Breaking Symmetry: Fluctuating Asymmetry and Geometric Morphometrics as Tools for Evaluating Developmental Instability under Diverse Agroecosystems

Abstract

Fluctuating asymmetry (FA), in contrast with other asymmetries, is the bilateral asymmetry that represents small, random developmental differences between right and left sides. After nearly a century of using traditional morphometrics in the estimation of FA, geometric morphometrics (GM) now provides new insights into the use of FA as a tool, especially for assessing environmental and developmental stress. Thus, it will be possible to assess adaptation to various environmental stressors as particular triggers for unavoidable selection pressures. In this review, we describe measures of FA that use geometric morphometrics, and we include a flow chart of the methodology. We also describe how this combination (GM + FA) has been tested in several agroecosystems. Nutritional stress, temperature, chemical pollution, and population density are known stressors experienced by populations in agroecosystems.

Does stress mess with rodents’ heads? Influence of habitat amount and genetic factors in mandible fluctuating asymmetry in South American water rats (Nectomys squamipes, Sigmodontinae) from Brazilian Atlantic rainforest remnants

“…Several studies have documented a positive relationship between Fluctuating Asymmetry (FA) and stress levels in populations of many species (Anciães & Marini, 2000;Hoelzel et al, 2002;Leamy et al, 1999;McKenzie & Clarke, 1988;Pankakoski, 1985;Parsons, 1990Parsons, , 1992Sarre, 1996;Schmeller et al, 2011). Higher FA levels have been found in populations of birds, voles (Marchand et al, 2003), field mice (Maestri et al, 2015), shrews (Sánchez-Chardi et al, 2013), and lizards (Lazić et al, 2015) living in disturbed or less suitable habitats, as well as in populations of shrews (White & Searle, 2008) and roe deer (Zachos et al, 2007) exhibiting reduced genetic variation (see reviews in Benítez et al, 2020;Klingenberg, 2015). Therefore, populations in optimal conditions tend to exhibit low FA levels, while those exposed to stressful conditions have higher levels of average FA (Shadrina & Vol'pert, 2016).…”

Investigating Human Torso Asymmetries: An Observational Longitudinal Study of Fluctuating and Directional Asymmetry in the Scoliotic Torso

“…This research line remained latent until the recent appearance of new methodologies applied to the study of the asymmetric properties of the human torso. Specifically, geometric morphometrics (GMM) has been used for decades in other fields of biological research [6] and has recently brought new quantitative and qualitative variables to the study of idiopathic scoliosis [7]. Thus, higher levels of fluctuating asymmetry have been evidenced in other clinical conditions different from scoliosis in the form of positive correlation between asymmetries and symptoms [8].…”

A Geometric-Morphometric Analysis of the Heterochely in the Red Sea Hermit Crab “Clibanarius Signatus”, and Its Developmental Stability and Modularity

“…Generally, the right and left chelae formed by the same genome, and their symmetry in the post-larval stage reflect the crab's ability to canalize development against pressures [44] , but the appearance of chelae asymmetry in adults illustrate that developmental trajectory was changed developmentally or genetically under environmental stress, which breaks the symmetry in a fixed direction [6,10,26] . The environmental components, that may break symmetry and lead to heterochely in adults of C. signatus, may be the dextral shell architecture, foraging behavior and intra/interspecific competitions [3] .…”

“…Therefore, FA detected in chela of both sexes of C. signatus possibly result from a stressful development and consequently high developmental instability related to the alternative pathway. In addition, the higher FA level in females than males may reflect the higher stress they face during intraspecific competition for the better shells that fulfill a large space for egg incubation [17,44] .…”