Host compatibility as a critical factor in management unit recognition: population‐level differences in mussel–fish relationships

Abstract

Summary1. The recognition of management units (MUs) that respect interpopulation distinctions in management needs is central to many biological applications addressing species conservation, biological invasions and ecosystem processes. 2. We present a methodological approach for the evaluation of population-level differences in the host compatibility of natural populations of affiliate (dependent) species. Two experiments were performed to diagnose the sources of variability in the relationships between an endangered freshwater mussel Unio crassus and its host fish species in a fragmented river system in Central Europe. 3. Despite the common approach applied to the conservation of U. crassus throughout the study area, we identified differences in the ability of U. crassus to infest particular host fish species between nearby and recently isolated mussel populations. These differences could strongly influence their reproductive success under a constant conservation regime. 4. The observed differences were accompanied by genetic and morphometric distinctions, as revealed by microsatellite, mtDNA and elliptic Fourier descriptor analyses. The genetic data indicated substantial reproductive isolation, which could have resulted in adaptive or random changes responsible for the differences in host compatibility. 5. We showed that experimental testing of physiological host compatibility can be effectively used for the detection of different MUs of U. crassus, with direct implications for the management of host populations. In combination with traditional genetic and morphometric techniques, this approach may provide a general framework for the recognition and care of management units of affiliate species. 6. Synthesis and applications. Population-level evaluations of host compatibility should be utilized in management unit recognition and the formulation of management targets for affiliate species. We demonstrated that small-scale cross-compatibility testing can be effectively used to diagnose the sources of variability in host relationships with direct management implications. This approach can enhance the targeting of management actions in many biological applications addressing species conservation, biological invasions and ecosystem processes.

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

“…2C). Such an analysis should be supported by a clear ecological mechanism or should be concordant with other independent ecological features, as suggested by Douda et al (2014). Applying EFA to mussel shells requires extensive testing against many different ecological backgrounds in a large number of rivers and populations, in order, for example, to test the number of harmonics applied (e.g., 8 suggested in the methodological paper by Crampton, 1995 versus 20 used by Preston et al, 2010) and to standardize meaningful shape patterns useful for identifying habitat characteristics or for taxonomy.…”

Gender-Associated Mitochondrial DNA Heteroplasmy in Somatic Tissues of the Endangered Freshwater MusselUnio crassus(Bivalvia: Unionidae): Implications for Sex Identification and Phylogeographical Studies

“…More recently, Douda et al. () took advantage of mtDNA and microsatellite analyses to support recognition of U. crassus management units.…”

Population-specific responses to an invasive species

“…Female mussels discharge ripe larvae into the water column where they attach to a host fish, remain encysted for several days and finally metamorphose into juvenile mussels. Hosting mussel larvae is costly to fish [19], leading to fish adaptations to reject them [20] and population-specific compatibility between native mussels and their fish hosts [21]. The adaptations of mussels to eject bitterling eggs and adaptations of fish to reject mussel larvae are independent, and different physiological mechanisms are involved.…”

“…Given the high population-specificity of relationships with fish hosts in European unionids [21], we predicted a variable capacity of A. woodiana larvae to develop on R. amarus from different populations. We predicted significant avoidance of Danubian A. woodiana, but a maladaptive utilization of Baltic A. woodiana mussels with ovipositions followed by egg ejection [34,35].…”