Is asexual reproduction more important at geographical limits? A genetic study of the seagrass Zostera marina in the Ria Formosa, Portugal

Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

“…P ID was calculated for each locus using adult allele frequencies in the population and then multiplied across loci to give an overall P ID (Waits et al, 2001). Asexual reproduction is a common reproductive strategy in many coral species and will influence estimates of population structure and mating system (for example, Ayre and Hughes, 2000;Billingham et al, 2003;Baums et al, 2005). I therefore assessed the importance of asexual reproduction within my populations by first comparing the number of colonies sampled (N) to the number of unique multi-locus genotypes (N g ) detected.…”

The vegetative arctic freshwater green alga Zygnema is insensitive to experimental UV exposure

“…The strong tendency in the occurrence of asexual populations are reported in a species' geographical limits (e.g. further north of Northern Hemisphere), at high altitudes, and in resource poor environments (Billingham et al, 2003;Eckert, 2002;Kearney, 2003;Peck et al, 1998). On the other hand, the greater sensitivity of the sexual reproductive phase compared to the asexual vegetative phase to environmental stress factors, i.e.…”

Genetic diversity of a clonal angiosperm near its range limit: the case of Cymodocea nodosa at the Canary Islands

“…Levels of genetic differentiation are highly variable among individual seagrass meadows; even so, a trend for higher differentiation at species distribution limits has been detected (e.g. Billingham et al 2003). The population of Cymodocea nodosa in the Canary Islands is peripheral to the general range of the species: the Canary Islands represent the western distributional limit, and are close to the southern distributional limit (Green & Short 2003).…”

“…Seagrass meadows with extremely low levels of genotypic richness, which are highly dependent on vegetative growth, have been observed mainly at distributional edges (e.g. Reusch et al 1999, Alberto et al 2001, Billingham et al 2003). This effect is even more pronounced in dioecious species like Cymodocea nodosa, because both male and female genotypes are needed to produce sexual propagules.…”

“…Such analyses have revealed a wide range of genotypic richness across seagrass populations, from monoclonal stands (Reusch et al 1999, Billingham et al 2003 to highly diverse stands (Reusch 2001, Coyer et al 2004, Diekmann et al 2005. Seagrass meadows with extremely low levels of genotypic richness, which are highly dependent on vegetative growth, have been observed mainly at distributional edges (e.g.…”