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Journal of Experimental Marine Biology and Ecology 246 2000 69–83
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Large scale population structure and gene flow in the planktonic developing periwinkle, Littorina striata, in
Macaronesia Mollusca: Gastropoda
a , a
a,b
Hans De Wolf , Ron Verhagen , Thierry Backeljau
a
Ecophysiology and Biochemistry Group and Evolutionary Biology Group ,
University of Antwerp RUCA Groenenborgerlaan 171, B-2020 Antwerp, Belgium
b
Royal Belgian Institute of Natural Sciences KBIN, Vautierstraat 29, B-1000 Brussels, Belgium
Abstract
Allozymes were used to investigate the genetic structure of 42 populations of the planktonic developing, Macaronesian periwinkle Littorina striata, throughout its entire geographic range
Azores, Madeira, Canary Islands and Cape Verde Islands. This periwinkle is presumed to have a high dispersal and gene flow potential, because it has a planktonic development. It is therefore
expected to show little population genetic differentiation. Indeed, based on Wright’s hierarchical F-statistics, no significant genetic differentiation could be detected among populations, at any of
the specified hierarchical levels i.e. population, island, and archipelago. Nevertheless, the Cape Verde Islands seemed genetically more diverse highest mean number of alleles per locus. The
number of loci revealing a significant genetic heterogeneity increased with increasing distance between populations, while private alleles based gene flow Nm estimates also revealed a
tendency towards a geographical pattern. The distribution of rare and private alleles, might account for these observations which suggested some geographical effect. Because of the low
frequency at which these alleles occur, their influence on the genetic population structure is negligible, and not picked up by F-statistics.
2000 Elsevier Science B.V. All rights reserved.
Keywords : Allozymes; Gene flow; Littorina striata; Macrogeography; Planktonic development; Macaronesia
1. Introduction
Marine organisms with high dispersal potential often show only limited population genetic differentiation, because gene flow is usually positively correlated with dispersal
Corresponding author. Tel.: 132-3-218-0347; fax: 132-3-218-0497.
E-mail address : dewolfruca.ua.ac.be H. De Wolf,
0022-0981 00 – see front matter
2000 Elsevier Science B.V. All rights reserved. P I I : S 0 0 2 2 - 0 9 8 1 9 9 0 0 1 7 7 - X
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. De Wolf et al. J. Exp. Mar. Biol. Ecol. 246 2000 69 –83
ability e.g. Crisp, 1978; Palumbi, 1994, 1996. In marine gastropods, for example, species with planktonic dispersing larvae display higher levels of gene flow and less
population genetic differentiation e.g., Mitton et al., 1989; Benzie and Williams, 1992; Brown and Murray, 1995, than nonplanktonic developing species with poor dispersal
capacity e.g. Johannesson et al., 1993; Johnson and Black, 1995; Rolan-Alvarez et al., 1995; Trussell, 1996. Nevertheless, even in species with high dispersal abilities there
are several factors that may limit actual dispersal and or gene flow, thus creating opportunities for genetic differentiation as well Palumbi, 1994, 1996. These limitations
include: invisible gene flow barriers, isolation by distance, behavioral limits to dispersal, selection, and the recent history of a species Palumbi, 1994, 1996.
For instance, in the Macaronesian i.e. Azores [AZ], Madeira [MA], Canary Islands [CA] and Cape Verde Islands [CV] planktonic developing periwinkle, Littorina striata,
King and Broderip, 1832, no genetic population differentiation is detected at mi- crogeographical scales i.e. 5–100 m De Wolf et al. 1998a, whereas preliminary
allozyme data tentatively suggest a tendency towards an isolation by distance IBD relationship among more distant populations i.e. up to 500 km within an archipelago
AZ Backeljau et al., 1995. In addition, esterase and random amplified polymorphic DNA RAPD patterns reveal a higher degree of genetic variability in the CV than in the
other archipelagos De Wolf et al. 1998b,c.
In this paper we explore the population genetics of L . striata at macrogeographic
scales by surveying allozyme data from populations covering the entire known geographic distribution of the species i.e. up to 2000 km. We particularly aim at
assessing whether the allozyme variation reveals a macrogeographical patterning and if so, whether this patterning is indeed related to IBD.
2. Materials and methods
