Selection of landmarks and semilandmarks in fishes for geometric morphometric analyses: a comparative study based on analytical methods

Abstract

Summary: We applied and compared three different sets of landmarks and semilandmarks commonly used in studies of fish assemblages to identify a standardized method of landmark selection that includes the maximum amount of morphological information of species. The different landmark-based methods used produced differences regarding the distribution of casestudy species within the morphospace. We suggest that adding landmarks and semilandmarks that provide more specific information about anatomical structures with important roles in the biology of species, such as transformed fins or sensory organs, contributes to a clearer differentiation of species within the morphospace and a better interpretation of their occupancy. In addition, three types of method were used to establish how species are distributed within morphospace. The results demonstrated that aggregation points methods, including analyses based on quadrants or distances, are more appropriate for this purpose than indices of morphological disparity. The results also confirmed that although numerical methods are needed to test the statistical significance of outcomes, graphical methods provide a more intuitive interpretation of morphospace occupancy. The kernel density and Gabriel graph were useful to infer the morphospace zone where species are more densely grouped, improving the knowledge of space occupancy and structural complexity of fish assemblages.Keywords: morphological traits; landmarks; geometric morphometrics; diversity; point pattern; morphospace; marine fishes. Selección de puntos homólogos (landmarks) y equidistantes (semilandmarks) en peces para análisis de morfometría geométrica: un estudio comparativo basado en métodos analíticosResumen: En el presente estudio se compara la estructura de una comunidad de peces a partir del análisis morfológico de puntos homólogos (landmarks) y equidistantes (semilandmarks) en las especies de dicha comunidad. Para este propósito, se utilizaron tres metodologías distintas descritas en la literatura a la hora de definir dichos puntos con el fin de identificar cuál de ellas incluía la máxima cantidad de información morfológica posible sobre las especies. Las tres opciones proporcionaron diferentes resultados en relación a la distribución de las especies dentro del morfoespacio. Los resultados sugirieron que la incorporación de puntos que proporcionen información más específica sobre estructuras anatómicas que tienen papeles importantes en la biología de las especies, como aletas modificadas u órganos sensoriales, contribuye a una diferenciación más clara de las especies y a una mejor interpretación de la ocupación del morfoespacio. Adicionalmente, varios métodos numéri-cos y gráficos se emplearon con el fin de establecer cómo las especies se distribuyen dentro del morfoespacio. Los resultados demostraron que los métodos de agregación de puntos, incluyendo análisis basados en cuadrantes o distancias, fueron más apropiados para este propósito que los índices de disparidad morfológica. Además, los resultados tam...

A morphometric dive into fish diversity

“…, Farré et al. ). However, a comparison of landmark‐based approach and outline analysis showed no significant differences (Loy et al.…”

“…, Farré et al. ) that are located on the outline, easily recognizable, and present on all species: (1) snout tip; (2) anterior insertion of the dorsal fin; (3) dorsal and (4) ventral insertion of the caudal fin; and (5) insertion of the pelvic fin (Fig. b).…”

“…However, homologous points are often hard to define between various shapes—for example, between species from different families, and the number and position of homologous landmarks vary between studies and organisms (Farré et al. ). In contrast, outline analyses consider the whole outline.…”

“…The technique has been used extensively in the last decades to study intraspecies fish morphology (Loy et al 2000, Klingenberg et al 2003, Costa and Cataudella 2007, Elmer et al 2010). However, homologous points are often hard to define between various shapes -for example, between species from different families, and the number and position of homologous landmarks vary between studies and organisms (Farr e et al 2016). In contrast, outline analyses consider the whole outline.…”

Geometric morphometrics reveal interspecific and sexual differences in bill morphology in four sympatric planktivorous petrels

“…According to this, these RWs were used to spatially represent the distribution of individuals based on their morphological characteristics and axis orientation (morphospace). In the present study, the morphospaces were created using two‐dimensional representations from the first two relative warps (RW1 and RW2), since they explained a high percentage (77.63% for the profile and 85.53% for the dorsal view of the bill) of the total morphological variability observed (Farré et al ., ).…”