Gonzalo A. Collado

Monophyly, candidate species and vicariance in Biomphalaria snails (Mollusca: Planorbidae) from the Southern Andean Altiplano

Collado, G. A., Vila, I. & Méndez, M. A. (2011). Monophyly, candidate species and vicariance in Biomphalaria snails (Mollusca: Planorbidae) from the Southern Andean Altiplano. —Zoologica Scripta, 40, 613–622.

Hidden diversity in spring snails from the Andean Altiplano, the second highest plateau on Earth, and the Atacama Desert, the driest place in the world

BackgroundThe Chilean Altiplano and the Atacama Desert in northern Chile harbor isolated hydrological systems or oases where it is possible to find minute aquatic snails of the genus Heleobia whose taxonomy is uncertain and where many populations remain unknown. Here, we obtained samples from 30 localities distributed in the region and used molecular (12S and 16S mitochondrial genes) and morphological (penis) characters to investigate diversity of this poorly known fauna.ResultsMolecular phylogenetic analysis consistently recovered five clades, one of which constitutes a cryptic species previously assigned to a species recognized in the area. Four other clades contained sequences of one nominal species consistent with its type locality and at least two additional candidate species, which were corroborated by a particular penis morphology. Furthermore, some morphological differences in penis morphology were observed in two Altiplano populations not resolved by the DNA sequences, providing support for two additional candidate species in the genus. A molecular clock analysis allowed tracing the origin of lineages back to the Early Pleistocene.ConclusionsWe found support for recognizing four nominal species, one undescribed species and at least other four candidate species of the genus Heleobia in northern Chile. We also suggest that the current level of species diversity of Heleobia in the region is underestimated by the use of conchological criteria to recognize species and by the limited sampling conducted to date.

Morphological changes in the reproductive system of females Acanthina monodon (Pallas, 1774) (Gastropoda: Muricidae) affected by imposex from the coast of central Chile

Summary “Imposex” (imposed sex) is an abnormal anatomical condition of female gastropods in which they develop male sex organs. Imposex is induced by organotin pollutants from antifouling paints and was detected in Chilean gastropods for the first time in 1999. This study examined morphological changes associated with imposex in populations of the marine snail Acanthina monodon on the Chilean coast. Specimens were collected from two differentially polluted sites (Las Cruces and Matanzas) outside the active port of San Antonio, Chile. Sex was anatomically determined by the presence of a normal penis in the male and the presence of the capsule gland in the female. Histological study of the reproductive system in females with imposex was conducted by observing longitudinal and cross sections of individual organs and whole specimens; 54.2% of all females showed evidence of imposex, with a maximum value of 94.7% at Las Cruces, and a minimum value of 37.6% at Matanzas. Imposex-affected females demonstrated involution in some reproductive organs and masculinization symptoms included the presence of a pseudopenis, which was significantly shorter than the normal penis in males. In severe cases of imposex, the normal tissue of the capsule gland regresses.

Structure of the spermatozoa of two sympatric species of Fissurella Brugière, 1789 (Mollusca: Archaeogastropoda) from the southeast coast of South America

Summary This study analyzes the structure of the spermatozoa of Fissurella latimarginata and Fissurella cumingi, two sympatric keyhole limpet species from the coast of Chile. Observations were made using light and scanning and transmission electron microscopy. The spermatozoa of these species are of the ect-aquasperm type, typical of molluscs having external fertilization. They are composed of a conical acrosome, with a deep posterior subacrosomal imagination, a truncated conical nucleus, and a mid-piece containing a ring of five mitochondria, from which emerges a flagellum. The spermatozoa of the two species have quantitative and qualitative differences between different structural components. The total mean length of the head of F. latimarginata spermatozoa was significantly longer than that of F. cumingi. Components of the heads of the spermatozoa including the acrosomes and nuclei also showed interspecific differences. The morphology of the spermatozoa of these species constitutes a valid taxonomic character which supports the proposal that F. latimarginata and F. cumingi are valid species.

Morphology of the spermatozoon in two sympatric species of Fissurella Bruguière, 1789 (Mollusca: Vetigastropoda) from Southern Chile

Summary Light and electron microscopy were used to analyze the morphology and ultrastructure of the spermatozoon of Fissurella nigra and Fissurella picta, two sympatric species of keyhole limpets from the southern Chilean coast. The spermatozoa of both species are of the aquasperm type, typical of species with external fertilization. Each species had its own distinctive spermatic morphology, particularly in relation to size. Proceeding from anterior to posterior, the spermatozoa of both species each consists of an elongated head with a conical acrosome having a deep subacrosomal space and truncated conical nucleus, followed by a midpiece containing five mitochondria associated in a compact ring around the proximal and distal centrioles, and, at the end, a flagellum. The spermatozoon head of F. nigra is almost twice as long as that of F. picta. This difference constitutes the first morphological evidence that the size of the spermatozoon could represent a candidate for the maintenance of reproductive isolation between these two sympatric species.

Unravelling cryptic species of freshwater snails (Caenogastropoda, Truncatelloidea) in the Loa River basin, Atacama Desert

Species recognition in freshwater snails of the genus Heleobia Stimpson, 1865 in the Loa River basin is a difficult task to perform because these snails are similar in shell morphology. In this complex hydrological network, the genus comprises two endemic species, but the taxonomic status of other previously undescribed sympatric and allopatric populations is uncertain. Here we examined DNA sequences from cytochrome c oxidase subunit I (COI) gene and morphological data to investigate species boundaries along the system. Phylogenetic trees were inferred using maximum parsimony, neighbour joining, maximum likelihood and Bayesian inference methods based on samples ranging from the outlet of the Loa River on the Pacific coast to more than 4,200 m altitude in the Andes. Although not always well supported, four clades were consistently recovered in the phylogenies, one corresponding to Heleobia loaensis (Biese, 1947), another to Heleobia opachensis (Biese, 1947), and two more additional cryptic lineages. Additionally, a fifth cluster of sequences not recovered in these analyses was inferred in the BEAST analysis. Outline-based geometric morphometrics of the shell was useful to differentiate a single lineage sustaining that typological discrimination in Heleobia is challenging. Our results also indicate that all lineages diverged by independent non-adaptive allopatric processes during the Middle Pleistocene.

Morphology of the spermatozoon of the limpet Fissurella crassa Lamarck, 1822 (Mollusca: Vetigastropoda)

Summary Fissurella crassa is a keyhole limpet, which inhabits the middle rocky intertidal zone of the southwest coast of South America. The present study details the ultrastructure of the spermatozoon of this species. These cells are of the aquasperm type, typical of species that release free gametes into seawater. The conical head of the spermatozoon contains a truncated conical, elongated nucleus with a subconical acrosome with a rounded anterior tip, and a deep subacrosomic space. The midpiece of the spermatozoon is typically formed of six mitochondria arranged in a ring around the proximal and distal centrioles, from which emerges the 9 + 2 axoneme of the flagellum. The spermatic morphology is characteristic by the shape and size of the nucleus and acrosome, showing two differentiated zones and a deep subacrosomic space, which are valid taxonomic criteria to distinguish F. crassafrom other fissurellid species.

No more machismo in Callyntra (Coleoptera: Tenebrionidae): Callyntra femina , a new species discovered based on female genitalia and genetic evidence

Callyntra is a genus of tenebrionid beetles endemic to the Southern Cone region of South America, with 23 species occurring in Chile and one shared with Argentina. The recent descriptions of new species were commonly based on the male genitalia structure, underestimating the utility of the female genitalia for this purpose. Analysis of the ovipositor structure of a series of females assigned to Callyntra carbonaria from the Bío-Bío and Araucanía in Southern Chile, have resulted in the discovery of a new species, Callyntra femina sp. nov., which was corroborated through molecular analysis using COI and 16S gene fragments. The phylogenetic analysis recovered C. femina as sister to a clade composed of C. rossi, C. carbonaria and C. riverai, being genetically more similar to C. rossi.

A new species of Heleobia (Caenogastropoda: Cochliopidae) from the Chilean Altiplano

Cochliopidae Tryon, 1866 is a diverse family of caenogastropods that lives in a wide variety of aquatic habitats primarily in the New World (Hershler &Thompson 1992). In Chile, the species of the group have been traditionally assigned to the genus Littoridina Souleyet, 1852 using conchological characters (Biese 1944, 1947; Stuardo, 1961; Valdovinos 2006) but according to anatomical studies and phylogenetic analysis the majority of them have been reassigned to the genus Heleobia Stimpson, 1865 (Hershler & Thompson 1992; Collado et al. 2011a; Kroll et al. 2012; Collado et al. 2013; Collado et al. 2016). Here we formally describe a new species of the genus Heleobia from Spring 1 in the Carcote saltpan, Chilean Altiplano, based on molecular and morphological characters. Snails from this locality were previously shown to be distinct based on DNA sequences (Collado et al. 2013; Collado et al. 2016).

Genetic, morphological, and life history traits variation in freshwater snails from extremely high environments of the Andean Altiplano

BackgroundThe isolated watersheds of the southwestern Andean Altiplano constitute a natural laboratory to study the evolutionary divergence of freshwater biota. Field observations showed that Biomphalaria snails from Parinacota, Colpa, and Caquena have different shell sizes. We performed morphometric analysis and common garden experiment to evaluate whether the observed shell variation has a genetic base and if this variation is manifested in other morphological characters and life history traits.ResultsNetwork analysis revealed that the snails of Parinacota form a lineage genetically distinct from Caquena and Colpa. The morphometric analysis of the shell showed that the Parinacota snails were larger than Caquena and Colpa, both in nature and laboratory conditions, but there was no evidence of difference in the shape of the shell when compared using multivariate analyses. The number of eggs per ovicapsule was the only life history trait that was significantly different between lineages, although this difference may be also attributed to size of the progenitor; the oviposition rate did not differ between lineages or localities, and the hatching size and growth rate differed only at the locality level, not lineages.ConclusionThe results suggest that shell size of the snails has a genetic basis associated to the phenotype, while the expression and evolution of life history traits in extreme high environments are highly influenced by proximal causes.