Der Micos-Fisch,Höhlenfisch in statu nascendi oder Bastard ?

The Micos Population–cave fish in statu nascendi or hybrid? Observations on the evolution of cavernicoles The Micos-Cave in the Sierra de la Colmena in the State of San Luis Potosi, Mexico, contains a cavernicolous population of Astyanax mexicanus, whose members are for the most part blind, but, in contrast to other cave dwelling populations of the same species, appear almost normal in their pigmentation. Besides these, there are also large eyed and pigmented specimens to be found in this cave. Any transitional stages between the blind and the normal visioned fish are lacking. Offspring of the blind cavernicoles that are raised under light conditions develop a superficially lying eye which is markedly smaller than normal, attaining its size proportional to the light-intensity of the experimental conditions. The size and structure of the eye-remnants of the blind fish as well as the eyes of their offspring are considerably more variable than in the river specimens. Crossings of the blind Micos fish with the river fish Astyanax and also with a blind and unpigmented troglobiont of the same species - Sabinos fish - result in both cases in a more or less intermediate F¹-hybrid. A strict inbreeding within the Micos fish, selecting specimens with especially large eyes, produced animals whose eyes are comparable to those of the river fish after only three offspring generations. Electrophoresis studies on the allozyme variability at various loci prove that the Micos fish is genetically only slightly different compared to the river fish. On the other hand in some allele frequencies there is an alternative variation between the two. The Micos fish also differs from the typical troglobionts which are monomorphic at almost all loci examined and also possess alleles that are not found in the river form. Based on the genetic constitution, the Micos fish and the river fish found in the cave do not form a panmictic population. It is also doubtful that the Micos fish is the progeny of a hybrid swarm which previously resulted from a cross between a real troglobiont and the newly arrived river fish, because the Micos fish is in every characteristic genetically very similar to the river fish, whereas no clear traces of troglobiont relationship are found. Thus the Micos fish actually appears to be a cave form in statu nascendi against which the river fish that find their way in from time to time cannot compete.     

Sex recognition in surface- and cave-dwelling Atlantic molly females (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, Poeciliidae,Teleostei): influence of visual and non-visual cues

Cave fishes need to rely on non-visual senses, such as the sense of smell or the lateral line to communicate in darkness. In the present study, we investigated sex identification by females of a cave-dwelling livebearing fish, Poecilia mexicana (cave molly), as well as its surface-dwelling relatives. Unlike many other cave fishes, cave mollies still possess functional eyes. Three different modes of presentation of the stimulus fish (a male and an equally sized female) were used: (i) the stimulus fish were presented behind wire-mesh in light, allowing the focal female to perceive multiple cues, (ii) the experiment was carried out under infrared conditions, such that only non-visual cues could be perceived and (iii) the stimulus fish were presented in light behind transparent Plexiglas, allowing for the use of visual cues only. Females of all populations examined preferred to associate with the stimulus female in at least one of the treatments, but only when visible light was provided, suggesting that far-range sex recognition is limited or even absent in the cave molly under naturally dark conditions.     

Size-dependent male mating behaviour and sexual harassment in a population of Atlantic mollies (Poecilia mexicana) from a sulphur creek

The Atlantic molly Poecilia mexicana inhabits a variety of habitats. In previous studies, small males from clear-water populations showed considerably more sexual behaviours than large males. Males from a sulphur creek, the El Azufre, or from a sulphur cave (cave molly) showed comparatively low sexual activity, and typical size-dependent mating behaviour was either absent or large males showed even more sexual behaviour than smaller ones. Sexually deprived cave molly males increased their sexual activity, but small males still did not show more sexual behaviour than large ones, suggesting that the genetic basis for typical size-dependent mating behaviour has been lost. Likely, the extreme abiotic conditions (hypoxia and toxic hydrogen sulphide) have selected against energetically costly behaviours. In this paper, we examined how El Azufre males would respond to sexual deprivation. We found these males to also increase their sexual activity after sexual deprivation but, unlike cave mollies, small males now showed more sexual behaviour than large ones, suggesting that the genetic basis for this behaviour is not lost in this population. Differences between populations may be due to the less harsh characteristics of El Azufre (e.g. less H₂S), resulting in weaker selection against energy-consuming behaviours. Furthermore, we tested for potential costs of male sexual harassment for females in terms of reduced feeding efficiency in the presence of a male, as was shown for P. mexicana from a clear-water population, but was not found in cave mollies or the El Azufre fish. Test females were either starved for 1 week to increase hunger levels or male sexual deprivation and female starvation were combined; however, we found no evidence for male sexual harassment even after these treatments. Our results parallel previous findings in the cave molly and suggest that El Azufre males have lost specific behavioural traits that cause sexual harassment.     

Matrotrophy in the cave molly: an unexpected provisioning strategy in an extreme environment

Maternal provisioning of animal embryos may be entirely through yolk deposited in the unfertilized egg (lecithotrophy) or may include post-fertilization nutrient transfer (matrotrophy) in varying degrees. Current theory suggests that the extent of post-fertilization provisioning is resource-dependent, with higher levels of matrotrophy being advantageous in more productive environments. In this study, we investigated post-fertilization embryo provisioning in a livebearing fish, Poecilia mexicana, from two different habitats (a toxic cave and a non-toxic surface habitat) that impose different energetic demands and therefore differ in resources available for reproduction. We predicted that fish in the benign habitat would be more matrotrophic than those from the toxic cave. We used two different techniques for this assay: (1) the matrotrophy-index analysis (MI) for field-collected fish and (2) both MI and radio-tracer assay for laboratory-reared females. According to the interpretation of the matrotrophy index, both populations are purely lecithotrophic, while the radio-tracer assay found females from both populations to actively transfer nutrients to developing embryos at approximately the same rate. Our results suggest that P. mexicana, which was traditionally classified as lecithotrophic, is capable of incipient matrotrophy, and that matrotrophy can contribute to embryo provisioning even in populations from resource-limited environments. Furthermore, the analysis of laboratory-reared animals provides evidence for a genetic component to the large offspring size in cave mollies, which had so far only been described from the field. Specifically, our results suggest matrotrophy occurs in species interpreted as lecithotrophic using the MI approach. Hence, to avoid misclassification, both techniques should ideally be employed in concert, rather than individually. Finally, our results provide further insights into the possible evolutionary pathway from lecithotrophic oviparity to matrotrophic viviparity.     

A new species of Pseudopecoelus von Wicklen, 1946 (Digenea: Opecoelidae) from the orange roughy Hoplostethus atlanticus Collett, 1889 (Trachichthyidae) from off southeastern Australia

A new species, Pseudopecoelus sewelli, is described from the deep-sea fish Hoplostethus atlanticus from off southeastern Australia. It is an elongate form with considerable variation in such important characters as the anterior vitelline extent, the sucker ratio and the egg-size. The features distinguishing this species from five related forms are combinations of the sucker ratio, egg-size, lobation of gonads, presence or absence of a cirrus-sac and the position of the genital pore.     

EVOLUTION OF ADULT MORPHOLOGY AND LIFE-HISTORY CHARACTERS IN CAVERNICOLOUS PTOMAPHAGUS BEETLES

Morphological and life-history characters were determined for a series of six increasingly cavernicolous species of eastern United States Ptomaphagus beetles. Contrary to expectations, dimensions of only some adult structural characters uniformly covary as an overall measure of evolutionary adaptation for cave life. Adult reproductive characters that show adaptation for cave life are loss of reproductive seasonality and production of fewer and larger eggs. Significant change in pre-imaginal life-cycle stages was not found. This is in contrast to cavernicolous bathysciine beetles of Europe which show remarkable adaptive trends in pre-imaginal stages, but larval adaptations are not strongly coevolved with adult cave-adaptive characters. This suggests that evolution of cave adaptation in adult endopterygote insects occurs before and independently from that in larvae.     

Description of the male of Sclerocypris tuberculata (Methuen, 1910) (Crustacea,Ostracoda, Megalocypridinae)

The male of Sclerocypris tuberculata (Methuen), thus far unknown, is here described. Relying on the morphology of the copulatory appendages and of the prehensile palps, it appears that this taxon belongs to a separate species group, together with S. zelaznyi and perhaps also S. sarsi. There are some interesting sexual dimorphic characters in the valve morphology: males have shorter valves with a dorsal margin which runs nearly parallel to the ventral one (more elongated valves with sloping dorsal margin in females) and there is lobe-like projection of the valve margin on the ventro-caudal corner of the LV in females which is lacking in the male. Furthermore, the female genital region has a very aberrant morphology, and all specimens from the present collection possess the tuberculated and noded valves.     

Molecular phylogeny reveals the repeated evolution of complex male genital traits in the New Zealand moth genus Izatha (Lepidoptera: Xyloryctidae)

Male genitalia are among the most rapidly evolving and divergent morphological structures and sexual selection is known to drive this phenomenon in many taxa. Because of their diversity, even within a single genus, genital characters are frequently used to infer relationships among closely‐related species. Moths within the genus Izatha (Xyloryctidae) are ideal candidates for investigating the phylogenetic patterns of genital evolution as they display great variation in male genital structure and complexity. We determined the evolutionary relationships among 31 species of Izatha by constructing a molecular phylogeny of the genus based on the mitochondrial cytochrome oxidase subunit I gene and the isocitrate dehydrogenase and carbamoylphosphate synthase domain protein nuclear genes. This allowed estimations of ancestral male genital character states and patterns of male genital diversification using maximum‐likelihood models. The genus is divided into two well‐supported clades and two poorly supported clades at the root of the phylogeny with incomplete phylogenetic resolution within two species groups, likely due to rapid speciation. Izatha display a number of apomorphic phallic traits including cornuti (sclerotized spines) which are either discharged into the female during copulation (deciduous cornuti) or fixed to the male phallus (compound and fish‐hook cornuti). Within the genus, there is a reduction of secondary genital characters – the uncus and gnathos – but an elaboration of another grasping structure, the juxta; the potential origin and functionality of these male genital traits are discussed. Overall, some male genital characters provided a good indication of species relationships; however, several parts of the complex male genitalia of Izatha show evidence of homoplasy and convergence highlighting the problems of using these traits in determining species relationships. Additionally, this convergence has highlighted that complex genital structures may evolve repeatedly and independently within a lineage.     

Hadodiaptomus dumonti n. gen., n. sp., a new freshwater stygobitic calanoid (Crustacea: Copepoda: Calanoida) from Vietnam (South Asia) and a new member of the subfamily Speodiaptominae Borutzky, 1962

A new species of freshwater stygobitic calanoid, Hadodiaptomus dumonti n. gen., n. sp., from a cave in Vietnam (South Asia) is described. It is the ninth taxon from the order Calanoida described from freshwater subterranean (i.e. cave) environments. It is the fourth member of the subfamily Speodiaptominae Borutzky, 1962. It differs from stygobitic taxa in Europe and Mexico by numerous characters, especially in the armature of P1–P5, antenullas, mouth parts and genital segments in both sexes. Arthrodial membrane development from CII to CV is different from epigean as well as from subterranean taxa. These differences suffice to raise a new genus–Hadodiaptomus, characterised by two-segmented exopodites and endopodites of P1–P4 and reduced P5 endopodites in both sexes. Males are without widened segments 13–18 on right A1. Relations with other stygobitic taxa of the subfamily Speodiaptominae are discussed.     

Non‐Visual Mate Choice Ability in a Cavefish (Poecilia mexicana) is not Mechanosensory

One of the most important decisions any female has to make is selecting a mate. In many animals, this involves a strong visual component, but in cave‐dwelling fishes, mate preferences have to be exercised in darkness. In a cave‐dwelling Poeciliid fish, the cave molly (Poecilia mexicana), visual mate choice is still possible because they have functional, albeit reduced eyes. In a previous laboratory study, it was documented that females prefer larger males in light and in darkness. In the present study, we investigated the role of the mechanosensory lateral line in this mate preference. We temporarily knocked out the lateral line using antibiotics. We found that even in the functional absence of the lateral line, females showed a clear preference for larger males, indicating that the lateral line is not crucial for mate choice. This points toward a strong role of chemical communication in cave molly mate choice.     

Separation possibilities and genital measurement variations in two cryptic species of European pierid butterflies,Leptidea juvernica Williams, 1946 and L. sinapis (Linnaeus, 1758)

Of the three recently separated cryptic butterfly species of the Leptidea sinapis complex, the two species L. sinapis and L. juvernica occur sympatrically and syntopically in central Europe. As the separation of these species requires genital or genetic characters, their correct identification is a fundamental problem to be solved prior to any biological and distributional studies. In the present study a morphometric approach was applied to test for separation possibilities and to examine genital measurement variations based on large population samples of the two species (347 females and 636 males). Butterflies were collected at 456 localities distributed across Poland. Specimens of both sexes could be separated using either the shape or the length of the antrum bursae (females), phallus and saccus (males). Intraspecific seasonal differences in these measurements may affect the discrimination of males only. Genital characters were significantly larger in butterflies of the spring brood than in those of the second brood. In females, antrum bursae length ranges were separated by an interval, allowing for the exact identification of each specimen. In males, no such intervals were found between phallus and saccus length ranges, which slightly overlapped. Discriminant analysis resulted in 100% of males correctly classified. The present study confirmed the validity of interspecific differences in the shape of phallus and saccus for species identification without measurements. The length of these two characters discriminates the two species when separation is limited to specimens from the same generations. As an alternative for discriminant analysis, either phallus length and vinculum width or phallus length and the ratio of the ventral edge of genital capsule length and saccus length (VEL/SL ratio) is recommended for the practical separation of the two species. The differences in the shape and size of the copulatory organs of the two species seem to indicate reproductive isolation due to mechanical incompatibility of their genitals.     

Description of a new species of Triplophysa (Teleostei: Nemacheilidae) from Guizhou Province,China

A new cave‐dwelling fish species Triplophysa guizhouensis is described based on specimens collected from Guizhou, China, in a subterranean system interconnected with the Hongshui River drainage. The species can be distinguished from its congeners by a combination of characters: eyes present; caudal fin with 14 branched rays; inner gill rakers of first gill arch 8–10; posterior chamber of air bladder developed; and body posterior of dorsal fin scaled. A key to species of Triplophysa in the Pearl River basin is provided.     

ARE PARALLEL MORPHOLOGIES OF CAVE ORGANISMS THE RESULT OF SIMILAR SELECTION PRESSURES?

The amphipod Gammarus minus is present in both caves and springs, with cave populations showing elaborated (size and antennae) and reduced (eye) characters relative to spring populations. Earlier studies have shown that cave populations resulted from independent invasions of hydrologically isolated subterranean drainages and that there is genetic variation for both elaborated and reduced characters. In this study we tested the hypothesis that a similar pattern of selection on isolated cave populations is responsible for the parallel evolution of cave morphologies. We used variation in mating success and fecundity to test for the presence of directional selection on eye, antennal, and body size characters in a set of cave and spring populations during a series of seasonal cross-sectional samplings. We found significant directional selection for smaller eyes in caves and larger eyes in springs, which supports the hypothesis that selection is responsible for reduced eye size in cave populations. We also found selection for larger body and antennal size in cave populations, which is consistent with the hypothesis that parallel patterns of selection in caves are responsible for the elaboration of body and antennal size. However, we found selection for larger body and antennal size in spring populations that is not consistent with the observed divergence of spring and cave populations. We suggest that unmeasured components of viability selection could be more important in springs than in caves and may act against the selection for larger size found in spring populations.     

Predation of a cave fish (Poecilia mexicana, Poeciliidae) by a giant water-bug (Belostoma, Belostomatidae) in a Mexican sulphur cave

Abstract.  1. Caves are often assumed to be predator-free environments for cave fishes. This has been proposed to be a potential benefit of colonising these otherwise harsh environments. In order to test this hypothesis, the predator–prey interaction of a belostomatid (predator) and a cave fish (prey) occurring in the Cueva del Azufre (Tabasco, Mexico) was investigated with two separate experiments.
2. In one experiment, individual Belostoma were given a chance to prey on a cave fish, the cave form of the Atlantic molly ( Poecilia mexicana ), to estimate feeding rates and size-specific prey preferences of the predator. In the other experiment, population density of Belostoma was estimated using a mark–recapture analysis in one of the cave chambers.
3. Belostomatids were found to heavily prey on cave mollies and to exhibit a prey preference for large fish. The mark–recapture analysis revealed a high population density of the heteropterans in the cave.
4. The absence of predators in caves is not a general habitat feature for cave fishes. None the less predation regimes differ strikingly between epigean and hypogean habitats. The prey preference of Belostoma indicates that cave-dwelling P. mexicana experience size-specific predation pressure comparable with surface populations, which may have implications for life-history evolution in this cave fish.     

Growth, summer cohort output, and observations on the reproduction of brook silverside, Labidesthes sicculus (Cope) in the Kawartha Lakes, Ontario

The brook silverside, Labidesthes sicculus (Cope), is unique in Canadian waters, as it completes its life cycle in 1 year. Previous studies based on scale ageing had suggested the species was an “annual,” but we confirmed this for the first time by otolith analysis. Growth rates from both back-calculation, and the Gompertz model, indicated an asymptote near the end of the summer, and average summer growth rates of 0.77 and 0.70 mm/day, respectively. The Gompertz model gave the best fit (n = 201, r = 0.744) with an L∞ of 85.4 mm TL, and instantaneous growth rate, g, of 0.0264. Back-counting daily growth increments allowed us to show that broods of young fish were produced throughout the summer, from late May to mid August, with maximum hatch taking place in mid-July. The species is a “batch” (serial) spawner, with only a fraction of the eggs ripening in the ovary and being released at as yet undetermined intervals. Eggs of the larger immature fish in the first summer developed from 0.05 to 0.21 mm in diameter (preserved) by fall, and in mature fish of the following spring and summer, developed to 1.2 mm in diameter (preserved), 1.4 mm fresh, at spawning. Attached to each egg was a filament averaging 2.0 cm in length, adhesive in nature, and presumably for attachment to vegetation. The egg also had microscopic hairs on its surface. No evidence was found to support temperature-dependant sex determination, nor were embryos or sperm found in the ovaries of spawning females, unlike Labidesthes sicculus vanhyningi, (the southern subspecies) which has internal fertilization. The Canadian species possesses a genital papilla through which the eggs were released, and an apparently much smaller male genital papilla than the southern subspecies.     

The offspring size/fecundity trade-off and female fitness in the Atlantic molly (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, Poeciliidae)

Across a variety of taxa, large offspring have been demonstrated to have a fitness advantage over smaller offspring of the same species. However, producing large offspring often comes at the cost of having to produce fewer young, and the payoff (and thus, evolutionary outcome) of this trade-off is expected to vary between environments. Atlantic mollies (Poecilia mexicana: Poeciliidae, Teleostei), inhabiting a sulfidic cave and various non-sulfidic surface habitats in Tabasco (Mexico), are reproductively isolated and evolved divergent female life-history traits: females of the cave ecotype produce considerably fewer, but larger offspring. Stressful (sulfidic) environments may favor the production of larger offspring, as they are better able to cope with chemical stressors. It remains to be determined though if increased offspring survival outweighs the fitness cost of producing fewer but larger offspring even under benign laboratory conditions. We tested 30-day newborn survival of offspring from wild-caught P. mexicana females from diverging populations in a low-density, no predation, no cannibalism, and ad-libitum-food, benign laboratory environment. Survival rates were highly skewed towards larger cave molly offspring; however, surface molly females still had a higher fitness than cave molly females in terms of higher total numbers of surviving offspring. Our study provides evidence for an innate fitness advantage of larger cave molly offspring. Furthermore, the observed differences in life-history strategies could promote further divergence and reproductive isolation among these ecotypes of P. mexicana, because cave molly females immigrating into the adjacent surface habitats would most likely be selected against.     

Parallel evolution leads to reduced shoaling behavior in two cave dwelling populations of Atlantic mollies (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>, Poeciliidae,Teleostei)

Shoaling behavior protects fishes from avian and piscine predation, but at the same time costs of group living arise due to several mechanisms including increased food competition. Most cave fishes live in an environment in which avian and piscine predators are lacking, and cave environments are often characterized by low food availability, leading to increased food competition. Altogether, this should favor the reduction of shoaling in cave fishes. We compared shoaling behavior (i.e. the tendency to associate with a stimulus shoal) among surface dwelling populations of the Atlantic molly, Poecilia mexicana, and two cave forms of that species. The first cave population of P. mexicana originated from the Cueva del Azufre and was previously recognized as the only cave form of a poeciliid fish. The second cave population examined came from a cave that was discovered only recently (Cueva Luna Azufre). In both cave forms shoaling behavior was reduced compared with surface dwelling mollies.     

Relaxed purifying selection of rhodopsin gene within a Chinese endemic cavefish genus <Emphasis Type="Italic">Sinocyclocheilus</Emphasis> (Pisces: Cypriniformes)

The cyprinid fish genus Sinocyclocheilus, as the most cavefish rich genus, includes many species showing striking adaptation to caves and convergent reduction or even loss of eyes and pigmentation. RH1 is responsible for dim vision. In order to explore the evolution of RH1 gene in this genus, we sequenced the complete gene from 28 individuals of 16 representative species of Sinocyclocheilus, with cave and surface species included. Phylogenetic analyses supported the monophyly of Sinocyclocheilus and polyphyly of the cave species. Codon models implemented in PAML were used to infer the evolution of RH1. We found that Sinocyclocheilus had a significantly higher evolutionary rate for amino acids than other cyprinid fishes compared, which might be the result of relaxation of purifying selection and could be ascribed to cave habit of this genus. In contrast to previous hypotheses, both cave and surface lineages exhibited a similar rate of molecular evolution, so the RH1 of cave species may still be functional, although these species were highly adapted to cave environment. Two amino acid substitutions (D83G and E122V) that were not reported before were found, which may be useful for site-directed mutagenesis in the future. Handling editor: Christian Sturmbauer     

Cave molly females (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>) avoid parasitised males

Cave mollies (Poecilia mexicana) inhabit a dark Mexican cave, where visual communication is impossible. I observed the preference of cave molly females to associate with a non-infected male or a male infected with a pathogenic bacterium (Mycobacterium sp.) which causes the formation of large blisters around the eyes of infected fish. Females preferred to stay near the non-infected male only when the two stimulus males were separated from the female by transparent Plexiglas in light, but not when the males were separated by a wire-mesh in light (where vision was to some extent hindered, but the females perceived non-visual cues) or in darkness (where only non-visual cues were available). I conclude that the visually mediated preference for non-infected males has been maintained during the colonisation of the lightless habitat, but a preference for this trait on the basis of non-visual cues did not evolve. The cave habitat may be poor in pathogens, resulting in low selection pressure to evolve a non-visual preference for males without bacterial infection.Communicated by R.F. Oliveira     

Fine Structure of the Female Genital System in Phytoseiid Mites with Remarks on Egg Nutrimentary Development, Sperm-Access System, Sperm Transfer, and Capacitation (Acari, Gamasida, Phytoseiidae)

The fine structure of the female genital system is described in two phytoseiid species: Phytoseiulus persimilis Athias-Henriot (mating females) and Typhlodromus rhenanoides Athias-Henriot (overwintering females). The female genital tract is composed of an unpaired gonad, the uterus (oviduct I), and the vaginal duct (oviduct II). The latter leads to the vagina (genital atrium), into which a pair of vaginal glands opens. The gonad (ovary s.l.) has two components: the ovary (s.str.) where germ cells develop and the lyrate organ serving as a nutrimentary compartment. In the ovary (s.str.), somacells and germ cells are observed. The germ cells surround a central tissue, to which they have direct contact with a nutritive cord at least in the previtellogenic phase during oogenesis. In fertilized females, cells likely representing capacitated sperm cells are also found in the ovary. The lyrate organ has two arms that extend anteriorly but join in their posterior part in front of the ovary (s.str.). The lyrate organ is composed of a somatic (supporting) and a nutritive tissue. The nutritive tissue, which is a syncytium, is continuous with the central tissue. The uterus starts from the ventral region of the central tissue. Finally, the ultrastructure of the sperm-access system, composed of paired solenostomes, major and minor ducts, emboli, calyces, and vesicles, is reported and functional aspects are discussed. The minor ducts end in the somatic tissue of the ovary s.str. However, because of its extremely reduced lumen and the peculiar morphology of its beginning, it seems unlikely that the minor duct lumen serves as a simple route for the sperm towards the ovary.