Allozyme Analysis Research Articles

Patterns of genic diversity and structure in a species undergoing rapid chromosomal radiation: an allozyme analysis of house mice from the Madeira archipelago

The chromosomal radiation of the house mouse in the island of Madeira most likely involved a human-mediated colonization event followed by within-island geographical isolation and recurrent episodes of genetic drift. The genetic signature of such processes was assessed by an allozyme analysis of the chromosomal races from Madeira. No trace of a decrease in diversity was observed suggesting the possibility of large founder or bottleneck sizes, multiple introductions and/or a high post-colonization expansion rate. The Madeira populations were more closely related to those of Portugal than to other continental regions, in agreement with the documented human colonization of the island. Such a Portuguese origin contrasts with a study indicating a north European source of the mitochondrial haplotypes present in the Madeira mice. This apparent discrepancy may be resolved if not one but two colonization events took place, an initial north European introduction followed by a later one from Portugal. Asymmetrical reproduction between these mice would have resulted in a maternal north European signature with a nuclear Portuguese genome. The extensive chromosomal divergence of the races in Madeira is expected to contribute to their genic divergence. However, there was no significant correlation between chromosomal and allozyme distances. This low apparent chromosomal impact on genic differentiation may be related to the short time since the onset of karyotypic divergence, as the strength of the chromosomal barrier will become significant only at later stages.

Morphological and Allozymic Variation in Hynobius boulengeri and H. stejnegeri (Amphibia: Urodela: Hynobiidae)

We studied morphological and allozymic variation in populations of Japanese salamanders, Hynobius boulengeri and H. stejnegeri. Adult H. boulengeri showed sexual dimorphism, and juveniles differed greatly from adults in many morphological characters. From the results of multivariate analyses of morphological characters, the populations were divided into four groups: (I) H. boulengeri from Honshu, (II) H. boulengeri from Shikoku, (III) H. boulengeri from the Sobo-Katamuki Mountains of Kyushu and H. stejnegeri, and (IV) H. boulengeri from the Amakusa Islands and the Osumi Peninsula. Phenotypic relationships among the four groups were identical to relationships clarified by allozymic analyses, except for group IV, which was included in group III in the allozyme tree. Some morphometric characters were significantly correlated with environmental variables. We consider H. stejnegeri to be a valid species based on its unique color pattern, morphometric characters, and allelic composition, even though it was nested within group III of H. boulengeri by both morphological and allozymic analyses. We propose that group I from Honshu and group II from Shikoku should be treated as H. boulengeri sensu stricto and H. hirosei, respectively. Resolving the taxonomic status of the remaining populations of groups III and IV from Kyushu requires further study.

Isozyme variability amongElymusspecies indigenous to the Tibetan and Inner Mongolian Plateaus

AbstractUtilizing allozyme markers, genetic relationships were investigated for 40 populations representing 10Elymusspecies indigenous to the Tibetan and Inner Mongolian Plateau regions. From the allozyme analysis, the genetic diversity within populations (He) was very low, ranging 0.0160–0.1680. At the species level, Nei's gene diversity and Shannon's information index ranged 0.0800–0.2528 and 0.1173–0.3769, respectively. Allzoyme locus diversity across the 40 populations suggested that polymorphic loci contributed to 72.1% of the total allozyme diversity (HT = 0.2979) while only 27.9% was indicated within populations. A low occurrence of gene flow among populations (Nm), based onGstcalculations, was calculated to be 0. 1932. With respect to potential gene flow (Nm) at the species and population level, a lower frequency of gene flow occurred between populations within species than between species. In general, species ofE. geminatusandE. glaucus,and the nationally protected plantE. breviaristatus,indicated the lowest level of genetic variability. From a geographic standpoint, accessions obtained from different regions indicated a wide range of genetic diversity values. Populations indigenous to the Tibetan Plateau suggested a higher level of genetic diversity than those sampled from the Inner Mongolian Plateau.

Evolutionary Relationships and Reproductive Isolating Mechanisms in the Rice Frog (Fejervarya limnocharis) Species Complex from Sri Lanka, Thailand, Taiwan and Japan, Inferred from mtDNA Gene Sequences, Allozymes, and Crossing Experiments

The rice frog (Fejervarya limnocharis) species complex is widely distributed, from India to Japan, and most prevalently in Southeast Asia. Conspicuous morphological variation has been reported for this species complex throughout its distribution range. In the present study, we used mtDNA gene sequence and allozyme analyses to infer evolutionary affinities within this species complex using eight populations (Sri Lanka; Bangkok and Ranong in Thailand; Taiwan; and Hiroshima, Okinawa, Ishigaki and Iriomote in Japan). We also conducted crossing experiments among four populations from Japan, Thailand, and Sri Lanka in order to find out more about the reproductive isolating mechanisms that might exist among the East, Southeast, and South Asian populations of this species complex. The crossing experiments revealed that the Sri Lanka population is reproductively isolated from the Hiroshima, Bangkok, and Ranong populations by complete hybrid inviability, and that the Bangkok population may be reproductively isolated from the Hiroshima population by partial hybrid inviability. Thus, it is not unreasonable to regard the Sri Lanka population as a species separated from F. limnocharis. The mtDNA and allozyme data showed that the Ranong population is most closely related to the Bangkok population in nuclear genome, but more similar to the Okinawa and Taiwan populations in mtDNA genome. The present, preliminary survey may raise questions about the species status of these particular populations and also about the nature of the biological species concept.

Population Genetic Structure of Endemic and Endangered Yellow Catfish, Horabagrus brachysoma, Using Allozyme Markers

The allozyme variation and population genetic structure of Horabagrus brachysoma in three natural populations from the southern part of the Western Ghats region, India, were investigated by polyacrylamide gel electrophoresis. Variations at 14 loci from 14 enzyme systems were analyzed. The allozyme analysis revealed a high level of genetic variation in this species, with an average of observed alleles per locus of 2.357 and observed heterozygosity of 0.178. The positive value of the fixation index (FIS=0.507) implied a significant deficiency of heterozygosity at the population level. The highly significant probability (P<0.0001) for the overall loci suggested that the three sample sets were not part of the same gene pool.

Adaptive rather than non-adaptive evolution of Mimulus guttatus in its invasive range

Adaptive and non-adaptive evolutionary processes are likely to play important roles in biological invasions but their relative importance has hardly ever been quantified. Moreover, although genetic differences between populations in their native versus invasive ranges may simply reflect different positions along a genetic latitudinal cline, this has rarely been controlled for. To study non-adaptive evolutionary processes in invasion of Mimulus guttatus, we used allozyme analyses on offspring of seven native populations from western North America, and three and four invasive populations from Scotland and New Zealand, respectively. To study quantitative genetic differentiation, we grew 2474 plants representing 17 native populations and the seven invasive populations in a common greenhouse environment under temporarily and permanently wet soil conditions. The absence of allozyme differentiation between the invasive and native range indicates that multiple genotypes had been introduced to Scotland and New Zealand, and suggests that founder effects and genetic drift played small, if any, roles in shaping genetic structure of invasive M. guttatus populations. Plants from the invasive and native range did not differ in phenology, floral traits and sexual and vegetative reproduction, and also not in plastic responses to the watering treatments. However, plants from the invasive range produced twice as many flower-bearing upright side branches than the ones from the native populations. Further, with increasing latitude of collection, vegetative reproduction of our experimental plants increased while sexual reproduction decreased. Plants from the invasive and native range shared these latitudinal clines. Because allozymes showed that the relatedness between native and invasive populations did not depend on latitude, this suggests that plants in the invasive regions have adapted to the local latitude. Overall, our study indicates that quantitative genetic variation of M. guttatus in its two invasive regions is shaped by adaptive evolutionary processes rather than by non-adaptive ones. Obwohl sowohl adaptive als auch nichtadaptive evolutionäre Prozesse eine wichtige Rolle für biologische Invasionen spielen können, wurde ihre relative Bedeutung bisher kaum quantifiziert. Zudem wurde bisher kaum dafür kontrolliert, ob genetische Unterschiede zwischen Populationen in fremden und einheimischen Gebieten nicht einfach durch unterschiedliche Positionen entlang eines durch geographische Breite verursachten genetischen Gradienten bedingt sein können. Um nichtadaptive evolutionäre Prozesse bei der Invasion von Mimulus guttatus zu untersuchen, benutzten wir Allozymanalysen von Nachkommen von sieben einheimischen Populationen aus Nordamerika und von drei und vier invasiven Populationen aus Schottland und Neuseeland. Um quantitativgenetische Differenzierung zu untersuchen, zogen wir 2474 Pflanzen aus 17 einheimischen und sieben invasiven Populationen in einem Experimentiergarten unter permanenter oder nur zeitweiser Bewässerung auf. Die fehlende Allozymdifferenzierung zwischen den einheimischen und invasiven Gebieten zeigt an, dass mehrere Genotypen nach Schottland und Neuseeland eingeführt wurden und dass Gründereffekte und genetische Drift wenn überhaupt nur eine kleine Rolle für die genetische Struktur invasiver M. guttatus Populationen spielen. Pflanzen aus den einheimischen und invasiven Gebieten unterschieden sich weder phänologisch noch in sexueller oder vegetativer Reproduktion oder in ihren plastischen Reaktionen auf die Bewässerungsbehandlungen. Allerdings produzierten Pflanzen aus dem invasiven Gebiet doppelt so viele blütentragende aufrechte Seitentriebe. Außerdem nahm mit zunehmendem Breitengrad sowohl für einheimische als auch für invasive Herkunftspopulationen die vegetative Reproduktion der experimentellen Pflanzen zu, während die sexuelle Reproduktion abnahm. Da die Allozyme anzeigten, dass die Verwandtschaft zwischen einheimischen und invasiven Populationen nicht vom Breitengrad abhing, deutet das darauf hin, dass sich die Pflanzen in invasiven Gebieten an den lokalen Breitengrad angepasst haben. Insgesamt zeigt unsere Studie, dass die quantitativgenetische Variation von M. guttatus in seinen beiden invasiven Regionen durch adaptive, und nicht durch nicht-adaptive, evolutionäre Prozesse geprägt ist.

Genetic Relationships and Reproductive-isolation Mechanisms among the Fejervarya limnocharis Complex from Indonesia (Java) and Other Asian Countries

In order to elucidate the genetic relationships and reproductive-isolation mechanisms among the Fejervarya limnocharis complex from Indonesia and other Asian countries, allozyme analyses and crossing experiments were carried out using 208 individuals from 21 localities in eight Asian countries. The allozyme analyses revealed that 17 enzymes examined were controlled by genes at 27 loci, and that 7.9 phenotypes were produced by 5.2 alleles on average. The two species recognized in F. limnocharis sensu lato from Southeast Asia (i.e., F. limnocharis sensu stricto and F. iskandari) were found to occur sympatrically at three localities (Bogor, Cianjur and Malingping), all on Java, Indonesia. Fejervaya iskandari was dominant at each of these localities and showed substantial geographic genetic variation. Laboratory-produced hybrids between F. limnocharis and F. iskandari from Java became underdeveloped and died at the tadpole stage, suggesting that these species are completely isolated by hybrid inviability. Hybrids between topotypic F. limnocharis and the Malaysian and Japanese conspecific populations developed normally to metamorphosis. Likewise, hybrids between topotypic F. iskandari and the Thailand and Bangladesh conspecific populations also showed normal viability throughout larval development. The present allozyme analyses and crossing experiments strongly suggested the presence of two distinct forms, the large type and the small type, in the F. limnocharis complex from Asia, and further subdivision of the large type into the F. limnocharis assemblage and the F. iskandari assemblage. The small type was found in samples from India, Thailand, Bangladesh and Sri Lanka, and included at least three different species. The sample from Pilok, Thailand, was considered to represent an undescribed species.

Morphological and allozyme diversity in the Hieracium nigrescens group (Compositae) in the Sudety Mountains and the Western Carpathians

The overall pattern of morphological variation and genetic diversity (allozyme analysis) was studied in the Hieracium nigrescens group ( H. nigrescens s.l. , H. alpinum ≥ H. murorum ) in the Sudety Mountains and the Western Carpathians. A morphological analysis was performed on 180 plants from 12 populations belonging to six a priori dis- tinguished taxa. Altogether, 25 characters were measured or scored. Morphometric (canonical discriminant analysis) data separated five taxa, evaluated here at the species rank: H. chrysostyloides, H. decipiens, H. nigrescens (all from the Sudety Mountains), H. jarzabczynum, and H. vapenicanum (the Western Carpathians). A distinct local popula- tion from Mount Babia hora (the Western Carpathians) comprised a further possible taxon, given the preliminary name ' H. babiagorense '. Genetic diversity was studied in 17 populations of H. chrysostyloides, H. decipiens, H. jarzabczynum , H. nigrescens , H. vapenicanum and ' H. babiagorense ' using five enzyme systems. All a priori recognized species were proved to be genetically homogeneous, each consisting of one unique multilocus allozyme genotype, except ' H. babiagorense ' which shared the same genotype with H. jarzabczynum . For the first time, a chromosome number is reported for H. vapenicanum (2 n = 3x = 27) and previously published numbers were confirmed for H. chrysostyloides (2 n = 5x = 45), H. decipiens (2 n = 4x = 36), H. jarzabczynum (2 n = 4x = 36), H. koprovanum (2 n = 4x = 36), and H. nigrescens (2 n = 4x = 36). All species have been shown to be endemic to either the Sudety Mountains or the Western Carpathians. Except for the species studied, two further ones ( H. apiculatum, H. nivimontis ) are recognized in the area, giving a total of seven species from the Hieracium nigrescens group in the area studied. The morphologically slightly different local population from Mount Babia hora/Babia Gora (' H. babiagorense ') requires further study. Two new combinations are proposed: Hieracium jarzabczynum (Paw l . & Zahn) Mraz & Chrtek f. and Hieracium vapenicanum (Lengyel & Zahn) Chrtek f. & Mraz. © 2007 The Linnean Soci- ety of London, Botanical Journal of the Linnean Society , 2007, 153 , 287-300. ADDITIONAL KEYWORDS: apomixis - Asteraceae - chromosome numbers - flow cytometry - polyploidy. R ˇ

Direct and indirect measures of dispersal in the fairy shrimp Branchipodopsis wolfi indicate a small scale isolation‐by‐distance pattern

We compared dispersal rates and patterns using both spatial genetic structure as well as direct measures of dispersal in Branchipodopsis wolfi, a freshwater anostracan inhabiting clusters of spatially fragmented and temporally unpredictable ephemeral rock pools in southeastern Botswana. For a total of 29 populations from three rock pool sites, the active population component was subjected to allozyme analysis for four loci and gene flow between populations was estimated. For a subset of the pools, we quantified the number of viable floating dormant eggs and larvae dispersing into overflow traps during flood events. Genetic and geographic distances were significantly correlated within each site. Gene flow estimates indicated from 0.6 to 227 migrants per generation. This relatively high effective dispersal rate corresponds with our direct observation of peak dispersal between pools during floods. Up to 784 viable dormant eggs and 301 larvae were trapped at one overflow during one single rainfall event. We determined that a distance of 50 m is already an effective barrier to gene flow for this species. There is ample effective genetic communication between different populations within each rock pool site, but this communication is limited by distance.

The recent spread of Artemia parthenogenetica in Western Australia

In Western Australia, populations of Artemia parthenogenetica in coastal salt lakes at Rottnest Island and Lake Hayward, and in salterns at Port Hedland and Shark Bay, are widely accepted to have been introduced by humans. Further, within the past 10 years, populations of A. parthenogenetica have been found in inland playa salt lakes in the wheatbelt of south-west Western Australia, where none had been recorded in previous salt lake studies. Here we hypothesise that birds act as transport vectors for Artemia cysts both within Australia and between the Asian and Australian continents. Allozyme analysis was used to identify clonal types (multi-locus genotypes), clonal frequencies, genotypic diversities and genotypic identity of six populations (three coastal, three inland). Overall, the inland populations displayed almost identical genotypic structure to the coastal population from Lake Hayward, indicating that Lake Hayward could be the major source for dispersal and colonisation of inland populations. Results support the hypothesis of dispersal inland by nomadic bird species. Furthermore, evidence suggests that the inland and Lake Hayward populations may be an example of a metapopulation. The greater variety of genotypes present in the Rottnest population indicates that this population has received a large number of small immigrations, or that it received one large introduction. The former may indicate a long period of suitable salinities, providing a greater time-span over which migration and succession of clonal types could occur in comparison to other populations. While we cannot rule out the possibility of human introduction of A. parthenogenetica to Rottnest, the hypothesis of cyst dispersal along the Austral-Asian flyway remains possible.

Local adaptation to serpentine soils in Pinus ponderosa

Local adaptation to serpentine soils is studied using both transplant experiments and molecular genetic techniques. In long-lived species, such as pines, it is unclear how soon after germination local adaptation becomes detectable. Here I present results of a 36-year reciprocal transplant experiment using Pinus ponderosa, along with allozyme analyses from the same trees. Using a repeated measures analysis of variance, there is evidence for adaptation to serpentine soils; however, significant differences between source soil types do not become apparent until 20 years after the start of the experiment. Analysis of allozyme data showed no evidence for differentiation between the serpentine and non-serpentine populations. Comparing the performance of families over the course of the experiment found that there was little correlation between performance after 1 or 4 years of growth in the field and performance after 36 years. This suggests that short-term transplant experiments may not provide definitive evidence for adaptation to serpentine soils. A literature survey of all transplant studies using pine species growing on and off of serpentine soils found that studies that lasted fewer than 2 years showed no evidence for adaptation. However, in the two experiments (this one included) that lasted more than 2 years, both showed evidence for adaptation to serpentine soils. More long-term experiments are required to validate these results.

Life cycle and genetic differences of two Branchipus schaefferi populations from Morocco (Anostraca: Crustacea)

AbstractThe somatic growth, longevity, and reproduction of two Moroccan anostracan populations from different climatic areas were studied under standardized laboratory conditions. Both populations were subjected to allozyme analyses covering four loci, and molecular analyses of the variable regions, the Internal Transcribed Spacers (ITS1 &amp; ITS2) intervening the nuclear ribosomal genes (18S, 5.8S, 28S rDNA). The ecological characteristics of the life cycle of each population are presented, together with their genetic differences and phylogenetic relationships.

Genetic structure of gilthead seabream, Sparus aurata, in the Central Mediterranean Sea

Abstract The gilthead seabream, Sparus aurata, represents an important economic resource for Mediterranean aquaculture. In spite of its wide geographic distribution and economic importance, only recently studies have been carried out on the genetic composition of natural populations, which have revealed a picture of a heterogeneous degree of genetic differentiation among S. aurata populations. In this study an allozyme analysis of samples from six different collecting sites along the Italian and Croatian coasts was carried out, covering an area in the Central Mediterranean sea that has yet to be investigated through gene-enzyme systems. Data on 26 gene loci, 10 of which are polymorphic, indicate a slight but significant genetic structure (FST = 0.0167) of the species. A hierarchical analysis of population subdivision made it possible to identify three different assemblages found in the Adriatic Sea, Tyrrhenian Sea and Sardinian Channel, though an isolation by distance model can be rejected. The results are discussed in the light of previous literature and taking conservation into consideration.

Comparison of Mating Systems in Populations of Gleditsia japonica var. koraiensis

The mating systems of two groups of natural populations of Gleditsia japonica var. koraiensis in Korea were determined using allozyme analysis. The result suggests that G. japonica var. koraiensis is predominantly outcrossing. The tm values of eight populations in Korea varied from 0.667 (Mdh-1) to 0.938 (ldh-1), giving an average 0.820. Population and individual outcrossing estimates were associated with flowering tree density or degree of spatial isolation. The reason for relatively low outcrossing rates of some populations could be attributed to reduction of effective population sizes of sib for the medicine, small population size, and isolation of flowering mature trees. The heterozygote excesses were observed in some natural populations, whereas other populations exhibited varying degrees of inbreeding and heterozygotes deficit. Thus, selection against homozygotes operated in the progeny populations throughout the life cycle.

Genetic diversity and mating system of the threatened plant Kirengeshoma palmata (Saxifragaceae) in Korea

The endangered herb Kirengeshoma palmata, from eastern Asia, has had its population severely reduced in number through habitat loss and fragmentation. All of the individuals within five subgroups at Mt. Baek-un-san, in the southern part of Korea, were genetically surveyed by allozyme analysis. Genetic diversity levels within subgroups were relatively high, and a consistently high outcrossing rate as well as a negligible biparental mating rate were confirmed by this study. Several groups of visibly connected ramets were observed in a clustered distribution which suggested cloning. Absence of mating partner rather than pollinators decreased seed production in small mating groups. The present genetic structure of the five subgroups was probably the result of local extinction of intervening populations. Because K. palmata may be a self-incompatible species, populations with few genets face lowered seed set due to mate scarcity. Thus, this type of population may be at an increased risk of extinction as a result of inbreeding depression, loss of genetic variability, and reduced sexual reproduction. The small, genetically depauperate subgroups may need an input of seeds or plants from other populations in China or Japan in order to regenerate, but the possibility of outcrossing depression leads us to recommend outbreeding among the local subgroups of Mt. Baek-un-san to restore genetic variability.

Long-term occurrence of hybrids between Japan Sea and Pacific Ocean forms of threespine stickleback, Gasterosteus aculeatus, in Hokkaido Island, Japan

The distribution patterns of two genetically divergent forms (Japan Sea and Pacific Ocean forms) of Gasterosteus aculeatus and their hybrids in the Hokkaido Island, Japan were investigated. Hybrid frequencies and the mating pattern of natural F1-hybrids and backcrosses, were examined by using allozyme analysis. The distribution patterns matched those previously reported. All three sympatric localities in eastern Hokkaido Island included hybrids between the two forms in each year examined. A low frequency of hybrids of sticklebacks has been maintained in areas of sympatry of the two forms in Hokkaido Island for several years. The proportion of F1-hybrids was significantly lower than expected by random mating in six samples from four sympatric populations, suggesting form-assortative mating. Mating crosses of natural F1-hybrids existed in both patterns. Natural F1-hybrids backcrossed more frequently with Pacific Ocean form than Japan Sea form. However, the proportions of backcross individuals in two of three samples were not significantly different from the expected proportions by random mating between F1-hybrids and their parent forms. In other samples, despite the Pacific Ocean form predominant in a population, F1-hybrid predominantly backcrossed with the Japan Sea form. These results support the hypothesis of gene flow from Pacific Ocean to Japan Sea forms.

Genetic Variation and Population Structure of Oriental Migratory Locust, Locusta migratoria manilensis, in China by Allozyme, SSRP-PCR, and AFLP Markers

Allozyme analysis, microsatellite primer PCR (SSRP-PCR), and amplified fragment length polymorphism (AFLP) techniques were used to assess genetic diversity and population structure of the Chinese oriental migratory locust, Locusta migratoria manilensis. A total of 299 PCR markers (67 SSRPs and 232 AFLPs) were detected in eight populations, of which 98.7% were polymorphic markers. The proportion of polymorphic loci (95.5-98.8%) by SSRP+AFLP markers indicated no significant differences between populations, and all populations exhibited a similar level of variability; results of the allozyme analysis demonstrated that 19 loci gave rise to a lower level of polymorphism (55.6-66.7%). The genetic distances between the populations were relatively low. Shannon's index and Nei's gene diversity showed low differentiation among the populations. Allozyme analysis, however, reflected greater similarity and smaller differentiation between the populations than those shown by SSRP and AFLP markers. Neighbor-joining dendrograms derived from both the allozyme and SSRP+AFLP markers showed that the genetic distances among Chinese oriental migratory locust populations were not greatly influenced by geographic distance and breeding habitats.

Direct and indirect effects of predation on the genetic structure of a Daphnia population

Communicating editor: K.J. Flynn The effects of fish predation on zooplankton communities are well documented, but relatively little is known about how predation structures the genetic composition of individual populations. This study illustrates how a perturbation in the timing and strength of predation by rainbow trout directly and indirectly altered the genetic composition of a Daphnia pulicaria population in a Minnesota (USA) lake. Trout were stocked in autumn in the first 2 years of the study and in spring in the second 2 years. In autumn stocking years, predation was highest over winter and in spring but relatively low during summer stratification. In contrast, in spring stocking years, predation was low over winter and high during summer stratification. In all years, the Daphnia population became genetically differentiated with respect to depth, as summer stratification became more pronounced. In addition, allozyme analyses of trout stomach contents revealed selective predation on Daphnia in the metalimnion. In spring stocking years, when trout were abundant during the summer, this directly caused a shift in the dominant clone type from a metalimnetic to a hypolimnetic specialist. The fisheries manipulation indirectly affected the genetic composition of the Daphnia population by altering the importance of recruitment from diapausing embryos in the sediment (the egg bank). In autumn stocking years, when the over-wintering population was small, genotype frequencies in early summer indicated the recent emergence of sexually derived individuals from the egg bank. Conversely, in spring stocking years when over-wintering populations of Daphnia were large, no emergence events were detected.

On the presence of Daphnia galeata in Lake Orta (N. Italy)

Lake Orta is a very interesting environment because of its history of heavy chronic pollution and biota re-colonization. It was the first deep lake in Italy in which allozyme techniques were used to investigate clonal diversity. In 1986, a newly established Daphnia obtusa population, able to colonize stressed environments, resulted composed by just one multilocus genotype, detected through an analysis of 27 different allozymes, fifteen of which active and stable for up to 12 generations. This result was interpreted as indicative of a colonization by a single clone, able to establish after a strong selection. This species was allochthonous for the lake, and in 1996 was replaced by a Daphnia longispina of the same morphotype as that originally described from its pelagic environment, the latter apparently remaining the only Daphnia species also in the lake’s littoral until 2001, i.e. until a regular sampling to monitor the lake was accomplished. During an accidental sampling in 2004, for detecting the occurrence and prevalence of parasites in Daphnia parental species and hybrids in several lakes located North and South of the Alps, Daphnia galeata was first found in Lake Orta’s pelagic environment, as revealed by morphological and allozyme analyses. Lake Orta zooplankton was then resampled in June 2006, to detect species as well as clonal composition of the Daphnia population, using the same techniques of morphotype and allozyme analyses. We expected to find low clone diversity and the occurrence of hybrids, whose success is enhanced in disturbed environments. Although preliminary, our results confirm that clone diversity Lake Orta’s Daphnia population is low, thus suggesting a recent colonization by D. galeata and providing evidence for a founder effect. In addition, the detection of the M variant at the AO locus, we interpret as a rare allele of D. galeata/D. longispina hybrids, perfectly fits the hypothesis of an enhancement of hybrid success in disturbed environments such as the once heavy polluted Lake Orta.

Sistema de reprodução em populações de Eschweilera ovata (Cambess.) Miers

O sistema de reprodução de duas populações de Eschweilera ovata foi quantificado por análise de isoenzimas em estrutura de progênies usando os modelos misto de reprodução e cruzamentos correlacionados. Desvios do modelo misto de reprodução foram evidenciados entre as freqüências alélicas dos óvulos e do pólen e pela heterogeneidade nas freqüências alélicas do pólen que fecundou as diferentes árvores. A taxa de cruzamento multilocos foi alta em ambas populações Camarugipe (t m =0,999±0,004) e Itaparica (t m=0,985±0,023). A alta variação na taxa de cruzamento individual (t variando de 0,320 a 1,000) indicou que a espécie não é auto-incompatível. Diferenças positivas e significativamente diferentes de zero foram detectadas entre a taxa de cruzamento multiloco e uniloco, indicando cruzamentos endogâmicos em ambas populações Camarugipe (t m-t s =0,066±0,014) e Itaparica (t m-t s =0,073±0,016) e possível estruturação genética espacial. Valores altos de cruzamentos biparentais foram detectados nas populações (Camarugipe, r p=0,577±0,088; Itaparica r p =0,423±0,070), demonstrando que as progênies são constituídas principalmente por misturas de meios-irmãos e irmãos-completos. O coeficiente de coancestria nas progênies de ambas as populações (Camarugipe, tetaxy=0,211; Itaparica tetaxy =0,191) foi superior ao esperado em progênies de meios irmãos (0,125). Os resultados foram discutidos sob a ótica de amostragens para melhoramento, conservação genética e coleta de sementes para recuperação ambiental.