Abstract
Comparative phylogeography of commensal species may show congruent patterns where the species involved share a common history. Temnosewellia is a genus of flatworms, members of which live in commensal relationships with host freshwater crustaceans. By constructing phylogenetic trees based on mitochondrial COI and 28S nuclear ribosomal gene sequences, this study investigated how evolutionary history has shaped patterns of intraspecific molecular variation in two such freshwater commensals. This study concentrates on the flatworm Temnosewellia albata and its critically endangered crayfish host Euastacus robertsi, which have a narrow climatically-restricted distribution on three mountaintops. The genetic data expands upon previous studies of Euastacus that suggested several vicariance events have led to the population subdivision of Euastacus robertsi. Further, our study compared historical phylogeographic patterning of these species. Our results showed that phylogeographic patterns shared among these commensals were largely congruent, featuring a shared history of limited dispersal between the mountaintops. Several hypotheses were proposed to explain the phylogeographic points of differences between the species. This study contributes significantly to understanding evolutionary relationships of commensal freshwater taxa.
Highlights
There are many examples of commensal relationships between aquatic organisms, perhaps none more prevalent than in the relationship between crustacean hosts and Platyhelminthes
In this study we present the first comparative phylogeographic analysis of the ectocommensal flatworm Temnosewellia albata Sewell, Cannon & Blair, 2006 (Platyhelminthes, Temnocephalida, Temnocephalidae) and its critically endangered host crayfish Euastacus robertsi Monroe, 1977 (Arthropoda, Decapoda, Parastacidae); freshwater invertebrates of headwater streams
Temnosewellia albata A total of 63 T. albata individuals were taken from 20 crayfish hosts sampled across five locations on three mountaintops (>700 m above sea level)
Summary
There are many examples of commensal relationships between aquatic organisms, perhaps none more prevalent than in the relationship between crustacean hosts and Platyhelminthes. Both marine and freshwater crustaceans worldwide have been shown to have persistent infestations of Platyhelminthes flatworms (McDermott, Williams & Boyko, 2010; Ohtaka et al, 2012). These flatworms are mostly host-specific and the most prevalent of just three, known, external symbionts on Euastacus (McCormack, 2012). The close association between the host and its ectocommensal may be exploited to develop an understanding of the phylogeographic history of both species
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