 1 , 8 ). Both were found on leaves at a height of about 2 m above the ground . The female had a large nest that might have contained eggs, between two attached Banyan leaves. The same species was also seen on the balcony of the Maulana Hotel on Banda Neira, but was not collected at that time ( Figure 10 :1-3). Both specimens will be deposited in the Florida State Collection of Arthropods ( FSCA), Gainesville .

Etymology. The species group name, aurantipilosus (Lat., adj., m.), refers to the prominent fringe of orange setae extending below legs I and II of the male.

Diagnosis. Genitalia of the male and female Artabrus aurantipilosus are not significantly different from those of the closely related, but widely parapatric, A. erythrocephalus . Unlike the male A. erythrocephalus , the male A. aurantipilosus is generally dark brown, with a prominent fringe of long orange setae beneath legs I and II, extending from each patella to the metatarsus. The female A. aurantipilosus is light yellowbrown and translucent. Neither the male nor the female exhibits the bright green colouration characteristic of A. erythrocephalus .

Description of male ( Figures 9-10 ). Body length close to 1 cm. The prominent chelicerae and face are dark brown or dark red-brown. The pedipalps are lighter brown. The carapace is dark brown and glossy, with red-orange scales around the eyes at the margins of the eye region, and few scattered orange scales elsewhere. Each ALE is more than half the diameter of an AME, with the bottom of the ALE situated at the height of the center of the AME. The PME are closer to the ALE than to the PLE. The dorsal opisthosoma is brown with some black mottling, with indistinct lateral striations. The venter of the opisthosoma is more uniform brown, with black and white rings at the rear. In front of the spinnerets is a small tuft of red setae extending laterally on either side ( Figures 9 :7, 10:1), appearing as the extension of a red lateral stripe. The spinnerets are surrounded by bright orange setae. Legs I and III have a prominent ventral fringe of long, orange setae from at least the patella to the metatarsus, and also carry many orange scales along the sides. Except for the femora, legs III and IV are lighter brown. Each pedipalp has relatively long basal segments (from coxa to tibia), and a simple RTA. The embolus is long, recurved proximomedially near the tegulum as in the related A. erythrocephalus , curving laterodistally (extending counterclockwise in the distal direction on the left pedipalp as viewed from below).

Description of female ( Figure 11 ). Body length close to 1 cm. Scale and setation patterns of the female A. aurantipilosus resemble those of the related A. erythrocephalus , but the female A. aurantipilosus is often green or light green in colour. The eye region of A. aurantipilosus is darker red-brown, with a less distinct pattern of off-white scales than those seen in the female A. erythrocephalus , and unlike that species orange scales are not present around the eyes. The eye arrangement is like that of the male. The carapace is mostly glabrous, with scattered off-white scales. The pattern of scales that cover the dorsal opisthosoma, and account for the lateral striations of the opisthosoma, are very similar to those of the female A. erythrocephalus , but the lateral striations are more off-white in A. aurantipilosus . Venter of opisthosoma almost uniform off-white in colour. Variation in the appearance of the genitalia of the female A. erythrocephalus has not been documented, but the epigynum of A. aurantipilosus is similar to the published drawings for that species.

Habitat and biogeography. Banda Neira is a small (~ 1 km by 3 km) island that is situated only 100 m from Gunung Api, a very active volcano with a long history of both lava flows and explosive pyroclastic flows ( Figures 12-14 ; Badan Geologi 2014; Hidayat et al. 2020). This island has a long history of European trade, occupation and conflict dating back to the arrival of the Portuguese in 1511, driven by the high value of cultivated spices to include nutmeg and mace ( Loth 1995). Today the island can be divided into a relatively flat and densely populated sector south of the airport, and a mountainous, less populated sector to the north. A considerable amount of tropical vegetation, as well as ruins associated with the earlier European occupation, remains on both inhabited and less inhabited parts of the island ( Figure 15 ).

Banda Neira is quite isolated from known populations of A. erythrocephalus . The existence of this distinctive Artabrus on a small island near the eastern edge of Wallacea poses several questions. First, how and when did it get there? With a long history of human habitation and spice trade in the area, including more than 500 years of more recent European presence, there has been more than enough time for the introduction and subsequent evolution of A. erythrocephalus into a distinct local form. Rapid evolution would be favored by random effects or genetic drift associated with a small population size ( Ellstrand & Elam 1993; Masel 2011; Xiong et al. 2017; Costanzi & Steifetten 2019). This could be impacted by the presence of Artabrus on nearby islands, particularly if there is frequent movement of the human population between these islands. The distinctive native flora of the southern Moluccas, including the Banda Islands, is quite different from the flora of Sunda ( Rutgrink et al. 2018), and the more recent introduction of plants as well as human settlement have also contributed to the unique vegetation found there. It is quite possible that the success of Artabrus on Banda Neira is the result of synanthropy.

Is Artabrus aurantipilosus endangered? If this species is restricted to Banda Neira, or to both Banda Neira and the nearby Banda Api, then it is certainly as endangered as the human settlements are on those islands as a result of highly unpredictable volcanic activity. It is far safer if its range extends to other islands in the area. The general theory of island biogeography suggests that smaller islands can support less biodiversity, and that continued existence of populations that have survived is precarious ( MacArthur & Wilson 1967). Although this is generally supported by the comparison of larger island biota, there are exceptions when it comes to smaller islands ( Chisholm et al. 2016) that to some extent may be due to environmental diversity that is produced by human activity. Isolation is also thought to reduce species diversity on islands, but there may be compensation for the physical isolation of Banda Neira in the level of human traffic to and from this island (lack of economic isolation; Helmus et al. 2014). We still know little about the behaviour of Artabrus species, and the niche dimensions that support their success in the places where they are found. Is A. aurantipilosus a facultative or an obligatory synanthrope on Banda Neira?

Figures

Figure 1. Known distribution of the two Artabrus species in the East Indies. A. erythrocephalus (green circles) ranges from the southern end of the Malay Peninsula to Sumbawa. A. aurantipilosus sp. nov. (red circle) has only been found far to the east, on one small island, Banda Neira, to the south of Seram. Numbers in circles correspond to records in Table 1. Unnumbered records for A. erythrocephalus are based on validated reports posted on iNaturalist.

Figure 8. Type locality for Artabrus aurantipilosus, sp nov., on Banda Neira. 1, Location (inset) of the Banda Islands south of Seram in the Wallacean biogeographic province. 2, Detail of the larger Banda Islands showing Banda Neira just to the east of the live volcano, Gunung Api (Banda Api). 3, Further detail in contour map of the central Banda Islands, showing the type locality (small red circle) in the more settled part of Banda Neira, near sea level. Image credits: 1-2, NASA/USGS Landsat; 3, © OpenStreetMap contributors, base map and data from OpenStreetMap and the OpenStreetMap Foundation.

Figure 9. Living holotype ♂ (HC-BN2m) Artabrus aurantipilosus, sp nov. Photo credits: 1-8, T. Hurni-Cranston.

Figure 10. Artabrus aurantipilosus, sp nov. 1-3, Adult male with missing legs I and II, found on hotel balcony (Figure 15:6) but not collected. 4-8, Ventral views of holotype ♂ (specimen HC-BN2m) in alcohol. 7-8, Pedipalps, including mirror image of right pedipalp (7).

Figure 11 (continued on next page). Paratype ♀ (HC-BN2f) Artabrus aurantipilosus, sp nov. 1-6, Views of spider in life. Photo credits: 1-9, T. Hurni-Cranston; 10-13, D. E. Hill.

Figure 12. Views of Banda Neira and nearby Gunung Api. 1, Aerial view taken during approach to the airport on Banda Neira from the North. 2, View of Banda Neira, looking toward the east from the summit of Gunung Api. 3, View of Gunung Api to the west of Banda Neira. Photo credits: 1, Bluemotion Banda, with permission; 2-3, Hike Indonesia, used under Creative Commons Attribution 2.0 Generic (CC BY 2.0) license.

Figure 13. Antique map of the central Banda Islands by Van Baarsel (1818). The drawing at bottom (facing north) shows an eruption of Gunung Api to the west, and the settlement on Banda Neira to the east.

Figure 14. Two views of volcanic activity on Gunung Api in 1988. 1, Explosive eruption including pyroclastic flows. 2, Steaming lava on the northwestern slopes of Gunung Api. Banda Neira can be seen in the background. Photo credits: 1-2, Tom Casadevall, USGS.

Figure 15 (continued on next page). Ground-level views of Banda Neira. 1-2, Foot paths through tropical vegetation. 3, Descending street. 4-5, Streets on the southern part of the island. 6, Maulana Hotel, a remaining Dutch colonial building. One ♂ Artabrus aurantipilosus (Figure 10:1-3) was found on the balcony of this hotel, but not collected. Photo credits: 1-5, 7-9, T. Hurni-Cranston; 6, Charlie and Jennifer McNamara, used with permission.