Semen collected from 3-year-old male Houbara bustards contained large proportions (6-40%) of spermatozoa with large nuclei. In these spermatozoa, the length of the nucleus was up to twice the mean length of the nucleus in normal spermatozoa. The lengths of the acrosome, midpiece and flagella were all normally distributed, but the length of the nucleus formed a bimodal distribution. The proportion of spermatozoa with large nuclei varied among males, but not among different semen samples collected from the same male throughout the breeding season. The proportion of motile spermatozoa with large nuclei was half that of normal spermatozoa, but their velocity was significantly greater. After insemination into females, spermatozoa with large nuclei were observed in the outer perivitelline layer of eggs laid, indicating that they were stored and transported within the oviduct and reached the egg at about the time of fertilization. Furthermore, there was no difference in the ability to produce viable progeny in females that were mated with males producing greater proportions of spermatozoa with large nuclei compared with those producing 'normal' spermatozoa. Thus, the abnormal spermatozoa did not appear to impede fertility. There were no signs of triploidy in the males that produced spermatozoa with large nuclei, or in their progeny, as demonstrated by the size of erythrocytes. Therefore, it appears that the spermatozoa with large nuclei were the result of aberrant spermatogenesis.
SUMMARYFlexibility of metabolic rates within a species allows for the colonization of different habitats along an altitudinal and thus temperature gradient. The distribution range of amethyst sunbirds (Chalcomitra amethystina) within southern Africa includes an altitudinal gradient from the Drakensberg to the coast of KwaZulu-Natal. We expected that over this altitudinal gradient amethyst sunbirds would exhibit variation in winter metabolic rates, particularly basal metabolic rates (BMR) and resting metabolic rate (RMR) pre-and post-acclimation. Sunbirds from three locations, Underberg (1553 m above sea level; asl), Howick (1075 m asl) and Oribi Gorge (541 m asl) were used for this study. Upon capture, metabolic rate was measured indirectly by quantifying oxygen consumption (V O2 ) using flow-through respirometry, at 5 and 25°C. Birds were then acclimated at 25°C for 6 weeks on a 12 h:12 h L:D cycle. V O2 was measured post-acclimation at eight different temperatures (15, 5, 10, 20, 30, 28, 25 and 33°C). We found little variation in winter V O2 between individuals from the same locality, whereas significant variation was observed in V O2 at the same temperatures between individuals from the different localities and thus between altitudes. In particular, winter BMR decreased significantly with decreasing altitude post-acclimation. This study emphasizes the need to understand plasticity/flexibility in metabolic rates and to acknowledge altitudinal differences within a species, to make accurate predictions about the thermal physiology of a species and its responses to changes in ambient temperatures.
1. Spermatozoa in semen samples from 8 individual male domestic fowls were shown to have a differential and characteristic ability to hydrolyse holes in the inner perivitelline layer from laid eggs in an in vitro assay. 2. The number of holes produced by samples of spermatozoa per unit area of inner perivitelline layer in vitro was linearly correlated with sperm ATP content (r = 0.85) and motility (r = 0.76). 3. The number of holes formed in the inner perivitelline layer in vitro was also linearly correlated with the numbers of holes formed in the inner perivitelline layer of eggs fertilised in vivo, in inseminated hens (r = 0.90); and was correlated logarithmically with the proportion of fertile eggs laid by these hens.
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