Selection on incremental variation of eye size in a wild population ofDaphnia

Abstract

Several studies of eye morphology have analysed macroevolutionary patterns in the diversity of eyes, and although these studies are often linked to environment or behaviour, they provide only indirect evidence of selection. Specific data to show the microevolutionary potential for adaptation by natural selection in eye morphology have been lacking. We document directional selection on eye size, an important determinant of visual capabilities, in a wild population of the freshwater microcrustacean Daphnia. We show that even slight changes in eye size may have major consequences for fitness. An increase in eye diameter of 19.9 μm - slightly more than one standard deviation - is associated with an increase in clutch size of one egg, or an increase of nearly 20% of the mean clutch size. Furthermore, relative eye size is genetically variable and thus could evolve in response to the observed selective pressure. We conclude that selection on incremental variation in eye size may have led to differences observed on broader taxonomic scales.

The evolution of vertebrate eye size across an environmental gradient: phenotype does not predict genotype in a Trinidadian killifish

“…() showed that eye size is under selection in a natural population of Daphnia and also that changes in eye size have clear fitness consequences; small increases (∼1%) in the eye diameter of Daphnia obtusa increase reproductive outputs by 20% (Brandon et al. ). Research on bluefin killifish explored plasticity in opsin expression in fish under different light conditions (Fuller et al.…”

“…This variation provides the raw materials for contrasting ecological conditions to favor evolutionary shifts in eye size and structure, but tests for microevolutionary shifts in eye size are conspicuously absent (but see Brandon et al. ).…”

“…Light availability has long been viewed as an important selective force on the evolution of eyes and is associated with both increased and decreased eye size across taxa (Von Salvini-Plawen and Mayr 1977;Hiller-Adams and Case 1985;Fernald 2004a, b;Moser et al 2004;Ross and Kirk 2007;Hall 2008;Tobler et al 2008;Somanathan et al 2009;Schmitz and Wainwright 2011;Veilleux and Lewis 2011;Hall et al 2012;Martinez-Ortega et al 2014). However, recent work has begun to explore variation in eye size within species (Glazier and Deptola 2011;Pearce and Dunbar 2012;Brandon et al 2015). This variation provides the raw materials for contrasting ecological conditions to favor evolutionary shifts in eye size and structure, but tests for microevolutionary shifts in eye size are conspicuously absent (but see Brandon et al 2015).…”

“…However, recent work has begun to explore variation in eye size within species (Glazier and Deptola 2011;Pearce and Dunbar 2012;Brandon et al 2015). This variation provides the raw materials for contrasting ecological conditions to favor evolutionary shifts in eye size and structure, but tests for microevolutionary shifts in eye size are conspicuously absent (but see Brandon et al 2015).…”

Natural selection favours a larger eye in response to increased competition in natural populations of a vertebrate

“…Indeed, studies have shown that ecological factors such as habitat complexity, foraging, diel activity and predation are associated with evolved differences in eye size (Banks, Sprague, Schmoll, Parnell, & Love, ; Beston, Dudycha, Post, & Walsh, in press; Beston, Wostl, & Walsh, ; Brandon, James, & Dudycha, ; Caves et al, ; Glazier & Deptola, ; Hammerschlag et al, ; Thomas et al, , ; Veilleux & Kirk, ; Zaret & Kerfoot, ). Although such studies provide information on the relationship between eye size and the environment, the vast majority of this work has compared eye size across species (but see Beston, Wostl, et al, ; Beston et al, in press; Brandon et al, ; Lönnstedt, McCormick, & Chivers, ). Despite years of research, very little work has experimentally tested how natural selection shapes the evolution of complex traits, such as the vertebrate eye.…”