Isabel Meneses

SPORELING COALESCENCE AND INTRACLONAL VARIATION IN GRACILARIA CHILENSIS (GRACILARIALES, RHODOPHYTA)

This study evaluates the hypothesis that spore coalescence may cause intraclonal variation. Spore coalescence might allow the occurrence of unitary thalli that in fact correspond to genetically different, coalesced individuals. Plant portions simultaneously derived from these chimeric individuals may exhibit dissimilar growth responses even when incubated under similar abiotic conditions. Testing of the hypothesis included various approaches. Transmission electron microscopy observations of early stages of sporeling coalescence indicated that polysporic plantlets were formed by groups of spores and their derivatives. Even though adjacent cells in two different groups may fuse, these groups maintained an independent capacity to grow and form uprights. Laboratory‐grown plantlets showed a significant correlation between the initial number of spores and the total number of erect axes differentiated from the sporeling. Construction and growth of bicolor individuals indicated the chimeric nature of the coalesced individuals. Coalesced, bicolor holdfasts had green and red cells, which subsequently produced green and red uprights, respectively. Individuals fronds were also chimeric, as indicated by the production of green and red branchlets from single, red uprights. The existence of mixed tissues was further substantiated by random amplified polymorphic DNA analysis. The banding pattern produced by branchlets of a unisporic thallus was consistently monomorphic, whereas the patterns produced by the polysporic thallus were polymorphic. Growth rates of polysporic thalli had larger data dispersal and variation coefficients than oligosporic or monosporic thalli. Therefore, all results support the original hypothesis and suggest that coalescence might be ecologically more important than previously thought.

Differences in the early stages of development of gametophytes and tetrasporophytes of Chondracanthus chamissoi (C.Ag.) Kützing from Puerto Aldea, northern Chile

Abstract Gametophytes of Chondracanthus chamissoi are more abundant in the field than tetrasporophytes. This differential phase ratio is well known in the literature for other members of the Gigartinaceae and has been explained as the result of either stochastic events or differential reproductive or physiological capacities between the phases. The comparison of both phases of Chondracanthus chamissoi in their early stages of development under laboratory conditions were summarised. Despite the higher biomass of reproductive tetrasporophytes recorded in summer (the seasonal maxima), significantly more carpospores are released per gram than tetraspores. During the following processes of settlement and germination, tetraspores show higher average values mainly due to their persistence in time. These differences tend to disappear in winter when the capacity of spores to develop normally appears to be lower. On the other hand, sporophytic growth rates are higher than gametophytic growth rates for most conditions of day length, light intensity and temperature. With no other external factors considered, the higher abundance of gametophytes in the field appears to be a result of the higher capacities of tetraspores to settle and germinate after an extended period of time suspended in the water column.

Strain selection and genetic variation in Gracilaria chilensis (Gracilariales, Rhodophyta)

Strain selection processes in seaweed often have assumed that sterile clones could be maintained for long periods in a diversity of environments without major genetic changes. However, clonal species such as Gracilaria chilensis exhibit intra-clonal variation in performance and ongoing studies suggest such changes may be due to rapid changes in DNA composition associated with growth, via mitotic recombinations. Therefore performance of a given ramet in this type of seaweed should be understood as the dynamic outcome of rapid reactions between the environment and the changing genotype of the selected strain. To evaluate this idea, we measured changes in genetic variability, as detected by DNA-fragment polymorphism using RAPDs-PCR, exhibited by clones of G. chilensis after two transfers to different environmental conditions (from field to controlled laboratory conditions and from the laboratory to large-scale tank culture). The transfer to laboratory conditions reduced the frequency of low similarity values and increased the frequency of intermediate similarity values in DNA banding patterns, suggesting the branchlets produced under controlled laboratory conditions have less genetic variability (evaluated as total DNA polymorphism) than plants recently collected in the field. Tank incubation reduced the total range of similarity and significantly increased the frequency of high similarity values. Results thus suggest the dynamic of genetic changes in vegetative clones of Gracilaria chilensis that is fast and strongly affected by the external environment.

Patterns and breaking points in the distribution of benthic algae along the temperate Pacific coast of South America

De acuerdo a estudios biogeograficos realizados hace 20 anos, las especies de algas marinas bentonicas de la costa temperada del Pacifico de Sudamerica se agrupan en 5 componentes de distinta afinidad geografica. Cada uno de estos componentes posee una distribucion diferencial a lo largo de estas costas entre los 4o y los 55oS. De esta forma su contribucion a la flora varia dependiendo de la latitud. La composicion de las especies cambia en determinadas latitudes de manera que se pueden reconocer tres grupos: uno se encuentra de 4o a 6oS, otro de 6o a 30oS y el tercero de 30o a 55oS. A partir de 1980, el aporte de nuevos estudios en algas ha permitido una revision de esta caracterizacion fitogeografica. La presencia /ausencia de las especies, separadas dentro de cada division por afinidad geografica, fue registrada para cada grado de latitud entre los 4o y los 56oS, y usada para analizar la similitud en la composicion de especies y los posibles cambios en sus patrones de distribucion. Los resultados muestran los mismos 5 componentes geograficos encontrados 20 anos atras con distribuciones similares. Las diferencias observadas consisten en: una incursion mas al sur de elementos subtropicales, una disminucion en el numero de especies endemicas y en su contribucion relativa en el extremo sur de Sudamerica y, la presencia de dos puntos de quiebre en la composicion de las especies, a los 12o y a los 42oS. Otros dos puntos de quiebre se presentan en las Phaeophyta a los 20oS y en las Rhodophyta a los 33oS. La inclusion de especies con un solo registro no afectan significativamente la distribucion de las especies a lo largo de estas costas

A reassessment of the phytogeographic characterization of Temperate Pacific South America

El estudio de los patrones de distribucion geografica de las algas marinas bentonicas en la costa temperada de Sudamerica (5-55 oS) permitio en 1980 caracterizar estas costas como con un alto grado de endemismo y con intercambio floristico limitado con localidades situadas en el Pacifico Tropical o con las islas oceanicas del Pacifico Sur dispuestas a distintas distancias de la costa. Este bloqueo parcial al intercambio de especies explicaria la baja riqueza de especies de estas costas en comparacion con costas climaticamente equivalentes pero con un numero mayor de vias de emigracion asi como el patron latitudinal de riqueza de especies que en esta zona muestra un incremento en el numero total de especies hacia latitudes mayores. En las ultimas dos decadas en esta zona se ha realizado un numero cercano a 30 estudios taxonomicos de algas bentonicas y fitogeograficos, agregando un numero significativo de nuevos registros para el area. Una puesta a prueba de esta caracterizacion fitogeografica a la luz de estos nuevos hallazgos indica que los nuevos datos agregan sustentacion a la caracterizacion biogeografica, incluyendo la importancia relativa de distintos componentes floristicos a distintas latitudes en estas costas, el caracter aislado de esta flora y el patron latitudinal de incremento en riqueza de especies hacia latitudes mayores

Phylogeography of the genus Spongites (Corallinales, Rhodophyta) from chile

Both the records and the descriptions of the crustose species of coralline algae on the southeastern coast of South America are from the early 1900s. Unlike other algae species on the coast of Chile, the biogeography and distribution of crustose corallines have not been studied despite their abundance. Through recent studies, it has been determined that the genus Spongites is the most conspicuous genus along the rocky intertidal of the Chilean coasts. It is also common to the entire coast of the Southern Hemisphere; however, the relationship between species and the possible reasons for their distribution is unknown. We used nuclear and mitochondrial genetic markers and SEM observations of morphological characters to examine Spongites samples from the Southern Hemisphere and to establish the phylogeographic relationships of Chilean Spongites with specimens from other southern coasts. The combination of these analyses revealed the following: (i) a monophyletic clade that represents the Chilean Spongites and (ii) a paraphyletic clade for South African, New Zealand, and Argentine samples. Consequently, we postulate two nonexclusive hypotheses regarding the relationship of Spongites species in the Southern Hemisphere: (i) a complex history of extinction, speciation, and recolonization that might have erased original Gondwanan split patterns, and (ii) an Antarctic Peninsula origin for the Chilean Spongites species.

Assessment of populations ofGracilaria chilensis (Graeilariales, Rhodophyta) utilizing RAPDs

Phenotypic variability and mixing of material due to massive cultivation for commercial purposes has contributed to the taxonomic confusion ofGracilaria in Chile. At least four species with cylindrical thalli and similar morphology have been recorded. However, since establishment ofG. chilensis, most of the collected thalli have been attributed to this species despite the lack of diagnostic features. In an attempt to resolve whetherGracilaria from 3 localities where it grows in natural and artificial populations belongs to the same species, gametophytic samples were compared by applying RAPD-PCR to their total DNA. This was analysed using 25 different 10-mer primers from which 21 revealed polymorphism within and between populations. Similarity matrices and cluster analyses were performed based on the presence/absence of bands representing fragments of DNA generated by random amplification. Similarity values between two of the populations were equivalent to those detected within a third, indicating the mixing of genetic material due to transplant between the two former localities. Similarities between samples of ChileanGracilaria andG. tenuistipitata from Sweden are considerably lower (0.45–0.53) than those between populations from Chile (0.74–0.88), confirming the existence of a single specific taxon,G. chilensis, in these three localities.

Enhanced DNA extraction and PCR amplification of SSU ribosomal genes from crustose coralline algae

As crustose Corallinales on the coasts of Chile are usually flat, thin,strongly adherent to the rocks and with a high concentration ofpolysaccharides,there is a need to improve DNA extraction for molecular studies. The paperdescribes a protocol to achieve this, which includes steps for disruption ofcell walls and precipitation of polysaccharides and proteins; this leads to aPCR-quality product. The DNA obtained permitted amplification of SSU and rbcLgenes from small amounts of material (< 1 g) of several generaand species of Corallinales. Comparison of the sequences of small SSU fragments(approximately 500 bp), combined with morphological characters,together provide sufficient resolution to distinguish organisms at the genusandspecies levels.

Molecular genetic identification of crustose representatives of the order Corallinales (Rhodophyta) in Chile

Knowledge on species of the order Corallinales along the coast of Chile is still scarce despite a number of studies and records of other divisions of seaweeds made since the early 20th century. This lack of information is more dramatic among crustose representatives of the order, thus depriving biogeographic studies of a thorough analysis and resulting in inadequately representative accounts of biodiversity. The currently changing taxonomy of the group makes it difficult to identify and differentiate among taxa based on morphological and developmental characters. Therefore, the use of molecular tools has been adopted in this study in order to facilitate identification and comparison of crustose corallines collected at the rocky intertidal between 27 degrees and 48 degrees S along the Pacific temperate coast of South America. A sequence 600bp (in length) from the SSU-rDNA gene was used to identify five taxa to the genus level: Lithophyllum, Spongites, Mesophyllum, Synarthrophyton, and Leptophytum. In all cases, the genus distinction based on morphological characters coincide with designations based on variation in the ribosomal DNA gene sequence. Spongites is the most frequently occurring genus and is found in all localities sampled while the others appear occasionally. Taxa recognition at species level must be examined with caution considering that morphological variability is not well understood in Chile because the SSU-rDNA region sequence does not always stand alone as an unambiguous means of identifying all coralline species. In such cases, more rapidly evolving markers are needed. For example, sequences from the ITS (rDNA) region often provide greater resolution among closely related species and genera. However, the methodology presented here remains a useful tool for species-level identification.

Foam as a dispersal agent in the rocky intertidal of central Chile

Culture studies under controlled laboratory conditions have demonstrated that seafoam contains macroalgal propagules which may contribute to the macroalgal populations common in the rocky intertidal of two localities from central Chile. Although macroalgal propagules are more abundant in the seawater of these localities than in the seaform, seafoam facilitates the attachment of spores and algal propagules and the subsequent development of the germlings by providing a suitable wet and calm environment during low tides.