Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure

This study identifies environmental predictors of the condition of two introduced tilapia species (Oreochromis leucostictus and Tilapia zillii) that are known to have divergent trophic niches (planktivore and herbivore, respectively) in 17 crater lakes in western Uganda. We asked whether fish condition differs among lakes characterized by differences in fishing pressure and catchment deforestation; and we related relative condition factor to gradients of environmental variation across lakes. Lakes characterized by severe catchment deforestation tended to be lakes with high fishing pressure, so it was difficult to explore independent and interactive effects. However, mean relative condition factor was higher in populations with high fishing pressure compared to populations with low fishing pressure for both O. leucostictus and T. zillii. The condition of O. leucostictus populations was higher in lakes with severely deforested catchments; but mean relative condition factor of T. zillii did not differ between deforestation categories. Principal components analysis (PCA) was used to describe the major environmental gradients of variation among the lakes; and PCA factor scores were regressed against relative fish condition. The association between fish condition and environmental gradients was stronger for O. leucostictus than for T. zillii. For O. leucostictus, fish condition was related to PC1 (43% of the variance) and factors that loaded most heavily included Chl-a, water transparency, lake area and depth, suggesting higher condition in lakes characterized by higher primary productivity and smaller size. For T. zillii, PC3 (11%) was the only axis related to fish condition; and factors that loaded most heavily included lake area (positive), and conductivity and total nitrogen (negative). Some of the larger lakes are characterized by higher availability of macrophytes that may positively affect the food base for T. zillii.     

Fish habitat suitability and community structure in the equatorial Lake Naivasha,Kenya

Habitat suitability indices indicate how fish species respond to different habitat types. We assessed effects of habitat characteristics on fish distribution in an equatorial lake, Lake Naivasha, Kenya, where habitats vary according to substrate, depth and turbidity. Using monthly data between 2008 and 2010 using multi-mesh gill nets, catch per unit effort was used as a relative abundance measure to identify how habitat variables drive fish distribution. The focus was on commercial fishes: two introduced species (Cyprinus carpio and Micropterus salmoides) and two naturalised species (Oreochromis leucostictus and Tilapia zillii). Analyses revealed distinct preferences for different habitat variables by all commercial species except for C. carpio. For example, O. leucostictus preferred shallow waters with silt–clay substrates whilst M. salmoides preferred deeper waters with sandy/rocky substrates. Conversely, C. carpio showed no specialised habitat requirements. Niche overlaps were significantly lower between O. leucostictus and its respective sympatric species than between other species, a likely result of its territorial behaviour. The continued environmental degradation of Lake Naivasha may imperil the preferred habitats of the niche restricted M. salmoides, O. leucostictus and T. zillii. By contrast, the ubiquity of C. carpio may facilitate their invasion, and consequently sustain their dominance in the lake’s commercial fishery.     

Cranial shape variation in jacarean caimanines (Crocodylia,Alligatoroidea) and its implications in the taxonomic status of extinct species: The case of Melanosuchus fisheri

Melanosuchus niger (Crocodylia, Alligatoroidea) is one of the six living caimanine species widely distributed throughout the Amazon River basin today. Although there is only one extant species of Melanosuchus, fossil material assigned to this genus, represented by M. fisheri, has been reported from the late Miocene in South America. However, the validity of this taxon has been questioned and a recent investigation indicates that the referred specimen of M. fisheri (MCZ 4336) actually belongs to Globidentosuchus brachyrostris, while those diagnostic characters present in the holotype (MCNC 243) fall into the spectrum of intraspecific variation of M. niger. Here, we compare the skull shape of the holotype of M. fisheri with the ontogenetic series of the four jacarean species (M. niger, Caiman yacare, Caiman crocodilus, and Caiman latirostris) using 2D‐geometric morphometric analyses in two different views. The analyses indicate that MCNC 243 falls into the morphospace of M. niger and C. latirostris. Despite strong shape similarities between juveniles of C. latirostris and MCNC 243, further anatomical comparisons reveal notable differences between them. In contrast, no concrete anatomical differences can be found between MCNC 243 and M. niger, although shape analyses indicate that MCNC 243 is relatively robust for its size. Thus, this study is able to confirm that the genus Melanosuchus was present in the late Miocene, but it still remains unclear if MCNC 243 should be treated as a junior synonym or probably a sister species of M. niger. Its Miocene age favors the second option, but as the shape analyses were also not able to extract any diagnostic characters, it should be retained as Melanosuchus cf. niger.     

Extent and degree of hybridization between exotic (Spartina alterniflora) and native (S. foliosa) cordgrass (Poaceae) in California, USA determined by random amplified polymorphic DNA (RAPDs)

Spartina alterniflora, smooth cordgrass, native to the eastern USA, was introduced into south San Francisco Bay ≈ 25 years ago. It has spread by purposeful introduction of rooted plants and dispersal of seeds on the tides. Previous work suggested that S. alterniflora was competitively superior to the native California cordgrass, S. foliosa, and that the two species hybridized. The present study determined the spread of S. alterniflora and S. foliosa × alterniflora hybrids in California and examined the degree of hybridization. We used nuclear DNA markers diagnostic for each species to detect the parental species and nine categories of hybrids. The California coast outside San Francisco Bay contained only the native species. All hybrid categories exist in the Bay, implying that several generations of crossing have occurred and that hybridization is bidirectional. Hybrids were found principally near sites of deliberate introduction of the exotic species. Where S. alterniflora was deliberately planted, we found approximately equal numbers of S. alterniflora and hybrid individuals; S. foliosa was virtually absent. Marshes colonized by water-dispersed seed contained the full gamut of phenotypes with intermediate-type hybrids predominating. The proliferation of hybrids could result in local extinction of S. foliosa. What is more, S. alterniflora has the ability to greatly modify the estuary ecosystem to the detriment of other native species and human uses of the Bay. To the extent that they share these engineering abilities, the proliferation of cordgrass hybrids could grossly alter the character of the San Francisco Bay.     

Widespread colonisation of Tanzanian catchments by introduced Oreochromis tilapia fishes: the legacy from decades of deliberate introduction

From the 1950s onwards, programmes to promote aquaculture and improve capture fisheries in East Africa have relied heavily on the promise held by introduced species. In Tanzania these introductions have been poorly documented. Here we report the findings of surveys of inland water bodies across Tanzania between 2011 and 2017 that clarify distributions of tilapiine cichlids of the genus Oreochromis. We identified Oreochromis from 123 sampling locations, including 14 taxa restricted to their native range and three species that have established populations beyond their native range. Of these three species, the only exotic species found was blue-spotted tilapia (Oreochromis leucostictus), while Nile tilapia (Oreochromis niloticus) and Singida tilapia (Oreochromis esculentus), which are both naturally found within the country of Tanzania, have been translocated beyond their native range. Using our records, we developed models of suitable habitat for the introduced species based on recent (1960–1990) and projected (2050, 2070) East African climate. These models indicated that presence of suitable habitat for these introduced species will persist and potentially expand across the region. The clarification of distributions provided here can help inform the monitoring and management of biodiversity, and inform policy related to the future role of introduced species in fisheries and aquaculture.

     

The production of hybrids with high ecological amplitude between exotic Spartina densiflora and native S. maritima in the Iberian Peninsula

Aim Hybridization is a common and potent mechanism of plant evolution that has the potential to be evolutionary significant in its own right, and hybrids are common between invasive and native congeneric species. Our aims were to document the existence and nature of new Spartina hybrids arising between introduced Spartina densiflora and native S. maritima in tidal marshes of the Iberian Peninsula, to examine the actual and potential range of hybrids in the intertidal zone, and to analyse the seed set of hybrids. Location South‐West Iberian Peninsula. Methods Hybrids were characterized using chloroplast and nuclear DNA, and ploidy assessments. The ecological tolerance of the hybrids was studied using vegetation surveys and transplant experiments. Results We found that both parental species have been seed parents to hybrids and that all hybrids had an additive pattern of species‐specific nuclear markers consistent with F₁ hybrids. Hybrid chromosome numbers varied between 2n = ca. 65 and 2n = ca. 94–97, while S. maritima had 2n = ca. 60 and S. densiflora had 2n = ca. 70. Hybrids grew in three discrete locations along the intertidal zone but were capable of growing throughout the ranges of both parental species in transplanted gardens, and in most cases, grew better than the parental species. While the potential exists for the origination of another invasive Spartina hybrid species, thus far hybrid plants are not fertile, limiting their ability to invade and spread. Main conclusions We recommend the eradication of all of the currently quite limited hybrid cordgrass and to fight the S. densiflora invasion in the Iberian Peninsula to prevent the origination of a new invasive allopolyploid Spartina species.     

Spatial patterns of hybridization between bull trout, <Emphasis Type="Italic">Salvelinus confluentus</Emphasis>, and brook trout, <Emphasis Type="Italic">Salvelinus fontinalis</Emphasis> in an Oregon stream network

Hybridization with introduced species represents a serious threat to the persistence of many native fish populations. Brook trout (Salvelinus fontinalis) have been introduced extensively throughout the native range of bull trout (S. confluentus) and hybridization has been documented in several systems where they co-exist and is seen as a significant threat to the persistence of bull trout populations. We identified a group of diagnostic microsatellite loci to differentiate bull trout and brook trout and then used these loci to examine the spatial distribution of hybrids in the Malheur River basin, Oregon USA. In random samples of approximately 100 fish from each of three creeks we identified 181 brook trout, 112 bull trout and 14 hybrids. Although bull trout, brook trout and hybrids were found in all three creeks, they were not evenly distributed; brook trout were primarily found in the lower sections of the creeks, bull trout further upstream, and hybrids in the areas of the greatest overlap. One creek with a population of brook trout in a headwater lake provided an exception to this pattern; brook trout were found distributed throughout the creek downstream of the lake. Several post-F1 hybrids were identified suggesting that hybrids are reproducing in the Malher River Basin. Mitochondrial DNA analysis indicated that both female bull trout and brook trout are involved in hybridization events. Analysis of population structure suggested that brook trout have established multiple spawning populations within the Malheur system. Data presented in this study suggest that relative abundance of brook trout and habitat quality are important factors to consider when evaluating the threat of hybridization to bull trout populations.     

NATURAL HYBRIDS BETWEEN ORYZOPSIS AND STIPA. I. ORYZOPSIS HYMENOIDES × STIPA SPECIOSA

Johnson , B. Lennart . (U. California, Los Angeles.) Natural hybrids between Oryzopsis and Stipa. I. Oryzopsis hymenoides × S. speciosa. Amer. Jour. Bot. 47(9): 736–742. Illus. 1960.—Spontaneous, sterile hybrids between Oryzopsis hymenoides and Stipa speciosa heretofore have been referred to O. bloomeri, which species in an earlier paper was shown to consist of a series of hybrids between O. hymenoides and various species of Stipa. On many morphological characters (O. hymenoides × speciosa) is intermediate between its parents and similar to the other hybrids formerly classed as O. bloomeri. It is distinct from the other hybrids on characters which reflect S. speciosa, except with respect to indument of the awn which is recessive. Somatic chromosome counts are: O. enoides, 48; S. speciosa, 64; hybrid, 56. Both parents exhibit regular bivalents at meiosis. The hybrid shows only occasional bivalents and mostly asynchronous splitting or random distribution of univalents at metaphase I. Pollen abortion is complete. No evidence of natural amphiploidy or introgression was found.     

Hybridization between Atlantic Salmon Salmo salar L. and Brown Trout S. trutta L. upon Artificial Propagation

Samples of Salmo salar and S. trutta were examined in 12 Russian fish hatcheries. With protein markers, hybrids of the two species were found in three hatcheries of the Baltic Sea basin. Some fishes had a phenotype intermediate between theS. salar and S. trutta phenotypes by morphological traits, but did not differ genetically from one of the parental species. Possible consequences of hybridization and ways to prevent it are discussed.     

Production and characterization of arboreous and fertile <Emphasis Type="Italic">Solanum melongena</Emphasis> + <Emphasis Type="Italic">Solanum marginatum </Emphasis>somatic hybrid plants

In crop plants the shift from being annuals to perennials may allow future agricultural systems requiring less energy inputs. The practicability of this was tested for Solanum melongena. Leaf protoplasts of S. melongena (2n = 2x = 24) and one of the related arborescent species Solanum marginatum (2n = 2x = 24) were electrofused and fertile somatic hybrids with arborescent habit regenerated. The magnetic cell sorter (MACS) technique was used for the selection of heterokaryons. The hybrid nature of 18 regenerated plants was assessed on the banding patterns generated by inter-simple sequence repeat PCR. When taken to maturity in the greenhouse, hybrids grew more vigorously compared to the parental species. Their morphological traits were intermediate between those of S. melongena and S. marginatum. Hybrids flowered and produced an average of 85% stainable viable pollen and fertile fruits. The somatic hybrids were maintained in the greenhouse for more than 3 years and continued to produce flowers developing into two types of fruits with plentiful seeds. Fruits were either striated green containing non-germinable seeds or yellow with fully germinable seeds. Their S₁ progenies showed common features with S₀ hybrids, including fertility and arborescent habit. Cytologically, somatic hybrids exhibited the expected chromosome number of 2n = 4x = 48, while chromosome pairing during microsporogenesis was associated with a low frequency of intergenomic pairing. It is concluded that an arborescent perennial species has been obtained by somatic hybridization. The usefulness of this species per se or in eggplant breeding will depend not only on the transmission of the arborescent habit to cultivated eggplant varieties, but also on the variability that should be created from backcrossing the S. melongena + S. marginatum hybrids to S. melongena.     

Hybridization between the endemic brown algae Carpophyllum maschalocarpum and Carpophyllum angustifolium (Fucales): Genetic and morphological evidence

Hybridization is an important evolutionary process, which can have significant effects on biodiversity. While hybridization is well known in plants, less is known about the prevalence of hybridization in other kingdoms. Hybridization in the field has been confirmed in brown algae in a few cases, mainly in the northern hemisphere genus Fucus. Putative hybrids have been found in the New Zealand endemic species Carpophyllum angustifolium and Carpophyllum maschalocarpum. We used nuclear‐encoded molecular data (ITS2) and morphometrics to confirm hybridization between C. angustifolium and C. maschalocarpum. Putative hybrid thalli were collected that had heterozygous ITS2, each copy corresponding to one of the parental species from that population. Morphological analysis also showed that the three classes (two parental species and hybrids) were easily distinguishable in these populations. It was found that the hybrids had an intermediate morphology to the parent species. Some individuals with C. angustifolium morphology had hybrid ITS2 ribotypes suggestive of backcrossing between the hybrids and C. angustifolium. Our data reveal another case of hybridization within the Fucales and suggests that further research on how these species remain separate is needed.     

Production of asymmetric hybrids between Solanum tuberosum and irradiated S. brevidens

Summary Asymmetric somatic hybrids were obtained by fusion of Solanum tuberosum (PDH40) protoplasts with 300- or 500-Gy irradiated protoplasts of S. brevidens. These radiation doses were sufficient to prevent the growth of the S. brevidens protoplasts. Putative hybrids were selected on the basis of phenotype from regenerated shoots and identified with a S. brevidens-specific probe. From these, 31 asymmetric hybrids were confirmed by morphological characteristics, isoenzyme patterns and RFLP analysis. The morphology of the asymmetric hybrids was intermediate between that of S. tuberosum and symmetric hybrids of both species (obtained without irradiation treatment). Chromosome counts from 17 asymmetric hybrids showed that the chromosome number of the hybrids ranged from 31 to 64. The asymmetric hybrids probably had one or two genome complements (i.e. either 24 or 48 chromosomes) from S. tuberosum and 7–22 chromosomes from S. brevidens. There was no clear correlation between the radiation dose and the degree of elimination of the S. brevidens genome.     

Differences in ploidy levels of inter-specific hybrids obtained by reciprocal crosses between Primula sieboldii and P. kisoana

Differences in ploidy level were found in inter-specific hybrids obtained by reciprocal crosses between Primula sieboldii and P. kisoana. When P. sieboldii was used as the maternal parent, the inter-specific hybrids were triploids; when P. kisoana was the maternal parent, the inter-specific hybrids were diploids. The possibility of diploid female gamete formation in P. sieboldii is discussed as a causal factor in the production of triploids occasionally found in crosses between diploids of this species. Received: 28 December 1999 / Accepted: 10 January 2000     

Seasonal rhythm of physiological indexes,liver protein level,and biotransformation biomarkers in Zosterisessor ophiocephalus and Gobius niger from a low contaminated lagoon (Ghar El Melh lagoon,Tunisia)

This study assessed seasonal variation of total liver proteins level (LPLs) and biotransformation biomarkers in two fish species, G. niger and Z. ophiocephalus, during a one year-survey in the low contaminated Ghar-El-Melh lagoon, Tunisia. Analyzed biomarkers were compared with physiological indexes such as the condition index, hepato-somatic index, and gonado-somatic index and environmental parameters. A significant annual rhythms of glutathione-S-transferase and ethoxyresorufin-O-deethylase activities were validated by cosinor. The highest peak (acrophase) of activities occurred in summer likely related to the elevated seawater temperature. Midline Estimating Statistic of Rhythm and amplitudes were higher in Z. ophiocephalus than in G. niger. The results showed, as well, an acrophase of (LPLs) in spring coinciding with reproductive period in Z. ophiocephalus and beginning of reproductive period in G. niger. This study established a baseline for the selected enzymatic activities in gobies, which required information for a correct interpretation of biomarker responses in environmental monitoring.     

Trophic interactions between native and introduced fish species in a littoral fish community

The trophic interactions between 15 native and two introduced fish species, silverside Odontesthes bonariensis and rainbow trout Oncorhynchus mykiss, collected in a major fishery area at Lake Titicaca were explored by integrating traditional ecological knowledge and stable‐isotope analyses (SIA). SIA suggested the existence of six trophic groups in this fish community based on δ¹³C and δ¹⁵N signatures. This was supported by ecological evidence illustrating marked spatial segregation between groups, but a similar trophic level for most of the native groups. Based on Bayesian ellipse analyses, niche overlap appeared to occur between small O. bonariensis (<90 mm) and benthopelagic native species (31·6%), and between the native pelagic killifish Orestias ispi and large O. bonariensis (39%) or O. mykiss (19·7%). In addition, Bayesian mixing models suggested that O. ispi and epipelagic species are likely to be the main prey items for the two introduced fish species. This study reveals a trophic link between native and introduced fish species, and demonstrates the utility of combining both SIA and traditional ecological knowledge to understand trophic relationships between fish species with similar feeding habits.     

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.     

SYSTEMATICS AND POPULATION GENETICS OF FIRE ANTS (SOLENOPSIS SAEVISSIMA COMPLEX) FROM ARGENTINA

Specimens of seven fire ant species collected from their native ranges in Argentina were studied by protein electrophoresis and morphological analysis. Concordance between the genetic and morphological character sets is strong (96% agreement on identifications), suggesting that recognition of reproductively isolated populations and partitioning of intra- and interspecific variation can in most cases be achieved using appropriate characters of either type in this taxonomically difficult group. Genetic differentiation between native (Argentina) and introduced (USA) conspecific populations of two species, Solenopsis invicta and S. richteri, is rather typical of the differentiation existing between conspecific populations found within either country. Furthermore, there appears to have been little reduction of variability (heterozygosity) at enzyme loci following colonization by either species of the United States, although some rare alleles have been lost in the introduced populations. Hybridization is rare between S. invicta and S. richteri where their native ranges overlap in central Argentina, in contrast to the extensive hybridization of these species in the United States, suggesting that prezygotic barriers to gene flow have been compromised in introduced populations. Phylogenetic analysis of the seven species indicates that S. invicta and S. richteri are relatively distantly related within the S. saevissima complex. Given that hybrids between these species in the United States suffer little apparent loss of fitness, genomic incompatibilities generally may be insufficient to create effective postzygotic barriers to interspecific gene flow in this group of ants.     

Diagnostic features and biometry of head bones for identifying Carassius species in faecal and archaeological remains

The identification of fish species from head bone remains is employed in various sciences, including archaeology, paleontology and field ecology, with the estimation of fish size from biometric relationships being useful in the assessment of predation pressure exerted by increasing numbers of piscivorous species (e.g. Eurasian otter Lutra lutra and great cormorant Phalacrocorax carbo). This is particularly relevant for crucian carp, Carassius carassius, which is in decline in Europe due to changes in land use and to increasing numbers of non‐native Carassius species (i.e. goldfish C. auratus, gibel carp C. gibelio), which hybridize with C. carassius. However, diagnostic keys and biometric relationships are lacking for C. carassius and its most common hybrids, crosses with C. auratus. The present paper addresses this gap in knowledge, providing diagnostic keys and biometric relationships for the head bones of all Carassius species found in Europe as well as for C. carassius × C. auratus hybrids. All bone size to body length relationships were statistically significant. Similarly, all bone size to body weight relationships were significant for C. carassius, C. auratus, and C. gibelio, but none were significant for C. carassius × C. auratus hybrids. Diagnostic structures were found to distinguish easily between the Carassius species and hybrids, which will assist in determining the identity and sizes of prey found in faecal and archaeological remains.     

Length–weight relationships of fish species in the freshwater rift valley lakes of Kenya

This study reports length–weight relationships for 10 species of fish encountered in the only two freshwater lakes wholly in the Rift Valley of Kenya, Naivasha and Baringo. In Lake Naivasha, none of the species analysed was native to the lake. Two were introduced species non‐native to East Africa (Micropterus salmoides, Cyprinus carpio), with three native to East Africa but not to the lake (Tilapia zillii, Oreochromis leucostictus, Barbus paludinosus). In Lake Baringo, all species were native (Oreochromis niloctictus baringoensis, Labeo cylindricus, Barbus intermedius autralis, Barbus lineomaculatus, Clarias gariepinus). Specimens were collected by gill netting in September 2004 and October 2005. With the exception of B. lineomaculatus, the b values in the relationship W = aL^b were between 2.90 and 3.22.