Morphological variation in diadromous and landlocked populations of the spotted galaxias,Galaxias truttaceus,in Tasmania,south-eastern Australia

Synopsis A comparison of a suite of morphometric measurements and meristic counts of individuals of two landlocked lacustrine and two diadromous riverine populations of Galaxias truttaceus was carried out utilising both univariate and canonical variate analyses. Lacustrine fish had fewer dorsal and anal fin rays than did riverine fish. Differences were not as clear for gill rakers and vertebrae. Comparisons of serial counts were made with two derived lacustrine species, G. auratus and G. tanycephalus, also from Tasmania. Lacustrine G. truttaceus varied in the same direction as the derived species, relative to riverine G. truttaceus. From an analysis of 12 body measurements, the first canonical variate clearly separated lacustrine fish from riverine fish largely based on measurements associated with fins (pre-anal fin length, length of anal base, pre-dorsal fin length, maximum length of dorsal fin and inter-orbital width). An overall value for the correct classification of fish into groups based on locality was 84%. The percentage of fish classified into the wrong habitat (lake or stream) was much less than the percentage classified between localities within habitats. Overall morphological variation was greater between than within habitats. It is suggested that the differences in water movement and food type may in part account for the differences shown and that selective pressures peculiar to the lacustrine environment may be causing the lake populations to diverge from the riverine populations.     

Form changes in the sea bass, Dicentrarchus labrax (Moronidae: Teleostei), after acclimation to freshwater: an analysis using shape coordinates

Synopsis Morphological changes in the sea bass, Dicentrarchus labrax (Perciformes: Moronidae), were investigated after an experimental acclimation trial to freshwater. The sea bass is an euryhaline species occurring in the Mediterranean and west Atlantic from 30° N to 55° N. Part of the offspring of a pool of breeders was acclimated to freshwater at 9 months of age while maintaining the original stock in marine water. The effect of acclimation to freshwater over the entire form of the fish was studied through geometric morphometrics (shape coordinates). Changes in the form were shown graphically as landmark displacements though age classes 7,12, 15, 19 and 24 months and were discussed in the light of integrated growth. A significantly faster growth in freshwater was detected. Shape coordinates analyzed through multivariate statistics show that significant differences in shape arise after acclimation to freshwater. Moreover, the uniform component of shape change reveals a major effect of stretching or compression perpendicular to the body axis which is common and conservative in both trials. Differences are discussed in terms of selection and ecophenotypism.     

Population structure and biology of alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) in the Saint John River,New Brunswick

Synopsis Examination of more than 2,000 alewives (Alosa pseudoharengus) and blueback herring (A. aestivalis) from various areas in the Saint John River, N.B., showed differences in their morphometric and meristic characters. They differed also in length and age, compositions, spawning time, length and age at maturity, back-calculated lengths, and growth parameters. Within each species, between-area comparisons showed significant differences in some of their meristic characteristics.To test a homing hypothesis for alewives, a multivariate analysis was performed on eight meristic characters. Two discriminant function programs, discriminant analysis for two groups and a multiple group stepwise discriminant analyses were used. Values of the generalized Mahalanobis D² and percent overlap in frequency distributions of meristic characters suggest that considerable straying of fish, especially between adjacent areas occurs during upstream spawning migration.This article is one of several papers presented at the Second European Ichthyological Congress, Paris, 8–15 September 1976, to be published in Environmental Biology of Fishes.     

Three-dimensional models of chick embryo somites obtained by mathematical methods applied to ultrastructural data

Summary A model of a thoracolumbar somite of a chick embryo at the 53rd incubation hour was obtained by mathematical methods, after identification of somite cell types by means of electron microscopy.Each specific district occupied by the cell types was precisely determined.On the basis of these observations, the somite was three-dimensionally reconstructed and the spatial positions of the primitive myotome, dermatome, sclerotome, undifferentiated mesoderm and myocele were precisely identified.     

Molecular systematics of pinniped hookworms (Nematoda: Uncinaria): species delimitation,host associations and host-induced morphometric variation

Hookworms of the genus Uncinaria have been widely reported from juvenile pinnipeds, however investigations of their systematics has been limited, with only two species described, Uncinaria lucasi from northern fur seals (Callorhinus ursinus) and Uncinaria hamiltoni from South American sea lions (Otaria flavescens). Hookworms were sampled from these hosts and seven additional species including Steller sea lions (Eumetopias jubatus), California sea lions (Zalophus californianus), South American fur seals (Arctocephalus australis), Australian fur seals (Arctocephalus pusillus), New Zealand sea lions (Phocarctos hookeri), southern elephant seals (Mirounga leonina), and the Mediterranean monk seal (Monachus monachus). One hundred and thirteen individual hookworms, including an outgroup species, were sequenced for four genes representing two loci (nuclear ribosomal DNA and mitochondrial DNA). Phylogenetic analyses of these sequences recovered seven independent evolutionary lineages or species, including the described species and five undescribed species. The molecular evidence shows that U. lucasi parasitises both C. ursinus and E. jubatus, whereas U. hamiltoni parasitises O. flavescens and A. australis. The five undescribed hookworm species were each associated with single host species (Z. californianus, A. pusillus, P. hookeri, M. leonina and M. monachus). For parasites of otarids, patterns of Uncinaria host-sharing and phylogenetic relationships had a strong biogeographic component with separate clades of parasites from northern versus southern hemisphere hosts. Comparison of phylogenies for these hookworms and their hosts suggests that the association of U. lucasi with northern fur seals results from a host-switch from Steller sea lions. Morphometric data for U. lucasi shows marked host-associated size differences for both sexes, with U. lucasi individuals from E. jubatus significantly larger. This result suggests that adult growth of U. lucasi is reduced within the host species representing the more recent host–parasite association. Intraspecific host-induced size differences are inconsistent with the exclusive use of morphometrics to delimit and diagnose species of Uncinaria from pinnipeds.     

Family Ismaridae Thomson (Hymenoptera,Diaprioidea), new to fauna of Iran

Occurrence of the family Ismaridae Thomson is recorded for the first time from Iran, represented by a single species, Ismarus rugulosus Förster, 1850. A series of diagnostic characters and morphometric ratios for this species is presented, as well as a distribution map throughout the Holarctic region.     

Fgf8 haploinsufficiency results in distinct craniofacial defects in adult zebrafish

Significant progress has been made toward understanding the role of fgf8 in directing early embryonic patterning of the pharyngeal skeleton. Considerably less is known about the role this growth factor plays in the coordinated development, growth, and remodeling of the craniofacial skeleton beyond embryonic stages. To better understand the contributions of fgf8 in the formation of adult craniofacial architecture, we analyzed the skeletal anatomy of adult ace(ti282a)/fgf8 heterozygous zebrafish. Our results revealed distinct skeletal defects including facial asymmetries, aberrant craniofacial geometry, irregular patterns of cranial suturing, and ectopic bone formation. These defects are similar in presentation to several human craniofacial disorders (e.g., craniosynostosis, hemifacial microsomia), and may be related to increased levels of bone metabolism observed in ace(ti282a)/fgf8 heterozygotes. Moreover, skeletal defects observed in ace(ti282a)/fgf8 heterozygotes are consistent with expression patterns of fgf8 in the mature craniofacial skeleton. These data reveal previously unrecognized roles for fgf8 during skeletogenesis, and provide a basis for future investigations into the mechanisms that regulate craniofacial development beyond the embryo.     

Multivariate discrimination among cryptic species of the mite genus Chaetodactylus (Acari: Chaetodactylidae) associated with bees of the genus Lithurgus (Hymenoptera: Megachilidae) in North America

Twenty-seven morphological characters from 111 heteromorphic deutonymphs of the mite genus Chaetodactylus Rondani (Acari: Chaetodactylidae) were analyzed. The mites were collected from four species of bees of the genus Lithurgus Berthold (Hymenoptera: Megachilidae) in continental North America. Principal component and canonical variates analyses on Darroch and Mosimann shape and size-and-shape variables revealed the presence of three cryptic species. Chaetodactylus gibbosi sp. n. (Florida) is geographically isolated from C. lithurgi sp. n. distributed in Texas, New Mexico, Arizona, Colorado, and Idaho. Sympatric C. lithurgi and C. abditus sp. n. (USA: Arizona, Mexico: Socorro Is.) are seasonally isolated in Arizona. Chaetodactylus gibbosi is associated with a single bee species, Lithurgus gibbosus Smith in Florida. The host range of C. lithurgi includes bees flying predominantly in the spring: L. apicalis Cresson, L. littoralis Cockerell, and western L. gibbosus. Chaetodactylus abditus sp. n. is associated with L. planifrons Friese and L. echinocacti Cockerell, flying predominantly in the fall in Arizona. No distinct groups separated by geographic locality or size were detected in any species. A six-variable model developed by the canonical variates analysis and estimated using jackknife resampling and external validation (n=100) is capable of classifying the three species with 100% accuracy. Factors that influenced speciation of cryptic species of Chaetodactylus associated with Lithurgus are discussed. Based on morphological and geographical data and data on mite associates, the western and eastern populations of the bee L. gibbosus are distinct. Therefore, the taxonomic status of L. gibbosus s. lat. should be reevaluated.     

Identification of a host-associated species complex using molecular and morphometric analyses,with the description of Gyrodactylus rugiensoides n. sp. (Gyrodactylidae,Monogenea)

Gyrodactylus rugiensis was originally described as a parasite occurring on the marine gobies Pomatoschistus minutus and Pomatoschistus microps. In our preliminary survey this species was also frequently found on Pomatoschistus pictus and Pomatoschistus lozanoi. Subsequent molecular analysis of the internal transcribed spacers rDNA region revealed that this parasite actually represents a complex of two apparently cryptic species, one restricted to P. microps and the other shared by P. minutus, P. lozanoi and P. pictus. Morphometric analyses were conducted on 17 features of the opisthaptoral hard parts of specimens collected from all four host species. Standard discriminant analysis showed a clear separation of both genotypes by significant differences in marginal hook and ventral bar features. Statistical classifiers (linear discriminant analysis and nearest neighbours) resulted in an estimated misclassification rate of 4.7 and 3.1%, respectively. Based on molecular, morphological and statistical analyses a new species, Gyrodactylus rugiensoides is described. This species seems to display a lower host-specificity than generally observed for Gyrodactylus species as it infects three sympatric host species.However, seasonal and host-dependent morphometric variation is shown for G. rugiensoides collected on P. pictus. Host-switching and gene flow might be important factors preventing speciation on closely related and sympatric host species. The presence of host associated species complexes in this Gyrodactylus-Pomatoschistus system is also confirmed by the presence of two host-dependent genotypes within G. micropsi found on P. minutus and P. lozanoi, and P. microps, respectively. By comparing host and parasite phylogeny, phylogenetic and ecological factors influencing host-specificity are discussed.