Long-Day Inhibition of Reproduction and Circadian Photogonadosensitivity in Zembra Island Wild Rabbits (Oryctolagus cuniculus)

Abstract

We investigated the effects of photoperiod on testicular activity in wild rabbits (Oryctolagus cuniculus) captured on Zembra Island (North Tunisia) and maintained in experimental photoperiodic conditions. Sexually inactive animals were subjected to alternate 3-mo periods of short days (8L:16D) and long days (16L:8D) for 1 yr. Testicular activity increased significantly and then decreased to levels equivalent to or lower than those measured during sexual quiescence after 1 mo of 8L:16D or 16L:8D, respectively. Eight groups of sexually active animals were also exposed to 8L:16D for 60 days. The light phase was divided into two photofractions (7.5 and 0.5 h). The short photofraction interrupted the dark phase 9.5-18.5 h after the beginning of the main photofraction. Testicular activity was inhibited if the short photofraction interrupted the dark phase 12.5 h or more after the beginning of the main photofraction. These results clearly confirm that photoperiod affects reproduction in this species: Short days stimulate reproduction, whereas long days inhibit it. The asymmetric pattern of skeleton photoperiods used demonstrated the existence of a circadian rhythm for photogonadosensitivity, with the photosensitive phase beginning 12.5 h after dawn. In this species, photoperiod length controls both the beginning and the end of the reproductive period. These results differ from those obtained with continental populations of wild rabbits, in which reproduction is inhibited by short day length. This difference may reflect genetic drift linked to the geographic isolation of this population, which is known to have been present on this small island for more than 2000 yr.

Effects of photoperiod on testicular functions in male sprague-dawley rats

“…Previous work on young male F344 and BN rats indicated that reproductive and body masses were reduced by SP (Heideman and Sylvester, 1997;Lorincz et al, 2001). SP has also been observed to have an inducing effect on male reproductive parameters in Zembra Island wild rabbits (Oryctolagus cuniculus) (Ben Saad and Maurel, 2002).…”

“…Depending on the species, photoperiod may either trigger onset of the reproductive period (a stimulating effect), or initiate gonadal regression (an inhibitory effect). In long-day breeding species, the seasonal increase ij sexual activity occurs when the amount of daylight increases, and in short-day breeding species, the reproductive season is triggered by the shortening of day length, (Ben Saad and Maurel, 2002). Melatonin, a 5-methoxyindole synthesized by the pineal gland, plays a major role in photoperiod-mediated control of reproduction in mammals with seasonal breeding patterns determined by day length in their natural environment, and the circadian pattern of melatonin secretion constitute an endocrine message that provides information regarding the photoperiod (Reiter, 1986;Reiter, 1991;Arendt, 1995;1995;Goldman, 1999).…”

Effect of Exogenous Melatonin Treatment on the Reproductive Characteristics and Progeny of Male Rats Exposed to Different Periods From Light and Darkness

“…Also, Olayaki et al (2008) showed that there was significant reduction in reproductive organ mass, viability, counts, and sperm motility when rats were exposed to short photoperiod. On the other hand, Ben Saad and Maurel (2002) reported that short photoperiod has an improvement effect on male reproductive characteristics in wild rabbits. Moreover, long photoperiod resulted in non-significant increase in sperm properties, but it increased the testis weight (Olayaki et al 2008).…”

What Are the Keys to the Adaptive Success of European Wild Rabbit (Oryctolagus cuniculus) in the Iberian Peninsula?

“…These reproductive differences between domestic and wild rabbit depend on some candidate genes that regulate clock functions and reproduction [ 74 ]. Reproductive activity is mainly determined by factors that mainly affect males, such as their photoperiod (some studies have indicated that testicular activity and growth are affected by circadian cycles [ 75 , 76 ]), and others that affect both females and males, such as social interactions and climatology [ 77 ]. However, the most relevant factor related to reproduction seasonality seems to be nutrition.…”