Systematics of the Madagascar Anelosimus spiders: remarkable local richness and endemism, and dual colonization from the Americas

Abstract

Despite the alarming rates of deforestation and forest fragmentation, Madagascar still harbors extraordinary biodiversity. However, in many arthropod groups, such as spiders, this biodiversity remains mostly unexplored and undescribed. The first subsocial Madagascan species of the theridiid spider genus Anelosimus were described in 2005 when six new species were found to coexist in the Périnet forest fragment within Andasibe-Mantadia NP. However, this discovery was based only on a few specimens and the extent of this Madagascan radiation has remained unknown. We here report on a thorough survey of >350 colonies from Périnet, and three pilot surveys into additional Madagascar forests (Ambohitantely, Ranamofana, and Montagne d’Ambre). The morphological, molecular and natural history data from these surveys facilitated a revised taxonomy and phylogenetic hypothesis of Madagascan Anelosimus. This subsocial clade currently comprises six previously known (Anelosimus andasibe Agnarsson & Kuntner, 2005, Anelosimus may Agnarsson, 2005, Anelosimus nazariani Agnarsson & Kuntner, 2005, Anelosimus sallee Agnarsson & Kuntner, 2005, Anelosimus salut Agnarsson & Kuntner, 2005, Anelosimus vondrona Agnarsson & Kuntner, 2005) and 10 new species: Anelosimus ata sp. n., Anelosimus buffoni sp. n., Anelosimus darwini sp. n., Anelosimus hookeri sp. n., Anelosimus huxleyi sp. n., Anelosimus lamarcki sp. n., Anelosimus moramora sp. n., Anelosimus tita sp. n., Anelosimus torfi sp. n., Anelosimus wallacei sp. n.. With the exception of Anelosimus may and Anelosimus vondrona, all other species appear to be single forest endemics. While additional sampling is necessary, these data imply a much higher local richness and endemism in Madagascan forests than in any other comparable area globally. The phylogenetic results establish a sister clade relationship between the subsocial Anelosimus in Madagascar and the American ‘eximius group’, and between the solitary Anelosimus decaryi on Madagascar and a solitary American clade. These findings imply duplicate colonizations from America, an otherwise rare biogeographical pattern, calling for more detailed investigation of Anelosimus biogeography.

Phylogeography of a good Caribbean disperser: Argiope argentata (Araneae, Araneidae) and a new ‘cryptic’ species from Cuba

“…n. and Argiope argentata can be diagnosed from one another, and other related Argiope species, on the basis of the following unique, synapomorphic, mtDNA nucleotide substitutions at the following standard DNA barcode alignment positions in each species (following Agnarsson et al (2015)):…”

Limited role of character displacement in the coexistence of congenericAnelosimusspiders in a Madagascan montane forest

“…In Madagascar, however, initial sampling yielded six subsocial species building very similar webs within a single montane rainforest fragment (Fig. ; Agnarsson and Kuntner ); more intensive sampling revealed the coexistence of 10 Anelosimus species in this habitat (Agnarsson et al ). This sympatric assemblage of species belongs to a monophyletic Madagascar radiation (Agnarsson et al , ), but it is unclear whether or not they are each other's closest relatives at local scales, what the age of this radiation is, and if they show any evidence of character displacement and microhabitat preferences.…”

“…To test the monophyly and placement of Madagascan Anelosimus , and the relationship among Madagascan species, we added 2–3 specimens of each putative species to the global Anelosimus phylogeny presented in Agnarsson (). Further, to test the monophyly of the species assemblages in each forest and thus test the allopatry hypothesis, we added specimens of species currently being described (Agnarsson et al ) from three other Madagascan forests: the Ambohitantely Reserve (a total of eight specimens representing four putative species), Montagne d'Ambre (a single available specimen), and Ranamofana (multiple specimens of a new species). We extracted DNA as described above, and, in addition to COI, amplified two additional mitochondrial genes (16S, ND1) and two nuclear genes (28S, ITS2) using primers and protocols as described elsewhere (Agnarsson et al ).…”

Evidence for Miocene overwater colonization in CaribbeanCyrtognathaspiders

“…Amongst island systems some of the best studied in terms of biogeographic research are Hawaii 6–8 , Galapagos 9–11 , Azores 12–14 , Canary 15–17 and Solomon 18–20 islands, as well as large continental fragments such as Madagascar 21–23 and New Zealand 24–26 . However, the Caribbean island system 27–30 is the single most ‘published’ island system in biogeography literature (Google Scholar title hits 237 compared with 195 for the second, New Zealand).…”