Genetic subdivision of a sea star with high dispersal capability in relation to physical barriers in a fjordic seascape

Abstract

We used allozymes to investigate the population genetics of the sea star Coscinasterias muricata throughout New Zealand, with emphasis on populations inhabiting the fjords on the west coast of the South Island. Mean genetic variability measured by Wright's F st for all the New Zealand populations was 0.061, indicating a moderate level of genetic divergence on a New Zealand wide scale. F st for populations from the fjord region was generally lower, ranging from 0.024 to 0.028, but it deviated from zero for all the loci examined. Evidence of isolation by distance was found when all populations were used in an analysis of log of the extent of gene flow between a pair of populations (M ) against the log of geographic distance (r 2 = 0.57, p < 0.001, Mantel test). Thus, a pattern of isolation by distance seems evident on this larger scale. However, pair-wise comparisons of genetic distances, measured as F st , of populations on the regional scale of the fjords on the west coast of the South Island showed no correlation, since high variation of F st (0.001 to 0.09) between populations separated by 20 to 105 km was detected. The overall pattern of genetic variation revealed in a cluster analysis of genetic identity, I, grouped all the fjord populations together with maximum genetic identities of 94.6% to the other South Island populations, but within the fjord region, populations were not segregated according to geographical location. We suggest that the relatively isolated hydrography of each fjord is a most likely explanation for why fjord populations form genetic clusters that are inconsistent with geographical distance. The New Zealand fjords changed from freshwater systems about 12 000 to 6500 yr ago, and genetic equilibrium for the populations that colonized the fjords may not have been reached yet. We suggest that the recent colonization of the fjords, and the physical isolation from the open coast and each other, are important in explaining the genetic pattern of fjord populations of C. muricata.

Understanding marine reserve function in a seascape genetics context: Nucella lapillus in Strangford Lough (Northern Ireland) as an example

“…Bell & Okamura 2005). Genetic isolation has also been detected in planktonic-dispersing sea stars from semienclosed fjords (Sköld et al 2003, Perrin et al 2004. It was interesting to note that the levels of genetic differentiation among N. lapillus samples observed in the present study are similar to those reported by Bell & Okamura (2005) between samples from Lough Hyne and nearby coastal areas (F ST = 0.15 to 0.25).…”

“…Jessopp et al 2007). Genetic studies of organisms living in fjordlands have shown that hydrographic and physical barriers impede gene flow and result in genetic structuring even in planktotrophic species with high dispersal capability (Sköld et al 2003, Perrin et al 2004 and references therein). Similarly, substantial levels of population genetic structuring and isolation have been observed in rafting gastropod species in small and very isolated sea loughs (Bell & Okamura 2005).…”

Patterns of larval distribution and settlement of Concholepas concholepas (Bruguiere, 1789) (Gastropoda, Muricidae) in fjords and channels of southern Chile

“…Differences in larval sizes were significantly explained principally by temperature, location and the interaction between location and temperature, suggesting an effect of local hydrology on larval size. Although field studies have shown the potential for plankton retention zones in fiords of southern Chile (Cáceres & Valle-Levinson 2004) and other studies in North America and New Zealand have shown that larval retention can be produced by local hydrology (Wing et al 1995, Churchill et al 1999, Sköld et al 2003, further investigations are needed to directly assess these effects in the inland seas of Chile.…”

Prey base shifts in red rock lobster Jasus edwardsii in response to habitat conversion in Fiordland marine reserves: implications for effective spatial management

“…Evidence for the fragmented nature of populations and communities across the region is found in genetic studies (Sköld et al 2003, Perrin et al 2004) and in descriptions of the variability in community diversity across the landscape (Francis et al 1989, Smith 2001. Studies of population structure in species such as blue cod Parapercis colias (Rodgers & Wing 2008) and the New Zealand sea urchin Evechinus chloroticus (Lamare 1998 indicate that, for some species, the inner-fjord habitats support relatively isolated subpopulations linked by some dispersal from the outer coast.…”