Measuring Lizards

Gekko japonicus (with scale).jpg

A colleague of mine received an email titled “measuring lizards” with this study attached.  This blog post discusses the questions posed and further information about this interesting intersection of scientific inquiry and mathematical modeling.

Here’s what started this blog:

I would greatly appreciate your help in making sure I know how to do the correct calculations for comparing museum lizard specimens (in alcohol for years) vs. live specimens. We have been measuring live lizards for the past 10 years and it has been hypothesized that ectotherms (cold blooded animals) will actually get smaller with climate change. However, I believe our lizards are showing the opposite trend.

SVL lizard.tiff

Apparently, there are several different measurements to consider including:

  1. Snout vent length (SVL)
  2. Head width
  3. Tail length

Items 2 and 3 seem intuitive, but if, like me, you are not sure what snout vent length may represent, I offer this handy guide and definition (from the awesome cool curriculum / project on lizards — link in the references below) —>

Here’s a link to more info regarding lizard measurments.


For the author of the email, the area of interest centers around these questions / problems:

  • I want to compare the measurements between museum specimens and live specimens. The authors have Table 2. which shows Fixation (formalin) and Preservation (alcohol) shrinkage. Then Table 3 has relative (to SVL) effects. I think they must be comparing the SVL with each measurement, but I am not sure. 
  • I believe Table 4. Is the comparison of table 2 & 3.
  • Finally, on Page 326 right before the “Discussion” the authors give an equation for comparing live vs. museum specimens. I was trying to figure out where it came from.

Here are the tables referenced: (click for full-size images)

lizard table2.tiff


lizard table3.tiff


lizard table4.tiff

Finally, here is the section re: the formula in question, "Comparisons between day 0 (fresh) and day 60 (conserved) allows us to recalculate fresh body size and shape dimensions, at least on population level (for absolute measurements and relative measurements, table 4). The conversion equations that should improve the reliability of morphological comparisons of life and conserved specimens on population level for SVL: [SVL(museum specimens)+ SVL(museum specimens) °ø  0.037] =  SVL(fresh)."

As always, I'd love to hear from you.  Especially, I would love to hear if you have answers to the inquiry presented, if you have additional information on lizard dataviz and math modeling, or if you have other comments about this blog post!

References:

LINK for more research on measuring lizards

LINK for a cool lizards project / curriculum of study

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Author:  Dr. Diana S. Perdue

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