Host fishes and infection strategies of freshwater mussels in large Mobile Basin streams, USA

We investigated host fishes, timing and modes of glochidial release, and host-attraction strategies for 7 species of freshwater mussels from the Buttahatchee and Sipsey rivers (Mobile Basin), Alabama and Mississippi, USA. We determined hosts as fish species that produced juvenile mussels from laboratory-induced glochidial infections. We established the following primary mussel/host relationships: Elliytio nrcn with Etl~~~tomu nrtcsinc and Percitza ~zigr#scintu; Fusconain cerina with 6 species of minnows (Cyprinidae); Lm7psilis ormtn with Micropkrus sahoidcs; Mcdionidus acutissimus with 8 species of darters (Percidae); Obtnwrin unicolor with Anrmmytn bcnili, A. nrcridinrm, and Et/lenstomn art&v; Phrobemn decisunr with Cyril~elln wrmstn; and Quadruin aspernta with lctnlurus punttatus. For most mussel species, host use was similar to that of closely related species, indicating that, in general, this trait is highly conserved at the generic level. Four mussel species used host-attraction strategies that targeted their specific host fish. Fusronnin cerirla and I! dmisurn released glochidia in conglutinates that elicited feeding responses from fishes in the field and in the laboratory. Gravid female Dmrpsilis ornatn and M. ncutissimus displayed mantle lures. Host-attraction strategies were less apparent for E. arcn and (2. nspmdn, but these species released glochidia in association with copious mucous secretions, which may serve to entangle fishes, facilitating host infection. No host-attraction strategy was apparent for 0. uiiicolor. Kr?/ zards: host-parasite relationship, life history, Unionidac, Bivalvia, mussels, glochidia, Mobile Basin. The southeastern United States supports the most diverse freshwater mussel fauna on earth. This fauna also is distinguished as one of the most endangered groups of organisms in North America (Neves et al. lYY7). The basic life histories of many southeastern mussel species are poorly known. To complete development, larvae (glochidia) of most mussel species must undergo a brief period as ectoparasites on the gills or fins of fishes. Host specificity ranges from generalists, able to parasitize a wide variety of fishes, to specialists, whose glochidia can develop on only a few, usually closely related fish species (Haag and Warren 1997). Larvae cncountering an unsuitable host are rejected by the fish immune system (O’Connell and Neves 1099). Many species display remarkable adaptations to facilitate transmission of glochidia to hosts, including display of lures and release of glochidia in packets that mimic food items of host fishes (e.g., Barnhart and Roberts 1997, Haag and Warren lYYY, Watters 1999, Jones and Neves 2002). Knowledge of host fishes, host-attraction strategies, an d other aspects of reproductive biology is lacking or incomplete for many North American mussel species. This lack of knowledge hampers conservation efforts and limits our understanding of the ecology of these animals. The Mobile Basin of Alabama, Georgia, Mississippi, and Tennessee is home to a unique, highly endangered mussel fauna including a large number of endemic species (Stansbery 1976, Lydeard and Mayden 1995). The Buttahatchee and Sipsey rivers support the best remaining examples of large-stream Mobile Basin mussel communities. Host information exists for a number of headwater species in the Mobile Basin (Haag and Warren 1997, Haag et al. 1999), but hosts are unknown for most large-stream species in the basin. We investigated host fishes, timing and modes of glochidial release, and host-attraction strategies for 7 species of mussels from the Buttahatchce and Sipsey rivers: Alabama spike (EIliptio nrcn), Gulf pigtoc (Fuscouaia cerina), southern pocketbook (Laqwilis orunto), Alabama mot casinshell (MeJiorlidus achssimus), Alabama hickorynut (Obtn~~7rin frrricoh), southern clubsheii (I’lrlrlobc~~rn dccimm), and Alabama orb (Q~rrrdmln nsprnrtn). With the exception of E C~Virla and L. ormta, all of these species are endemic