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Rising temperatures have important consequences for somatic growth, but observed relationships between temperature and growth can vary in both magnitude and direction. The key to understanding such variation is knowing how temperature affects both the amount of energy available for growth and the efficiency with which surplus energy is assimilated into the body. We tested the hypothesis that patterns of temperature-dependent growth are driven by differential sensitivities of energy intake and expenditure to temperature. Larvae of California grunion Leuresthes tenuis were reared across a range of temperatures and 2 levels of food availability. Energy intake was measured from feeding rate, and energy expenditure was evaluated by measuring respiration and excretion rates. When food was abundant, both intake and expenditure increased with temperature, but intake increased more rapidly. These results suggest that high temperatures should lead to faster growth, and these predictions were confirmed by a separate experiment. In contrast, when food was restricted, the increase in energetic demand with temperature outpaced energy intake, suggesting a dwindling surplus of energy at high temperatures. This predicted reversal of the effects of temperature on growth was also confirmed experimentally. Finally, we compared patterns of energetics and growth to test the effects of temperature on food assimilation efficiency. When food was unlimited, assimilation efficiency decreased rapidly with temperature. When food was restricted, assimilation efficiency remained relatively high. Overall, our results emphasize the value of a bioenergetic perspective for illuminating why and how growth rates are likely to change in a warming ocean.
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How modularity and heterotrophy complicate the understanding of the causes of thermal performance curves: the case of feeding rate in a filter-feeding animal
ABSTRACT Warming global temperatures have consequences for biological rates. Feeding rates reflect the intake of energy that fuels survival, growth and reproduction. However, temperature can also affect food abundance and quality, as well as feeding behavior, which all affect feeding rate, making it challenging to understand the pathways by which temperature affects the intake of energy. Therefore, we experimentally assessed how clearance rate varied across a thermal gradient in a filter-feeding colonial marine invertebrate (the bryozoan Bugula neritina). We also assessed how temperature affects phytoplankton as a food source, and zooid states within a colony that affect energy budgets and feeding behavior. Clearance rate increased linearly from 18°C to 32°C, a temperature range that the population experiences most of the year. However, temperature increased algal cell size, and decreased the proportion of feeding zooids, suggesting indirect effects of temperature on clearance rates. Temperature increased polypide regression, possibly as a stress response because satiation occurred quicker, or because phytoplankton quality declined. Temperature had a greater effect on clearance rate per feeding zooid than it did per total zooids. Together, these results suggest that the effect of temperature on clearance rate at the colony level is not just the outcome of individual zooids feeding more in direct response to temperature but also emerges from temperature increasing polypide regression and the remaining zooids increasing their feeding rates in response. Our study highlights some of the challenges for understanding why temperature affects feeding rates, especially for understudied, yet ecologically important, marine colonial organisms.
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- Award ID(s):
- 1948788
- PAR ID:
- 10584890
- Publisher / Repository:
- The Company of Biologists Ltd
- Date Published:
- Journal Name:
- Journal of Experimental Biology
- Volume:
- 227
- Issue:
- 12
- ISSN:
- 0022-0949
- Page Range / eLocation ID:
- jeb247776
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1242/jeb.247776
