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Self-fertilization in hermaphroditic species might or might not be advantageous based on the level of inbreeding or outbreeding depression and the opportunity to outcross. This study examined whether chemoattractants can influence selfing rates through changes in sperm swimming behavior in the hermaphroditic tunicate Ciona robusta. The first set of experiments tested sperm preference in a dichotomous choice chamber by allowing the sperm to choose between wells with no eggs and wells with eggs, while the second experiment gave sperm a choice between self eggs and non-self eggs from another C. robusta individual. We found that sperm were about 5 times more likely to be captured in wells with eggs than in empty wells (P < 0.001) and that they were about 1.6 times more likely to be captured in wells with non-self eggs than in those with self eggs (P = 0.002). Additionally, we found that although sperm were activated by water pretreated with eggs, there was no difference in sperm swimming speed and motility in water treated with pooled-egg water compared to self-egg-treated water (P = 0.636 and P = 0.854, respectively). Our results indicate that while chemoattractant identity does not affect the basic mechanics of sperm activation and thus fertilization ability, it can cause sperm to aggregate near non-self eggs in greater numbers. This may allow for sperm to fertilize non-self eggs in greater numbers when available while still retaining the ability to fertilize self eggs. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the effects of co-exposure to heat and psychological stress on sperm DNA and semen parameters among male rats. The study was conducted on 40 healthy adult male Wistar rats. The rats were randomly categorized into four groups of same size consisting of a control group, a heat stress, psychological and co-exposure groups. The heat stress group was exposed to a temperature of 36 °C at 20% relative humidity. The psychological stress exposure group was subjected to three stressors including exposure to strobe light, noise and tilting cage. According the results,the co-exposure group had lower mean sperm parameters including sperm count (17.22 ± 4.22 10 6 /ml), motility (42.63 ± 12.95 %), viability (48.50 ± 23.25 %), normal morphology (56 ± 7.5%), progressive motility (11.61 ± 7.81%), non-progressive motility (31.18 ± 7.77%), curvilinear velocity (24.11 ± 3.81 μm/s) and straight-line velocity (3.2 ± 1.4 μm/s) when compared with those of the other groups (P = 0.001). Mean sperm immobility (57.36 ± 12.95%) and non-progressive motility (37.93 ± 11.15%) in the co-exposure group was higher compared to the other groups (P = 0.001 and P = 0.333, respectively). Assessment of damage to sperm DNA revealed that the heat exposure group had a higher percentage of sperm DNA damage (9.44 ± 6.80 %) compared to others (P = 0.185). In case of all of exposure scenario, the chance that the semen quality decreased compared to the control group has been increased. In general the combined stress had a greater significant effect on sperm parameters compared to other exposure groups, except for DNA damage., Competing Interests: The authors report no declarations of interest., (© 2021 The Authors.)