One of the more challenging aspects of working with rare and imperiled species is that there is often a fundamental lack of basic biology or natural history data available to use in conservation projects. This can be especially true for many reptile and amphibian species, which are often difficult to study due to low detectability and long periods of time spent in locations where they are simply not available (e.g., underground). Many funding sources and scientific journals have also moved away from a focus on natural history information, making it challenging to get this type of work off the ground and disseminate it to a broad audience. Furthermore, the legal restrictions placed on endangered species can make some types of studies out of reach, making an already difficult challenge even harder to overcome.
These are the issues that I was recently pondering when wondering how many eggs flatwoods salamanders are capable of laying and, more importantly, if the number of eggs was related to female body size as has been documented for many species. The relationship between body size and reproductive output has important implications for understanding how population sizes fluctuate through time, which is one of the projects that I am currently working on for my dissertation. Larger females laying more eggs would likely be a good thing for a rare salamander population.
So, what do we already know about flatwoods salamander clutch size in relation to female body size? Almost nothing! There are scattered reports in the literature describing clutch sizes, but these are often approximate and rarely have a female body size associated with them. For example, Goin (1950) reports several estimates of clutch size, but body size is either lacking or clutch size estimates come from odd times of the year (suggesting that some eggs may have already been laid). The best source currently available is Anderson and Williamson (1976) who report that they counted the eggs in nine gravid female salamanders and also measured body length of the same individuals. Frustratingly, although the authors indeed report a positive relationship between body size and clutch size, they do not share the equation for this relationship and only present data from four of nine salamanders that they measured. A sample size of four is certainly not ideal when attempting to understand complex demographic relationships, but the ability to generate new data points from existing flatwoods salamander populations is essentially nonexistent. Nobody is going to permit collecting gravid females (rightfully so), and flatwoods salamanders scatter their eggs, making it nearly impossible to count them accurately in the field.
In fact, the only potential source for ‘new’ data describing flatwoods salamander clutch sizes comes from individuals that have already been collected and preserved in museum collections. It turns out that the Georgia Southern University – Savannah Science Museum Herpetology Collection contains what is likely the largest number of preserved flatwoods salamanders of any museum in the world. Don’t feel too bad – the vast majority of these individuals were collected from wetlands that no longer exist. The collection contained six gravid females that had either already had eggs removed from the body cavity or had already been had the body cavity cut open by previous researchers. Just a little bit of counting 50-year-old salamander eggs would increase the total number of data points by 150%!
Thus, I recently found myself hunched over a dissecting scope for much of a Friday, painstakingly removing and counting eggs in several flatwoods salamander specimens. Despite being 50 years old, the specimens were well-preserved, and it proved only mildly tedious to count the several hundred salamander eggs. One of the trickiest parts may have been finding all of the eggs as the body cavities were absolutely packed (imagine 200 eggs inside a salamander just a few inches long!). I placed the eggs that I removed in their own small vials that were then put into the larger vial with the adult specimen. Both the eggs and adults will remain in the GSU collection where they are available for other researchers to use as needed.
Overall, one tedious day of work more than doubled the available data to relate body size in flatwoods salamanders to clutch size. This type of work, especially for a species this rare, would not be possible without the historic museum specimens. As expected, the new data points reinforced that there is a positive relationship between female body size and clutch size. This relationship will be an important part of the population modeling that I am currently working on for flatwoods salamanders to better understand how populations respond to climate change. Expect to see more about that in the future.
A special thanks to Drs. Lance McBrayer and Ray Chandler for letting me pull eggs out of the specimens and assisting with the specimen loan.
Anderson, J. D., and G. K. Williamson. 1976. Terrestrial mode of reproduction in Ambystoma cingulatum. Herpetologica 32:214–221.
Goin, C. J. 1950. A study of the salamander, Ambytoma cingulatum, with the description of a new subspecies. Annals of the Carnegie Museum 31:299–321.