Gymnodamaeus bicostatus (C.L. Koch, 1835)

Seniczak, Stanisław & Seniczak, Anna, 2011, Ontogenetic studies of three species of Gymnodamaeidae (Acari: Oribatida) with a focus on regressions of hysterosomal setae, Journal of Natural History 45 (5 - 6), pp. 361-391 : 373-381

Gymnodamaeus bicostatus (C.L. Koch, 1835)

( Figures 7B , 8B, 8C , 9 , 10A , 11–13 )

Damaeus bicostatus C.L. Koch, 1835 .

Eremaeus asperulus Berlese, 1882 .

Gymnodamaeus bicostatus: Kulczynski 1902 ; Sellnick 1928; Willmann 1931; Grandjean 1954; Sellnick 1960; Kunst 1971; Bulanova-Zachvatkina 1975; Marshall et al. 1987; Woas 1992; Pérez-Íñigo 1997; Subías 2004; Weigmann 2006; Weigmann and Mourek 2008.

Diagnosis

Adults oval ( Figure 9 ), dark brown and of medium size (636–756 µm). Rostrum triangular, distally rounded, with small depression on level of setae le; lateral outline with large pedotecta I and II. Setae ro and le rather long, positioned on transverse ridge in frontal part of prodorsum, other transverse ridge posterior to these setae. Seta ex rather short, seta in minute. Bothridium well-developed, rounded, sensillus long, with narrow, barbed head.

Notogaster almost flat, oval, with cerotegument granules but without distinct cuticular pattern, and five pairs of setae (h 2, h 1 and p 1 – p 3) in posterior part ( Figures 9 , 10A ). Formulae of epimeral setae and number of genital, aggenital and anal setae as in A. reticulatus , but only two pairs of adanal setae present. Formula of leg setae (trochanter to tarsus, solenidia in parentheses): I – 1-5-4(1)-5(2)-20(2); II – 1-4-4(1)- 5(1)-16(2); III – 2-3-3(1)-4(1)-15; IV – 1-2-3-4(1)-12. Legs tridactylous.

Juveniles generally similar to adult, but cuticle less sclerotized and unpigmented. Prodorsal setae ro and le relatively long, pair ro slightly more widely spaced than le; seta ex short, seta in minute. Larva with 11 pairs of gastronotal setae (h 3 absent), and large setae dm and dp; nymphs with 10 pairs of these setae (d -series absent, h 3 and p -series present), and setae c 3 and lp short. Nymphs with large excrescence in posterior part of body, with one pair of small and one pair of longer and curved setae.

Description of juvenile stages. Larva oval, elongated ( Figure 11 ), body unpigmented. Prodorsum triangular, rostrum rounded. Lateral outline with large depression on level of leg I, and smaller depression on level of leg II. Setae ro and le rather long and thick, curved, barbed, covered with granules of cerotegument and connected with ridges; ro shorter than le, but mutual distance of pair ro slightly greater than that of le. Seta ex short, seta in minute. Bothridium well-developed, rounded, sensillus long, with narrow, barbed head. Prodorsum covered with granules of cerotegument, posterior part with transverse folds, lateral parts plicate.

Gastronotum with 11 pairs of setae positioned on apophyses, including seta h 2 positioned laterally to posterior part of anal valves ( Figure 12A ). Setae dm and dp rather long, thick, barbed and positioned on large apophyses, other setae smaller. Setae of c -series small; setae of l -series longer and barbed, length increasing from seta la to lp. Seta h 2 shorter than h 1, and barbed. Lateral part of gastronotum with depression between setae c 3 and la. Paraproctal valves (segment PS) with two pairs of small setae. Cupules ia, im, ip and ih as in A. reticulatus . Gastronotum plicate, and covered with granules of cerotegument.

Nymphs oval, unpigmented. Gastronotum of protonymph with 10 pairs of setae: setae h 3, p 1 – p 3 appear and remain in deutonymph and tritonymph; setae la, lm and d -series lost and remain absent in deutonymph and tritonymph ( Figure 12B ), as in A. reticulatus . Setae p 2 and p 3 shorter than seta h 2, but longer than setae of ad -series; all setae barbed. All nymphs with large posterior excrescence ( Figure 12B ), with short, but thick seta on dorsal side (h 1), and longer, anteriorly curved seta on lateral side (p 1). Numerical changes of setae in nymphs as in A. reticulatus ( Table 2). Anogenital region finely plicate, with granules of cerotegument which often form lines.

Exuviae present in all nymphs, and well-connected with gastronotum ( Figures 7B , 13 ). Shape of prodorsum and prodorsal setae of tritonymph as in larva. Bothridium well-developed, rounded, sensillus long, with slimmer head than in larva. Setae of c -series short, setae lp and h - and p -series longer and barbed. Setae lp, h 3, h 2 and p 1 positioned in row on margin of gastronotum, length increasing from lp to p 1. Cupules ia, im, ip, ian, iad, ips and ih as in A. reticulatus . Tarsus I with two solenidia, ω 1 slightly longer than ω 2 and pointed, ω 2 blunt ( Figures 8B, C ). Famulus ε relatively longer than in A. reticulatus . Tibia with two solenidia, ϕ 1 long, ϕ 2 short, but relatively longer than in A. reticulatus .

Summary of ontogenetic transformations

During ontogeny of G. bicostatus , five pairs of setae are present on the prodorsum. Setae ro and le are rather long, seta ex is short, and seta in is minute. The bothridium is well-developed and rounded in all instars, and the sensillus has a long, narrow, and barbed head, which is more slender in the nymphs and adult than in the larva. The larva has 11 pairs of gastronotal setae, while the nymphs have 10 pairs; numeric changes of setae in the juveniles are similar to those in A. reticulatus , except for number of adanal setae ( Table 2). The adult loses setae of c -series, lp and h 3, such that only five pairs of notogastral setae remain (h 1, h 2 and p -series). The formulae of coxisternal, and aggenital setae are as in A. reticulatus . Ontogeny of cupules ia, im and ip are as in A. reticulatus ; in the adult lyrifissures ih, ips, iad and ian are difficult to observe under the cerotegument.

Distribution and ecology

Gymnodamaeus bicostatus is considered to have a holarctic distribution ( Subías 2004; Weigmann 2006) and a microphytophagous feeding style ( Schuster 1956; Schatz 1996). It inhabits dry steppe soil in East Tyrol ( Austria) and has been considered a xerophilic species ( Mihelčič 1964; Schatz 1996), but Schuster (1960) considered its preference to be for moderately dry and moderately fresh habitats. Rajski (1967) found this species in Dicrano-Pinetum and Querco-Carpinetum forest associations, with preference for acid soils. In central Europe this species inhabits dry and warm forest floor, mosses and lichens, and even lives arboreally ( Weigmann 2006), but probably has wide tolerance to temperature ( Weigmann and Mourek 2008).

This species occurs in different parts of Poland ( Olszanowski et al. 1996), but is neither frequent nor abundant. In Dicrano-Pinetum and Querco-Carpinetum it was found in small numbers ( Rajski 1967), with sample frequencies of 11% and 29%, respectively. From 17 forest soils investigated by Seniczak (1978) in different parts of Poland, this species occurred in small numbers in three of them of different humidities: in soil humus types xeromoder, typical moder and hygromor. Among 28 young Scots pine stands investigated in the regions polluted by factories, it was present in small numbers in two of them, with indistinct reaction to pollutants: on the trees it was present far from the source of pollution ( Dąbrowski 1999), while in the soil it occurred nearer to this source ( Klimek 2000).

Figures

Figure 7. Lateral aspect of tritonymph; scale bars 100 µm. (A) Arthrodamaeus reticulatus; (B) Gymnodamaeus bicostatus. Explanation of labels in text.

Figure 8. Part of tibia and tarsus I of tritonymph; scale bars 20 µm. (A) Arthrodamaeus reticulatus, paraxial aspect; (B) Gymnodamaeus bicostatus, paraxial aspect; (C) G. bicostatus, fragment of tarsus with solenidia; (D) Jacotella neonominata, paraxial aspect. Explanation of labels in text.

Figure 9. Gymnodamaeus bicostatus, adult, dorsal aspect; scale bar 100 µm. Legs partially drawn. Explanation of labels in text.

Figure 10. Adult, anogenital region; scale bars 100 µm. (A) Gymnodamaeus bicostatus; (B) Jacotella neonominata. Explanation of labels in text.

Figure 11. Gymnodamaeus bicostatus, larva, dorsal aspect; scale bar 100 µm. Legs partially drawn. Explanation of labels in text.

Figure 12. Gymnodamaeus bicostatus; scale bars 50 µm. (A) Anal region of larva; (B) anogenital region of tritonymph. Explanation of labels in text.

Figure 13. Gymnodamaeus bicostatus, tritonymph, dorsal aspect; scale bar 100 µm. Legs partially drawn. Explanation of labels in text.