Role of testosterone and photoperiod on seasonal changes in horn growth and sperm variables in the Iberian ibex: a model for polygynous wild bovids

Effect of seasons and photoperiods on seminal attributes and sperm morphology in Holstein Friesian × Sahiwal crossbred dairy bulls

Cattle being non-seasonal breeding species, effects of photoperiods on sperm traits and morphology had been reported inadequately in breeding bulls. To elucidate the plausible existence of effects of photoperiods and seasons, seminal traits of Holstein Friesian × Sahiwal crossbred dairy bulls (N = 557) were analysed using different statistical models. A present study revealed that the biological rhythm of reproduction oscillated almost in parallel to the annual changes of natural photoperiods even in non-seasonal breeding species like cattle bulls. Semen traits diminished to the lowest in winter solstice (WS ± 45 days), progressively increased with the rising day length of spring (vernal equinox ± 45 days), reached a peak in summer solstice (SS ± 45 days), and then gradually reduced with decreasing photoperiod of the autumn equinox (AE ± 45 days). From summer solstice to winter solstice, sperm concentration reduced by 90.53 million/ml (8.85%), total sperm count/ejaculate decreased by 785 million (13.87%), total motile sperm count/ejaculate reduced by 17.59%, and total post-thaw motile sperm counts/ejaculates diminished by 38.64%. In short-duration photoperiods (≤ 12 h), bulls had a significantly (P < 0.01) higher incidence of major, minor, tail abnormality and total aberrant sperm% compared to that of long-duration photoperiods (> 12 h). Solstice equinox-based seasonal classification provided better insight into photoperiodicity on bulls' semen quality and sperm traits as compared to conventional meteorological classification of seasons. It was concluded that photoperiods affect sperm productivity, semen quality, and sperm morphology in non-seasonal breeding species like dairy bulls, maintained at transitional latitude (29° N) tropical climate. Bulls' reproductive ability was more influenced by the phases of increasing/decreasing day length duly primed by climax/trough of photoperiods, compared to mere long/short duration of photoperiods.

Influence of circulating testosterone concentration on sperm cryoresistance: The ibex as an experimental model

BACKGROUND

Recent studies have noted that the circulating testosterone concentration may affect the ability of spermatozoa to survive cryopreservation. However, few attempts to confirm such a relationship have been made. Wild ruminant species have very marked seasonal changes in their reproductive function and strong annual changes in their plasma testosterone concentration.

OBJECTIVES

The present work examines the influence of induced changes in testosterone secretion on sperm variables following conventional slow freezing and ultra-rapid freezing, using the Iberian ibex as an experimental model.

MATERIALS AND METHODS

In a first experiment, testosterone levels were reduced in the middle of the rutting season (December) using the antiandrogen cyproterone acetate (CA). In a second experiment, testosterone levels were increased at the end of the rutting season (January) via the use of the androgen testosterone propionate (TP).

RESULTS

During December, the testosterone concentration was found to be higher in the blood and seminal plasma of untreated males than in those of CA-treated males (p < 0.001 and p < 0.05, respectively). Compared with controls, the TP-treated animals had higher blood plasma testosterone concentrations but lower seminal plasma testosterone concentrations during January (p < 0.01 and p < 0.001, respectively). The seminal vesicles of the TP-treated males were larger than those of untreated males (p < 0.05). When CA was administered, sperm viability improved compared with controls (p < 0.05), irrespective of the freezing protocol followed. For the ultra-rapid freezing procedure, the cryoresistance ratio for motility decreased when TP was administered (p < 0.05). The values for fresh sperm morphometric variables decreased during the 50 days after the end of CA treatment (p < 0.001) and increased over the same time after the end of TP treatment (p < 0.001).

DISCUSSION AND CONCLUSION

The circulating testosterone concentration appears to influence sperm cryoresistance. This may explain the seasonal changes seen in sperm freezability in some species, independent of fresh sperm quality.

Photoperiod and melatonin treatments for controlling sperm parameters, testicular and accessory sex glands size in male Iberian ibex: A model for captive mountain ruminants

This study examines whether photoperiod and/or melatonin treatments can improve sperm variables outside the breeding season in the Iberian ibex-a model species for wild mountain ruminants-thus helping in the collection of high quality sperm beyond the normal breeding season for depositing in genetic resource banks. Adult Iberian ibex males (n=17) were divided into four treatment groups: (1) controls under the natural photoperiod (control group; n=4), (2) treatment with melatonin implants on December 22nd, February 22nd and April 22nd (group WS-M; n=5), (3) treatment with short photoperiod cycles, i.e., 2 months of long days followed by melatonin implants (to emulate 2 months of short days) throughout the year (group PHPld+M; n=4), and (4) treatment with melatonin implants on June 22nd and August 22nd (group SS-M; n=4). The interaction treatment x season had a strong influence on testis size (P<0.05), the size of the seminal vesicles (P<0.001), the percentage of abnormal sperms (P<0.05), and percentage non-progressive (P<0.05) and progressive (P<0.001) sperm motility. In groups WS-M and PHPld+M, the normal springtime physiological reductions in testis size, non-progressive sperm motility and acrosome integrity were prevented. The values for the studied sperm variables were, however, reduced in the natural breeding season at the end of the experimental period in group PHPld+M, although not in group WS-M. The pattern of melatonin administration in group SS-M conferred no advantages on reproductive functionality. These results suggest that lengthening the short day period after the winter solstice (the WS-M treatment) extends reproductive activity in this species, allowing good quality sperm to be recovered for conservation purposes during the non-breeding season.

Seasonal dimorphism in the horny bills of sparrows

Bill size is often viewed as a species-specific adaptation for feeding, but it sometimes varies between sexes, suggesting that sexual selection or intersexual competition may also be important. Hypotheses to explain sexual dimorphism in avian bill size include divergence in feeding niche or thermoregulatory demands, intrasexual selection based on increased competition among males, or female preference. Birds also show seasonal changes in bill size due to shifts in the balance between growth rate and wear, which may be due to diet or endogenous rhythms in growth. Insight into the function of dimorphism can be gained using the novel approach of digital x-ray imaging of museum skins to examine the degree to which the skeletal core or the rhamphotheca contribute to overall dimorphism. The rhamphotheca is ever-growing and ever-wearing, varying in size throughout life; whereas the skeletal core shows determinant growth. Because tidal marsh sparrows are more dimorphic in bill size than related taxa, we selected two marsh taxa to investigate dimorphism and seasonality in the size of the overall bill, the skeletal core, and the rhamphotheca. Bill size varied by sex and season, with males having larger bills than females, and bill size increasing from nonbreeding to breeding season more in males. Skeletal bill size varied with season, but not sex. The rhamphotheca varied primarily with sex; males had a larger rhamphotheca (corrected for skeletal bill size), which showed a greater seasonal increase than females. The rhamphotheca, rather than the skeletal bill, was responsible for sexual dimorphism in overall bill size, which was particularly well developed in the breeding season. The size of the rhamphotheca may be a condition-based character that is shaped by sexual selection. These results are consistent with the evidence that bill size is influenced by sexual selection as well as trophic ecology.