A new genus and species of long-clawed mouse (Rodentia: Muridae) from temperate rainforests of Chile

Morphological comparisons of long-clawed mice in southern South America reveal the existence of four genera, only three of which are named. The fourth genus is described and compared with Geoxus, Chelemys and Notiomys. External, cranial and dental characters indicate that the new mouse is most closely related to Geoxus , the raton topo or mole mouse. Geoxus and the new form may be distinguished using both qualitative and quantitative characters. The incipient specializations of the new mouse for fossorial life suggest that it represents an early offshoot along the line leading to the more highly specialized Geoxus. Discovery of a new mammalian genus in Chile, where naturalists have been active for more than two centuries, indicates the importance of continued biological surveys, even in ostensibly well-studied regions. The new mouse reinforces the strong differentiation of faunas inhabiting southern beech ( Nothofagus ) forests in South America, where generic endemism of rodents and marsupials reaches 67%.     

The diversification of South American murid rodents: evidence from mitochondrial DNA sequence data for the akodontine tribe

Phylogenetic relationships based on 801 base pairs (bp) of the mitochondrial cytochrome b gene are examined for eight genera and 28 species of the akodontine tribe of South American murid rodents. The akodontine tribe comprises some 35% of the total diversity of the subfamily Sigmodontinae, but the current taxonomy at virtually all levels is uncertain because of inadequate generic diagnoses and assessments of variation and trends in traditional morphological characters. Monophyly of the tribe cannot be resolved by the sequence data, based on comparisons to outgroup taxa in three other tribes (Oryzomyini, Phyllotini, and Thomasomyini). However, highly corroborated monophyletic units within the group are obtained in a variety of both parsimony and distance analyses. These include a redefined and numerically dominant genus Akodon (with Microxus and Hypsimys as synonyms), Bolomys, Lenoxus, Oxymycterus, and a strongly supported assemblage that includes the central Andean Chroeomys and 'Akodon' andinus and the southern Abrothrix, 'Akodon' olivaceus, and the long-clawed mice of the genera Notiomys, Geoxus, and Chelemys. Sequence divergence within species is typically less than 5%, although levels can reach 10% for some highly polytypic forms. Divergence among genera within the tribe reaches 35% in corrected estimates, a level that is as great as that among representatives of different tribes. Changes in the current classification of akodontines are suggested based on these data, and the timing and place of origin of the tribe and its radiation is discussed.     

New studies on allozyme genetic distance and variability in akodontine rodents (Cricetidae) and their systematic implications

Allozyme genetic distance and variability were studied by horizontal starch gel electrophoresis in 11 species of rodents of the tribe Akodontini representing four different genera. One species of the phyllotine Calomys was used as an outgroup for comparisons. Thirty presumptive loci were assessed in a total of 172 specimens. Only three of 30 loci were found to be monomorphic in the whole sample. Levels of polymorphism ( P ) and mean heterozygosity ( H ) were dependent on esterase loci which increase H values by 6.26% on average. Nei's jackknife genetic distances among conspecific populations were found not to differ significantly with geographic distance. Phenetic and cladistic interspecific analysis coincided in indicating the monophyletic nature of the akodontine clade, and its splitting into two sharply differentiated subclades: one comprising species referred to as Abrothrix, Chelemys and Geoxus , another comprising species of Akodon (including Deltamys ) and Oxymycterus. Thus, the separateness of a southern Andean branch in the cladogenesis of the Akodontini was confirmed, as well as the early recognition of Abrothrix as a full genus, and the recent claim of Spotorno to include in this genus other species formerly classified as Akodon jelskii, Ak. andinus and Ak. olivaceus.     

Phylogenetics of the speciose and chromosomally variable rodent genus Ctenomys (Ctenomyidae, Octodontoidea), based on mitochondrial cytochrome b sequences

The tuco-tucos [Ctenomys) are subterranean rodents that are widespread in southern South America. On the basis of its 60 living species, Ctenomys is one of the most speciose mammalian genera and displays great chromosomal variation. In order to study the mode of speciation in Ctenomys and to evaluate the role of chromosomes in cladogenesis, it is essential to generate an accurate phylogeny of the genus. From such a phylogeny it should be possible to identify particular species lineages worthy of further study. Following the success in 1998 of Lessa & Cook in generating a phylogeny of 10, mostly Bolivian, species from mitochondrial cytochrome b sequences, we sequenced a further 18, mostly Argentinian, species. By combining our datasi't with that of Lcssa & Cook's we were able to confirm six species lineages within Ctenomys. These lineages correspond well to taxonomic groups suggested on the basis of morphology and biogeographv. At least two of the species groups (the Boliviano-Matogrossense and Chaco) arc very variable chromosomally, and are worthwhile systems to examine the possibility of chromosomal spec iation. While, in general, multiple specimens of the named species did form monophyletic groups on the basis of the cytochrome b analysis, there were some exceptions. Thus, C. bergi and C yolandae did not form separate clades in the phylogenetic analysis, nor did C. roigi and C. dorbignyi. The molecular analysis was also very informative with regards species designations for C. boliviensis and related forms.     

Paleoparasitological analysis of rodent coprolites in holocenic samples from Patagonia, Argentina

The aim of the present study was to examine the parasite fauna present in rodent coprolites collected from Cerro Casa de Piedra (CCP7), located in Perito Moreno National Park (P.N.PM., 47 degrees 57'S and 72 degrees 05'W), Santa Cruz Province, Argentina. Eight coprolites obtained from the layer XIII of CCP7, with an antiquity considered as 7,920 +/- 130 yr B.P, were examined for parasites. Each coprolite was whole processed, rehydrated, homogenized, spontaneously sedimented, and examined using light microscopy. Eggs of parasites were measured and photographed. All the samples were parasitized by nematodes, with 267 eggs of Trichuris sp., 24 eggs of an aspidoderid, and 3 capillariid eggs. The rodent host was tentatively identified as a species of Ctenomys, the hypogeic rodents endemic to South America. The finding of Paraspidodera in Patagonian samples represents new evidence that strengthens the co-phylogenies between nematodes of this genus and Ctenomys and reinforces the value of parasites as tags in paleoparasitology.     

Ancient DNA reveals Holocene loss of genetic diversity in a South American rodent

Understanding how animal populations have evolved in response to palaeoenvironmental conditions is essential for predicting the impact of future environmental change on current biodiversity. Analyses of ancient DNA provide a unique opportunity to track population responses to prehistoric environments. We explored the effects of palaeoenvironmental change on the colonial tuco-tuco (Ctenomys sociabilis), a highly endemic species of Patagonian rodent that is currently listed as threatened by the IUCN. By combining surveys of modern genetic variation from throughout this species' current geographic range with analyses of DNA samples from fossil material dating back to 10,000 ybp, we demonstrate a striking decline in genetic diversity that is concordant with environmental events in the study region. Our results highlight the importance of non-anthropogenic factors in loss of diversity, including reductions in smaller mammals such as rodents.     

Polymorphism of eimerian oocysts can be a problem in naturally infected hosts: an example from subterranean rodents in Bolivia

Since 1986, 364 tuco-tucos (Ctenomys spp.) representing 7 species were collected from 16 major collecting areas representing at least 4 distinct ecological habitats in Bolivia, South America. All were examined for coccidia, and 125 (34%) had oocysts in their feces including 84 of 236 (36%) Ctenomys boliviensis from tropical palm/savanna habitats; 1 of 3 (33%) Ctenomys conoveri from a chaco thorn forest; 3 of 7 (33%) Ctenomys frater from medium altitude grass habitats; and 6 of 8 (75%) Ctenomys lewisi and 31 of 35 (88%) Ctenomys opimus from high altitude/puna habitats. None of 3 Ctenomys leucodon (high altitude/puna) or 72 Ctenomys steinbachi (tropical palm/savanna) were passing oocysts when examined. The 5 infected host species all had oocysts of Eimeria opimi Lambert, Gardner, and Duszynski, 1988, in their feces. These oocysts and their sporocysts varied greatly in size, both within and between host species, but qualitative characters (e.g., residua and wall texture) remained constant. Our conclusion, that all oocysts seen were E. opimi, was supported by multigroup discriminant analysis of 256 individual oocysts, 30-67 selected randomly from each Ctenomys sp. Minimum polygons enclosing the centroid (= multivariate mean) and the spread of individuals for each species group (OTU) showed significant overlap in discriminant space, and Geisser classification showed a 55% miss rate of individuals being classified into the wrong OTUs. Thus, oocyst and sporocyst lengths and widths cannot be used to separate morphotypes of E. opimi from different Ctenomys spp. from different geographic regions of Bolivia.     

Molecular Relationships Among Octodontidae (Mammalia: Rodentia: Caviomorpha)

We examined ten species of octodontid rodents and representatives of three outgroups in a complete 13 × 13 DNA-hybridization matrix. The results were indexed as differences in median melting-point depressions (T,_ms), symmetrized, subjected to phylogenetic analysis using FITCH, bootstrapped, and exhaustively taxon-jackknifed. Within Octodontidae, four clades were recovered with 100% bootstrap and complete jackknife support: Tympanoctomys barrerae with Octomys mimax, Octodontomys gliroides alone, Octodon spp., and Aconaemys spp. with Spalacopus cyanus; the latter two clades were closer to each other than either was to Octodontomys or Octomys-Tympanoctomys, but were slightly nearer to and united with Octodontomys, with 89% bootstrap support. However, relationships among the three Aconaemys species and Spalacopus were not completely resolved by our experiments. Ctenomys coyhaiquensis, Abrocoma bennetti, and Lagostomus maximus represented successive outgroups to Octodontidae, while one-way comparisons with Cavia porcellus and Microcavia australis suggested that these caviids are almost as distant from octodontoids as is the chinchilloid Lagostomus. When the data were suitably corrected for percentage hybridization and saturation, division of the distances by the rate previously determined for most amniotes (0.48%/myr) suggested that the basal divergence among the caviomorph rodents examined occurred about 59 myrbp, and that Octodontidae originated 40 myrbp and diversified into extant lineages beginning 14 myr ago. Calibration against the date of the earliest known caviomorph (late Eocene or about 37.5 myrbp) gave a rate of 0.75%/myr, which would suggest later dates for subsequent caviomorph cladogenesis. It is notable that, based respectively on the slower or faster rates, the tetraploid Tympanoctomys barrerae must have diverged from its sister-taxon Octomys mimax 10 or 6.5 myr ago.     

Energy and distribution in subterranean rodents: sympatry between two species of the genus Ctenomys

The low basal metabolic rate (BMR) observed in subterranean rodents, compared to that of surface-dwelling species of comparable size, has been proposed to be an adaptation to underground life. Two main hypotheses have been proposed to explain this finding, the cost of burrowing and the thermal stress. The former states that the low BMR is due to the high cost of extending the tunnel system whereas the other relates it to the possibility of overheating in burrows where evaporative and convective heat exchange are restricted. Additionally, both hypotheses related the energetics of subterranean rodent with spatial distribution. The genus Ctenomys is an excellent model to evaluate the cost of burrowing or thermal stress, since they are widely distributed, with members differing markedly in body mass. The aim of this study was to assess digging and basal energetics in two Ctenomys species that live in sympatry in a coastal grassland, but differ in their microspatial distribution by soil preference. We used the obtained energetic data to test both energy-distribution hypotheses. We measured BMR and digging metabolic rate (DMR) through open flow respirometry in two species exposed to soft and hard soils. In brief, DMR in Ctenomys talarum (100-170 g), as in Ctenomys australis (250-600 g), was unaffected by soil hardness. Within thermoneutral zone of each species, DMR/RMR quotient was lower in the smaller species. Our data did not support the thermal stress hypothesis, but the cost of burrowing hypothesis was not rejected. Other alternative hypotheses are proposed to explain the distribution of C. talarum and C. australis.     

Haematological correlates of burrowing in Ctenomys

Haematological parameters related to O2 transport and regulation of acid-base equilibrium were determined for two species of Ctenomys. The oxygen capacity values of Ctenomys blood are similar to those of other fossorial mammals. Ctenomys blood has almost half the number of red blood cells of Rattus blood but the amount of Hb in each blood cell is 2-2.5 times higher. Blood pH is within typical mammalian values. Concentration of inorganic phosphate is higher in Ctenomys than in rats while bicarbonate and protein values are within typical mammalian range.     

Phylogeny and adaptive diversity of rodents of the family Ctenomyidae (Caviomorpha): delimiting lineages and genera in the fossil record

Differentiation of genera of the modern (Late Miocene to Recent) South American rodent family Ctenomyidae would have been linked to the acquisition of disparate adaptations to digging and life underground. In accordance with this hypothesis, the delimitation of lineages and genera in the ctenomyid fossil record is evaluated here following an adaptation-rooted criterion that involves both an assessment of the monophyly and of the adaptive profiles of recognized clades. The application of such a criterion, including morphofunctional information, delimited four cohesive lineages among crown ctenomyids (i.e. euhypsodont species of the Late Miocene to Recent): Eucelophorus (Early Pliocene–Middle Pleistocene), Xenodontomys-Actenomys (Late Miocene–Pliocene), Praectenomys (Pliocene) and Ctenomys (including Paractenomys ; Pliocene–Recent); in addition, the results supported the status of Xenodontomys as a paraphyletic ancestor of Actenomys . The cladogenesis that gave rise to the crown group would have occurred immediately after the acquisition of euhypsodonty in a Xenodontomys simpsoni -like ancestor during the Late Miocene. This putative ancestor would have had fossorial habits and moderate digging specializations, an adaptive profile maintained in Xenodontomys-Actenomys . Eucelophorus and Ctenomys would have independently evolved subterranean habits at least since the Pliocene. Although the earliest history of the only living representative, Ctenomys , is known only fragmentarily, remains from Esquina Blanca (Uquía Formation), in north-western Argentina, suggest a minimum age of around 3.5 Ma (Early–Late Pliocene) for the differentiation of the genus. This date agrees with recent molecular estimates.     

Fourfold polyphyly of the genus formerly known as Upucerthia, with notes on the systematics and evolution of the avian subfamily Furnariinae

The traditional avian subfamily Furnariinae, a group of terrestrial ovenbirds typical of the Andean and Patagonian arid zones, consists of the genera Furnarius, Cinclodes, Geositta, Upucerthia, Chilia, and Eremobius. We investigated phylogenetic relationships within the Furnariinae, with particular attention to the nine species of the genus Upucerthia, using nuclear and mitochondrial DNA sequences from all genera in the subfamily. Upucerthia was found to be highly polyphyletic, its constituent species forming four non-sister clades: (1) a basal lineage consisting of two Upucerthia species, U. ruficaudus and U. andaecola, as well as the monotypic genera Eremobius and Chilia; (2) a lineage consisting of U. harterti and U. certhioides, two species behaviorally divergent from other Upucerthia species; (3) a lineage consisting of U. serrana, which is not closely related to any other Upucerthia species; and (4) a lineage, sister to Cinclodes, consisting of the four Upucerthia species U. dumetaria, U. albigula, U. validirostris, and U. jelskii. The larger Furnariinae was also found to be highly polyphyletic; the terrestrial open country ecotype characteristic of this subfamily occurs in four unrelated clades in the family Furnariidae, including a basal lineage as well as derived lineages. Although the large degree of divergence among Upucerthia clades was not previously recognized, owing to ecological, behavioral, and morphological similarities, the groupings correspond closely to relationships suggested by plumage. This is in contrast to studies of other avian genera in which plumage patterns have been shown to be extensively convergent. The generic names Upucerthia and Ochetorhynchus are available for two of the former Upucerthia clades; new generic names may be warranted for the other two.     

土圞儿属和旋花豆属(豆科)的叶表皮特征及其系统学意义

应用光学显微镜和扫描电子显微镜观察了豆科Leguminosae土圞儿属Apios和旋花豆属Cochlianthus植物的叶表皮特征。在光学显微镜下,大多数种类的叶表皮细胞形状（表面观）为不规则型,垂周壁式样为浅波状或波状,只有一个种——和Apios gracillima Dunn叶表皮细胞为多边形,垂周壁式样为较平直。在扫描电子显微镜下,多数种类的叶片蜡质纹饰通常为片状或颗粒状,一些种叶表皮未见蜡质纹饰;气孔器外拱盖内缘通常为浅波状或近平滑。在这两个属内,上述叶表皮特征在物种内较稳定,因此对于解决属内种间和属间关系有一定的系统学意义。本研究得出以下结论：（1）A．gracillima叶的上表皮细胞为多边形,垂周壁平直或弧形,A．delavayi Franch．叶的上表皮细胞为不规则形,垂周壁波状,二者存在明显差异,因此A．gracillima应处理为一独立的种,而不是A．delavayi下的一个变种;（2）A．priceana B．L．Rob．在叶表皮细胞形状、垂周壁式样、气孔器类型和蜡质纹饰形态等方面与土圞儿属中其他种不存在显著区别,因此土圞儿属内两个亚属的划分是不合理的;（3）土圞儿属多为5或7小叶,无毛或近无毛,叶表皮细胞垂周壁波状或近平直,而旋花豆属3小叶,密被柔毛,叶表皮细胞垂周壁浅波状,本文支持它们为两个独立的属的分类处理。     

Molecular analysis of populations of Ctenomys (Caviomorpha,Rodentia) with high karyotypic variability

The tuco-tucos (Ctenomys) are South American subterranean rodents that are some of the most chromosomally variable of all mammals. In this study we focus on Ctenomys of the "Corrientes species group" from that Argentine province and consisting of C. dorbignyi, C. perrensi, C. roigi and unnamed populations (Ctenomys sp.). A diploid range of 41-70 has been demonstrated for these taxa with multiple Robertsonian changes, pericentric inversions, heterochromatic modifications and other chromosomal rearrangements. To analyse the molecular variation in the Corrientes group, a 402 base pair fragment of mitochondrial cytochrome b was sequenced in 75 individuals from 26 populations. This generated 15 different haplotypes which were subjected to phylogenetic analysis. The different species within the Corrientes group failed to form monophyletic groups in the phylogenetic trees we generated and the divergences between haplotypes were low. Therefore, these molecular data demonstrate the recent subdivision of the Corrientes group with a substantial accumulation of chromosomal differences. Through our new chromosomal data and cytochrome b studies, we are able to subdivide the Ctenomys sp. populations into two groups and hypothesize on their relationships with the described Corrientes group species. Further studies are needed to establish the basis of the phenomenal chromosomal variation in this group.     

Functional morphology and paleobiology of the pliocene rodent Actenomys (Caviomorpha: Octodontidae): the evolution to a subterranean mode of life

The Pliocene caviomorph rodent Actenomys has long been recognized as an early fossorial representative of the subfamily Ctenomyinae (Octodontidae), which includes one living genus, Ctenomys (tuco-tucos), and several species widely distributed in South America. To assess the de gree of specialization for digging in Actenomys , we performed morphological comparisons with other octodontid genera (Octodon, Spalacopus , and Ctenomys) of known mode of life and behaviour. As a whole, our results indicate that, in terms of morphological specializations for digging, Actenomys occupies an intermediate position between Octodon , a generalized semi-fossorial rodent which forages above ground, and Ctenomys-Spalacopus , two highly specialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)–two traits which affect the out-forces exerted by several forelimb muscles–were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches arc as flared as those of the generalized Octodon. Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly-specialized chisel-tooth digging species. Based upon the stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.     

Cytogenetics Status of Four Ctenomys Species in the South of Brazil

This report is a review of 20 years of cytogenetics studies in tuco-tucos from the south of Brazil and the implications for the evolution of these species as well as the relation of these data with the geological history of the Coastal Plain of southern Brazil. Two forms of Ctenomys torquatus, 2n = 44 and 46, are separated by a geographic barrier. Ctenomys flamarioni shows a constant karyotype (2n = 48) and presents high variability in FN due to constitutive heterochromatin variation. Ctenomys minutus presents the highest chromosomic variation among the species in the south of Brazil (2n = 42–50) with three chromosomic hybrid zones. Ctenomys lami, like C. minutus, presents a high chromosomic variation due to fusions and fissions of chromosome pairs 1 and 2. Both species present a close evolutionary relationship, including a chromosomic hybrid zone.     

Ectomycorrhizal fungi associated with ponderosa pine and Douglas-fir: a comparison of species richness in native western North American forests and Patagonian plantations from Argentina

The putative ectomycorrhizal fungal species registered from sporocarps associated with ponderosa pine and Douglas-fir forests in their natural range distribution (i.e., western Canada, USA, and Mexico) and from plantations in south Argentina and other parts of the world are listed. One hundred and fifty seven taxa are reported for native ponderosa pine forests and 514 taxa for native Douglas-fir forests based on available literature and databases. A small group of genera comprises a high proportion of the species richness for native Douglas-fir (i.e., Cortinarius, Inocybe, and Russula), whereas in native ponderosa pine, the species richness is more evenly distributed among several genera. The comparison between ectomycorrhizal species richness associated with both trees in native forests and in Patagonia (Argentina) shows far fewer species in the latter, with 18 taxa for the ponderosa pine and 15 for the Douglas-fir. Epigeous species richness is clearly dominant in native Douglas-fir, whereas a more balanced relation epigeous/hypogeous richness is observed for native ponderosa pine; a similar trend was observed for Patagonian plantations. Most fungi in Patagonian Douglas-fir plantations have not been recorded in plantations elsewhere, except Suillus lakei and Thelephora terrestris, and only 56% of the fungal taxa recorded in Douglas-fir plantations around the world are known from native forests, the other taxa being new associations for this host, suggesting that new tree + ectomycorrhizal fungal taxa associations are favored in artificial situations as plantations.     

Karyotype evolution in South American subterranean rodents Ctenomys magellanicus (Rodentia: Octodontidae): chromosome rearrangements and (TTAGGG)n telomeric sequence localization in 2n=34 and 2n=36 chromosomal forms

Ctenomys is the most numerous genus of South American subterranean rodents and one of the most karyotypically diverse clades of mammals known. Ctenomys magellanicus is the southernmost species of the group and the only one living in Isla Grande de Tierra del Fuego (Argentina). This species presents two chromosomal forms, i.e. 2n=34, and 2n=36 (FN=68). Recent studies suggest that genetic divergence between both karyotypic forms resulted from a chromosomal speciation process. In order to identify the chromosomal rearrangement involved in the process of karyotype evolution in this species, we used chromosome banding techniques and fluorescence in situ hybridization with a telomeric probe to metaphase chromosomes of the two chromosomal forms of Ctenomys magellanicus. Chromosome analysis of Giemsa-stained and G-banding preparations showed that Cm34 and Cm36 karyotypes differ in one rearrangement involving chromosomes A9 from Cm34 and B12 and B17 from Cm36. In addition FISH analysis showed that all of the chromosomes from both chromosomal forms exhibit a telomeric-only distribution pattern of the (TTAGGG)n sequence, indicating that none of the chromosomal forms of Ctenomys magellanicus has true telocentric chromosomes. Our results suggest that a chromosome fission event would have occurred during the process of karyotype evolution in this species.     

Duplaccessorius andinus n. gen., n. sp. (Dactylogyridae: Ancyrocephalinae) from the gills of Percichthys trucha (Perciformes: Percichthyidae) in Patagonia, Argentina

During a parasitological survey of Patagonian freshwater fishes, specimens of a new species of Monogenea were collected from the gills of Percichthys trucha (Perciformes: Percichthyidae). This species is described as the only member of a newly proposed genus of Ancyrocephalinae. Duplaccessorius n. gen. (Dactylogyridae, Ancyrocephalinae) is characterized by hooks with 2 subunits, gonads in tandem, a coiled male copulatory organ with counterclockwise rings, an accessory piece formed by 2 distinct parts, and a nonsclerotized sinistrolateral vagina with a funnel shape vestibule. Duplaccessorius andinus n. sp. infects the gills of P. trucha (Cuvier and Valenciennes, 1840) from Andean Patagonian lakes, being the first species of Ancyrocephalinae described from a South American percichthyid.     

Intra-genomic ribosomal RNA polymorphism and morphological variation in Elphidium macellum suggests inter-specific hybridization in foraminifera

Elphidium macellum is a benthic foraminifer commonly found in the Patagonian fjords. To test whether its highly variable morphotypes are ecophenotypes or different genotypes, we analysed 70 sequences of the SSU rRNA gene from 25 specimens. Unexpectedly, we identified 11 distinct ribotypes, with up to 5 ribotypes co-occurring within the same specimen. The ribotypes differ by varying blocks of sequence located at the end of stem-loop motifs in the three expansion segments specific to foraminifera. These changes, distinct from typical SNPs and indels, directly affect the structure of the expansion segments. Their mosaic distribution suggests that ribotypes originated by recombination of two or more clusters of ribosomal genes. We propose that this expansion segment polymorphism (ESP) could originate from hybridization of morphologically different populations of Patagonian Elphidium. We speculate that the complex geological history of Patagonia enhanced divergence of coastal foraminiferal species and contributed to increasing genetic and morphological variation.