Phenotypic Buffering in a Monogenean: Canalization and Developmental Stability in Shape and Size of the Haptoral Anchors of Ligophorus cephali (Monogenea: Dactylogyridae)

Abstract

Phenotypic variation results from the balance between sources of variation and counteracting regulatory mechanisms. Canalization and developmental stability are two such mechanisms, acting at two different levels of regulation. The issue of whether or not they act concurrently as a common developmental buffering capacity has been subject to debate. We used geometric morphometrics to quantify the mechanisms that guarantee phenotypic constancy in the haptoral anchors of Ligophorus cephali. Canalization and developmental stability were appraised by estimating inter- and intra-individual variation, respectively, in size and shape of dorsal and ventral anchors. The latter variation was estimated as fluctuating asymmetry (FA) between anchor pairs. The general-buffering-capacity hypothesis was tested by two different methods based on correlations and Principal Components Analyses of the different components of size and shape variation. Evidence for FA in the dorsal and ventral anchors in both shape and size was found. Our analyses supported the hypothesis of a general developmental buffering capacity. The evidence was more compelling for shape than for size and, particularly, for the ventral anchors than for the dorsal ones. These results are in line with previous studies of dactylogyrids suggesting that ventral anchors secure a firmer, more permanent attachment, whereas dorsal anchors are more mobile. Because fixation to the host is crucial for survival in ectoparasites, we suggest that homeostatic development of the ventral anchors has been promoted to ensure the morphological constancy required for efficient attachment. Geometric morphometrics can be readily applied to other host-monogenean models, affording not only to disentangle the effects of canalization and developmental stability, as shown herein, but to further partition the environmental and genetic components of the former.

Evolutionary morphology in shape and size of haptoral anchors in 14 Ligophorus spp. (Monogenea: Dactylogyridae)

“…Empirical evidence from L . cephali indicates a tighter control of the shape and size in ventral anchors perhaps because they seem to be responsible for firmer attachment [ 31 , 32 ]. Thus the differences observed could be explained in terms of different functional roles in attachment to the gills [ 27 ].…”

“…The parasite specimens were collected in the frame of previous studies of our group [ 22 , 27 – 31 ] in two marine areas of the Spanish Mediterranean Coast (the Ebro Delta, and Santa Pola Bay), a coastal Mediterranean lagoon (L’Albufera), and the Sea of Azov (Kerch Strait). In addition, part of the specimens of L .…”

Monogenean anchor morphometry: systematic value, phylogenetic signal, and evolution

“…We have shown in the present work that, if geometric morphometric data is used as a starting point, all the preceding questions can be simultaneously answered. In fact, the geometric morphometric approach is the key that unlocks the potential of shape information in the organs of interest for broader research questions, such as species and biogeographical population discrimination ( Vignon & Sasal, 2010 ), morphological integration (e.g., Vignon, Pariselle & Vanhove, 2011 ; Rodríguez-González et al, 2015a ), and more recently, canalization and developmental stability ( Llopis-Belenguer et al, 2015 ), all of which cannot be answered satisfactorily using traditional morphometric or qualitative methods.…”

Peer Review #1 of "Monogenean anchor morphometry: systematic value, phylogenetic signal, and evolution (v0.1)"

“…In fact, the geometric morphometric approach is the key that unlocks the potential of shape information in the organs of interest for broader research questions, such as species and biogeographical population discrimination (Vignon and Sasal, 2010), morphological integration (e.g. Vignon et al 2011;Rodríguez-González et al, 2015a), and more recently, canalization and developmental stability (Llopis-Belenguer et al 2015), all of which cannot be answered satisfactorily using traditional morphometric or qualitative methods.…”