The acrophase means 24h cycle. If the acrophase value came more than 24h assume, 25.78 ± 1.78 in cosinor analysis using the formula.
f(t) =A+ (B * Cos [2 * pi x(t-C)/24]
Where f(t) = gene expression level at a given time, A = mesor ,B = amplitude, t = time in hours, and C = acrophase.
Anyone suggest me that the acophase value more than 24 is it practically correct or not in fish species? I was getting some acrophase value more that 24. Kindly tell me the actual reason.
Thanks in advance.
Hi Saurav, the acrophase in your cosinor function refers to the time of the peak (or trough if the amplitude is negative) of your gene expression levels. Since a cosinor function is periodic (i.e. in your case the period is 24 hours), the peak of the gene expression levels recur every 24 hours. An acrophase of 25.8 hours simply means that the peak occurs at 25.8 hours, but also at 1.8 hours and 49.8 hours. You could verify the output of the software by plotting the gene expression values over time and look at the approximate time of the peak. Hence, there is nothing inherently incorrect about an acrophase of 25.8h and you could substract 24 to get a number between 0 and 24.
I'm not sure what statistical software you are using to get these numbers, but since you're using a non-linear model, you probably need to provide the software with initial estimates for the parameters in your model before doing the analysis. These initial estimates influence the acrophase returned by the software. Note that a linearized version of cosinor analysis can also be used, which does not require initial estimates and will always give you an acrophase that lies between 0-24h. You can read more about this here:
Cornelissen (2014): Cosinor-based rhythmometry. Theor Biol Med Model. 2014; 11: 16.
I hope this helps!
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