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Pericompsus (Pericompsus) carinatus Erwin 1974

Comprehensive Description

provided by Smithsonian Contributions to Zoology
Pericompsus carinatus

TYPE-LOCALITY.—Rio Araguaia at Santa Isabel, Mato Grosso, Brazil.

TYPE-SPECIMENS.—The holotype female and one paratype (teneral male) are in CAS. Both were collected by B. Malkin in 1957.

DESCRIPTION.—Form (Figure 155): Similar to P. rorschachinus, but easily distinguished from all members of the incisus group by the multicarinate elytra and acutely angulate humeral base.

Color: Testaceous, elytral cloud slightly infuscated.

Head: Narrower across eyes than width of pronotum; frontal furrows moderately impressed and evenly arcuate, each extended to posterior margin of eye; eyes large and prominent.

Pronotum (Figure 155): Large and nearly quadrate, sides shallowly sinuate in basal half; base narrowly lobed; hind angles about right; side margins narrowly reflexed; disc moderately convex and rugose.

Elytra: Each elytron with 7 punctate-striate interneurs; punctures contiguous and striate; each interval deeply concave, thus interneurs carinate to apex, interneur 8 well impressed and foveate well anterior to middle; fovea small, smaller in diameter than width of elytral explanation; humeral margin acutely angulate at base, concave anteriorly and connected to carinate base of interneur 4; side margins moderately explanate, minutely setulose in basal fourth; chaetotaxy as in P. ephippiatus; plica long and well developed externally.

Microsculpture: Moderately impressed nearly isodiametric reticulation on entire dorsal surface, granulate on head and pronotum.

Genitalia: Not studied.

Size: Length, 2.76–2.96 mm; width, 0.96–1.20 mm; 2 types measured.

VARIATION.—The sample is too small to meaningfully assess variation.

NATURAL HISTORY.—The types were collected in July, one was very teneral and the other was subteneral.

ETYMOLOGY.—Latin adjective, carina, meaning “keeled” or “ridged,” refers to the appearance of the elytra of these beetles.

LOCALITY RECORDS (Figure 159).—I have seen only the two types from Rio Araguaia at Santa Isabel, Mato Grosso, Brazil.

Natural History

The species of Pericompsus are riparian inhabitants, or are at least hygrophilus. All available records indicate proximity to streams, rivers, or (in Australia) wet places away from the actual river edge. The few records of substrate preference are sterile gravel bars, wet sandy clay, “swampy ground,” and sandbanks. From these data and some morphological similarities (elytral structure) I think it is probable that this group of Tachyina is one of the tropical ecological replacement groups of Nearctic riparian Bembidion. The other dominant tropical riparian group is commonly referred to as Genus Tachyura in North America. This group is very common in the Oriental Region and probably replaces Bembidion there. Although somewhat overlapping, the general ranges of Pericompsus species and Tachyura species are separated at their center. Beyond these centers to the north and to the south, in the more temperate areas of the world, Bembidion has its amphitropical centers. Aside from observations on the very common adults in the riparian situation, little is now known about the life history or ecological ranges of these riparian species.

There are many records of Pericompsus species collected at lights, especially “black-light,” and at light traps. With the exception of two Australian species whose members are wing-dimorphic (P. punctipennis) or wing-short (P. olliffi), all Pericompsus members are fully winged. Therefore, it is quite probable that these beetles are highly vagile. This probability is supported further by the large ranges of many species and by the fact that numerous island species are presently extant. In certain instances, specimens of species common only to one island have been collected at the proximate margin of the nearest adjacent island, indicating transport across water gaps. The occurrence of P. immaculatus near or on the beaches of Vera Cruz and Costa Rica and on the western flank of Cuba indicates recent crossings of large water gaps. Methods of transport across these gaps by Pericompsus species could be via air or rafting. These small beetles’ powers of flight would certainly take them high enough to be caught up in seaward wind currents. And since P. immaculatus lives on sea beaches they must be somewhat salt tolerant, thus capable of rafting.

I have seen several teneral adult beetles in the material studied. These teneral adults, when properly labeled by collectors, are good indicators as to when immature stages might be found and studied. However, since most Pericompsus species are represented by such scanty material, only tentative generalizations can be made at this time. It appears that the adult beetles are present in the fauna throughout the year. In the more temperate areas of the range of Pericompsus, teneral adults were found only during the spring and summer months (Australia—October, November, and January; United States—May through October). However, the pattern for the Neotropical Region where the majority of species exist is very complex, and I believe that it is due to available moisture in different geographical areas. The evidence for this and a detailed analysis will be presented in another part when all Tachyina can be discussed together.

Evolutionary and Zoogeographic Considerations

The members of Pericompsus comprise a group of generally derived Tachyina. These beetles share several apomorphic character states including the following: oblique tibial apex on the anterior tibiae, bifoveate mentum, reduced number of elytral interneurs (except one derived and two primitive species), well-defined elytral pattern (most species), peculiar ligule of the male genitalia, and foveate interneur 8 (most species). Some of the generally primitive (plesiomorphic) character states retained by some or all members of Pericompsus are the following: male with probasitarsus of anterior tarsi dilated and subspiniform and with modified setae beneath; female with four long setae arranged in a transverse row across sternum VI; some abdominal sterna with accessory setae (members of Upocompsus and Ediocompsus only); recurrent groove of elytra simple; presence of only isodiametric (or nearly so) reticulation. With these character states in mind, Figure 161 shows what I think happened to the ancestoral Pericompsus lineage. I reflect the changes in the ancestoral lineage in a subgeneric and species group classification as outlined in the checklist.

There are three major lines of evolution occurring in the external and genitalic forms of extant Pericompsus species.

The Australian Upocompsus group are the most primitive (Figure 3) of the Pericompsus. They are mostly riparian or at least subhygrophilus and they are the only Pericompsus group in which wing reduction occurs (2 species). Species are distributed in both the south temperate and tropical climes of Australia, from northern Queensland to Tasmania. The Upocompsus species undoubtedly have been isolated from the New World groups for some time. Whether the disjunction occurred in the northern part of the world or in the southern part of the world is not known at this time. When all Tachyina species have been studied, perhaps some hypotheses may be offered.

The Neotropical Eidocompsus group (Figure 25) are the least specialized (in regard to studied character states) of the two New World groups. For the most part this small group exhibits intermediate character states between Australian Upocompsus and New World Pericompsus sensu stricto. Ediocompsus species are riparian or sea beach inhabitants and some are highly vagile. Even so, these beetles are confined to tropical regions in the New World.

The New World Pericompsus (sensu stricto) group are the most specialized (Figure 1) species of the genus. There are more species in this group than the other two groups and some of the species are quite variable. This variability indicates to me that active change or evolution is occurring in the group and that the group is still actively speciating rather than declining. Pericompsus (sensu stricto) species are riparian or subhygrophilus and highly vagile. They are distributed in North Temperate, Neotropical, and South Temperate climes at elevations from sea level to 2300 meters. They are a dominant member of the lowland tropical riparian community.

All of the above subgeneric groups consist of one or more species groups. These groups are characterized in the taxonomic section. Their relationships will be further discussed in another part where all Tachyina groups can be compared.
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bibliographic citation
Erwin, Terry L. 1974. "Studies of the subtribe Tachyina (Coleoptera: Carabidae: Bembidiini), Part II: A Revision of the New World-Australian Genus Pericompsus LeConte." Smithsonian Contributions to Zoology. 1-96. https://doi.org/10.5479/si.00810282.162