NICHE PARTITIONING AND THE COEXISTENCE OF TWO CRYPTIC DICTYOTA (DICTYOTALES, PHAEOPHYCEAE) SPECIES FROM THE CANARY ISLANDS¹

Abstract

Coexistence in a homogeneous environment requires species to specialize in distinct niches. Sympatry of cryptic species is of special interest to both ecologists and evolutionary biologists because the mechanisms that facilitate their persistent coexistence are obscure. In this study, we report on two sympatric Dictyota species, D. dichotoma (Huds.) J. V. Lamour. and the newly described species D. cymatophila sp. nov., from the Canary Islands. Gene sequence data (rbcL, psbA, nad1, cox1, cox3, and LSU rDNA) demonstrate that D. dichotoma and D. cymatophila do not represent sister species. Rather, D. cymatophila and D. dichotoma have converged on a nearly identical morphology, only to be distinguished with detailed morphometric observations. Both species co-occur in eulittoral pools and the shallow subtidal in Tenerife. Even though D. cymatophila was more dominant in wave-exposed places and D. dichotoma in less exposed areas, the spatial distribution of both species overlapped in intermediate habitats. The species display radically different phenologies. D. dichotoma reached its highest density in winter and early spring and disappeared nearly completely in autumn, while D. cymatophila dominated the study site from July until November. The timing of gamete release also differs between both species, D. dichotoma releasing gametes twice every lunar cycle, while the release of gametes in D. cymatophila occurred roughly every other day.

Cryptic species in sympatry: nonrandom small-scale distribution patterns inBostrychia intricata(Ceramiales, Rhodophyta)

“…For example, in the Canary Islands, the brown alga Dictyota cymatophila Tronholm, M.Sansón & Afonso-Carrillo more frequently occurred in wave-exposed habitats, whereas D. dichotoma (Hudson) J.V.Lamouroux was found in less-exposed areas (Tronholm et al 2010). Additionally, physical conditions related to wave exposure limit the horizontal distribution of marine macroalgae, as found in the intertidal kelp Postelsia palmaeformis Ruprecht from the northeast Pacific (Nielsen et al 2006).…”

“…In intertidal ecosystems, many studies have previously demonstrated temporal and spatial niche differentiations (e.g. reproductive timing, tidal position and exposure level) among competing taxa, allowing them to coexist at small scales (Benzie et al 2000;De Troch et al 2003;Sampayo et al 2007;Tronholm et al 2010;Lai et al 2011;Zardi et al 2011). For example, within mid-intertidal pools along the northern Gulf of California, the brown alga Sargassum johnstonii Setchell & Gardner grew at a shallower depth than S. sinicola subsp.…”

“…Recently, molecular data have been used to solve taxonomic problems in marine species and uncover hidden diversity (Knowlton 2000;Zuccarello & West 2003Lindstrom 2008;Tronholm et al 2010). Cryptic species are a group of two or more morphologically indistinguishable species (Bickford et al 2007).…”

Taxonomy of Marine Macroalgae Used as Sources of Bioactive Compounds

“…In addition, morphological differences between some species are subtle and easily go unnoticed, particularly if specimens are not examined with suffi cient care. For example, using a combination of morphological and molecular data Tronholm et al ( 2010a ) showed that in the Canary Islands Dictyota cymatophila was confused with D. dichotoma for a long time. The two species are frequently found mixed in the fi eld, where they are usually impossible to distinguish; they can be recognized, however, based on differences in the phenology and in microscopic morphological characters.…”

Temporal variations of vegetative features, sex ratios and reproductive phenology in a Dictyota dichotoma (Dictyotales, Phaeophyceae) population of Argentina

“…Several studies have revealed cryptic species within morphologically defined species, falsifying the assumption that speciation events coincide with any morphological differentiation (Tronholm et al 2010a). Therefore, molecular work is currently conducted by us to precisely corroborate the identity of the present population and to evaluate the possibility that it could represent a cryptic species (Marine macroalgae collections in north Patagonian coasts to obtain DNA barcodes: iBol Project, CONICET).…”