Microsatellite genetic distances between oceanic populations of the humpback whale (Megaptera novaeangliae)

Abstract

Mitochondrial DNA haplotypes of humpback whales show strong segregation between oceanic populations and between feeding grounds within oceans, but this highly structured pattern does not exclude the possibility of extensive nuclear gene flow. Here we present allele frequency data for four microsatellite loci typed across samples from four major oceanic regions: the North Atlantic (two mitochondrially distinct populations), the North Pacific, and two widely separated Antarctic regions, East Australia and the Antarctic Peninsula. Allelic diversity is a little greater in the two Antarctic samples, probably indicating historically greater population sizes. Population subdivision was examined using a wide range of measures, including Fst, various alternative forms of Slatkin's Rst, Goldstein and colleagues' delta mu, and a Monte Carlo approximation to Fisher's exact test. The exact test revealed significant heterogeneity in all but one of the pairwise comparisons between geographically adjacent populations, including the comparison between the two North Atlantic populations, suggesting that gene flow between oceans is minimal and that dispersal patterns may sometimes be restricted even in the absence of obvious barriers, such as land masses, warm water belts, and antitropical migration behavior. The only comparison where heterogeneity was not detected was the one between the two Antarctic population samples. It is unclear whether failure to find a difference here reflects gene flow between the regions or merely lack of statistical power arising from the small size of the Antarctic Peninsula sample. Our comparison between measures of population subdivision revealed major discrepancies between methods, with little agreement about which populations were most and least separated. We suggest that unbiased Rst (URst, see Goodman 1995) is currently the most reliable statistic, probably because, unlike the other methods, it allows for unequal sample sizes. However, in view of the fact that these alternative measures often contradict one another, we urge caution in the use of microsatellite data to quantify genetic distance.

Microsatellite DNA variation reveals high gene flow and panmictic populations in the Adriatic shared stocks of the European squid and cuttlefish (Cephalopoda)

“…The differentiation between samples can be estimated from microsatellite data using statistics based on alternative evolutionary models (ie an infinite allele model, Kimura and Crow, 1964; a stepwise mutation model, Kimura and Ohta, 1978). The most suitable statistical analyses to evaluate the genetic relationships between populations are still a matter of debate (Goodman, 1997;Valsecchi et al, 1997;Gaggiotti et al, 1999;Hardy et al, 2003). For comparative purposes, we chose to use three different methods.…”

Segregation of migration by feeding ground origin in North Atlantic humpback whales (Megaptera novaeangliae)

“…Winter sightings are reported from the Cape Verde Islands for example (Hazevoet & Wenzel, 2000). If whales using these other regions constitute a separate breeding group, and if these individuals primarily feed in the eastern regions of the North Atlantic as genetic results suggest (Valsecchi et al, 1997), then fewer animals from these eastern areas would travel to the West Indies. Alternatively, it has been suggested that not all humpback whales migrate or complete migration each year (Brown et al, 1995;Craig & Herman, 1997).…”

“…Humpback whales are known to occur in the Cape Verde Islands in winter (Hazevoet & Wenzel, 2000), consistent with an eastern breeding area, though no re-sightings from this area have been confirmed. Genetic analysis of nuclear markers revealed a low but significant degree of heterogeneity between samples collected off Iceland and those collected in the western North Atlantic (Valsecchi et al, 1997). Recent findings that animals from Norwegian waters are sighted later in the West Indies season than the mean for other areas suggests that feeding ground origin may influence timing of occurrence in the West Indies.…”

“…Individuals from all North Atlantic feeding aggregations are known to congregate on a common breeding area in the West Indies for mating and calving (Katona & Beard, 1990;Stevick, Øien et al, 1999). Current evidence suggests that this behaviour leads to nearly random mating opportunities relative to feeding ground origin (Clapham, Mattila & Palsbøll, 1993), and this is reflected in the genetic structure of the population (Larsen et al, 1996;Palsbøll, Clapham, Jørgensen et al, 1998; but see Valsecchi et al, 1997). However, significant deviation has been reported in the number of individuals from different feeding areas identified in the West Indies (Katona & Beard, 1990).…”

Microsatellite DNA variation indicates low levels of genetic differentiation among cuttlefish (Sepia officinalis L.) populations in the English Channel and the Bay of Biscay

“…As it is still a matter of debate which is the most suitable statistic model to describe genetic variation among samples (see Goodman, 1997;Valsecchi et al, 1997;Gaggiotti et al, 1999;Hardy et al, 2003), both models were used to analyse the data of this study: The IAM-based F ST (Wright, 1969), which can also be estimated by θ (Cockerham and Weir, 1984), and the SMMbased R ST (Slatkin, 1995) were calculated pairwise for all four populations using the Arlequin software v.2.000. F ST and R ST values were tested for significant departure from zero using permutation procedures implemented in Arlequin v.2.000.…”