Discrimination of the species of the Crassiphycus corneus/C. usneoides complex (Gracilariaceae, Rhodophyta) through geometric morphometric analysis

Abstract

The results of the discrimination by geometric morphometry of the species within the Crassiphycus corneus/C. usneoides complex is presented, from the shape of its cortical, subcortical and medullary cells in the apical, medium and basal portions of thallus. Principal component analysis, based on the elliptic Fourier descriptors of cellular outline shapes and NP-MANOVA analysis, show that only the cortical cells in the medium portion were significantly wider in C. corneus than in C. usneoides. The isoperimetric quotients (Q) indicated that these cells were significantly more circular in C. corneus than in C. usneoides. We conclude that the outline analyses efficiently recovered phenotypic differences between the species defined by molecular systematics and considered to be cryptic, so far.

Molecular assessment of the species of Gracilariaceae (Gracilariales, Rhodophyta) from the Yucatan Peninsula, Mexico, including two new records for the Mexican Atlantic

“…In some cases, such as Gracilaria hayi, G. suzanneae, and G. curtissiae, the values of the interspecific distances ranged between 0.8 and 1.5 %, which is less than the range of interspecific values proposed by to delimit species of Gracilariaceae (from 2 to 3.4 %). From our results, a morphometic study of these species could provide additional evidence to support their phylogenetic independence, as it was in the case of Crassiphycus species, previously considered as cryptic species and currently discriminated by morphometric analysis (Vilchis et al 2019(Vilchis et al , 2020.…”

“…In their study they described that within the morphological spectrum of the two species included in the complex, there were two genetically independent entities, although morphologically indistinguishable. Recently, Vilchis et al (2019Vilchis et al ( , 2020 was able to discriminate both genetic entities, by applying morphometric techniques, both by the diameter in the middle and apical portion of the thallus (significantly larger in C. usneoides than in C. corneus) and by the shape of the cells (narrower in C. usneoides). Given that C. corneus and C. usneoides were circumscribed only with morphological evidence, the characters that were used for discriminated them overlap between the two species, so it may be that in Brazil only C. corneus is distributed.…”

“…However, although the monophyly of Gracilariaceae is well-supported by molecular data (Gurgel et al 2018(Gurgel et al , 2020, the morphological recognition of the species continues to be a difficult task and, in some cases, almost impossible because most species exhibit high morphological variability, leading to unclear species circumscriptions and an overlapping of characters (Bird & McLachlan 1982, Santelices & Valera 1993, Lyra et al 2015a, Núñez-Resendiz et al 2015. This overlapping has led to the uncovering of cryptic species (Saunders 2009) and confusion in their identification and geographic distribution ranges (Byrne et al 2002, Cohen et al 2004, Dreckmann et al 2018, Vilchis et al 2019, which currently generates an underestimation or overestimation of the actual diversity of species in the family (Dreckmann 2012, Dreckmann & Sentíes 2014. Different molecular markers have been successfully employed in studies of the Gracilariales allowing for the elucidation of species boundaries, phylogenetic relationships, and the recognition of new species (Kim et al 2008, Yang et al 2008, Muangmai et al 2014a,b, Ardito et al 2017, Hardesty & Freshwater 2018, Le et al 2020.…”

Análisis morfométrico de las especies simpátricas del complejo Crassiphycus corneus/C. usneoides (Gracilariaceae, Rhodophyta) en las costas mexicanas del Golfo de México y Mar Caribe

“…Esta situación ha podido ser resuelta eficazmente mediante análisis de morfometría (Kraan et al, 2001;Maderbacher et al, 2008;Abdel-Rahman et al, 2009;Grenat et al, 2012;Hidalgo et al, 2012;Borda y Ramírez, 2014), ya que complementan los análisis cualitativos cuantificando y evaluando estadísticamente la variación morfológica entre taxones (Umphrey, 1996;Calle et al, 2008;Toro et al, 2010;Navia et al, 2015). Para el grupo de las macroalgas los análisis morfométricos son escasos (Verbruggen et al, 2005;Hidalgo et al, 2012;Núñez-Resendiz et al, 2015;Vilchis et al, 2019). De acuerdo con Verbruggen et al (2005), se debe a que a simple vista estos organismos son poco adecuados para la investigación morfométrica, ya que sus estructuras y patrones de ramificación se caracterizan por una gran variación estocástica y plasticidad fenotípica.…”