Identification of ecophenotypic trends within three European freshwater mussel species (Bivalvia: Unionoida) using traditional and modern morphometric techniques

Abstract

Most species of freshwater mussels (Unionoida) show a wide variability in shell form and size but an understanding of which factors determine unionoid morphology is poor. We identified ecophenotypic trends in shell and internal characters within three unionoid species from two habitat types (marinas and river) of the River Thames, UK, using traditional and modern morphometric techniques. In marinas, all species grew to larger maximum sizes than in the river, which might be a result of higher temperatures and phytoplankton densities in marinas. Unio pictorum in marinas was more elongated than in the river and Fourier shape analysis revealed a trend from dorsally arched river specimens to straight dorsal and pointed posterior margins in marina individuals. The degree of shell elongation and shape of dorso-posterior margin were not associated with sediment composition, but were associated with the different hydrological characters of the two habitat types. Relative shell width was a poor indicator of collection site and influenced by allometric growth. Unlike U. pictorum, a difference in shell elongation of marina and river mussels could not be detected in Unio tumidus and Anodonta anatina. However, all three species showed the same trends regarding the shape of the dorso-posterior shell margin. This shell character may thus have broad ecological significance and could have considerable utility to palaeontologists, taxonomists, and conservation biologists.

Molecular Characteristics of Batanghari, Tambago, Orange, and Mandiangin Giant Gourami Strains

“…Several studies proved that many animal populations have various ecophenotypic individuals (Langerhans et al, 2003;Zieritz and Aldridge, 2009). Therefore, morphological variations in giant gourami strains from Sumatera and Kalimantan can be referred as to different ecophenotype.…”

What can we infer from the shell dimensions of the thick-shelled river mussel Unio crassus?

“…Regardless of the factors causing it and regardless of its adaptive significance, it seems to be a good indicator of mussels' microhabitats. For example, in Unio pictorum (Linnaeus, 1758) inhabiting a large lowland river, the Thames, Zieritz et al (2009Zieritz et al ( , 2010 found similar differences in shell morphology between sampled microhabitats (marina vs. river channel).…”

“…One reason for larger arching of the shell may be exposure of the posterior part of the shell to water current, which may physically cause twisting the shell towards the bottom due to distortion of the shell-secreting mantle margin (Zieritz & Aldridge, 2009). Regardless of the factors causing it and regardless of its adaptive significance, it seems to be a good indicator of mussels' microhabitats.…”

A comparative study of shell variation in two morphotypes of Lymnaea stagnalis (Mollusca: Gastropoda: Pulmonata)

“…The effect of water flow on shell morphology of freshwater molluscs was mostly assessed as significant (Baker 1928;Shileyko 1967;Lam and Calow 1988;Zieritz and Aldridge 2009). In my study, the water flow proved to be the only hydrological factor to influence appreciably the shell morphology in both morphotypes though the external differences between snails living in lotic and lentic habitats could not be perceived without statistical means.…”