Foveacheles thaleri Zacharda, 2010

Zacharda, Miloslav, Fong, Daniel, Hobbs Iii, Horton H., Piva, Erminio, Slay, Michael E. & Taylor, Steven J., 2010, 2474, Zootaxa 2474, pp. 1-64 : 58-63

Foveacheles thaleri Zacharda , n. sp. ( Figs 41–42)

Material examined

HOLOTYPE: adult female, Cyprus, Troodos , Cedar Valley , 1200 m a.s.l., coll. Barbara & Konrad Thaler, 14.2.1995, deposited in the Museum of Biological Diversity, Ohio State University, Type No. OSAL0007416; paratypes (deposited with the holotype): adult female, same data as holotype, OSAL0007417; adult female, Greece, Rhodos, Ilias, Salakos, 600 m a.s.l., coll. B. Knoflach, K. Thaler, 13.4.1996, OSAL0007418; Austria, the Carnic Alps, the summit of Poludnig mt., 2000 m a.s.l., coll. B. Knoflach, K. Thaler, 24.9.1994, deposited in collection of M. Zacharda.

Diagnosis

Cheliceral digits long, slender, arched; fixed digit smooth along masticatory surface, with distinct prebasal lateroventral fissure located distad of articulation of digits and proximad of insertion of proximal cheliceral seta; distal half of masticatory surface of movable digit with four to five prominent denticles. Proximal cheliceral seta inserted well distad of articulation of movable digit, tip of proximal seta does not reach insertion of distal seta. Distal cheliceral seta inserted in distinct, proximally open laterodorsal depression typical of Foveacheles . Palpal tarsus same length as femorogenu, with small apical tubercle and thirteen to fourteen pubescent setae. Prodorsal bothridial setae sc 1 reach to insertions of opisthosomal setae c 1. Setae c 1 reach to insertions of successive setae d 1. Rhagidial organ I comprised of four small rhagidial solenidia (ω) lying in separate and slightly oblique depressions; stellate famulus (ε) positioned laterad of the first proximal rhagidial solenidion antiaxially; rhagidial organ II with three rhagidial solenidia lying in tandem in confluent depressions and small spiniform famulus (ε) subtending proximal rhagidial solenidion. Coxae I, II, III, IV with 3-1- 6-3 finely pubescent setae, respectively. Neotrichy in genital region: ten pairs of aggenital setae.

Affinities

Foveacheles thaleri n. sp. is very similar to T. subterranea from which it can be distinguished by the following principal characteristics: (1) The distal half of masticatory surface of movable digit with four to five prominent denticles; in T. subterranea the movable digit is either smooth along its masticatory surface or only gently serrate along approximately distal third of masticatory surface. (2) Tip of the proximal cheliceral seta does not reach insertion of the distal seta; in T. subterraneaa the distance between insertions of the cheliceral setae is shorter and tip of the proximal cheliceral seta reaches insertion of the distal seta. (3) The distal cheliceral seta is inserted in the distinct proximally open depression which is typical of representatives of the genus Foveacheles ; in T. subterranea this depression is only vestigial, rather typical of Traegaardhia . (4) Six to eight genital setae on the genital valve each and ten pairs of aggenital setae in the genital region; in T. subterranea six setae on the genital valve each and seven to eight pairs of aggenital setae in the genital region.

F. thaleri n. sp. is also similar to F. titanica Zacharda & Elliott, 1985 from which it can be distinguished by the following principal characteristics: (1) The length of idiosoma ranges from 1296 to 1696 µm; in F. titanica it ranges from 1747 to 2330 µm. (2) The coxae I, II, III, IV are with 3-1-6-3 finely pubescent setae, respectively, and the trochanter IV with two setae; in F. titanica the coxae I, II, III, IV are with 3-1-6-5 setae, respectively, and the trochanter IV with three to four setae. The spiniform solenidion on the tibia I is laterodorsal, proximal; in F. titanica it is positioned medially. The spiniform solenidion on the tibia IV is absent; in F. titanica a tiny spiniform laterodorsal medial solenidion is on the tibia IV.

Etymology

The species is named in honour of Barbara and Konrad Thaler, the distinguished arachnologists at the University of Innsbruck, Austria, who collected this species. Feminine gender.

Description

Adult female (seven examined). Length of idiosoma 1486(1296–1696) µm. Ratio of leg I length to idiosomal length 1.28(1.11–1.56).

Gnathosoma . Subcapitulum broadly oval, subtriangular ( Fig. 42E); ratio of length to breadth 1.09(1.05– 1.11); distal hypostomal lips with spiniform internal and serrate external malar processes; adoral setae nude, overlapping apex of subcapitulum; proximal subcapitular setae pubescent, external pair same length as internal pair. Dorsal surface of chelicera with distinct deep saddle-shaped depression at level of bases of digits ( Fig. 42A,B); cheliceral digits long, arched; dorsal surface of fixed digit with distinct narrow rim between insertions of cheliceral setae; fixed digit terminates in three cusps, smooth along masticatory surface and with distinct prebasal lateroventral fissure located just distad of articulation of digits; movable digit with four to five prominent denticles along approximately distal half of masticatory surface ( Fig. 42B). Chelicera with two setae, proximal seta inserted distad of articulation of movable digit; tip of proximal seta does not reach insertion of distal seta; tip of distal seta overlaps apex of fixed digit. Length of chelicera 347(310–402) µm, dorsoventral width 140(129–158) µm, length of movable digit 152(138–175) µm, length of proximal and distal cheliceral setae 35(30–43) and 60(56–76) µm, respectively, distance between their insertions 47(33–53) µm. Ratios: cheliceral length to dorsoventral width 2.47(2.22–2.67), length of movable digit to length of chelicera 0.43(0.41–0.48), length of movable digit to dorsoventral width of chelicera 1.07(1.0–1.12). Palpal tarsus about same length as femorogenu ( Fig. 42F), and with small apical tubercle ( Fig. 42G); ratio of length to width of tarsus 3.54(3.12–4.07). Length of palpal trochanter, femorogenu, tibia and tarsus 64(59–73), 185(165–204), 98(82–119) and 198(165–231) µm, respectively. Number of setae and solenidia (in brackets) on palpal trochanter, femorogenu, tibia and tarsus 0-2-3-14(1), also 14(1) and 13(1) asymmetrically; tarsal solenidion spiniform, erect.

Prodorsum. Naso well-developed, with pair of internal vertical setae v 1 ( Fig. 41A). Bothridial setae sc 1 filiform, finely pubescent, their tips reach to insertions of opisthosomal setae c 1. Length of setae: v 1 91(82–99), v 2 153(112–181), sc 1 218(175–247), sc 2 274(224–303) µm.

Opisthosomal dorsum and anal region. Cupules ia positioned at level and slightly proximad of insertion of opisthosomal seta c 2; im lateral and just anterior to setae e 1; ip laterally between setae e 1 and f 1; ih positioned ventrolaterally, almost at level of insertions of adanal seta e ad 1 ( Fig. 41A,B). Setae c 1 reach to insertions of successive setae d 1; d 1 reach 0.75 of distance to insertions of setae e 1; e 1 reach about half of distance to insertions of setae f 1; f 1 reach almost to insertions of h 1. Length of setae: c 1 177(132–231), c 2 282(211–330), d 1 159(122–198), e 1 157(132–198), f 1 192(148–224), f 2 130(96–158), h 1 227(185–257), h 2 132(92–158), ps 1 172(138–198), ps 2 109(92–125), ps 3 67(59–82), ad 1 70(63–80) µm.

Podosoma. Coxae I, II, III, IV with 3-1-6-3 finely pubescent setae, respectively.

Genital region. Genital valves each with six to eight finely pubescent genital setae (g) of similar length ( Fig. 41B), about 61(53–79) µm, arranged evenly along medial edge of valve. Ten pairs of aggenital setae (ag) of similar length, about 107(89–125) µm. Length of genital valves 228(181–274) µm.

Legs. Leg I 1892 (1632–2128) µm long, about 1.28(1.11–1.56) as long as idiosoma. Empodia of all legs setulose, longer than claws; claws each with small clawlet ventrobasally. Setal arrangement on leg segments as in T. subterranea n. sp. (see Figs. 39, 40). Number of setae and solenidia (solenidia and famulus (ε) bracketed), respectively, on legs I-II-III-IV: trochanters 1-1-2-2, basifemora + telofemora 5+5-6+5-4+4-4+4, genua 11(1)-8(1)-6(1)-6, tibiae 11(2)-8(2)-7(2)-6, tarsi 19(4+ε)−16(3+ε)−14−14. Genua I and II each with one erect spiniform distoventral solenidion (σ); genu III with one small spiniform lateromedial solenidion. Tibia I with one erect spiniform dorsoproximal solenidion (Φ), and one dorsodistal rhagidial solenidion; tibia II with one spiniform erect dorsoproximal solenidion, and one lanceolate dorsodistal solenidion recessed in deep pit with small surface pore; tibia III with two erect spiniform lateromedial solenidia arranged in tandem; solenidion on tibia IV absent. Tarsus I slender, its tip slightly tapers in lateral view, ratio length to width 7.0(5.50–8.25), with four rhagidial solenidia (ω) lying in tandem in separate depressions; stellate famulus (ε) inserted laterad of proximal rhagidial solenidion antiaxially ( Fig. 42C); tarsus II with three rhagidial solenidia lying in tandem in confluent depressions and small spiniform famulus (ε) subtending proximal rhagidial solenidion ( Fig. 42D) .

Discussion

In the Mediterranean Basin the peripheral southern border of the Alps with lower to intermediate elevations is considered one of the major Quaternary refuge areas and most important hotspots for high plant and animal biodiversity and local endemics ( Médail & Quézel 1997; Schönswetter et al. 2005; Schmitt 2009). A suture-zone of hybrid interactions between recently joined biota ( Remington 1968), and an area of plant species ( Pawlowski 1970) or insect population ( Garnier et al. 2004) origin is supposed to be located there. This applies also to life in the subterranean habitats of the Prealps ( Bologna & Vigna-Taglianti 1985; Culver & Pipan 2009). Karst genesis started in this region far before the Quaternary, and many alpine caves located along the southern border of the Alps are of Pliocene or even Miocene age ( Audra et al. 2007). We can assume that in those vast calciferous karst areas some of the psychrophilic soil rhagidiid mites actively occupied the mesovoid shallow substratum (MSS) ( Juberthie 2000; Culver & Pipan 2009) and subterranean voids in talus slopes (Růžička 1999) as well as caves, and had already started their evolutionary processes of speciation and adaptation to life in caves well before the Quaternary glaciation. This long-time persistence of fragmented subterranean habitats since the Pliocene or Miocene is consistent with long periods of post-colonization isolation and evolution as has been widely observed in high montane species in Europe ( Schmitt 2009). In contrast to possible pre-glacial immigrants that had already become adapted to life in caves, some other species of rhagidiids might have immigrated to cave refugia as late as at the beginning of, or during, the Quaternary glaciation when the snowline during the last glacial maximum (about 20,000 years BP) was at about 2000 m a.s.l. ( Schönswetter et al. 2005). Thus the caves and other subterranean paleorefugia ( Nekola 1999) enabled the pre-Quarternary troglobionts as well as the more recent Pleistocene immigrants to adapt to the periglacial cave environment, survive the glaciation there and continue their existence in the Holocene. Tentatively, these morphological adaptations, troglomorphisms, might reflect the specific subterranean niches that are occupied by particular species as well as the history of immigration and adaptation to specific subterranean conditions. Thus nowadays we can encounter rhagidiid mites with differently expressed traits of the derived troglomorphisms. Particularly these are the elongation of appendages and progressive development of sensory organs such as the increased length and number of the rhagidial solenidia on the tarsi (ω) and tibiae (Φ) of the first two pairs of legs ( Zacharda 1979; Zacharda 2000). These are, for example, more strikingly developed in Traegaardhia cavernarum , T. cavernicola , T. holsingeri , T. paralleloseta and T. vicenzaensis . In contrast, in T. dalmatina the rhagidial organ I is evidently developed regressively and comprised of only three rhagidial solenidia whereas in T. nasuta the rhagidial organ I is developed progressively and comprised of five rhagidial solenidia. Notwithstanding both T. dalmatina and T. nasuta are troglobionts with distinctly elongated appendages. In contrast, in T. similis , T. distisolenidiata , T. subterranea and partly also T. gracilis the rhagidial organs and appendages resemble rather those in the epigean rhagidiids. However, it is still in question whether these differently expressed troglomorphisms really positively correlate, as a morphological clock, with the duration of the underground ancestral history of these troglobionts, or reflect adaptations to different subterranean niches, or feeding habits, rather than differences in age. It was, for example, already discussed in the case of Troglocheles where the different species have differently and specifically developed rhagidial organs consisting of different numbers of sensory rhagidial solenidia ( Zacharda 2000). Nowadays molecular clock studies based on the differences in mtDNA sequences have documented that the time of adaptation of troglobionts to life in caves is estimated to be in the range of several hundred thousands to millions of years ( Culver & Pipan 2009), and perhaps these techniques might resolve this issue also in the troglomorphic Rhagidiidae .

Similarly, the American Traegaardhia -species occur in the Ozark Plateaus, the Interior Low Plateau and the Appalachian karst regions. These are considered hotspots for the relatively high species diversity of troglobionts in the southeastern U.S. A ( Culver & Pipan 2009). However, phyletic interrelations between the European and American geographically separated groups of species remain obscure. For a detailed discussion of the geographic and geologic relationships in these American karst areas one may consult, for example, Holsinger & Culver (1988) and Culver et al. (2003).

The genus Traegaardhia represents probably the polyphyletic group of species derived from two or more distinct ancestral lineages. Though the mites have similar cheliceral digits with the lateral insertion of distal cheliceral seta and are adapted, more or less, to life in caves in many but various morphological characters, non-sister lineages can be expected in this genus, perhaps as a result of convergent evolution.

Morphological differences between some Traegaardhia and Foveacheles -species are subtle such as, for example, between the hypogean T. subterranea n. sp. and the epigean Foveacheles thaleri n. sp.. It is consequently hypothesized that the cave-adapted troglomorphic Traegaardhia -species may be the phylogenetically derivative lineage(s) originating from the epigean Foveacheles -species. In this case the adaptive shift hypothesis, when interspecific differentiation between contiguous populations occurs via parapatric speciation, might hold up ( Culver & Pipan 2009).

In contrast, the striking morphological resemblance between rhagidial organs and chelicerae in Traegaardhia cavernarum , T. cavernicola , T. vicenzaensis , all from caves in northeastern Italian Prealps, as well as between T. dalmatina , T. nasuta , T. subterranea , suggests that these two groups of vicariants might be lineages of monophyletic origin that have resulted from the allopatric speciation, followed by relatively limited subsequent dispersal (sensu Lefébure et al. 2006). In this case the climatic relict hypothesis might apply ( Culver & Pipan 2009).