Hermaphroditism and sexual function inCirrhitichthys aureus and the other Japanese hawkfishes (Cirrhitidae: Teleostei)

The present paper deals with gonadal formation, sex succession and sexual function in the Japanese hawkfishes,Cirrhitichthys aureus (Temminck et Schlegel),C. aprinus (Cuvier),C. falco Randall,Cirrhitops hubbardi (Schultz) andCyprinocirrhites polyactis (Bleeker). Detailed studies were made forC. aureus collected from Suruga Bay, central Japan. In this species the gonad of a young fish of 21.8 mm SL had begun to initially differentiate into an ovary forming an early ovarian cavity of the parovarian type. The gonadal structures of 63 further specimens ofC. aureus, ranging from 23.9 to 114.3 mm SL, could be separated into three categories: viz., ovaries (7), ambisexual gonads (54) and secondary testes (2). Reproduction ofC. aureus in Suruga Bay took place from June to November. Although ovaries which appeared throughout the year presented only in the immature stage and occurred only in small fish ranging from 25.1 to 46.6 mm SL, functional gonads occurred in 32 ambisexual fish ranging from 61.5 to 113.5 mm SL and in one secondary male of 101.5 mm SL, collected during the reproductive season. The smaller ambisexual fish, ranging from 61.5 to 92.0 mm SL, showed active oogenetic processes in the major ovarian zones with many ripened eggs ovulating into the ovarian cavity. These gynogenic gonads undoubtedly functioned as female; however, distinct meiosis proceeded partially in the minor testicular zones with a few spermatozoa occurring in the vas deferens. The larger ambisexual specimens, ranging from 71.5 to 113.5mm SL, had slender androgenic gonads, which showed active spermatogenesis in various testicular zones and which might function as males with reduced ovigerous lamellae. The secondary males had testes occupied by seminal lobules, but which retained the ovarian cavity within. According to aquarium rearing experiments, in a pair ofC. aureus twice crossed mutually after spawning, functional sex changes occurred in twice, opposite directions, in a single gonad, i.e., from female to male and from male to female. These gonadal aspects in captiveC. aureus seemed to show an intermediate phenomenon between consecutive and simultaneous hermaphroditism. This finding also suggested thatC. aureus had similar sex succession characteristics to those of the serranid,Serranus fasciatus, studied by Hasting and Petersen (1986) and the gobiid,Trimma okinawae, studied by Sunobe (1990). We also established that normal functional hermaphroditism occurred in the four other cirrhitid species, which showed almost identical gonadal characteristics toC. aureus.     

Patterns of gonad structure in hermaphroditic gobies (Teleostei Gobiidae)

Synopsis Hermaphroditism has been reported for a small number of gobiid fishes, but the extent of this sexual pattern within the family is not known. Gonad structure was examined in one or more species from twenty-one gobiid genera. No evidence of hermaphroditism was found in the species selected from 14 genera. Laboratory studies supported the conclusion of gonochorism for the examined species in four of them:Asterropteryx, Bathygobius, Gnatholepis, andPsilogobius. Currently, the absence of precursive testicular tissues associated with the ovary in females, in conjunction with no retained ovarian features in the testes of males, appear to be reliable indicators of a gonochoristic sexual pattern in gobiid fishes. Evidence for hermaphroditism was observed in seven genera:Eviota, Trimma, Fusigobius, Lophogobius, Priolepis, Gobiodon, andParagobiodon. Protogyny was experimentally confirmed inE. epiphanes, and the gonad structure in another nine of ten species ofEviota suggested either protogyny or protogynous tendencies. With the exception ofGobiodon andParagobiodon, which exhibited similar gonadal structure, ovarian and testicular structure varied considerably among the hermaphroditic genera examined, both with regard to the configuration and to the degree of development of ovarian and testicular tissues, or testicular tissue precursors. Findings of this study indicate that hermaphroditic gonad structure will prove to be a useful trait in determining evolutionary relationships within the Gobiidae.     

Parasitic castration: host species preferences,size-selectivity and spatial heterogeneity

Summary This study investigates host-parasite population dynamics in a marine intertidal community of three barnacle host species (Balanus glandula, Chthamalus fissus andC. dalli). Our paper addresses the following questions: (1) Does prevalence (percentage parasitism) differ among the three host species? (2) What are the spatial and temporal population dynamics within the community? and (3) Does the parasite exhibit size-selective behaviour in any of the three host species? Significant differences in prevalence were found among the three host species; the parasitic castrator (Hemioniscus balani) most heavily infected the least abundant host. Parasitism occurred throughout the year and also showed significant spatial variation.H. balani showed size-selective parasitism inC. fissus, but not inC. dalli. Consequently, the population effects of parasitic castration inC. fissus depend both upon the host population size structure and the intensity of the parasite's size-selectivity.     

A review of hybridization in marine angelfishes (Perciformes: Pomacanthidae)

Synopsis Although hybridization of terrestrial and freshwater organisms has been well-studied, very little work has focused on hybridization among coral reef fish species. In the present paper, eleven examples of probable hybrids between marine angelfishes (Pomacanthidae) are reviewed. Evidence is presented which strongly suggests that the nominal speciesApolemichthys armitagei is invalid and that specimens previously identified as this species represent hybrids betweenA. trimaculatus andA. xanthurus. Of the remaining ten probable pomacanthid hybrids, five are inCentropyge (C. eibli x C. flavissimus, C. eibli x C. vrolikii, C. flavissimus x C. vrolikii, C. loricu0lus x C. potteri, andC. multifasciatus x C. venustus); one inHolacanthus (H. bermudensis x H. ciliaris), and four inPomacanthus (P. arcuatus x P. paru, P. chrysurus x P. maculosus, P. maculosus x P. semicirculatus, andP. sexstriatus x P. xanthometapon). An additional five examples of possible pomacanthid hybrids are described, two inCentropyge, two inChaetodontoplus and one inPomacanthus. Examination of hybrids may provide clues on reproductive behavior, dispersal capabilities, and phylogenetic relationships of species. More studies on hybridization in coral reef fish species, particularly those involving molecular techniques, are needed.     

Quantitative karyology of some species ofLuzula

The dimensions of metaphase chromosomes and nuclear DNA contents were measured in eight species ofLuzula. The 2 C DNA contents ranged from 8.51 pg inL. purpurea to 0.55 pg inL. pilosa. Total chromosome volume shows a linear relationship with DNA content; however, the total chromosome length of the complement of the different species is approximately constant. Nucleolar volume and the number of chromocentres in the different species also show a relationship with DNA content. Taken together, these data suggest that while chromosome fragmentation could have generated the present-day range of chromosome numbers in the genus, there have also been changes in the total quantity of DNA with the result that species with similar chromosome numbers have different DNA contents. The relationships of DNA content with chromosome volume inLuzula and other genera are compared and the differences discussed.     

Habitat Selectivity and Reliance on Live Corals for Indo-Pacific Hawkfishes (Family: Cirrhitidae)

Hawkfishes (family: Cirrhitidae) are small conspicuous reef predators that commonly perch on, or shelter within, the branches of coral colonies. This study examined habitat associations of hawkfishes, and explicitly tested whether hawkfishes associate with specific types of live coral. Live coral use and habitat selectivity of hawkfishes was explored at six locations from Chagos in the central Indian Ocean extending east to Fiji in the Pacific Ocean. A total of 529 hawkfishes from seven species were recorded across all locations with 63% of individuals observed perching on, or sheltering within, live coral colonies. Five species (all except Cirrhitus pinnulatus and Cirrhitichthys oxycephalus) associated with live coral habitats. Cirrhitichthys falco selected for species of Pocillopora while Paracirrhites arcatus and P. forsteri selected for both Pocillopora and Acropora, revealing that these habitats are used disproportionately more than expected based on the local cover of these coral genera. Habitat selection was consistent across geographic locations, and species of Pocillopora were the most frequently used and most consistently selected even though this coral genus never comprised more than 6% of the total coral cover at any of the locations. Across locations, Paracirrhites arcatus and P. forsteri were the most abundant species and variation in their abundance corresponded with local patterns of live coral cover and abundance of Pocilloporid corals, respectively. These findings demonstrate the link between small predatory fishes and live coral habitats adding to the growing body of literature highlighting that live corals (especially erect branching corals) are critically important for sustaining high abundance and diversity of fishes on coral reefs.     

Sexual system in the tanaidacean Falsapseudes bowmani (Crustacea: Malacostraca: Peracarida)

With more than 40,000 species, Malacostraca is the most diverse crustacean class. Most malacostracans are gonochoristic, but simultaneous hermaphrodites are also known. Tanaidacea is one of two malacostracan orders that includes simultaneously hermaphroditic species; so far, simultaneous hermaphroditism has been confirmed externally and internally in only two tanaidacean species, both in the genus Apseudes (Apseudidae). Here we show, through external and internal morphological observations of fixed specimens, that the apseudid Falsapseudes bowmani is a simultaneous hermaphrodite, making Falsapseudes the second tanaidacean genus in which simultaneous hermaphroditism has been confirmed both externally and internally. In this species, the epistome (a projection on the clypeus) was thick and elongate in large specimens but was thin and spiniform in smaller specimens; the brooding of eggs or embryos was observed only in thin‐epistome individuals, although a pair of ovaries was confirmed in both thick‐ and thin‐epistome individuals. This suggests that individuals with a thick epistome may act as males while also retaining the female reproductive organs.     

Karyosystematic studies on threeCrepis species (Asteraceae) endemic to Greece

This work examines the cytogeographical distribution, the morphological characters, and the karyotypes of threeCrepis species endemic to Greece (C. sibthorpiana, C. incana, andC. heldreichiana). C. sibthorpiana is diploid (2n = 2x = 8),C. incana is diploid (2n = 2x = 8) and tetraploid (2n = 4x = 16, 17), andC. heldreichiana is always dekaploid (2n = 10x = 40). The Giemsa positive bands, usually pairs of dots, are mainly centromeric inC. incana, while they are terminal inC. sibthorpiana (on the short arm of all chromosomes) and inC. heldreichiana (on both arms of all chromosomes). Intercalary C-bands are scarce and usually variable within karyotypes, individuals, and species. The most variable karyotype both in Feulgen and Giemsa preparations is that ofC. incana, in which also supernumerary chromosomes were observed, which are polysomic to standard set members. On the basis of morphological and karyological data the evolutionary relationships among the threeCrepis taxa are discussed.     

Quantitative nuclear DNA changes inEleusine (Gramineae)

2C nuclear DNA amounts were determined in 30 collections belonging to 10 species ofEleusine. About a 2.5-fold variation in genome size is evident in the genus. The 2C DNA amount in the diploid species ranged from 2.50 pg inE. verticillata to 3.35 pg inE. intermedia. In contrast, the tetraploid species showed a range from 4.95 pg inE. africana to 6.13 pg inE. floccifolia. At intraspecific level 10 collections ofE. coracana, 6 ofE. indica, 4 ofE. africana, 2 ofE. tristachya, and 2 ofE. kigeziensis did not show any significant variation. However, 2 collections ofE. floccifolia, connected with polyploidy, displayed about 90% variation. Polyploid species showed approximately double the genome size of that of their corresponding diploids. An evolutionary increase in DNA amount is evident inE. coracana during the course of its origin and domestication fromE. africana.     

Nectar flow and pollinators' efficiency in two co-occurring species ofCapparis (Capparaceae) in Israel

Two closely related species ofCapparis, C. ovata andC. spinosa, which are exposed to the same pollination environment were studied. The nectar volume and concentration ofC. ovata are higher than inC. spinosa. Both species have similar pollination efficiency, but the relative contribution of each pollinator is different.C. ovata is pollinated mainly hy hawkmoths while the principal pollinators inC. spinosa are bees.     

Hermaphroditism in tardigrades

Evidence is presented to show the existence of hermaphroditism in tardigrades, a phenomenon hitherto unknown for this phylum: specimens were obtained containing male and female germ cells in maturation in the same gonad. Hermaphroditic animals have been found in a few species of Isohypsibius; in many species of other genera and also of Isohypsibius, there is gonochorism.     

Evolutionary transitions among dioecy,androdioecy and hermaphroditism in limnadiid clam shrimp (Branchiopoda: Spinicaudata)

Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: dioecy to hermaphroditism. A fruitful approach to studying this latter transition can be sought by studying clades in which transitions between dioecy and hermaphroditism have occurred multiple times. Freshwater crustaceans in the family Limnadiidae comprise dioecious, hermaphroditic and androdioecious (males + hermaphrodites) species, and thus this family represents an excellent model system for the assessment of the evolutionary transitions between these related breeding systems. Herein we report a phylogenetic assessment of breeding system transitions within the family using a total evidence comparative approach. We find that dioecy is the ancestral breeding system for the Limnadiidae and that a minimum of two independent transitions from dioecy to hermaphroditism occurred within this family, leading to (1) a Holarctic, all‐hermaphrodite species, Limnadia lenticularis and (2) mixtures of hermaphrodites and males in the genus Eulimnadia. Both hermaphroditic derivatives are essentially females with only a small amount of energy allocated to male function. Within Eulimnadia, we find several all‐hermaphrodite populations/species that have been independently derived at least twice from androdioecious progenitors within this genus. We discuss two adaptive (based on the notion of ‘reproductive assurance’) and one nonadaptive explanations for the derivation of all‐hermaphroditism from androdioecy. We propose that L. lenticularis likely represents an all‐hermaphrodite species that was derived from an androdioecious ancestor, much like the all‐hermaphrodite populations derived from androdioecy currently observed within the Eulimnadia. Finally, we note that the proposed hypotheses for the dioecy to hermaphroditism transition are unable to explain the derivation of a fully functional, outcrossing hermaphroditic species from a dioecious progenitor.     

The evolution of mating systems in a group of brooding sea anemones (Epiactis)

Summary

The sea anemone genus Epiactis provides an unusually good opportunity to study the evolution of brooding and mating systems. The four Epiactis species on the Pacific coast of North America all brood their offspring up to the juvenile stage, but each has a different combination of internal vs. external brooding and gonochory vs. simultaneous or gynodioecious hermaphroditism. Two of the four species (E. prolifera and E. lisbethae) were indistinguishable with allozymes (20 loci), but could be differentiated using multilocus DNA fingerprinting. Phylogenetic analyses of the allozyme data by distance and parsimony methods using three outgroups suggest that the four nominal Epiactis species are polyphyletic, with the two internal brooders evolving independently of the two external brooders. This topology does not allow inferences about the evolutionary order of hermaphroditism, dioecy and gynodioecy. Separate sexes and obligate outcrossing are of ten believed to be ancestral, with hermaphroditism and the potential for self-fertilization being favored in taxa where restricted dispersal promotes inbreeding. Previous studies of population genetic structure in these Epiactis species is consistent with this hypothesis, as even the cross-fertile species were highly inbred.     

The xylem pressure potential of shrub species in an oak-hornbeam forest

Diurnal and seasonal changes of the xylem pressure potential (Ψ_xylem) were investigated in five species during three years. Intraspecific comparison was made on the basis of the mathematically expressed relationship Ψ_xylem of the individual species to Ψ_xylem inCrataegus oxyacantha, which exhibited the highest drought resistance. With increasing water stress the value for Ψ_xylem of the individual species decreases linearly in comparison with that ofC. oxyacantha, namely to −1.02 MPa inLigustrum vulgare, to −1.33 MPa inCornus mas, and to −2.09 MPa inEuonymus verrucosa. At a higher water deficit the value for Ψ_xylem of these species decreases more rapidly than inC. oxyacantha. On the basis of these findings, the relative drought resistance of the species may by evaluated, and from the value of Ψ_xylem forC. oxyacantha Ψ_xylem of the individual species may be derived. By measuring the difference between Ψ_xylem of free- and polyethylene-covered individuals the existence of water redistribution within the shrub individual was confirmed.     

The Evolution of Hermaphroditism from Dioecy in Crustaceans: Selfing Hermaphroditism Described in a Fourth Spinicaudatan Genus

The evolution of reproductive systems has intrigued evolutionary biologists for well over a century. Recent empirical and theoretical work has elucidated the evolution of dioecy (separate males and females) from hermaphroditism in many plant species. The reverse transition, evolving hermaphroditism from dioecy, has occurred many times in animals, and yet is poorly studied relative to its reverse analog in plants. Crustaceans in the sub-order Spinicaudata have evolved hermaphroditism from dioecy three separate times, in some cases forming all-hermaphroditic species and in others forming androdioecious (males + hermaphrodites) species. Herein we report evidence of hermaphroditism in a fourth spinicaudatan genus: the newly described Calalimnadia. We present sex ratio and anatomical evidence that Calalimnadia mahei comprises selfing hermaphrodites, with no males being found in over 10,000 offspring reared. We combine these reproductive results with those of other Spinicaudata to estimate the evolution of hermaphroditism in this crustacean sub-order. We use these genetic data combined with anatomical evidence to suggest that C. mahei represents a fourth, independent derivation of hermaphroditism from dioecy in these reproductively labile crustaceans.     

Genetic diversity inChaenomeles (Rosaceae) revealed by RAPD analysis

Genetic relatedness inChaenomeles was studied by RAPD analysis in 42 plants representing accessions of three wild species and one hybrid taxon. Amplification with 17 primers yielded a total of 156 polymorphic RAPD bands. Estimates of genetic relatedness suggest thatC. cathayensis andC. japonica are the most distantly related species, and that the former is comparatively homogeneous.Chaenomeles speciosa, which may have arisen through hybridization betweenC. cathayensis andC. japonica, takes an intermediate position between these two species. Analysis of diagnostic bands demonstrate that neitherC. speciosa norC. ×superba has any bands that do not occur in at least one ofC. cathayensis orC. japonica. Moreover,C. speciosa and the partly overlapping taxonC. ×superba are comparatively heterogeneous, which is also in accordance with a hybrid origin. Intraspecific variation was studied mainly inC. japonica; plants obtained from different sources of material formed well separated groups in the cluster analysis.     

Facultative monogamy in obligate coral-dwelling hawkfishes (Cirrh tidae)

Synopsis Obligate coral-dwelling hawkfishes have been hypothesized to be monogamous. This hypothesized mating system is at odds with what is known of those of other cirrhitids. Neocirrhites armatus, which inhabits Pocillopora spp. corals, and Oxycirrhites typus, which inhabits gorgonians and antipatharian corals, were examined for evidence of a monogamous mating system. Life history criteria that favor monogamy in reef fishes (Barlow 1986) were examined for these two species. Facultative monogamy was found in both. In this mating system, males are limited in their ability to acquire and maintain females, and thus have only a single mate, but may acquire additional females if conditions for doing so are favorable.     

Evidence for the wide distribution of repetitive DNA sequences in the genusStreptomyces

Summary Repeated DNA sequences were detected as rapidly reannealing sequences in the chromosomal DNA of 13 out of 14Streptomyces species using either hypochromicity measurements or hydroxyapatite chromatography. These sequences made up between approximately 4% and 11% of the total DNA of these species; only inStreptomyces rimosus were repeated DNA sequences not detected. The repeated sequences fall into a number of distinct percentage G+C (%G+C) classes, many being of rather low %G+C. Analytical density ultracentrifugation of the DNA of these species indicated satellite bands of low %G+C, and high-resolution thermal denaturation profiles indicated the presence of blocks of DNA of low G+C content too. No such satellite band could be found inStreptomyces coelicolor and no low-%G+C DNA could be detected in its thermal denaturation profile. The possible relationship of this repeated DNA, an unusual occurrence in a procaryote, to genetic instability and genetic control mechanisms inStreptomyces is discussed.     

SEXUAL REPRODUCTION IN CLOSTERIUM MONILIFERUM AND CLOSTERIUM EHRENBERGII1

Sexual reproduction in C. moniliferum is described for the first time. The morphology of conjugation is quite like that of C. ehrenbergii. Homothallic strains of both species usually produce single zygospores between daughter cells that have just divided. However, 2 homothallic clones of C. moniliferum form twin zygospores between conjugants which have paired before division and conjugation. This has not been observed in C. ehrenbergii. Heterothallic strains of both species form twin zygospores in the same manner. Heterotfiallisrn seems a well-established feature in both species. Germination and the survival of 2 products of meiosis arc typical of other desmids which have been investigated.     

Flow cytometric measurement of nuclear DNA content inCapsicum (Solanaceae)

Nuclei were isolated from leaf tissue of differentCapsicum species and the relative fluorescence intensity was measured by flow cytometry after propidium iodide staining.Pisum sativum nuclei with known nuclear genome size (9.07 pg) were used as internal standard to determine nuclear DNA content of the samples in absolute units. The 2C DNA contents ranged between 7.65 pg inC. annuum and 9.72 pg inC. pubescens, and the general mean of the genus was 8.42 pg. These values correspond, respectively, to 1C genome size of 3.691 (C. annuum), 4.690 (C. pubescens) and 4.063 (general mean) Mbp. In general, white-flowered species proved to have less DNA, with the exception ofC. praetermissum, which displayed a 2C DNA content of 9.23 pg. It was possible to divide the studied species into three main groups according to their DNA content, and demonstrate differences in DNA content within two of the three species complexes established on the basis of morphological traits.