Effects of age on sperm quality metrics in endangered Mississippi gopher frogs (Lithobates sevosus) from captive populations used for controlled propagation and reintroduction efforts

Abstract

A decline in sperm quality with age is a common prediction of senescence‐based hypotheses and empirical studies. While widely studied across taxa, there is little known on the effect of ageing on sperm quality in amphibians, especially in captive populations used for controlled propagation and reintroduction efforts. Here, we investigated variation in sperm quality metrics (i.e., motility, concentration, and morphology) in the endangered Mississippi gopher frog (Lithobates sevosus) among males of three age categories using individuals from captive breeding populations housed at three different zoological institutions. Different aged males across the species expectant lifespan (1–9, 1–2, 3–4, and 8–9‐year‐old subcategories) were chosen in an attempt to identify an optimal breeding age relevant for captive breeding programs. Moreover, we explored and statistically controlled for potential differences in sperm quality which may be attributed to the type of induction hormones and source populations that differed among institutions. Results indicated that males of different ages did not differ in sperm motility or concentration. However, we did find that older males (8–9 years old) had significantly longer sperm than other age categories and younger males (1–2 years old) had significantly more atypical sperm than other age categories. Furthermore, we found no significant differences in any sperm quality metrics between the different induction hormones or source populations used at the different institutions. Within a captive breeding program, this information is especially valuable as our results indicate that males that have only recently sexually matured may not be ready to breed, while older males maintain sperm quality metrics presumably related to fertilization success.

Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

“…Furthermore, viable tissue cryobanking should be considered in all future conservation strategies as a source of genetically diverse material that may be required in the future to combat the extinction crisis ( Comizzoli & Holt 2019 ). Great progress is already being made to save endangered species by using ART and aART, as demonstrated by the successful captive propagation and reintroduction using ART of endangered Mississippi gopher frogs in the United States ( Watt et al 2021 ), efforts to breed cheetahs and other endangered felids via ART and aART ( Wildt & Roth 1997 ) and the northern white rhino project to name just a few. However, despite the above example, the current focus is still primarily on mammalian taxa, and there is an urgent need for allowing these technologies to catch up across all others.…”

What are the contributions of maternal and paternal traits to fecundity and offspring development? A case study in an amphibian species, the spined toadBufo spinosus

“…Yet, it is likely that this effect is mediated through the quality of the sperm produced by larger—presumably older—males ( Gasparini et al 2010 ; Roth et al 2010 ). Although age-dependent sperm quality in amphibian species is expected to decrease through senescence ( Hettyey et al 2012 ), a study found that older males displayed the same fertilization capacity (e.g., motility and concentration) as younger males ( Watt et al 2021 ). In addition, it has also been shown that younger males produced more atypical spermatozoa than older males ( Watt et al 2021 ).…”

“…Although age-dependent sperm quality in amphibian species is expected to decrease through senescence ( Hettyey et al 2012 ), a study found that older males displayed the same fertilization capacity (e.g., motility and concentration) as younger males ( Watt et al 2021 ). In addition, it has also been shown that younger males produced more atypical spermatozoa than older males ( Watt et al 2021 ). Other complementary mechanisms could potentially involve size-specific macromolecular composition of spermatozoa affecting the duration of the first steps of fertilization (e.g., acrosome composition, chromatin unpacking) and/or the embryonic development ( Gusseck and Hedrick 1971 ; Lohka and Masui 1983 ; Carroll Jr et al 1991 ).…”