World phylogeography and male-mediated gene flow in the sandbar shark, Carcharhinus plumbeus

Abstract

The sandbar shark, Carcharhinus plumbeus, is a large, cosmopolitan, coastal species. Females are thought to show philopatry to nursery grounds while males potentially migrate long distances, creating an opportunity for male-mediated gene flow that may lead to discordance in patterns revealed by mitochondrial DNA (mtDNA) and nuclear markers. While this dynamic has been investigated in elasmobranchs over small spatial scales, it has not been examined at a global level. We examined patterns of historical phylogeography and contemporary gene flow by genotyping 329 individuals from nine locations throughout the species' range at eight nuclear microsatellite markers and sequencing the complete mtDNA control region. Pairwise comparisons often resulted in fixation indices and divergence estimates of greater magnitude using mtDNA sequence data than microsatellite data. In addition, multiple methods of estimation suggested fewer populations based on microsatellite loci than on mtDNA sequence data. Coalescent analyses suggest divergence and restricted migration among Hawaii, Taiwan, eastern and western Australia using mtDNA sequence data and no divergence and high migration rates, between Taiwan and both Australian sites using microsatellite data. Evidence of secondary contact was detected between several localities and appears to be discreet in time rather than continuous. Collectively, these data suggest complex spatial/temporal relationships between shark populations that may feature pulses of female dispersal and more continuous male-mediated gene flow.

Dietary overlap and partitioning among three sympatric carcharhinid sharks

“…LL: maximum log-likelihood; k: number of model parameters; AIC c : Akaike's information criterion corrected for small samples; ΔAIC c : differences between the current and top-ranked model AIC c ; wAIC c : AIC c weights; % DE: percent deviance explained , Lopez et al 2009, Cabrera-Chávez-Costa et al 2010, Markaida & SosaNishizaki 2010. This similarity occurred despite the sex-specific use of habitats driven by traits such as female philopatry, which has recently been identified in C. leucas (Tillett et al 2012) or the possibility of female mate avoidance (Feldheim et al 2001, 2004, Portnoy et al 2010, Veríssimo et al 2011. It would seem reasonable to assume that the greater energetic cost associated with egg production and gestation in females might result in preferences for prey yielding higher net energy profits, and thus differences in diet between males and females.…”

Two-year migration of adult female white sharks (Carcharodon carcharias) reveals widely separated nursery areas and conservation concerns

“…In some coastal-shark species, females have been shown to be philopatric to specific nursery regions [30][31][32][33]. Longer-term tracking could provide confirmation of such behavior in white sharks, and explain the presence of persistent YOY hotspots [8,24,25,34] and the genetic indication that females do not disperse [11].…”

Population structure of the loggerhead turtle Caretta caretta, a large marine carnivore that exhibits alternative foraging behaviors

“…Nevertheless, in some cases, population differentiation inferred from mtDNA sequences is stronger than that from microsatellites (e.g. FitzSimmons et al 1997b, Bowen et al 2005, Carreras et al 2007, Chen et al 2008, Lukoschek et al 2008, Okello et al 2008, Caparroz et al 2009, Hefti-Gautschi et al 2009, Portnoy et al 2010, and this has been attributed to sex differences in natal philopatry and dispersal. Individuals sampled at a location are usually treated as a single population in wildlife population genetics (Frankham et al 2002).…”