ANOSIM analysis results for the sampling data.

<div><p>For many years, parasite ecologists have debated the relative importance of phylogeny and ecology as drivers of parasite community structure. Here, we address this issue using data on the metazoan ectoparasite communities of different flatfish species. Twenty species of flatfish were collected along the continental shelf of the Southern Gulf of Mexico and examined for ectoparasites. Eight flatfish species were parasitized by at least one ectoparasite species. In total, 326 ectoparasites, representing 11 species (4 monogeneans, 4 copepods, 1 isopod, 1 branchiurid, and 1 leech) were removed from 1622 hosts examined. The highest prevalence (37.5%) occurred in <i>Bomolochus</i> sp1 from <i>Trinectes maculatus</i>, while the lower (0.1%) for <i>Argulus</i> sp., <i>Gnathia</i> sp. and <i>Trachellobdella lubrica</i> from <i>Cyclopsetta chittendeni</i>. Changes in the ectoparasite community structure per host species and region were evaluated using a Permutational Multivariate Analysis of Variance and represented by a multidimensional scaling analysis. Significant differences in the parasite species composition among regions and hosts were detected, but no significant interaction between regions and hosts occurred. A multivariate pairwise <i>t-test</i> detected significant differences in the parasite infracommunities between the Yucatan Shelf and the other two regions; in addition, significant differences were detected between <i>C</i>. <i>chittendeni</i> and the <i>Syacium</i> species as well as between <i>Ancylopsetta dilecta</i> and <i>Syacium papillosum</i>. In this case, there is no relationship between the patterns of ectoparasitic community structure and the inherent phylogenetic affinity of the hosts; instead, the variations in ectoparasitic communities are determined by a regional ecological component.</p></div>