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In a microchromosome-carrying laboratory stock of the normally all-female Amazon molly Poecilia formosa triploid individuals were obtained, all of which spontaneously developed into males. A comparison of morphology of the external and internal insemination apparatus and the gonads, sperm ploidy and behaviour, to laboratory-bred F(1) hybrids revealed that the triploid P. formosa males, though producing mostly aneuploid sperm, are partly functional males that differ mainly in sperm maturation and sexual motivation from gonochoristic P. formosa males.

Female choice can often drive the elaboration of male traits, leading to the evolution of secondary sexual traits. In the Mexican molly, Poecilia sphenops (Poeciliidae), some males exhibit a mustache-like structure on the upper maxilla, the function of which has not been previously recognized. The mustache consists of epidermal outgrowths at the edge of the scales that appear to have no sensory function. Trait expression varies within as well as among populations of P. sphenops, but is not linked to male body size polymorphism. In mate choice experiments, female P. sphenops exhibited a visual mating preference for males with mustaches, suggesting that the trait may be sexually selected. Since the mating behavior of P. sphenops involves contact of the male’s snout and the female genital region prior to copulation, we hypothesize that the mustache may also convey tactile signals to the female.

According to predictions based on recent foraging theory, animals encountering two or more patches that contain the same prey type at different densities should choose the higher density patch. If detectability varies among patches, foragers should trade off search costs with nutritional benefits to be gained from either patch type. To test this latter prediction, young Pyrenean salamanders (Euproctus asper) were confronted with both a conspicuous and a concealed patch consisting of living chironomid larvae enclosed in two glass micro-aquaria. During four experimental treatments, the prey density in the two patches was altered. The salamanders showed a clear preference for the conspicuous patch in three treatments, but switched to an increased choice of the concealed patch in the fourth treatment when only a single chironomid was presented in the conspicuous patch compared to 19 chironomids in the concealed patch. However, during treatments with high prey densities in the concealed patch, E. asper choice performance was probably influenced by a dominance of visual over extra-optical perception. During choice of the concealed patch, E. asper snapped at lower frequencies than during choice of the conspicuous patch, indicating a change in the foraging style related to prey encountered in darkness. These results provide novel insights into the behavioural tradeoffs met by foragers during diet choice and provide a basis for future modelling of choice scenarios among alternative habitat types.

The aggressive behaviour of hybrids between an epigeous and a cave-dwelling form of the toothcarp Poecilia sphenops was investigated in order to test whether a genetically determined reduction of aggressive behaviour exists in the cave population. The scores for five different elements of this behaviour as well as for the duration of fights support this hypothesis and suggest that aggressive behaviour in Poecilia spbenops is controlled by a closely linked polygenic system. On the basis of laboratory and field investigations, to aggressive behaviour is attributed the function of giving large ♂♂ a reproductive advantage within the framework of a body-size dependent rank order. Small ♀♀ appear to counteract this onesided selective advantage through a special strategy of sexual behaviour.

The chemical communication of the epigean Necturus maculosus and the cave-living Proteus anguinus are compared in laboratory conditions. In both species a specks-specific substance transferred by water could be shown, another was deposited on the substrate.

The inheritance of sexual behaviour patterns was studied in species hybrids of Poecilia mexicana and Poecilia velifera. In addition, the aggressive behaviour and some morphological characters have been investigated and checked for a possible correlation between and within these three different traits studied. All the characters are inherited polygenically. The minimum genetic factors could be estimated only for some characters.

Chemical information is known to be of great importance to cave animals in their lightless biotope. ♂ ♂ ♀♀, and subadults of the cave salamander Proteus anguineus were kept in darkened aquaria and studied using infra-red in order to determine how they sought contact with conspecifics. Adults were found to mark the substrate with a substance which is both stable for several days and unique to the individual. Sexually active ♀♀ were found to be recognized through a chemical transmitter sensed only upon body contact, and this prevents the attack by territorial ♂ in breeding condition. Zusammenfassung 1 Adulte und subadulte Tiere von Proteus anguineus, dem Grottenolm, wurden in Aquarien verschiedener Grose mit Hilfe eines Infrarotnahsichtgerates beobachtet. 2 Bei den adulten Tieren wird der gegenseitige Kontakt durch eine chemische Substanz ermoglicht, die an das Substrat abgegeben wird. Mit Hilfe dieser Substanz finden die Tiere auch in unbekannter Umgebung die gemeinsamen Ruheplatze unter Steinen. Bei den Jungtieren konnte dieses Phanomen nicht nachgewiesen werden. 3 Auf Grund von Zweifachwahlversuchen wurde festgestellt, das die Adulten in unbekannter Umgebung ein vorher bewohntes Versteck einem bisher unbewohnten vorziehen. Auch funf Tage lang nicht bewohnte Verstecke erwiesen sich hierbei noch als wirksam. Bestand die Wahl zwischen dem eigenen und einem fremden Versteck, so wurde das fremde bevorzugt, bei zwei fremden Verstecken mit einer chemischen Information unterschiedlichen Alters die frischere. 4 Die chemische Substanz lies sich durch Abreiben der Verstecksteine auf Watteattrappen ubertragen, die dann im Wahlversuch gegenuber Kontrollattrappen deutlich attraktiver waren. 5 Die Prufung von Wasser aus mit Olmen besetzten Aquarien ergab erst bei einer Besatzdichte von 3 Olmen pro 10 l Wasser eine positive Reaktion. 6 Sobald ein ♂ in Fortpflanzungsstimmung kommt, greift es im Versteck und in dessen Umgebung alle Tiere mit Ausnahme fortpflanzungsbereiter ♀♀ an. Diese werden nur nach direktem Kontakt offensichtlich auf Grund einer besonderen chemischen Information erkannt. 7 Nicht fortpflanzungsbereite Tiere beantworteten die Angriffe mit Flucht, fortpflanzungsbereite ♂ ♂ mit einem Gegenangriff. Als aggressive Elemente traten Schwanzschlag, Rammen und Beisen auf. 8 Bei Verwendung formgleicher Verstecke wurde das Versteck eines fruheren Angreifers auch in unbekannter Umgebung individuell erkannt und gemieden, nicht aber das eines anderen noch unbekannten aggressiven ♂. Resume 1 Des individus adultes et subadultes du Protee, Proteus anguineus, ont ete maintenus en aquariums de differentes dimensions et observes a l'aide d'un appareil a lumiere infrarouge a faible portee. 2 Le contact interindividuel entre les adultes est rendu possible a l'aide d'une substance chimique secretee contre le substrat. Grâce a cette substance, les animaux se retrouvent meme dans un environnement inconnu et peuvent ainsi rejoindre les endroits de repos communautaires. Ce phenomene n'a pas ete observe chez les subadultes. 3 A l'aide d'experiences a double choix, nous avons pu demontrer que les adultes, dans un environnement inconnu, preferent un dortoir ayant deja ete occupe a celui qui n'avait jamais ete frequente. Meme des dortoirs vieux de 5 jours exercent encore une attraction. Si l'animal avait le choix entre un dortoir propre a lui et un dortoir etranger, c'est le dernier qui a ete prefere. Si deux dortoirs etrangers etaient presentes dont l'information chimique etait de dates differentes, l'information plus recente a ete preferee. 4 Des leurres en coton, impregnes de cette substance chimique, se sont montres largement plus attractifs que les leurres de controle. 5 L'examen de l'eau provenant des aquariums occupes par Proteus anguinus ne declenche une reponse positive qu'a partir d'une densite de 3 protees par 10 l d'eau. 6 Pendant la periode de reproduction, un ♂ sexuellement actif attaque a partir de sa cachette et dans son environnement tous les autres animaux a l'exception des ♀♀ disposees a frayer. Ces ♀♀ ne sont reconnues qu'apres une prise de contact directe. 7 Les animaux qui ne sont pas prets a la reproduction reagissent a ces attaques par la fuite, les ♂ ♂ en activite sexuelle repondent par une contreattaque. Les elements agressifs observes etaient des coups de queue, heurts corporels et morsures. 8 En utilisant des cachettes de configuration egale dans un test experimental, celle d'un ♂ attaquant connu est identifiee individuellement et meme evitee dans un evironnement nouveau. Par contre, la cachette d'un ♂ egalement en activite sexuelle et agressif, mais individuellement encore inconnu, n'est pas identifiee.

Zusammenfassung 1 Die ♂♂ dreier Teilpopulationen der Hohlenform von Poecilia sphenops zeigen im Vergleich zu zwei oberirdischen Populationen eine graduelle Ruckbildung des Aggressionsverhaltens bis hin zum volligen Verlust bei der extremen Hohlenform, obgleich die optische Orientierung offensichtlich ungestort ist. 2 Das Reduktionsphanomen bleibt auch nach jahrelanger Aufzucht bei Licht sowie nach gemeinsamem Aufwachsen mit der oberirdischen Form erhalten. Beim Zusammentreffen mit dieser reagieren die Hohlenfische fast ausschlieslich sexuell. 3 Im Dunkeln, bei Verwendung eines Infrarotgerates, sind auch beim oberirdisch lebenden Vertreter keine aggressiven Handlungen mit Ausnahme des Schwanzschlages mehr zu beobachten. Deshalb wird eine vorwiegend optische Auslosung aggressiver Elemente angenommen. 4 Damit verlor nach Besiedlung des lichtlosen Biotops die Aggression bei P. sphenops offensichtlich ihren biologischen Sinn und konnte — wie dies auch entsprechend fur morphologische Strukturen gilt — zuruckgebildet werden. 5 Es wird versucht, diesen Reduktionsprozes als Folge des Fehlens eines die Aggression erhaltenden Selektionsdruckes auf Grund von allgemeinen Vorstellungen regressiver Hohlentierevolution (Kosswig 1960, 1963) zu erklaren.

Summary The Amazon molly, Poecilia formosa, is a gynogenetic, all-female fish. Its mating system relies on heterospecific matings with males of closely related sexual species. In mixed populations, males mate with conspecific sexual females and heterospecific asexual females. Such matings are not isolated dyadic interactions but rather elements of a communication network, because multiple females can observe these interactions. This is the only known case of heterospecific mate-copying and, thus, a system in which the potential for mate-copying could be influenced by the presence of another species. Here we show that mate-copying is exhibited by the sexual species P. mexicana and P. latipinna, and the asexual P. formosa . Both sexual and asexual females copy each other’s mate choice decisions in sympatry, but females from allopatric populations do not show heterospecific mate-copying. Males benefit from heterospecific matings with Amazon mollies because these increase their attractiveness to the conspecific sexual females. In mixed shoals, mate-copying potentially imposes costs as it increases a male’s attractiveness to heterospecific females. We argue that the net-effect of mate-copying is beneficial to males because the relative strength of mate-copying is lower in Amazon mollies. We hypothesize that an added benefit to males lies in the signal value of copulations.

Eine neue entwickelte Feldmethode macht die DNA-Extraktion aus der Mundschleimhaut geschutzter Vertebraten im Freiland sowie im Labor moglich. Die Methode fand bei der Probenahme zur Ermittlung der genetischen Variabilitat in drei ausgewahlten europaischen Gebieten mit insgesamt 13 Populationen der Europaischen Sumpfschildkrote Emys orbicularis Verwendung. Die Analyse der gewonnenen Proben ergab einen Gradienten in der Variabilitat des gewahlten genetischen Markers von der hoch diversen Region des Donana Nationalparks im Sudwesten von Spanien uber die deutlich weniger diversen Populationen Ostpolens bis hin zur Inzuchtsituation bei brandenburgischen Reliktpopulationen.

Aim The unisexual Amazon molly (Poecilia formosa) is a clonal, all-female fish but depends on sperm of heterospecific males to trigger embryogenesis. Thus, one very important factor shaping its geographical range is the presence of suitable host males. Several species of the genus Poecilia from Central America, Mexico and the USA can provide sperm in the laboratory, but are not utilized as hosts in nature. Consequently the potential geographic range of the Amazon molly is much larger than the actual range. This raises the question of what is responsible for the biogeographical range of the Amazon molly? Location Southern USA, Mexico and Central America. Methods We review the current data available for the distribution of the Amazon molly. We further tested whether salinity might hinder the dispersal of the species. Results Amazon mollies tolerate marine conditions. We review the available data on recent and human influenced introductions of Amazon mollies. Main conclusions We argue that male preferences are not responsible for the current range. We propose that prevailing near-shore marine currents act as an effective barrier against further dispersal. Furthermore, we discuss recent changes in the biogeography of the Amazon molly.

The Amazon molly, Poecilia formosa, is an all-female species that reproduces by gynogenesis, i.e., it relies on sperm of males of closely related species to trigger embryogenesis. Sperm is supplied by males of P. latipinna and P. mexicana. Amazon mollies live in sympatry with at least one of these species, a few populations live in sympatry with two sperm-donor species. As P. formosa is sperm dependent, it needs mechanisms for species and mate recognition. To investigate the effect of rearing conditions on sexual preferences of Amazon mollies, we raised Amazon mollies in sympatry with P. latipinna and P. mexicana males. We used simultaneous choice tests to determine the effect of age on female sexual preferences. Immature Amazon mollies do not exhibit a preference if given a choice between a P. latipinna and a P. mexicana male, whereas adult P. formosa do have a preference for the P. latipinna male. We used two different stimuli in this study, live males and videotapes of males.

Abstract The all-female fish Poecilia formosa uses sperm of Poecilia latipinna or P. mexicana for its gynogenetic reproduction. Normally, P. formosa lives in sympatry with only one of these species. Near Tampico, Mexico, one population of P. formosa is living in sympatry with both sperm-donor species. In the present study, using animated videos as stimuli, we examined whether P. formosa from Tampico show a sexual preference for males of one of the two species. We raised P. formosa females with males of P. latipinna or P. mexicana only, and as a control with males of both species simultaneously. We found that previous experience affects mating preferences in P. formosa. Females tend to prefer males of the species they were raised with.

Cytogenetic analyses were performed on a triploid hybrid individual produced in the laboratory by mating Poecilia formosa, an all-female gynogenetic diploid species, with a normal male of melanistic ornamental Poecilia sphenops (black molly). Direct chromosome preparations revealed 69 (3n) chromosomes in the somatic complement. This cytogenetic observation in conjunction with the pigmentation phenotype leads us to conclude that occasional failure of sperm exclusion may result in the presence of triploid hybrids even in the natural habitats. ? 1995 The Fisheries Society of the British Isles

Epigean and blind cave-dwelling populations of the characid Astyanax fasciatus differ in their agonistic behavior. Epigean specimens are characterized by intense aggressive behavior and territoriality in the laboratory, whereas the blind cave fishes are rarely aggressive and have totally lost the territorial behavior. These behavioral changes are genetically based. In the present study, a comparative analysis of the optical releasers for aggressive behavior has been performed in both epigean and cave-dwelling populations. It was expected that the regression of aggressive behavior should be accompanied by the regression of the genetically fixed optical releasers for aggression in the cave specimens. For the analysis of cave fishes, well-eyed F1-hybrids of cave and epigean specimens (Pachon × Teapao) as well as phylogenetically young cave specimens (Micos) selected for large eyes, have been used. In epigean specimens, aggression is most intensely released by a combination of the signals 'natural shape' and 'locomotion'. The cave populations exhibit a partial regression of the releaser 'natural shape'. 'Locomotion', however, has become a more effective releaser for aggression in cave fishes than it has in their epigean relatives. The results are discussed with respect to their evolutionary significance.

Reproductive isolation among locally adapted populations may arise when immigrants from foreign habitats are selected against via natural or (inter-)sexual selection (female mate choice). We asked whether also intrasexual selection through male-male competition could promote reproductive isolation among populations of poeciliid fishes that are locally adapted to extreme environmental conditions [i.e., darkness in caves and/or toxic hydrogen sulphide (H2S)]. We found strongly reduced aggressiveness in extremophile Poecilia mexicana, and darkness was the best predictor for the evolutionary reduction of aggressiveness, especially when combined with presence of H2S. We demonstrate that reduced aggression directly translates into migrant males being inferior when paired with males from nonsulphidic surface habitats. By contrast, the phylogenetically old sulphur-endemic P. sulphuraria from another sulphide spring area showed no overall reduced aggressiveness, possibly indicating evolved mechanisms to better cope with H2S.

The behavioural responses of the blind cave salamander Proteus anguinus and the Pyrenean salamander Euproctus asper (a facultative cave dweller) to living and dead chironomids offered in light or in darkness were studied experimentally. Both species were able to detect and locate single prey items positioned at distances of 30 cm. Proteus responded to dead prey in light faster and captured live prey in darkness earlier than E. asper. E. asper captured live prey in light earlier than in darkness. Proteus is well equipped to search for non-visual information and used an active, mechanically and chemically guided approach in all experiments. E. asper showed a more directed, visually dominated approach behaviour with live chironomids in light, but used an active, widely foraging mode with live prey in darkness and dead prey in light. E. asper may forage successfully both in epigean and hypogean habitats.

Abstract Pseudosexual behaviour is a rare phenomenon associated with unisexuality in vertebrates. In the gynogenetic, all-female teleost Poecilia formosa, rare individuals occur that resemble males of closely related gonochoristic species both in behaviour and external morphology. These masculinized gynogens and normal gynogens are members of the same clone, as demonstrated by DNA-fingerprinting. The behaviour of these masculinized gynogens is described and compared to the behaviour of the gonochoristic species Poecilia mexicana, P. latipinna and their hybrid as well as androgen-treated individuals of P. formosa. No statistically significant differences were found between masculinized gynogens and hormone-treated individuals nor between the gonochoristic P. mexicana and P. latipinna males. Differences exist between gonochoristic and unisexual species. Possible causes and effects of masculinized gynogens are discussed.

The galatheid Munidopsis polymorpha Koelbel, 1892, is found at high population density in an anchialine pool (Jameos del Agua) on Lanzarote. Ovigerous females on an average carry 14 eggs. Larval development is advanced. Only 2 zoeal stages, which are unable to undergo locomotion, precede molt to a small crab. Munidopsis polymorpha is not preyed upon in the Jameos del Agua. Population density is regulated less by available food than by the number of available hiding places for resting phases. Population density is probably increased by the fact that the highly territorial crabs periodically alternate in feeding in the same grazing areas and in hiding. The percentage ofovigerous females and the average number of eggs per female is negatively correlated with the number of specimens per area. During the years of investigation from 1976-1989, the number of ovigerous females and the average number of eggs per female have decreased considerably in parts of the pool. Consequently, the general population density has become drastically reduced. This is attributed to the construction and opening of the Jameos del Agua for tourism.

In many species, females prefer large males as mating partners. Male size can easily be determined visually. We examined how such mate choice evolves when individuals are deprived of sensory information previously used to determine male quality. Using a cave-dwelling population of Atlantic mollies, Poecilia mexicana, as a model, we asked whether the female mating preference for large male body size still occurs in this cave fish, or whether it is lacking due to the absence of visual communication in the cave environment. In simultaneous choice tests we compared the time females spent with a large or a small male. In the river-dwelling and cave-dwelling fish, as well as the population originating from the cave entrance, we found a significant preference for large males in light. Hence, the ancestral mating preference of surface-dwelling mollies has been maintained during the evolution of the cave form. However, only the cave population exhibited a mating preference in darkness. Determination of male body size appears to have been taken over by a non-visual sensory system, probably the lateral line.

Abstract Animals colonizing lightless subterranean habitats can no longer rely on visual signals to find mating partners. In the present study, we investigated the ability of males to recognize females in two surface and a cave dwelling population of a livebearing fish, Poecilia mexicana. In surface populations males discriminated between sexes with visual plus non-visual cues available and with visual stimuli only. In the cave form the ability to discriminate with solely visual stimuli is lacking. In all three populations, males did not recognize females in darkness (infrared observations), suggesting that sex recognition via far-field communication is lacking in surface and cave dwelling P.mexicana. Different preferences in large and small males to stay near a female or a male stimulus fish probably reflect differences concerning a trade-off between sexual and aggressive behaviour.

Sexual coercion is a common behaviour for males trying to compensate for being inferior in male competition and/or female choice. We measured the cost of male sexual harassment for females as reduced feeding time in three populations of the Atlantic molly (Poecilia mexicana). Of these populations, one originated from a typical river habitat, another from a lightless cave chamber and the third one from a small, milky creek outside the cave. We gave hungry females an opportunity to feed in the presence of either another female or a male. We found the following: (1) male sexual harassment represents a cost in the river dwelling population and both small and large males significantly reduce female feeding time; and (2) sexual harassment was not detected in the other two populations (cave and cave entrance). In the cave molly, small males are at a disadvantage in female choice, but predation by an aquatic heteropteran selects against large male body size.

Caecilians, members of the order Gymnophiona, are elongate, limbless and annulated animals with reduced eyes (Wake, 1985) and a unique organ at the head, the paired tentacle, which is connected with the vomeronasal organ via the tentacular duct (Schmidt and Wake, 1990). These morphological characters and behavioral studies suggest that the paired tentacle is involved in chemoreception (Himstedt and Simon, 1995).

Fluctuating asymmetry is defined as random deviation from perfect bilateral symmetry in otherwise symmetrical morphological traits and originates from developmental errors during ontogeny. It is thought to reflect the inability of a genotype to buffer itself effectively against environmental perturbations, thus providing an honest phenotypic indicator of genetic quality. It has been proposed that females use the degree of asymmetry in male ornaments to assess male quality in mate choice. We studied whether fluctuating asymmetry in vertical bars in the sailfin molly, Poecilia latipinna, is a criterion in female mate preference, as has been shown before in a swordtail, Xiphophorus cortezi. Using both live stimulus males and silicon models, we found that females have significant preferences both for bars per se and for males with symmetrical bars. The total number of bars and the degree of fluctuating asymmetry were negatively related so fluctuating asymmetry in bars may be an honest signal. This phenomenon may have influenced the evolution of the male courtship display in P. latipinna. Copyright 1998 The Association for the Study of Animal Behaviour.

The ecological conditions in caves are characterised by two main factors: nearly all caves have complete darkness and more or less constant temperature. The animals found in this habitat form a heterogeneous assembly. Some animals use caves only occasionally to avoid unfavourable conditions outside. Others, such as bats, enter caves regularly to rest during the day and in winter. But there are also many species which live permanently in caves. Omitting all the different classifications (Vandel 1965) of cave-living animals, we can call these true cave-dwellers ‘troglobionts’. Their striking morphological differences in comparison with their epigean relatives concern the reduction of the eye dark pigmentation. These reduction phenomena can be observed in many groups of animals. The degree of reduction in different species studied seems to be connected with the phylogenetical age of cave colonisation (Wilkens 1982).

The appearance of vertebrate species that reproduce without genetic recombination has been explained by their origin from a rare hybridization event between members of two distantly related species. For the first recognized vertebrate unisexual, the Amazon molly Poecilia formosa, mostly morphological and biochemical genetic information has been available so far with respect to its evolutionary origin. DNA sequence analyses of transcribed portions of the genome (tyrosine kinase proto-oncogenes) demonstrated its hybrid state unequivocally. Both alleles can be traced in a DNA sequence-based phylogenetic tree to extant species that represent the parental species or that are closely related to the corresponding extinct forms, namely P. mexicana limantouri and a so far taxonomically ill-defined north Mexican subspecies of the P. latipinna/P. velifera complex. A rough estimate from the mutation rates dates the hybridization event further back than would have been predicted on the basis of "Muller's ratchet" for an ecologically successful species.

A CENTRAL paradigm in evolutionary biology is that sexual reproduction is advantageous over asexuality1–5. One of the long-term disadvantages asexual forms have to face is Muller's ratchet6. In the absence of recombination, theoretically no genotype can ever produce offspring with fewer mutations than its own load. The accumulation of deleterious mutations and gene combinations that cannot be purged should lead to extinction of parthenogenetic forms within 104–105 generations7,8. Evidence is accumulating, however, that some of these might have survived for such periods or even longer9–14. In the Amazon Molly fish Poecilia Formosa we have detected a process that appears to compensate for disadvantages of asexuality, namely incorporation of subgenomic amounts of DNA from a bisexual host species by microchromosomes.

Do the blind cave salamander Proteus and its epigean relative Necturus use the chemical sense in searching for prey? Proteus shows a significant, and Necturus only a weak, preference for water which passes living prey before entering a choice chamber. Prey which was frozen before the test also gave the same result in both species. However, with this immobilized prey the time for a decision in the test was much longer. The results of ten series of tests demonstrate the importance of chemoreception for prey detection in Proteus . The weaker reactions in Necturus can be explained probably by the different biotope. Six other series of tests have been conducted to show that our results are not influenced by stimuli relating to mechanoreception, thigmotaxis and rheotropism.

[1) Auf Grund von Grose und Differenzierungsgeschwindigkeit wird bei M. velifera und M. latipinna zwischen Fruh- und Spat-♂ ♂ unterschieden. Die Spat-♂ ♂ von M. velifera bilden eine Dorsale aus, die meist hoher als der Korper ist. Auf einige Faktoren fur die Ausbildung der hohen Dorsale wird eingegangen. Die ♂♂ des zur Verfugung stehenden Stammes von M. latipinna bildeten dagegen keine hohe Dorsale aus2) Alle ♂♂ der beiden "hochflossigen" Arten M. velifera und M. latipinna (ausgenommen die Fruh- ♂♂ von M. latipinna) zeigen eine Schaubalz vor dem ♀ (Balzschwimmen), bei der die aufgestellte Dorsale dem ♀ in auffallender Weise dargeboten wird. Bei der "niedrigflossigen" Art M. sphenops fehlt dagegen eine solche optisch wirksame Balz. Andererseits sind Anschwimmen, Folgen und Nippen in ihrer Intensitat deutlich gesteigert. Die Einzelelemente des Rivalenverhaltens stimmen in qualitativer Hinsicht bei "hoch"und "niedrigflossigen" Arten recht gut uberein. 3) Von M. sphenops wurde eine Hohlenform untersucht, die sich von der oberirdischen Form durch fast vollstandiges Fehlen von aggressiven Reaktionen unterscheidet. Als Ursache der fehlenden Aggressivitat wird eine genetisch bedingte Degeneration des Rivalenverhaltens angenommen. Die Reduktion des Aggressionsverhaltens ist unter den Bedingungen des Hohenlebens vermutlich selektionistisch begunstigt. Da die Wirkung aggressiver Verhaltensweisen auf den Gegner im Dunkeln stark vermindert ist, durfte es fur das ♂ vorteilhafter sein, moglichst lange mit dem ♀ in Kontakt zu bleiben. Die aggressive Auseinandersetzung mit dem Rivalen aber wurde im allgemeinen dazu fuhren, das die Verbindung zum ♀ fur langere Zeit verloren geht. Das Fehlen einer Schaubalz beim oberirdischen M. sphenops, die deutlich gesteigerte sexuelle Aktivitat und vor allem die Fahigkeit der ♂ ♂ , auch sehr schnell schwimmenden ♀♀ nippend zu folgen, lassen die Annahme zu, das der oberirdisch lebende M. sphenops fur ein erfolgreiches Leben im Dunkeln pradisponiert ist. 4) Bei allen drei Arten wurde das zeitliche Auftreten der einzelnen Verhaltensweisen wahrend der Ontogenese registriert. Die Jungtiere der drei untersuchten Arten verfugen schon einige Tage nach der Geburt uber das vollstandige Rivalenverhalten. Die Einzelelemente des Sexualverhaltens erscheinen dagegen erst kurz vor oder mit beginnender geschlechtlicher Differenzierung. Die Form der Einzelelemente des Sexual- und Rivalenverhaltens unterscheidet sich nicht von derjenigen erwachsener Tiere. Auffallend ist aber die auserordentliche Haufigkeit aggressiver Verhaltensweisen bei Jungfischen. Die Einzelelemente folgten nicht in rein zufalliger und beliebiger Reihenfolge aufeinander, sondern es waren schon die gleichen Verhaltensfolgen zu beobachten wie bei erwachsenen Tieren. 5) Es wurden Kaspar-Hauser- ♂♂ aller drei Arten beobachtet. Die Entwicklung fast aller beschriebenen Elemente des Sexual- und Rivalenverhaltens ist von der Erfahrung mit Artgenossen unabhangig. 6) Ein Vergleich der bisher ethologisch untersuchten Arten der Gattung Poecilia i.w.S., d.h. im Sinne von ROSEN & BAILEY (1963), ergibt zum Teil erhebliche Unterschiede in der Balz. Zwei der bisher untersuchten Arten zeigen uberhaupt keine Anzeichen einer Schaubalz. Die Zuruckfuhrung der Balz auf einen Grundtypus scheint im Gegensatz zu den Verhaltnissen innerhalb der Gattung Xiphophorus nach den bisherigen Untersuchungen nicht moglich zu sein.., 1) Auf Grund von Grose und Differenzierungsgeschwindigkeit wird bei M. velifera und M. latipinna zwischen Fruh- und Spat-♂ ♂ unterschieden. Die Spat-♂ ♂ von M. velifera bilden eine Dorsale aus, die meist hoher als der Korper ist. Auf einige Faktoren fur die Ausbildung der hohen Dorsale wird eingegangen. Die ♂♂ des zur Verfugung stehenden Stammes von M. latipinna bildeten dagegen keine hohe Dorsale aus2) Alle ♂♂ der beiden "hochflossigen" Arten M. velifera und M. latipinna (ausgenommen die Fruh- ♂♂ von M. latipinna) zeigen eine Schaubalz vor dem ♀ (Balzschwimmen), bei der die aufgestellte Dorsale dem ♀ in auffallender Weise dargeboten wird. Bei der "niedrigflossigen" Art M. sphenops fehlt dagegen eine solche optisch wirksame Balz. Andererseits sind Anschwimmen, Folgen und Nippen in ihrer Intensitat deutlich gesteigert. Die Einzelelemente des Rivalenverhaltens stimmen in qualitativer Hinsicht bei "hoch"und "niedrigflossigen" Arten recht gut uberein. 3) Von M. sphenops wurde eine Hohlenform untersucht, die sich von der oberirdischen Form durch fast vollstandiges Fehlen von aggressiven Reaktionen unterscheidet. Als Ursache der fehlenden Aggressivitat wird eine genetisch bedingte Degeneration des Rivalenverhaltens angenommen. Die Reduktion des Aggressionsverhaltens ist unter den Bedingungen des Hohenlebens vermutlich selektionistisch begunstigt. Da die Wirkung aggressiver Verhaltensweisen auf den Gegner im Dunkeln stark vermindert ist, durfte es fur das ♂ vorteilhafter sein, moglichst lange mit dem ♀ in Kontakt zu bleiben. Die aggressive Auseinandersetzung mit dem Rivalen aber wurde im allgemeinen dazu fuhren, das die Verbindung zum ♀ fur langere Zeit verloren geht. Das Fehlen einer Schaubalz beim oberirdischen M. sphenops, die deutlich gesteigerte sexuelle Aktivitat und vor allem die Fahigkeit der ♂ ♂ , auch sehr schnell schwimmenden ♀♀ nippend zu folgen, lassen die Annahme zu, das der oberirdisch lebende M. sphenops fur ein erfolgreiches Leben im Dunkeln pradisponiert ist. 4) Bei allen drei Arten wurde das zeitliche Auftreten der einzelnen Verhaltensweisen wahrend der Ontogenese registriert. Die Jungtiere der drei untersuchten Arten verfugen schon einige Tage nach der Geburt uber das vollstandige Rivalenverhalten. Die Einzelelemente des Sexualverhaltens erscheinen dagegen erst kurz vor oder mit beginnender geschlechtlicher Differenzierung. Die Form der Einzelelemente des Sexual- und Rivalenverhaltens unterscheidet sich nicht von derjenigen erwachsener Tiere. Auffallend ist aber die auserordentliche Haufigkeit aggressiver Verhaltensweisen bei Jungfischen. Die Einzelelemente folgten nicht in rein zufalliger und beliebiger Reihenfolge aufeinander, sondern es waren schon die gleichen Verhaltensfolgen zu beobachten wie bei erwachsenen Tieren. 5) Es wurden Kaspar-Hauser- ♂♂ aller drei Arten beobachtet. Die Entwicklung fast aller beschriebenen Elemente des Sexual- und Rivalenverhaltens ist von der Erfahrung mit Artgenossen unabhangig. 6) Ein Vergleich der bisher ethologisch untersuchten Arten der Gattung Poecilia i.w.S., d.h. im Sinne von ROSEN & BAILEY (1963), ergibt zum Teil erhebliche Unterschiede in der Balz. Zwei der bisher untersuchten Arten zeigen uberhaupt keine Anzeichen einer Schaubalz. Die Zuruckfuhrung der Balz auf einen Grundtypus scheint im Gegensatz zu den Verhaltnissen innerhalb der Gattung Xiphophorus nach den bisherigen Untersuchungen nicht moglich zu sein..]

The fleshy genital-pad in females and the number of taste-buds in males and females of the cave-living M. sphenops show constructive tendencies in comparison with its epigean ancestor and M. velifera.

DARWIN's statement, that rudimentary parts of organisms are apt to be highly variable, is also true for the regressive structures of cavernicolous animals. On the other hand, adaptive traits develop under cave conditions, the variability of which is lowered rather than increased, compared to that of their precursors in the epigean population. These differences in the genetically controlled variability of constructive and degenerative features indicate action and nonaction of natural selection.

DNA fingerprinting demonstrated no sexual reproduction of the gynogenetic Amazon molly Poecilia formosa with Limia vittata as host species, in contrast with a single report that claims to have found sexual reproduction with such matings.

In clonal unisexual vertebrates, the genes specifying the males become dispensable. To study the fate of such genes the gynogenetic all-female fish Poecilia formosa was treated with androgens. Phenotypic males were obtained that exhibited the complete set of male characteristics of closely related gonochoristic species, including body proportions, pigmentation, the extremely complex insemination apparatus of poeciliid fish, sexual behavior, and spermatogenesis. The apparent stability of such genic structures, including those involved in androgen regulation, is contrasted by high instability of noncoding sequences. Frequent mutations, their clonal transmission, and at least two truly hypervariable loci leading to individual differences between these otherwise clonal organisms were detected by DNA fingerprinting. These observations substantiate the concept that also in "ameiotic" vertebrates certain compartments of the genome are more prone to mutational alterations than others.