With a pinch of salt: the fish gill, a surface of exchange for parasites

Abstract

Large-scale patterns of species diversity suggest that stability facilitates speciation. Conversely, fluctuating environments are expected to counteract speciation in host-parasite systems. Monogenea (Platyhelminthes, Neodermata) is a group of obligate flatworm ectoparasites living mostly on the gills and skin of fishes. Monogenean gill parasites are exposed to the aquatic environment which can be highly variable in oxygen and salinity levels. In addition, they are directly exposed to the environment of the fish gill, a continuously adapting organ, due to its physiological functions. While lates perches (Actinopterygii, Latidae) host various monogenean flatworms in the marine and estuarine environments of the Indo-Pacific region, only a single species, Dolicirroplectanum lacustre (Monogenea, Diplectanidae), infects the gills of African freshwater lates perches. These contrasting patterns of speciation on an intercontinental scale across various aquatic habitats provide the ideal study system to investigate the influence of environmental variability on host-parasite speciation. Thus far, we have investigated the population-level diversification of D. lacustre across several African lakes, where high levels of phenotypic plasticity have been revealed.

In order to compare the level of diversification in the parasites with that of the host, we have started the delineation of host units in African basins through morphometrics and geomorphometrics. With the aim to relate the levels of diversification to the stability in the environment of the fish gill, we will quantify the level of gill stress. Fluctuating asymmetry will be investigated using 3D CT scans, and using qPCR, ratios between mitochondrial and nuclear markers will be determined from gill tissue. We will contrast the resulting patterns of diversification in D. lacustre with the divergence of its marine congener Dolicirroplectanum penangi and the diplectanid Laticola latesi coinfecting Indo-Pacific latid Lates calcarifer.