Ontogeny of sexual dimorphism via tissue duplication in an ostracod (Crustacea)

Abstract

The adaptive significance of specific sexual dimorphism is well studied. However, the evolutionary history and ontogenic origins of the dimorphism are often unknown. As dimorphism represents two phenotypes generated from relatively similar genotypes, it is of interest to understand both its evolutionary and developmental/genetic underpinnings. Here, we present the first ontogenetic examination of the eyes of philomedid ostracods (Crustacea), which exhibit extremely sexually dimorphic lateral eyes. Adult male philomedids have large compound lateral eyes, whereas females have rudimentary lateral eyes. First, we show that eye dimorphism is unlikely to be due to additional genes present on a male-specific chromosome because karyotype analysis suggests philomedids are XX/XO. We then examine the ontogeny of eye development and find that in at least two species of Euphilomedes, this dimorphism is not generated solely by differences in tissue growth rates, as has been commonly shown for sexually dimorphic characters of other species. Instead, the dimorphism appears to arise during development via tissue duplication, where a single tissue becomes two, perhaps with different developmental potentials. The second eye field is only observed in male Euphilomedes, producing most of the adult eye tissue. We point out that tissue duplication is a developmental process with evolutionary implications because novel characters could evolve via alternative modification of the duplicated fields, analogous to the origin of new genes by gene duplication and alternative modification. Depending on the evolutionary history of the duplicated field, it may have either facilitated or directly caused the observed sexual dimorphism of philomedid ostracods.

Review of the firefly visual system (Coleoptera: Lampyridae) and evolution of the opsin genes underlying color vision

“…Changes in the amino acid sequence of the opsin protein or in the structure of the chromophore can alter the overall spectral sensitivity of these pigments. The number of expressed opsins and the range in sensitivity is known to vary across animals (Rivera and Oakley 2009;Briscoe and Chittka 2001;Land and Nilsson 2012). For example, in stomatopods (Crustacea), 6-15 different expressed opsins have been found (Porter et al 2009).…”

“…Given the niche diversity occupied by beetles, and by extension the diversity of visual conditions and eye morphologies, we expect that their modes of communication, specifically their visual communication, would also be highly variable and adaptive. Thus, the underlying molecular systems may also exhibit equal degrees of variability (Rivera and Oakley 2009). This is best tested in those lineages in which it is clear that visual communication plays an important role in life history.…”

“…Arthropods, specifically insects, are the most diverse group of animals on earth, and their visual systems reflect this diversity (Rivera and Oakley 2009). Three major opsin classes have been identified in insects: ultraviolet-sensitive (UVS), bluesensitive (BS) and long-wavelength-sensitive (LWS).…”

The amphipod Gammarus minus has larger eyes in freshwater springs with numerous fish predators

“…Captive populations of the fruit fly Drosophila melanogaster M eigen 1830 have evolved smaller eyes (Tan et al 2005). Eye size also varies with gender in ostracod crustaceans (Rivera & Oakley 2009) and with gender and social caste in some insects (e.g., Baker & Ma 2006; Meyer‐Rochow & Lau 2008; Rutowski et al 2009).…”

Two new sympatric species of Eusarsiella (Ostracoda: Myodocopida: Sarsiellidae) from the Florida Keys with a morphological phylogeny of Sarsiellinae

“…Together with the families Philomedidae Müller, 1906 andRutidermatidae Brady &Norman, 1896, Sarsiellidae is a member of the superfamily Sarsielloidea, which is particularly intriguing evolutionarily because it shows variation in genetically well-studied characters, especially lateral compound eyes (Rivera & Oakley 2009;Kornicker 1985). Although a nearly comprehensive morphological phylogeny was recently published (Karanovic 2012), molecular phylogenies including sarsiellids suffer from sparse species-level sampling (e.g., a single species in Yamaguchi & Endo 2003;Oakley & Cunningham 2002;Tinn & Oakley 2008), and unlike many ostracod lineages with rich fossil records, there are no known sarsiellid fossils (Siveter et al 2010).…”