Abstract
Alvinocaridid shrimps are emblematic representatives of the deep hydrothermal vent fauna at the Mid-Atlantic Ridge. They are adapted to a mostly aphotic habitat with extreme physicochemical conditions in the vicinity of the hydrothermal fluid emissions. Here, we investigated the brain architecture of the vent shrimp Rimicaris exoculata to understand possible adaptations of its nervous system to the hydrothermal sensory landscape. Its brain is modified from the crustacean brain ground pattern by featuring relatively small visual and olfactory neuropils that contrast with well-developed higher integrative centers, the hemiellipsoid bodies. We propose that these structures in vent shrimps may fulfill functions in addition to higher order sensory processing and suggest a role in place memory. Our study promotes vent shrimps as fascinating models to gain insights into sensory adaptations to peculiar environmental conditions, and the evolutionary transformation of specific brain areas in Crustacea.
Highlights
The alvinocaridid shrimps were discovered in 1985 during a mission of the deep submersible vehicle ALVIN (Rona et al, 1986) and are known to be widely distributed representatives of the deep hydrothermal vent fauna along the Mid-Atlantic Ridge (MAR; Desbruyeres et al, 2001; Desbruyeres et al, 2000; Gebruk et al, 1997; Segonzac et al, 1993)
The findings provide new insights for biologists studying animals associated with deep hydrothermal vents and are important for neuroscientists interested in brain function and evolution
Micro-CT scans show that the brain is located in the anterior region of the cephalothorax, and receives main sensory afferences from the antenna 1 (A1Nv) and antenna 2 (A2Nv) nerves anteriorly, from the eye nerves (ENv) posterodorsally, from the tegumentary nerves (TNv) laterally, and from the oesophageal connectives posteriorly (Figure 1D)
Summary
The alvinocaridid shrimps were discovered in 1985 during a mission of the deep submersible vehicle ALVIN (Rona et al, 1986) and are known to be widely distributed representatives of the deep hydrothermal vent fauna along the Mid-Atlantic Ridge (MAR; Desbruyeres et al, 2001; Desbruyeres et al, 2000; Gebruk et al, 1997; Segonzac et al, 1993). Active vents are dynamic environments, where geothermally heated seawater, the hydrothermal fluid, discharges from chimneys and cracks in the seafloor. Hydrothermal vent habitats, in addition to high hydrostatic pressure and the complete absence of sunlight, are characterized by steep gradients of temperature and concentration of chemicals (Bates et al, 2010; Johnson et al, 1988; Johnson et al, 1986; Le Bris et al, 2005). Vent organisms are well adapted to these physicochemical conditions, and alvinocaridid shrimps colonize in high abundance the walls of active chimneys, where the hydrothermal fluid mixes with the surrounding cold (4 ̊C) and oxygenated seawater.
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