Morfometría geométrica y sus nuevas aplicaciones en ecología y biología evolutiva: Parte 2 / Geometric morphometric and its new applications in ecology and evolutionary biology: Part 2

RESUMEN: La presente revisión entrega una visión actualizada del estudio de la morfometría geométrica y sus aplicaciones más actuales en ecología y biología evolutiva, metodología con una amplia variación en los últimos 5 años de su primera versión en International Journal of Morphology. La Morfometría geométrica es una herramienta que permite evaluar las variaciones morfológicas con factores subyacentes, siendo una herramienta más sensible que la morfometría tradicional, lo que permite detectar mínimos cambios de variación morfológica. Lo que la ha vuelto una herramienta notable para responder preguntas de biología comparada centradas en caracteres anatómicos. En sus comienzos fue una herramienta usada principalmente para responder preguntas taxonómicas, y para diferenciar a nivel de individuos, poblaciones o especies. No obstante, en los últimos años la cantidad de preguntas y problemáticas en las que se aplica, ha diversificado considerablemente, pasando a ser una herramienta muy precisa para responder preguntas de variación morfológica en contextos ecológicos y evolutivos. Ya ha pasado casi media década desde la última revisión del método, por lo que éste trabajo tiene como objetivo analizar los cambios metodológicos y los nuevos enfoques usados en Morfometría geométrica, y presentar una pequeña guía introductoria a éstos nuevos métodos, sus usos y aplicaciones.

SUMMARY: This study provides an updated vision of the study of Geometric Morphometrics and its most recent application in ecology and evolutionary biology, covering a wide variation in methodology occurring in the last 5 years since the first version published in the International Journal of Morphology. Geometric Morphometrics is a tool that allows evaluating morphological variations with underlying factors, with a higher sensitivity than traditional morphology, so that minimum changes of morphological variation can be detected. Therefore, it has turned into an outstanding tool to answer questions of comparative biology focused on anatomic characters. At the beginning, it was a tool mainly used to answer taxonomic questions and for differentiation at individual, population or species level. However, in the last years, the number of questions and problematic on which it is applied, has diversified considerably, turning it into a very accurate tool to answer questions of morphological variation in ecologic and evolutionary contexts. Almost half a decade has elapsed since the last revision of the method, so this work is intended to analyze the methodological changes and the new approaches used in Geometric Morphometrics, including a brief introductory guideline to these new methods, their uses and applications.

Sexual dimorphism and population differentiation in the Chilean Neotropical moth Macaria mirthae (Lepidoptera, Geometridae): a wing geometric morphometric example

Abstract Sexual shape dimorphism is the differentiation of male and female organisms based on their shape variation; this definition was proposed for the use of geometric morphometrics analysis where the geometric features of the shape are analyzed without the influence of the size. Macaria mirthae (Lepidoptera: Geometridae) is a moth that inhabits different valleys in the north of Chile principally associated to Acacia macracantha and lately Leucaena leucocephala both trees of the Fabaceae family. The Sexual dimorphism was analyzed in this species in order to corroborate studies on the use of wing as a sexual differentiation trait, and specific influence of localities was also evaluated. A clear shape variation was found where the male wings are more contracted compared to female wings. A climate influence is also suggested that could differentiate the wing shape from the individuals that inhabit two different valleys in the neotropical region of the north of Chile. This research supports previous studies identifying a clear Sexual shape dimorphism in the wing, as a selected trait, suggesting that oviposition and male competition of this group of moths is reflected in their wings. These differences raise the question whether Sexual shape dimorphism can be modulated by natural selection.

Modelando la varianza de la forma: morfometría geométrica aplicaciones en biología evolutiva / Modelling shape variance: geometric morphometric applications in evolutionary biology

La comparación de caracteres anatómicos entre organismos ha sido un elemento central de la biología comparada. Históricamente, la clasificación taxonómica y la comprensión de la diversidad biológica se han basado en descripciones morfológicas. En base a una revolución matemática cuantitativa, el estudio de la morfología ha tenido un importante énfasis gracias al desarrollo del análisis de la forma mediante la combinación de métodos estadísticos multivariados y nuevas maneras de visualización. El objetivo de la presente revisión es dar una visión actualizada sobre los avances del estudio de la morfometría geométrica (MG) en biología evolutiva, así como introducir a temáticas en fuerte desarrollo (e.g. estabilidad del desarrollo, integración y modularidad morfológicas, entre otras). Se espera proporcionar una visión amplia del uso de la MG en biología evolutiva, destacando la necesidad de aumentar el esfuerzo de investigación en esta disciplina, junto con llamar la atención acerca de la utilidad de la MG como una herramienta efectiva, precisa, amigable y barata para cuantificar y estudiar la variación morfológica.

The comparison of anatomical traits between organisms has been a central topic in comparative biology. Historically, taxanomic classification and biological diversity understanding have been based on morphological descriptions. Derived from a mathematical quantitative revolution, morphological studies have experienced an important renewal due to the development of shape analysis rooted in statistical multivariate methods and novel visualisation techniques. The aim of the present review is to provide an updated perspective regarding the progress in geometric morphometrics (GMM) applied to evolutionary biology, as well as introducing to cutting-edge subjects (e.g. developmental stability, modularity, morphological integration, among other themes). Thus, it is expected to provide a broad point of view with respect to the appliaction of geometric morphometrics in evolutionary biology, highlighting its usefulness as an effective, accurate, user-friendly and inexpensive method to quantify and study shape variation.

Egg laying site selection by a host plant specialist leaf miner moth at two intra-plant levels in the northern Chilean Atacama Desert

Egg laying site selection by a host plant specialist leaf miner moth at two intra-plant levels in the northern Chilean Atacama Desert. The spatial distribution of the immature stages of the leaf miner Angelabella tecomae Vargas & Parra, 2005 was determined at two intra-plant levels (shoot and leaflet) on the shrub Tecoma fulva fulva (Cav.) D. Don (Bignoniaceae) in the Azapa valley, northern Chilean Atacama Desert. An aggregated spatial pattern was detected for all the immature stages along the shoot, with an age dependent relative position: eggs and first instar larvae were clumped at apex; second, third and fourth instar larvae were mostly found at intermediate positions; meanwhile the spinning larva and pupa were clumped at basis. This pattern suggests that the females select new, actively growing leaflets for egg laying. At the leaflet level, the immature stages were found more frequently at underside. Furthermore, survivorship was higher for larvae from underside mines. All these results highlight the importance of an accurate selection of egg laying site in the life history of this highly specialized leaf miner. By contrast, eventual wrong choices in the egg laying site selection may be associated with diminished larval survivorship. The importance of the continuous availability of new plant tissue in this highly human modified arid environment is discussed in relation with the observed patterns.

Femoral functional adaptation: a comparison between hunter gatherers and farmers using geometric morphometrics / Adaptación funcional del fémur: una comparación entre cazadores-recolectores y agricultores usando morfometría geométrica

The transition from hunting and gathering to agriculture has been associated with a gracilization in human form, especially in long bones. This has been interpreted as result of an increasingly sedentary lifestyle and reduced workload in the farming populations. However the majority of these evidences have been based on the application of different biomechanical techniques or the qualitative assessment of distinct morphological traits on attachment sites. Hence, this study tried to address whether is possible to distinguish between two different populations (hunter-gatherers and farmers) by quantifying their femoral morphology applying geometric morphometrics. We compared 16 male left femora belonging to two populations of Native Americans from the same geographic region, yet temporally and behaviorally distinct, in order to test if geometric morphometrics were able to differentiate these based solely on the quantitative analysis of shape. The femora were scanned and then small portions of them were segmented in order to generate comparable 3D models. Hundred twelve equidistant landmarks were collected over the whole femoral sections and a Procrustes analysis was performed in order to obtain shape variables. Several PCAs were carried out to elucidate morphometric associations and cross-validated DAs were applied to distinguish between hunter-gatherers and farmers. These procedures were sequentially repeated using different landmarks subsets in order to try to establish the anatomical locations where bone functional adaptation mostly occurs: a) femoral cortex; b) medullary cavity; c) complete femoral section. The results here presented, showed that geometric morphometrics were able to distinguish between the two distinct lifestyles. Moreover, the contrasting results obtained from the analysis of the femoral cortex and the medullary cavity, suggest that long bone remodelling caused by lifestyle differences, mostly occurs on the outer surface of the femoral shaft. This study also showed a relative gracilization of the farmer as compared to the hunter-gatherers.

La transición desde la caza y la recolección a la agricultura ha sido asociada con una gracilización en la forma humana, especialmente en los huesos largos. Esto ha sido interpretado como resultado de un estilo de vida más sedentario y con menor carga de trabajo en las poblaciones agricultoras. Sin embargo, la mayoría de estas evidencias se han basado en técnicas biomecánicas o en la evaluación cualitativa de rasgos morfológicos en los sitios de inserción muscular. Este estudio intentó distinguir entre dos poblaciones diferentes (cazadores-recolectores y agricultores) mediante la cuantificación de su morfología femoral aplicando morfometría geométrica. Dieciséis fémures masculinos pertenecientes a dos poblaciones nativo americanas de la misma región geográfica, aunque temporal y conductualmente diferentes, fueron comparadas con la finalidad de probar si la morfometría geométrica era capaz de distinguirlas. Los fémures fueron escaneados y pequeñas porciones fueron segmentadas para generar modelos 3D. Se colectaron 112 hitos equidistantes sobre toda la superficie femoral y luego se realizó un análisis de Procusto para obtener variables de la forma. Diversos análisis de componentes principales se llevaron a cabo para establecer asociaciones morfométricas, así como también análisis discriminantes con validación cruzada para distinguir entre cazadores-recolectores y agricultores. Estos procedimientos fueron repetidos utilizando diferentes subconjuntos de hitos para establecer donde ocurre mayoritariamente la adaptación funcional del hueso: a) corteza femoral; b) cavidad medular; c) sección femoral completa. Los resultados aquí presentados mostraron que la morfometría geométrica permite distinguir entre ambos modos de vida. Además, los contrastantes resultados obtenidos del análisis de la corteza femoral y cavidad medular, sugieren que el remodelamiento óseo debido a diferentes estilos de vida ocurren mayoritariamente en la superficie de la diáfisis del fémur. Este estudio también mostró una relativa gracilización de la población agricultora al ser comparada con los cazadores-recolectores.

Latitudinal gradient effect on the wing geometry of Auca coctei (Guérin)(Lepidoptera, Nymphalidae)

Latitudinal gradient effect on the wing geometry of Auca coctei (Guérin) (Lepidoptera, Nymphalidae). When the environmental conditions change locally, the organisms and populations may also change in response to the selection pressure, so that the development of individuals may become affected in different degrees. There have been only a few studies in which the patterns of wing morphology variation have been looked into along a latitudinal gradient by means of geometric morphometrics. The aim of this work was to assess the morphologic differentiation of wing among butterfly populations of the species Auca coctei. For this purpose, 9 sampling locations were used which are representative of the distribution range of the butterfly and cover a wide latitudinal range in Chile. The wing morphology was studied in a total of 202 specimens of A. coctei (150 males and 52 females), based on digitization of 17 morphologic landmarks. The results show variation of wing shape in both sexes; however, for the centroid size there was significant variation only in females. Females show smaller centroid size at higher latitudes, therefore in this study the Bergmann reverse rule is confirmed for females of A. coctei. Our study extends morphologic projections with latitude, suggesting that wing variation is an environmental response from diverse origins and may influence different characteristics of the life history of a butterfly.

Asimetría fluctuante: una herramienta morfo-funcional para medir estabilidad del desarrollo / Fluctuating asymmetry: a morpho-functional tool to measure development stability

La capacidad de un organismo para producir un fenotipo ideal, pese a las perturbaciones encontradas durante su desarrollo, es el mecanismo causal de la estabilidad del desarrollo (ED). Esta capacidad es utilizada para evaluar variedad de tipos de estrés y la capacidad genotípica de corregirlos. La herramienta de medición más utilizada para estimar la ED es la asimetría fluctuante (AF), siendo esta una medida de las pequeñas desviaciones al azar que ocurren entre el lado izquierdo y derecho de rasgos bilateralmente simétricos. El estudio de AF, por su simplicidad de manejo y rapidez en la obtención de resultados, se ha convertido en un foco de interés para la biología, y durante los últimos años el aumento en artículos publicados usando AF para evaluar perturbaciones en la ED ha sido progresivo, pero aun así existen muchas interrogantes de cuales son las causas subyacentes que generan la AF. La presente revisión recopila información sobre el avance en los estudios del uso de la AF, su metodología, mecanismos, ventajas y controversias en el tiempo, y propone que es estrictamente necesario generar una mejor comprensión de esta herramienta, producto de eso, la utilización de modelos más exactos de estudio que signifiquen (o justifiquen) un enfoque unificado en el análisis de los patrones en AF y ED.

The ability of an organism to produce an ideal phenotype, despite the disturbances encountered during its development is the causal mechanism of the developmental stability (DS). This ability is used to evaluate a variety of stress types and the genotypic ability to correct them. The measurement tool mostly used to estimate the DS is the fluctuating asymmetry (FA), this being a small measure of random deviations that occur between the left and right sides of bilaterally symmetrical features. The study of FA management in its simplicity and speed in obtaining results has become the focus of interest in biology, and during the last years, and although there has been a progressive increase in published articles using FA to evaluate disturbances in the DS, many questions remain as to what constitutes the underlying causes that generate FA. This review compiles information on the progress in studies of FA use, its methodology, mechanisms, benefits and controversies in time, and proposes that it is strictly necessary to generate a better understanding of this tool, and as a result the use of more precise study models that justify a unified approach to the analysis of patterns in FA and DS.