Assessing niche width of endothermic fish from genes to ecosystem

Abstract

Endothermy in vertebrates has been postulated to confer physiological and ecological advantages. In endothermic fish, niche expansion into cooler waters is correlated with specific physiological traits and is hypothesized to lead to greater foraging success and increased fitness. Using the seasonal co-occurrence of three tuna species in the eastern Pacific Ocean as a model system, we used cardiac gene expression data (as a proxy for thermal tolerance to low temperatures), archival tag data, and diet analyses to examine the vertical niche expansion hypothesis for endothermy in situ. Yellowfin, albacore, and Pacific bluefin tuna (PBFT) in the California Current system used more surface, mesopelagic, and deep waters, respectively. Expression of cardiac genes for calcium cycling increased in PBFT and coincided with broader vertical and thermal niche utilization. However, the PBFT diet was less diverse and focused on energy-rich forage fishes but did not show the greatest energy gains. Ecosystem-based management strategies for tunas should thus consider species-specific differences in physiology and foraging specialization.pelagic | tuna | Thunnus | evolution | endothermy

Diel patterns in swimming behavior of a vertically migrating deepwater shark, the bluntnose sixgill (Hexanchus griseus)

“…The enhanced thermal inertia of sixgill sharks may confer ecological and physiological advantages at cold temperatures as suggested for fishes with endothermic capacities. Endothermic fishes have evolved specialized anatomical and physiological mechanisms for retaining metabolic heat enabling higher levels of activity for longer durations when diving below the mixed layer to exploit deep forage resources more effectively than ectothermic species [81][82][83]. However, some large ectothermic sharks also undertake diel vertical migrations into cold temperatures below the thermocline to exploit deep forage resources (e.g., [4,31,[84][85][86]).…”

The adaptive capacity of lake food webs: from individuals to ecosystems

“…Researchers in large marine ecosystems are also combining diet analysis and archival tag data with molecular tools (expression of genes related to cold tolerance) to study the coupling of warm suface with cold deepwater habitats by tunas (Madigan et al. ). Important considerations and remaining questions in moving from small to very large systems include (1) what level of detail (e.g., from micro to macro habitats) is necessary for anticipating whole system‐ or population‐specific responses to stressors like climate change and species invasions, and (2) how coexisting generalist and specialist fishes in various habitats and at different trophic positions collectively respond and sustain energy and nutrient flow in the face of changing environmental conditions.…”

Fisheries conservation on the high seas: linking conservation physiology and fisheries ecology for the management of large pelagic fishes

“…Regional endothermy affects numerous biological characteristics of relevance to fisheries, including high somatic and gonadal growth rates ( Dickson, 1995 ; Brill, 1996 ). However, energetic benefits of cold tolerance and elevated metabolic rates are context dependent; they are likely to be advantageous when quality prey is abundant, but not when such prey is scarce ( Madigan et al ., 2015 ). Collectively, regional endothermy of pelagic fishes enables geographical and vertical niche expansion and increased access to prey (e.g.…”

“…Collectively, regional endothermy of pelagic fishes enables geographical and vertical niche expansion and increased access to prey (e.g. Block et al ., 1993 ; Dickson, 1995 ; Lowe et al ., 2000 ; Schaefer and Fuller, 2010 ; Madigan et al ., 2015 ).…”