Queen–worker ratio affects reproductive skew in a socially polymorphic ant

The partitioning of reproduction among individuals in communally breeding animals varies greatly among species, from the monopolization of reproduction (high reproductive skew) to similar contribution to the offspring in others (low skew). Reproductive skew models explain how relatedness or ecological constraints affect the magnitude of reproductive skew. They typically assume that individuals are capable of flexibly reacting to social and environmental changes. Most models predict a decrease of skew when benefits of staying in the group are reduced. In the ant Leptothorax acervorum, queens in colonies from marginal habitats form dominance hierarchies and only the top‐ranking queen lays eggs (“functional monogyny”). In contrast, queens in colonies from extended coniferous forests throughout the Palaearctic rarely interact aggressively and all lay eggs (“polygyny”). An experimental increase of queen:worker ratios in colonies from low‐skew populations elicits queen–queen aggression similar to that in functionally monogynous populations. Here, we show that this manipulation also results in increased reproductive inequalities among queens. Queens from natural overwintering colonies differed in the number of developing oocytes in their ovaries. These differences were greatly augmented in queens from colonies with increased queen:worker ratios relative to colonies with a low queen:worker ratio. As assumed by models of reproductive skew, L. acervorum colonies thus appear to be capable of flexibly adjusting reproductive skew to social conditions, yet in the opposite way than predicted by most models.     

THE EVOLUTION OF WORKER STERILITY IN HONEY BEES: AN INVESTIGATION INTO A BEHAVIORAL MUTANT CAUSING FAILURE OF WORKER POLICING

Normally, worker honey bees (Apis mellifera) only lay eggs when their colony is queenless. When a queen is present, worker egg-laying is controlled by mutual “policing” behavior in which any rare worker-laid eggs are eaten by other workers. However, an extremely rare behavioral phenotype arises in which workers develop functional ovaries and lay large numbers of eggs despite the presence of the queen. In this study, microsatellite analysis was used to determine the maternity of drones produced in such a colony under various conditions. One subfamily was found to account for about 90% of drone progeny, with the remainder being laid by other subfamilies or the queen. No evidence of queen policing was found. After a one-month period of extreme worker oviposition in spring, the colony studied reverted to normal behavior and showed no signs of worker oviposition. However, upon removal of the queen, workers commenced oviposition very quickly. Significantly, the subfamily that laid eggs when the queen was present did not contribute to the drone production when the colony was queenless. However, another subfamily contributed a disproportionately large number of drones. The frequency of worker oviposition appears to be determined by opposing selective forces. Individual bees benefit from personal reproduction, whereas other bees and the colony are disadvantaged by it. Thus a behavioral polymorphism can be maintained in the population in which some workers can escape worker policing, with balancing selection at the colony level to detect and eliminate these mutations.     

Optimal colony fissioning in social insects: testing an inclusive fitness model with honey bees

In most species of social insects, when a queen departs from her parental nest to found a new colony, she leaves on her own. In some species, however, the departing queen leaves accompanied by a portion of the parental colony’s workers and there is a permanent fissioning of the worker force. Little is known about how the adult workers in colonies of fissioning species distribute themselves between the old and the new colonies. We examined this problem, building on Bulmer’s (J Theor Biol 100: 329–339, 1983) model for the optimal splitting of a colony’s adult workforce during colony reproduction. We first created an inclusive fitness model of optimal colony fissioning that applies to species in which fissioning gives rise to two autonomous colonies. The model predicts the optimal “swarm fraction”, which we define as the proportion of the adult workers in a fissioning colony that join the departing queen. We then tested the model by comparing the predicted and observed swarm fractions in honey bees. We found a close match between predicted (0.76–0.77) and observed (0.72 ± 0.04) swarm fractions. Evidently, worker honey bees distribute themselves between the old and new colonies in a way that jointly maximizes the inclusive fitness of each worker. We conclude by discussing additional ways to test the model.     

Morphological variability of intercastes in the ant Temnothorax nylanderi: pattern of trait expression and modularity

Ants have distinct morphological castes (queens and workers), but aberrant queen-worker “intercastes” occasionally occur, both in wild and laboratory conditions. Intercastes are rare, however, such novel phenotypes may have evolutionary significance. Their morphology is highly variable in any given species, providing valuable information about the integration of queen traits (e.g. ocelli, wings, complex segmentation of thorax, large gaster and ovaries, spermatheca). Generally, these traits are all diminished or absent in workers. We used multivariate morphometry to analyze an exceptionally large sample of 101 intercastes of Temnothorax nylanderi. We determined distributions and correlations of traits, and confirmed the mosaic nature of intercastes. Queen-specific traits are not expressed coherently in intercastes, but the possible patterns of trait combination are limited. A large number of small-sized intercastes had disproportionately larger head, ocelli and gaster but smaller thorax. In contrast, queen-like growth of thorax and rudimentary wings only occurred in large-sized intercastes. This is the most comprehensive analysis of intercaste variability, and suggests the existence of constraints on recombination of caste-specific modular traits.     

REVISING A CLASSIC BUTTERFLY MIMICRY SCENARIO: DEMONSTRATION OF MÜLLERIAN MIMICRY BETWEEN FLORIDA VICEROYS (LIMENITIS ARCHIPPUS FLORIDENSIS) AND QUEENS (DANAUS GILIPPUS BERENICE)

Batesian and Müllerian mimicry relationships differ greatly in terms of selective pressures affecting the participants; hence, accurately characterizing a mimetic interaction is a crucial prerequisite to understanding the selective milieux of model, mimic, and predator. Florida viceroy butterflies (Limenitis archippus floridensis) are conventionally characterized as palatable Batesian mimics of distasteful Florida queens (Danaus gilippus berenice). However, recent experiments indicate that both butterflies are moderately distasteful, suggesting they may be Müllerian comimics. To directly test whether the butterflies exemplify Müllerian mimicry, I performed two reciprocal experiments using red-winged blackbird predators. In Experiment 1, each of eight birds was exposed to a series of eight queens as “models,” then offered four choice trials involving a viceroy (the putative “mimic”) versus a novel alternative butterfly. If mimicry was effective, viceroys should be attacked less than alternatives. I also compared the birds' reactions to solo viceroy “mimics” offered before and after queen models, hypothesizing that attack rate on the viceroy would decrease after birds had been exposed to queen models. In Experiment 2, 12 birds were tested with viceroys as models and queens as putative mimics. The experiments revealed that (1) viceroys and queens offered as models were both moderately unpalatable (only 16% entirely eaten), (2) some birds apparently developed conditioned aversions to viceroy or queen models after only eight exposures, (3) in the subsequent choice trials, viceroy and queen “mimics” were attacked significantly less than alternatives, and (4) solo postmodel mimics were attacked significantly less than solo premodel mimics. Therefore, under these experimental conditions, sampled Florida viceroys and queens are comimics and exemplify Müllerian, not Batesian, mimicry. This compels a reassessment of selective forces affecting the butterflies and their predators, and sets the stage for a broader empirical investigation of the ecological and evolutionary dynamics of mimicry.     

New data on programmed aging — slow phenoptosis

This review summarizes the latest data on biochemistry and physiology of living organisms. These data suggest that aging, i.e. coordinated age-dependent weakening of many vital functions leading to gradual increase in the probability of dying, is not common to all organisms. Some species have been described whose probability of death does not depend on age or even decreases with age, this being accompanied by constant or increasing fertility. In the case of the naked mole rat (a non-aging mammal), a mechanism has been identified that protects this animal from cancer and the most common age-related diseases. The high molecular weight polysaccharide hyaluronan, a linear polymer composed of multiple repeated disaccharide of glucuronic acid and glucosamine, plays the key role in this mechanism. Hyaluronan is accumulated in the intercellular spaces in the organs and tissues of the naked mole rat. This polysaccharide provides early contact inhibition of cell division (anti-cancer effect). In addition, hyaluronan prevents the development of certain types of apoptosis, in particular, those induced by reactive oxygen species (ROS) (geroprotective effect preventing ROS-induced decrease in cellularity in the organs and tissues of aging organisms). Extraordinary longevity of the naked mole rat (over 30 years, which is long for a rodent the size of a mouse) is connected to its eusocial lifestyle, when only the “queen” and its few “husbands” breed, while the huge army of non-breeding “subordinates” provide the “royal family” with protection from predators, food, and construction and maintenance of an underground labyrinth size of a football field. This way of life removes the pressure of natural selection from the “family” and makes aging — the program that is counterproductive for the individual but increases “evolvability” of its offspring — unnecessary. The example of the naked mole rat demonstrates the optional character of the aging program for the organism. Many facts indicating that aging can be regulated by an organism provide another argument in favor of optionality of aging. Cases have been described when aging as a program useful for the evolution of offspring but counterproductive for the parental individual slows under conditions that threaten the very existence of the individual. These conditions include food restriction (the threat of death from starvation), heavy muscular work, decrease or increase in the environmental temperature, small amounts of poisons (including ROS; here we speak about the paradoxical geroprotective effect of the low doses of prooxidants that inhibit apoptosis). On the other hand, aging can be inhibited (and maybe even cancelled) artificially. This can be done by turning off the genes encoding the proteins participating in the aging program, such as FAT10, p66shc, and some others. In addition, the gene of the antioxidant enzyme catalase can be addressed into mitochondria, where it will split mitochondrial hydrogen peroxide, the level of which increases with age. However, today the simplest way to slow down the aging program is the use of mitochondria-targeted low molecular weight antioxidant compounds of plastoquinonyl decyltriphenylphosphonium-type (SkQ1), which prolong the life of animals, plants, and fungi and inhibit the development of many age-related diseases and symptoms.     

REPRODUCTIVE CONFLICT IN BUMBLEBEES AND THE EVOLUTION OF WORKER POLICING

Worker policing (mutual repression of reproduction) in the eusocial Hymenoptera represents a leading example of how coercion can facilitate cooperation. The occurrence of worker policing in “primitively” eusocial species with low mating frequencies, which lack relatedness differences conducive to policing, suggests that separate factors may underlie the origin and maintenance of worker policing. We tested this hypothesis by investigating conflict over male parentage in the primitively eusocial, monandrous bumblebee, Bombus terrestris. Using observations, experiments, and microsatellite genotyping, we found that: (a) worker‐ but not queen‐laid male eggs are nearly all eaten (by queens, reproductive, and nonreproductive workers) soon after being laid, so accounting for low observed frequencies of larval and adult worker‐produced males; (b) queen‐ and worker‐laid male eggs have equal viabilities; (c) workers discriminate between queen‐ and worker‐laid eggs using cues on eggs and egg cells that almost certainly originate from queens. The cooccurrence in B. terrestris of these three key elements of “classical” worker policing as found in the highly eusocial, polyandrous honeybees provides novel support for the hypothesis that worker policing can originate in the absence of relatedness differences maintaining it. Worker policing in B. terrestris almost certainly arose via reproductive competition among workers, that is, as “selfish” policing.     

Zhishifenzi [Chinese intellectuals] and power

An appetizing smell of beetroot soup came wafting from the kitchen, with it the rhythmic sound of chopping... Ye Zhiqiu ... was in a mood to play some prank out of keeping with her age... So she tried to repress her elation, to behave like a middle-aged Chinese woman. Perhaps she didn't try hard enough, for a little of it came bubbling out as she called in her rusty French, “Qu'est-ce qu'on mange au dejeuner?” Mo Zheng promptly called back from the kitchen, “De la soupe au potiron, de saucisson et du pain.” Good lad, he hadn't forgotten his French. That came of his upbringing in a cultured family.¹     

Techniques for keeping wheat bulb fly larvae (Leptohylemyia coarctata) in sterile conditions

Three techniques are here described with special reference to investigation of bacterial diseases, as recently reported by Hamid (1966). Wheat seed without chemical dressing is sown in boxes and allowed to grow 10 cm high. Plants are then lifted. After washing off soil and discarding the roots and apical half of the leaves, the central succulent part of the plant is chopped up with scissors into very fine pieces. These pieces are crushed in a basin and after adding sufficient water to give a thick suspension, finally macerated for about 5 minutes (a top-drive macerator, Townson and Mercer Ltd. was used). This thick suspension is then centrifuged for 5 minutes at a speed of 5000 revolutions per minute and filtered through a Seitz filter. In the following techniques the filtrate is referred to as “nutrient solution” and the suspension as “macerated wheat”. Rigid bacteriological standards of sterility are maintained throughout the techniques.     

Entrainment of Stage 2 Sleep Spindles by Weak,Transcerebral Magnetic Stimulation in an “Epileptic” Woman

The proportions of Stage 2 spindles present per second over the prefrontal and temporal lobes of a patient who had been experiencing complex partial epileptic-like experiences and disturbances in sleep patterns for four years following a closed head injury were measured while a weak (1microT) burst-firing magnetic field was applied transcerebrally through the temporoparietal regions. In several successive segments during the exposure the onsets of the spindles were significantly correlated (rhos between 0.30 and 0.40) with the onset of the field that was presented once every 3 s for about 0.7s. Lag/lead analyses indicated only the contemporary occurrence of the fields and the spindles were significantly correlated over time. These results suggest that some states of consciousness, particularly those associated with the “epilepsy spectrum disorder” may be more sensitive to entrainment or “synchronization” by weak complex magnetic fields whose temporal structures are designed to simulate natural brain activity.     

Discovering gorilla

On July 16, 1847, a missionary newly arrived in New York City from West Africa packed a collection of bones in a box and shipped them off to a colleague in Massachusetts. In a letter, Thomas S. Savage (Fig. 1), a graduate of Yale College and Yale Medical School, admitted to being “quite unwell,” probably meaning “utterly wretched.” He had already endured tropical diseases in Liberia off and on for more than a decade, and he'd seen his first two wives languish and die there, probably of malaria. He wasn't the sort to complain lightly.     

Showing off,handicap signaling,and the evolution of men's work

Zahavi's 1 , 2 handicap principle makes “waste” a common outcome of signal selection because the cost of a signal guarantees its honesty. The capacity to bear the cost reveals the show‐off's hidden qualities. While displays take many forms, some also provide fitness‐related benefits to the audience in addition to information about the show‐off. Zahavi 3 has used the handicap principle to explain both merely wasteful displays and altruistic behavior. Here we focus on the distinction between these two kinds of display and the importance of benefits other than information in show‐off explanations of a particular puzzle in human evolution: men's work. Males of other primate species do not contribute any significant fraction of the food consumed by females and juveniles. Our own species is different. When people live on wild foods, hunting is usually a specialty of men, and meat is commonly a substantial component of everyone's diet. Here we explore the hypothesis that this unique male subsistence contribution may have evolved as hunting large animals became a focus of competitive display.     

Disturbed Sleep in Shift Workers,Day Workers,and Insomniacs

Very little is known about differences in sleep between day and shift workers in representative samples of the population. This study compared a national representative sample (N=3400) of shift (with night shifts) and day workers regarding the different types of sleep disturbances and also the level of sleep symptoms with that of insomnia patients. The results showed very few differences between shift and day workers; only “too little sleep” and “nodding off at work” were marginally higher among shift workers. The results also showed that the complaints of insomnia patients for most sleep disturbances corresponded to the 2nd–16th percentile of the shift workers' levels of complaints. The results suggest, at least with the present questionnaire methodology, that shift work does not appear to be a major source of sleep disturbances and that their complaint levels bear no resemblance to those seen in insomniac patients.     

Walking back the cat: Unsupervised classification as an aid in “remote” fossil prospecting

Counterintelligence analysts use a technique called “walking back the cat'' to reveal “moles” or others passing on disinformation in which they compare what they now know as fact against what their agents or informers had told them to expect about certain persons or events. 1 Thus, “walking back the cat” is a perfect metaphor for working backwards; that is, retracing the complex development of an event and examining the “run up” to it in order to gain useful insights about how that event unfolded. Perhaps paleoanthropology can profit from such an approach.     

The evolution of creationists in the United States: Where are they now,and where are they going?

The history of anti-evolutionism in the United States begins only in the early decades of the 20th century but has evolved considerably since then. Various versions of the movement (“equal time” for creationism, “creation science”, “intelligent design”) have developed over time, but they have made few positive contributions to serious discourse about science and religion. Their main goal has been to try to stop the teaching of evolution. The most recent version of creationism, “intelligent design” (ID), has little in common with William Paley's 18th-century version: ID posits an interventionist Deity who regularly interferes in natural processes to produce complex biological structures and functions. The 2005 “intelligent design” trial in Dover, Pennsylvania, destroyed any pretensions that the movement had to scientific integrity. However, anti-evolutionists continue to foment discord at local levels, where opposition to the teaching of evolution can be presented without strong resistance. Scientists can best demonstrate their concern by becoming involved in federal, state, and local administrative processes that determine curricula and develop and adopt textbooks and other instructional materials. To cite this article: K. Padian, C. R. Biologies 332 (2009).     

Wer hat die Initiative bei den Ausflügen der Jungkönigin,die Königin oder die Arbeitsbienen?

Zusammenfassung An insgesamt 16 Völkern wurden unter verschiedenen Bedingungen die Vorgänge untersucht, die zu den Ausflügen der jungen Bienenkönigin führen. Die Beobachtung ergab, daß die junge Königin nur flugbereit wird, wenn sie von den Arbeitsbienen in bestimmter Weise traktiert und durch den Stock gehetzt wird. Starke Aggressivität eines Volkes seiner jungen Königin gegenüber und starke Ausbildung der Arbeiterinnenovarien fallen zusammen, sind jedoch nicht miteinander gekoppelt.

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Summary In 16 colonies of bees the behaviour of worker bees and of young virgin emergency-queens has been observed. The result is that the virgin does not become ready to fly unless she is treated in a certain way by the worker bees.On normal conditions (5 colonies observed) the newly emerged queen does not receive any attention from the workers in the first hours of her life. But from her first midday forth the bees give her great attention by touching, licking, feeding, and facing her. Some workers near the queen show a remarkable vibration of their abdomens in vertikal direction. Besides the queen is frequently attacked by workers who push her, cling on to her, pull her by her legs and wings, and sometimes overthrow her. The queen usually reacts upon such attacks by trying to defend herself, by piping, which causes a sudden numbnes of the bees, and by running away. The flight of the queen stimulates the workers to chase and attack her all the more and often it comes to methodical huntings after the queen. For the queen, the result is increased want of food and an increase of her bodily efficiency until she is ready to fly. Last preparations for flying are made by the queen herself: hurriedly she rushes about on the combs and suddenly she turns to light until she finds the entrance of the hive.—After each flight of the queen the attacks of the bees loose in strength, but become harder again before she starts next time. The attacks are not stopped till the queen begins laying.Observations at a colony dequeened long before receiving a newly emerged queen (strengthened attacks upon the queen) and observations at colonies made of newly emerged bees (no attacks upon the queen) proved the queen to be sooner ready to fly the more she is attacked by the workers. Mild treatment may cause the flights of the queen to be put off or even to be left undone.Colonies attacking their queens hard always contain a high percentage of anatomical laying workers. There seems to be a relation between aggressiveness (towards the queen) and ovary development in worker bees. There is however no direct relation: one colony that did not get any pollen (so that worker's ovaries could not develop) was attacking its virgin queen as well as normal control colonies.

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Résumé Le comportement des Abeilles ouvrières et des jeunes reines remplaçantes, nouvellement écloses et vierges, a été observé dans 16 colonies. Il se manifesta que la jeune reine n'est prête à s'envoler que si elle est traitée d'une certaine façon par les ouvrières.Dans des conditions normales (5 colonies observées), les ouvrières ne tiennent aucun compte de la reine qui vient d'éclore. Or, dès le milieu de la première journée de sa vie, l'intérêt des ouvrières est très vif; elles touchent la reine, elles la lèchent, elles la nourrissent et se conforment sur elle. Quelques Abeilles à proximité de la reine manifestent un tremblement étrange de l'abdomen, dans le sens vertical. De plus, la reine est souvent attaquée par des ouvrières; elles la poussent, elles se cramponnent à elle, elles la tirent par les pattes et les ailes, et la renversent. La reine, par réaction, se défend ou s'enfuit; ou elle chante, ce qui fait tomber les Abeilles en torpeur. La fuite de la reine excite les Abeilles à la poursuite qui, parfois, dégénère en chasse acharnée. Le besoin alimentaire de la reine en devient plus fort, ses capacités physiques augmentent, jusqu'au moment où elle est enfin apte à l'envol. Elle s'élance alors avec frénésie par-dessus les rayons; tout à coup, elle se tourne vers la lumière et finit par trouver le trou de vol. Chaque fois que la reine rentre d'un vol, les attaques des Abeilles diminuent; mais elles redeviennent plus intenses jusqu'au départ suivant de la reine. Les attaques ne cessent que si la reine commence à pondre.Des observations faites dans une colonie orphelinée longtemps avant l'introduction de la jeune reine vierge (attaques renforcées contre la reine), ainsi que l'étude d'une colonie de jeunes Abeilles (pas d'attaques contre la reine) ont montré que la reine devient d'autant plus vite apte à l'envol qu'elle est attaquée par les ouvrières. Si la reine est traitée avec douceur, ses essors peuvent être fortement retardés ou même ils n'ont pas lieu.Chez les colonies qui attaquent vigoureusement leur jeune reine, on trouve toujours un grand pourcentage d'ouvrières pondeuses. Il semble donc qu'un rapport existe entre l'agressivité (contre la reine) et la formation des ovaires chez les ouvrières. Ce rapport, cependant, n'est pas direct: une colonie dépourvue de pollen, où, par conséquent, les ovaires des ouvrières ne pouvaient pas se développer, attaqua sa jeune reine aussi vigoureusement que les autres colonies de contrôle normales.

     

A triple test cross analysis to detect epistatic gene effects in cabbage (Brassica oleracea var. capitata L.): An updated methodology

The cross-pollinated crop Brassica oleracea var. capitata L. shows good heterotic heterosis at high output; better standing of the plants; early maturity; larger and more homogeneous heads; consistency of head compactness; and disease-tolerance in F1 hybrids. There is very limited information documented on the epistasis of essential cabbage characters. We expand the research in this study to include an upgraded test to cross-design for enrolling and estimating epistasis and other genetic variance components controlling head yield and component traits in cabbage. The data was obtained from 45 families produced by crossing 15 lines with three testers; SC 2008–09, E-1-3-1&2, and their single cross F1, was subjected to triple test cross analysis. The current study results confirmed “j + 1” form of epistasis which is a major component for all traits. The plant spread, non-wrapper leaves, nethead/grossweight, polar/equatorial diameter, marketable head yield per plot, iron content and dry matter lugged both “j + 1” and 'i' type with the predominance of the 'i' type of interaction. Except for head shape index, equatorial diameter, head compactness was more noticeable when observed in dominance component. The degree of dominance is in the partial range, but both the head shape index/compactness and equatorial diameter showed over dominance. For maximum part, superiority was shown in both the directions. Appropriate breeding procedures are proposed to exploit the different forms of gene effects discovered for genetic improvement of head yield and quality traits.     

Delimitating species in paleoanthropology

Evolutionary biologists created a large twentieth‐century literature about delimiting biological species. Paleontologists contributed the unique complications of deep time. Toward century's end, one participant wrote: “In all probability more paper has been consumed on the questions of the nature and definition of the species than any other subject in evolutionary and systematic biology.” 1     

Das Triplett aus zwei Monophyla und einem Paraphylum als Baustein des phylogenetischen Systems

The triplet consisting of two monophyletic taxa and one paraphyletic taxon as constructive element of the phylogenetic system Evolution has produced very many novelties (apomorphies). Most of them are small and relatively inconstant, these are more or less indicative of the phylogenetic relationships between closely related species. They cannot be the constitutive character of a supraspecific taxon that exists since a long time and comprises many diversified species. Such a taxon of higher rank can only be characterized by an improbable, rare novelty that has developed only once and has been preserved in all descendent species. Two consecutive apomorphies of this persistent type (‘fixed apomorphies’) characterize three supraspecific taxa, the triplet “A”, “B” and “A minus B” (Fig. 1). The group “A minus B” is rejected in Hennig's theory because it is ‘paraphyletic’, but it is not an artefact created by the systematicist. It is an inevitable mathematical consequence of the differentiatison of the group “B” within the group “A”. Being the result of a subtraction, it is necessarily associated with the two monophyletic partners in the triplet, as it is delimited on one side by the synapomorphy of the group “A”, of which it is a part, and on the other side by the autapomorphy of the separate group “B”. Traditional classifications often include paraphyletic groupings that are inconsistent with phylogenetics, e. g. the Reptilia and the Apterygota. The fault in such cases is that these groups are extended beyond the limits of a triplet and cover more than a single interval between consecutive monophyletic taxa. Paraphyletic groups are admitted in the phylogenetic system only for bridging the gaps in our cladistic information. According to HENNIG'S theory, all supraspecific taxa should be arranged two by two as sister-groups originating from one ancestral species and comprising all descendents of that species. The fixed evolutionary novelties which characterize higher supraspecific taxa are, however, rare and scattered. It is highly improbable that they have developed in sister species, therefore the taxa marked by them cannot be sister-groups (except in very rare cases). In HENNIG'S earlier papers, e. g. in his system of Lepidoptera (1953: 46–49), the alleged ‘sister-groups' are, in reality, the groups “B” and “A minus B” of a triplet (see Fig. 2). In his revised concept (1957 and later), two autapomorphic groups which are most closely related in the recent fauna (“B” and “C” in Fig. 3) are called ‘sister-groups’. But these have originated independently from different ancestors in a plesiomorphic complex of extinct species and are more closely related to parts of this complex than to each other. True sister-groups (“Bx” and “Cx” in Fig. 4) would be formed if these related plesiomorphic species were included, but this extension of the ’backward‘ border of the taxon is not justified by synapomorphy (in the terms of logic, it is a ’metabasis‘), and it would make the classification of fossil species impossible, unless these show at least one synapomorphy with either “B” or “C”. In the system of the recent fauna the sister-groups are identical with the autapomorphic groups, because the plesiomorphic species are extinct. The natural system based on synapomorphies and autapomorphies is the triplet-system as outlined in Figure 6. It is not a new type of classification, but its theoretical foundation was missing, and precise instructions were needed for its use in phylogenetics. The information obtained by HENNIG'S method is entirely preserved in this system and can be retrieved from it, and both recent and extinct species can be classified together. The disadvantage of the triplet-system is that it contains twice as many taxa as HENNIG'S classification. This complexity will limit its use in the practice of taxonomy, but it may be simplified by transforming the system into a sequence of paraphyletic taxa terminating in a single monophylum.