Low Genetic Diversity and High Invasion Success of Corbicula fluminea (Bivalvia, Corbiculidae) (Müller, 1774) in Portugal

Abstract

The Asian clam, Corbicula fluminea, is an invasive alien species (IAS) originally from Asia that has spread worldwide causing major ecological and economic impacts in aquatic ecosystems. Here, we evaluated C. fluminea genetic (using COI mtDNA, CYTb mtDNA and 18S rDNA gene markers), morphometric and sperm morphology variation in Portuguese freshwater ecosystems. The COI marker revealed a single haplotype, which belongs to the Asian FW5 invasive lineage, suggesting a common origin for all the 13 Portuguese C. fluminea populations analysed. Morphometric analyses showed differences between the populations colonizing the North (with the exception of the Lima River) and the Centre/South ecosystems. The sperm morphology examination revealed the presence of biflagellate sperm, a distinctive character of the invasive androgenetic lineages. The low genetic variability of the Portuguese C. fluminea populations and the pattern of sperm morphology have been illuminating for understanding the demographic history of this invasive species. We hypothesize that these populations were derived from a unique introductory event of a Corbicula fluminea FW5 invasive androgenic lineage in the Tejo River, which subsequently dispersed to other Portuguese freshwater ecosystems. The C. fluminea asexual reproductive mode may have assisted these populations to become highly invasive despite the low genetic diversity.

Fig 1. Hydrological data of the studied Portuguese rivers.

Location of the sampled sites and additional information about length and area of the river and lake basins in Portuguese territory [55,56].

Fig 2. Bayesian phylogenetic tree of the mtDNA COI gene from Corbicula genus.

Both Bayesian Inference posterior probabilities (BI) and Maximum Likelihood bootstrap values (ML) are indicated at the nodes.* Indicates the presence of monoflagellate sperm, ** indicates the presence of biflagellate sperm, ^α represents androgenetic lineages confirmed by cytological studies [25,32,73,74].

Fig 3. Principal Component Analysis.

The PCA showing the relationship of the PC1 and PC2 components of Corbicula fluminea populations from rivers of the North, Centre and South of Portugal, and the Lima River (North Portugal). Each circle represents one specimen corresponding to a specific river. The N cluster in the light red oval circle represents C. fluminea populations from the northern rivers and C/S in light green oval represents the centre and southern rivers cluster.

Fig 4. Sperm morphology of Corbicula fluminea from Portugal.

Biflagellate sperm of a specimen of C. fluminea from the Douro River (Microscopy photograph acquired by Olympus SZX10 microscope with an integrated Olympus D72 camera).

Fig 5. Worldwide map representing the Corbicula spp. distribution from the native and the non-native range.

N indicates the number of haplotypes. Exclusively from the native-range two groups II and V (N = 10 haplotypes and N = 14 haplotypes, respectively). Group I is represented by 9 haplotypes and group IV by 7. The non-native range group I represents 4 haplotypes (North America, N = 1; South America, N = 2 and Europe N = 1). Group III englobes a total of 6 haplotypes; (Africa, N = 1; South America, N = 1; Europe N = 3 and Oceania, N = 1). Group IV presents a total of 3 haplotypes (North America N = 1, Europe N = 1 and Africa N = 1).

Fig 6. Dispersal routes of Corbicula spp. invasive lineages.

Established Corbicula spp. dispersal routes are represented by continuous lines and dash lines correspond to other possible spread routes.