Influence of Parasitism on Shoal Choice in the Banded Killifish (Fundulus diaphanus,Teleostei, Cyprinodontidae)

Banded killifish, Fundulus diaphanus, were presented individually with a choice of ‘shoaling’ with either of two conspecific stimulus shoals, one consisting of fish with externally visible black spots (indicating the presence of a parasitic trematode worm, Crassiphiala bulboglossa), the other consisting of fish without such spots. Both parasitized and unparasitized test fish significantly preferred to shoal with unparasitized stimulus shoals over parasitized ones. The relative preference of unparasitized killifish for unparasitized shoals increased with increasing degree of parasite load in parasitized stimulus fish. However, no significant preference by unparasitized fish for unparasitized shoals was observed if unparasitized shoals were presented versus mixed shoals consisting of parasitized and unparasitized fish. We conclude that killifish preferred unparasitized shoals over parasitized shoals only if all fish in the respective stimulus shoals were phenotypically uniform (either with or without black spots). A final experiment showed that killifish used black spots as an indicator of parasite presence to make their shoal choice. The significance of these results for the formation of parasite-assorted shoals is discussed.     

Antipredator Benefits of Schooling Behaviour in a Cyprinodontid Fish,the Banded Killifish (Fundulus diaphanus)

Fish schools are believed to provide antipredator benefits to their members. Two potential antipredator benefits, the dilution and confusion effects, of schooling were investigated in the laboratory using banded killifish (Fundulus diaphanus). Individual risk of being attacked and killed by a fish predator (white perch, Morone americana) declined with increasing killifish school size in a manner closely predicted by the dilution hypothesis. Perch were apparently not confused by schooling killifish since fish in groups of one did not suffer a disproportionately greater predation rate than fish in all larger school sizes. However, killifish straggling from the school were preferentially attacked and more successfully captured compared with school members. Schooling in the banded killifish therefore confers a considerable antipredator benefit to individual group members, at least through a dilution effect, and straying from a school has an associated increased risk of mortality to predation, which selects for schooling behaviour.     

A comparative chromosome study of twenty killifish species of the genus Fundulus (Teleostei: Cyprinodontidae)

Female karyotypes from ovarian cell cultures of 20 species of killifish (Fundulus) ranged in diploid number from 32 to 48, but in arm number (NF) from 48 to 52. The small F chromosomes, which constituted the fundamental elements in the karyotype, were evenly graded in length. The large biarmed chromosomes (L), which were about twice the length of the average Fs, characterized only those species with 2N less than 48 chromosomes. And among these species, an increase in complement by a pair of L's was always accompanied by a decrease of two pairs of A's, indicating Robertsonian changes by the centric fusion of two A's to form one L chromosome. Other diagnostic chromosome characters included: the number and structure of biarmed and satellited F chromosomes and the percentage of F's with relatively short short-arms (SSA). Besides centric fusion, mechanisms of chromosomal evolution in Fundulus probably included pericentric inversion, producing biarmed F chromosomes from acrocentric F's and partial loss of a chromosome segment producing smaller biarmed F chromosomes from larger ones. The percentage of SSA chromosomes generally decreases from relatively primitive to specialized species. The presumably most primitive species have only SSA type acrocentric F chromosomes. The 20 Fundulus species were classified into 2 major groups according to the percentage of SSA chromosomes: the SSA group, including 3 subgroups, had more than 50% SSA's; the LSA group, including 2 subgroups, had fewer than 50% SSA's. This classification based only on karyotypic characters generally agreed with others based on gross morphological characters. A possible evolutionary scheme is proposed to account for the derived killifish karyotypes.     

The myxozoan fauna of Fundulus diaphanus (Cyprinodontidae) from freshwater localities in eastern North America: prevalence, community structure, and geographic distribution

Membership and richness of infracommunities and component communities of myxozoan fauna of the banded killifish (Fundulus diaphanus) from freshwater localities in Ontario, Quebec, New York State, New Brunswick, Nova Scotia, and Maryland were studied. Five species of parasites were found: Myxobolus diaphanus (Fantham, Porter, and Richardson, 1940) (connective tissue throughout the body and head), Myxobolus funduli (Kudo, 1918) (interlamellar), Myxobolus neurophilus (Guilford, 1963) (optic tectum of the brain), Myxobolus sp. (connective tissue, typically adjacent to vertebrae), and Sphaerospora sp. (kidney tubules). The most abundant species locally and regionally was M. diaphanus, occurring at prevalences of 14.2 to 93.3% at 6 of 9 localities. Myxobolus funduli and Myxobolus sp. were at 3 and 2 localities respectively, while M. neurophilus and Sphaerospora each occurred at single localities. Four of the 5 myxozoans appear to be specific to fundulids, the exception being M. neurophilus, which is typically a parasite of Perca flavescens. Mean infracommunity richness was 0-1.2. Component community richness was 0-3 species. The fauna is similar in composition to that described from the spottail shiner (Notropis hudsonius) in the Great Lakes in being dominated by histozoic myxobolids and in having maximum prevalence at any single locality correlate positively with geographical distribution. Moreover, mean infracommunity richness was correlated with percentage of hosts infected with any species at a locality, and maximum infracommunity richness was correlated with component community richness. Probably because fewer species of myxozoans of fundulids occur in the regional pool, myxozoan communities encountered in the present study are generally less rich than those described from N. hudsonius. It appears that dispersal of relatively resilient myxospores through such a mechanism as piscivory effectively distributes these parasites over the landscape, while the more delicate actinospores serve to ensure colonization by amplifying species' prevalence at a specific locality and thereby contributing to initial establishment. As such, these types of myxozoans, though they are autogenic, having their entire life cycle normally completed within the aquatic environment, behave more like allogenic parasites that rely on birds and mammals as definitive hosts.     

Phylogeography of the banded killifish (Fundulus diaphanus): glacial races and secondary contact

Spatial patterns of morphological and genetic polymorphisms between the two banded killifish sub-species ( Fundulus diaphanus diaphanus and F. d. menona ) provide evidence that these sub-species represent distinct evolutionary lineages corresponding to glacial races of Atlantic and Mississippian origins. Individuals with intermediate phenotypes in Lake Ontario and the upper St Lawrence River probably result from secondary contacts between these races. The hybrid zone unexpectedly extends to Lake Erie and involves the introgression of the F. d. diaphanus mitochondrial genome into fish with morphology like that of F. d. menona .     

Spontaneous occurrence of a synchronous hermaphrodite in the banded killifish, Fundulus diaphanus (Lesueur)

An intersex specimen of the banded killifish, Fundulus diaphanus , was encountered during the analysis of the annual gametogenic cycle of this species. The simultaneous presence of mature spermatozoa and ova suggests that the potential for self-fertilization existed in this fish. The spontaneous occurrence of this intersex individual, although a rare event, indicates the potential for the development of the synchronous hermaphroditic condition under natural environmental conditions in this normally gonochoristic species.     

The Effects of Predation Risk, Food Abundance, and Population Size on Group Size of Brown-Headed Cowbirds (Molothrus ater)

Social and ecological conditions can influence flock formation (e.g. number of flocks, flock size, etc.) depending on the degree of social attraction of a species. We studied group formation in brown‐headed cowbirds (Molothrus ater) over short time periods (30 min) in two semi‐natural experiments conducted under controlled conditions. First, we determined the shape of the relationship between intake rate and flock size by manipulating group size in a single enclosure. Second, we assessed the role of population size, food abundance, and predation risk, and their interactions, in flock size formation in a system of four enclosures (two with and two without food) connected to a central refuge patch. In the first experiment, we found that pecking rates peaked at intermediate flock sizes (three to six individuals), which was influenced by greater availability of foraging time and more aggressive interactions in large groups. In the second experiment, flock sizes in the patches with food increased with population size likely due to the benefits of patch exploitation in groups. Flock size decreased after predator attack probably because refuge availability reduced perceived predation risk more than flocking in larger groups. Food abundance had minor effects, varying flock sizes between the two patches with food, under high food availability conditions when population size was high, probably due to social cohesion effects. Our results suggest that: (1) this species has an inverted‐U food intake–group size relationship with a range of intake‐maximizing flock sizes rather than a single peak, (2) the presence of a near refuge modifies the expected benefits of group patch exploitation under high predation risk, and (3) an increase in population size would more likely be translated into rapid increases in the size of the flocks rather than in more new flocks.     

Effects of Predation Risk on Habitat Selection by Water Column Fish, Benthic Fish and Crayfish in Stream Pools

Predation risk can affect habitat selection by water column stream fish and crayfish, but little is known regarding effects of predation risk on habitat selection by benthic fish or assemblages of fish and crayfish. I used comparative studies and manipulative field experiments to determine whether, (1) habitat selection by stream fish and crayfish is affected by predation risk, and (2) benthic fish, water column fish, and crayfish differ in their habitat selection and response to predation risk. Snorkeling was used to observe fish and crayfish in, (1) unmanipulated stream pools with and without large smallmouth bass predators (Micropterus dolomieui >200 mm total length, TL) and (2) manipulated stream pools before and after addition of a single large smallmouth bass, to determine if prey size and presence of large fish predators affected habitat selection. Observations of microhabitat use were compared with microhabitat availability to determine microhabitat selection. Small fish (60–100 mm TL, except darters that were 30–100 mm TL) and crayfish (40–100 mm rostrum to telson length; TL) had significantly reduced densities in pools with large bass, whereas densities of large fish and crayfish (> 100 mm TL) did not differ significantly between pools with and without large bass. Small orangethroat darters (Etheostoma spectabile), northern crayfish (Orconectes virilis), and creek chubs (Semotilus atromaculatus) showed significantly greater densities in pools without large bass. The presence of large smallmouth bass did not significantly affect depths selected by fish and crayfish, except minnows, which were found significantly more often at medium depths when bass were present. Small minnows and large and small crayfish showed the greatest response to additions of bass to stream pools by moving away from bass locations and into shallow water. Small darters and sunfish showed an intermediate response, whereas large minnows showed no significant response to bass additions. Response to predation risk was dependent on prey size and species, with preferred prey, crayfish and small minnows, showing the greatest response. Small benthic fish, such as darters, are intermediate between small water column fish and crayfish and large water column fish in their risk of predation from large smallmouth bass.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish,Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish, Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Isolation and characterization of eight polymorphic microsatellite markers in Aphanius fasciatus (Teleostei: Cyprinodontidae)

The first set of eight polymorphic microsatellites markers was successfully optimized from a partial genomic library enriched for an AC motif of the killifish Aphanius fasciatus Nardo, 1827 (Teleostei, Cyprinodontidae), a brackish‐water fish widely distributed along the coasts of the Mediterranean Sea. The developed loci proved to be polymorphic, displaying from two to six alleles per locus with expected heterozygosity ranging from 0.277 to 0.752. All loci were under Hardy–Weinberg equilibrium, except Af8 that showed significant heterozygotes deficiency, and there was no evidence of linkage associations between any pair of loci. Markers reported here will be potentially useful in monitoring of genetic population structure in this species.     

Chromosomal Mapping and Molecular Characterization of Ribosomal RNA Genes in Lebias fasciata (Teleostei, Cyprinodontidae)

Chromosome location of major (18S, 5.8S and 28S) and 5S ribosomal RNA genes (rDNAs) was examined in Lebias fasciata collected from different Italian blackish-waters, using silver (Ag)- and chromomycin A3 (CMA3)-staining and/or fluorescence in situ hybridization (FISH). Both 18S and 5S rDNA probes for FISH were obtained with polymerase chain reaction-directed cloning from genomic DNA of the examined species. Nucleolar organizer regions (NORs) containing the major rDNAs showed intraspecific polymorphism in number as detected by Ag-and CMA3-staining and FISH with the 18S rDNA probe. On the other hand, 5S rDNA loci constantly occurred on one chromosome pair and co-localized with a pair of the major rDNA loci as evidenced by two-color FISH using the 5S and 18S rDNA probes. Sequential CMA3- and Ag-NOR staining and FISH revealed apparent inactivation of some NORs. The cloned 5S rDNA was found to contain some TATA-like sequences that might play an important role in the regulation of gene expression.     

A Study of the Evolutionary Relationships of Fundulus Topminnows (Teleostei: Fundulidae)

A hypothesis of the evolutionary relationships of thirty-fourspecies of Fundulus and their closer relatives is presented.The study is restricted to morphological characters which couldbe determined to be primitive or derived using the methods ofphylogenetic systematics. Following Parenti, a family Fundulidaeis recognized. It is composed of four genera of North Americankillifishes. (Cyprinodontidae as usually constitutedis polyphyletic.)No convincing characters demonstrate that Fundulus is a naturalgroup (a monophyletic group). However, all species of Fundulusshare four derived characters with Lucania. The sister group(closest genealogical relative) of Fundulus plus Lucania isa group composed of the genera Adinia and Leptolucania. Fourmonophyletic groups of Fundulus can be recognized based on sharedderived characters: (1) subgenus Fundulus (seven species excludingthree species placed in Fontinus); (2) subgenus Fonlinus (sixspecies); (3) subgenus Xensima (five species); and (4) subgenusZygonectes (thirteen species). Three species, F. (Plancterus)zebrinus, F. lima, and F. parvipinnis are of uncertain affinitieswithin the Lucania-Fundulus clade     

Variation Among Four Health Indices in Natural Populations of the Estuarine Fish, Fundulus heteroclitus (Pisces, Cyprinodontidae), from Five Geographically Proximate Estuaries

Variation among four commonly used health indices was examined in the mummichog, Fundulus heteroclitus. The four indices were liver glycogen content (LGC), liver-somatic index (LSI), condition index (K) and RNA–DNA ratio. Fish were collected from five coastal locations in southeastern Connecticut. Fish health, as determined by these four indices, varied considerably among estuaries and between sexes. The relationship between each index and specimen length was significantly different among estuaries for either sex. When regressed against length, the slopes for the indices ranged from positive to negative. For each index, significant differences existed among some of the length-centered means at each estuary for either sex. Estuary rank for one index did not necessarily correlate with the estuary rank for another index. The significance of this variability and its impact on the use of the indices as bioindicators of environmental perturbation is discussed.     

Regional differences of the argentea and sclera in the eye ofPoecilia reticulata P. (Teleostei: Cyprinodontidae)

Summary The argentea of thePoecilia reticulata eye is divided into a black-iridescent dorsal and a silvery-iridescent ventral region. An opaque black patch lies on the dorso-ventral meridian passing through the optic nerve. The structure and ultrastructure of the various layers of the argentea and sciera are described. Three types of crystals occurring in the iridophores of the argentea have been found. The possible functional significance of the regional structural differences of argentea and sciera are discussed.     

A Chromosome study of four species and a hybrid of the killifish genus Fundulus (Cyprinodontidae)

The chromosomes of four killifish species (F. diaphanus, F. heteroclitus, F. majalis and F. parvipinnis) and a hybrid (F. diaphanus × F. heteroclitus) were studied. The karyotype studies were based on observations from both squash and air-dry preparations, the latter of which were prepared from in vitro primary cell cultures from ovaries. The consistent presence of one to several pairs of species-specific marker chromosomes, and the differential expression of acrocentric short arms in karyotypes of different species were useful in determining interspecific relationships. These characters did not show any noticeable variation interand intra-individually, and retained their original forms even in the hybrid complement which was the composite of chromosome complements of both parental species. Male heterogamety was confirmed in F. diaphanus and F. parvipinnis in which the X chromosomes resemble each other being submetacentric and having an identifiable secondary constriction. The occurrence of the cytological heterogamety in fishes is briefly discussed.