They say that old people regress back to kids when they age. My first paper – a side-kick born out of MSc-thesis – was focussed on vertebral numbers of adders (Vipera berus; see the paper here). Now I find myself counting vertebral numbers again, this time in sticklebacks.
Apart of being a testimony of aging, this interest on stickleback vertebral numbers was spurred by curiosity to find an answer to a simple question: given that increased number of vertebrae often leads to increased body size (e.g. in snakes and pigs), can increased number of vertebrae be a proximate explanation for occurrence of gigantism in pond ninespine sticklebacks (Pungitius pungitius)?
We probed this question by using data from 12 populations of ninespine sticklebacks known to differ genetically in mean body size, as well as to show a high degree of female-biased sexual size dimorphism. After controlling for the confounding effects of habitat, sex and population of origin, there was weak and habitat specific positive association between body size and number of vertebrae. However, viewed across different populations, there was no correlation between mean body size and number of vertebrae. Likewise, although females (the larger sex) had on average more vertebrae than males, the degree of sexual dimorphism in number of vertebrae and body size were uncorrelated across populations. Furthermore, there was no relationship between latitude and mean number of vertebrae, revealing that vertebral numbers in the nine-spine stickleback do not follow Jordan’s rule (i.e. increase with increasing latitude). All in all, the results suggest that vertebral number only have a very limited influence on intraspecific patterns of body size variation in the nine-spined stickleback.
Shikano T. & J. Merilä (2011) Body size and number of vertebrae in the nine-spined stickleback (Pungitius pungitius). Biological Journal of the Linnean Society, in press.