Diet partitioning in summer of two syntopic neogobiids from two different habitats of the lower Vistula River, Poland

Monkey goby Neogobius fluviatilis and racer goby N. gymnotrachelus, both native to the Ponto‐Caspian region, were discovered in Polish rivers during the mid‐1990s and currently they are invading the River Vistula. Preliminary studies were carried out on the diet of both species at two sites in the lower River Vistula, one lotic (main channel of the river downstream of the W?oc?awek river reservoir) and the other lentic (left bank, middle section of the W?oc?awek Reservoir). Significant differences were noted in diet between the two species and within species according to habitat, in particular the types of chironomid taxa taken. Over a single diel cycle, monkey goby were captured between 07:00 and 19:00 hours only, feeding more intensively on chironomid larvae than the racer goby, which was captured at most times of day. The wide diet plasticity of these non‐native fish species favours their expansion.     

Diel-feeding activity in early summer of racer goby Neogobius gymnotrachelus (Gobiidae): a new invader in the Baltic basin

The first recording of the Ponto‐Caspian racer goby in Poland was during 1995 in the River Bug (River Vistula system). Within 5 years, the species had spread to the downstream section of the Vistula. One of the potential impacts of invasive species on native fauna is competition for food. Therefore, the diel patterns in diet composition and gut fullness coefficient (FC) of racer goby were examined at one study site in the W?oc?awski Reservoir (lower River Vistula), during May 2003. An average of 20 individuals were examined each 4 h over one 24‐h period (125 fish in total). The proportion of main food items and diet width did not differ among three size‐groups (43–59, 60–79 and 80–97 mm total length), and the relative biomass ratio of main food categories did not differ over the diel cycle. Amphipods constituted 11–70% of total gut content biomass and were found on average in 84% of analysed alimentary tracts. The second prey types were chironomid larvae (16–63% of total food biomass; frequency occurrence: 61–91%), and to a lesser extent chironomid pupa, ceratopogonid larvae, oligochaets, dipteran imagines and copepods, with fish larvae found in the gut of eight gobies. Gut fullness coefficient (FC) differed significantly over the 24‐h period, with the highest value at night and in early morning. In conclusion, racer goby forages mainly on benthos and has a nocturnal‐feeding activity. No significant diet overlap was found between racer goby and native percids, i.e. Eurasian perch Perca fluviatilis and ruffe Gymnocephalus cernuus.     

Structure of the gut of the racer goby Neogobius gymnotrachelus (Kessler, 1857)

The morphological and histological features of the gut of juvenile racer goby Neogobius gymnotrachelus [range of body mass 0·2–0·9 g and standard length ( L _S) 20·0–38·8 mm] were examined in fish collected from the Włocławek Reservoir on the Vistula River, Poland. Evidence is provided of the stomachless nature of the gut of the racer goby. The intestine of the juveniles lacks the intestinal bulb. A particular feature of the racer goby gut is the secretory oesogaster (the transitional region where the secretory oesophagus merges into the intestine) with multicellular alveolar glands that secrete via a common duct to the surface between the mucosal folds. The cells in the secretory oesogaster alveolar glands are periodic-acid-Schiff (PAS) positive indicating the presence of neutral mucopolysaccharides. It is hypothesized that the secretory oesogaster is evidence of the loss of the functional stomach in this species. There are two sphincters: the oesogaster–intestinal and the intestinal–rectal in the racer goby gut. It can be concluded that the oesogaster–intestinal sphincter is functionally related to the gastro-intestinal sphincter described in many fish species having a stomach. Enterocytes with a distinct brush border and only a few goblet cells are observed in the epithelium along the whole intestine. The existence of vacuoles in the supranuclear region of the rectal enterocytes is also confirmed.     

Diet and feeding habits of monkey goby (Neogobius fluviatilis) in a newly invaded area

The monkey goby (Neogobius fluviatilis) is one of the Ponto-Caspian species that in recent decades made substantial East-to-West invasions in European inland waters. Now the species is present in the Danube as far as its Slovakian section. In the last decade the species also invaded the Western Bug and Vistula rivers, in the latter it is numerous nearly as far as its delta. The purpose of our study was to define the diet spectrum, feeding preferences, spatial and size related changes in diet and diurnal feeding activity of this goby. Another goal was to predict which groups of native prey would be most affected by the presence of this exotic predator in newly invaded areas. The study was carried out at three sampling locations in the Vistula River system. The food spectrum of the monkey goby was broad. The fish consumed insect larvae and pupae, crustaceans, annelids, gastropods and fish. Chironomid larvae were a prevalent food category in all sampling sites, followed by amphipod crustaceans at one site and by trichopteran larvae and chironomid pupae at another. At the third site, there was no distinct subdominant food category. According to the values of the Ivlev’s selectivity index, the preferred food category were chironomid larvae. No significant differences in diet were found over the 24-h cycle. There was no variation among different fish size groups. From our studies and from the available literature data it can be concluded that the species, due to its ability to use locally available food resources, displays a generalistic and highly flexible feeding strategy.     

Seasonal abundance and feeding patterns of the invasive racer goby (Babka gymnotrachelus) in the littoral zone of a lowland European river

Environmental Biology of Fishes - The racer goby (Babka gymnotrachelus), a Ponto-Caspian gobiid, has successfully established in several European rivers since the 1990s, and its range is expanding;...     

Reproductive biology of racer goby Neogobius gymnotrachelus in the Włocławski Reservoir (Vistula River, Poland)

Initial studies on the reproductive parameters and spawning behaviour of racer goby Neogobius gymnotrachelus, one of three Ponto‐Caspian gobiid species recently invading Polish waters, were carried out in W?oc?awski Reservoir (lower River Vistula, Poland), where spawning lasted from April to August. Males were on average about 23.3% longer and 53.8% heavier than females. The smallest female with mature gonads was 58 mm TL (estimated age 2+ years), and males were sexually mature at 59 mm TL (age of 1+ years). Gonado‐somatic index at the beginning of spawning was seven times larger in females (mean = 8.4) than that in males (mean = 1.2). Mean absolute fecundity was 952 eggs per female (361–2236). Egg diameter ranged from 0.140 to 1.558 mm, being of bi‐modal distribution, which suggests two or three spawning bouts. Length–frequency analysis of juveniles revealed a multimodal distribution. Specialized reproductive behaviour (nest construction and parental care of eggs) and an extended spawning period increase the probability that racer goby can successfully establish self‐sustaining populations in novel environments.     

Ontogenetic variability in the external morphology of monkey goby, Neogobius fluviatilis (Pallas, 1814) and its relevance to invasion potential

In the previous decade, four species of non-native gobies have invaded the middle section of the river Danube and its tributaries. An effective tool for understanding biological invasions is the evaluation of various biological traits (morphological, life history, ontogenetic) within an epigenetic context. The present study examines the external morphology of monkey goby Neogobius fluviatilis (Pallas, 1814) from the mouth of the River Hron, the morphological differences among three goby species (monkey, bighead and round) and the relevance of these differences for invasive potential. Monkey goby reach their definite phenotype very early in their ontogeny and thus represent a strongly precocial (specialized) species with direct development. The morphological differences between monkey and two other goby species also reflect its strong specialization for sandy substrata and smaller prey types. Thus, monkey goby are not expected to spread to new areas as fast as the round and bighead gobies, and their distribution is likely to be limited to sandy and/or sandy-gravel substrata. If this assumption is correct, then the potential adverse impact of monkey goby on native fauna or even ecosystem is likely to be less than that of the bighead and round gobies. Handling editor: K. Martens     

Spread of alien (non-indigenous) fish species <Emphasis Type="Italic">Neogobius melanostomus</Emphasis> in the Gulf of Gdansk (south Baltic)

The round goby (Neogobius melanostomus) was first noticed in the Gulf of Gdansk in 1990. This Ponto-Caspian fish was most likely introduced to the Baltic environment from ships ballast water. During the first years of invasion, slow population growth was observed in the initially colonized regions. From 1994, round goby gradually spread in all shallow water zones of the Gulf of Gdansk. The area occupied by the population and the number of fish grew rapidly. By the end of the nineties, round goby became a dominant fish in shallow waters of the western part of the Gulf of Gdansk, where the fish used all solid substrates on the bottom, including concrete piers, big stones or even dumped waste for spawning and refuge. The presence of round goby in the Vistula Lagoon and shallow waters near Rugia (Western Baltic) was noticed for the first time in 1999. The present state, size and condition of the round goby population in the Gulf of Gdansk led us to predict a continual spread of this species into new regions of the Baltic. In addition, the population of round goby is so large that the species has started playing a part in commercial fishing in the Gulf of Gdansk.     

Local-scale invasion pathways and small founder numbers in introduced Sacramento pikeminnow (Ptychocheilus grandis)

Given the general pattern of invasions with severe ecological consequences commonly resulting from multiple introductions of large numbers of individuals on the intercontinental scale, we explored an example of a highly successful, ecologically significant invader introduced over a short distance, possibly via minimal propagule pressure. The Sacramento pikeminnow (Ptychocheilus grandis) has been introduced to two coastal rivers in northern California where it poses a risk to threatened and endangered fishes. We assayed variation in seven microsatellite loci and one mitochondrial DNA gene to identify the source populations and estimate founder numbers for these introductions. Our analysis suggests that successful invasion of the Eel River was likely the result of a single transfer of 3–4 effective founders from nearby within the species’ native range: Clear Lake or its outflow Cache Creek. The other introduced population (Elk River), known from only seven individuals, likely represents secondary expansion from the introduced Eel River population. Our findings highlight the threat posed by close-range invaders and the ability of some fishes to rapidly invade ecologically suitable areas despite small effective founding numbers.     

Invasion genetics of a freshwater mussel (Dreissena rostriformis bugensis) in eastern Europe: high gene flow and multiple introductions

In recent years, the quagga mussel, Dreissena rostriformis bugensis, native to the Dnieper and Bug Limans of the northern Black Sea, has been dispersed by human activities across the basin, throughout much of the Volga River system, and to the Laurentian Great Lakes. We used six published microsatellite markers to survey populations throughout its native and introduced range to identify relationships among potential source populations and introduced ones. Mussels from 12 sites in Eurasia, including the central Caspian Sea and one in North America (Lake Erie), were sampled. Field surveys in the Volga River basin suggested that the species first colonized the middle reach of the river near Kubyshev Reservoir, and thereafter spread both upstream and downstream. Evidence of considerable gene flow among populations was observed and genetic diversity was consistent with a larger, metapopulation that has not experienced bottlenecks or founder effects. We propose that high gene flow, possibly due to multiple invasions, has facilitated establishment of quagga mussel populations in the Volga River system. The Caspian Sea population (D. rostriformis rostriformis (=distincta)) was genetically more distinct than other populations, a finding that may be related to habitat differences. The geographical pattern of genetic divergence is not characteristic of isolation-by-distance but, rather, of long-distance dispersal, most likely mediated by commercial ships' ballast water transfer.     

Competitive interactions for food resources between invasive racer goby Babka gymnotrachelus and native European bullhead Cottus gobio

Racer goby is one of several Ponto–Caspian gobiids spreading throughout European rivers and concurrent with recent declines in threatened populations of a native species of similar biology, the European bullhead. Although suggestive of competitive interactions, evidence thereof is scarce, so we examined behavioural interactions between racer goby and bullhead (single specimens of each species together, also pairs of each species) under experimental conditions (shared space with two shelters) to determine whether the invader displaces the native species when food resources are limited. Food (live chironomids) was added to a single feeder at rates below satiation levels twice over 24 h (once in light and once in darkness), with fish behaviour (aggressive interactions: attacks and threatening) and feeding activity (time spent near or inside the feeder) recorded using video cameras and infrared illumination. Racer goby exhibited aggressive behaviour towards bullhead (mean = 2.5 aggressive events h^?1), but rarely the inverse (threatening only, mean = 0.05 events h^?1), significantly limiting bullhead foraging time (by 62 %) and being faster to reach food in the feeding time in 76 % of cases. Gobies were more aggressive during daylight (77 % of all aggressive events occurring in light), and both species spent more time on feeding activities in darkness (88 and 66 % of all time spent in the feeder by bullheads and gobies, respectively). However, the adverse impact of goby on bullhead was independent of light conditions. Our results suggest that under natural conditions, racer goby are likely to displace bullhead during feeding, with potential consequences for foraging efficiency.     

Invasion Genetics of Ponto-Caspian Gobies in the Great Lakes: A ‘Cryptic’ Species, Absence of Founder Effects, and Comparative Risk Analysis

Genetic variability and structure of nonindigenous vs native populations are compared for the Eurasian round goby Neogobius melanostomus and the tubenose goby Proterorhinus marmoratus, which both invaded Lake St. Clair of the North American Great Lakes about 1990. The round goby spread rapidly to all of the Great Lakes and the tubenose goby largely has been restricted to Lake St. Clair, with some recent range extension into western Lake Erie. Risk analyses may indicate whether genetic variability of colonizers is predictive of their relative invasive and establishment successes. The present investigation examined DNA sequence variation across the left domain of the mitochondrial DNA cytochrome b gene in round and tubenose gobies from Eurasian and Great Lakes locations. We also sequenced six additional Neogobius species (including the monkey N.␣fluviatilis, racer N. gymnotrachelus, and bigheadN. kessleri gobies that have been ‘on the move’ in Europe) and the knout goby Mesogobius batrachocephalus from the Black Sea in order to develop diagnostic genetic characters to identify them in case of future and/or undetected invasions and to delineate their phylogenetic relationships. Results show that a diverse number of haplotypes characterize round and tubenose goby populations from both North America and Eurasian sites, fitting a risk analysis prediction of high genetic variability in their successful introductions. Phylogenetic results indicate that the current genus Neogobius is paraphyletic and that the subgenusApollonia thus should be elevated to the level of genus, containingApollonia (N.) melanostomus (the round goby) andA. (N.) fluviatilis (the monkey goby). In addition, there appear to be two separate species of Proterorhinus marmoratus, a marine P. marmoratus Pallas 1814 in the Black Sea (matching the original type locality), and a ‘cryptic’ freshwater species in the Danube and Dnieper Rivers and probably other Eurasian freshwater habitats, as well as invasive in the Great Lakes. We suggest resurrecting the name P. semilunaris Heckel 1837 for the freshwater species (a taxon that was originally described from rivers draining into the Aegean Sea and the Danube River, but was later placed in synonymy with P. marmoratus). An erratum to this article is available at .     

Invasion genetics of the Eurasian round goby in North America: tracing sources and spread patterns

The Eurasian round goby Neogobius melanostomus ( Apollonia melanostoma ) invaded the North American Great Lakes in 1990 through ballast water, spread rapidly, and now is widely distributed and moving through adjacent tributaries. We analyse its genetic diversity and divergence patterns among 25 North American ( N  = 744) and 22 Eurasian ( N  = 414) locations using mitochondrial DNA cytochrome b gene sequences and seven nuclear microsatellite loci in order to: (i) identify the invasion's founding source(s), (ii) test for founder effects, (iii) evaluate whether the invasive range is genetically heterogeneous, and (iv) determine whether fringe and central areas differ in genetic diversity. Tests include F _ST analogues, neighbour-joining trees, haplotype networks, Bayesian assignment, Monmonier barrier analysis, and three-dimensional factorial correspondence analysis. We recovered 13 cytochrome b haplotypes and 232 microsatellite alleles in North America and compared these to variation we previously described across Eurasia. Results show: (i) the southern Dnieper River population was the primary Eurasian donor source for the round goby's invasion of North America, likely supplemented by some alleles from the Dniester and Southern Bug rivers, (ii) the overall invasion has high genetic diversity and experienced no founder effect, (iii) there is significant genetic structuring across North America, and (iv) some expansion areas show reduced numbers of alleles, whereas others appear to reflect secondary colonization. Sampling sites in Lake Huron's Saginaw Bay and Lake Ontario significantly differ from all others, having unique alleles that apparently originated from separate introductions. Substantial genetic variation, multiple founding sources, large number of propagules, and population structure thus likely aided the goby's ecological success.     

Relative abundance of Ponto‐Caspian gobiids in the lower Vistula River (Poland) 3‐ to 4 years after first appearance

In the years 2000–2001, specimens of two Ponto‐Caspian gobiids (racer goby Neogobius gymnotrachelus and monkey goby Apollonia fluviatilis) were recorded for the first time in the lower Vistula River, which is a part of the central inland corridor used by Ponto‐Caspian species to migrate in Europe. In 2004, seine net surveys were made in the river course to examine relative abundance of the non‐indigenous gobiids in the local small‐fish community. Altogether 4420 specimens with total lengths ranging from 10 to 340 mm (mostly <100 mm) belonging to 18 species were recorded in 70 hauls. Monkey goby was one of the subdominant species (18.1% of total number of fish captured; 64.3% frequency of occurrence in hauls) together with bleak Alburnus alburnus (21.0, 54.3), roach Rutilus rutilus (18.2, 67.1) and three‐spined stickleback Gasterosteus aculaetus (17.3, 37.1). Racer goby was less abundant but quite common (2.5, 32.9), similar to common bream/white bream Abramis brama/Blicca bjoerkna (6.4, 47.1), Eurasian perch Perca fluviatilis (5.7, 57.1), dace Leuciscus leuciscus (4.2, 40.0) and European bitterling Rhodeus sericeus amarus (3.4, 27.1). The study shows that Ponto‐Caspian gobiids dispersed successfully in the lower Vistula, becoming species common to its nearshore zone 3‐ to 4 years after their first appearance.     

Invasive species are less parasitized than native competitors, but for how long? The case of the round goby in the Great Lakes-St. Lawrence Basin

There is increasing evidence that parasitism represents an unpredictable dimension of the ecological impacts of biological invasions. In addition to the risk of exotic pathogen transmission, other mechanisms such as parasite-release, could contribute to shaping the relationship between introduced species and native communities. In this study, we used the Eurasian round goby (Neogobius menalostomus) in the Great Lakes-St. Lawrence River ecosystem to further explore these ideas. As predicted by the parasite-release hypothesis, recently established populations of round goby were parasitized by a depauperate community of generalist helminths (8 taxa), all commonly found in the St. Lawrence River. In comparison, two native species, the logperch (Percina caprodes) and spottail shiner (Notropis hudsonius), were the hosts of 25 and 24 taxa respectively. Round gobies from each of 3 sampled localities were also less heavily infected than both indigenous species. This is in contrast to what is observed in round goby’s native range where the species is often the most parasitized among gobid competitors. This relative difference in parasite pressure could enhance its competitiveness in the introduced range. However, our study of an older population of round goby in Lake St. Clair suggests that this advantage over native species could be of short duration. Within 15 years, the parasite abundance and richness in the round goby has more than doubled whereas the number of parasite species per fish has increased to levels of those typical of fish indigenous to the St. Lawrence-Great Lakes watershed.     

Historic speciation and recent colonization of Eurasian monkey gobies (Neogobius fluviatilis and N. pallasi) revealed by DNA sequences,microsatellites, and morphology

Aim Hidden diversity within an invasive ‘species’ can mask both invasion pathways and confound management goals. We assessed taxonomic status and population structure of the monkey goby Neogobius fluviatilis across Eurasia, comparing genetic variation across its native and invasive ranges. Location Native populations were analysed within the Black and Caspian Sea basins, including major river drainages (Dnieper, Dniester, Danube, Don and Volga rivers), along with introduced locations within the upper Danube and Vistula river systems. Methods DNA sequences and 10 nuclear microsatellite loci were analysed to test genetic diversity and divergence patterns of native and introduced populations; phylogenetic analysis of mtDNA cytochrome b and nuclear RAG‐1 sequences assessed taxonomic status of Black and Caspian Sea lineages. Multivariate analysis of morphology was used to corroborate phylogenetic patterns. Population genetic structure within each basin was evaluated with mtDNA and microsatellite data using F_ST analogues and Bayesian assignment tests. Results Phylogenetic analysis of mitochondrial and nuclear sequences discerned a pronounced genetic break between monkey gobies in the Black and Caspian Seas, indicating a long‐term species‐level separation dating to c. 3 million years. This pronounced separation further was confirmed from morphological and population genetic divergence. Bayesian inference showed congruent patterns of population structure within the Black Sea basin. Introduced populations in the Danube and Vistula River basins traced to north‐west Black Sea origins, a genetic expansion pattern matching that of other introduced Ponto‐Caspian gobiids. Main conclusions Both genetic and morphological data strongly supported two species of monkey gobies that were formerly identified as subspecies: N. fluviatilis in the Black Sea basin, Don and Volga Rivers, and the Kumo‐Manych Depression, and Neogobius pallasi in the Caspian Sea and Volga River delta. Genetic origins of introduced N. fluviatilis populations indicated a common invasion pathway shared with other introduced Ponto‐Caspian fishes and invertebrates.     

Parasite fauna of native and non‐native populations of Neogobius melanostomus (Pallas, 1814) (Gobiidae) in the longitudinal profile of the Danube River

Parasite fauna of round goby Neogobius melanostomus (Pallas, 1814) in the Danube River was investigated in both its native range (two sites in the Bulgarian stretch of the Danube) and non‐native range of distribution (Croatian, Slovak and Austrian stretches) during 2005 and 2006. The aim was to identify possible changes in parasite communities associated with the introduction of a host into the new environment. A total of 29 metazoan parasite species were found to parasitize round goby in the Danube River; twelve of these parasite species were found in both the native and non‐native range of distribution. Introduction of a novel parasite species to the non‐native range via the round goby was not found. Eight parasite species occurred only in the native range and nine species only in the non‐native range of the round goby distribution. Losses of native parasite species in non‐native round goby populations and/or acquiring of novel parasite species in a new environment were not significant. Thirteen parasite taxa were recorded for the first time in round gobies. Three parasite taxa (Diplostomum spp., Pomphorhynchus laevis and Raphidascaris acus) were found in high prevalence and abundance at each sampling site in both the native and non‐native range. Parasite species diversity was assessed for each sampling site and season using three diversity indices (the Shannon, Simpson and Equitability indices), with the highest same‐season values found in a non‐native site in Slovakia (1.38, 0.69 and 0.60, respectively) and the lowest in a native site in Bulgaria (0.28, 0.12 and 0.14, respectively). Species diversity was higher in both non‐native round goby populations (Slovak and Austrian) compared to native Bulgarian populations. However, diversity indices values varied among almost all sampling sites.     

Invasion phylogeography of the Ponto-Caspian crustacean Limnomysis benedeni dispersing across Europe

Aim  Limnomysis benedeni Czerniavsky, 1882 is a mysid crustacean native to the Ponto-Caspian (Black and Caspian Sea) rivers and estuaries, and has recently spread across Europe through intentional and unintentional introductions. We explored the structuring of genetic variation in native and non-native populations with an aim to trace the sources of the invasions, and to infer whether the spread has occurred through a single or multiple invasion waves.
Location  Native estuaries in the Ponto-Caspian basin (Volga, Don, Dnieper, Dniester, Danube) and the recently colonized range along the Danube–Rhine river systems and Lithuania.
Methods  A fragment of the mitochondrial COI gene was sequenced to assess genetic affinities and diversity in native and recently established populations.
Results  The genetic diversity in the native regions is organized into several strongly diverged haplotype groups or lineages, partly allopatric, partly sympatric. All these lineages have also spread beyond the native range. Even the recent rapid dispersal across Europe along the Danube–Rhine system towards the North Sea basin involved several lineages from the Danube delta sector. The structuring of genetic diversity among invaded sites suggests multiple invasion events to the Danube–Rhine drainage. This contrasts with data from some other Ponto-Caspian species, where a single haplotype seems to have occupied most invaded areas. There is no evidence that intentionally stocked reservoirs in the Baltic Sea basin would have contributed to further unintentional spread of L. benedeni.
Main conclusions  Limnomysis benedeni is spreading across Europe using the southern invasion corridor. The invasion most likely involved several waves from differentiated sources in the native Danube delta area.     

Genetic patterns across an invasion's history: a test of change versus stasis for the Eurasian round goby in North America

Biological invasions comprise accidental evolutionary experiments, whose genetic compositions underlie relative success, spread and persistence in new habitats. However, little is known about whether, or how, their population genetic patterns change temporally and/or spatially across the invasion's history. Theory predicts that most would undergo founder effect, exhibit low genetic divergence across the new range and gain variation over time via new arriving propagules. To test these predictions, we analyse population genetic diversity and divergence patterns of the Eurasian round goby Neogobius melanostomus across the two decades of its North American invasion in the Laurentian Great Lakes, comparing results from 13 nuclear DNA microsatellite loci and mitochondrial DNA cytochrome b sequences. We test whether ‘genetic stasis’, ‘genetic replacement’ and/or ‘genetic supplement’ scenarios have occurred at the invasion's core and expansion sites, in comparison with its primary native source population in the Dnieper River, Black Sea. Results reveal pronounced genetic divergence across the exotic range, with population areas remaining genetically distinct and statistically consistent across two decades, supporting ‘genetic stasis’ and ‘founder takes most’. The original genotypes continue to predominate, whose high population growth likely outpaced the relative success of later arrivals. The original invasion core has stayed the most similar to the native source. Secondary expansion sites indicate slight allelic composition convergence towards the core population over time, attributable to some early ‘genetic supplementation’. The geographic and temporal coverage of this investigation offers a rare opportunity to discern population dynamics over time and space in context of invasion genetic theory vs. reality.     

Microsatellite loci for Ponto-Caspian gobies: markers for assessing exotic invasions

We developed and tested eight polymorphic microsatellite loci for Ponto‐Caspian ‘neogobiin’ gobies, many of which are invasive in Eurasia and North America, whose study will aid understanding of the population genetics underlying their success. We tested samples from one to two locations from 12 taxa in the recently revised genera Babka, Benthophilus, Mesogobius, Neogobius = Apollonia, Ponticola and Proterorhinus; including the bighead, Caspian, knout, monkey, racer, round, tadpole and tubenose gobies; and taxa from introduced vs. native populations, those diverging between fresh and marine waters, and those differentiated between the Black and Caspian Seas. Populations conformed to Hardy–Weinberg equilibrium expectations, averaging five to 15 alleles per locus and 0.11 to 0.67 mean heterozygosity. Allelic variation significantly differentiated among all taxa and populations.