CHAPTER 50
Sexual Reproduction and Recruitment in Posidonia Oceanica (L.)
Delile, a Genetic Diversity Study
L. Orsini', s. Acunto:Z, L. Piazzil, and G. Procaccini'
ABSTRACT
The aim of our analysis was to provide evidence of the contribution that sexual reproduction has
for increasing genetic diversity in P. oceanica meadows. The genetic diversity of three established populations and three adjacent seedling patches located along the Tuscany coast were
surveyed. Seedling patches had higher values of heterozygosity and number of distinct genotypes but comparable number of alleles in respect to adult meadows, as ascertained using
microsatellite marker. Assuming that seedlings are the result of sexual reproduction, high levels
of inbreeding and self-fertilization can account for the slight increase of genetic variability. Our
results also indicate that recruitment can occur from propagules originating outside the local
population, limiting population genetic isolation at the given spatial scale.
Introduction
The genetic structure of seagrass populations is
the result of sexual reproduction) clonal growth
and gene flow among localities (Les 1988;
Procaccini and Mazzella 1998). Sexual reproduction plays the role of introduction and inheritance of genetic variation, ensuring adequate
genetic plasticity for survival and evolution of
populations in changing environments (Les
1988).
Posidonia oceanica is an endemic Mediterranean seagrass, that forms widespread meadows
along the coasts of the whole basin. The P. oceanica meadows are composed by donal patches
(Caye and Meinesz 1992; Procaccini and Mazzella
1998), the expansion of which would depend upon the past andlor recent history of successful
sexual reproductive events and recruitment in a
given locality. Nonetheless) sexual reproduction
is sporadic and the overall low genetic diversity
recently found in Western Mediterranean populations of such species (Procaccini et al. 1996;
Procaccini and Mazzella 1996,1998) suggests that
clonal propagation is the main reproductive
mode for maintaining and expanding established
meadows. Climatic conditions are changing in
the Mediterranean basin, and man-induced
modifications of the coastline are determining
habitat loss and meadow regression especially in
highly urbanized areas. The capability of P.
oceanica to adapt to new and changing environmental conditions through the adaptation of new
and well fit genotypes is therefore important to
ascertain.
Sexual reproduction is a sporadic event in P.
oceanica meadows and few records report in situ
germinating seeds along the coasts of Italy (e.g.
Meinesz et al.1993; Gambi et a1.1996; Piazzi et al.
1996). Posidonia is a monoecious genus with
populations composed by a mosaic of clonal
patches of different sizes. Because of that, fecundation might occur between male and female
flowers belonging to the same shoot. to the same
clone or to genetically similar individuals. The
level of inbreeding, in fact. appears to be extremely high in natural populations (Procaccini
and Mazzella 1998).
In this paper we wish to describe the levels of
genetic diversity observed as a result of sexual
reproduction. Microsatellite DNA markers were
surveyed to establish population genetic variation in three well established populations and in
three adjacent patches of germinating seeds
(seedlings) located along the Tuscany coast. The
mature meadows can be the result of either don1 Stazione Zoologica "A. Dohrn", Laboratorio di Ecologia del Benthos, 80077 Ischia (Napoli), Italy
2 Dipartimento di Scienze dell'Uomo edell' Arobiente, Universita di Pisa, 56126 Pisa, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
e Springer-Verlag Italia 2001
Sexual Reproduction and Recruitment in Posidonia Oceanica (L.)
Delile, a Genetic Diversity Study
L. Orsini', s. Acunto:Z, L. Piazzil, and G. Procaccini'
ABSTRACT
The aim of our analysis was to provide evidence of the contribution that sexual reproduction has
for increasing genetic diversity in P. oceanica meadows. The genetic diversity of three established populations and three adjacent seedling patches located along the Tuscany coast were
surveyed. Seedling patches had higher values of heterozygosity and number of distinct genotypes but comparable number of alleles in respect to adult meadows, as ascertained using
microsatellite marker. Assuming that seedlings are the result of sexual reproduction, high levels
of inbreeding and self-fertilization can account for the slight increase of genetic variability. Our
results also indicate that recruitment can occur from propagules originating outside the local
population, limiting population genetic isolation at the given spatial scale.
Introduction
The genetic structure of seagrass populations is
the result of sexual reproduction) clonal growth
and gene flow among localities (Les 1988;
Procaccini and Mazzella 1998). Sexual reproduction plays the role of introduction and inheritance of genetic variation, ensuring adequate
genetic plasticity for survival and evolution of
populations in changing environments (Les
1988).
Posidonia oceanica is an endemic Mediterranean seagrass, that forms widespread meadows
along the coasts of the whole basin. The P. oceanica meadows are composed by donal patches
(Caye and Meinesz 1992; Procaccini and Mazzella
1998), the expansion of which would depend upon the past andlor recent history of successful
sexual reproductive events and recruitment in a
given locality. Nonetheless) sexual reproduction
is sporadic and the overall low genetic diversity
recently found in Western Mediterranean populations of such species (Procaccini et al. 1996;
Procaccini and Mazzella 1996,1998) suggests that
clonal propagation is the main reproductive
mode for maintaining and expanding established
meadows. Climatic conditions are changing in
the Mediterranean basin, and man-induced
modifications of the coastline are determining
habitat loss and meadow regression especially in
highly urbanized areas. The capability of P.
oceanica to adapt to new and changing environmental conditions through the adaptation of new
and well fit genotypes is therefore important to
ascertain.
Sexual reproduction is a sporadic event in P.
oceanica meadows and few records report in situ
germinating seeds along the coasts of Italy (e.g.
Meinesz et al.1993; Gambi et a1.1996; Piazzi et al.
1996). Posidonia is a monoecious genus with
populations composed by a mosaic of clonal
patches of different sizes. Because of that, fecundation might occur between male and female
flowers belonging to the same shoot. to the same
clone or to genetically similar individuals. The
level of inbreeding, in fact. appears to be extremely high in natural populations (Procaccini
and Mazzella 1998).
In this paper we wish to describe the levels of
genetic diversity observed as a result of sexual
reproduction. Microsatellite DNA markers were
surveyed to establish population genetic variation in three well established populations and in
three adjacent patches of germinating seeds
(seedlings) located along the Tuscany coast. The
mature meadows can be the result of either don1 Stazione Zoologica "A. Dohrn", Laboratorio di Ecologia del Benthos, 80077 Ischia (Napoli), Italy
2 Dipartimento di Scienze dell'Uomo edell' Arobiente, Universita di Pisa, 56126 Pisa, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
e Springer-Verlag Italia 2001