The taxonomy and diversity of Platerodrilus (Coleoptera, Lycidae) inferred from molecular data and morphology of adults and larvae

Larva, Pupa or Adult? The Female of Platerodrilus Case (Coleoptera: Lycidae)

The anatomy and genitalia of a larviform female were studied for the first time in the family Lycidae. The structure of the exo- and endoskeleton of a Platerodrilus female was found to be not much different from that of its larva, with external genital appendages barely differentiated. The reproductive system was found to include an unpaired spermatheca, and paired oviducts and ovaries. The structure of the integument was found to also be peculiar, with two layers of cuticle differing in structure. On the other hand, the labrum and mandibles were found to be quite unlike the larval ones: the labrum was undivided and the mandibles fully metamorphosed. This odd combination of morphological characters may be interpreted in two ways. First, it may be hypothesized that this is a pupa. However, its genital appendages are simpler than those of “normal” Lycidae pupae; wings or their rudiments are completely absent; there are very few features of imaginal morphology in the external structure. Therefore, we propose another hypothesis—this is the stage preceding the pupa, which Hinton (1946) designates as ‘prepupa’.

The first fossil immature of Elmidae: an unusual riffle beetle larva preserved in Baltic amber

Elmidae, riffle beetles, have both adult and immature stages that show specializations for water environments. Fossils of adults of Elmidae are already known from amber, however a record of immatures was so far lacking. We report here the first fossil larva of Elmidae, preserved in Baltic amber. To be able to access details of the body hidden by inclusions and "Verlumung" we conducted, in addition to optical documentation methods, micro-CT and synchrotron documentation methods. The larva is characterised by prominent dorso-lateral and lateral processes and a plate-like ventral operculum at the end of the abdomen. The new fossil has similarities in the general body shape and the prominent characters with some modern larvae of Elmidae. The posterior protrusions on the trunk end possibly represent gills, which would imply that fossil larvae of Elmidae also led a water-related life style similar to modern representatives.

Fossil evidence of elytra reduction in ship-timber beetles

Beetles (Coleoptera) comprise about one quarter of all described animal species. One of the main contributors to their evolutionary success is the elytra, or hardened forewings, which have protective functions while maintaining their ability to fly. Unlike other beetles, some ship-timber beetles (Lymexylidae) have extremely small elytra and largely exposed functional hindwings. There is little fossil evidence illuminating the evolutionary history of short elytra in lymexylids. Here, I report five well-preserved lymexylid fossils in mid-Cretaceous and Cenozoic ambers from Myanmar (ca. 99 million years ago [Mya]), Russia (ca. 44 Mya), and the Dominican Republic (ca. 16 Mya). Three Cretaceous fossils have strongly reduced, shortened elytra, with unexpected variation in elytral size and shape, whereas very small, modified elytra are found only in much younger Dominican amber. These morphologically diverse extinct lymexylids shed new light on the early origin and evolutionary history of elytra reduction and its diverse variation in the ship-timber beetles. Based on the striking morphological similarities with extant lymexylids, these extinct taxa might have had the same, or similar, ecological, behavioural, and flight modes as the extant ship-timber beetles.

The complete mitogenome of the trilobite beetle, Platerodrilus sp. (Elateroidea: Lycidae)

The nucleotide sequence of the complete mitogenome of the trilobite beetle, Platerodrilus sp. was determined. This is the first complete mitogenome reported for the family Lycidae (Elateroidea: Coleoptera). The newly determined sequence is 16,394 bp long and shows a relatively high AT content (76.2%). The gene arrangement of the trilobite beetle mt genome is the same found in other related beetle mitogenomes. The reconstructed tree recovered Elateroidea as a strongly supported monophyletic group but could not resolve phylogenetic relationships among studied elateroid families, including Lycidae.

Molecular phylogeny reveals high diversity, geographic structure and limited ranges in neotenic net-winged beetles platerodrilus (coleoptera: lycidae)

The neotenic Platerodrilus net-winged beetles have strongly modified development where females do not pupate and retain larval morphology when sexually mature. As a result, dispersal propensity of females is extremely low and the lineage can be used for reconstruction of ancient dispersal and vicariance patterns and identification of centres of diversity. We identified three deep lineages in Platerodrilus occurring predominantly in (1) Borneo and the Philippines, (2) continental Asia, and (3) Sumatra, the Malay Peninsula and Java. We document limited ranges of all species of Platerodrilus and complete species level turnover between the Sunda Islands and even between individual mountain regions in Sumatra. Few dispersal events were recovered among the major geographical regions despite long evolutionary history of occurrence; all of them were dated at the early phase of Platerodrilus diversification up to the end of Miocene and no exchange of island faunas was identified during the Pliocene and Pleistocene despite the frequently exposed Sunda Shelf as sea levels fluctuated with each glacial cycle. We observed high diversity in the regions with persisting humid tropical forests during cool periods. The origins of multiple species were inferred in Sumatra soon after the island emerged and the mountain range uplifted 15 million years ago with the speciation rate lower since then. We suppose that the extremely low dispersal propensity makes Platerodrilus a valuable indicator of uninterrupted persistence of rainforests over a long time span. Additionally, if the diversity of these neotenic lineages is to be protected, a high dense system of protected areas would be necessary.