nomos LXXVII

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Organic Evolution in terms of the Implicate and Explicate Orders.

Part LXXIII

Diptera (midges, mosquitoes, flies) (V)

The evolutionary diversification in the Order Diptera revisited.

Lifting many-veined (empidoid) functional wing-type

Empis livida, Empididae. 8-9 mm.
(After SEVERA, in Thieme's insektengids voor West- en Midden-Europa, 1977)

8 : Empis tessellata Fabr., Empididae. about 14 mm.
9 : Hilara maura Fabr., Empididae. about 6.5 mm.
(After CHINERY, in Elseviers Insektengids voor West-Europa, 1983)

Sciadocera rufomaculata White, Sciadoceridae [= Sciadoceratidae].
(After TILLYARD, 1926, in ROHDENDORF, 1964)

( Description of empidoid wing-type according to ROHDENDORF, 1951)

Representatives of the type
To the lifting many-veined (empidoid) type belong [the] many species of the family Empididae and the rare relict flies Sciadoceratidae of the Southern Hemisphere [the latter family belongs, according to ROHDENDORF, 1964, to the superfamily Platypezidea (= Clythiidea), which itself belongs, not to the infraorder Asilomorpha [largely Brachycera-orthorrapha], to which the Empididea belong, but to the infraorder Myiomorpha [largely Brachycera-cyclorrapha].

Size of wings
Absolute size of wings is not large, their length does not exceed 10-11 mm, usually significantly smaller, sometimes not larger than 1 mm (some Corynetinae). Relative size of the wings is equal to the body, more rarely exceeding it a little. Magnitude of the surface of the wings is known only of certain species of the genera Empis (0.161-0.284 cm²), Ocydromia (0.057 cm²) and Noeza (0.070 cm²) : These figures do not characterize the surface area of the larger species of the genus Empis and especially [not characterize] the many minute forms possessing small wings. The weight of the wings is not known. The load is studied in the above mentioned forms, and is equal to 0.072-0.098 gr/cm² in representatives of the genus Empis, 0.035 gr/cm² in those of Ocydromia, and 0.028 gr/cm² in Noeza.

Some examples of wings of the empidoid functional type :

Figure 1. Wings of representatives of the lifting many-veined (empidoid) type. From top to bottom :
Tachista brevipennis Ros., Empididae. Length about 1.5 mm. (After ENGEL)
Sciadocera patagonica Schm., Sciadoceratidae [= Sciadoceridae]. Length about 4 mm. (After SCHMITZ)
Rhamphomyia platyptera Panz., Empididae. Wing of female.(After LINDNER)
Rhamphomyia platyptera Panz., Empididae. Wing of male. (After LINDNER)
Homalocnemis nigripennis Phil., Empididae. Length about 5 mm. (After COLLIN)
Ceratomerus mediocris Coll., Empididae. Length about 3 mm.(After COLLIN)
(All in ROHDENDORF, 1951)

Shape of the wings
The wings of this type are elongate, their length exceeds their width 2.5-3 times. Very rarely are the wings longer, 3..5 to almost 4 times longer than their width (some Corynetinae, upper image in Figure 1). Still more rarely the wings are shortened, only two times longer than their width (Sciadoceratidae, 2nd image of Figure above). Anterior margin of the wing moderately convex, sometimes straight only in its proximal half (Empidinae, 3rd and 4th image of Figure above), where the apex in these cases is well expressed, usually, however, it is not differentiated. Hind margin as a rule convex, only sometimes weakly bulging (narrow-winged Corynetinae). Anal lobe variable in its structure, often it strongly bulges almost in the form of a rectangular outgrowth (Empidinae, Ocydromiinae, Noezinae), sometimes only in the form of a lightly inclined, almost not projecting seem (many groups, including Sciadoceratidae). Some peculiar Corynetinae possess long tongue-like wings of which the anterior and posterior margin have a notable indentation. Some species of empidids are very characteristic as a result of a markedly sexual dimorphism in wing structure, significantly broadened in females of certain Empidinae, obtaining an extremely unusual shape, undoubtedly not allowing to perform a high-frequency wing-beat. This feature may be compared with the broad-wingedness of certain insects (Rohdendorf, 1949). The alula as a rule is absent, more rarely it is present in the form of a small projection.

To the above images of empidoid wings, given by ROHDENDORF, we here add some from HENNIG, 1954 :

Figure 2. Wing-venation of representatives of the family Empididae.
224 - Dolichocephala irrorata Fall. 225 - Clinocera inermis Lw. 226 - Chelifera melanocephala Hal. 227 - Gloma fuscipennis Meig. 228 - Leptopeza flavipes Meig. 229 - Hybos culiciformis Fabr. 230 - Bicellaria nigra Meig. 231 - Hemerodromia raptoria Meig. 232 - Asymphyloptera discrepans Coll. ( [this last one] after Collin, 1933). [for 233 HENNIG does not give a subscript. The wing undoubtedly belongs to the genus Tachista (Empididae) ].
(After HENNIG, 1954)

The last three wings of the above Figure (231, 232, 233), although being wings of empidids, may not belong to the lifting many-veined (empidoid) functional wing-type, as also the following empidid wings :

Wings of Empididae. After LINDNER, E., Die Fliegen der palaearktischen Region

Nevertheless, ROHDENDORF does consider, for example, the wings of Tachista brevipennis, Figure 1, top image ( Empididae) to belong to the present functional wing-type, despite its rather poor venation. Apart from 231 (Hemerodromia) and 232 (Asymphyloptera), 233, Tachista, may belong to ROHDENDORF's corynetoid subtype of empidoid wings, described below, while 231 may belong to ROHDENDORF's atalantoid subtype.

Skeleton of the wing (of the empidoid type)
The very characteristic feature of this type is the development of a moderate costalization consisting of a softening of the posterior wing-margin almost always lacking the costal vein which runs until the wing-tip only. Subcostal vein almost always weak, free at its end or even totally coalescing with the radial vein. Radial veins [including the Radius proper] in the form of three strong branches : sometimes there is a fourth one in the form of a fork. The radial veins not shifted towards the anterior margin and always end up in the distal part of the anterior wing-margin whereby the last branch runs into the wing's apex. Medial veins weaker than the Radials, they exist as three or two branches. The Cubital vein is of considerably variable size : sometimes it is rather long forming a well-expressed cubital (= anal of earlier authors) cell (Brachystomatinae, Figure 1, 5th image, and Noezinae), but more often it is shortened and at its end curved back, or even completely reduced without a trace (some Corynetinae). The cross-vein r-m always well developed. The cross-vein m-cu is usually absent and is taken up into the Medial vein-system. Usually there are closed cells, the intermedial and the basal ones, which sometimes are partly reduced (the intermedial in many Empidinae) or are significantly shortened (as a result of shift of cross-veins in Sciadoceratidae). The basiala is well differentiated : the phragma is absent, more rarely noticeable in the form of a condensed fold. The alula in the form of a rudimentary seem at the posterior margin of the basiala. Scales are not developed : there is only a remnant of the wing-scale. Chaetaria are present in the form of small, sometimes hardly visible areas on the upper elements of the basiala.

Coverings of the wing
Microtrichia usually cover the whole wing, only sometimes they are absent in its central region. Macrotrichia (bristles) are only sometimes present on the main veins and on the posterior wing-margin, reaching a markedly large size on the anal lobe, on the remnants of alula and wing-scale. Long hairs or bristles, and also scales are absent on the wings.

Functional features
The way of life of the representatives of this type are known only in very general terms for species of the family Empididae which live in moist places amidst rich vegetation always in the immediate vicinity of water-basins or swampy soil. The larvae of these flies are predators as well as the imagines which in addition also consume vegetable saps. Flight in the life-activities of the empidids is an important function : On the one hand flight guarantees the collection of food for them, on the other hand many minute species perform characteristic "dances", flying in great numbers above water-basins and meadows. There are also observations about the role of flight in the sexual activity of certain species. There do not exist exact data about the features and properties of the flight of empidids. The known data on load do not allow to judge about the qualities of the flight-function. Observing the behavior of species of the genus Empis on flowers, on may easily note that these flies take flight relatively "unwillingly", making it possible to grab them with the hands, and that they actively move about the plant with the help of their large and strong legs.

History and transformations of the type
Reliable paleontological documents on the history of the empidoid type are only present from tertiary times onwards. A relatively rich fauna of these insects is known, preserved in baltic amber (upper Eocene). However, as in the majority of other cases of findings in Tertiary faunas of representatives of Nematocera and brachycerous flies, these materials do contribute almost nothing to the clarification of the evolution of the individual systems of organs, apparently being systematically very close to the recent very diverse fauna. Mesozoic representatives of the group are unknown. Indications exist as to the discovery of some flies (genus Empidia Weyenbergh, 1869 -- Handlirsch, 1908, page 634) in the upper Jurassic of Bavaria being similar to empidids. However the existing descriptions do not offer sufficient grounds to verify these data. Only the study of the recent fauna might clarify the paths of evolution of the type.
Studying the wings of various empidids and of the characteristic Sciadocera, one may easily determine the presence of definite sharply expressed groups, subtypes.

1. The first, undoubtedly original subtype, possessing the least changed wings with rich venation is the brachystomatoid subtype, for which is characteristic the presence of a long Subcostal vein, four Radial [including the Radius proper] and three Medial branches, and, especially, a long cubital cell formed by the converging cubital and anal veins [CuA and 1A]. In addition, the Costal vein runs all around the wing although it is thinner and more delicate along the wing's hind-margin. This subtype includes few, clearly relict forms of the subfamily Brachystomatinae (the genera Brachystoma, Homalocnemis, see Figure 1, fifth image, and others) and is a connecting link between the tabanoid (cyrtosioid subtype) ( Part LXXI, 9th subtype) and the lifting many-veined (empidoid) types.

2. The most diverse subtype, including the main mass of empidids, is the microphoroid subtype, for which it is characteristic the reduction [i.e. shortening] of the cubital cell, being more simple [i.e. shorter] than the [so-called] posterior basal [cell] [with the latter apparently is meant the cell lying directly above it] (as a result of shortening and curving of the Cubital vein), the weakening of the Subcostal vein, the frequent reduction of the fourth radial vein [i.e. the 3rd branch of the Radial Sector] and the strong development of the anal lobe reaching a large size. A rudimentary phragm is present in the basiala. Costalization of the venation is strongest expressed precisely in this subtype. To it belong representatives of the subfamilies Empidinae, Figure 1, 3rd and 4th image, Ocydromiinae and Noezinae, the most species-rich groups of Empidids. This subtype was the point of departure for the origin of the vast muscoid type [later to be introduced].

To ROHDENDORF's figures of wings of the microphoroid subtype may be added that of Microphorus velutinus (Empididae) :

and that of Hormopeza obliterata (Empididae), in which the Radial Sector is 3-branched :

3. Fairly diverse groups together form the special atalantoid subtype, characterized by the development of peculiar wings narrowed in their basal part. Anal lobe not projecting, in the form of a smooth outgrowth. The cubital cell and the number of Radial and Medial branches as in the previous subtype. Sometimes the cubital cell is totally reduced (Ceratomerinae, Figure 1, bottom image ). Characteristic is the shortening of the Subcostal and first Radial vein [i.e. the Radius proper] never running beyond the middle of the anterior wing-margin. To this subtype belong many species of the subfamilies Atalantinae, Hemerodromiinae, and Ceratomerinae.

To ROHDENDORF's figure of a wing of this subtype we must add some more wings. Note that in them, as also in the wing depicted by ROHDENDORF, the Radial Sector is 3-btanched :

Wing-venation of Hemerodromia raptoria Meig. Empididae. (atalantoid subtype) (After HENNIG, 1954)

Wing of Lamposoma cavaticum Becker. Empididae. (atalantoid subtype) (After LINDNER, in Die Fliegen der palaearktischen Region)

4. A very peculiar structure of the wings is found in representatives of the corynetoid subtype, which is characterized by a decrease of absolute size (up to 1 mm!) and by the relative lengthening of the wings, almost always lacking the cubital cell, the Subcostal vein, and a projecting anal lobe. Media always with only two branches. Intermedial cell [= discoidal cell] coalesced with the posterior basal one [i.e. now forming just one single cell] and shifted to the base of the wing. The wing as a whole has a characteristic tongue-like shape. To this subtype belong the characteristic species of the subfamily Corynetinae (= Tachydromiidae of earlier authors!, Figure 1, first image ).

To the one Figure given by ROHDENDORF of a wing representing the corynetoid subtype we may add the following from LINDNER, Die Fliegen der palaearktischen Region :

3 - Tachista annulimana, Empididae.
4 - Tachista brevipennis, Empididae.
5 - Tachista calcanea, Empididae.
6 - Tachista connexa, Empididae.
7 - Tachista costalis, Empididae.
8 - Tachista interrupta, Empididae.
9 - Tachista ornatipes, female. Empididae.
10 - Tachista sabulosa, Empididae.
11 - Tachista terricola, Empididae.
In the next two Corynetas (one of them already earlier depicted) the cubital cell is still more or less present :
12 - Coryneta cursitans, Empididae.
13 - Coryneta stigma, Empididae.
14 - Stilpon lunata, Empididae.
15 - Stilpon nubila, Empididae.

5. A very special structure of the wings is found in the sciadoceratoid subtype. Shape of wings shortened. The wings have an all-out convex anterior margin and a still more convex posterior margin. Subcostal vein very short, ending up in the Radius. The three Radial veins are unbranched. The Medial veins are weaker, three branches. There is almost no cubital vein. All cross-veins have shifted towards the base of the wing. Anal lobe weakly convex. The basiala is individualized, apparently with a rudimentary phragm. The wing as a whole has a very characteristic look as a result of its radiating straight veins. To this subtype belong the few relict forms of the family Sciadoceratidae ( second image of Figure 1 ).

Evaluating the variability and evolutionary pathways of the empidoid type, one can clearly see the microphoroid wings as representing the most progressive subtype (= 2nd subtype of the present type), in the wings of which one finds the most clearly expressed processes of costalization, together with the individualization and strenghening of the basiala. The other subtypes show various narrow-specialized features : such as the narrowing of the wings and the disappearance of the anal lobe, which we saw in the atalantoid wings or in the radiating venation in the sciadoceratoid subtype. Finally, a significant narrowing of the wings, decrease of their general size, dilution of the venation, the presence, in addition, of "reduced-winged" or even of totally wingless forms -- all this is characteristic of the corynetoid subtype and non-flying empidids [the latter] undoubtedly having originated from those who had wings of that subtype. It is completely legitimate to consider the corynetoid subtype as representing a regressive form of empidoid wings. The first, primitive brachystomatoid subtype is still insufficiently known, and judging more precisely about its evolutionary significance is not yet possible.
Considering the pathways of changes in the empidoid type as a whole, we must first of all note the presence of regressive stages in evolution. Indeed, although the development of the progressive microphoroid subtype has taken place, not less so we may distinguish the regressive corynetoid subtype. In addition to these subtypes there are also narrow-specialized forms in the form of the atalantoid, sciadoceratoid, and, probably, brachystomatoid subypes of wings. All this forces us to conclude that the flight-functional qualities of empidoid wings are not high, and that the overall direction of evolution of this type only partly shows the character of progressive development, [and is] in a significant degree narrow-specialized.
The source of the empidoid type were special forms of tabanoid wings, namely of its cyrtosioid subtype. The intensification of costalization processes that took place in these predatory flies (Empididae), decrease of body size together with the general subordinated significance of the flight-function (as a result of the powerfully developed legs and living amidst vegetation) -- all this determined the formation of the empidoid type in which the perfection of the flight-abilities were held up and even led to the loss of this function. The interaction of all mentioned demands and conditions (lengthening of the body + powerful legs + predatism + living among dense vegetation) determined the present condition of this type of wings.

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In the next document we will set up the venational derivational lines and morphoklines of the representatives of the empidoid type.

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