Isanopus

Introduction

The xanthopygine genus Isanopus occurs in tropical and montane rainforests from Mexico to Brazil. The genus is rare in collections and this may be due to the habitat preferences of the species. Most recent materials have been collected in treefall litter, with a very small number of specimens (less than ten) collected in flight intercept or malaise traps.

Characteristics

Isanopus can be distinguished from all other xanthopygine staphylinids by the following  characters: 

• antennomeres 5–10 are elongate and slender, typically at least 2.5 times longer than wide, although in I. sahlbergi  and I. eptaskouros less than that 
• paramere reduced, generally less than half the length of the median lobe
• the punctuation pattern of the pronotum: the midline of the pronotum is impunctate and there is a single row of punctures on each side of the midline separated by a distance of at least 2–3 punctures from the more lateral rows, the distance between those rows small, usually 0.5–1 puncture, and the antero-lateral parts of the pronotum are densely punctuated
  

  Click on an image to view larger version & data in a new window

  

  From left to right: antennae of I. ashei and punctuation pattern of I. hinojosai © 2008 Stylianos Chatzimanolis

  

  Aedeagus of I. ashei showing the reduced paramere. © 2008 Stylianos Chatzimanolis

Isanopus looks superficially similar to some species of Xanthopygus (for example: X. alienus Bernhauer, 1905, X. calidus (Erichson, 1839), X. chrysopygus (Nordmann, 1837), X. cyanelytrius (Perty, 1830), X. elegans Bernhauer, 1905 and X. flohri Sharp, 1884) but can be easily distinguished from them by the general morphology of the head (in Xanthopygus the temporal area posterior to the eyes greatly expanded), as well as the other diagnostic characters of the genus. Additionally, Oligotergus mexicanus (Sharp, 1884) and O. prolixus (Sharp, 1884) have superficially similar antennae, but they can be easily distinguished from Isanopus by the usually densely punctuated pronotum, and the shape of the aedeagus with the paramere considerably longer than the median lobe.

Discussion of Phylogenetic Relationships

A phylogenetic analysis of 19 adult morphological characters from six ingroup taxa resulted in a single most parsimonious tree (Chatzimanolis 2008). Isanopus is robustly hypothesized to be monophyletic with high bootstrap and Bremer support values. Despite the absence of any homoplasy on the tree, the characters used in the analysis do not provide enough phylogenetic resolution to determine the position of I. sahlbergi and I. tenuicornis. It is worth mentioning here that I. ashei, I. hinojosai and I. sallaei are distributed exclusively in Central America in contrast to the three other species of Isanopus that are distributed in South America.

References

Chatzimanolis S. 2008. A revision of the neotropical beetle genus Isanopus Sharp, 1876 (Coleoptera: Staphylinidae: Staphylinini). J. Nat. Hist. 42(25-28): 1765-1792.

Information on the Internet