Chapter 2 Seagrass Genetics and Evolution
45
relatively few individuals sampled for each species
as is appropriate for phylogenetic analysis. In comparison, fine scale estimates of inbreeding and population structure within populations in Europe and
the USA have provided insight into the interaction between ecology and evolutionary strategies
in this species (Ruckelshaus, 1998; Williams and
Orth, 1998; Reusch et al., 1999d; Reusch, 2001a;
Olsen et al., 2004). However, the connection between
the broadest scale process and the evolution of this
species is only now being revealed through studies
using high resolution, species-wide population genetic analysis (Olsen et al., 2004).
Thus, a significant issue in the interpretation of
genetic data are the level of diversity detected using particular genetic markers. This issue has been
exemplified in the early studies that utilized allozymes to detect genetic diversity (e.g. McMillan,
1991) and which revealed very high levels of genetic homogeneity (see Les, 1988 for discussion).
Although subsequent studies on the same species
using allozymes revealed significantly greater polymorphism than early studies (Ruckelshaus, 1995;
Waycott, 1995; Ruckelshaus, 1996; Waycott et al.,
1997; Waycott and Sampson, 1997; Ruckelshaus,
1998; Waycott, 1998), DNA based markers revealed even higher levels of variability (Waycott,
1995; Waycott et al., 1996; Waycott, 1998; Reusch
et al., 1999d; Reusch et al., 1999c; Reusch et al.,
2000).
New approaches are being developed continuously that allow improved interpretations of the different hierarchical processes of interest (e.g. Zhang
and Hewitt, 2003). For example, there is now a growing interest in studying adaptive genetic polymorphism at the DNA level. To undertake such studies,
however, polymorphism in genes of adaptive significance must be analysed. There are a number of
candidate genes to begin these studies, for example
genes related to photosynthesis (Garc´ ıa-Gil et al.,
2003) or to heat stress (Heckathorn et al., 1996),
which can be inferred from model plants. Marker
loci provide one view on the measurement of genetic diversity; the future of many genetic studies
will be to understand the effects, polymorphism and
fitness consequences of loci that selection will actually operate upon (see, for example, Mitchell-Olds,
2001 and references therein). It is therefore worthwhile to invest in the most variable and informative
marker (currently microsatellite markers for population analyses and DNA sequences of multiple loci for
phylogeny) available within the constraints of time
and budget for a project.
To ensure adequate future survival of seagrasses,
globally, a greater understanding of the relationships
between species, the baseline genetic variability of
species, their reproductive biology and unique adaptive traits is needed and such knowledge will become
increasingly available, as discussed in this chapter.
Acknowledgments
The authors wish to thank their many collaborators
and colleagues who have contributed to the work
they present here in review. In particular, we wish to
acknowledge the many useful discussions with (in alphabetical order) Penny Barnes, Bill Dennison, Tim
Carruthers, Jim Coyer, Carlos Duarte, Wilson Freshwater, Jud Kenworthy, Jeanine Olsen, Tom Philbrick,
Ester Serrao, Di Walker, Susan Williams, and many
others. We also wish to honour the memory of two
of our mentors, Lucia Mazzella and Sid James, who
provided inspiration and support.
References
Ackerman JD (1995) Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms. Evol Ecol 9: 139–
153
Ackerman JD (1997) Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. Influence of floral
morphology on fluid flow. Am J Bot 84: 1099–1109
Agardh CA (1821) Species Algarum rite cognitae cum synonymis differentis specificis et descriptionibus succinctis,
vol 1, Gryphiswaldiae, Mavritii
Alberte RS, Suba GK, Procaccini G, Zimmerman RC and Fain
SR (1994) Assessment of genetic diversity of seagrass populations using DNA fingerprinting: Implications for population
stability and management. Proc Nat Acad Sci USA 91: 1049–
1053
Alberto F, Correia L, Arnaud-Haond S, Billot C, Duarte CM and
Serr˜ ao E (2003a) New microsatellite markers for the endemic
Mediterranean seagrass Posidonia oceanica. Mol Ecol Notes
3: 253–255
Alberto F, Correia L, Billot C, Duarte CM and Serr˜ ao E (2003b)
Isolation and characterization of microsatellite markers for the
seagrass Cymodocea nodosa. Mol Ecol Notes 3: 397–399
Alberto F, Mata L and Santos R (2001) Genetic homogeneity in
the seagrass Cymodocea nodosa at its northern Atlantic limit
revealed through RAPD. Mar Ecol Prog Ser 221: 299–301
Angel R (2002) Genetic diversity in Halodule wrightii using
Random Amplified Polymorphic DNA. Aquat Bot 74: 165–
174
Ara˜ no KG, Ouborg JN and de Ruyter van Steveninck E (2003)
Chloroplast DNA phylogeography of Indo-Pacific seagrasses
(Abstract). Gulf Mex Sci 21: 126
45
relatively few individuals sampled for each species
as is appropriate for phylogenetic analysis. In comparison, fine scale estimates of inbreeding and population structure within populations in Europe and
the USA have provided insight into the interaction between ecology and evolutionary strategies
in this species (Ruckelshaus, 1998; Williams and
Orth, 1998; Reusch et al., 1999d; Reusch, 2001a;
Olsen et al., 2004). However, the connection between
the broadest scale process and the evolution of this
species is only now being revealed through studies
using high resolution, species-wide population genetic analysis (Olsen et al., 2004).
Thus, a significant issue in the interpretation of
genetic data are the level of diversity detected using particular genetic markers. This issue has been
exemplified in the early studies that utilized allozymes to detect genetic diversity (e.g. McMillan,
1991) and which revealed very high levels of genetic homogeneity (see Les, 1988 for discussion).
Although subsequent studies on the same species
using allozymes revealed significantly greater polymorphism than early studies (Ruckelshaus, 1995;
Waycott, 1995; Ruckelshaus, 1996; Waycott et al.,
1997; Waycott and Sampson, 1997; Ruckelshaus,
1998; Waycott, 1998), DNA based markers revealed even higher levels of variability (Waycott,
1995; Waycott et al., 1996; Waycott, 1998; Reusch
et al., 1999d; Reusch et al., 1999c; Reusch et al.,
2000).
New approaches are being developed continuously that allow improved interpretations of the different hierarchical processes of interest (e.g. Zhang
and Hewitt, 2003). For example, there is now a growing interest in studying adaptive genetic polymorphism at the DNA level. To undertake such studies,
however, polymorphism in genes of adaptive significance must be analysed. There are a number of
candidate genes to begin these studies, for example
genes related to photosynthesis (Garc´ ıa-Gil et al.,
2003) or to heat stress (Heckathorn et al., 1996),
which can be inferred from model plants. Marker
loci provide one view on the measurement of genetic diversity; the future of many genetic studies
will be to understand the effects, polymorphism and
fitness consequences of loci that selection will actually operate upon (see, for example, Mitchell-Olds,
2001 and references therein). It is therefore worthwhile to invest in the most variable and informative
marker (currently microsatellite markers for population analyses and DNA sequences of multiple loci for
phylogeny) available within the constraints of time
and budget for a project.
To ensure adequate future survival of seagrasses,
globally, a greater understanding of the relationships
between species, the baseline genetic variability of
species, their reproductive biology and unique adaptive traits is needed and such knowledge will become
increasingly available, as discussed in this chapter.
Acknowledgments
The authors wish to thank their many collaborators
and colleagues who have contributed to the work
they present here in review. In particular, we wish to
acknowledge the many useful discussions with (in alphabetical order) Penny Barnes, Bill Dennison, Tim
Carruthers, Jim Coyer, Carlos Duarte, Wilson Freshwater, Jud Kenworthy, Jeanine Olsen, Tom Philbrick,
Ester Serrao, Di Walker, Susan Williams, and many
others. We also wish to honour the memory of two
of our mentors, Lucia Mazzella and Sid James, who
provided inspiration and support.
References
Ackerman JD (1995) Convergence of filiform pollen morphologies in seagrasses: Functional mechanisms. Evol Ecol 9: 139–
153
Ackerman JD (1997) Submarine pollination in the marine angiosperm Zostera marina (Zosteraceae). I. Influence of floral
morphology on fluid flow. Am J Bot 84: 1099–1109
Agardh CA (1821) Species Algarum rite cognitae cum synonymis differentis specificis et descriptionibus succinctis,
vol 1, Gryphiswaldiae, Mavritii
Alberte RS, Suba GK, Procaccini G, Zimmerman RC and Fain
SR (1994) Assessment of genetic diversity of seagrass populations using DNA fingerprinting: Implications for population
stability and management. Proc Nat Acad Sci USA 91: 1049–
1053
Alberto F, Correia L, Arnaud-Haond S, Billot C, Duarte CM and
Serr˜ ao E (2003a) New microsatellite markers for the endemic
Mediterranean seagrass Posidonia oceanica. Mol Ecol Notes
3: 253–255
Alberto F, Correia L, Billot C, Duarte CM and Serr˜ ao E (2003b)
Isolation and characterization of microsatellite markers for the
seagrass Cymodocea nodosa. Mol Ecol Notes 3: 397–399
Alberto F, Mata L and Santos R (2001) Genetic homogeneity in
the seagrass Cymodocea nodosa at its northern Atlantic limit
revealed through RAPD. Mar Ecol Prog Ser 221: 299–301
Angel R (2002) Genetic diversity in Halodule wrightii using
Random Amplified Polymorphic DNA. Aquat Bot 74: 165–
174
Ara˜ no KG, Ouborg JN and de Ruyter van Steveninck E (2003)
Chloroplast DNA phylogeography of Indo-Pacific seagrasses
(Abstract). Gulf Mex Sci 21: 126