First record of pughead deformity in redear sunfish Lepomis microlophus (Günther, 1859)

The first record of pughead deformity in redear sunfish Lepomis microlophus is presented based on a single specimen captured from a wild population in a small Oklahoma reservoir. The pugheaded specimen was compared to normal fish from the same population. The pugheaded fish had slightly poorer body condition, although total length was comparable to normal individuals of the same age. Poorer condition may have resulted from difficulty feeding due to incomplete mouth closure and restricted gape caused by severe deformity of the anterior neurocranium and upper jaw. Extreme drought conditions leading to deteriorated water quality during early development may have resulted in the deformity of the redear sunfish. The incidence rate of pugheadedness in this redear sunfish population was below 1%, comparable to rates reported in other wild freshwater fish populations.     

DO EMBRYOS INFLUENCE MATERNAL INVESTMENT? EVALUATING MATERNAL‐FETAL COADAPTATION AND THE POTENTIAL FOR PARENT‐OFFSPRING CONFLICT IN A PLACENTAL FISH

The evolution of matrotrophy introduces the potential for genomic conflicts between mothers and embryos. These conflicts are hypothesized to accelerate the evolution of reproductive isolation and to influence the evolution of life-history traits, reproductive structures, and genomic imprinting. These hypotheses assume offspring can influence the amount of maternal investment they receive and that there is a trade-off between maternal investment into individual offspring and maternal survival or fecundity. We used field data and laboratory crosses to test whether these assumptions are met in the matrotrophic poeciliid fish Heterandria formosa . Comparisons of life histories between two natural populations demonstrated a trade-off between the level of maternal investment into individual embryos and maternal fecundity. Laboratory crosses between individuals from these populations revealed that offspring genotype exerts an influence on the level of maternal investment and affects maternal fecundity through higher rates of embryo abortion and lower numbers of full-term offspring. Our results show that the prerequisites for parent–offspring conflict to be a potent evolutionary force in poeciliid fish are present in H. formosa. However, determining whether this conflict has shaped maternal investment in nature will require disentangling any effects of conflict from those of several ecological factors that are themselves correlated with the expected intensity of conflict.     

Modeling the jaw mechanism of Pleuronichthys verticalis: The morphological basis of asymmetrical jaw movements in a flatfish

Several flatfish species exhibit the unusual feature of bilateral asymmetry in prey capture kinematics. One species, Pleuronichthys verticalis, produces lateral flexion of the jaws during prey capture. This raises two questions: 1) How are asymmetrical movements generated, and 2) How could this unusual jaw mechanism have evolved? In this study, specimens were dissected to determine which cephalic structures might produce asymmetrical jaw movements, hypotheses were formulated about the specific function of these structures, physical models were built to test these hypotheses, and models were compared with prey capture kinematics to assess their accuracy. The results suggest that when the neurocranium rotates dorsally the premaxillae slide off the smooth, rounded surface of the vomer (which is angled toward the blind, or eyeless, side) and are “launched” anteriorly and laterally. The bilaterally asymmetrical trajectory of the upper jaw is determined by the orientation of the “launch pad,” the vomer. During lower jaw depression, the mandibles rotate about their articulations with the quadrate bones of the suspensoria. The quadrato‐mandibular joint is positioned farther anteriorly on the eye side than on the blind side, and this asymmetry deflects the lower jaw toward the blind side. Asymmetry in the articular surfaces of the lower jaw augments this effect. Thus, it appears that fish with intermediate forms of this asymmetrical movement could have evolved from symmetrical ancestors via a few key morphological changes. In addition, similar morphological modifications have been observed in other fish taxa that also produce jaw flexion during feeding, which suggests that there may be convergence in the basic mechanism of asymmetry. J. Morphol. 256:1–12, 2003. © 2003 Wiley‐Liss, Inc.     

Experimental evolution in Heterandria formosa, a livebearing fish: group selection on population size

Group selection has historically been an important and controversial subject in evolutionary biology. There is now a compelling body of evidence, both theoretical and experimental, that group selection not only can be effective, but can be effective in situations when individual selection is not. However, experiments in which true population-level traits have been shown to evolve in response to group selection are currently limited to two species of flour beetle in the genus Tribolium and RNA viruses. Here we report the results of an experiment wherein we imposed group selection via differential extinction for increased and decreased population size at 6-week intervals, a true population-level trait, in the poeciliid fish Heterandria formosa. In contrast to most other group selection experiments, we observed no evolutionary response after six rounds of group selection in either the up- or down-selected lines. Populational heritability for population size was low, if not actually negative. Our results suggest that group selection via differential extinction may be effective only if population sizes are very small and/or migration rates are low.     

Costs and benefits of polyandry in a placental poeciliid fish Heterandria formosa are in accordance with the parent-offspring conflict theory of placentation

In viviparous species, a conflict over maternal resource allocation may arise between mothers and embryos, between siblings, and between maternal and paternal genes within an embryo due to relatedness asymmetries. We performed two experiments to study the effects of polyandry and brood relatedness on offspring growth in a placental fish (Heterandria formosa). Polyandry was beneficial as it increased the probability of pregnancy, possibly to avoid genetic incompatibility. However, females mated to four males produced offspring that had a longer maturation time than those of monandrous females. When within-brood relatedness was manipulated, the size of the newborn offspring decreased with time in low-relatedness treatment, whereas in highly related broods, offspring size was constant. Low within-brood relatedness may lead to less cooperative offspring in terms of resource extraction from the mother, which may lead to impaired development during gestation. Offspring conflict may thus reduce the benefits of polyandry in viviparous species.     

The functional meaning of “prey size” in water snakes (Nerodia fasciata, Colubridae)

The evolutionary success of macrostomatan (enlarged-gape) snakes has been attributed to their ability to consume large prey, in turn made possible by their highly kinetic skulls. However, prey can be “large” in several ways, and we have little insight into which aspects of prey size and shape affect skull function during feeding. We used X-ray videos of broad-banded water snakes (Nerodia fasciata) feeding on both frogs and fish to quantify movements of the jaw elements during prey transport, and of the anterior vertebral column during post-cranial swallowing. In a sample of additional individuals feeding on both frogs and fish, we measured the time and the number of jaw protractions needed to transport prey through the buccal cavity. Prey type (fish vs. frog) did not influence transport kinematics, but did influence transport performance. Furthermore, wider and taller prey induced greater movements of most cranial elements, but wider prey were transported with significantly less anterior vertebral bending. In the performance trials, heavier, shorter, and wider prey took significantly more time and a greater number of jaw protractions to ingest. Thus, the functional challenges involved in prey transport depend not only upon prey mass, but also prey type (fish vs. frog) and prey shape (relative height, width and length), suggesting that from the perspective of a gape-limited predator, the difficulty of prey ingestion depends upon multiple aspects of prey size.     

Direct and correlated responses to artificial selection on acute thermal stress tolerance in a livebearing fish

Abstract.— Tradeoffs in performance or fitness across environments have important implications regarding the nature of evolutionary constraints. It remains controversial whether tradeoffs such as these reflect genetic correlations that are genuine evolutionary constraints. However, if such long-term genetic constraints do exist, they must be due to underlying pleiotropy such that alleles that confer high performance in one environment invariably confer low performance in another. The distribution of genetic correlations within and among populations can provide insight about the existence of such pleiotropic tradeoffs. The long-term association of certain teleost fish taxa with particular abiotic environments suggests that tradeoffs in performance across environments have constrained the geographic distribution of those taxa. Here we report the results of an experiment in which we artificially selected on acute heat- and cold-stress tolerance in two stocks of the poeciliid fish Heterandria formosa from source populations with different thermal histories. Unexpectedly, we observed no direct responses to selection. Under certain conditions, fish from the different source populations differed significantly in cold tolerance, but not in heat tolerance. The results suggest there are no strong pleiotropic tradeoffs between heat- and cold-stress tolerance in these populations.     

Cranial kinesis in lizards (Lacertilia): Origin,biomechanics, and evolution

Various methods of investigation of cranial kinesis are compared. The biomechanical model of the amphikinetic cranial mechanism of lizards developed by Frazzetta (1962) corresponds to the skulls of species with the dependent streptostyly. A new modification of this model is proposed for species with the independent streptostyly, which conforms to the results of experimental investigations of cranial kinesis in living lizards. The lacertilian amphikinesis has developed on the basis of the pleurokinesis inherited from fish ancestors of tetrapods. Movable connections of the maxillo-buccal segments with the axial skull persisted in the amphikinetic skull and were completed by the transversal flexible connections in the dermatocranial roof and loose connections of dermatocranium with the braincase. The development of new movable intracranial connections could have been preceded by transformations in the jaw musculature (formation of the pterygoideus muscle and inclined position of the external jaw adductor), which caused longitudinal jaw movements. Development of new movable connections within the skull was triggered by paedomorphosis processes. In various lacertilian groups, the cranial kinesis was improved by the development of various forms of streptostyly and flexipalatality.     

Unique features of pedicellate attachment of the upper jaw teeth in the adult gobiid fish Sicyopterus japonicus (Teleostei,Gobiidiae): Morphological and structural characteristics and development

Sicyopterus japonicus (Teleostei, Gobiidae), a hill‐stream herbivorous gobiid fish, possesses an unusual oral dentition among teleost fishes on account of its feeding habitat. By using scanning electron microscopy, light microscopy, and transmission electron microscopy, including vital staining with tetracycline, we examined the development of the attachment tissues of the upper jaw teeth in this fish. The functional teeth of S. japonicus had an asymmetrical dentine shaft. The dentine shaft attached to the underlying uniquely shaped pedicel by means of two different attachment mechanisms. At the lingual base, collagen fiber bundles connected the dentine shaft with the pedicel (hinged attachment), whereas the labial base articulated with an oval‐shaped projection of the pedicel (articulate attachment). The pedicel bases were firmly ankylosed to the crest of the thin flange of porous spongy bone on the premaxillary bone, which afforded a flange‐groove system on the labial surface of the premaxillary bone. Developmentally, the pedicel and thin flange of spongy bone were completely different mineralized attachment tissues. The pedicel had a dual origin, i.e., the dental papilla cells, which differentiated into odontoblasts that constructed the internal surface of the pedicel, and the mesenchymal cells, which differentiated into osteoblasts that formed the outer face of the pedicel. A thin flange of spongy bone was deposited on the superficial resorbed labial side of the premaxillary bone proper, and later rapid bone remodeling proceeded toward the pedicel base. These unique features of pedicellate tooth attachment for the upper jaw teeth in the adult S. japonicus are highly modified teeth for enhancing the ability of individual functional teeth to move closely over irregularities in the rock surfaces during the scraping of algae. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Scanning electron microscopic study of the structures associated with lips of an Indian hill stream fish Garra lamta (Cyprinidae, Cypriniformes)

The surface architecture of the structures associated with the lips of a hill stream fish Garra lamta was examined by scanning electron microscopy. In this teleost, the lips are inconspicuous and associated with prominent horny jaw sheaths. Furthermore, the upper and lower lips are associated with a greatly enlarged rostral cap and an adhesive pad, respectively. The rostral cap has a proximal mucogenic region and a distal keratinized region. The adhesive pad is differentiated into central mucogenic and peripheral keratinized regions. At the mucogenic regions of the rostral cap and the adhesive pad, the surface of the epithelial cells is characterised by well developed microridges, which reflect their high secretory activity. The mucus may lubricate the surface and protect the epithelia from abrasions at these regions, which are likely to be subjected to wear and tear during frequent friction and adhesion of the fish to the substrate. Taste buds may help the fish to locate food and trigger a 'pick-up' reflex. The epithelial cells at the surface of the keratinized regions of the rostral cap and the adhesive pad are modified as clusters of spine like unculi, which may assist the fish in its firm anchorage to the substrate. The epithelial cells at the surface of the horny jaw sheaths are modified as polygonal unculi, each appears much like a tooth that has a characteristic sharp edge at the margin. These may be regarded as an adaptation to browsing or scraping food materials from the substrate.     

Small male mating advantage and reversed size dimorphism in poeciliid fishes

Despite interspecific differences in the absolute efficiency rate of copulatory thrusting in Poecilia reticulata, Phalloceros caudimaculatus, Heterandria formosa, Girardinus falcatus and Gambusia holbrooki small males had a significant advantage. These differences are discussed in the light of the interspecific differences in morphology and sexual behaviour. The results of the present study offer an alternative explanation for the pronounced reversed size dimorphism observed in this family of fishes. The greater efficiency of small males in achieving matings when females are unreceptive might also explain why genetically small males are maintained in natural populations of many poeciliids, in spite of the large size advantage in both intrasexual competition and female choice.     

ADAPTIVE MATERNAL ADJUSTMENTS OF OFFSPRING SIZE IN RESPONSE TO CONSPECIFIC DENSITY IN TWO POPULATIONS OF THE LEAST KILLIFISH, HETERANDRIA FORMOSA

Given a trade-off between offspring size and number and an advantage to large size in competition, theory predicts that the offspring size that maximizes maternal fitness will vary with the level of competition that offspring experience. Where the strength of competition varies, selection should favor females that can adjust their offspring size to match the offspring's expected competitive environment. We looked for such phenotypically plastic maternal effects in the least killifish, Heterandria formosa , a livebearing, matrotrophic species. Long-term field observations on this species have revealed that some populations experience relatively constant, low densities, whereas other populations experience more variable, higher densities. We compared sizes of offspring born to females exposed during brood development to either low or high experimental densities, keeping the per capita food ration constant. We examined plastic responses to density for females from one population that experiences high and variable densities and another that experiences low and less-variable densities. We found that, as predicted, female H. formosa produced larger offspring at the higher density. Unexpectedly, we found similar patterns of plasticity in response to density for females from both populations, suggesting that this response is evolutionarily conserved in this species.     

A biomechanical model for analysis of muscle force,power output and lower jaw motion in fishes

Fish skulls are complex kinetic systems with movable components that are powered by muscles. Cranial muscles for jaw closing pull the mandible around a point of rotation at the jaw joint using a third-order lever mechanism. The present study develops a lever model for the jaw of fishes that uses muscle design and the Hill equation for nonlinear length-tension properties of muscle to calculate dynamic power output. The model uses morphometric data on skeletal dimensions and muscle proportions in order to predict behavior and force transmission mediated by lever action. The computer model calculates a range of dynamic parameters of jaw function including muscle force, torque, effective mechanical advantage, jaw velocity, bite duration, bite force, work and power. A complete list of required morphometrics is presented and a software program (MandibLever 2.0) is available for implementing lever analysis. Results show that simulations yield kinematics and timing profiles similar to actual fish feeding events. Simulation of muscle properties shows that mandibles reach their peak velocity near the start of jaw closing, peak force at the end of jaw closing, and peak power output at about 25% of the closing cycle time. Adductor jaw muscles with different mechanical designs must have different contractile properties and/or different muscle activity patterns to coordinate jaw closing. The effective mechanical advantage calculated by the model is considerably lower than the mechanical advantage estimated from morphological lever ratios, suggesting that previous studies of morphological lever ratios have overestimated force and underestimated velocity transmission to the mandible. A biomechanical model of jaw closing can be used to interpret the mechanics of a wide range of jaw mechanisms and will enable studies of the functional results of developmental and evolutionary changes in skull morphology and physiology.     

Dissolved oxygen and fish distribution in a Florida spring

This study examined the distribution and relative abundance of fishes along a dissolved oxygen gradient in Singing Springs, Florida. Over the 1-year study, dissolved oxygen concentration in the spring exhibited a strong gradient ranging from an average of 0.20 mg l^–2AM¹ at the boil to 1.81 mg l^–2AM¹ 110 meters downstream. Seasonal variation in dissolved oxygen was very low relative to the spatial variation along the spring gradient. Fish community composition was evaluated monthly at the boil of the spring, 45 m downstream just after the confluence of the spring and the main river, and 110 m downstream. The fish community in the spring was characterized by species generally considered to be tolerant of low oxygen. Gambusia holbrooki was the most abundant species at all sites comprising an average of 88.1% of the fish captured at the boil, 63.2% of the fish captured at 45 m, and 74.8% of the fish captured at 110 m downstream. The diversity of fishes (G. holbrooki, Heterandria formosa, Notropis harperi, Lucania goodei, and Poecilia latipinna) increased with distance from the boil. Although there were some seasonal differences in patterns of diversity and community structure, the inter-site differences were much more apparent throughout the study. It is likely that the pattern of variation in dissolved oxygen interacts with the respiratory abilities of the fishes to affect the distribution pattern and community composition along the gradient.     

Multiple paternity and population genetic structure in natural populations of the poeciliid fish, Heterandria formosa

Heterandria formosa Agassiz, exhibits internal fertilization, internal brooding of embryos, sperm storage and an extreme level of superfetation. In this study we used microsatellite markers to examine variation among seven populations that exhibited significant variance in their histories of population density. We found that the populations were genetically distinct and that the heterozygosity increased as population density increased. We also examined paternity in three of those populations and found that the number of sires per female and the number of sires per brood increased with population density. Overall, the rates of multiple paternity are quite low relative to other species. The correlations with population density suggest that contact rates play a critical role in the breeding system in this species but the low rates of multiple paternity suggest that females may exert control over fertilization of their ova.     

The oral sucker of Gyrinocheilus aymonieri (Teleostei: Cypriniformes)

The sucker was studied in young and mature fish by light microscopy, histochemistry, transmission and scanning electron microscopy, X-ray probe microanalysis, dissection, staining preparations of whole skeletons, and watching the animals in aquaria. The fleshy lips are supported by highly flexible, chondroid tissues, the structure and histochemistry of which differ substantially from those of cartilage. They allow the sucker to evert when the fish attaches to a stone or aquarium wall and are connected to the maxillae, premaxillae and dentaries. Lining the inside of the lips are two horny rasps, each with several regular rows of small hooks. The scraping blades of these hooks are keratinized and point towards the mouth. They increase the coefficient of friction for adhesion and enable the fish to feed on encrusting algae. Between the posterior rasp and the -anterior margin of the mandible are two invaginations of the lower lip that extend the sucker chamber beneath large hollows in the dentaries. The anterior margin itself contacts the outer surface of the maxillary oral valve when the mouth is closed, and isolates the sucker chamber from the rest of the buccal and pharyngeal cavities. Contrary to previous views, it is thought that a true vacuum is produced, and that attached fish spend long periods without taking water in through the mouth. The attachments of the principal jaw muscles are described and their role in sucker action discussed. There are similarities with the jaw mechanism of catostomids.     

Development of the Osteocranium in Natrix natrix (Serpentes,Colubridae) Embryogenesis II: Development of the jaws,palatal complex and associated bones

Snakes differ from the other vertebrates with their hyperkinetic skull. To establish the developmental features of the skull bones, involved in prey capture and ingestion, the Grass snake Natrix natrix (Serpentes, Colubridae) embryos are studied at all the successive stages of embryogenesis. Thirty-five N. natrix embryos are examined. Twenty embryos are studied with histological methods; fifteen embryos are cleared and double-stained with alizarin red and alcian blue. The sequence of appearance and formation of the upper and lower jaw bones, palatal complex and associated bones is described in accordance with the table of developmental stages. New features in the ossification mode of some bones are revealed: each bone, namely, the vomer, septomaxilla and maxilla, is formed from three separate ossification centres. Three ossification centres in the maxilla, two ossification centres in the bodies of the septomaxilla and vomer, as well as the unknown additional ossification centre in the vomer had not been previously described in snake embryos. The new data can be used in further comparative research on the reptile skull development and vertebrate phylogeny.     

Notes on the typology of the skull of the Myrmecophagidae (Mammalia, Edentata)

The skulls of Myrmecophaga, Tamandua, and Cyclopes are klinorhynch; the upper jaw is situated rostral to the neurocranium and to a varying degree ventral to the plane of the median basis cranii. The median part of the base of the neurocranium is the structure to which the anatomical modifications in the median plane are referred. The kyphosis, which determines the situation of the upper jaw, is prebasically located either within the upper jaw (Myrmecophaga, Tamandua) or at its basis (Cyclopes).     

SPECIES-WIDE POPULATION STRUCTURE IN A SOUTHEASTERN U.S. FRESHWATER FISH,HETERANDRIA FORMOSA: GENE FLOW AND BIOGEOGRAPHY

The phylogeography of the freshwater fish fauna of the southeastern United States has almost achieved paradigm status in evolutionary biology (Avise 1992), and the major geographic features responsible for shaping species distributions are well-characterized. Nevertheless, variation among species in distributions of allele or haplotype frequencies suggests that species-specific processes (e.g., migration) may also play a role in establishing those distributions. There has also been relatively little investigation into how population structure may differ among subregions in the Southeast, for example, on the Florida peninsula versus the U.S. mainland to the northwest and/or northeast. The geology of the peninsula is such that both physical and biotic fluctuations may have been (and still be) particularly important in establishing the population structure of freshwater taxa. This possibility leads to two interesting questions in population genetics. (1) Does gene flow in freshwater species of the region better approximate a one- or two-dimensional pattern? (2) Are populations on the peninsula farther from migration-genetic drift equilibrium than their counterparts on the mainland? These questions were addressed by examining the population strucuture of a livebearing fish, Heterandria formosa; several features of the biology of the species make it particularly likely that recent gene flow has been important in its evolution. I surveyed electrophoretic variation in 34 populations distributed throughout the species range. The phylogeographic patterns observed are in general concordance with those found in other species, although with some differences. A two-dimensional hypothesis of gene flow on the Florida peninsula better explains the data than does a one-dimensional one. There is no evidence that populations on the peninsula are farther from migration-drift equilibrium than those to the northwest. Populations in the northeast have lower genetic diversity than those to the south and west and show no isolation by distance; those results are consistent with a recent range expansion into the northeast, although smaller historical effective population sizes could also explain the pattern.