Carnegie Museum of Natural History

Secondary contact between previously allopatric lineages offers a test of reproductive isolating mechanisms that may have accrued in isolation. Such instances of contact can produce stable hybrid zones—where reproductive isolation can further develop via reinforcement or phenotypic displacement—or result in the lineages merging. Ongoing secondary contact is most visible in continental systems, where steady input from parental taxa can occur readily. In oceanic island systems, however, secondary contact between closely related species of birds is relatively rare. When observed on sufficiently small islands, relative to population size, secondary contact likely represents a recent phenomenon. Here, we examine the dynamics of a group of birds whose apparent widespread hybridization influenced Ernst Mayr’s foundational work on allopatric speciation: the whistlers of Fiji (Aves: Pachycephala). We demonstrate 2 clear instances of secondary contact within the Fijian archipelago, one resulting in a hybrid zone on a larger island, and the other resulting in a wholly admixed population on a smaller island. We leveraged low genome-wide divergence in the hybrid zone to pinpoint a single genomic region associated with observed phenotypic differences. We use genomic data to present a new hypothesis that emphasizes rapid plumage evolution and post-divergence gene flow.

Acid mine drainage (AMD) remediation facilities can produce treatment byproducts with near ore grade concentrations of rare-earth elements (REEs), cobalt, and manganese. High concentrations of these critical metals in treatment solids are often associated with hydrous manganese oxides (HMOs) through adsorption and/or coprecipitation. Chemical and microbial oxidation processes can influence HMO formation, mineralogy, and sorption efficiency. Here, we investigate the adsorption of rare-earth elements and yttrium (REY), cobalt, and nickel over 31 days by (1) abiotic HMO (δ-MnO₂ and c-disordered H+ birnessite) produced by chemical oxidation and (2) bitotic HMO produced by Mn-oxidizing fungi, Paraphaeosphaeria sporulosa and Stagonospora sp. After 31 days, ∼70% of REY was adsorbed by abiotic HMO, whereas >99% of REY was adsorbed by biotic HMO and/or fungal biomass within 7 days. Biotic HMO also adsorbed ∼30% Ni and ∼75% Co; however, Co and Ni adsorption by abiotic HMO was negligible. Both biotic and abiotic HMOs were initially poorly crystalline. However, over the course of the experiment, abiotic HMO was transformed to more crystalline phases, resulting in a reduced adsorption capacity and significant desorption of Co and Ni. In contrast, the biotic HMO remained stable and resistant to structural changes over time. This study demonstrates that biotic HMOs are highly efficient at adsorbing Co and REY and that fungal biomass can also play a significant role in this process, particularly for REY.