First evidence of sexual dimorphism in olfactory organs of deep-sea lanternfishes (Myctophidae)

Finding a mate is of the utmost importance for organisms, and the traits associated with successfully finding one can be under strong selective pressures. In habitats where biomass and population density is often low, like the enormous open spaces of the deep sea, animals have evolved many adaptations for finding mates. One convergent adaptation seen in many deep-sea fishes is sexual dimorphism in olfactory organs, where, relative to body size, males have evolved greatly enlarged olfactory organs compared to females. Females are known to give off chemical cues such as pheromones, and these chemical stimuli can traverse long distances in the stable, stratified water of the deep sea and be picked up by the olfactory organs of males. This adaptation is believed to help males in multiple lineages of fishes find mates in deep-sea habitats. In this study, we describe the first morphological evidence of sexual dimorphism in the olfactory organs of lanternfishes (Myctophidae) in the genus Loweina. Lanternfishes are one of the most abundant vertebrates in the deep sea and are hypothesized to use visual signals from bioluminescence for mate recognition or mate detection. Bioluminescent cues that are readily visible at distances as far as 10 m in the aphotic deep sea are likely important for high population density lanternfish species that have high mate encounter rates. In contrast, myctophids found in lower density environments where species encounter rates are lower, like those in Loweina, likely benefit from longer-range chemical or olfactory cues for finding and identifying mates.

OLFACTORY PERCEPTION IN JUVENILE SALMON: II. CONDITIONED RESPONSE OF JUVENILE SOCKEYE SALMON (ONCORHYNCHUS NERKA) TO LAKE WATERS

Sockeye salmon smolts were conditioned to distinguish between waters from two natural sockeye nursery systems, Great Central Lake (from which the smolts were obtained) and Cultus Lake. The attractant from each water was volatile, but that from Great Central Lake was the more readily volatilized of the two. Volatile material from Great Central Lake water was collected and shown to evoke a response in the group of fish conditioned to whole Great Central Lake water.