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

Abstract

Abstract. Intraspecific variation in eye size in relation to ecological factors has not been well studied. Here, for the first time, we show that larger eyes in a freshwater crustacean may be associated with the presence of predators. In central Pennsylvania (USA), individuals of the amphipod crustacean Gammarus minus have significantly larger eyes in two freshwater springs with numerous fish predators (Cottus cognatus) than in three springs with few or no fish predators. Although we do not know the precise causes of these differences, this study and previous work on cave populations of G. minus suggest that eye size is an evolutionarily malleable trait that may respond to multiple selection pressures, either directly or indirectly. Three plausible explanations for the eye‐size variation observed among our study populations include (1) larger eyes may enable amphipods to better detect and avoid fish predators, (2) fish predation favors nocturnal or shallow interstitial activity that is facilitated by larger, more light‐sensitive eyes, or (3) the presence of fishes is associated with other environmental factors that may favor relatively large eyes. Available evidence suggests that the first hypothesis is the most viable explanation, but further study is required.

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

“…Research has also considered connections between predators and eye size variation (Brown et al. ; Glazier and Deptola ; Lonnstedt et al. ).…”

“…). Glazier and Deptola () showed that Gammarus minus from ponds with fish predators had larger eyes than crustaceans in ponds that lacked predators (Glazier and Deptola ). These latter studies in particular foreshadow that the evolution of eye size is likely to be molded by contrasting predation regimes.…”

“…). However, recent work has begun to explore variation in eye size within species (Glazier and Deptola ; Pearce and Dunbar ; Brandon et al. ).…”

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, ).…”

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

“…A similar pattern exists in animals that inhabit dim light environments, which have larger eyes relative to those that inhabit bright environments (Bauer et al ., ; Thomas et al ., ; Hall, ; Somanathan et al ., ; Schmitz & Wainwright, ; Veilleux & Lewis, ). Eye size differences have also been documented between populations that may have different visual needs (Protas et al ., ; Glazier & Deptola, ), although these examples are far fewer than the differences documented across species. Although eye size is not the only component that determines an animal's visual capabilities (Land & Nilsson, ), it is certainly an important trait which figures prominently into our understanding of how larger environmental differences and behavioural tasks affect variation of visual structures at macroevolutionary scales.…”