Reproductive biology of a Red Sea goby, Silhouettea aegyptia, and a Mediterranean goby, Pomatoschistus marmoratus, in Lake Timsah, Suez Canal

The reproductive biology of the Red Sea goby Silhouettea aegyptia , and Mediterranean Pomatoschistus marmoratus , has been studied in Lake Timsah, Suez Canal. Male: female sex ratio was 1: 1 7 in S. aegyptia and 1: 2 7 in P. marmoratus . Size at first maturity was 20 mm ( s.l. ) in S. aegyptia and 24 mm in P. marmoratus . The breeding season of S. aegyptia extended from March to September with most gonadal activity in May, whereas in P. marmoratus , it stretched from. November until the following April with a peak in February. Hepatosomatic index for both species exhibited monthly fluctuations and an inverse correlation with gonadosomatic index was evident. Oocyte size-frequency distribution indicated several modes at 400, 600 and 800 μm during the breeding season. Fecundity of S. aegyptia ranged from 152 to 782 with an average of 468 eggs, whereas in P. marmoratus it varied between 293 and 1300 with an average of 603 eggs. Fecundity was related curvilinearly to fish length, body weight and ovary weight. Recruitment of young fish to the adult populations occurred in late July and early August for S. aegyptia and during March for P. marmoratus . Life history pattern indicated that both species of gobies are successful colonists of Lake Timsah, Suez Canal.     

First record of Kudoa (Myxosporea) in Pomatoschistus microps in the Rhône Delta, France

Myxosporidiosis due to Kudoa sp. has been recorded in gobies Pomatoschistus microps , collected from the Etang du Vaccarès (Rhône Delta, France).     

Protein differences among the Mediterranean species of the genus Spicara

Protein electrophoresis (PAGE) was used to study the three morphologically different species of Spicara (S. flexuosa, S. maena, S. smaris). Of the 28 enzymatic and additional myogenic loci, five monomorphic loci (LDH-1*, G6PD-1*, PGI-1* and two PMMs*) were species-specific markers of S. smaris with respect to S. flexuosa and S. maena. Four of the 28 enzymatic loci were polymorphic (EST-1*, GLDH*, PEPD*, PGI-2*). Discriminating genetic markers were not identified between S. flexuosa and S. maena. Genetic distance (D) as calculated by Nei's index (1978), between S. smaris v. S. maena and S. flexuosa showed a value, respectively of Z) = 0·137 and 0·141. Between S. flexuosa and S. maena the value was Z)=0-006. From the data it can be inferred that S. flexuosa and S. maena are conspecific, despite morphological differences.     

Genetic differentiation between the freshwater subspecies of Gasterosteus aculeatus in Southern California

Samples of Gasterosteus aculeatus microcephalus and the endangered G. aculeatus williamsoni were obtained from downstream and headwaters regions, respectively, of the Santa Clara River system in southern California and electrophoretically examined for the products of 45 loci, six of which were polymorphic. Significant departures from Hardy-Weinberg expectations were evident in genotypic distributions at four of the polymorphic loci indicating a severe restriction of gene flow within the drainage. The genetic distance between these two subspecies was calculated as D = 0.034 ± 0.029, a value comparable to that reported between G. aculeatus microcephalus and G. aculeatus aculeatus from different drainages in northern California.     

Genetic diversity and evolutionary history of the Tyrrhenian treefrog Hyla sarda (Anura: Hylidae): adding pieces to the puzzle of Corsica–Sardinia biota

The Corsica–Sardinia archipelago is a hotspot of Mediterranean biodiversity. Although tempo and mode of arrival of species to this archipelago and phylogenetic relationships with continental species have been investigated in many taxa, very little is known about the current genetic structure and evolutionary history subsequent to arrival. In the present study, we investigated genetic variation within and among populations of the Tyrrhenian treefrog Hyla sarda, a species endemic to the Corsica–Sardinia microplate and the surrounding islands, by means of allozyme electrophoresis. Low genetic divergence (mean D_nei = 0.01) and no appreciable differences in the levels and distribution of genetic variability (H_E: 0.06–0.09) were observed among all but one populations (Elba). Historical demographic and isolation‐by‐distance analyses indicated that this diffused genetic homogeneity could be the result of recent demographic expansion. Along with paleoenvironmental data, such expansion could have occurred during the last glacial phase, when wide and persistent land bridges connected the main islands and a widening of lowland areas occurred. This scenario is unprecedented among Corsica–Sardinia species. Together with the lack of concordance even among the few previously studied species, this suggests either that species had largely independent responses to paleoenvironmental changes, or that most of the history of assembly of the Corsica–Sardinia biota is yet to be written. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 159–167.     

Distribution of genetic diversity within and between Western Mediterranean island populations of the black rat Rattus rattus (L. 1758)

Genetic diversity was estimated by allozyme analysis at 26 loci in black rat populations (Rattus rattus) from 15 western Mediterranean islands (Hyéres, Corsica, Sardinia and related islets). Although overall variability levels were low (H = 0.025), the mean heterozygosity values for the islands were similar to those for three reference mainland populations. Within the islands, however, genetic diversity varied in relation to island size and geographic isolation. In particular, most small insular populations were significantly more variable than those on both large and isolated islands. The generic relationships between island populations were established by F_ST analyses indicating possible geographic origins and patterns of colonization. The maintenance of unexpectedly high levels of variability in the small island populations is discussed in relation to changes in the demographic and social structure observed in these populations. These island populations of black rat illustrate how genetic diversity may be efficiently maintained in a series of interconnected spatially fragmented populations.     

Allozyme differentiation of bonito in the Mediterranean Sea

Bonito Sarda sarda samples collected in three areas from the Mediterranean Sea exhibited considerable genetic heterogeneity over all locations. This provided preliminary evidence for two different groups of bonito, one for the Ligurian and the Ionian Seas and the other for the Aegean Sea.     

An environmental gradient dominates ecological and genetic differentiation of marine invertebrates between the North and Baltic Sea

Environmental gradients have emerged as important barriers to structuring populations and species distributions. We set out to test whether the strong salinity gradient from the marine North Sea to the brackish Baltic Sea in northern Europe represents an ecological and genetic break, and to identify life history traits that correlate with the strength of this break. We accumulated mitochondrial cytochrome oxidase subunit 1 sequence data, and data on the distribution, salinity tolerance, and life history for 28 species belonging to the Cnidaria, Crustacea, Echinodermata, Mollusca, Polychaeta, and Gastrotricha. We included seven non‐native species covering a broad range of times since introduction, in order to gain insight into the pace of adaptation and differentiation. We calculated measures of genetic diversity and differentiation across the environmental gradient, coalescent times, and migration rates between North and Baltic Sea populations, and analyzed correlations between genetic and life history data. The majority of investigated species is either genetically differentiated and/or adapted to the lower salinity conditions of the Baltic Sea. Species exhibiting population structure have a range of patterns of genetic diversity in comparison with the North Sea, from lower in the Baltic Sea to higher in the Baltic Sea, or equally diverse in North and Baltic Sea. Two of the non‐native species showed signs of genetic differentiation, their times since introduction to the Baltic Sea being about 80 and >700 years, respectively. Our results indicate that the transition from North Sea to Baltic Sea represents a genetic and ecological break: The diversity of genetic patterns points toward independent trajectories in the Baltic compared with the North Sea, and ecological differences with regard to salinity tolerance are common. The North Sea–Baltic Sea region provides a unique setting to study evolutionary adaptation during colonization processes at different stages by jointly considering native and non‐native species.     

Conservation implications of high genetic variation in two closely related and highly threatened species of Crambe (Brassicaceae) endemic to the island of Gran Canaria: C. tamadabensis and C. pritzelii

We used data from 12 allozyme loci for two endemic Brassicaceae from Gran Canaria (the endangered narrow endemic Crambe tamadabensis and its more widespread congener C. pritzelii) to assess whether their genetic diversity patterns reflect their phylogenetic closeness and contrasting population sizes and distribution areas, and to derive conservation implications. Genetic diversity values are high for both species and slightly higher in C. tamadabensis, despite its narrow distribution in north‐western Gran Canaria. At odds with the generally high interpopulation diversity levels reported in Canarian endemics, values of G_ST in C. tamadabensis and C. pritzelii are rather low (0.067 and 0.126, respectively). We construe that the higher genetic structure detected in C. pritzelii is mainly a result of unbalanced allele frequencies and low population sizes at the edges of its distribution. The overall high allozyme variation detected in C. tamadabensis and C. pritzelii is nevertheless compatible with an incipient but consistent genetic differentiation between the two species, modulated by recurrent bottlenecks caused by grazing and drift. Our data suggest that conservation efforts aimed at maintaining the existing genetic connectivity in each species and ex situ conservation of seeds are the best strategies to conserve their genetic diversity.     

Genetic variability in Irish populations of the invasive zebra mussel, Dreissena polymorpha: discordant estimates of population differentiation from allozymes and microsatellites

1. The recent arrival and explosive spread of the zebra mussel, Dreissena polymorpha (Pallas), in Ireland provided a rare opportunity to study the population genetics of an invasive species.
2. Eight polymorphic allozyme loci ( ACO-1, ACO-2 , EST-D, GPI, IDH-2, MDH, OPDH and PGM ) were used to investigate genetic diversity and population structure in five Irish populations, and the results were compared with those from a previous microsatellite study on the same samples.
3. The mean number of alleles per locus (2.7 ± 0.1) was similar to the mean for the same loci in European populations, suggesting that Irish founder populations were large and/or multiple colonization events took place after foundation. A deficiency of heterozygotes was observed in all populations, but was uneven across loci.
4. Pairwise comparisons, using Fisher's exact tests and F _ST values, revealed significant genetic differentiation among populations. The overall multilocus F _ST estimate was 0.118 ± 0.045, which contrasted with an estimate of 0.015 ± 0.007 from five microsatellite loci on the same samples in a previous study.
5. Assuming that microsatellites can be used as a neutral baseline, the discordant results from allozymes and microsatellites suggest that selection may be acting on some allozyme loci, specifically ACO-1, ACO-2 , IDH-2 and MDH, which contributed most to the significant differentiation between samples.     

Genetic differentiation and gene flow of two sparidae subspecies, Diplodus sargus sargus and Diplodus sargus cadenati in Atlantic and south-west Mediterranean populations

A total of nine enzymes coded by 14 loci were assayed for each of six populations (from the north-eastern Atlantic and the Mediterranean) of two sea bream subspecies ( Diplodus sargus sargus and Diplodus sargus cadenati ). Diagnostic alleles were observed for each subspecies, although there were several common alleles. Estimates of variance in allele frequencies among samples ( F _ST) revealed significant differences ( P  < 0.05) among both subspecies. Genetic divergence was found between Atlantic and Mediterranean samples: values for genetic distances were higher than 0.163. Furthermore, D. sargus cadenati populations displayed a higher mean weight and length than D. sargus sargus populations and significant differences in growth were found among subspecies and populations. These results are discussed in terms of levels of gene flow and its respective relationships with water circulation in the Strait of Gibraltar and geological events.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 705–717.     

Genetic differentiation of freshwater pond copepods at arctic sites

Freshwater pond copepod species at a low-arctic site show distributional and life history differences which may reflect different dispersal efficiencies. In order to ascertain levels of gene flow among populations, cellulose acetate gel electrophoresis was used to examine allozyme variation in Heterocope septentrionalis, Hesperodiaptomus victoriaensis and Leptodiaptomus tyrrelli near Churchill, Canada. Differentiation of gene frequencies among populations of these species, plus Hesperodiaptomus eiseni and Hesperodiaptomus arcticus at other sites along Hudson Bay was moderate. The variation in gene frequencies was less than that of other passively dispersing organisms from the same habitats, and only slightly greater than that reported for an intertidal copepod with pelagic larvae. The mean number of dispersers exchanged among populations per generation, estimated from Wright's island model, averages 4.1 for the three species. Dispersal efficiency, calculated using population size estimates, revealed differences among the three species. However, these differences were not consistent with that expected from their distributional patterns. This suggests that factors other than dispersal alone determine the distributions of copepod species.     

Evidence of genetic selection for growth in new recruits of a marine fish

Abstract A cohort of Diplodus sargus, a coastal marine fish abundant in the Mediterranean Sea, has been surveyed from its settlement following the pelagic larval stage up to 4 months of age, when the juveniles are moving to adult habitats in order to assess selective processes. We followed the mortality by looking at the decrease in population abundance and, simultaneously, the genetic structure using allozymes and the growth associated with each genotype to test for a relationship between genotype and phenotype. The recruitment survey demonstrated that 80% of individuals arrived within a single night and that they show very similar age providing a discrete pulse of new recruits that we followed for changes in survival and allele frequencies. After 4 months, there was a total mortality of 80.8%, with the disappearance of 181 of 224 fish that initially colonized the rocky barrier. The decrease in number followed a logarithmic model with a maximum decrease in the early period (first 30 days). The model derived from the 4 months of data demonstrates that most of the mortality in the cohort occurs over the first 120 days following settlement and the model predicted a final abundance of 10 individuals after 1 year. Within the same period of 4 months, we observed significant decrease in multilocus heterozygosity. Such a decrease in heterozygosity partly resulted from a purge of the Pgm-80* allele. Together with this major change in a natural population, an aquarium experiment demonstrated that individuals with Pgm-80* alleles show significantly lower growth than other new recruits. We propose that the decrease in frequency of Pgm-80* in the natural environment is the result of targeted predation that eliminates smaller individuals and therefore individuals bearing Pgm-80*. The potential metabolic effect as well as a scenario that could lead to the maintenance of polymorphism is discussed.     

Phylogeography of the common goby, Pomatoschistus microps, with particular emphasis on the colonization of the Mediterranean and the North Sea

The phylogeographical patterns of a small marine fish, the common goby, Pomatoschistus microps, were assessed at 12 sites along the northeastern Atlantic coasts and the western Mediterranean Sea. A combination of two genetic markers was employed: cellulose acetate allozyme electrophoresis (CAGE) and sequence analysis of a 289 bp fragment of the mitochondrial locus cytochrome b. Both markers were congruent in revealing significant differences between samples (global FST = 0.247 for the allozymes and PhiST = 0.437 for the mitochondrial DNA data) and a pattern of isolation-by-distance. Phylogeographical analyses yielded a shallow branching structure with four groups. Three of those were confined to the Atlantic basin and showed a star-like pattern. The fourth group contained a central haplotype occurring at the edges of the species' distribution, accompanied by a few more rare variants, which were restricted to the Mediterranean Sea. A genetic break was observed around the British Isles, with distinct haplotypes dominating at either side of the English Channel. A significantly negative correlation between the degree of genetic diversity and latitude was recorded both for mitochondrial DNA (mtDNA) and allozymes in the Atlantic basin. Gene flow analysis suggested that recolonization of the North Sea and the coasts of western Scotland and Ireland may have taken place from a glacial refugium in the Southern Bight of the North Sea. These results are discussed in the perspective of possible postglacial migration routes of marine fish along the northeastern Atlantic coasts.     

Genetic diversity and differentiation between the two remaining populations of the critically endangered Mediterranean monk seal

The Mediterranean monk seal Monachus monachus , is a critically-endangered species of which only two populations, separated by c . 4000 km, remain: the eastern Mediterranean (150–300 individuals) and the Atlantic/western Sahara populations (100–130 individuals). We measured current levels of nuclear genetic variation at 24 microsatellite loci in 12 seals from the eastern Mediterranean and 98 seals from the western Sahara population and assessed differences between them. In both populations, genetic variation was found to be low, with mean allelic richness for the loci polymorphic in the species of 2.09 and 1.96, respectively. For most loci, the observed allele frequency distributions in both populations were discontinuous and the size ranges similar. The eastern Mediterranean population had 14 private alleles and the western Sahara had 18, but with a much larger sample size. Highly significant differences in allele frequencies between the two populations were found for 14 out of 17 loci. F _ST between the two populations was 0.578 and the estimated number of migrants per generation was 0.046, both clearly indicating substantial genetic differentiation. From a conservation perspective, these results suggest that each population may act as a source for introducing additional genetic variation into the other population.     

小毛莨居群的遗传分化及其与空间隔离的相关性

采用聚丙烯酰胺凝胶电泳技术,对分布于华中地区的11个小毛莨（Ranunculus ternatus）居群的遗传分化进行了检测。对8个酶系统17个酶位点上的分析结果表明,该种各居群的各项遗传多样性指标处于一个相对较低的水平：多态位点比率（P）为0－53.0％,平均每位点等位基因数（A）为1－1.647,平均预期杂合度（He）和观察杂合度（Ho）分别为0－0.108和0－0.102。居群间遗传一致度甚高（I＝0.9754-0.9991）。根据Nei 's传距离所作出的聚灰分析表明,豫南信阳地区3个居群与湖北省武汉地区8个居群之间关系较远。而在武汉地区,长江以北的居群及长江以南的部分居群分别相聚在一起,用GPS定位方法得到居群间空间距离并据此聚类,该种的遗传分化与地理因素的相关性,并推测出长江的隔离作用加强了两岸居群间的遗传分化,同时发现一个生于独特生境的居群在表型和遗传结构上都已与其他邻近居群有了很大分异,由于该居群在所检测的酶位点上均无特有等位基因出现,作者认为不宜将其作为新种或新变种处理。     

Effects of current and historic habitat fragmentation on the genetic structure of the sand goby Pomatoschistus minutus (Osteichthys,Gobiidae)

Habitat fragmentation is a major force that will influence the evolution of a species and its distribution range. Pomatoschistus minutus, the sand goby, has a North Atlantic–Mediterranean distribution and shows various level of habitat fragmentation along its geographic repartition. The use of mitochondrial sequences of the cytochrome b (cyt b) gene and two co‐dominant sets of nuclear markers (introns and microsatellites) allowed us to describe the relationships between P. minutus populations belonging to several different geographical regions of Europe and to assess the structure of populations inhabiting the Golfe du Lion, along the French Mediterranean coast. The present study confirms that the taxon located in the Adriatic Sea (Venice) should be considered as a distinct species, separated approximately 1.75 Mya. The comparison of P. minutus between the Atlantic and western Mediterranean coasts using polymorphic co‐dominant markers revealed that they belong to two demographically independent units, and thus could be considered as well as distinct species, more recently separated (0.3 Mya). The Pleistocene glaciations seem therefore to have played an important role in the diversification of this complex. Finally, at a regional scale in the Golfe du Lion, P. minutus appears to form a single huge homogeneous population. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 175–198.     

Worldwide genetic differentiation in the common fouling barnacle,Amphibalanus amphitrite

Amphibalanus amphitrite is a common fouling barnacle distributed globally in tropical and subtropical waters. In the present study, the genetic (mitochondrial cytochrome oxidase subunit I) and morphological differentiation in A. amphitrite from 25 localities around the world were investigated. The results revealed three clades within A. amphitrite with a genetic divergence of ~ 4% among clades, whereas there were no diagnostic morphological differences among clades. Clade 1 is widely distributed in both temperate and tropical waters, whereas Clade 3 is currently restricted to the tropical region. The deep divergence among clades suggests historical isolation within A. amphitrite; thus, the present geographical overlaps are possibly a result of the combined effects of rising sea level and human-mediated dispersals. This study highlights the genetic differentiation that exists in a common, widely distributed fouling organism with great dispersal potential; future antifouling research should take into account the choice of lineages.     

Genetic differentiation and speciation among four Phyllotreta species (Coleoptera: Chrysomelidae)

Among the four closely related Phyllotreta species P. dilatata Thomson, 1866, P. flexuosa (Illiger, 1794), P. ochripes (Curtis, 1837) and P. tetrastigma (Comolli, 1837) several systematic problems occur due to the existence of colour pattern variation and morphological similarity. All four species feed on Brassicaceae, but P. tetrastigma , P. flexuosa and P. dilatata are monophagous in the field, whereas P. ochripes is oligophagous. Genetic differentiation and systematic relationships of the four species are studied by means of allozyme electrophoresis of 10 variable loci, with a total of 30 allelomorphs. Of the six alleles that are present only in a single species, none is diagnostic. Rogers modified genetic distance and Cavalli-Sforza & Edwards arc distance between all populations are calculated and Distance Wagner trees are constructed, revealing three major groups. P. ochripes is separated first, being the most distant species. The three other species are more closely related, and within this group P. dilatata is separated from the other two. The last group contains the populations of P. tetrastigma and P. flexuosa. In the differentiation between the different species host plant shifts and consequent genetic differentiation have been important.