Dear Authors,

I would like to note that your study was not longitudinal, but cross-sectional. Longitudinal studies investigate the development of one individual over time. Baerlocher et al. (2007) for example investigated the change of telomere length over time in several individual baboons (see also Ujvari and Madsen, 2009). A longitudinal sampling of different organs of zebrafish will be difficult, as it is questionable if any fish will survive e.g. a heart biopsy. Cross-sectional data, however, do not always reflect telomere dynamics over time in a population (e.g. Haussmann and Mauck, 2008), mainly because of high variations between individuals of the same age group. Unfortunately, the pooling of samples within the different age groups in this study prevents an assessment of this phenomenon in zebrafish.

Sincerely,

Dr. Thorsten Horn


References

Baerlocher GM, Rice K, Vulto I, Lansdorp PM (2007). Longitudinal data on telomere length in leukocytes from newborn baboons support a marked drop in stem cell turnover around 1 year of age. Aging Cell 6: 121-123.

Haussmann MF and Mauck RA (2008). Telomeres and longevity: Testing an evolutionary hypothesis. Mol Biol Evol 25: 220-228.

Ujvari B and Madsen T (2009). Short telomeres in hatchling snakes: erythrocyte telomere dynamics and longevity in tropical pythons. PLoS One 4: e7493.