Organic Evolution in terms of the Implicate and Explicate Orders.

Part XXVII :

The evolutionary diversification in the Order Diptera.

Example of two totally different groundplans nevertheless suited to be fitted into the same ecological niche.

Each organic family-groundplan intrinsically defines a definite set of potential ecological niches. If a potential ecological niche actually exists in the Explicate Order its noëtic counterpart constitues the existential conditions of this groundplan. And the noëtic content of this groundplan can only be projected into the Explicate Order when it carries with it the noëtic content of those existential conditions. This projection is then in the Explicate Order experienced (by us) as an evolutionary process in which an existing species adapts itself to a given ecological niche. And this colonization of such a new ecological niche often results in the appearance of a new species, that is, the original species splits into two species. In this way a family-groundplan is fanning out over the ecological landscape resulting in its multiplication or differentiation, that is, the appearance of the many species and species groups (genera) of the family.
From this we would expect that the respective ranges of possible ecological niches inherent in different groundplans do not overlap, that is, we do not expect that instances of two clearly different groundplans can occupy the same ecological niche. Said differently, we do not expect to find two (or more) species that are not taxonomically related to each other living in one and the same ecological niche (where "ecological niche" should be understood as a given set of living conditions. Such a set can be instantiated, that is, it can exist in the form of a number of individual cases of it to which we can point with the finger). In fact there exist different species -- representing widely different groundplans -- that do live in precisely the same (larval) ecological niche. And such a fact is of course important for the theory of groundplans. We shall present an example concerning the behavior of the larvae of (1)  Myrmeleon  formicarius,  being a member of the family Myrmeleontidae (Ant Lion flies) belonging to the insect Order Neuroptera, suborder Planipennia (which is by some considered to be an Order), and (2)  Vermileo  vermileo,  being a member of the family Rhagionidae (= Leptidae) belonging to the insect Order Diptera.
The next Figures depict the respective imagines. Because we cannot not find a picture of (2) -- Vermileo  vermileo,  we instead give one of  Rhagio  which certainly gives us a good idea of the family-groundplan of the imagines of Rhagionidae :

Figure 1 :  Imago of  Myrmeleon  formicarius,  Ant Lion (Order Neuroptera). Wing-span 65-75 mm.
(After ZAHRADNIK, in Thieme's Insektengids, 1977)

Figure 2 :  Imago of  Rhagio  scolopaceus  (Order Diptera). 13-18 mm.
(After ZAHRADNIK, in Thieme's Insektengids, 1977)

Let's now go ahead with the example, taken from WEBER in his  Grundriss der Insektenkunde, 1966, p. 324-326 :

Figure 3 :  Constructors of sandpit traps.
a, a' -- Myrmeleon  formicarius,  larva, dorsal view, and funnel with ambushing animal in profile. (After DOFLEIN)
b, b' -- Vermileo  vermileo,  larva. (After BUCHNER, redrawn)
c -- Typical habitat, profile, schematic.
(From WEBER, 1966)

The Ant Lion, the larva of the Planipennian  Myrmeleon  formicarius (See Figure 3, left), living in central and southern Europe, and the Worm Lion, the larva of the Leptid (= Rhagionid)  Vermileo  vermileo (See Figure 3, center), living in the mediterranean countries, show in their overall structure all prototypic characters of the taxonomic groups to which they belong. The Ant Lion, with a well-differentiated head, with powerful pincers (Mandibles + Maxillae), and possessing true legs, is just as clearly a member of the Planipennia as the legless hemicephalous (= head not clearly differentiated) Worm Lion is a dipterous larva. The only similarity between them consists of the fact that the posterior end of their body is more heavily thickened and bristled, as is otherwise usual in the respective groups (in Figure 3, b, the bristles are not drawn). Both species are markedly stenök (narrowly confined ecologically) and stenotopous (very locally living). Sometimes they (that is, larvae of both species) can be found together at precisely the same type of locality, in places where there is homogeneous fine and dry, and therefore easily mobile, sand, especially under overhanging edges of paths or roadsides (see Figure 3, right), where sandstone disintegrates and where rain seldomly can interfere. Slopes facing south are preferred because of the rich incidence of solar rays.
Both larvae are ambushing predators that construct funnel traps in the sand, in which funnels small prey animals, chiefly ants which are abundant in such places, accidentally fall because they are unable to have a grip at the inclined funnel walls and rolling sand. At the bottom lurks the predator buried in the sand, only having projected its anterior body part above the surface while adopting a characteristic posture. The Ant Lion (Figure 3, a') is with its thick bristled trunk well-anchored in the sand. Only the prothorax with head are mobile with repect to the trunk, and also these are essentially only able to be swung (albeit quite extensively) in the central plane. With the sucking pincers, that are held open while the animal is lurking, and which are able to forcefully grab, the predator takes its victim in order to suck it empty while extra-intestinally digesting it. When the prey is trying to liberate itself sand rolls on the head of the predator and triggers a violent to and fro flinging, usually frustrating the prey's liberation attempt, because as a result of the sand flinging around, the funnel walls get into motion. The necessary hold against the liberation attempts of the seized prey is accomplished by the predator being firmly anchored in the sand. It is also so accomplished by the Worm Lion in virtue of its thickened bristled posterior body part. But the Worm Lion lurks while lying on its back, and correspondingly its eyes are placed ventrally, while they are dorsally placed in the Ant Lion. With its anterior end it winds itself around the prey animal in order to also suck it empty while extra-intestinally digesting it. The Worm Lion does not show the swinging movement when seizing the prey. But it does show it while constructing its funnel, which in both species is done in essentially the same way. Both, when placed on sand, directly disappear beneath the surface, they show marked positive thigmotaxis, that is striving for having their body, apart from its anterior end, into possibly all-round contact with solid objects. On sand this boils down to having themselves buried into it. The Ant Lion pushing its body backwards over the sand with the help of its anteriorly placed fore-legs (atypical of larvae of Planipennia) and holding its posterior end against the bottom, jerkily pushes itself into the sand. It is held in this position by its chiefly forwardly pointing bristles. The Worm Lion accomplishes this by bending its trunk, and both species then fling, when undisturbed, with their anterior end the sand away, and in this way gradually construct their regularly formed funnel, which, at least in the case of the Ant Lion, independent from the animal's body size, becomes as large as its period of starvation had been large.
So a few interpenetrating reactions, which in the two species, corresponding to the differences in their respective morphological constitution, differ somewhat, but are as to their result identical, thus effect the amazing conformity of funnel construction and the seizing of prey. Both, construction and seizing, are possible in dry fine sand (or correspondingly fine earth, wood rot, and the like) only, and such a substrate is only present in certain limited localities where also the prey animals live. These necessary places could not actively have been found by the larvae with the means at their disposal. But they do not need to look for them, because in both species the adult female knows where to deposit her eggs, that is, in places where the living conditions of the larvae are present (also the pupae rest in sand). In the case of  Vermileo  (worm-lion) it has been demonstrated that the female fly, before laying eggs, checks the substrate as to its quality by dragging her dangling hindlegs over it, while with respect to  Myrmeleon  (ant-lion) one is not further informed in this respect.

While in the case of  Vermileo  the imagines take food from flowers, the imago of  Myrmeleon  is known to be unable to take food. Its life therefore is short. ( WEBER, 1966).

Before we are going to discuss this example of WEBER's in the context of our theory of organic groundplans, some additional information might be instructive. RICHARDS & DAVIES, 1977, in  Imms' General Textbook of Entomology,  p. 999, while dealing with the family Rhagionidae, add :

Females of  Vermileo  and  Lampromyia  (Hemmingsen, 1963) lay their eggs in sand, and the larvae construct conical pitfalls for the capture of their prey, after the manner of 'ant lions'. The 5th segment of the larva bears a ventral mobile pseudopod which assists in seizing and holding the prey. The 10th and 11th segments each carry a transverse row of long hooklets which serve as organs for boring and fixation (cf. Wheeler, 1930).

So, according to this additional information there exists, in the Rhagionidae, in addition to  Vermileo,  yet another species the larva of which lives in the same way.

In the example of WEBER we have seen that the ecological niche of at least the   l a r v a e  of two taxonomically unrelated insects is identical. In describing and defining the ecological niche of a given insect species the habitats of larvae as well as of the adults must be taken into account. In the case of  Vermileo  and  Myrmeleon  the adults of the former take nectar (from flowers), and this is only to fuel its flight-muscles. As seems to follow from WEBER's account, no other food is taken. The adult of the latter (Myrmeleon) flies (around), but does not take food at all. So the way of life of the respective adults does not differ significantly. Therefore it is allowed to consider the whole ecological niche of the two species  Vermileo  (Diptera) and  Myrmeleon  (Neuroptera) to be identical, or at least virtually identical, while the respective groundplans invoved differ sharply from one another. So it is not  a  priori  impossible that two substantially differing groundplans have instances that occupy precisely the same ecological niche.
Also this example demonstrates that, apart from certain exceptional cases (such as in epizoic diptera), a groundplan's significance is only partially, or sometimes not at all, ecological, that is, its significance is mainly formal.
In the case of the ancestral family (whatever this may be) of the Myrmeleontidae (ant-lion flies) we may suppose that while (this ancestral family) radiating into various ranges of the ecological landscape, and thus successively occupying and adapting to the various potential ecological niches circumscribed by its groundplan, instances of it stumble upon a peculiar member of the set of potential ecological niches :  ambushing ants in specially constructed pitfalls. Initial circumscription of this niche, followed by injection into the Implicate Order, noëtic reaction, and projection of the reaction-product back into the Explicate Order (as generally described earlier) result in the definitive adaptation of the larvae to such a way of life and in the establishment of a new neuropterous family, the Myrmeleontidae. But what is interesting here is that the dipterous family Rhagionidae, while radiating into the ranges of the ecological landscape and successively occupying its potential ecological niches, it, while stumbling upon it, finds out that  "ambushing ants in specially constructed pitfalls"  turns out to be among its potential ecological niches as well. And also here, initial circumscription of this niche, followed by injection into the Implicate Order, noëtic reaction, and projection of the reaction-product back into the Explicate Order result in the definitive adaptation of the larvae to such a way of life and in the establishment of a new dipterous species,  Vermileo  vermileo  ( Here the acquired adaptations are apparently not far-reaching enough to effect a transformation of the original groundplan of the Rhagionidae into a new groundplan).
This concludes our exposition of the fact that it is not as a rule impossible for two different groundplans to have instances that occupy the same ecological niche.

Later, some general insights that still further develop the theory of organic groundplans will be added .  .  . 

In the foregoing four documents (Parts XXVII, XXVI, XXV, and XXIV) we have discussed the idea of groundplan and its relation to ecology and the Implicate Order. The theory of groundplans expounded in these documents is meant to be a general theory, i.e. a theory that is supposed to apply not only to Diptera, and to all insects for that matter, but also to all organisms. Organic evolution is not a process aimed at an ongoing improvement of biological structures, that is, not a process exclusively concerned with intensifying existing adaptations of organisms to their environment. Of course evolution, as we experience it in the Explicate Order (or how it takes place in that Order), is surely driven by ecological factors, that is, by the successive colonization of new ecological niches. And adaptation plays a role therein. But as can already be seen in the Explicate Order, evolution also turns out to be driven by purely formal factors, factors that is, whose nature is not ecological. We have seen this in the morphology of dipterous insects, where we can distinguish a number of different body groundplans that apparently have only little ecological significance, and are mainly of a formal nature. And in order to understand this we have described these groundplans and their (formal) evolution in terms of an analogy based on mineral stability diagrams. The formal derivation (= noëtic evolution) in the Implicate Order of one groundplan (in its noëtic form) from another (also in its noëtic form), where, of course, biological adaptation cannot play a role, is described in terms of unidirectional phase transitions as they take place in certain physical substances when thermodynamic conditions change. Subsequent projections of the noëtic forms of the newly derived groundplans are seen in the Explicate Order as evolutionary transformations of one organic groundplan into another. However, a noëtic form of a groundplan can only project into the Explicate Order if it is provided with the noëtic forms of conditions of existence in this Order. And it is these conditions that contain the relevant adaptations to a certain ecological niche existing in the Explicate Order.

Preceding all these expositions of organic groundplans we were studying the evolution of wing-venation in nematocerous diptera (crane-flies, mosquitoes, midges, etc.). The last family group we have looked into in this respect were the Rhyphidea. And because these have apparently formed the evolutionary point of departure of all the higher Diptera (including rhagionids, horse-flies, robber-flies, hover-flies, and all the muscoid flies [acalyptrates and calyprates] ),  much attention was given to the possible evolutionary transition leading from rhyphoid to muscoid flies. And in that exposition the theory of groundplans was born.

In the next document we will pick up again our exposition of the evolution of wing-venation in Diptera (first finishing the Nematocera and then passing on to the rest of the Diptera).

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