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| (b) female of Phyllium elegans, (d) female of Phyllium hausleithneri, (e) couple of Phyllium rubrum and (f) male of Phyllium letiranti. in Bank, Cumming, ... et Bradler, 2021. Photographs by Bruno Kneubühler. |
Abstract
The insect order Phasmatodea is known for large slender insects masquerading as twigs or bark. In contrast to these so-called stick insects, the subordinated clade of leaf insects (Phylliidae) are dorso-ventrally flattened and therefore resemble leaves in a unique way. Here we show that the origin of extant leaf insects lies in the Australasian/Pacific region with subsequent dispersal westwards to mainland Asia and colonisation of most Southeast Asian landmasses. We further hypothesise that the clade originated in the Early Eocene after the emergence of angiosperm-dominated rainforests. The genus Phyllium to which most of the ~100 described species pertain is recovered as paraphyletic and its three non-nominate subgenera are recovered as distinct, monophyletic groups and are consequently elevated to genus rank. This first phylogeny covering all major phylliid groups provides the basis for future studies on their taxonomy and a framework to unveil more of their cryptic and underestimated diversity.
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| Fig. 1: Photographs of leaf insect specimens (Phylliidae). a, b phenotypic variations of Phyllium elegans females, c female of Phyllium letiranti, d female of Phyllium hausleithneri, e couple of Phyllium rubrum and (f) male of Phyllium letiranti. Photographs by Bruno Kneubühler. |
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| Fig. 6: Schematic overview of the historical biogeography of Phylliidae. a–c Palaeogeography of SE Asia and the SW Pacific (adapted from Hall72) showing the northward movement of the Sahul shelf and the drift of the fragments of the Philippines and Wallacea. The dotted line in (a) indicates which landmasses will be connected via the Vitiaz arc (~30 mya). Note that the depiction of landmasses does not necessarily imply that they were emergent at that time. Both Sunda and Sahul shelves may have been exposed as dry land during low sea–level stands. d Main dispersal events of extant leaf insects with origin in the Australasian/Pacific region (0). The numbering illustrates our suggested chronological order of colonisation. Colour code corresponds to Fig. 5. Bo Borneo, Ha Halmahera, Ja Java, Pa Palawan, NC New Caledonia, NG New Guinea, SCA South Caroline arc, So Solomon Islands, Su Sulawesi, Sum Sumatra. |
Sarah Bank, Royce T. Cumming, Yunchang Li, Katharina Henze, Stéphane Le Tirant and Sven Bradler. 2021. A Tree of Leaves: Phylogeny and Historical Biogeography of the Leaf Insects (Phasmatodea: Phylliidae). Communications Biology. 4: 932. DOI: 10.1038/s42003-021-02436-z
