Sleep

Analysis of checkerboard sharks’ metabolic rates suggests they’re sleeping

Analysis of checkerboard sharks' metabolic rates suggests they're sleeping

2 day and night (i.e. monitoring body mass) from intermittent flow respirometry measurement periods (all activity states included) over a 24-h period (L: D 12: 12). (c) Boxplot of residuals of ṀO2 in three activity states (independent of photoperiod) using subsampled data points from all measurement periods with an applied criterion of an R2 > 0.8 and a duration greater than 90 s. (d) Boxplot of residuals of ṀO2 in (c), but partitioned by photoperiod (day, night). (e) Regression of undersampled residuals of ṀO2 versus subsample duration (blue indicates sleep; gray indicates rest); all data meets the criteria for an R2 > 0.8 and lasting longer than 90 s; the vertical line indicates 5 min of inactivity. For (b,c,d), the solid black lines indicate the means; dashed lines indicate medians; the edges of the boxes represent the quartiles; the whiskers reflect the maximum and minimum values; gray circles represent individual samples (random scatter on x-axis); significant pairwise contrasts are denoted by the letters a, b, and c. Credit: Biology Letters (2022). DOI: 10.1098/rsbl.2021.0259″ width=”800″ height=”529″/>

Figure 1. (a) Drawings of upright (i) and flat (ii) body postures, and open (iii) and closed (iv) eyes used to score behavioral data from video recordings. (b) Boxplot of day and night residual ṀO2 values ​​(i.e. monitoring body mass) of periods of intermittent flow respirometry measurements (all activity states included) over a 24-h period (L:D 12:12). (c) Boxplot of residual ṀO2 values ​​over three activity states (independent of photoperiod) using subsampled data points from all measurement periods with an applied criterion of one R2 > 0.8 and a duration greater than 90 s. (d) Boxplot of residual ṀO2 values ​​in (c), but partitioned by photoperiod (day, night). (e) Regression of undersampled residual ṀO2 values ​​versus subsample duration (blue indicates sleep; gray indicates rest); all data meets the criteria for an R2 > 0.8 and a duration greater than 90 s; the vertical line indicates 5 min of inactivity. For (b,c,d), the solid black lines indicate the means; dashed lines indicate medians; the edges of the boxes represent the quartiles; the whiskers reflect the maximum and minimum values; gray circles represent individual samples (random scatter on x-axis); significant pairwise contrasts are denoted by the letters a, b, and c. Credit: Biology Letters (2022). DOI: 10.1098/rsbl.2021.0259

A team of researchers from La Trobe University, the University of Western Australia and the University of Auckland have found evidence that at least one type of shark sleeps. In their article published in the journal Biology Lettersthe group describes measuring the metabolic rates of seven wild checkerboard (carpet) sharks temporarily held in a tank and what it revealed about their possible sleep patterns.

Previous research has suggested that some species of sharks sleep, while in others this seems questionable, as they must keep moving to absorb oxygen from the water. This research involved shocking resting sharks to see if they reacted as quickly as they did when active, for example. In this new effort, the researchers looked for more concrete evidence.

The team chose checkerboard sharks because they live off the coast of New Zealand where the study was conducted, and because they are known to have resting periods. They captured seven and released them into large tanks in an outdoor laboratory lit by natural light – each was fed sardines for two weeks before the experiments began and each was removed from food for 48 hours before the start of the experiment. start experiments to make sure they reach a post-absorptive state. The researchers measured the sharks’ metabolism using a submerged acrylic respirometry chamber over 24-hour periods, focusing more specifically on the shark’s oxygen levels.

They found reduced oxygen levels in all sharks during rest periods, indicating that they were sleeping. They also found that the sharks closed their eyes at rest, another indicator of sleep, and they tended to keep their bodies flat. The researchers note that such behavior is consistent with sleep in many other creatures, although they acknowledge that closing the eyes is not necessarily a sign of sleep, as other creatures have been known to sleep with their eyes closed. open, and there were occasions when the sharks in the study did not close their eyes during rest periods.

The researchers conclude that the cumulative evidence is strong for checkerboard shark sleep.


Sharks of different species hunt prey at different times to avoid each other


More information:
Michael L. Kelly et al, Energy conservation characterizes sleep in sharks, Biology Letters (2022). DOI: 10.1098/rsbl.2021.0259. royalsocietypublishing.org/doi….1098/rsbl.2021.0259

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