Single Origin of the Mascarene Stick Insects: Ancient Radiation on Sunken Islands? Sven Bradler1* , Nicolas Cliquennois2 and Thomas R

Single Origin of the Mascarene Stick Insects: Ancient Radiation on Sunken Islands? Sven Bradler1* , Nicolas Cliquennois2 and Thomas R

Bradler et al. BMC Evolutionary Biology (2015) 15:196 DOI 10.1186/s12862-015-0478-y RESEARCH ARTICLE Open Access Single origin of the Mascarene stick insects: ancient radiation on sunken islands? Sven Bradler1* , Nicolas Cliquennois2 and Thomas R. Buckley3,4,5 Abstract Background: The study of islands as model systems plays a key role in understanding many evolutionary processes. Knowledge of the historical events leading to present-day island communities is pivotal for exploring fundamental mechanisms of speciation and adaptation. The remote Mascarene archipelago (Mauritius, Réunion, Rodrigues), considered to be the product of an age-progressive trend of north-to-south volcanic activity in the Indian Ocean, hosts a remarkably diverse, endemic and threatened concentration of flora and fauna that has traditionally been considered to be biogeographically related to Madagascar and Africa. To explore the evolutionary diversity of the Mascarene stick insects (Phasmatodea), we constructed a global phylogeny from approximately 2.4 kb of mitochondrial and nuclear sequence data of more than 120 species representing all major phasmatodean lineages. Results: Based on the obtained time-calibrated molecular tree we demonstrate that the current phasmid community of the Mascarene archipelago, which consists of members of four presumably unrelated traditional subfamilies, is the result of a single ancient dispersal event from Australasia and started radiating between 16–29 million years ago, significantly predating the age of Mauritius (8–10 million years). Conclusions: We propose that the Mascarene stick insects diversified on landmasses now eroded away, presumably to the north of Mauritius. In consequence, ancient islands have probably persisted in the Indian Ocean until the emergence of Mauritius and not only served as stepping stones for colonisation events during sea-level lowstands, but as long-lasting cradles of evolution. These ancient landmasses most likely allowed for adaptive speciation and served as significant sources of diversity that contributed to the biomes of the Mascarene archipelago and the megadiverse Madagascar. Background the Indian Ocean that separated from Madagascar The Indian Ocean harbours a number of major terrestrial about 61–83.5 million years ago (mya) [6]. Although biodiversity hotspots including Madagascar and nearby less well-studied, biologically speaking, than the Hawaiian archipelagos of the Comores, Seychelles and Mascarenes and Galápagos Islands, the Mascarene archipelago appears [1]. While Madagascar and the granitic Seychelles are of to be likewise rich in biodiversity, notably in endemics [7]. old continental origins, the Mascarene Islands Mauritius Unfortunately, the Mascarene Islands, Mauritius and and Réunion have been shown to be much younger as the Rodrigues in particular, have already lost a significant result of the similar process of plate movement over a sta- amount of this endemic diversity since human settlement tionary volcanic hot spot that formed the Hawaiian archi- in the 17th century due to habitat destruction [7, 8]. pelago and the Galápagos Islands in the Pacific [2–5]. Understanding the biogeographic processes leading to Recent studies suggest the presence of Precambrian, albeit endemic diversity is crucial both to interpretation of currently submerged continental fragments underneath their evolutionary history and to the establishment of the Mascarene Plateau covered by magmatic deposits in conservation strategies [9]. The majority of the extant species diversity of the Mascarene Islands has been de- scribed as the result of recent colonisations from outside * Correspondence: [email protected] the archipelago and divergence within the contemporary 1Johann-Friedrich-Blumenbach-Institute of Zoology and Anthropology, Georg-August-University Göttingen, Berliner Str. 28, 37073 Göttingen, island system, often with immigrating lineages derived Germany from Madagascar and Africa [10–14]. Yet, unexpectedly, Full list of author information is available at the end of the article © 2015 Bradler et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bradler et al. BMC Evolutionary Biology (2015) 15:196 Page 2 of 10 numerous faunal elements are related to more remote We sampled ~2.4 kb of nuclear and mitochondrial regions such as Asia and the Indo-Pacific [7, 15–18]. In sequence data from 121 phasmatodean individuals (repre- some taxonomic groups like skinks and stick insects, colo- senting 120 spp.) and 1 individual (Metoligotoma)ofthe nisations of the Mascarenes appear to have involved long- outgroup Embioptera (webspinners). The relaxed clock distance dispersals from the Australian region ranging model placed the root on the branch between the Embi- between 5600–7000 km [19, 20]. optera and Phasmatodea (Fig. 2), consistent with previous Stick and leaf insects (insect order Phasmatodea) are insect phylogenies [25–29]. The next split was between particularly informative organisms for historical biogeo- Timema and the Euphasmatodea, again consistent with graphic research due to their limited dispersal capabilities, previous phylogenetic reconstructions of the Phasmatodea manageable species numbers and ease of sampling. Phas- [25, 30]. The recovered phylogeny was consistent with matodeans are predominantly large nocturnal herbivores, current phylogenetic hypotheses on stick and leaf insects exhibiting extreme forms of plant mimicry (Fig. 1), with including some ambiguities at deeper nodes, e.g., the very limited flight capability. Stick insects must be con- radiation of major phasmatodean lineages, which are sidered as being non-volant although they often possess currently poorly resolved [24, 31, 32]. We observed strong wings, which they generally use to control descent from support for several monophyletic groups, including Aschi- the canopy rather than for sustained flying [21]. The phasmatinae (Maximum likelihood bootstrap [MLB] = 98, Mascarene islands harbour stick insects from four Bayesian posterior probability [BPP] = 0.99), Cladomorphi- traditional subfamilies and one taxon incertae sedis nae (MLB = 94, BPP = 0.98), Lanceocercata (MLB = 97, [22, 23], suggesting repeated transoceanic colonisations of BPP = 0.98), Lonchodinae (BPP = 0.97), Pharnaciini the archipelago by unrelated phasmatodean lineages. (MLB = 75, BPP = 0.99), Phylliinae (MLB = 100, BPP = 0.99) However, previous studies demonstrated that geographical and Stephanacridini (MLB = 98, BPP = 0.99). Clades less distribution rather than traditional classification and mor- well supported, but also monophyletic in accordance phological similarity reflects the evolutionary relationships with previous studies [24, 30–32] are Heteropteryginae among stick and leaf insects [20, 24]. Here we provide (BPP = 0.93), Necrosciinae (BPP = 0.94), Pseudophasmati- another example of an unexpected adaptive radiation of nae (BPP = 0.91) and Diapheromerinae (BPP = 0.63). Some stick insects in geographical isolation and that further- further, previously unrecognized groupings that receive more, the age of this radiation predates the origin of the good support comprise a Malagasy lineage Achrioptera + islands that these species currently inhabit. Anisacanthidae + Damasippoididae (MLB = 61, BPP = 0.98) and an African clade of paraphyletic Gratidiini (Gratidia, Results Zehntneria)+Phalces (Bacillinae) (MLB = 100, BPP = 0.98). This study represents the most comprehensive study Bacillidae (Antongilia, Phalces, Xylica) and Pachymorphinae addressing the global phylogeny of stick and leaf in- (Clonaria, Gratidia, Pachymorpha, Sceptrophasma, Spino- sectstodateandthefirstonetoincludearepresen- tectarchus, Zehntneria) were recovered as polyphyletic. tative sampling from landmasses of the Indian Ocean, Within Lanceocercata we corroborated earlier findings e.g., from Madagascar and the Mascarene archipelago. that Platycraninae is monophyletic (MLB = 100, BPP = 1) Fig. 1 Photos of Mascarene stick insects. a Couple of Apterograeffea reunionensis (Platycraninae) from Réunion. b Male of Epicharmus marchali (Xeroderinae) from Mauritius. c Female of Rhaphiderus spiniger (Tropidoderinae) from Réunion Bradler et al. BMC Evolutionary Biology (2015) 15:196 Page 3 of 10 Fig. 2 (See legend on next page.) Bradler et al. BMC Evolutionary Biology (2015) 15:196 Page 4 of 10 (See figure on previous page.) Fig. 2 Chronogram of the sampled stick insect specimens with taxa distributed across the Indian Ocean highlighted in tones of red. Numbers at nodes indicate bootstrap values (left) and clade posterior probabilities (right); grey bars show 95 % highest probability density. Circled numbers refer to fossil calibration points: (1) Renphasma [56], (2) Eophasma [61], (3) fossil Malacomorpha [63], (4) fossil Clonistria [63]. Pl Pliocene, Qu Quaternary including Graeffea seychellensis, but excluding Apterograef- endemic stick insect from Rodrigues, Xenomaches incom- fea, and a clade comprising all taxa from New Caledonia modus (Butler, 1876), which is

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