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Chapter: The Diversity of Fishes: Biology, Evolution, and Ecology: Fish genetics

Habitat preference - Fish genetics

In resolving population structure of marine fishes, most attention has focused on the dispersive larval stage.

Habitat preference

In resolving population structure of marine fishes, most attention has focused on the dispersive larval stage. However the movements and feeding activities of adults play a role in shaping population structure, especially for fishes in the pelagic zone. For example, population structure in wide-ranging tunas, billfishes, and pelagic sharks is usually measured on the scale of ocean basins: East versus West Atlantic in the Bluefin Tuna Thunnus thynnus (Carlsson et al. 2007), North versusSouth Atlantic in the White Marlin Tetrapturus albidus (Graves & McDowell 2006), Indian versus Pacific in the Swordfish Xiphias gladius (Lu et al. 2006), and Atlantic versus Indian-Pacific in the Whale Shark Rhincodon typus (Castro et al. 2007).

 

A few demersal (bottom-dwelling) fishes conduct reproductive or seasonal migrations, but most are sedentary, and for this reason the corresponding habitat preferences are seldom considered in predicting population structure. However, habitat preference can have a strong influence on the distribution of genetic diversity in fishes. Usually ecosystem specialists (those with very specific feeding or habitat requirements) have more population structure than generalists, as demonstrated by genetic comparisons of reef .fishes across the Amazon barrier. This turbid plume of fresh water was long regarded as a barrier that divided the West Atlantic reef fauna into northern (Caribbean) and southern (Brazilian) provinces. However, fresh water is less dense than salt water, and may form a surface layer with a saltwater “wedge” below. Trawl surveys conducted under the Amazon plume demonstrated the presence of many marine fishes that are usually associated with coral reefs (Collette & Rützler 1977). An mtDNA survey of West Atlantic wrasses (genus Halichoeres) across the Amazon barrier demonstrates a strong connection between habitat use and genetic structure. Halichoeres maculipinna, a reef species with specialized diet and feeding morphology, has an ancient evolutionary separation between Brazil and the Caribbean (sequence divergence d =0.065 in cytochrome b). In contrast, H. bivittatus is found in a variety of habitats in addition to coral reefs and shows no strong genetic separation across the Amazon barrier (Rocha et al. 2005a). Notably, H. bivittatus was collected in the trawl surveys under the Amazon plume, whereas H. maculipinna was not. Combined, these genetic and field studies indicate that habitat preference and speciesecology can be as important as geography and larval dispersal in defining the distribution of genetic diversity in fishes (Choat 2006).

 

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