No abstract

No abstract

No abstract

No abstract

Dosidicus gigas and Sthenoteuthis oualaniensis (Teuthoidea: Ommastrephidae: Ommastrephinae) are abundant, ecologically important squid that co-occur in the eastern tropical Pacific. Little is known about the genetic basis of population structure in either species, although the presence of 2 species within S. oualaniensis has been suggested. We report here on a comparative population genetic study of D. gigas and S. oualaniensis using the mitochondrial marker NADH dehydrogenase subunit 2. Despite the high potential for dispersal in these active swimmers, both species exhibit a distinct biogeographic break at 5 to 6°N. S. oualaniensis contains multiple deeply divergent, geographically segregated clades, whereas D. gigas shows only mild divergence between northern and southern hemisphere populations. We suggest that dispersal and genetic mixing across the eastern tropical Pacific may be impeded by both oceanographic and ecological factors. KEY WORDS: Biogeographic comparison · Eastern Pacific · Ommastrephid squid · Population genetic structure Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 418: [165][166][167][168][169][170][171][172][173][174][175][176][177][178] 2010 ML. Nigmatullin et al. (2001) suggested that the 3 sizeat-maturity forms may be incipient species, or at least distinct stocks. However, other researchers have proposed separating D. gigas into only 2 stocks, one 'northern' and one 'southern,' based on supposed migration patterns rather than size at maturity (Wormuth 1976, Nesis 1983, Clarke & Paliza 2000.Tagging studies on individuals of the large form of Dosidicus gigas have revealed that they make extensive use of the prominent oxygen minimum zone (OMZ) in the eastern Pacific, indicated with a white hashed line in Fig. 1. This zone provides a refuge from predators that cannot tolerate hypoxia, and also appears to be a favored hunting area of these large D. gigas (Gilly et al. 2006b).In the eastern tropical Pacific, the range of Dosidicus gigas overlaps with that of Sthenoteuthis oualaniensis (Lesson, 1830), the purpleback flying squid, a species of growing commercial interest (Zuyev et al. 2002, Xinjun et al. 2007). S. oualaniensis, however, does not extend into the temperate Pacific but it is found across the tropical and subtropical Pacific and Indian Oceans (Fig. 1). This transoceanic range is typical of the subfamily Ommastrephinae, to which both species belong. The northsouth distribution of D. gigas is unique and may belie an ecological connection between this species and the OMZ.Sthenoteuthis oualaniensis comprises multiple forms (Nesis 1983, Dunning 1998 These morphologies demonstrate 2 distinct gladius structures in western specimens Table 1. Dosidicus gigas and Sthenoteuthis oualaniensis. Size-at-maturity forms (Nesis 1983, Dunning 1998. ML: mantle length. nd: no morphological differences other than size at maturity are known for the forms of D. gigas with the photophore is found throughout the species range and co-occurs wit...