A global meta‐analysis of temperature effects on marine fishes’ digestion across trophic groups

Abstract

Aim The temperature constraint hypothesis proposes that marine herbivorous fishes are rare at high latitudes relative to carnivorous fishes because low temperatures impair the digestion of plant material. To test this hypothesis, we compared the effects of temperature on the digestive performance and investment in digestion of marine fishes across trophic groups. Location Global marine ecosystems. Major taxa studied Marine fishes. Methods We analysed data from 304 species consuming a range of diets to quantify the effects of temperature on three indicators of digestive performance and investment: gut passage time, absorption efficiency, and gut length. Results Decreasing temperatures increase gut passage time in fishes consuming macroalgae more than fishes consuming other fish or invertebrates. Low temperatures do not impair absorption efficiency in fishes regardless of diet, but herbivores have lower absorption efficiencies than carnivores overall. Gut length decreases with decreasing temperature in all trophic groups. Main conclusions Our analyses reveal limited evidence to support the temperature constraint hypothesis. Low temperatures slow digestion more in fishes consuming macroalgae than those consuming animal prey; however, this may not reflect a meaningful disadvantage for herbivores but rather could be explained by greater representation of fishes relying on microbial fermentation at high latitudes. Herbivorous fishes absorb nutrients and energy from their food in similar proportions regardless of temperature, in contrast to the expectations of the temperature constraint hypothesis. Decreased gut length was associated with decreasing temperature across all trophic groups, likely due to improved food quality at high latitudes, which should benefit all trophic groups by reducing their required investment in gut tissues. Altogether, our findings run counter to the general hypothesis that low temperatures disadvantage the digestion of plant material and suppress the diversity and abundance of herbivorous fishes at high latitudes.

Selection for high growth displaces costs of digestion from SDA to SMR in divergent ecotypes of rainbow trout

“…Total assimilation efficiency in both ecotypes was largely insensitive to ration size, suggesting that optimal assimilation is relatively conserved for a given phenotype. These results are somewhat consistent with previous studies on vertebrate taxa where digestive efficiency either varied minimally with meal size (in snakes: Cox & Secor, 2007; fish: Knight et al, 2021) or decreased with meal size over time (Jobling et al, 1977; Kotrschal et al, 2014; Legler et al, 2010; Solomon & Brafield, 1972). Decreasing AE with increasing ration may, therefore, reflect the lower capacity of digestive enzymes to penetrate and degrade the centre of larger ingested food masses.…”

Divergence in digestive and metabolic strategies matches habitat differentiation in juvenile salmonids

“…Mechanistically, the lower growth efficiency of the faster‐growing phenotype (i.e., steelhead trout) appears to be driven by higher postprandial metabolic costs (e.g., Billerbeck et al, 2000 ) and lower nutrient assimilation (e.g., Knight et al, 2021 ) associated in part with a shortened gut residence time. The lower AE and higher postprandial metabolism (i.e., SDA) that we observed in steelhead trout, however, may not fully account for the substantial differences in growth efficiency between species.…”

“…The ecological implications of digestive physiology in wild fish remain somewhat underappreciated despite their relevance to many ecological processes, including biological invasions (Steell et al, 2019 ), adaptive differentiation (Rosenfeld et al, 2020 ), or trophic specialization (Knight et al, 2021 ). By explicitly demonstrating the multivariate divergence of digestive strategies between juvenile coho salmon and steelhead trout, and how this divergence matches variation in growth and energetics, our study highlights the key role of digestive physiology in potential adaptive differentiation between species that have specialized to different ecological niches along a gradient of resource availability.…”

“…The ecological implications of digestive physiology in wild fish remain somewhat underappreciated despite their relevance to many ecological processes, including biological invasions (Steell et al, 2019), adaptive differentiation (Rosenfeld et al, 2020), or trophic specialization (Knight et al, 2021). By explicitly demonstrating the multivariate divergence of digestive strategies between juvenile coho…”

Temperature, species identity and morphological traits predict carbonate excretion and mineralogy in tropical reef fishes

“…Our results provide evidence in support of this control given that we find a strong positive association between temperature and the probability of fishes excreting ACMC across families. Regardless of the underlying mechanism (increased gut residence times at lower temperature 75 have been suggested 38 ), carbonates excreted by fish in warmer temperatures would contain more ACMC and less HMC (Supplementary Fig. 7), suggesting higher solubility and a reduced export of carbonate particles into the deep sea 12,35 .…”