Current patterns, habitat discontinuities and population genetic structure: the case of the kelp Laminaria digitata in the English Channel

Abstract

Laminaria digitata is the dominant species of the dense, continuous kelp stands in the English Channel and on the Atlantic coasts of France, where it is harvested for its high quality alginates. However, in spite of its ecological and economic importance, our knowledge of the level and organisation of genetic diversity in this species is scant. Here, using comprehensive hierarchical sampling and 7 microsatellite loci, we explored the roles of dispersal strategies, current regimes and habitat discontinuities in shaping genetic structure of L. digitata populations. Our results show that continuous, non-fragmented forests of L. digitata were genetically differentiated at distances greater than 10 km, despite the absence of clear population boundaries. Furthermore, a pattern of isolationby-distance indicated that gene flow occurred preferentially among adjacent populations following a stepping-stone model. In addition, we analysed the direction of migration using assignment tests and found that currents appeared to play a minor role in orienting gene flow, except in the Gulf of Saint Malo gyre. In contrast, habitat discontinuities were found to accentuate genetic differentiation and resulted in reduced genetic variation of isolated stands. In the context of a potential over-exploitation of kelp stands in Brittany, this study suggests that the existence of neighbouring populations can be vital to maintaining high levels of gene flow and thus, genetic diversity in this species.

Interactive effects of UV radiation and temperature on microstages of Laminariales (Phaeophyceae) from the Arctic and North Sea

“…Admittedly, Bolton & Lüning (1982) did not find ecotypic differentiations in thermal responses within gametophytes of S. latissima isolates from France, Brittany, Norway, or HLG or from L. digitata isolates from Canada and HLG. But investigations by Billot et al (2003) found genetic differentiations in continuous, nonfragmented forests of L. digitata at distances greater than only 10 km. The different capacities for sporophyte formation of S. latissima demonstrated here through crossing experiments between Arctic and HLG isolates support additionally an ecotypic differentiation in S. latissima (Fig.…”

Nonrandom Larval Dispersal Can Steepen Marine Clines

“…Fortunately, when sharp clines occur in species with sedentary adults, it facilitates experimental methods that can distinguish between patterns produced by dispersal barriers versus postdispersal selection (Koehn et al 1980;Bierne et al 2003;Gilg and Hilbish 2003;Toro et al 2004). Also, directional gene flow has been detected in several marine systems (Wares et al 2001;Billot et al 2003) and estimates should improve through the use of high-resolution genetic markers (Estoup et al 1999;Mountain et al 2002) and analyses designed to take advantage of them (Falush et al 2003;Wilson and Rannala 2003;Hey et al 2004). Thus, the experimental tools exist to test for patterns of nonrandom gene flow that could accentuate differentiation within a species.…”

Estudos populacionais em Gracilaria birdiae e G.caudata (Gracilariales, Rhodophyta): aspectos fenológicos, fisiológicos e moleculares

“…Essa flutuação randômica da frequência dos genes é denominada de deriva genética . O fluxo gênico é o processo migratório de alelos que ocorre preferencialmente entre populações adjacentes (Billot et al, 2003). Entretanto, a descontinuidade de habitats, tais como a presença de desembocaduras de rios e trechos de substrato impróprio, entre outros, pode criar barreiras para o fluxo gênico e favorecer a diferenciação genética (Kimura & Weiss, 1964;Faugeron et al, 2001;Billot et al, 2003).…”

“…O fluxo gênico é o processo migratório de alelos que ocorre preferencialmente entre populações adjacentes (Billot et al, 2003). Entretanto, a descontinuidade de habitats, tais como a presença de desembocaduras de rios e trechos de substrato impróprio, entre outros, pode criar barreiras para o fluxo gênico e favorecer a diferenciação genética (Kimura & Weiss, 1964;Faugeron et al, 2001;Billot et al, 2003). Estudos indicam que para as algas a diferenciação genética pode ocorrer a partir de distâncias relativamente curtas, maiores que um metro e menores que 10 km (Billot et al, 2003).…”

“…Entretanto, a descontinuidade de habitats, tais como a presença de desembocaduras de rios e trechos de substrato impróprio, entre outros, pode criar barreiras para o fluxo gênico e favorecer a diferenciação genética (Kimura & Weiss, 1964;Faugeron et al, 2001;Billot et al, 2003). Estudos indicam que para as algas a diferenciação genética pode ocorrer a partir de distâncias relativamente curtas, maiores que um metro e menores que 10 km (Billot et al, 2003). Além disso, modos de dispersão distintos para gametas e/ou esporos podem resultar em variações na estrutura genética (Sosa & Lindstrom, 1999;Valero et al, 2001).…”