The most vagile host as the main determinant of population connectivity in marine macroparasites

Although molecular ecology of macroparasites is still in its infancy, general patterns are beginning to emerge, e.g. that the most vagile host in a complex life cycle is the main determinantof the population genetic structure of their parasites. This insight stems from the observation that populations of parasites with only freshwater hosts are more structured than those with terrestrial or airborne hosts. Until now, the same has not been tested for marine systems, where, in theory, a fully marine life cycle might sustain high dispersal rates because of the absence of Obvious physical barriers in the sea. Here, we tested whether a marine trematode parasite that utilises migratory birds exhibited weaker population genetic structure than those whose life cycle utilises marine fish as the vagile host. Part of the mitochondrial cytochrome c oxidase 1 (COI) gene wassequenced from individual sporocysts from populations along the Atlantic coast of Europe and North Africa. Strong population structure (Φ-ST = 0.25, p < 0.0001) was found in the fully marinetrematode Bucephalus minimus (hosted by fish), while no significant structure (Φ-ST = 0.015, p = 0.19257) was detected in Gymnophallus choledochus (hosted by birds). However, demographicmodels indicate recent colonisation rather than high dispersal as an alternative explanation of the low levels of structure observed in G. choledochus. Our study is the first to identify significant genetic population structure in a marine autogenic parasite, suggesting that connectivity between populations of marine parasites can be limited despite the general potential for high dispersal of their hosts in the marine environment

Reproduction of the genus Fucus

Fucus species (Phaeophyceae) inhabit intertidal rocky shores in temperate regions. It is a very important primary producer and an ecosystem engineer. The first event in the life history of Fucus is the production of gametes and, subsequently, zygotes by external fertilization, which is influenced by many environmental factors. What are the optimal conditions for Fucus species to spawn? I will elaborate on this and conclude that optimal conditions for the reproductive success of Fucus are to synchronously spawn during the afternoon (Fucus needs to be photosynthetically active) at low tide or slack high tide with calm water conditions (due to the water motion mechanism). Males and females should be in close proximity. Also the high quantity and longevity of gametes, the large egg cells (to increase the target area for sperm) and chemotaxis heighten the reproductive success. It depends on the species if lower temperatures are advantageous – for some species the reproductive success and dispersal is good, but the germling survival is very low at lower temperatures (i.e. during winter or early spring).