Project description - Systematic revision of Vatesus Sharp, 1876

By naming and classifying organisms systematics is the backbone of biology and it provides the basic vocabulary for all biological research. Systematics involves two interdependent disciplines – taxonomy and phylogenetics. Taxonomy is the science of recognizing, describing and naming species, while phylogeny studies the relationship of taxa, i.e. their evolutionary history. I aim to provide information about both aspects for Vatesus beetles. Thanks to project funding by the DFG, I started the project in November 2019. Let me know if you have any suggestions or if you would like to join - collaborations are very welcome. 

Tomographic scan of Vatesus cf. clypeatus sp. 2.  Highlighted in color is the male genitalia (aedeagus). Scan: Sebastian Schmelzle

Ambiguity in Vatesus taxonomy - I have studied army ant-associated insects since 2008 - first on Southeast Asian Leptogenys army ants and since 2013 on Neotropical Eciton army ants. Ever since I started my work, I came across difficulties in species identifications. This is because the taxonomy of many symbiont taxa is shaky. Notable among Neotropical army ant symbionts were one of the most abundant and charismatic taxa: rove beetles of the genus Vatesus Sharp, 1876 (Staphylinidae: Tachyporinae: Vatesini). As outlined here, many aspects of the biology of Vatesus beetles have been uncovered, while, at the same time, their taxonomy has remained untouched since the latest revisions by Borgmeier and Seevers in the late 1950s and early 1960s. One additional species was later described by Kistner in 2006, Vatesus berghoffae in honor of Stefanie Berghoff's research on army ants and their associated arthrpods. The genus contains 26 formally described species. For several reasons, however, species identifications of Vatesus is extremely problematic, and essential work is needed to illuminate the true diversity of these remarkable beetles . By modern standards, historical species descriptions lack sufficient detail to capture phenotypic variation in the group. For example, few measurements are ever provided in these earlier species descriptions, aside from total body, despite the fact that the quantitative dimensions of body parts differ substantially between taxa. Crucially, genitalia descriptions and illustrations, which provide universally accepted essential characters for beetle taxonomy, are missing for all but two species. Species-level identifications of newly collected specimens can  thus not be trusted based on prior taxonomic work on Vatesus, creating a serious impediment to any kind of research on these beetles.

In 2013 and 2014, I have studied Vatesus beetles at one location, La Selva Biological Station in  Costa Rica. During these studies it became clear through DNA barcoding and genitalia dissection that distinct Vatesus species can be extremely similar in their external morphology (article). Hence, my previous studies demonstrated the need for a taxonomic revision of this staphylinid genus using multiple complementary character systems.  I will undertake this endeavor to form the crucial foundation for future biological studies of these fascinating symbiotic beetles.

Neivamyrmex associated Vatesus species.

Vatesus characteristics - Vatesus beetles are symbionts of Neotropical army ants of the subfamily Dorylinae (Cheliomyrmex, Eciton, Nomamyrmex, Neivamyrmex, and Labidus). Their body shape is limuloid (horseshoe crab-shaped) - a protective ecomorphology that has evolved convergently in many myrmecophilous beetle groups (see Joe Parker's excellent review). The tribe Vatesini contains the single genus Vatesus.  The genus differs from other tachyporine staphylinids primarily by its specialized head structure and by its association with army-ant societies. 

There is no doubt that many Vatesus species still await scientific discovery and description. Most army ants, and in particular their symbiont fauna, are notoriously understudied. Take for example subterranean army ants where there is little knowledge about any aspect of their biology. There are over 100 species of Neivamyrmex ants, but Vatesus species have only been described as symbionts from three of them. On the right you can see four species of Vatesus with associated Neivamyrmex ants collected at La Selva, Costa Rica. As Vatesus beetles are rather specific to one or a few host ants as far as we know (see Vatesus biology), it seems plausible that multitude of species await discovery and formal description. Flight interception traps might be a good method to collect dispersing Vatesus beetles of subterrean army ants, and over 100 specimens were collected this way. I am looking forward to have a look at these samples, which are deposited at the Snow Entomological Museum.

 

Seevers characterized the genus as follows:

„Head capsule so modified that most of the vertex, the clypeus, and the labrum lie in a horizontal plane and are visible only in ventral view; head so covered by the large convex pronotum that only a small part of the vertex and the large, reniform eyes are visible from the front; mouthparts directed caudad when head is at rest; the species are obligate ecitophiles."

Project objectives and methods - The aim of the project is to provide a systematic revision of the rove beetle genus Vatesus. Species boundaries will be uncovered  by detecting and defining interspecifically non-overlapping diagnostic characters. For this, I will combine morphological characters with DNA barcodes. Diagnostic morphological characters will be robustly defined and quantified based on synchrotron-micro-CT scans (SRµCT), allowing for qualitative and quantitative analyses of beetles’ external and internal morphology. Consistent differences in diagnostic characters across geographic ranges will be interpreted as an absence of gene flow between putative taxa, thus supporting their interpretation as distinct species. Evolutionary relationships among species will finally be resolved via a molecular phylogenetic analysis.  Below I outline the steps involved in the project’s workflow.

Workflow of the Vatesus project. 1. First step is to obtain specimen loans from museums and individual’s collections. 2. Type material will be photographed, and qualitative characters of external morphology studied. 3. The next step is to extract DNA from entire specimens for DNA analyses using both type specimens and undescribed material. 4. Clustering of genetic data will unveil possible candidate species. 5. Representative specimens of each candidate species and all holotypes will be scanned using synchrothron X-ray micro-tomography (SRµCT). 6. Finally, acquired data will be analysed together using multivariate statistics. 

Functional morphology of Vatesus legs - SRµCT will allow me to additionally reconstruct functional properties of Vatesus anatomy. Here is an example of a front-leg. Muscle tissue (left) and 3-D model of a Vatesus foreleg movement (right). Vatesus anatomy is adapted to survive occasional ant attacks. Their teardrop-shaped, slippery body with extended pronotum and elytra protects them from injuries. This is because beetles literally slip away during ant attacks. Additionally, the legs have a protective morphology and can be retracted so that no points of attack are available for the ants. Vatesus legs are quite robust, compact and powerful. Extensive muscle tissue (see left image) allows swift movements and endurance. Vatesus beetles must follow host emigrations to keep host contact. Following host emigrations night after night over hundreds of meters is quite a challenge  for such small critters, especially if you have such a robust and massive body.   

3-D models created by Sebastian Schmelzle

Vatesus cf. clypeatus,

 collected in an emigration of Eciton lucanoides at La Selva Biolog. Stat., CR

Species list - The following list gives an overview of all described species (adapted from Seevers). The holotype of the genus Vatesus (V. latitans) was described by Sharp for a single Brazilian specimen in 1876. Further species were described by Wasmann, Bruch, Mann, Bernhauer, Seevers, Borgmeier, and Kistner. Synonyms of the genus are Xenocephalus and WasmannotheriumNote that some species were synomized (e.g., V. panamensis, V. henrici-schmidti are synomized with  V. clypaetus). Vatesus clypeatus is described as a species complex.

V. amapaensis Borgmeier, 1961; Host: Labidus praedator F. Smith; Locality: Brazil Amapá (Oiapoque).

V. argentinus Bruch, 1932, Seevers, 1958, Borgmeier, 1961; Host: Probably Labidus coecus Latreille; Locality: Argentina, Brazil

V. berghoffae Kistner 2006, Host: Cheliomyrmex morosus; Locality: Panama.

V. brasiliensis Seevers 1958; Host: unknown; Location: Argentina: Misiones, Brazil: Rio de Janeiro.

V. brevicornis Wasmann, 1925; Host: Labidus coecus Latreille; Locality: Brazil: Minas Gerais.

V. cincinnati Borgmeier, 1961; Host: Neivamyrmex pilosus F. Smith; Locality: Brazil: Mato Grosso (Cuiabá).

V. clypeatus Wasmann, 1887; Hosts: Eciton burchellii Westwood, Eciton hamatum Fabricius, Eciton vagans Olivier, Eciton mexicanum Roger; Locality: Brazil: Santa Catarina (Blumenau), Panama: Barro Colorado Island, Costa Rica: Hamburgfarm, Mexico: Chiapas (Jetja, and Modelo Forest) and Oaxaca (Loma Bonita).

V. panamensis Mann, 1925; Host: Eciton hamatum Fabricius; Locality: Panama: Barro Colorado Island.

V. henricischmidti Wasmann, 1929; Host: uncertain, Eciton hamatum and/or E. vagans (see Borgmeier); Locality: Costa Rica: La Caja (corrected by Borgmeier).

V. gemellus Borgmeier, 1961; Host: Nomamyrmex esenbecki Westwood (a number of records), and Eciton mexicanum Roger (1 record); Locality: Brazil: Golds (Campinas).

V. gigas Wasmann, 1909, Seevers, 1958, Borgmeier, 1961; Host: Eciton rapax F. Smith; Locality: Brazil: Amazonas (Ponte Alegre), Colombia: Putumayo.

V. goeldii Wasmann, 1900, Holmgren, 1908, Seevers, 1958, Borgmeier 1961; Host: Neivamyrmex leffionis F. Smith; Location: Brazil: Rio de Janeiro (Teresopolis), Santa Catarina (Joinville), Parana (Rio Negro).

V. goianus Borgmeier, 1961; Host: Eciton dulcium Forel; Location: Brazil: Goiás (Campinas).

V. gracilis Borgmeier, 1961; Host: Nomamyrmex hartigi Westwood; Location: Brazil: Goiás (Campinas).

V. latitans Sharp, 1876, Seevers, 1958, Borgmeier, 1961; Host: Eciton quadriglume Haliday; Locality: Brazil: Paraná, Santa Catarina (Joinville).

V. limulus Wasmann, 1900, Seevers, 1958; Borgmeier, 1961; Host: Eciton quadriglume Haliday; Locality: Brazil: Rio de Janeiro (Teresopolis).

V. lucidus Mann, 1926, Seevers, 1958; Host: Neivamyrmex gibbatus Borgmeier; Locality: Costa Rica: Hamburgfarm, Panama: Barro Colorado Island, British Honduras: Rio Temas.

V. mexicanus Bernhauer, 1917, Seevers, 1958; Host: Labidus coecus Latreille; Locality: Mexico: Vera Cruz (Cordoba), Costa Rica: San Jose.

V. paraguayensis Seevers, 1958; Host: Labidus sp.; Location: Paraguay: Horqueta.

V. perplexus Borgmeier, 1961; Host: Labidus praedator F. Smith; Location: Brazil: Sao Paulo (Juquia).

V. praedatorius Seevers, 1958; Host: Labidus praedator F. Smith; Locality: Panama: Barro Colorado Island, Costa Rica: Hamburgfarm.

V. punctipennis Bernhauer, 1917, Seevers, 1958, Borgmeier, 1961; Host: Labidus praedator F. Smith; Locality: Brazil: Rio de Janeiro, Minas Gerais (Passa Quatro), Santa Catarina (Nova Teutonia), Sao Paulo (Boracea), Goids (Campinas).

V. rettenmeyeri Seevers, 1958, Borgmeier, 1961; Host: Nomamyrmex esenbecki crassicornis F. Smith; Locality: Panama: Barro Colorado Island.

V. rufus Wasmann, 1909, Seevers, 1958, Borgmeier, 1961; Hosts: Labidus coecus Latreille, Nomamyrmex hartigi and N. esenbecki; Locality: Brazil: Rio Grande do Sul (Sao Leopoldo), Santa Catarina (Nova Teutonia), Goiás (Campinas).

V. schmalzi Wasmann, 1900, Seevers, 1958, synonymized with V. latitans.

V. schneirlai Seevers, 1958, Borgmeier, 1961; Host: Nomamyrmex esenbecki crassicornis F. Smith; Locality: Panama: Barro Colorado Island.

V. schuppi Wasmann, 1890, and 1895, Seevers, 1958, Borgmeier, 1961; Host: Labidus praedator F. Smith; Locality: Brazil: Rio Grande do Sul (Sao Leopoldo), Argentina: Chaco.

V. simulans Borgmeier, 1961; Host: Labidus coecus Latreille; Locality: Brazil: Golds (Campinas).

V. splendidus Wasmann, 1925, Seevers, 1958, Borgmeier, 1961; Host: Labidus coecus Latreille; Locality: Brazil: Santa Catarina (Blumenau and Nova Teutonia).

V. trilobita Wasmann, 1894, and 1900, Seevers, 1958, Borgmeier, 1961; Host: Labidus praedator F. Smith; Locality: Brazil: Rio de Janeiro (Teresopolis), Sao Paulo, Santa Catarina (Nova Teutonia).