Toward Developing Models to Study the Disease, Ecology, and Evolution of the Eye in Mollusca*

Abstract

Several invertebrate systems have been developed to study various aspects of the eye and eye disease including Drosophila, Planaria, Platynereis, and most recently, the cubozoan jellyfish Tripedalia; however, molluscs, the second largest metazoan phylum, so far have been underrepresented in eye research. This is surprising as mollusc systems offer opportunities to study visual processes that may be altered by disease, vision physiology, development of the visual system, behavior, and evolution. Malacologists have labored for over a century as morphologists, systematists, physiologists, and ecologists in order to understand the structural and functional diversity in molluscs at all levels of biological organization. Yet, malacologists have had little opportunity to interact with researchers whose interests are restricted to the biology and development of eyes as model systems as they tend not to publish in the same journals or attend the same meetings. In an effort to highlight the advantages of molluscan eyes as a model system and encourage greater collaboration among researchers, I provide an overview of molluscan eye research from these two perspectives: eye researchers whose interests involve the development, physiology, and disease of the eye and malacologists who study the complete organism in its natural environment. I discuss the developmental and genetic information available for molluscan eyes and the need to place this work in an evolutionary perspective. Finally, I discuss how synergy between these two groups will advance eye research, broaden research in both fields, and aid in developing new molluscan models for eye research. Abstract: Several invertebrate systems have been developed to study various aspects of the eye and eye disease including Drosophila, Planaria, Platynereis, and most recently, the cubozoan jellyfish Tripedalia; however, molluscs, the second largest metazoan phylum, so far have been underrepresented in eye research. This is surprising as mollusc systems offer opportunities to study visual processes that may be altered by disease, vision physiology, development of the visual system, behavior, and evolution. Malacologists have labored for over a century as morphologists, systematists, physiologists, and ecologists in order to understand the structural and functional diversity in molluscs at all levels of biological organization. Yet, malacologists have had little opportunity to interact with researchers whose interests are restricted to the biology and development of eyes as model systems as they tend not to publish in the same journals or attend the same meetings. In an effort to highlight the advantages of molluscan eyes as a model system and encourage greater collaboration among researchers, I provide an overview of molluscan eye research from these two perspectives: eye researchers whose interests involve the development, physiology, and disease of the eye and malacologists who study the complete organism in its natural environment. I discuss the developmental and genet...

The Evolution of Eyes in the Bivalvia: New Insights*

“…However, Gehring and Ikeo (1999) considered Pax6 and its homologs to be the control gene for eye development in metazoans although it is now known that a number of others (including eya), for example, dachshund (Shen and Mardon 1997) and sine oculis (Pignoni et al 1997) are also able to induce ectopic eye expression in Drosophila. Serb (2008, fig. 1) provides a model of the network of genes that regulates eye formation in Drosophila.…”

Do you see what I see? Optical morphology and visual capability of ‘disco’ clams (Ctenoides ales)

“…Due to the variety of eye types in Limidae, eye evolution within this group needs to be solved using a more comprehensive phylogeny and detailed eye studies of more limid bivalves. Many molecular studies elucidate the phylogenetic relationships of a few limid bivalves ( González et al, 2015 ; Giribet and Wheeler, 2002 ; Plazzi et al, 2011 ; Serb, 2008 ), but none include a comprehensive analysis of the relationships among Ctenoides , Lima , Limaria , and the outgroup Pectinidae (scallops). This line of research should be of great interest in the context of invertebrate eye evolution and convergent evolution of complex morphological traits, and is being pursued in future studies by the authors.…”

Eye development and developmental expression of crystallin genes in the long arm octopus, Octopus minor

“…Phylum Mollusca has developed different types of eyes such as the concave mirror eye, the pinhole eye, and the camera-type eye with considerable variation (Land, 1965;Land and Fernald, 1992;Serb and Eernisse, 2008;Ogura et al, 2013). Coleoid cephalopods such as octopuses, cuttlefish and squid possess camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), photoreceptor cells, similar to vertebrate eyes (Serb, 2008). Despite the similarities in overall structure, the role of opsin family members in phototransduction within the photoreceptors, the camera-type eyes of vertebrates and cephalopods are thought to have evolved independently and thus represent a classic example of convergent evolution (Yoshida et al, 2015).…”