Troglocheles archetypica, Zacharda, 2000

Zacharda, Miloslav, 2000, New species of the genus Troglocheles (Acari: Prostigmata: Rhagidiidae) from Oetztal Alps, Tyrol, with a key to adult species of the genus, Journal of Natural History 34 (3), pp. 463-478 : 464-472

Troglocheles archetypica n. sp.

(®gures 1±3)

Material examined

All from Austria, Tyrol, Oetztal Alps, Obergurgl (11ss02¾E, 46ss52¾N). HOLOTYPE: adult female. Obergurgler Schartl-mountain range, W of Obergurgl, upper border of alpine subnival zone about 2700 m altitude, under stones at foot of a talus slope covered with wet soil with Polytrichum spp. , moss and Salix herbacea , 7 September 1993, coll. M. Zacharda. PARATYPE: adult female, Rotmoostal, S of Obergurgl, under stones at upper border of alpine subnival zone with initial vegetation composed of mosses and Cerastium cerastoides on slope of Kirchenhugl-mt, about 2700±2800 m altitude, 1 September 1993, coll. M. Zacharda; deposited in the Canadian National Collection of Insects and Arachnids, Ottawa, in micropreparations, Type No. 22,406.

D iagnosis

Rhagidial organs I and II each consist of four oblique separate solenidia. Famulus e stellate in rhagidial organ I and spiniform in rhagidial organ II, positioned antaxially between ®rst and second proximal rhagidial solenidia. Spiniform solenidia on tibiae I, II and III minute. Tibia IV lacks solenidion. Bothridial setae sc 1 distinctly overlapping disjugal suture.

D escription

Adult female (two examined). Length of idiosoma 800±1200 m m. Ratio of leg I length to idiosomal length 0.8±1.36.

Gnathosom a. Subcapitulum slender, oval, subtriangular (®gure 2D); length to breadth ratio 1.40±1.48; distal hypostomal lips with spiniform internal malar and serrate external malar processes; adoral setae nude; proximal subcapitular setae ciliate, external pair longer than internal pair. Dorsal surface of chelicera with distinct saddle-shaped depression slightly distal to level of bases of digits (®gure 2A); cheliceral digits long, slender; ®xed and movable digits smooth along masticatory surface. Chelicerae with two setae inserted distad of articulation of movable digit; tip of proximal seta overlaps insertion of distal seta; tip of distal seta overlaps apex of ®xed digit. Length of chelicera 270±290 m m, dorsoventral width 102±109 m m, length of movable digit 132±135 m m, length of proximal and distal cheliceral setae 20 and 53±59 m m, respectively, distance between their insertions 16 m m. Ratio of cheliceral length to dorsoventral width 2.60±2.66; ratio of length of movable digit to length of chelicera 0.45±0.49; ratio of length of movable digit to dorsoventral width of chelicera 1.21±1.31. Palpus long and slender, with relatively slender tarsus (®gure 2E); ratio of length to width of tarsus 2.7±3.0. Length of palpal trochanter, femorogenu, tibia and tarsus 43, 125, 40 and 89 m m, respectively. Number of setae and solenidia (in brackets) on palpal trochanter, femorogenu, tibia and tarsus 0-2-3-10(1), respectively; tarsal solenidion spiniform, erect.

Prodorsum. Naso well-developed, with pair of internal vertical setae v 1. Bothridial setae sc 1 ®liform, ®nely pubescent, overlap disjugal suture. Setae v 2 strikingly short. Length of setae: v 1 46±56, v 2 36, sc 1 102± 105, sc 2 112±122 m m. A pair of eyes visible external to bases of sc 2 (®gure 1A).

Opisthosomal dorsum. Complement and arrangement of dorsal setae and cupules typical for Rhagidiidae (®gure 1A); three pairs of cupules; ia positioned laterally between setae c 1 and d 1, im lateral and just anterior to setae e 1, ip lateral and slightly anterior to f 1. Setae c 1, d 1, e 1 and f 1 reach 0.50, 0.52, 0.50 and 0.60 of distance to insertion of successive seta, respectively. Length of setae: c 1 63, c 2 119, d 1 59±63, e 1 59 ±63, f 1 82, f 2 53±59, h 1 115, h 2 59±63 m m.

Podosom a. Coxisternal plates (epimeres) I, II, III, IV with 3-1-5-3 ®nely pubescent setae, respectively (®gure 1B).

Genital region. Genital valves each with ®ve ®nely pubescent setae of similar length, 20±23 m m, arranged evenly near medial edge of valves. Five pairs of aggenital (paragenital) setae of similar length, 26±30 m m. Genital valves 99±132 m m long (®gure 1B). Cupules ih positioned ventrolaterally, distad of posteriormost pair of aggenital setae.

L egs. Leg I 960±1088 m m long, 0.8±1.36 as long as idiosoma. Empodia of all legs setulose, broadly oval in dorsoventral view, not overlapping claws; claws without accessory points or ventrobasal spurs. Number of setae and solenidia (solenidia and famulus, e, bracketed), respectively, on legs I-II-III-IV (®gure 3): trochanters 1-1-2-2; basifemora +telofemora 5 +5-6 +5-4 +4-3 +4; genua 10 (1)-7(1)-6 (1)-6(0); tibiae 11(2)-7(2)-5 (2)-5; tarsi 17 (4 + e)-14(4 + e)-13-13. Genua I and II each with one erect spiniform distoventral solenidion, genu III with one lateroventral medioproximal small spiniform solenidion. Tibia I with one dorsal medioproximal erect spiniform solenidion, and one dorsodistal rhagidial solenidion; tibia II with one laterodorsal medioproximal spiniform erect solenidion, and one lanceolate dorsodistal solenidion recessed in deep pit with small surface pore; tibia III with two erect spiniform laterodorsal medioproximal solenidia arranged in tandem; tibia IV unusually without solenidion. Tarsi II, III, IV each with two oar-like ciliated subapical setae (®gure 3E). Tarsus I robust, with tip abruptly truncated in lateral view (®gure 2F), ratio length to width 4.41 ±4.72, with four rhagidial solenidia lying obliquely in separate depressions, stellate famulus e inserted antaxially between ®rst and second proximal rhagidial solenidia (®gure 2B); tarsus II with four rhagidial solenidia in separate oblique depressions and small spiniform famulus e inserted antaxially between ®rst and second proximal solenidia (®gure 2C).

A nities

Troglocheles archetypica n. sp. is very similar to T. vandeli Zacharda, 1987 from which it can be distinguished via ®ve principal characteristics. (1) The spiniform solenidia on tibiae I, II and III are short, minute; in T. vandeli they are strikingly long. (2) The two laterodorsal proximal spiniform solenidia lying in tandem on tibia III are of the same length; in T. vandeli the proximal solenidion is conspicuously longer than the distal one. (3) Tibia IV lacks the spiniform solenidion; in T. vandeli a long, laterodorsal proximal solenidion is present on tibia IV. (4) The spiniform famulus e in rhagidial organ II is positioned laterad of the proximal rhagidial solenidion; in T. vandeli it is proximal, subtending the proximal rhagidial solenidion. (5) The bothridial setae sc 1 distinctly overlap the disjugal suture; in T. vandeli they overlap the disjugal suture only slightly.

Etymology

The name archetypica reēcts the morphological archetype evident in this newly discovered species of the genus Troglocheles . Feminine gender.

De®nition of new species groups

The troglomorphic representatives of the cave-dwelling troglobitic species have extremely variable sensory rhagidial organs on tarsi I and II with numerous rhagidial solenidia ( table 1). In contrast, epigeic rhagidiid mites, generally have constant numbers of the rhagidial solenidia with usually four on tarsi I and four or three on tarsi II. Additional characters which distinguish and de®ne the separate species include the position of the solenidia on tibiae I and IV, the position of setae on the ®xed digit of the chelicera and the number of ciliated setae on the epimeres (the epimeral formula). These have proved to be useful criteria for distinguishing three groups of variable troglobitic species: the vornatscheri , strasseri and gineti species groups (cf. table 1 and Key to adult Troglocheles ).

Representatives of the strasseri species group have 3-1-5-3 setae on epimeres I-II- III-IV, respectively, the spiniform solenidion on tibia I is positioned dorsomedially or medio-proximally and the distance between insertions of the cheliceral setae on the ®xed digit is almost the same as the length of the proximal cheliceral seta.

Similarly, the representatives of the vornatscheri species group have 3-1-5-3 epimeral setae, the distance between insertions of the cheliceral setae on the ®xed digit is, again, almost the same as the length of the proximal cheliceral seta; but, the spiniform solenidion on tibia I is positioned dorsodistally.

In contrast with representatives of the vornatscheri and strasseri species groups, T. gineti has 3-1-4-3 epimeral setae. The insertions of the cheliceral setae are strikingly far apart so that the tip of the proximal cheliceral seta does not reach the insertion of the distal seta ( Zacharda, 1980: 656, ®gure 70A).

The extreme and unusual variability of rhagidial organs I and II was found in three specimens designated by Willmann in his private collection as T. strasseri tiroliensis ( Zacharda, 1980) and ®ve of T. gineti by Rack (1974). All were collected in di erent cave localities ( table 1). It is not possible to decide whether these represent the same variable species or a group of separate species/subspecies from geographically segregated caves. In contrast, four adults of T. strasseri sensu stricto from one cave locality, i.e. HartelsgrabenhoÈhle cave in Styria, Austria, one adult female of T. strasseri from a shaft near Na Lazi, Slovenia ( Willmann, 1932), and seven adults of Troglocheles spp. , strasseri species group, from another separate cave locality, i.e. TuÈ rkenloch cave in Lower Austria, have their rhagidial organs comprising di erent, but locally constant numbers of the rhagidial solenidia (cf. table 1).

Phylogenetic relationships

The mode of active allopatric speciation suits well the evolutionary scenario of the cave- dwelling species T. vandeli , T. strasseri , T. vornatscheri and T. gineti . It is reasonable to assume that their shared ancestor, a psychrophilous montane species, actively occupied geographically segregated cave refuges in the Alpine periglacial zone during the Pleistocene glaciation (®gure 7). Subsequent speciation began together with adaptive morphological changes resulting in adaptive autapomorphic troglomorphisms. In this sense the terms cave vicariance, and cave vicariants were repeatedly used by Zacharda (1980, 1985, 1987).

A modi®ed evolutionary scenario can also be used to explain the situation seen in the troglomorphic representatives of the genus Troglocheles with di erent traits of the adaptive apomorphic troglomorphisms. As shown in table 1, there are large distinctions between troglomorphisms, as expressed among the particular species. In T. vandeli they are the least distinct, whilst in T. gineti they are the most expressed. Tentatively, these distinctions can reēct di erent, shorter or longer (and evolutionarily older) cave occupation when the species with the most distinct troglomorphisms started their development in cave habitats well before the period of Pleistocene glaciation. Invasion of cave systems would undoubtedly have been post-Pleistocene in glacial regions, though not in regions which were not glaciated.

Troglobitic and troglomorphic T. strasseri , T. vornatscheri and T. gineti are derived descendants of a common ancestor. Troglomorphisms in T. vandeli from the Pyrenees ( Zacharda, 1987), are the least distinct, including enlarged spiniform solenidia on the tibiae. This suggested that a morphological ancestral archetype of the contemporary representatives of the genus Troglocheles is an epigean rhagidiid mite with the unique synapomorphic oar-like subapical setae on tarsi II, III and IV, but, as in the majority of other rhagidiid mites, with the`normal’ proportioned (not enlarged and attenuated) appendages, and number of rhagidial solenidia, type and arrangement of leg spiniform solenidia.

T. archetypica either evolved from a paleoendemic ancestor in alpine unglaciated nunataks during the period of Pleistocene glaciation and subsequently dispersed to unglaciated alpine biotopes during the postglacial Holocene, or quite recently during the Holocene. It is not known whether the hypothetical epigean ancestor still exists. If so, then it resembles T. archetypica , but with a complete set of the short spiniform solenidia on the leg segments.

The morphological traits of the recently discovered T. archetypica n. sp. ®ts the concept of such an epigean archetype ancestor. However, the loss of spiniform solenidia on tibiae IV is uniquely secondarily apomorphic in T. archetypica . These solenidia are commonly present in most rhagidiid mites including the derived troglomorphic species T. strasseri , T. vornatscheri , T. gineti , T. vandeli and T. aggerata n. sp. Thus T. archetypica exhibits a mixture of the retained archetypic traits of the hypothetical epigean ancestor and the secondarily derived apomorphic loss of the solenidia. This is the reason why T. archetypica is considered to be derived from the hypothetical shared ancestor also.

It is known that some species of rhagidiid mites are adapted to habitats with permanently low temperature and high moisture. For example, in the Czech Republic the relict arctic rhagidiid mite Rhagidia gelida Thorell ( Zacharda, 1993) completes its life cycle on cool talus slopes retaining year-round ice reservoirs (Zacharda, unpubl. data). Winter subnival activity of rhagidiid mites was reported and widely discussed by Aitchison (1979) and they also occur on nunataks and in other icefree biotopes in Antarctica ( Womersley and Strandtmann, 1963; Strandtmann, 1967).

Nunataks occurred also in the Alps during the Pleistocene glaciation (Janetschek, 1956; SchmoÈlzer, 1962; Reisigl and Keller, 1987; Thaler, 1990, 1998). It is probable that an Alpine cool-adapted Troglocheles species survived the Pleistocene glaciation on ice-free nunataks and that some of its descendants have invaded caves where they speciated to form presently known troglobitic and troglomorphic species.

Species of the genus Troglocheles of uncertain status (species incertae sedis)

These species have been identi®ed to be representatives of the genus Troglocheles based on the original drawings that show the typical oar-like tarsal setae. However, the original descriptions of these species are so poor or confused that they cannot be distinguished from the other representatives of the genus. These species are as follows:

Rhagidia odontochela Turk, 1972 from the Ogof Cynnes cave , Brecon, UK. The descriptions of tarsus I with three rhagidial solenidia and tarsus II with four rhagidial solenidia are apparently confused, as such numbers of the rhagidial solenidia are very unusual among adult Troglocheles ( Turk, 1972) . Type material does not exist ( Turk, private communication) and the species’ taxonomic status can only be elucidated when new material is examined .

Rhagidia conciana Lombardini, 1951 from`grotta di Costalta n.14 V.T.’ cave, Val di Sella, Venezia Tridentina, the Venezian Alps, Italy ( Lombardini, 1951). The number of three rhagidial solenidia on tarsus I that is given in the original description is very unusual (and improbable) for an adult specimen. Type material does not exist and the species has never been revised ( Zacharda, 1980).