Arachnid Science: Article Reviews
Page 1 of 4 | © 2005-2010 text by Stephanie Shorter, Ph.D.
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Brown, C.A. 2004. Life histories of four species of scorpion in three families (Buthidae, Diplocentridae, Vaejovidae) from Arizona and New Mexico. Journal of Arachnology. 32: 193-207.
This study is one of few that have compared the ways in which females of different scorpion species distribute their reproductive efforts. For 63 wild caught female specimens of four scorpion species (Centruroides exilicauda, Vaejovis spinigerus, Diplocentrus peloncillensis, and Psedouroctonus apacheanus) Brown recorded five measures (female size, litter size, offspring size, variability of offspring size, and reproductive investment Ð calculated in both absolute terms and relative to female size). Relationships among these all of these variables were examined. The key finding was that larger females did not yield larger babies. In cases where the female yielded more offspring, there was no trade-off between offspring size and the total number of offspring yield per reproductive season. Therefore, the general strategy to increase reproductive success for a female scorpion must be to increase the number of fixed-sized babies, rather than increase the size of each baby in the litter, or some combination of these strategies. Litter size increases only until a certain point, and where that limit is set for a species likely predicts the minimum number of offspring that should be produced in the wild to ensure that a sufficient number survive until dispersal from the mother's back.
This paper is rich with many other interesting results, too numerous to all get attention here. One intriguing observation involved the two Centruroides exilicauda specimens that were collected while carrying second instar juveniles. Later both of these females produced a second litter in captivity without being introduced to a male. Whether the same male's sperm produced both litters or if the females had mated with two or more males prior to their capture has not yet been determined.
This life history study is exemplary in several ways. The author provides a justification for why certain analyses were done and why certain measures were used in those analyses. For example, carapace length appears to be the most consistent way to quantify the female's body size. Therefore, this measure is preferable to body mass, which is more vulnerable to fluctuations due to recent feeding history and other factors. Another strong feature of this paper is that, where possible, Brown rules out alternative explanations for his results. Because the scorpion samples were collected across different years, an analysis was done to examine the degree to which the conclusions drawn from these scorpions may be contaminated by resource differences that may have existed at the site when the two collecting trips occurred. Additionally, Brown investigated the influence that incubating in captivity may have had on offspring yield. He examined whether the number of days that the gravid mother was captive before giving birth affected the litter mass and found no consistent patterns across species. This study could serve as a model for any hobbyist interested in contributing to the scientific literature using measurements from his or her own captive breeding successes.