Semen collection, ejaculate characteristics and in vitro manipulation of spermatozoa from six species of captive flying-fox (Pteropus spp.)

Abstract

Seminal characteristics are described in six Pteropus species including the critically endangered P. rodricensis. Spermic ejaculates (~40 μL) were collected using electro-ejaculation on 406 of 413 attempts. All flying-fox species had mean percentages of acrosome- and plasma-membrane (PM)-intact spermatozoa of >66% and >73%, respectively; the predominant sperm abnormalities found across all species were damaged, folded or missing acrosomes, bent midpieces and coiled tails. Seminal pH ranged from a low of 7.5 in P. giganteus to a high of 8.2 in P. alecto with the other species in between. Electro-ejaculates recovered in short succession from P. alecto revealed no differences in sperm quality, allowing spermatozoa to be utilised for multi-treatment experiments that evaluated the effects of transportation, incubation temperature and in vitro physico-chemical environments on acrosome and PM integrity. Pteropus alecto spermatozoa were successfully held at ~27°C and 37°C for up to 6 h before a reduction in PM integrity (P = 0.003) was observed. Acrosome and PM integrity decreased (P < 0.000) when P. alecto spermatozoa were incubated at 37°C for 30 min in a Tris–citrate buffer of pH 9.0 but remained stable at pH 5.0 to 8.0. Pteropus alecto mean (± s.e.m.) seminal osmolality was 307.0 ± 2.5 mOsm kg–1; nevertheless, spermatozoa were tolerant of media ranging from 160 to 1190 mOsm kg–1 but exposure to media of ≤160 mOsm kg–1 resulted in increased acrosome damage (P < 0.000).