Metabolic trade-offs associated with homeostatic adjustments in pelagic and benthic cephalopods: Comparative evaluations of NH4+/H+ transport machinery in gills

Abstract

Cephalopods are ancient mollusks that can be found in many different ecological niches in the ocean ranging from the intertidal zone to the deep-sea abyss. In order to adapt to a lifestyle in various habitats, cephalopods have evolved a variety of locomotory modes to accommodate their respective habitats. Most cephalopods have relatively high metabolic rates due to their less efficient swimming mode by jet propulsion. This lifestyle is characterized by a high level of energy expenditure, fueled exclusively by protein diets that are rapidly digested and may produce metabolic nitrogenous waste NH3/NH4 +accumulation and acid-base disturbances. This study observed that the NH4 +transport rate in pelagic bigfin reef squid (Sepioteuthis lessoniana) is two times faster than benthic common octopus (Octopus vulgaris). Inhibition of Na+/H+ exchangers (NHEs) showed significant disruption of NH4 + and H+ excretory processes in gills of octopus but not in squid. However, inhibition of vacuolar-type H+-ATPase (VHA) significantly disrupts NH4 + and H+ transport rates in gills of both animals. Accordingly, for NH4 + and H+ homeostasis, benthic octopus with lower aerobic respiration rates utilize both active and Na+-driven secondary transport machinery. In order to avoid NH4 + accumulated in the blood, pelagic squids with higher aerobic respiration rates prefer active NH4 + and H+ transport mechanisms that consume ATP intensively.

Ecology of Saline Watersheds: An Investigation of the Functional Communities and Drivers of Benthic Fauna in Typical Water Bodies of the Irtysh River Basin

“…In freshwater environments, ammonia ions exhibit a significant positive correlation with functional traits such as exoskeletal or external protection, habitat preference, morphology, and feeding habits. This positive correlation aligns well with the characteristics of freshwater environments, where ammonia ions likely act as a critical nitrogen source, influencing the ecological niche allocation and functional traits of benthic organisms [50,51]. Benthic organisms may adjust the level of their exoskeleton or external protection based on ammonia ion abundance to better adapt to ammonia-dominated living conditions [52].…”

Gill histology and ultrastructure in Aplysia depilans (Mollusca, Euopisthobranchia)

“…Therefore, these gills seem to have a role in ion exchanges in addition to respiratory function (Jonas, 1986; Rodriguez et al, 2019). Ion regulation is known to occur in the gills of cephalopods, crustaceans, and fish (Lin et al, 2022; McNamara & Faria, 2012; Zimmer & Perry, 2022), and was considered an ancestral function of gills (Sackville et al, 2022).…”