DEFINING TAXON BOUNDARIES IN MEMBERS OF THE MORPHOLOGICALLY AND GENETICALLY PLASTIC GENES CAULERPA (CAULERPALES, CHLOROPHYTA)¹

Abstract

Numerous attempts to capture the morphological variability of the genus Caulerpa have resulted in an unstable classification of numerous varieties and formae. In the present study we attempted to test taxon boundaries by investigating morphological and genetic variation within and between seven taxa of Caulerpa, supposedly belonging to four species, sampled at different sites in a Philippine reef system. Using both field and culture observations, we described the relation between the variability of a set of morphological characters and ecological parameters, such as wave exposure, light intensity, and substrate type. Statistical analyses showed that the limits between two (out of three) ecads of the C. racemosa (Forsskål) J. Agardh complex were obscured by the presence of morphological plasticity. Other studied taxa of Caulerpa (i.e. C. cupressoides [Vahl] C. Agardh, C. serrulata [Forsskål] J. Agardh, and two formae of C. sertularioides [S. Gmelin] Howe) could be grouped based on morphology despite the presence of morphological plasticity. Our results indicated a strong association between light intensity and several quantitative morphological variables. Genetic diversity of these taxa was assessed by partial sequencing chloroplast rbcL and tufA genes and the ycf10-chlB chloroplast spacer. In all phylogenetic analyses, C. serrulata, C. cupressoides, C. sertularioides, and the three ecads of C. racemosa emerged as distinct genetic units. Despite the presence of morphological plasticity and morphological convergence, a subset of morphological characters traditionally used in taxonomic delimitation still had sufficient discriminative power to recognize the terminal phylogenetic clades.

Nitrogen load and irradiance affect morphology, photosynthesis and growth of Caulerpa prolifera (Bryopsidales: Chlorophyta)

“…The formation of extra assimilators and/or stolons or rhizoids is hence merely a consequence of small-scale differences in cell-wall stretching. It is known that gravity and light climate are important factors in assimilator and rhizoid formation (Collado-Vides 2002b, de Senerpont Domis et al 2003. The present results indicate that nutrient availability also has its effect on morphogenesis.…”

“…The form of the individuals is supported and maintained by numerous ingrowths of cell-wall material, the trabeculae (Jacobs 1994). Although great interspecific morphological variability exists, all species follow a common architectural scheme, consisting of a creeping stolon bearing various erect assimilators and rhizophores with rhizoid clusters (Collado-Vides 2002a, de Senerpont Domis et al 2003. The rhizoids do not only function as a holdfast, but are also involved in nutrient uptake from the sediment (Williams 1984, Chisholm et al 1996.…”

GENETIC PATTERNS IN THE CALCIFIED TROPICAL SEAWEEDS HALIMEDA OPUNTIA, H. DISTORTA, H. HEDERACEA, AND H. MINIMA (BRYOPSIDALES, CHLOROPHYTA) PROVIDE INSIGHTS IN SPECIES BOUNDARIES AND INTEROCEANIC DISPERSAL1

“…Moreover, genetic, biological, and morphological boundaries between some species may become fuzzy through hybridization. Recent work in the related genus Caulerpa (Famà et al 2000, Durand et al 2002, de Senerpont Domis et al 2003 and in several coral genera (Veron 1995, Van Oppen 2001 also shows considerable intraspecific genetic diversity and ill-defined species boundaries.…”

Morphological plasticity and variable spatial patterns in different populations of the red alga Rissoella verrucosa

“…Lewis et al 1987), whereas population-specific responses to changes in abiotic conditions have been inferred mostly from comparisons of contrasting habitats and in the laboratory (e.g. de Senerpont Domis et al 2003). Our study adds to a limited number of investigations showing that phenotypic differences in a marine alga can be reversed by changes in environmental conditions, using a field-based transplant experiment (see also Blanchette 1997 andSerisawa et al 2002).…”