Cryptonychini, Chapuis, 1875

Borowiec, Lech, Świętojańska, Jolanta & Sekerka, Lukáš, 2019, Revision of the tribe Cryptonychini (Coleoptera: Chrysomelidae: Cassidinae) of New Caledonia, Zootaxa 4690 (1), pp. 1-71 : 64-70

Diversity of Cryptonychini with emphasis on biogeography

As demostrated in the introduction chapter, Cryptonychini were until recently rather poorly known due to their specific habits and hidden way of life. The tribe currently contains 167 species and subspecies classified in 21 genera; 114 of them restricted to Australo-Papuan Region. Cryptonychus (30 species) and Gyllenhaleus (3 species) are restricted to tropical Africa; monotypic Xiphispa and Gestronella (6 species) are restricted to Madagascar with one species of Gestronella reported also from Reunion; monotypic Nesohispa Maulik, 1913 in Seychelles; Brontispa with the widest distribution ranging from Mauritius and Rodriguez (2 species), Philippines (1 species), Palau (1 species), New Guinea and surrounding islands (10 species), Somolons (1 species), Northern Australia (2 species), Micronesia (2 species), Samoa (1 species), New Caledonia (2 species), one species B. longissima ( Gestro, 1885) is distributed from New Hebrides to Taiwan and continental SE Asia but its original range was probably much smaller as it is an invasive pest of the coconut tree introduced to many places; Octodonta in Indonesia and Malaysia (3 species), Philippines (3 species), New Guinea and surrouding islands (3 species); monotypic Drescheria in Java; Callistola in Palau (3 species), Moluccas (3 species), Solomons (5 species), New Guinea and surrounding islands (30 species) and supposedly one species in Australia; Ceratispa (23 species), Ischnispa (2 species), Oxycephala (2 species), Palmispa (2 species), Plesispa (7 species) restricted to New Guinea, with exception of Plesispa reichei Chapuis, 1875 —a widespread pest of Nipa palm; Aulostyrax (2 species) and Calamispa (1 species) in Solomon Islands; and finally Caledonispa (5 species), Isopedhispa (4 species), Paratorquispa (1 species), Stephanispa (2 species), Teretrispa (4 species), Torquispa (2 species), and Wanatispa (2 species) restricted to New Caledonia. To sum up the majority of the diversity is in wet tropical areas of Australasia and the diversity rapidly decreases towards the west and is basically limited by the Huxleyʼs line, with the exception of two species found on Java. No native species occurs in mainland SE Asia, Sumatra or Borneo. In Africa most of the diversity is in tropical rainforests of western and central Africa, and Madagascar with a few species in the Mascarenes and Seychelles.

There are several possibilities for explaining present day dististribution of Cryptonychini , e.g. Gondwanan origin, vicariance or dispersion. Unfortunately none can be properly tested because of the lack of data. Up to day there is no fossil evidence for Cryptonychini nor any molecular phylogeny. Reconstruction of the molecular phylogeny is complicated because of unavailability of fresh material due relative rarity of the beetles caused by their hidden way of life. Although Gondwanan distribution is one of the alternatives we find it quite unlikely because the taxa are generally uniformly characterized by combination of low number of homoplasies with nearly no apomorphies.

Moreover most of genera as well as species within them are quite similar and rather difficult to be identified what could suggest dispersion. This can be also supported by their host plants as Pandanaceae were considered that they may have Gondwanan origin, however, recent studies suggest dispersion ( Gallaher et al. 2015). The disjunction of Afrotropical and Australasian Cryptonychini could be also explained by vicariance. This can be supported by the host plants as Heads (2010) explained the diversity of New Caledonian palms by vicariance. On the other hand, strictly speaking about the beetles, their disjunction could simply be an artefact of sampling effort considering that they were, with several exceptions, rather seldom collected as demonstrated by their absence in historic collections and the fact that J. L. Gressitt collected and described ca ⅔ of the Australasian known diversity working mainly in New Guinea. Therefore it would be desirable to reconstruct molecular phylogeny of Cryptonychini to better understand their diversity and distribution pattern.

The biogeography of New Caledonia is complicated and the opinions changed rapidly over the past decades (e.g. Grandcolas 2016, Heads 2018). Currently it is widely accepted that New Caledonia was at least partly submerged. Also more and more studies support that many of the New Caledonian biota can be explained by dispersion, which however does not explain the presence of basal organisms such as Amborella Baill. (e.g. Heads 2018).