Genetic relationships among Merluccius species

Abstract

Genetic data from nine species of Merluccius (Euro±African species merluccius, capensis, paradoxus, polli, senegalensis; American species bilinearis, productus, hubbsi, australis) from 21 informative allozyme loci provided insights into the phylogenetic and biogeographical relationships within the genus. The highest values of polymorphic loci and mean heterozygosity occur in the four American species. These values are consistent with large population sizes during speciation (through vicariant processes), and continuing through to the present. Conversely, the lower values of Euro±African species are consistent with bottlenecks occurring during or subsequent to speciation. Euro±African and American species formed two distinct clades. In the former group, merluccius, capensis and senegalensis clustered together as the most derived species, with distinct relationships between polli and paradoxus from an earlier divergence. Similarly, productus, australis and hubbsi clustered closely as the most derived American species, clearly diverging from the more ancestral bilinearis. Analyses including comparative data previously published for M. gayi indicated a close pairing to hubbsi. The data support a north-west Atlantic origin of the genus with unsampled M. albidus of broad Caribbean distribution proposed as the most primitive extant species.Keywords: allozymes, biogeography, hake, Merluccius, phylogeny. IntroductionThe genus Merluccius (Ra®nesque) (Gadiformes: Merlucciidae) has a broad latitudinal distribution in the Atlantic and Paci®c Oceans. In the most complete revision on the genus, Inada (1981) recognized 12 species (Table 1). The existence of an additional species, M. hernandezi from the Gulf of California, has also been indicated but its taxonomic status is uncertain (Cohen et al., 1990). The degrees of divergence, phylogenetic relationships and biogeography within Merluccius have generated considerable speculation (Szidat, 1955; Inada, 1981; Kabata & Ho, 1981).Two major hypotheses for the origin and dispersal of Merluccius agree that hakes originated in the Atlantic and entered the Paci®c through the then-open Panamanian seaway. They di er, however, in details of the origins of the Argentine hake M. hubbsi. A proposed eastern origin of M. hubbsi from a South Paci®c stock that rounded Cape Horn to reach Argentina (Szidat, 1955; Inada, 1981) contrasts with a postulated derivation from a western North Atlantic stock (Kabata & Ho, 1981; Ho, 1990).The morphological similarities among species and the uncertainty of phylogenetic relationships, suggest the application of molecular techniques. These methods have provided critical insights towards resolving similar problems in other teleost taxa. Estimated divergence among ®sh taxa, traditionally based on morphological measurements, may mask true genetic relationships, which are more precisely re¯ected by molecular genetic data (Grant, 1987). Allozyme electrophoresis has been a widely applied molecular method for comparing levels of genetic divergence between taxa (...

Regional variability in reproductive traits of European hake Merluccius merluccius L. populations

“…However, it seems that there is neither geographical nor genetic evidence to support the location of a barrier between the stocks (Mattiucci et al, 2004;Castillo et al, 2005). In fact, several previous studies on the ecotypes of European hake species do not support the existence of a boundary between Northern and Southern hake stocks (Roldán et al, 1998(Roldán et al, , 1999Lundy et al, 2000;Pineiro et al, 2007) and more conclusive studies based on biological evidence are required to demonstrate the separation of populations within the present stocks range (Lundy et al, 1999).…”

Clarifying the taxonomic status of Merluccius spp. in the northeastern Pacific: a combined morphological and molecular approach

“…MrModelTest version 2.2 (Nylander 2004) was employed to determine the model of sequence evolution that best fitted our dataset and be included in MrBayes. A combined sequence of M. bilinearis, the most divergent taxon among the American species (Roldán et al 1999;Quinteiro et al 2000;Grant and Leslie 2001;Campo et al 2007) retrieved from GenBank, was included as outgroup; and combined sequences of M. gayi and M. productus, American species from the west coast of the southern and northern East Pacific, respectively, retrieved from GenBank, were also included (Table 3).…”

“…Biogeographic and phylogenetic studies have established that hake are a monophyletic group that originated in the North Atlantic during the Oligocene; during the Miocene, it split into two main clades (Inada 1981;Kabata and Ho 1981;Ho 1990;Roldán et al 1999;Quinteiro et al 2000;Grant and Leslie 2001;Campo et al 2007). The Euro-African clade consisting of hake from the coasts of Western Europe and Western Africa (M. merluccius, M. capensis, M. senegalensis, M paradoxus, and M. polli) and an American clade that includes hake from the Atlantic (M. bilinearis, M. albidus and M. hubbsi) and Pacific (M. gayi, M. productus, M. angustimanus and M. australis) sides of North America.…”

Phylogeny of the genus Merluccius based on mitochondrial and nuclear genes

“…A few studies have been published about the evolution of the genus Merluccius based on genetic data. Roldán et al (1999) traced genetic relationships among nine Merluccius species on the basis of variation at 21 allozyme loci; Quinteiro et al (2000) analyzed sequence variation of the left domain of the mitochondrial DNA control region (450 base pairs) for 26 individuals of 11 species; Grant and Leslie (2001) made a review of previous published genetic data bearing on the phylogeny of hakes in the genus Merluccius, and combined them with new 20 allozyme loci data. According to these and other morphological and biogeographical studies, hakes may have emerged in the North Atlantic during the middle Oligocene (Kabata and Ho, 1981;Inada, 1981;Fedotov and Bannikov, 1989).…”