Abstract
The genetic homogeneity of the Monterey Spanish mackerel Scomberomorus concolor population in the Gulf of California was confirmed using nine nuclear microsatellite loci in combination with mitochondrial cytochrome b gene sequences. Samples were collected from the upper and central Gulf areas, representing the two main biogeographical regions of the Gulf. The analyses support the existence of a single panmictic population of S. concolor inhabiting the Gulf of California which in terms of fishery management represents a single genetic stock. Additionally, the contemporary effective population size estimated for the S. concolor population (Ne = 3056.9) was high and similar to another pelagic species. The gene flow seems to be bidirectional between the upper and central Gulf, which coincides with the seasonal movements between both regions related to spawning and feeding activities. A population expansion event was detected, which agrees with a colonization-expansion hypothesis of the S. concolor population in the Gulf.
Highlights
The Gulf of California (GC) is a long, narrow, semi-isolated basin which was formed by tectonic rifting, separating the peninsula of Baja California from the mainland approximately 5–12 million years ago (Carreño & Helenes, 2002)
As results for population divergence did not change by omitting this locus, it was decided to keep it for further analyses
Based on the seasonal movements related with spawning and feeding and the findings presented in this study, it is possible to conclude that S. concolor comprises one single genetic transient population and that most of its young and adult members distribute seasonally in both Gulf regions, while the youngest individuals remain in the upper part for growth and posterior recruitment (Valdovinos-Jacobo, 2006)
Summary
The Gulf of California (GC) is a long, narrow, semi-isolated basin which was formed by tectonic rifting, separating the peninsula of Baja California from the mainland approximately 5–12 million years ago (Carreño & Helenes, 2002). Based on the environment and changes in the ichthyofaunal composition, the GC is divided into two distinct biogeographic regions, the upper and the central Gulf (Riginos, 2005). The upper Gulf is shallow, has extreme tidal heights (up to 10 m) and a wide range of sea surface temperatures (SST) (e.g., low temperature in winter and high temperature in summer) (Brusca et al, 2005). This has resulted in significant genetic differences between populations of both biogeographic regions for some reef fish species (Riginos & Nachman, 2001; Riginos & Victor, 2001)
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