First Evidence of Aggressive Chemical Mimicry in the Malagasy Orb
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First evidence of aggressive chemical mimicry in the Malagasy orb weaving spider Exechocentrus lancearius Simon, 1889 (Arachnida: Araneae: Araneidae) and description of a second species in the genus Scharff, Nikolaj; Hormiga, Gustavo Published in: arthropod systematics & phylogeny Publication date: 2012 Document version Publisher's PDF, also known as Version of record Document license: Unspecified Citation for published version (APA): Scharff, N., & Hormiga, G. (2012). First evidence of aggressive chemical mimicry in the Malagasy orb weaving spider Exechocentrus lancearius Simon, 1889 (Arachnida: Araneae: Araneidae) and description of a second species in the genus. arthropod systematics & phylogeny, 70(2), 107-118. http://www.senckenberg.de/files/content/forschung/publikationen/arthropodsystematics/asp_70_2/04_asp_70_2 _scharff_hormiga_107-118.pdf Download date: 26. sep.. 2021 Arthropod Systematics & Phylogeny 107 70 (2) 107 – 118 © Senckenberg Gesellschaft für Naturforschung, eISSN 1864-8312, 28.09.2012 First evidence of aggressive chemical mimicry in the Malagasy orb weaving spider Exechocentrus lancearius Simon, 1889 (Arachnida: Araneae: Araneidae) and description of a second species in the genus NIKOLAJ SCHARFF 1 & GUSTAVO HORMIGA 2 1 Natural History Museum of Denmark, Zoological Museum and Center for Macroecology, Evolution and Climate, Universitetsparken 15, DK-2100 Copenhagen, Denmark [[email protected]] 2 Department of Biological Sciences, The George Washington University Washington, D.C. 20052, USA [[email protected]] Received 17.i.2012, accepted 13.vii.2012. Published online at www.arthropod-systematics.de on 28.ix.2012. > Abstract The araneid genus Exechocentrus Simon, 1889 and its type species Exechocentrus lancearius were originally described based on a single female specimen from Madagascar, which was missing the abdomen. The first complete adult specimen, a female, of Excechocentrus lancearius was collected in 2000. A second adult female of Excechocentrus sp. was discovered in 2009, about 300 km away from the first locality. We redescribe the neotype ofExechocentrus lancearius and describe the second adult female as Exechocentrus madilina new species. We also report some observations on the natural history of Exechocentrus lancearius, including photographs of its highly modified foraging web, which provide indirect evidence of aggressive chemical mimicry. > Key words Systematics, taxonomy, bolas spiders, spider webs, silk, Madagascar. Introduction The spider family Araneidae comprises more than selected species of male moths that are lured by sex 3000 species in 171 genera (PLATNICK 2012; see also pheromones (EBERHARD 1977, 1980; YEARGAN 1988; DIMITROV et al. 2012), and includes the well known STOWE et al. 1987), or by the highly modified ladder common orb-weavers, which produce geometric or- orb webs of Scoloderus spp. (STOWE 1986). bicular snares to capture a wide variety of airborne The Malagasy genus Exechocentrus is rare and prey. No less than 48 of the 171 described genera monotypic. It was recently placed in the araneid sub- (28%) are monotypic (i.e., include only one species; family Cyrtarachninae (EMERIT 2000), which includes PLATNICK 2012) and many species are rare and have genera that have reduced webs (or have entirely aban- been collected only a few times since their original doned foraging webs) and includes members that use description. Although the vast majority of spiders are aggressive chemical mimicry to lure male moths as generalist predators, Araneidae includes a number prey, such as the aforementioned genus Mastophora of specialists that target a very narrow range of prey Holm berg, 1876 (JOCQUÉ & DIPPENAAR-SCHOEMAN 2006; items. Spectacular examples of such prey specializa- DIP PEN AAR-SCHOEMAN 1997; GRISWOLD 2003), which tion are provided by Mastophora spp., which prey on Emerit placed in the tribe Mastophoreae, under the 108 SCHARFF & HORMIGA: Bolas spiders from Madagascar sub family Cyrtarachninae. Other authors have sug- juvenile from Berlin is complete, with abdomen, and gested that Mastophoreae should be considered its had Simon known this specimen, he would certainly own subfamily (STOWE 1986; SCHARFF & CODDINGTON have described the peculiar abdomen, with two long 1997), Mastophorinae, and this is followed herein. dorsal apophyses. The specimen in Berlin was col- The genus Exechocentrus and its type species Ex lected by Johann Maria Hildebrandt (1847 – 1881), a echocentrus lancearius were originally described by German explorer who collected plants and animals in SIMON (1889) based on a single female specimen from the Afrotropical region from 1872 until he died of yel- Madagascar, which was missing the abdomen (and low fever in Madagascar in 1881, at the age of 34. therefore the genitalia, assuming that it was an adult The original label data does not reveal collecting date, specimen). Simon probably felt compelled to describe but from Hildebrandt’s collecting itineraries (BEENTJE this species, despite the incompleteness of the speci- 1998), we know that he collected in Madagascar from men, because of its unusual carapace, covered with 1879 until his death in 1881, and that South Central bizarre spines and projections. Simon redescribed Madagascar was visited between last half of 1880 to the same specimen in 1895 and added the first illus- early 1881. The juvenile specimen in Hamburg could trations of the cephalothorax and leg I (SIMON 1895: therefore, in theory, have been available to Simon figs. 951 – 953). No other species of Exechocentrus when he described Exechocentrus lancearius in 1889, has been described since Simon’s original description. but no direct or indirect evidence suggests that Simon In fact, it took 83 years before more specimens of Ex ever examined Hildebrandt’s specimen. echocentrus were ‘discovered’ (EMERIT 1978). EMERIT The first adult specimen, a female, of Excechocen (2000) provided an illustration of a juvenile speci- trus was collected by researchers from the California men from Ambohivoangy, Madagascar. He suggested Academy of Sciences near Andranomay in 2000. A that it was conspecific with Exechocentrus lancearius second adult female was collected by us in the vicin- based on the unusual morphology of the cephalotho- ity of Ranomafana National Park in 2009 (this speci- rax. A more detailed description of Exechocentrus, men was designated as the neotype of Exechocen based on immature females collected by J. Millot in trus lancearius Simon, 1889 by SCHARFF & HORMIGA 1946 and M. Emerit in 1963, was presented by EMERIT 2012). As far as we have been able to determine, no (1980), who also compared the juvenile specimens to other specimens of Exechocentrus exist in collec- the holotype (which consists of only a cephalothorax). tions. These two localities are 300 km apart and the The juvenile specimens all came from forest areas two adult specimens clearly represent two different east and northeast of the capital Antananarivo (Forêt species. Given the high diversity of spiders in Mada- d’Ambohivoangy, Forêt de la Mandraka and Forêt de gascar and how poorly known most of its arthropods Périnet). Emerit (2000) also suggested that Execho are (GRISWOLD 2003) it is very likely that further spe- centrus could be related to the mastophorines (Aranei- cies of Exechocentrus exist on the island. We describe dae-Cyrtarachninae, Mastophoreae – bolas spiders), here the neotype for Exechocentrus lancearius and particularly to the genus Acantharachne Tullgren, the foraging web of this species based on our field ob- 1910 from Madagascar and Africa, whose members servations. We also describe the specimen from An- also have bizarre spines on the carapace and large ab- dranomay as a new species of Exechocentrus. dominal tubercles. EMERIT (2000) thereby suggested that this Malagasy species may forage using a bola, although no direct observations supported the implied hunting strategy. During our world-wide search for specimens in Materials and methods museums we discovered a juvenile Exechocentrus in the Museum für Naturkunde of the Humboldt Uni- versity in Berlin. The museum catalogue entry reads “23919 Exechocentrus lancearius Sim.*, 1female, S. Specimens were examined and illustrated using a Centr. Madagaskar, Hildebrandt Typus, Ann. Soc. ent. Leica M205A stereoscopic microscope equipped with France (6) 8 p. 227, 1889.” According to the curator a Leica DFC420 camera and LAS software. Further (Dr. Jason Dunlop), a ‘*’ in the catalogue entry usu- details were studied and illustrated using a Leica ally denotes a type specimen, and the museum there- DMRM compound microscope with a drawing tube. fore assumed that it represented an original syntype. Photographs were taken with a BK+ Imaging System This is however impossible because Simon’s original from Visionary Digital (http://www.visionarydigital. description (SIMON 1889) only mentioned the cepha- com) equipped with a Canon EOS 7D camera. Single lothorax and legs. Later, SIMON (1895: p. 887) specifi- images were combined with Helicon Focus version cally mentioned that the only known specimen of Ex 5.0 to increase depth of field (www.heliconsoft.com, echocentrus lancearius is missing the abdomen. The Helicon Soft Ltd.). All morphological measurements Arthropod Systematics & Phylogeny 70 (2) 109 A B Fig. 1. Exechocentrus “lancearius” Simon, 1889 – Simon’s specimen (MNHN 8339). A: cephalothorax and legs, ventral view; B: cephalothorax and legs, dorsal view. Scale bars: 1 mm. A B Fig. 2. Exechocentrus “lancearius” Simon,