Predation and competition within an assemblage of larval newts (Triturus)

The impact of crested newts (Triturus cristatus) on the smaller-bodied palmate and smooth newts (T helveticus and T vulgaris) was studied during the larval stages using a combination of field and laboratory experiments In pond enclosures T cristatus larvae had no effect on the two smaller species over the first four weeks of development By eight weeks, however. T cristatus had achieved a size advantage which enabled it to eliminate T helveticus and severely reduce T vulgaris by predation In laboratory trials under food-limited conditions, T helveticus and T vulgaris were slightly smaller when raised with T cristatus, suggesting that this predatory effect was complemented by interspecific competition during early development Predation of the smaller species started when T cristatus reached a threshold size of c 27 mm No reciprocal effects on T cristatus growth or survival were observed Although T cristatus may be a significant predator of congeneric species in natural ponds, other factors, such as differences in microhabitat selection, higher-order predator-prey interactions and the occasional desiccation of pond habitats may facilitate coexistence between the species     

Fecundity of the newts Triturus cristatus, T. marmoratus and their natural hybrids in relation to species coexistence

The two larger newt species in Europe, Triturus cristatus and T. marmoratus , have largely exclusive distributions but live in sympatry in a small area in western France, where they also hybridize. Triturus cristatus is increasing in abundance in the area at the expense of T. marmoratus , although this study shows that T. marmoratus has higher relative lifetime reproductive success. Triturus marmoratus lays more eggs than its relative under controlled conditions, and more T. marmoratus eggs in relation to its relative abundance are found in natural breeding sites. The hybrids are even more fecund, but their eggs and embryos have a lower survival rate.
The data are compared for age at maturity and species longevity, and estimates of lifetime reproductive success show that T. marmoratus females are more fecund than T. cristatus females. There are no differences between the species in survival of the embryos. It is therefore not clear why T. cristatus is replacing T. marmoratus , but changes in terrestrial habitats due to human activity might be the explanation.     

The effect of pH on feeding behaviour in newt larvae (Triturus: Amphibia)

The feeding responses of three species of newt larvae were compared under circumneutral and sublethal acid conditions. Under acid conditions (pH 4.5) feeding behaviour was suppressed in palmate newts, Triturus helveticus, and smooth newts. T. vulgaris , but not in crested newts, T. cristatus. At low pH, approach and orientation towards food occurred in T. helveticus and T. vulgaris , but snapping was inhibited; T. cristatus snapped and consumed food immediately it was offered under the same conditions. These differences are not consistent with the apparent greater tolerance of T helveticus for acidified ponds. The observations suggest that the chemosensory system of T. helveticus and T. vulgaris may be impaired at low pH.     

Hybridization between invasive Spartina densiflora (Poaceae) and native S. foliosa in San Francisco Bay, California, USA

Rapid evolution in contemporary time can result when related species, brought together through human-aided introduction, hybridize. The significant evolutionary consequences of post-introduction hybridization range from allopolyploid speciation to extinction of species through genetic amalgamation. Both processes are known to occur in the perennial cordgrass genus, Spartina. Here we report the existence of a third recent Spartina hybridization, discovered in 2002, between introduced S. densiflora and native S. foliosa in San Francisco Bay, California, USA. We used nuclear and chloroplast DNA analysis and nuclear DNA content with chromosome counts to examine plants of morphology intermediate between S. densiflora and S. foliosa in a restored marsh in Marin County, California. We found 32 F(1) diploid hybrids and two triploid plants, all having S. densiflora and S. foliosa as parents; there is also evidence of a genetic contribution of S. alterniflora in some hybrids. None of these hybrids set germinable seed. In 2007 we found a hybrid over 30 miles away in a marsh where both parental species occurred, suggesting hybridization may not be a localized phenomenon. The presence of diploid and triploid hybrids is important because they indicate that several avenues existed that may have given rise to a new allopolyploid species. However, such an event is now unlikely because all hybrids are targets of eradication efforts.     

Massive genetic introgression in threatened northern crested newts (<Emphasis Type="Italic">Triturus cristatus</Emphasis>) by an invasive congener (<Emphasis Type="Italic">T. carnifex</Emphasis>) in Western Switzerland

Genetic pollution through introgressive hybridization of local species by exotic relatives is a major, yet neglected aspect of biological invasions, particularly in amphibians where human introductions are frequent. In Western Switzerland, crested newts make an interesting case: the Italian species Triturus carnifex was introduced at least a century ago within the range of the native and threatened T. cristatus. To understand the genetic consequences of this introduction and inform wildlife management authorities, we conducted a genetic survey on the remaining northern crested newt populations known in the area, using newly-developed species-diagnostic nuclear (microsatellites) and mitochondrial (control region) DNA markers. We documented massive nuclear introgression by the T. carnifex genome, which has completely replaced T. cristatus in most populations, especially in the Geneva area where the introduction was originally reported. However, many of these individuals retained the ancestral T. cristatus mtDNA, which could be explained by asymmetric introgression between the two species, stemming from demographic and/or selective processes. Analyses of genetic diversity support multiple events of T. carnifex releases, most-likely of proximate North Italian origin. We pinpointed the last indigenous populations in the region and recommend to prioritize their protection. Our study demonstrates the invasive potential of introduced taxa through introgressive hybridization, alerts about the underestimated rate of illegal amphibian translocations, and emphasizes the need for genetic analyses to monitor such invasions.     

The annual number of breeding adults and the effective population size of syntopic newts (Triturus cristatus, T. marmoratus)

Pond-breeding amphibians are deme-structured organisms with a population genetic structure particularly susceptible to demographic threats. We estimated the effective number of breeding adults (Nb) and the effective population size (Ne) of the European urodele amphibians Triturus cristatus (the crested newt) and T. marmoratus (the marbled newt), using temporal shifts in microsatellite allele frequencies. Eight microsatellite loci isolated from a T. cristatus library were used, five of which proved polymorphic in T. marmoratus, albeit with high frequencies of null alleles at two loci. Three ponds in western France were sampled, situated 4-10 kilometers apart and inhabited by both species. Parent-offspring cohort comparisons were used to measure Nb; samples collected at time intervals of nine or 12 years, respectively, were used to measure Ne. The adult population census size (N) was determined by mark-recapture techniques. With one exception, genetic distances (FST) between temporal samples were lower than among populations. Nb ranged between 10.6 and 101.8 individuals, Ne ranged between 9.6 and 13.4 individuals. For the pond where both parameters were available, Nb/N (overall range: 0.10-0.19) was marginally larger than Ne/N (overall range: 0.09-0.16), which is reflected in the temporal stability of N. In line with the observed differences in reproductive life-histories between the species, Nb/N ratios for newts were about one order of magnitude higher than for the anuran amphibian Bufo bufo. Despite of the colonization of the study area by T. cristatus only some decades ago, no significant genetic bottleneck could be detected. Our findings give rise to concerns about the long-term demographic viability of amphibian populations in situations typical for European landscapes.     

Effects of Cover on Loud Trill-Call and Soft Seet-Call Use in the Crested tit Parus Cristatus

Predation is one of the main factors responsible for winter mortality in small birds. Contact vocalizations of crested tits ( Parus cristatus ) can be divided into two categories: long- and short-range communication calls. The long-range calls are loud, frequency-modulated trills, which are well suited for acoustic communication over long distances. The short-range calls, in contrast, are soft, high-pitched tones, which are strongly attenuated as they radiate through the environment. As the predation cost in this species is mostly associated with the use of loud calls, we investigated whether crested tits adjust the use of loud trill-calls and of soft seet-calls to changes in habitat safety. We arranged two feeding sites that differed with respect to predicted safety, and observed the utterance of loud trill-calls and soft seet-calls. Calling rates of the loud trill-calls were highest when male crested tits foraged at the safe site. The loud trill-calls were given significantly less often while visiting risky feeders placed just a few metres away from the safe sites. The soft seet-calls were uttered both at risky and safe feeders at similar rates. This study suggests that the long-range part of contact communication in crested tits is strongly affected by the level of perceived predation risk. In accordance with the data on hearing ability of predators, dominant male crested tits decrease their exposure to predation in risky habitats by choosing a less risky type of communication with high-pitched sounds.     

ASYMMETRIC VIABILITY OF RECIPROCAL-CROSS HYBRIDS BETWEEN CRESTED AND MARBLED NEWTS (TRITURUS CRISTATUS AND T. MARMORATUS)

Hybridization between divergent lineages often results in reduced hybrid viability. Here we report findings from a series of independent molecular analyses over several seasons on four life stages of F₁ hybrids between the newts Triturus cristatus and T. marmoratus . These two species form a bimodal hybrid zone of broad overlap in France, with F₁ hybrids making up about 4% of the adult population. We demonstrate strong asymmetry in the direction of the cross, with one class ( cristatus -mothered) making up about 90% of F₁ hybrids. By analyzing embryos and hatchlings, we show that this asymmetry is not due to prezygotic effects, as both classes of hybrid embryos are present at similar frequencies, implicating differential selection on the two hybrid classes after hatching. Adult F₁ hybrids show a weak Haldane effect overall, with a 72% excess of females. The rarer marmoratus -mothered class, however, consists entirely of males. The absence of females from this class of adult F₁ hybrids is best explained by an incompatibility between the cristatus X chromosome and marmoratus cytoplasm. It is thus important to distinguish the two classes of reciprocal-cross hybrids before making general statements about whether Haldane's rule is observed.     

An examination of hybridization between the cattail species typha latifolia and typha angustifolia using random amplified polymorphic DNA and chloroplast DNA markers

Typha glauca represents a significant portion of the biomass of the wetlands surrounding the Great Lakes, USA. It is generally accepted to be a form of hybrid between T. latifolia and T. angustifolia, which itself appears to be an exotic introduction from Europe. Based on morphological and isozyme data, conflicting theories have been proposed for the hybrid nature of T. glauca: it has been described as a hybrid swarm, a distinct hybrid species and an F1 hybrid. Therefore, we developed random amplified polymorphic DNA (RAPD) and chloroplast DNA markers, specific to the parental species, to assess hybrids. Ten RAPD primers gave 17 fragments specific to T. angustifolia and 13 fragments specific to T. latifolia. All of the interspecific hybrids contained each of the species-specific markers, indicating an F1 hybrid status. Furthermore, all hybrids tested contained the T. angustifolia chloroplast haplotype, which is consistent with differential interspecific crossing success found previously. Additional confirmation of an F1 hybrid status was gained by examining seedlings from T. glauca. These progeny were expected to be advanced-generation hybrids, as opposed to the F1 hybrid parent. Analysis of the seedlings revealed segregating marker patterns consistent with patterns observed in experimental advanced-generation hybrids, although these advanced hybrids do not appear to be a significant part of mature stands. Our data do not provide support for extensive gene flow between T. latifolia and T. angustifolia. However, our results suggest that hybridization between the native and introduced Typha species has impacted the native population through the spread of the F1 hybrid, T. glauca.     

Variable extent of hybridization between invasive sika (Cervus nippon) and native red deer (C. elaphus) in a small geographical area

Instances of hybridization between endemic and alien species pose a threat to species integrity but also provide us with an opportunity to study the dynamics of gene flow between two species as they first meet. Here, we used variation at 22 highly differentiated microsatellite loci and one mitochondrial DNA (mtDNA) marker in a sample of 735 individuals, to investigate the genetic consequences of an introduction of Japanese sika deer ( Cervus nippon ) for native red deer ( C. elaphus ) on the Kintyre Peninsula in Scotland. We investigated population structure, estimated null-allele frequency and assigned individual hybrid scores using a Bayesian clustering algorithm implemented in structure 2.2. The dataset clearly divided into two clusters and generally, introgression into red and sika was low. However at one site, West Loch Awe, 43% of individuals were hybrids. MtDNA introgression indicated that hybridization was occurring between red-deer hinds and sika-deer stags. We argue that the pattern of differential introgression across the study area is primarily due to the rarity of hybridization events between the two species and the limited time the two species have been in contact (< 120 years). This contrasts with the causes of classic mosaic hybrid zones (selection induced by habitat variability). Currently, it seems possible that, in time, the level of hybridization found at West Loch Awe could also be found across the whole of the peninsula.     

Crop-to-weed gene flow in the genus Sorghum (Poaceae): Spontaneous interspecific hybridization between johnsongrass,Sorghum halepense,and crop sorghum,S. bicolor

The role of crop-to-weed gene flow is often controversial and overlooked. As a consequence, the likelihood of spontaneous crop-to-weed hybridization in most crop/weed systems is generally unknown. The lack of data relating to the formation of crop/weed hybrids has particular contemporary significance when considering the wide scale commercial release of transgenic crop plants and the potential for escape of engineered genes via crop-to-weed hybridization. We created an experimental system whereby we could examine the incidence and rate of spontaneous crop-to-weed hybridization between Sorghum bicolor and S. halepense, johnsongrass. An isozyme marker was used to identify hybrid plants through progeny testing. Incidence and rate of hybridization were highly variable with respect to weed distance from the crop, location of the study site, and year the study was performed. Crop/weed hybrids were detected at distances of 0.5–100 m from the crop. Interspecific hybridization can and does occur in this system at a substantial and measurable rate. Transgenes introduced into crop sorghum can be expected to have the opportunity to escape cultivation through interspecific hybridization with johnsongrass. Traits that prove to be beneficial to weeds possessing them can be expected to persist and spread. This is an issue that needs to be addressed when developing biosafety guidelines for the commercial release of transgenic sorghums.     

Natural hybridization and introgression in sympatric Ligularia species (Asteraceae, Senecioneae)

The difficulty in clarifying species of genus Ligularia Cass.has been attributed to rapid and continuous allopatric speciation in small and isolated populations,combined with interspecific diploid hybridization in the Qinghai-Tibetan Plateau and adjacent areas.However,no concrete example has been reported to prove this hypothesis.We studied a natural mixed population of six species of Ligularia in which some individuals were morphologically intermediate between L.subspicata and L.nelumbifolia.Based on DNA sequences (trnC-E trnL-rpL32,trnQ5'rpsl6,trnK-rpsl6,and internal transcribed spacer) and inter-simple sequence repeat data,we concluded that putative hybrids are primarily products of hybridization between L.nelumbifolia and L.subspicata.The other four species or additional,unknown species may also be involved in hybridization.This hybridization is bidirectional but asymmetrical.Hybrid individuals were mostly the first generation,but F2 and later-generation hybrids were also present.Moreover,the backcrossed individuals detected indicate that natural gene flow occurs among at least three Ligularia species.Hybrids may become stabilized to form new species or may function as intermediates in evolutionary diversification.     

No evidence for niche segregation in a North American Cattail (Typha) species complex

Interspecific hybridization can lead to a breakdown of species boundaries, and is of particular concern in cases in which one of the parental species is invasive. Cattails (Typha spp.) have increased their abundance in the Great Lakes region of North America over the past 150 years. This increase in the distribution of cattails is associated with hybridization between broad-leaved (Typha latifolia) and narrow-leaved cattails (T. angustifolia). The resulting hybrids occur predominantly as F(1)s, which are known as T. × glauca, although later-generation hybrids have also been documented. It has been proposed that in sympatric populations, the parental species and hybrids are often spatially segregated according to growth in contrasting water depths, and that this should promote the maintenance of parental species. In this study, we tested the hypothesis that the two species and their hybrids segregate along a water-depth gradient at sites where they are sympatric. We identified the two parental species and their hybrids using molecular genetic markers (SSR), and measured shoot elevations (a proxy for water depth) at 18 sites in Southern Ontario, Canada. We found no evidence for niche segregation among species based on elevation. Our data indicate that all three lineages compete for similar habitat where they co-occur suggesting that there is potential for an overall loss of biodiversity in the species complex, particularly if the hybrid lineage is more vigorous compared to the parental species, as has been suggested by other authors.     

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.     

Interspecific hybridization between diploid species of Lotus (Leguminosae)

An interspecific hybridization study has been carried out between seven diploid species of Lotus (L. alpinus Schleich., L. japonicus (Regel) Larsen, L. filicaulis Dur., L. schoelleri Schweinf., L. krylovii Schischk. and Serg., L. tenuis Waldst. et Kit., and L. corniculatus var. minor Baker) closely related to L. corniculatus L. A total of 139 interspecific hybrids were produced in 16 combinations of the 7 species. Nine of these crosses were produced for the first time and four were obtained by means of embryo-culture. The growth habit, number of florets per umbel, flower color expression, HCN reaction and 15 metrical traits were compared between parents and hybrids. The relative case with which some hybrids were produced suggested that during the early evolutionary history of the genus species diversification could have originated through interspecific hybridization and subsequent gene differentiation. In some crosses, the hybrids resembled one parent more closely than the other. This close morphological affinity between the hybrids and one of their parents would make it extremely difficult to detect such hybrids in natural populations and probably aceounts for the prevailing belief that there is little or no hybridization in nature.     

The potential for genetic assimilation of a native dandelion species, Taraxacum ceratophorum (Asteraceae), by the exotic congener T. officinale

Exotic plant species can threaten closely related native congeners through asymmetric hybridization and subsequent backcrossing, the process known as genetic assimilation. I explore the initial stages of this process in Taraxacum ceratophorum (Asteraceae), the native alpine dandelion, and the invasive apomict T. officinale. In central Colorado, seven T. ceratophorum populations all occur in sympatry with T. officinale. In one large population on Pennsylvania Mountain, surveys further revealed that flowering phenologies and visiting insect taxa overlap almost completely for both Taraxacum species. Together these results indicated that heterospecific pollen transfer is likely. Crossing experiments showed that T. ceratophorum is an obligate outcrosser, and interspecific hand pollinations resulted in 37.3% seed set. However, molecular analysis of the F1 offspring indicated that only 33.2% of germinating seeds were hybrids; the remainder were selfed offspring produced from a breakdown in self-incompatibility (the mentor effect). Although the mentor effect helps reduce the production of hybrids, the asymmetrical direction of hybridization creates the potential for genetic assimilation of T. ceratophorum by T. officinale.     

Microhabitat selection and feeding relations of smooth and warty newts, Triturus vulgaris and T. cristatus, at an upland pond in mid-Wales

The utilization of microhabitat and food resources by Triturus vulgaris and T. cristatus was studied in an upland pond in mid-Wales. From April to June T. vulgaris was more evenly distributed across the pond than T. cristatus , which showed a preference for the middle of the pond and the bottom of the water column. From July to September however, when most T. vulgaris had left the pond, T cristatus was evenly distributed within the water column and a much higher proportion was captured around the shorelines. Both species appear to be generalist predators with diets limited by prey size. Zooplankton were the most important prey for T. vulgaris , while leeches formed the bulk of the diet of T. cristatus . However, T. cristatus did not select larger-sized zooplankton than T. vulgaris . Large body size therefore enables T. cristatus to consume a wider range of prey sizes than T. vulgaris . Microhabitat niche overlap was greater than feeding niche overlap between the species.     

Influence of introduced fish Percottus glenii (Odontobutidae, Pisces)

Monitoring of 28 waterbodies has been carried out since 1994 in the region of reserve "Lake Glubokoe" (Moscow region, Russia). It was revealed that species diversity as well as abundance of larval amphibians correlate negatively with presence of introduced fish, rotan, Perccottus glenii (Odontobutidae). Newts (Triturus cristatus, T. vulgaris) and frogs (Rana temporaria, R. arvalis, R. lessonae) as a rule are not capable to breed in waterbodies colonised by rotan. In contrast, toads (Bufo bufo) breed successfully in such sites. Larvae of toads are comparatively less edible for rotan and pass their metamorphosis. Persistence of amphibians to predation of rotan decreases in the row: B. bufo (R. temporaria, R. arvalis and R. lessonae), T. vulgaris, T. cristatus. The Crested newt (T. cristatus) is the most endangered species and could extinct in next years.     

Variation in frequency of hybrids and spatial structure among Ipomopsis (Polemoniaceae) contact sites

Rates of hybridization vary among angiosperm taxa. Among-taxon variation in hybridization rate has been used to compare the importance of pre- and post-zygotic reproductive isolating mechanisms. Variation in rates of hybridization within a single-species pair would suggest that local conditions also affect reproductive isolation within a single taxonomic context. In this study, contact sites of Ipomopsis aggregata-Ipomopsis tenuituba were surveyed for variation in frequency of hybrids, and spatial structure. Floral morphology was used to identify parent species and hybrids in seven contact sites in the western Rocky Mountains, USA. Contact sites varied widely in elevational range, the degree to which morphological variation was clinal rather than mosaic and the frequency of hybrids. Two sites provided a strong contrast between a clinal, unimodal site and a mosaic, bimodal site. This natural variation among contact sites of the same species pair provides an opportunity to assess the effect of local ecological conditions and spatial structure of parent populations on reproductive isolation, while controlling for between-taxon variation.     

Hybridization between two sympatrically breeding species of fur seal at Iles Crozet revealed by genetic analysis

Introgressive hybridization occurs when closely related taxa overlap in distribution and is often associated with historically isolated populations coming into contact as a result of anthropogenic disturbance. There is evolutionary and conservation interest in detecting hybridization to determine its implications on future species composition, especially for threatened and recovering taxa such as subantarctic (Arctocephalus tropicalis) and Antarctic (A. gazella) fur seals, which were driven to the brink of extinction by human exploitation. Hybridization between these species has been reported at two locations and they breed sympatrically at a third site, Iles Crozet. While hybrid individuals have previously been identified based on phenotype, individuals can be difficult to classify based on these characteristics alone. Genotypic hybrid identification has been successful in several species, including fur seals. In this study we conducted an assignment test using microsatellite data to identify hybrids and to measure the frequency of hybridization at Iles Crozet. Samples were collected from 372 individuals and screened with 6 polymorphic microsatellite markers. MtDNA genotypes were also determined for individuals identified as hybrids or backcrosses based on microsatellite genotype. Phenotype, microsatellite and mtDNA genotype were then compared in order to identify hybrids. The results indicate that 1% of the population have hybrid genotypes and at a minimum, 2.4% of the population are backcrossed to parental species. We found that the two species are genetically distinct from one another and given the low rate of hybridization it is unlikely that they will fuse. These results suggest that there is a mechanism for species recognition that acts as a barrier to hybridization. It therefore seems unlikely that fur seals are threatened by significant introgression. Further investigation of fur seal mating systems would provide valuable insight into the mechanisms governing hybridization and species recognition in mate choice.