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Abstract Females and males can exhibit striking differences in body size, relative trait size, physiology, and behavior. As a consequence, the sexes can have very different rates of whole-body energy use, or converge on similar rates through different physiological mechanisms. Yet many studies that measure the relationship between metabolic rate and body size only pay attention to a single sex (more often males), or do not distinguish between sexes. We present four reasons why explicit attention to energy-use between the sexes can yield insight into the physiological mechanisms that shape broader patterns of metabolic scaling in nature. First, the sexes often differ considerably in their relative investment in reproduction, which shapes much of life-history and rates of energy use. Second, males and females share a majority of their genome but may experience different selective pressures. Sex-specific energy profiles can reveal how the energetic needs of individuals are met despite the challenge of within-species genetic constraints. Third, sexual selection often pushes growth and behavior to physiological extremes. Exaggerated sexually selected traits are often most prominent in one sex, can comprise up to 50% of body mass, and thus provide opportunities to uncover energetic constraints of trait growth and maintenance. Finally, sex-differences in behavior such as mating-displays, long-distance dispersal, and courtship can lead to drastically different energy allocation among the sexes; the physiology to support this behavior can shape patterns of metabolic scaling. The mechanisms underlying metabolic scaling in females, males, and hermaphroditic animals can provide opportunities to develop testable predictions that enhance our understanding of energetic scaling patterns in nature.
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This content will become publicly available on October 1, 2025
When the Going Gets Tough, the Females Get Going: Sex‐Specific Physiological Responses to Simultaneous Exposure to Hypoxia and Marine Heatwave Events in a Ubiquitous Copepod
ABSTRACT The existence of sex‐specific differences in phenotypic traits is widely recognized. Yet they are often ignored in studies looking at the impact of global changes on marine organisms, particularly within the context of combined drivers that are known to elicit complex interactions. We tested sex‐specific physiological responses of the cosmopolitan and ecologically important marine copepodAcartia tonsaexposed to combined hypoxia and marine heatwave (MHW) conditions, both of which individually strongly affect marine ectotherms. Females and males were acutely exposed for 5 days to a combination of either control (18°C) or a high temperature mimicking a MHW (25°C), and normoxia (100% O2sat.) or mild hypoxia (35% O2sat.). Life‐history traits, as well as sex‐specific survival and physiological traits, were measured. Females had overall higher thermal tolerance levels and responded differently than males when exposed to the combined global change drivers investigated. Females also showed lower metabolic thermal sensitivity when compared to males. Additionally, the MHW exerted a dominant effect on the traits investigated, causing a lower survival and higher metabolic rate at 25°C. However, egg production rates appeared unaffected by hypoxia and MHW conditions. Our results showed that MHWs could strongly affect copepods' survival, that combined exposure to hypoxia and MHW exerted an interactive effect only on CTmax, and that sex‐specific vulnerability to these global change drivers could have major implications for population dynamics. Our results highlight the importance of considering the differences in the responses of females and males to rapid environmental changes to improve the implementation of climate‐smart conservation approaches.
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- Award ID(s):
- 1947965
- PAR ID:
- 10556627
- Publisher / Repository:
- John Wiley and Sons
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 10
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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