| dc.description.abstract | Thirteen-lined ground squirrels (13LGS; Ictidomys tridecemlineatus) are small, omnivorous,
fossorial, hibernating sciurid rodents. As favored models for studies of hibernation and conebased
visual function, they have only recently been bred in captivity on any sort of scale, and
only here at UW Oshkosh. 13LGS are reflex ovulators, mating only in spring with a ~28 day
gestation period. Increasingly, the UW Oshkosh 13LGS Colony fields client requests for
pregnant females, in order to facilitate the first steps of transgenic modification and for
embryological studies. These aims require a far better understanding of the captive 13LGS’s
reproductive endocrinology than we currently have. This project was to ascertain whether
enzyme-linked immunosorbent assay (ELISA) of squirrel fecal samples can be used to noninvasively
detect pregnancy in a low-stress manner. To this end, competitive ELISAs for 11- and
3-hydroxyprogesterone were conducted on a group of thirteen females, comprising proven dams
bred in the Colony or captured from the wild. Feces were collected thrice weekly during the
spring of 2016 and frozen for subsequent steroid hormone extraction. Feces collections ceased as
soon as a litter was noted. Competitive ELISA tests against the metabolite 11- and 3-
hydroxyprogesterone were run using kits (Arbor Assays, Ann Arbor, MI), setting data against
seven different time points between hibernation exit and birth of a litter. An ANOVA with
repeated measures was run on the ELISA data to identify any significant differences in fecal
hormone-metabolite between these time points. Then a pairwise t-test with a Bonferroni
correction was run to determine where the differences lay. A Wilcoxon rank sum test was run on
the captive-bred vs. wild-caught animals to determine significant differences; a Spearman’s rank
correlation was performed to determine a possible correlation between litter size and
progesterone concentration; and a Student’s t-test was run on data from pregnant and nonpregnant
animals to determine significant differences. Eleven of 13 dams produced litters in the
spring of 2016. Fecal ELISA data from the 2 non-pregnant females demonstrated no rise in fecal
hormone-metabolite at any time point over four weeks. In contrast, data from the 11 parous
females all demonstrated a pronounced rise in fecal hormone-metabolite, with most animals
displaying progesterone withdrawal in the final week of gestation. Compared to baseline fecal
hormone-metabolite levels on the day of pairing with a male, this rise was statistically significant
halfway through gestation, with a >20-fold increase just a week into gestation. No significant
differences were noted based on whether a pregnant female was wild-caught or captive-bred, nor
with size of the litter. A technical replicate revealed the apparent decomposition of fecal 11- and
3-hydroxyprogesterone over 14 weeks, despite being stored frozen. This study has yielded a
step-by-step protocol by which 11- and 3-hydroxyprogesterone may be monitored non-invasively
through competitive ELISA of fecal pellets, permitting the detection of pregnancy at least 2
weeks prior to the birth of a litter. It further confirms the 13LGS as consistent with other sciurids
in its status as a placental mammal that undergoes progesterone withdrawal late in gestation. | en |
