Abstract
The phylogeny and taxonomy of freshwater mussels of the genus Castalia in South America is complicated by issues of morphological plasticity and limited molecular genetic data. We present field data on the distributions of the nominal Castalia ambigua and C. inflata in the upper Paraguay River basin in Brazil based on original occurrence data at 23 sample sites and on historical records. The upper basin has distinct highland and lowland regions, the latter including the Pantanal wetland, where “C. ambigua” occurs in the highlands and “C. inflata” occurs in both regions. At Baixo Stream in the highlands, we observed individuals with shell morphologies of either C. ambigua or C. inflata, and also individuals with intermediate shell morphology. DNA sequence variation in the upland Baixo Stream and two representative lowland populations were screened. Two mitochondrial and three nuclear genes were sequenced to test hypotheses regarding the number of species-level phylogenetic lineages present. Reported individual DNA sequences from Amazon-basin C. ambigua and other Castalia and outgroup species were included in the analysis as outgroups. Individuals from the Paraguay River basin exhibited 17 haplotypes at the mitochondrial cytochrome oxidase I (COI) gene and nine at mitochondrial 16S rRNA. Analysis of haplotype networks and phylogenetic trees of combined COI + 16S rRNA sequences among individuals with the respective shell morphologies supported the hypothesis that C. ambigua and C. inflata from the Paraguay River basin belong to the same species and one phylogenetic lineage. No variation was observed at the nuclear 18S rRNA internal transcribed spacer, 28S rRNA, or H3NR histone genes among individuals used in this study. Across all markers, less variation was observed among Paraguay basin populations than between Paraguay and Amazon basin populations. Our results collectively suggest that: (1) “C. ambigua”, “C. inflata”, and morphologically intermediate individuals within the upper Paraguay drainage represent one phylogenetic lineage, (2) a phylogeographic divide exists between Castalia populations occurring in the Paraguay and Amazon River basins, and (3) the evolutionary and taxonomic uncertainties that we have identified among Castalia species should be thoroughly assessed across their distribution using both morphological and molecular characters.
Highlights
South America has a rich diversity of 168 native freshwater mussel species, with a recent description [1] and wide variation in richness among the continent’s hydrogeographic regions [2,3,4].Despite the important ecological services provided by freshwater mussels and the need for their conservation in the context of rapid economic development and associated ecological change, South American mussels remain largely under-studied
Data from individuals collected at 70 sample sites in the upper Paraguay River basin showed that C. ambigua occurred at 5 sites (Table 1, Figure 1B, inset map) and C. inflata at 19
Castalia inflata was associated with the lowlands, marginal shallow lakes, and oxbow lakes of the Cuiabá River in areas influenced by the spring flood pulse [22,23]
Summary
South America has a rich diversity of 168 native freshwater mussel species, with a recent description [1] and wide variation in richness among the continent’s hydrogeographic regions [2,3,4].Despite the important ecological services provided by freshwater mussels and the need for their conservation in the context of rapid economic development and associated ecological change, South American mussels remain largely under-studied. South America has a rich diversity of 168 native freshwater mussel species, with a recent description [1] and wide variation in richness among the continent’s hydrogeographic regions [2,3,4]. Among South American mussels, species of the genus Castalia Lamarck, 1819 (Unionoida: Hyriidae) are distributed through many major basins of South America (Figure 1A). The distribution of Castalia ambigua Lamarck, 1819 is found in four of the eight major Brazilian basins: the Amazon, Paraguay, and Paraná, with a restricted distribution in the Uruguay River basin [5,6]. Castalia inflata d’Orbigny, 1835 is distributed in the Paraguay River basin and the middle-lower Parana basin, with occurrence in Argentina, Paraguay, Uruguay, and Bolivia [5,7]. Baseline data on species’ distributions are lacking in many regions
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