Page 8 - Tomasello_Borra_etal2009

Tomasello, Di Maida, Calvo, Pirrotta, Borra & Procaccini Seagrass meadows at the extreme of environmental tolerance

A 12 n.s. those found outside the lagoon. This situation could
generate inbreeding among the confined P. oceanica
mm year–1 11 shoots with genetic drift and possible selection of adapted
10 genotypes in the northern basin of the lagoon. The lower
Récif Plateau Nubia Marsala Favignana growth rate in the lagoon as inferred from lepidochrono-
9 logical data and the lack of flowering are indicative of
8 Site persistent stressful conditions.

7 ** n.s. The Atolls population exhibits a lower number of
alleles, lower percent of polymorphic loci, lower clonal
6 diversity and higher heterozygosity excess relative to the
5 other sites included in the present analysis. Different rea-
sons can account for the high heterozygosity. First, in the
Atollis literature high heterozygosity has been positively corre-
lated with fitness, particularly when organisms live in
B9 unfavorable environmental conditions. This has been
demonstrated experimentally in mice for functional traits
8 represented by allozymes (Teska et al. 1990). In theory it
should not apply if the markers utilized are truly neutral,
n year–1 which is generally assumed for microsatellites (Hansson &
Westerberg 2002). Nevertheless, it has been demonstrated
7 that microsatellites have a range of different functions
within the genome (Li et al. 2002) and we cannot exclude
*** the possibility that some loci utilized here show patterns
not consistent with neutrality (see Oetjen & Reusch 2007
6 Récif Plateau Nubia Marsala Favignana for Zostera marina). Secondly, excess of heterozygosity in
Atollis neutral markers can also derive from the combined effect
of linkage disequilibrium and partial inbreeding (Hansson
Site & Westerberg 2002), a scenario which could easily apply
to the Stagnone populations. Nevertheless, our results do
Fig. 4. Estimate of mean rhizome elongation (A) and annual leaf for- not completely support this latter option. All populations
mation (B). Estimate of mean rhizome elongation have been retro- analysed here, in fact, have a negative Fis value, but the
spectively corrected, as if all shoots have been sampled with same value is consistently lower in the Atolls population than
age, corresponding to the grand mean (8.1 years). Significance: *** in the others, showing lower inbreeding in the more
P < 0.001; ** P = 0.001–0.01; ns, P > 0.05. Bar indicates standard confined locality. The highest number of loci showing
error. potential linkage, instead, is present at the Atolls site.

Stagnone di Marsala coastal lagoon. Each atoll is com- In general, species inhabiting temporally variable or
posed of multiple genotypes, which falsifies the hypothesis spatially heterogeneous environments exhibited higher
of their monoclonal structure. Nonetheless, the atolls
show characteristics of genetic isolation, namely the exis-
tence of alleles and genotypes which are distinct from

Table 4. Average frequency of meadow (FF, flowering years per year), shoot flowering probability (Pf, inflorescence Æ shoot)1 Æ year)1), and flow-
ering intensity (inflorescences Æ shoot)1, calculated from meadows FI means) for the six sampling sites.

number of
shoots

present previous number of time horizon Time
site study study total shoots (FF and Pf) FF ± SE (nstation) Pf (nstation) horizon (FI) FI ± SE (nstation)

Atolls 40 99 139 84–04 0.00 (ns = 1) 0.0000(ns = 1) 92–00 0.00(ns = 1)
Re´ cif 40 53 93 89–04 0.188(ns = 1) 0.0051(ns = 1) 94–99 0.017 ± 0.002(ns = 1)
Plateau 38 11 49 92–04 0.077(ns = 1) 0.0022(ns = 1) –
Nubia 42 202 92–04 0.282 ± 0.082(ns = 2) 0.0087 ± 0.0008(ns = 2) –
Marsala 41 167 244 88–04 0.249 ± 0.018(ns = 2) 0.0092 ± 0.0041(ns = 2) 95–99 0.028 ± 0.015(ns = 2)
Favignana 42 234 208 80–04 0.217 ± 0.063(ns = 2) 0.0108 ± 0.0016(ns = 2) 94–99 0.013 ± 0.005(ns = 2)
total 243 766 276 80–04 0.196 ± 0.036(ns = 9) 0.0072 ± 0.0015(ns = 9) 85–99 0.032 ± 0.015(ns = 2)
1009 85–00 0.026 ± 0.007(ns = 8)

Marine Ecology 30 (2009) 288–300 ª 2009 Blackwell Verlag GmbH 295