Chikunia nigra (O. PICKARD-CAMBRIDGE, 1880)

Chikunia nigra View in CoL (misidentified).

Type material

Male holotype from northern central Bali , near Lake Beretan , −8.271211, 115.165842, collected in July 2017, legit L. Grinsted, in the Smithsonian MNH, Washington DC GoogleMaps .

Material examined

Multiple additional male and female specimens from type locality and nearby (−8.271211, 115.165842 to −8.282525, 115.164386; Fig. 3), collected in July 2017, legit L. Grinsted. Two females GoogleMaps from Malaysia, Pahang Tanah Rata , 4.46°N, 101.40°E, 1500 m, 21–22 May 2005, legit I. Agnarsson. GoogleMaps

Etymology

The species epithet honours Professor Trine Bilde, Aarhus University, for her significant scientific contributions to the field of behavioural ecology and social evolution in spiders and for her inspiring role as a PhD supervisor to L. Grinsted. The discovery of C. bilde by L. Grinsted in 2010 was a direct result of Professor Bilde’s approval and encouragement of an exploratory expedition to Bali. Professor Bilde is a strong female role model of high scientific integrity.

Diagnosis (Smith et al., 2019: 345)

Chikunia bilde differs from Chikunia nigra in the blunt terminus of the male abdomen (Smith et al., 2019: fig. 7H, I) and in the male leg colouration that gives legs a stripy appearance (yellow-brown stripes; Fig. 1G). Furthermore, C. bilde differs in the conformation of male palp with embolus covering the tegulum almost entirely, and short and transparent conductor (Smith et al., 2019: figs 7J, 8), and in having a conspicuous epigynum with oval to round spermathecae and spiralling copulatory ducts (Smith et al., 2019: fig. 7A–L). In habitus, C. bilde females tend to have larger bulbous abdominal humps than C. nigra . Furthermore, C. bilde females differ from C. nigra by lacking the dark brown or black tarsus of leg I.

Description

Female: Total length 2.83 mm. Cephalothorax 1.13 mm long, 1.01 mm wide, 0.61 mm high, dark brown with faint tan patches stretching across the midsection. Chelicerae shift from tan in colour to a medium brown as they transition outward from the body ( Fig. 7B). Sternum 0.71 mm long, 0.56 mm wide, dark brown and extending halfway through coxae IV. Abdomen 1.88 mm long, 2.42 mm wide, 1.59 mm high, subtriangular with large bulbous humps on both laterals ( Fig. 7A, B). Large dark brown-coloured patches laterally, a dark brown patch present at the posterior of the abdomen, and a dark brown streak running dorsally in a groove between the two humps ( Fig. 7A–C). Abdomen tapers distinctly behind humps. Eyes approximately equal in size, ALE 0.09 mm, AME 0.10 mm in diameter. All eyes within one eye diameter apart from each other excluding the anterior median, which are 0.10 mm apart. Leg I femur 1.93 mm, patella 0.37 mm, tibia 1.32 mm, metatarsus 1.20 mm and tarsus 0.81 mm. All legs tan in colour. Leg formula 1423.

Male: Total length 2.34 mm. Cephalothorax 1.06 mm long, 0.86 mm wide, 0.61 mm high, black in colour. Sternum 0.63 mm long, 0.58 mm wide, dark brown in colour extending to past coxae IV. Abdomen 1.29 mm long, 1.01 mm wide, 0.88 mm high, dark brown in colour with brown speckled pattern covering entire abdomen, oval in shape, and lacking any humps or ridges; narrows slightly to an abruptly blunt posterior ( Fig. 7G–I). Eyes approximately equal in size, ALE 0.08 mm, AME 0.09 mm in diameter. All eyes within one eye diameter apart from each other excluding the anterior median, which are 0.10 mm apart. Leg I femur 2.17 mm, patella 0.35 mm, tibia 1.39 mm, metatarsus 1.37 mm and tarsus 0.75 mm. Legs gradually darken moving from the coxae all the way to the tarsus. Coxae are white in colour. Femora fade from white to tan to dark brown where they meet the patella. Metatarsus and tarsus both medium brown in colour. Leg formula 1423.

Variation: Female total length 2.64–3.18 mm, femur I 0.94–1.48 mm; male total length 2.09–2.78 mm, femur I 1.62–2.19 mm. Female abdomen coloration varies greatly ( Fig. 9J–O). Colours range from bright yellow to orange, amber, various shades of brown and black. Black abdomens are uniformly coloured, whereas all other colour variants have a clearly defined black or dark brown pattern running dorsally. Additionally, the very tip of the abdomen can be black or dark brown, and often there is a dark brown or black patch, of varying size, on the tip of each of the abdominal humps.

FIELD OBSERVATIONS

Within a dense mixed-species colony, nearest neighbouring females with a brood were of the same species significantly more often than would be expected by chance ( Figs. 10, 11). This was true for both C. nigra and C. bilde (Pearson’s χ 2 test with Yates’ continuity correction: C. nigra χ 2 = 4.52, d.f. = 1, P = 0.034; C. bilde χ 2 = 4.45, d.f. = 1, P = 0.035). Within the colony, we recorded 48 C. nigra , of which 39 had a same-species nearest neighbour, and 30 C. bilde , of which 19 had a same-species nearest neighbour.

Distances to nearest neighbours ranged from 1 to 14 cm, with both mean and median = 7.0 cm. There was no significant difference between species in the distance they kept to their nearest neighbour ( Fig. 11; t -value = 0.32, P = 0.75), nor was there a significant difference in distances kept to nearest same-species vs. different-species neighbour ( Fig. 11, t -value = −0.99, P = 0.33; the interaction term between the two factors was also not significant: t -value = −0.34, P = 0.73).