Estudio de la diversidad del género Pseudamnicola y su radiación endémica en la región íbero-balear. Taxonomía, filogenia y corología

Abstract

The genus Pseudamnicola Paulucci, 1878 of the family Hydrobiidae Stimpson, 1865 comprises a group of very small freshwater snail species distributed throughout the Mediterranean basin. Two subgenera are generally recognized within the genus: Pseudamnicola s. str., which is distributed throughout the Mediterranean basin, and Corrosella Boeters, 1970, which is only found in the Iberian Peninsula and southern France. Corrosella was initially described as genus but later placed within Pseudamnicola. Despite being one of the most diverse hydrobiid genera, there are few works that combine molecular analyses with detailed morphological and anatomical descriptions, mainly due to difficulties related to their small size and simplified anatomy. In view of this fact, this work constitutes the most comprehensive revision of the genus using an integrative approach that combines morphological, biogeographical and molecular analyses. Previous works have demonstrated that the Ibero-Balearic region constitutes a hotspot of hydrobiid diversity. There are 13 valid species (11 of which are endemic) of the genus Pseudamnicola in this region. In 1988, Boeters revised several species of both subgenera in his monograph of the Ibero-Balearic hydrobiids: P. (Corrosella) navasiana (Fagot, 1907) and P. (C.) hinzi Boeters, 1986 from northern Iberia, P. (C.) luisi Boeters, 1984 and P. (C.) falkneri (Boeters, 1970) from southern Iberia, P. (Pseudamnicola) subproducta (Paladilhe, 1869) from several Iberian localities and the Balearic Majorca and Minorca Islands and P. (P.) gasulli Boeters, 1981 from southeastern Iberia and Ibiza Island. Boeters later also described a new species, P. (C.) hydrobiopsis Boeters, 1999, from the southern Iberian Peninsula. More recently, four new species of the nominotypical subgenus were described for the Balearic Islands, from localities formerly assigned to P. (P.) subproducta, thus questioning the presence of this species on this archipelago. Majorcan species were named P. (P.) beckmanni Glöer and Zettler, 2007, P. (P.) granjaensis Glöer and Zettler, 2007 and P. (P.) artanensis Altaba, 2007, and the Minorcan species was named P. (P.) meloussensis Altaba, 2007. Furthermore, P. (C.) astieri (Dupuy, 1851) from southern France and P. (P.) conovula (Frauenfeld, 1863), whose type locality is Pag Island (Croatia) though also was cited for Sardinia (Italy) and Tunisia, were also reported for the Iberian Peninsula.

Based on the original descriptions of these Ibero-Balearic species, sample collection was performed first by visiting the type localities, then the surrounding areas, and finally other regions for which the genus has been cited. In addition, previously collected samples available at the Museo Nacional de Ciencias Naturales were studied, as well as the type material preserved in other European museum collections. In total, approximately 150 Ibero-Balearic Pseudamnicola populations were studied of which 128 belong to P. (Corrosella) and 30 to P. (Pseudamnicola). For morphological and anatomical approaches, males and females from most localities were dissected and examined for commonly described hydrobiid characters related to the shell, penis, female genitalia, radula and nervous system, among other less common characters. Combined data from mitochondrial (16S rRNA and COI) and nuclear ribosomal (18S and 28S rRNA) fragments from 51 P. Corrosella) and 20 Ibero-Balearic P. (Pseudamnicola) populations were genetically analyzed. Additional populations from other Mediterranean regions were also included in order to better understand the evolutionary history of the group. Phylogenetic and coalescence analyses were performed to examine patterns and causes of diversification. Furthermore, speciation factors such as water conductivity, altitude and geographic distances were studied by assessing the possible influence on speciation processes of environmental and geographical variables. From a systematic point of view, both anatomical and molecular analyses revealed: i) the existence of seven new species of P. (Corrosella) from the Iberian Peninsula; ii) that the Iberian records formerly ascribed to P. (C.) astieri actually correspond to a new cryptic species, P. (C.) hauffei Delicado and Ramos, 2012; iii) the validation of the Balearic species as different taxa from P. (P.) subproducta; iv) that P. (P.) conovula does not seem to occur in the Ibero-Balearic region; v) the genus Pseudamnicola should be considered composed of three genera: Pseudamnicola s. str., Corrosella and a new genus with P. (P.) gasulli as the type species. Overall, the most valid traits for differentiating between the studied species formerly included within the genus Pseudamnicola are: shell length/shell width ratio, the shape and length of the seminal receptacle, the length of the bursa copulatrix and bursal duct, the pigment extension on the renal oviduct, the shape and dimensions of the penis and the dimensions of the prostate gland.

Phylogenetically, these three genera were monophyletic in all analyses; however, the evolutionary relationships among them still remain uncertain. The reestablished genus Corrosella is composed of 12 Iberian species and C. astieri from southern France, clustered in three well-supported lineages, which grouped the northern species in two clades and the southern ones in a third clade (which was further divided into two clades in coalescence analyses). Speciation processes that influenced these diversification patterns may be related to habitat fragmentation and isolation, which may have occurred in three independent events during the Miocene (approximately 10 Ma, 5 Ma and 2 Ma). Within the Ibero-Balearic Pseudamnicola s. str. spp., the Minorcan species P. meloussensis is clustered with the Iberian species P. subproducta, whereas the three Majorcan species are comprised within a unique clade. Dating studies showed that the separation of the Balearic Islands from the continent occurred prior to the divergence between Iberian and Balearic species, and therefore, the presence of this group on the islands is likely related to two later transmarine colonizations followed by vicariance. This speciation mechanism may be common within Pseudamnicola s. str. spp., as the pattern of genetic variation reflects dispersal factors associated with this group. Furthermore, coalescence analyses showed evidence for a possible radiation of this genus mainly during the Messinian Salinity Crisis (5.9-5.3 Ma). During this, the conditions were ideal for dispersal processes in terrestrial fauna, with the subsequent interruption of the gene flow due to the aperture of Gibraltar Strait and the filling of the Mediterranean Basin. This combination of factors may have caused the radiation phenomenon in the group. Overall, statistical tests revealed that diversification patterns of Pseudamnicola s. l. spp. were strongly related to habitat fragmentation or dispersion events rather than to environmental conditions. However, habitat-related factors seem to have played a larger role during the deep divergent split leading to the three genera. Furthermore, these three groups display different evolutionary patterns caused by differences in tempo and mode of diversification, which may be related to habitat: Corrosella spp. occur in isolated springs and stream headwaters of mountainous regions, whereas species belonging to Pseudamnicola and the new genus inhabit brackish streams, lagoons and low river stages where waters remain connected, thus allowing gene flow between populations. In conclusion, by taking an integrative approach, this thesis provides a better understanding of the systematics and evolution of the family Hydrobiidae, which is essential for managing and preserving the species current habitats and populations.