Oral administration of GnRH via a cricket vehicle stimulates spermiation in tiger salamanders (Ambystoma tigrinum)

Abstract

More than 50% of caudates are threatened with extinction and are in need ofex-situbreeding programs to support conservation efforts and species recovery. Unfortunately, many salamander populations under human care can experience reproductive failure, primarily due to missing environmental cues necessary for breeding. Assisted reproductive technologies (ARTs) are a useful suite of techniques for overcoming or bypassing these missing environmental cues to promote breeding. Exogenous hormones are used to stimulate natural breeding behaviors or gamete expression forin-vitrofertilization or biobanking and are typically administered intramuscularly in caudates. While effective, intramuscular injection is risky to perform in smaller-bodied animals, resulting in health and welfare risks. This research investigated the spermiation response to hormone administration through a non-invasive oral route using the tiger salamander (Ambystoma tigrinum) as a model species. Male salamanders were randomly rotated six weeks apart through four treatments (n = 11 males/treatment) in which animals received a resolving dose of gonadotropin-releasing hormone (GnRH) as follows: (1) Prime-Only (0.0 µg/g); (2) Low (0.25 µg/g); (3) Medium (1.0 µg/g); and (4) High (2.0 µg/g). All males were given a GnRH priming dose (0.25 µg/g) 24 hours prior to the resolving dose. Exogenous hormone was delivered inside of a cricket (Gryllodes sigillatus) that was presented as a food item by tweezers. Sperm samples were collected at 1, 3, 6, 9, 12, and 24 hours after the resolving dose and analyzed for quantity and quality. For all treatments, sperm concentration was produced in an episodic pattern over time. The Prime-Only treatment had a lower (p < 0.05) percent of sperm exhibiting normal morphology compared to treatments utilizing a resolving dose of GnRH. Overall, oral administration of GnRH is a feasible route of inducing spermiation in salamanders, yielding sperm of sufficient quantity and quality forin-vitrofertilization and biobanking efforts.

Comparing novel sperm extenders for the internally-fertilizing tiger salamander (Ambystoma tigrinum)

“…The expression of anuran sperm into urine typically results in lower concentrations and higher volumes that favor a low osmolality (<100 mOsm) fertilization environment (Arregui et al, 2021). In comparison, hormonally induced internally-fertilizing salamanders produce both spermic urine and small volumes of milt (Chen et al, 2022;Chen et al, 2023), that more closely resembles the appearance of fish milt or semen in mammalian species. Furthermore, salamander sperm motility may not be activated by lowering the osmolality and can be difficult to observe as the sperm velocity can be low and the spermatozoa tend to spin in circles with little to no forward motion (Gillis et al, 2021).…”