LAUSR

Mugil cephalus generally inhabits coastal areas and migrates to the open sea to reproduce. Based on tagging studies, it has been suggested that this species could present philopatric behavior, which would be reflected in the genetic structure. To test philopatry in M. cephalus, 11 locations in the Gulf of Mexico (GOM) and three in the Mexican Pacific (MP) were sampled. 151 and 177 specimens were analyzed using mtDNA, COI and control region, respectively. Ten microsatellite loci were examined in a total of 311 individuals. COI results showed that GOM and MP do not share haplotypes. Each littoral represents a distinct genetic group with a genetic distance of 5.4%. However, historical genetic flow was found between these two regions, which could represent a remnant of the connection at the Isthmus of Panama or due to the interconnection of rivers during the Pleistocene on the Isthmus of Tehuantepec. The GOM presented panmixia (FST = 0.001 COI, 0.023 control region, and 0.039 microsatellites), and the high gene flow between locations (Nm > 139) could lead to the underestimation of the markers of philopatric behavior. The MP also presented panmixia using COI (FST = 0); however, it showed two genetic groups (north and south) using microsatellites in both sexes (FST = 0.176 ♂ and 0.144 ♀). Given the evidence that the Tehuanos winds can produce a barrier between the locations of the MP, particularly during the spawning season, it is possible that genetic structure is the result of this barrier rather than philopatry.