PRJNA704566
This collection of assembled ddRAD-seq loci was collected from 54 species of Unionid mussel. Our samples were collected from various museum sources and the field. Assembly
North American watersheds contain the worlds highest diversity of freshwater mussels (Unionoida), and up to 40 species can co occur in a single riffle. They collectively exhibit little evidence for ecological differentiation during the long lived, benthic phase of their life cycle. In contrast, their brief parasitic larval phase involves the infection of a wide diversity of fish hosts. Gravid female mussels have evolved multiple methods for increasing the probability of infecting a host fish. Some species use a passive broadcast strategy: placing high numbers of larvae in the water column and relying on chance encounters with potential hosts for infection. Most species have a proactive strategy that entails the use of prey mimetic lures to change the behavior of the hosts by eliciting a feeding response through which they become infected. Gravid females collectively produce two main lure types: a mantle tissue lure (on the females body) and a brood lure, containing infective larvae, that she releases into the external environment. In this study, we used a phylogenomic approach (ddRADseq) to place the diversity of infection strategies used by 54 North American lampsiline mussels into an evolutionary context. Ancestral state reconstruction recovered evidence for the early evolution of mantle lures in this clade, with brood lures and broadcast infection strategies both being independently derived twice. The most common infection strategy, occurring in our largest ingroup clade containing members of four genera, is a mixed one in which mimetic mantle lures are apparently the predominant infection mechanism, but gravid females also release simple, non mimetic brood lures at the end of the season. This mixed infection strategy clade shows some evidence of an increase in diversification rate and most members use bass (Micropterus and Ambloplites spp.) as their predominant fish hosts. Broad linkage between infection strategies and predominant fish host genera is also seen in other lampsiline clades: worm like mantle lures of Toxolasma spp. with sunfish (Lepomis spp.); insect larvae like brood lures (Ptychobranchus spp.), or mantle lures (Medionidus spp., Obivaria spp.), or mantle lures combined with host capture (Epioblasma spp.) with a spectrum of darter (Etheostoma and Percina spp.) and sculpin (Cottus spp.) hosts, and tethered brood lures (Hamiota spp.) with bass (Micropterus and Ambloplites spp.). Our phylogenetic results confirm that discrete lampsiline mussel clades exhibit considerable specialization in the primary fish host clades their larvae parasitize, and in the host infection strategies they employ to do so. They are also consistent with the hypothesis that larval resource partitioning of fish hosts is an important factor in maintaining species diversity in mussel assemblages. We conclude that, taking their larval ecology and host infection mechanisms into account, lampsiline mussels may be legitimately viewed as a cryptic adaptive radiation.