Research Article |
Corresponding author: Robert Perger ( robertperger@hotmail.com ) Academic editor: Danilo Harms
© 2021 Robert Perger, Nadine Dupérré.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Perger R, Dupérré N (2021) Myrmecotypus mazaxoides sp. nov. – a new ground-dwelling, carpenter ant-resembling sac spider species from the Bolivian orocline, with indirect evidence for species-specific mimicry (Araneae, Corinnidae, Castianeirinae). Zoosystematics and Evolution 97(1): 273-280. https://doi.org/10.3897/zse.97.64766
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A new ant-resembling spider species of the subfamily Castianeirinae, Myrmecotypus mazaxoides sp. nov., from the Sub-Andean area of the Bolivian orocline is described. Adults of M. mazaxoides sp. nov. resemble the carpenter ant Camponotus cf. melanoticus Emery, 1894 and were observed on the ground of savanna-like habitats close to the entrances of formicaries of this ant. This study is the first to report a ground-dwelling species of Myrmecotypus O. Pickard-Cambridge, 1894; all the other species are arboreal.
Arachnid, Bolivia, Camponotus, myrmecomorph, South America
The Neotropical Castianeirinae genus Myrmecotypus O. Pickard-Cambridge, 1894 is a group of slender, fast-running spiders and currently includes 13 species (World Spider Catalog 2021). Six species are reported from South America, of which five have been recorded from Bolivia: Myrmecotypus haddadi Perger & Rubio, 2021, M. iguazu Rubio & Arbino, 2009, M. niger Chickering, 1937, M. rubrofemoratus Perger & Rubio, 2021, and M. tahyinandu Perger & Rubio, 2020 (World Spider Catalog 2021).
Potential ant models have been proposed for six of the known 13 species of Myrmecotypus (
Spiders and ants were collected manually from the ground and herbaceous vegetation. Photographs of live spiders and ants and their habitats were taken with a Panasonic Lumix GX-80 system camera fitted with a Panasonic H-HS3030 macro lens. Color and distribution of setae were described from photos of live specimens. Spiders were euthanized with ethyl acetate and stored in 70% ethanol. Preserved specimens were examined in 70% ethanol under a Nikon SMZ-U dissection microscope and identified using original and re-descriptions and keys (e.g.,
The descriptions refer to adult specimens. Morphological terms and description formats follow the recent studies on Castianeirinae spiders (
The following indices (sensu
The following abbreviations are used in the text: AER, anterior eye row; AME, anterior median eyes; ALE, anterior lateral eyes; PER, posterior eye row; PLE, posterior lateral eyes; PME, posterior median eyes.
Arachnological collections are abbreviated as follows (curators in parenthesis):
The ecoregion affinities of the species were investigated by visualizing the coordinates and a shape file of the regionalization of Bolivian ecosystems by
In this study, an indirect, correlative method is employed to support mimicry, without studying the impact of receiver responses on mimic fitness. While correlations do not imply causality, correlative approaches are useful for investigating putative cases of resemblance between taxa and extrapolating the consequences of mimicry beyond a single, well-studied population (
For the analysis of ant resemblance, we considered all ants that were collected in the surveyed location and were about the same body length as the spiders. The similarity was analyzed, based on a qualitative, descriptive assessment of integument color, shine, structure (e.g., appressed, erected, short, long) and color of setae and shape of body parts (e.g., abdomen shape: fusiform or ovate; apically pointed or rounded).
Subfamily Castianeirinae Reiskind, 1969
Myrmecotypus fuliginosus O. Pickard-Cambridge, 1894 (by original designation)
Cephalic region wide (cephalic index range 64–89), carapace narrowed (carapace index ˂ 60), without thoracic groove but with slight depression instead; PER wider than AER and almost straight to moderately recurved, AME larger than ALE, PME–PME greater than PME–PLE, PLE situated close to lateral margin of cephalic area; abdomen only very slightly petiolated; tibia I ventral spines paired in 2–2, 3–2, 3–3 or 4–4 arrangement; trochanter IV notch usually absent, with only a tiny one, if present (
Ecoregion distribution of Myrmecotypus mazaxoides sp. nov., according to the regionalization by
Holotype ♂ and ♀ allotype; BOLIVIA: Santa Cruz department, Santa Cruz de la Colina, Urubo; 17.760833°S, 63.24°W, 432 m. a.s.l., 21–28 Dec. 2019, R. Perger leg.; Cerrado-like grassland in urbanization (
Amongst species of Myrmecotypus, an elongated and constricted abdomen is only found in M. mazaxoides sp. nov. (Figs
Females of M. mazaxoides sp. nov. can be distinguished from those of M. lineatus by the following characteristics: dorsum dark brown with an anthracite-greyish appearance in live condition (Fig.
Body length 4.69; carapace length 2.17, width 1.11, carapace index 51; cephalic width 0.72, cephalic index 65; sternum length 0.93, width 0.67, sternum index 72; abdomen length 2.42, maximum width anterior part 0.76, maximum width posterior part 1.04, abdominal index 43; petiole length 0.10, width 0.29; dorsal sclerite length 2.32 (width agrees with abdominal width); epigastric sclerite length 0.62, width 0.74; ventral sclerite length 0.95, width 0.51; inframamillary sclerite length 0.09, width 0.15. AER 0.47; AME-AME 0.08; AME-ALE 0.02; PER 0.60; PME-PME 0.14; PME-PLE 0.11.
Carapace
(Fig.
Eyes. Eight sub-equal eyes formed in two rows; PER distinctly recurved; AER slightly recurved.
Chelicerae. Orange-brown, shiny, with separated erect dark setae, area between retro- and promarginal rows of cheliceral teeth orange-white with dense white setae, two retromarginal teeth and two promarginal teeth, with distal tooth reduced to small denticle.
Abdomen
(Figs
Legs. Coxae II and III translucent white, trochanters II and III dark yellow; coxae and trochanters I and IV reddish-brown; legs mostly sparsely covered with fine, golden setae, including feathery setae, dense in some areas, femora and tibia with separated, erect, long setae; femora I and II proximal fifths reddish, distal four-fifths laterally translucent, white and dark stripes along dorsal edges, remainder of legs I and II reddish-yellow; tibia I promarginal with 3 spines, retromarginal with 2 spines; femora and tibiae III and IV reddish-brown, dark grey stripes along dorsal sides; remainder of leg III orange-light brown; leg IV tarsus yellow; legs III and IV lined with short, appressed white feathery setae.
Palp. Pedipalp tibia with two distinct, long setae and several shorter setae (Fig.
Body length 6.23; carapace length 2.85; width 1.35; carapace index 47; cephalic width 1.00; cephalic index 74; sternum length 1.19; width 0.80; sternum index 67. Abdomen length 3.15; maximum width anterior part 1.24; maximum width posterior part 1.45; abdominal index 46; petiole length 0.16; width 0.45; dorsal sclerite length 1.04; width 0.88; epigastric sclerite length 0.74; width 0.92; inframamillary sclerite length 0.16; width 0.35. AER 0.59; AME-AME 0.10; AME-ALE 0.03. PER 0.80; PME-PME 0.18; PME-PLE 0.13.
Lateral constriction of abdomen indistinct (Fig.
Epigyne
(Fig.
Females (BL 6–6.5 mm) were larger than males (BL 4.8–5.2 mm). Sexual dimorphism in coxae color (coxae II-III translucent whitish in male, II–IV in female). The number of clearly distinguishable transversal bands of feathery setae on the abdomen varied between one or two in the median constriction and three or four closely before the apex. While the abdominal constriction of the male is determined by the shape of the large dorsal sclerite, it varied in females according to the nutritional or reproductive state and could be similarly constricted as in males.
The specific epithet, mazaxoides, is derived from the Castianeirinae genus “Mazax” and “oeidēs” (Greek) = resembling or looking like and refers to the general resemblance of the habitus of this species to species of Mazax.
This species is only known from the type locality in the recently established urbanization of Santa Cruz de la Colina, Urubo, Santa Cruz department. This urbanization included empty plots with savanna grasslands, plant successions and bushes or houses with gardens. According to the ecoregion delineation by
Myrmecotypus mazaxoides sp. nov. co-occurred with four different species of Castianeira (not determined) in the same habitat, three of which were commonly observed and had a dark body (blackish or black with grey) and red legs. A single male of Mazax cf. ramirezi Rubio & Danişman, 2014, was collected as well, among individuals of M. mazaxoides sp. nov.
Eleven ant species with a similar or larger body length than adults of M. mazaxoides sp. nov. (BL 4.8–6.5 mm) were found in the investigated plots. However, all individuals of the new species were collected close to the entrance of subterranean formicaries of Camponotus cf. melanoticus Emery, 1894. Myrmecotypus mazaxoides sp. nov. and C. cf. melanoticus shared an elongated, sub-oval abdomen, a weakly shiny, dark brown integument with anthracite tinge, fine brassy pubescence and sparse white setae on the posterior abdomen, and completely red legs (Fig.
No other ant species with a weakly shiny, greyish body, short brassy pubescence or completely red legs was observed in the studied area. Two additional ant species had an oval abdomen, but one of those species had a brown pronotum and a black, shiny abdomen (Camponotus cf. fastigatus Roger, 1863), and the other species a reddish forebody and abdomen with golden pubescence (Camponotus cf. blandus Smith, F., 1858).
When the first author approached the individuals of M. mazaxoides sp. nov., they were hiding under ground vegetation (e.g., Fig.
For about six months, the colony of C. cf. melanoticus was expelled by a colony of the larger Camponotus renggeri Emery, 1894, which was attracted by mealybugs on a nearby stand of introduced Croton plants. During the absence of C. cf. melanoticus, no individuals of M. mazaxoides sp. nov. were observed, despite a similar sampling effort. After the removal of the mealybugs by the main author, C. renggeri stayed away and the site was re-colonized by C. cf. melanoticus and M. mazaxoides sp. nov., indicating a strong mimetic relationship between these ants and spiders.
Because of the elongated, constricted abdomen, the general habitus of M. mazaxoides sp. nov. resembles that of Mazax species. Myrmecotypus and Mazax share a moderate to extremely weak thoracic groove and the AER straight to (moderately) recurved. Additionally, there is an overlap of the number of the tibia I ventral spines (Myrmecotypus: 2–2, 3–2, 3–3 or 4–4; Mazax: 3–3, 4-4, 5–5, or 6–6).
Both genera differ concerning their cephalic index (in Mazax the thoracic part is wider, resulting in a cephalic index of 53–64; in Myrmecotypus 64–92). In Mazax the AME are smaller than the ALE (larger in Myrmecotypus) and the abdomen has a distinct, rugose abdominal petiole (only slightly petiolated in Myrmecotypus). Additionally, except for both sexes of M. ajax Reiskind, 1969, males (and some females) of all known species of Mazax have the second pair of abdominal setae heavily sclerotized into spines.
In M. mazaxoides sp. nov., the subequal size of the eyes, the 3–2 ventral spination of tibia I and the elongated, constricted abdomen suggest that M. mazaxoides sp. nov. represents a transitional form between Mazax and Myrmecoptypus. However, because of the cephalic index (♂65; ♀74), the moderately developed petiole, and the simple abdominal setae, we tentatively place M. mazaxoides sp. nov. in Myrmecotypus.
Considering the uncertain relationships between Myrmecotypus and Neotropical Apochinomma and the possibility that Myrmecotypus is a polyphyletic group (
Based on co-occurrence patterns and morphological similarities, such as a moderately elongated, truncate forebody, short petiole, and sub-globose abdomen,
The morphological resemblance of M. mazaxoides sp. nov. to Myrmecotypus and Mazax, the latter being an exclusively ground-dwelling genus, and the occurrence of M. mazaxoides sp. nov. in ground habitats suggests that this species represents a transitional form between ground-dwelling and arboreal Castianeirinae lifestyles. A phylogenetic analysis may not only shed light on the generic relationships of Castianeirinae but also on the evolutionary history of ant mimicry in this subfamily.
Danilo Harms is thanked for granting permission to work in the Zoological Museum Hamburg, Universität of Hamburg, Germany, and Gonzalo D. Rubio (National Research Council of Argentina (CONICET), Experimental Station of Agriculture, Misiones, Argentina) and Brogan L. Pett (College of Life and Environmental Sciences, University of Exeter, United Kingdom) for a fruitful exchange of ideas on castianeirine taxonomy. Many thanks are extended to Charles Haddad (University of the Free State, Bloemfontein, South Africa) and Tamás Szűts (University of Veterinary Medicine Budapest, Budapest, Hungary) for reviewing and improving the manuscript.