Research Article |
Corresponding author: Michael S. Caterino ( mcateri@clemson.edu ) Academic editor: Jan Klimaszewski
© 2018 Michael S. Caterino, David R. Maddison.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Caterino MS, Maddison DR (2018) An early and mysterious histerid inquiline from Cretaceous Burmese amber (Coleoptera, Histeridae). ZooKeys 733: 119-129. https://doi.org/10.3897/zookeys.733.23126
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We describe a new genus and species of Histeridae from Upper Cretaceous Burmese amber, Amplectister tenax Caterino & Maddison, gen. & sp. n. This species represents the third known Cretaceous histerid, which, like the others, is highly distinct and cannot easily be placed to subfamily. It exhibits prosternal characters in common with Saprininae, but other characters appear inconsistent with this possibility. The abdominal venter is strongly concave, and the hind legs are enlarged and modified for grasping. We hypothesize that this represents the earliest example in Histeridae of modifications for phoresy on social insects.
amber fossil, Upper Cretaceous, phoresy, inquiline
The early diversification of the beetle family Histeridae is poorly understood. Phylogenetic relationships among extant taxa have been difficult to resolve (
Recent work has begun to reveal a much greater diversity of early Histeridae than previously suspected. Until quite recently the family’s fossil record extended no more than about 40 MYBP (
The original piece of amber (Fig.
Amplectister tenax Caterino & Maddison, sp. n.
Many features distinguish this extinct genus: overall body form quite elongate and flattened (Figs
The genus name (masculine) means ‘the hugging Hister’, referring to its modifications for grasping, from the Latin amplexus.
Holotype specimen, of unknown sex; type locality: Northern Myanmar: probably Hukawng Valley, collected in 2016; deposited in Oregon State Arthropod Collection, specimen OSAC_0002900057. The specimen was purchased by DRM from Yanling Ying in January 2017. Most of his specimens are from the Noije Bum mine or nearby, Kachin State; a few are from around Nam Sakhaw in Sagaing Division (NW of Haungpa); fewer are from elsewhere in other areas in Kachin State.
Many body surfaces encrusted with thin off-white granular substance and/or thin film of air; textures and surface sculpture difficult to assess. An oblique planar fracture below the anterior part of the body distorts some observations of ventral anterior structures.
Total body (pronotum + elytra) length: 1.41 mm; maximum (humeral) width: 1.02 mm (for all measurements see Table
Frons broad, anteriorly prominent (Figs
Pronotum (Figs
Scutellum present, small, triangular; elytra (Fig.
Propygidium (Fig.
Prosternum (Figs
Mesoventrite (Figs
Abdominal venter (Fig.
Legs (Figs
Measurement | mm |
---|---|
Pronotum+elytral (PE) length | 1.41 |
Pronotal length | 0.41 |
Pronotal width | 0.98 |
Elytral length | 1.00 |
Humeral width | 1.02 |
Propygidium length | 0.10 |
Pygidium length | 0.24 |
Head width | 0.37 |
Prosternum length | 0.33 |
Mesoventrite length | 0.10 |
Metaventrite length | 0.37 |
Profemur length | 0.35 |
Protibia length | 0.29 |
Mesofemur length | 0.47 |
Mesotibia length | 0.43 |
Metafemur length | 0.73 |
Metatibia length | 0.57 |
The species name means tenacious, referring to its grasp, from the Latin tenax.
In the same piece of amber as the original specimen were one beetle of the family Eucinetidae (Fig.
Histerid systematics has relied heavily on the form of the prosternum for classification and phylogenetics (
Amplectister shows some similarities to the recently described Cretonthophilus, sharing short subpyramidal antennal scapes, frontal carinae, concave sides of mandibles, subdepressed body form, elytral and pronotal lateral margins not colinear, and epipleurae carinate, as well as various features of the legs (profemora able to receive protibia, all tibiae flattened, weakly expanded apically, with spines along inner margins). However, our limited understanding of early histerid phylogeny cannot yet distinguish whether any of these could be synapomorphies of the two. Furthermore, significant differences are numerous. The form and manner of reception of the antennal club on the prosternum is very different, with Cretonthophilus having a hypomeral cavity far removed from the prosternal lobe. The form of the antennal club itself is also quite different, with that of Cretonthophilus showing deep and distinct sutures between the club’s three antennomeres. Cretonthophilus also has an elongated prosternal lobe, and distinct protibial grooves for reception of its protarsus. These phylogenetically compelling characters suggest that Cretonthophilus and Amplectister occupy distinct branches of early histerid phylogeny. Regarding possible similarities with Pantostictus burmanicus, very little can be said due to the lack of phylogenetically informative characters originally described, or visible in the type specimens, which we have recently examined.
The remarkable ventral modifications of Amplectister seem clearly adapted for grasping. Grasping in insects serves several purposes and takes a variety of forms. It seems unlikely that the purpose in Amplectister is for grasping prey, since in other insects that grasp prey the raptorial modifications are on anterior portions of the body (e.g., in mantises, mantispids, and various Heteroptera), whereas in Amplectister the grasping structures are on posterior regions of the body. Some insects show modifications for grasping various substrates, to resist removal by predators, or to prevent being dislodged (elongate legs and enlarged tarsal claws in lotic systems, for example). As the grasping modifications involve only the hind legs in Amplectister, rather than all legs, this also seems unlikely.
The posterior location of these modifications on the body suggest courtship as another possible function, and in many insects males exhibit grasping modifications for retaining hold and position on a mate (e.g.
We suggest instead that the most likely explanation is related to some form of inquilinism. Histeridae exhibit a variety of symbiotic relationships with other organisms, as obligate inhabitants of bird and mammal nests, as well as guests in ant and termite colonies (
We would like to thank Mike Ivie for helpful suggestions, and George Poinar for allowing DRM to examine the type specimens of Pantostictus from his personal collection. We also thank two anonymous reviewers whose comments improved the manuscript.