Identification of the resting cyst of Cochlodinium polykrikoides Margalef (Dinophyceae,Gymnodiniales) in Korean coastal sediments

This study provides the first morphological features of resting cysts of Cochlodinium polykrikoides collected from Korean coastal sediments. Evidence for the existence of resting cysts of C. polykrikoides is based on the morphological and molecular phylogenetic data of the germinated cells and a resting cyst. The morphology of the resting cysts differed from that reported previously in sediments and culture experiments. The distinct feature is that the cyst body was covered by the reticulate ornaments and spines.     

Intra-specific variability in the thirteen known populations of the fairy shrimp Chirocephalus ruffoi (Crustacea: Anostraca): resting egg morphometrics and mitochondrial DNA reveal decoupled patterns of deep divergence

Chirocephalus ruffoi is a fairy shrimp endemic to the Italian peninsula, where it is known only from thirteen high mountain locations. Twelve of these are in the Northern Apennines while the thirteenth is about 700 km away in the Calabrian Apennines (Southern Italy). We quantified degree of genetic divergence within the species by sequencing a fragment of the mitochondrial DNA encoding for Cytochrome Oxidase I. We then combined genetic data with the re-analysis of two different datasets on the morphometrics of the resting eggs (cysts) produced by the species as an adaptation to survive seasonal droughts. Genetic data revealed profound divergence; we identified four clusters of haplotypes within the species phylogeography, three in the Northern Apennines and one in the Calabrian Apennines with most of the genetic variation (≈70%) being apportioned among haplogroups. We found high variability in cyst morphometrics, especially in cyst size and height of the spines ornamenting the surface. Genetic and morphometric data are decoupled suggesting that cyst morphology is either under selection or a plastic trait. We, therefore, caution against using cyst morphology for taxonomic purposes in anostracans.     

Genetic, morphological, and ecological diversity of spatially separated clones of Meseres corlissi Petz & Foissner, 1992 (Ciliophora, Spirotrichea)

ABSTRACT. We investigated the intraspecific variation of the spirotrich freshwater ciliate Meseres corlissi at the level of genes (SSrDNA, ITS), morphology (14 characters), and ecophysiology (response to temperature and pH). Five of the eight clonal M. corlissi cultures isolated from five localities on four continents were studied at all levels. The null hypothesis was that geographic distance plays no role: M. corlissi lacks biogeography. The intraspecific variation was low at the genetic level (0%–4%), moderate at the morphological level (5%–15%), and high at the ecophysiological level (10%–100%). One clone, isolated from subtropical China, differed significantly at all levels from all other clones, suggesting limited dispersal and local adaptation among M. corlissi . However, other clones from distant areas, such as Australia and Austria, were genetically identical and differed only slightly in morphology and temperature response. We speculate that our findings may be typical for rare species; the chances may be equally high for both global dispersal of most and local adaptation of some populations in areas where dispersal has been permanently or temporarily reduced.     

Associations between physical isolation and geographical variation within three species of Neotropical birds

We studied effects of physical isolation on geographical variation in mtDNA RFLP polymorphisms and a suite of morphological characters within three species of neotropical forest birds; the crimson-backed tanager Ramphocelus dimidiatus, the blue-gray tanager Thraupis episcopus, and the streaked saltator Saltator albicollis. Variation among populations within continuous habitat on the Isthmus of Panama was compared with that among island populations isolated for about 10000 years. Putative barriers to dispersal were influential, but apparent isolation effects varied by species, geographical scale, and whether molecular or morphological traits were being assessed. We found no geographical structuring among the contiguous, mainland sampling sites. Migration rates among the islands appeared sufficient to maintain homogeneity in mtDNA haplotype frequencies. In contrast, variation in external morphology among islands was significant within two of three species. For all species, we found significant variation in genetic and morphological traits between the island (collectively) and mainland populations. Interspecific variation in the effects of isolation was likely related to differential vagility. These data generally corroborate other studies reporting relatively great geographical structuring within tropical birds over short distances. Behaviourally based traits - low vagility and high ‘sensitivity’ to geographical barriers - may underlie extensive diversification within neotropical forest birds, but more extensive ecological and phylogeographic information are needed on a diverse sample of species.     

Morphological features and viability of Scrippsiella trochoidea cysts isolated from fecal pellets of the polychaete Capitella sp.

To investigate the impact of grazing by the polychaete Capitella sp. on the two cyst morphotypes of Scrippsiella trochoidea, the typical morphotype with short calcareous spines (spiny-type cyst) and artificially induced the transparent type without calcareous spines (naked-type cyst), we examined the morphological features and germination capability of the two cyst morphotypes isolated from fecal pellets of the polychaete Capitella sp. produced in a restricted habitat. The morphological destruction was observed in both spiny- and naked type cysts after passage through the gut of Capitella sp., and this seemed to occur rapidly for naked-type cysts. In addition, the germination of both spiny- and naked-type cysts isolated from fecal pellets on day 2 of harvesting was significantly reduced and subsequently completely abolished, in contrast to previous findings from ingestion studies. Our results indicate that continual grazing by Capitella sp. within a restricted habitat can compromise the survival of S. trochoidea cysts.     

Protoperidinium tricingulatum sp. nov. (Dinophyceae), a new motile form of a round,brown, and spiny dinoflagellate cyst

A small, broadly ovoidal and heterotrophic dinoflagellate containing round, brownish, and spiny cyst was found in the water column of Huibertsplaat in the Wadden Sea off the coast of the Netherlands. This dinoflagellate had these conspicuous morphological characters: a five‐sided first apical plate (1′), only three cingular plates, and an extremely small first antapical plate. Based on these morphological features, Protoperidinium tricingulatum Kawami, vanWezel, Koeman et Matsuoka is described as a new species. The flagellar pore of P. tricingulatum is covered with a small fin, which rises from the left side of the right sulcal plate to the large V‐shaped posterior sulcal plate. This feature suggests that P. tricingulatum is assigned to the Abé's Monovela Group. The cyst stage of P. tricingulatum was positively linked to the vegetative stage by comparison of the ribosomal 5.8S rDNA, internal transcribed spacers (ITS1 and ITS2). Living cysts of P. tricingulatum are round, brownish, and covered with many slender spines bearing capitate or cauliforate distal ends. The cyst also possesses a theropylic archeopyle formed by a slit corresponding to parasutures between three apical and two apical intercaraly plates. These morphological characters indicate that this species is morphologically related to two dinoflagellate cyst‐genera Islandinium and Echinidinium.     

Incongruent phylogeographies in spite of similar morphology, ecology, and distribution:Phippsia algida andP. concinna (Poaceae) in the North Atlantic region

Phylogeographic and taxonomic relationships among 54 North Atlantic populations of the snowbed grass genusPhippsia were investigated based on isozymes and genetically based morphological variation. The results support recognition of two distinct species,P. algida andP. concinna, the latter with at least two subspecies. Both of these self-fertilizing arctic pioneer species were genetic allotetraploids almost without intrapopulational variation. The two species showed strikingly different phylogeographies in the North Atlantic region in spite of their similarity in morphology, habitat ecology, mating system, and dispersal ecology, and in spite of their present cooccurrence in many geographic areas, sometimes even in the same snowbeds. The same electrophoretic multilocus phenotype was observed in all populations ofP. algida, and although this species showed considerable morphological variation, the variation was unstructured geographically. Thus,P. algida showed a pattern similar to other arctic species investigated in the North Atlantic region; it has probably dispersed postglacially across the sea barriers among Greenland, Svalbard, Iceland, and Scandinavia. In contrast,P. concinna was virtually fixed for different multilocus phenotypes in the three main geographic areas analyzed (S Norway, Svalbard, Greenland), corresponding to fairly distinct divergence in morphology. This pattern suggests absence of postglacial among-area dispersal ofP. concinna in spite of all of its similarities with its congener; it may have immigrated to the North Atlantic from different source areas and/or survived the last glaciationin situ.     

Penile Morphology and Classification of Bush Babies (Subfamily Galagoninae)

The penile morphologies of nocturnal prosimians are complex and vary considerably between genera and species. Accordingly, comparative morphology can be useful in taxonomic studies, particularly when assessing the status of newly discovered species. I measured features of penile morphology—surface area of the glans penis; shape and size of the keratinized spines on the glans—for populations representing 14 species within the subfamily Galagoninae. Intraspecific variations in penile morphology were relatively minor. By contrast, there are significant differences in several morphological features among closely related, sympatric species, e.g., in the greater bush babies (Otolemur crassicaudatus and O. garnettii) and lesser bush babies (Galago senegalensis and Galago moholi). Assessment of glans area resulted in the recognition of a second needle-clawed form: Euoticus pallidus. Similar divisions exist in the dwarf and greater bush babies with respect to proportional spiny area and characteristics of spine size. I constructed a key based on the presence/absence of certain features—penile spines, dermal markings on the glans, penile lappets—as well as the shape of the baculum and possession of different spinal morphotypes. This key may be used to identify all 14 species of bush babies. Penile morphologies provide a useful guide to specific identity in the Galagoninae, which may be true also for other groups of nocturnal mammals.     

POSTGLACIAL RANGE FLUCTUATION,GENETIC SUBDIVISION AND SPECIATION IN THE WESTERN NORTH AMERICAN SPOTTED FROG COMPLEX,RANA PRETIOSA

The western North American complex of spotted frogs (Rana pretiosa) exhibits isolation-by-distance, genetic subdivision, and speciation in association with its extensive northward range shift in postglacial times. The southern relict populations of R. pretiosa species B existing at high altitudes or in desert springs have been subjected to restricted gene flow, high inbreeding, and bottlenecks to produce significant between-population genetic diversity. The more recently established northern populations, however, show genetic uniformity and isolation-by-distance, as estimated using Slatkin's (1993) statistic M?. Middle latitude populations have higher heterozygosities than populations at either extreme. Fixed differences in allozyme variation separate 21 populations of species B from five populations of R. pretiosa species A found in southwest Washington State and the Cascades Mountains of Oregon. Morphological variation of 20 metric characters among 38 samples, examined using multiple discriminant function analysis, could partially resolve partitioning among populations but specimens from the vicinity of the type series of R. p. pretiosa could not be assigned to either species A or species B. Speciation in these frogs may not be correlated with morphological evolution since comparatively neutral allozyme changes may be established more rapidly than changes in morphology.     

Body size variation and caste ratios in geographically distinct populations of the invasive big‐headed ant,Pheidole megacephala (Hymenoptera: Formicidae)

Body size is an important life history trait that can evolve rapidly as a result of how species interact with each other and their environment. Invasive species often encounter vastly different ecological conditions throughout their introduced range that can influence relative investment in growth, reproduction and defence among populations. In this study, we quantified variation in worker size, morphology and proportion of majors among five populations of a worldwide invasive species, the big‐headed ant, Pheidole megacephala (Fabricius). The sampled populations differed in ant community composition, allowing us to examine if P. megacephala invests differently in the size and number of majors based on the local ant fauna. We also used genetic data to determine if these populations of P. megacephala represented cryptic species or if morphological differences could be attributed to change following introduction. We found significant variation in worker mass among the populations. Both major and minor workers were largest in Australia, where the ant fauna was most diverse, and minor workers were smallest in Hawaii and Mauritius, where P. megacephala interacted with few to no other ants. We also found differences in major and minor worker morphology among populations. Majors from Mauritius had significantly larger heads (width and length) relative to whole body size than those from Hawaii and Florida. Minors had longer heads and hind tibias in South Africa compared with populations from Australia, Hawaii and Florida. The proportion of majors did not differ among populations, suggesting that these populations may not be subject to trade‐offs in investment in major size versus number. Our molecular data place all samples within the same clade, supporting that these morphologically different populations represent the same species. These results suggest that the variation in shape and morphology of major and minor workers may therefore be the result of rapid adaptation or plastic responses to local conditions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 423–438.     

Spatial patterns of variation in color and spine shape in the sea urchin Heliocidaris erythrogramma

Abstract. Here we report on the first quantitative survey of morphological variation in the sea urchin Heliocidaris erythrogramma within Western Australia and distinguish between two subspecies found to co‐occur in this region. We surveyed urchins at multiple spatial scales along the Western Australian coastline to assess variation in dermis and spine color and, using landmark‐based geometric morphometrics, spine morphology. Both color and morphology proved to be useful for separating subspecies within Western Australia. There were four major color morphs: red dermis/violet spines (56%), red/violet‐green (23%), red/green (7%), and white/green (10%). Members of the first two color morphs had bulbous spines with wide, flattened tips, a morphology that is unique to Western Australia and characteristic of H. e. armigera, and members of the latter two consistently exhibited the narrow, pointed spines typical of specimens of H. e. erythrogramma, which has a broader distribution. In Western Australia, H. e. armigera was relatively abundant both within and among sites, but H. e. erythrogramma was found only in a few localized patches. Shifts in the relative abundance of these two subspecies occurred at fine spatial scales (<5 km), although environmental correlates of these transitions were unclear. Contrary to expectations, neither dermis color nor spine morphology varied with relative wave exposure: individuals with a red dermis or thickened spine morphology occurred at most sites regardless of exposure, and while white dermis and thinner spines only occurred at high‐exposure sites, these features were not common across the majority of exposed sites. Both color morph frequencies and spine morphology remained stable within sites over the 3‐year duration of this study. While the ecological significance of this morphological variation remains unclear, the consistency of the association between color and spine morphology, occurring across fine spatial scales, suggests that strong environmental or genetic factors are involved in maintaining morphological differentiation between these two subspecies.     

Maternal age and spine development in the rotifer Brachionus calyciflorus: increase of spine length with birth orders1

1. Maternal effects have long been known to influence phenotypic plasticity in rotifers. Females in Brachionus calyciflorus and several other species produce long‐spined offspring when the predatory rotifer Asplanchna is present; B. calyciflorus also develops short spines when food concentrations are low. These spines protect against predation and decrease food threshold concentrations. 2. Some strains of B. calyciflorus develop long spines even in the absence of Asplanchna and other environmental stimuli. We demonstrate in this study that spine length in such cases is dependent on the age of the mother. 3. In strains from Florida and Georgia, offspring spine length increased significantly with birth order, sometimes to lengths formerly observed only in the presence of Asplanchna. Significant variation in this trait was found among and within clones of a strain. Offspring body size also increased with maternal age. This is the first time maternal age has been shown to affect rotifer morphology. 4. These birth‐order effects may have important ecological implications and explain phenotypic plasticity and polymorphism in body size and spine length in populations when predators are absent and food concentrations are high. They may be a bet‐hedging mechanism to assure adaptation to rapid changes in predation pressure or food conditions.     

Morphological and Biochemical Correlates in the Characterization of Sarcocystis spp.1

ABSTRACT. Isoenzyme electrophoretic techniques were applied to the characterization of seven Sarcocystis spp. that had been identified by conventional morphological studies. Cystozoites were harvested from macroscopic cysts from sheep, cattle, and mice and from microscopic cysts from sheep, cattle, and goats. Soluble cystozoite extracts were subjected to cellulose acetate gel electrophoresis and characterized at 15 of the 39 enzyme loci examined. Genetic relationships among isolates were examined by simple phenetic clustering. Two different morphological types of macroscopic cysts from sheep, identified as S. gigantea (syn. S. ovifelis) and S. medusiformis, consistently differed at 40% of the loci examined. Such genetic divergence confirms their separate morphotypic classification. Both differed from microscopic cyst isolates from sheep at 87% of the loci examined; however, two different morphotypes of microscopic cysts were found in the sheep sampled (thick-walled and thin-walled cysts). Until sufficient numbers of each type can be isolated and examined separately, both were regarded as belonging to the species S. tenella (syn. S. ovicanis). Macroscopic and microscopic cysts from cattle consistently differed at 80% of the loci thereby supporting their separate classification as S. hirsuta (syn. S. bovifelis) and S. cruzi (syn. S. bovicanis), respectively. Isolates from goats (microscopic cysts identified as S. capracanis) differed from S. tenella and S. cruzi at 20% and 47% of the loci, respectively. All macroscopic cyst isolates from the various host animal species (including S. muris from mice) differed from each other at nearly all loci. Isoenzyme electrophoretic techniques therefore provided genetic evidence supporting the classification of these various Sarcocystis spp. by their morphological characteristics.     

Vocalizations and morphology: interpreting the divergence among populations of Chough Pyrrhocorax pyrrhocorax and Alpine Chough P. graculus

Capsule Differences in vocalizations among populations are mostly explained on morphological bases, but historical factors may have played a significant role in differentiation processes.

Aims To investigate the relationships among vocal and morphological variation in two corvids: Chough and Alpine Chough.

Methods We used data from 11 populations of Chough and seven populations of Alpine Chough spanning the Palearctic distribution of the two species. Three data sets (morphometry, spectrotemporal parameters of trill calls and acoustic repertoire) were analysed and their variation compared with uni- and multivariate techniques.

Results In both species, morphological differences among populations were correlated to spectro-temporal variation of trills; in particular, frequencies of calls were negatively correlated to wing length (an indicator of body size). By considering only co-existing populations of the two species, the magnitude of morphological and spectrotemporal divergence was similar.

Conclusions In both species, birds from populations with similar morphology uttered similar call types and trills with close spectrotemporal features. In particular, larger-sized populations, as expressed by wing length, emitted lower pitched calls. However, the fact that dissimilarities in repertoire and morphology were correlated cannot be explained only by appealing to functional explanations, as the observed intraspecific morphological variability does not seem to be high enough to promote consistent changes in the pool of calls. In this case, historical factors might have contributed to the present pattern of differentiation.     

CYST–THECA RELATIONSHIP,LIFE CYCLE,AND EFFECTS OF TEMPERATURE AND SALINITY ON THE CYST MORPHOLOGY OF GONYAULAX BALTICA SP. NOV. (DINOPHYCEAE) FROM THE BALTIC SEA AREA1

A new species of Gonyaulax, here named Gonyaulax baltica sp. nov., has been isolated from sediment samples from the southeastern Baltic. Culture strains were established from individually isolated cysts, and cyst formation was induced in a nitrogen‐depleted medium. Although G. baltica cysts are similar to some forms attributed to Spiniferites bulloideus and the motile stage of G. baltica has affinities with G. spinifera, the combination of features of cyst and motile stage of G. baltica is unique. The culture strains were able to grow at salinity levels from 5 to 55 psu and formed cysts from 10 to 50 psu. Cultures at each salinity level were grown at 12, 16, and 20° C. Temperature‐ and salinity‐controlled morphological variability was found in the resting cysts. Central body size varied with temperature and salinity, and process length varied with salinity. Cysts that formed at extreme salinity levels displayed lower average process length than cysts formed at intermediate salinity levels, and central body length and width were lowest at higher temperature and lower salinity. Models for the relationship between central body size and temperature/salinity and process length and salinity have been developed and may be used to determine relative paleosalinity and paleotemperature levels. Our results on salinity‐dependent process length confirm earlier reports on short‐spined cysts of this species found in low salinity environments, and the model makes it possible to attempt to quantify past salinity levels.     

Population dynamics of galeate acritarchs at the Cambrian–Ordovician transition in the Algerian Sahara

Galeate acritarchs are a major component of Late Cambrian and Early Ordovician palynological assemblages. The populations of galeate acritarchs from the Cambrian–Ordovician transition section in borehole Nl-2 of the Algerian Sahara show a gradual increase in process length and in complexity of the process structures through the succession. While the number of striate elements at the process base, the number of distal ramifications, and the number of membranes between the processes increases progressively, the central body diameter shows only minor variation within the succession. The galeate acritarchs are here interpreted as probably being resting cysts of a microorganism similar to modern dinoflagellates. Published laboratory culture experiments on living dinoflagellates document a considerable morphological variation with respect to the process morphology of the resting cysts that can be produced by a single biologically defined species. Based on these experiments, it is possible to interpret the morphological changes in the galeate acritarchs as being possibly related to changing ecological conditions. By analogy to the cyst distribution of modern dinoflagellates, changing salinity may have played an important role. Depending on environmental parameters, and perhaps on the maturity attained before rupture of the outer membrane during cyst formation, the galeate acritarchs may show a wide variety of process morphologies that have to date been used to describe four genera (morphogenera) and 84 species (morphospecies).     

NATURAL SELECTION ON HYDROID COLONY MORPHOLOGY BY INTRASPECIFIC COMPETITION

Previous work on colonial hydroids in the genus Hydractinia has demonstrated that colony morphology is highly variable and determines intraspecific competitive ability. Competitive encounters are known to be common in nature, suggesting that intraspecific competition may be a major selective force acting on morphological variation. A replicated common garden experiment demonstrated a genetic basis to morphological variation and two data sets provided correlative support for the hypothesis of selection by intraspecific competition. First, morphologies inferior in competitive ability were less abundant in two adult, postcompetition, samples than in juvenile, precompetition, samples from the same populations. Second, among eight populations, the relative frequency of different morphologies was correlated with the frequency of intraspecific competition observed in each population. The direction of selection by competition on the morphological variation present in this species conflicts with recent predictions based on surveys across diverse taxa, suggesting limitations to the inference of competition as a past selective agent on the basis of present day correlations among species.     

Subspecies delineation amid phenotypic,geographic and genetic discordance in a songbird

Understanding the processes that drive divergence within and among species is a long‐standing goal in evolutionary biology. Traditional approaches to assessing differentiation rely on phenotypes to identify intra‐ and interspecific variation, but many species express subtle morphological gradients in which boundaries among forms are unclear. This intraspecific variation may be driven by differential adaptation to local conditions and may thereby reflect the evolutionary potential within a species. Here, we combine genetic and morphological data to evaluate intraspecific variation within the Nelson's (Ammodramus nelsoni) and salt marsh (Ammodramus caudacutus) sparrow complex, a group with populations that span considerable geographic distributions and a habitat gradient. We evaluated genetic structure among and within five putative subspecies of A. nelsoni and A. caudacutus using a reduced‐representation sequencing approach to generate a panel of 1929 SNPs among 69 individuals. Although we detected morphological differences among some groups, individuals sorted along a continuous phenotypic gradient. In contrast, the genetic data identified three distinct clusters corresponding to populations that inhabit coastal salt marsh, interior freshwater marsh and coastal brackish–water marsh habitats. These patterns support the current species‐level recognition but do not match the subspecies‐level taxonomy within each species—a finding which may have important conservation implications. We identified loci exhibiting patterns of elevated divergence among and within these species, indicating a role for local selective pressures in driving patterns of differentiation across the complex. We conclude that this evidence for adaptive variation among subspecies warrants the consideration of evolutionary potential and genetic novelty when identifying conservation units for this group.     

Cytology of lepidoptera. III. Giant cysts: A morphological trait of apyrene spermatogenesis in an Ephestia kuehniella strain

A comparative investigation of testicular eupyrene cysts (in larvae) and apyrene cysts (in pupae) of Ephestia kuehniella laboratory strains was conducted using light and electron microscopy. Eupyrene cysts in the first meiotic division contained 64 spermatocytes, which showed only moderate asynchrony. In one of the strains, a wild-type strain, L, normal-sized cysts occurred together with abnormally large cysts. These are called giant cysts in this article. One of the premeiotic cysts, early giant cysts, studied in detail, contained approximately a fourfold number of cells compared with the number in a eupyrene cyst of the same stage. In cysts harboring spermatocytes and spermatids, late giant cysts, cell differentiation was highly asynchronous. Failure in one of two control mechanisms in early cyst development may have caused the appearance of the cysts. Control of cell division might have been sloppy in apyrene spermatogonia. Hence, the spermatogonia within the cyst could have passed through additional division cycles. Alternatively, the giant cysts may have originated from more than one predefinitive gonial cell enclosed in a common envelope of sheath cells. As a third possibility, giant cysts could have arisen by fusion of normal cysts at a later stage. In either case, this is evidence that separation of eupyrene and apyrene pathways is earlier than was previously expected. In two other Ephestia strains, apyrene sperm development proceeded without formation of giant cysts. One was a mutant strain, a, and the other one was a recently established wild-type strain, Sbr. Apyrene sperm development is considered an example of degenerate evolution in which enhanced variability between species and even between populations of one species is a common phenomenon.     

Morphological vs. molecular delineation of taxa across montane regions in Europe: the case study of Gammarus balcanicus Schäferna, (Crustacea: Amphipoda)

Mountainous areas are characterized by substantial biodiversity and endemicity due to their complex geological history and habitat fragmentation. Hence, it can be assumed that particularly high species richness can be found in organisms with limited dispersal capabilities that inhabit mountain streams. A number of scientific papers focus on molecular phylogeography or traditional taxonomy of species or species groups inhabiting such habitats. However, there is a lack of studies that integrate morphological and molecular data to identify and delineate cryptic species. For practical reasons, uncovering cryptic diversity is crucial in taxa used in biomonitoring. Distinct species, hard to separate based on morphology only, may have different tolerance ranges towards a variety of factors. Thus, our goal is to combine the two approaches to reveal potential patterns of diversification within a species widely distributed across European mountains: the amphipod crustacean Gammarus balcanicus. The data were obtained from 13 populations spread across the range of the species. Individuals were initially ascribed to G. balcanicus based on conventional fauna key morpho‐anatomical diagnostic features and were further analysed for 23 additional features to explore any putative diversification. Morphometric data were analysed with use of the multiple correspondence analysis and anova . Molecular distances were calculated for 551‐bp‐long COI sequences. Test for isolation by distance was performed for both morphological and molecular data. The morphometric studies showed that some of the analysed features differed significantly between populations, although there was only a weak correlation between the morphological divergence and the between‐population geographical distances. Moreover, high morphological diversity was present within sites. A set of 42 COI haplotypes was identified among the 135 individuals sequenced. No haplotype was shared among populations. The molecular p‐distances within the nine localities presenting more than one haplotype were either almost null (ca. <0.003 for 7 localities) or relatively low (ca. 0.01–0.02 for 2 localities). In opposite, the molecular p‐distances between localities were mostly at a high level (94% of pairwise comparisons being >0.14), similar as between other well‐defined species of the genus Gammarus. Surprisingly, G. balcanicus appears to be polyphyletic based on topology of the neighbour‐joining tree. The level of genetic distance between localities was not correlated with their geographical proximity. Globally, combining spatial patterns of morphological versus molecular divergence indicates a high level of cryptic diversity within a species conventionally defined based upon fauna key morphological features. In this context, the name G. balcanicus should be applied only to the population from locus typicus, while the other populations represent a number of putative distinct species. We may expect that such phenomenon would apply also to other animal taxa with conserved morphology, which are widespread over different mountain ranges in Europe.