MORPHOMETRIC TAXONOMY OF SIPHONOUS GREEN ALGAE: A METHODOLOGICAL STUDY WITHIN THE GENUS HALIMEDA (BRYOPSIDALES)¹

Abstract

Species-level taxonomy of Bryopsidalean genera is often based on quantifiable morphological characters. Yet there are relatively few examples of statistically founded morphometric studies within this group of siphonous algae and macroalgae in general. Molecular phylogenetic studies have revealed cases of cryptic diversity in several Bryopsidalean genera and call for new approaches toward taxonomy. We present a combined molecular and morphometric approach toward Halimeda taxonomy using a selection of specimens representing the five natural lineages within the genus. A phylogeny was inferred from partial nuclear rDNA sequences (3 0 end of small subunit, internal transcribed spacer region 1, 5.8S, internal transcribed spacer region 2, and 5 0 end of large subunit) from our and previously studied specimens. Segment size and shape descriptors were acquired using different techniques, including landmark analysis and elliptic Fourier analysis. A broad range of anatomical structures was measured. Taxonomic utility of the different methods and characters was assessed using predictive discriminant analysis. Molecular data were used to delimit species groups. Segment morphological characters proved fairly good predictors for species membership, but anatomical variables yielded the best results. The good performance of morphometric taxon predictors offers perspectives, not only for future taxonomic case studies within problematic species complexes, but also for thorough examinations of the rich fossil record of Halimeda. Statistically founded morphometric studies can probably help elucidate taxonomic issues within other Bryopsidalean genera as well.Key index words: anatomy; Bryopsidales; Halimeda; morphology; morphometrics; phylogeny; siphonous algae; taxonomy Abbreviations: DA, discriminant analysis; EFA, elliptic Fourier analysis; ITS, internal transcribed spacer; TBR, tree bisection-reconnection Morphometric analysis, the mathematical investigation of shape, allows objective and statistically sound evaluation of morphological variation to answer a broad spectrum of biological questions. Macroalgae are at first sight less suited for morphometric investigation because their structures and branching patterns are marked by considerable stochastic variation and plasticity. Contrary to botanists and zoologists, phycologists do not have the habit of embracing morphometrics to answer their taxonomic and ecological questions. Nonetheless, during the last 5 years, a raise in interest for morphometrics could be observed (Sherwood and Sheath 1999, Kraan et al. 2001, Krellwitz et al. 2001, Collado-Vides 2002, Hubbard and Garbary 2002, Vieira and Necchi 2002, de Senerpont Domis et al. 2003, Kamiya et al. 2003, Haywood et al. 2004, Murray et al. 2004. Achievements of these studies include reports of morphological differences between taxa and the description of taxon boundaries.In the present study, we explore the taxonomic utility of morphometric methods in the genus Halimeda. This genus belongs to the Bryopsidales, a group of algae ch...

Species-specific consequences of ocean acidification for the calcareous tropical green algae Halimeda

“…A combination of unique anatomical characteristics and differing physiological processes could explain the relative differences in physiological responses to OA between these algae, which belong to genetically and morphologically distinct lineages (Verbruggen & Kooistra 2004, Verbruggen et al 2005. H. opuntia has more heavily branched, widely spaced siphons that may explain its high CaCO 3 content in comparison to H. taenicola, which has less branched but much thicker and more tightly packed siphons (Hillis 1959, Verbruggen et al 2005 (Fig. 1C,D), creating a smaller inter-utricular calcifying space that is more isolated from ambient seawater.…”

“…data). We worked with 2 species common in both habitats on Palmyra that differed greatly morphometrically and genetically (Verbruggen et al 2005). Halimeda opuntia (Opuntia lineage) is a heavily calcified and dense, matt-forming species that attaches to the substratum in numerous locations using small rhizoidal attachments.…”

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

“…A similar approach combined with interfertility studies could provide insights into the nature of subgroups uncovered in the present study. Furthermore, studies analyzing both morphometric and DNA sequence data (Verbruggen et al 2005) can reveal which morphological characters can be used to diagnose different species and their internal clades.…”

O gênero Halimeda (Bryopsidales, Chlorophyta) no litoral do estado da Bahia, Brasil

“…Isso pode estar relacionado com o fato desses organismos também se reproduzirem assexuadamente por fragmentação vegetativa, e por darem preferência por esse modo de reprodução (Walters et al 2002), que pode conferir uma economia energética para o indivíduo. Embora Halimeda seja um gênero conspícuo e fácil de ser reconhecido no campo, a identificação de suas espécies é difícil, estimulando a busca de métodos que auxiliem na taxonomia do grupo (Verbruggen et al 2005).…”

“…O material coletado foi encaminhado ao LAMAR e triado a olho nu. Para a identificação dos táxons em nível infragenérico, consultou-se obras comumente utilizadas para o gênero (Yamada 1941;Joly 1967;Hillis 1959;Littler & Littler 2000;Barata 2004;Bandeira-Pedrosa et al 2004a,b;Verbruggen et al 2005;Amorin et al 2006 Plantas moderadamente calcificadas, verdeescuras, esbranquiçadas quando secas, eretas, solitárias, até 15 cm alt., fixas ao substrato por um apressório discoide. Região internodal com os 2 ou 3 primeiros segmentos cilíndricos, aparentando um estipe, os demais planos, cuneados, subcuneados, discoides ou trapezoides, lisos, brilhantes, margens inteiras, até 20 mm larg.…”