Dl. Graf et Do. Foighil, The evolution of brooding characters among the freshwater pearly mussels (Bivalvia : Unionoidea) of North America, J MOLLUS ST, 66, 2000, pp. 157-170
Brooding characters have figured prominently in the classification of North
American freshwater pearly mussels (Bivalvia: Unionoidea). The purpose of
our study was to evaluate phylogenetic hypotheses of brooding character evo
lution in order to test homology statements suggested by earlier taxonomic
systems of the Unionoidea. Parsimony analysis of partial COI sequences from
29 species of freshwater mussels and 13 outgroups were used to derive a ph
ylogeny. Thirteen brooding characters (e.g., brooding period, marsupium arr
angement, structure of interlamellar septa, etc.) were traced onto this phy
logeny. Results indicate that long-term brooding (bradytictia) is the deriv
ed state among North American freshwater mussels: short-term brooding (tach
ytictia) is plesiomorphic. Bradytictia evolved independently in the Anodont
inae and Lampsilini, with unique morphological modifications derived in tho
se clades to facilitate long-term brooding.