Using 2009/2010 cropping season survey data from 181 randomly selected smallholder tobacco farmers, this study provides baseline information on tobacco farming in Mara region. Both descriptive and inferential statisti...Using 2009/2010 cropping season survey data from 181 randomly selected smallholder tobacco farmers, this study provides baseline information on tobacco farming in Mara region. Both descriptive and inferential statistics were employed in data analysis. Result indicates that farmers adopted tobacco farming from tobacco farmers in Kenya. Drought and inadequate supply of inputs were identified as the major production constraints. Others were incidence of pests and diseases, shortage of fire woods, poor extension services and hailstones. Low selling price and contradicting grading systems were the major tobacco marketing constraints. The study also revealed that access to extension services was similar across study districts with over 65.7% of the respondents accessing technical expertise mainly from Alliance One Tanzania employees. Given the positive and negative impacts of tobacco farming, majority of the respondents （95.6%） still were willing to proceed with tobacco farming as their main source of income. However, watermelon, maize and sunflower were ranked as first priority alternative cash crops to tobacco in Serengeti, Tarime and Rorya districts, respectively. This study concludes that tobacco farming still is the main household income source; hence, more investment is required to ensure sustainable economic develooment of rural communities in Mara reeion.展开更多
Producing sperm is costly and males have been selected to strategically adjust their sperm produc- tion and/or expenditure according to the fitness return associated with a specific mating. For exam- ple, males respon...Producing sperm is costly and males have been selected to strategically adjust their sperm produc- tion and/or expenditure according to the fitness return associated with a specific mating. For exam- ple, males respond to fluctuations in the mating opportunities by adjusting the number of ＂ready＂ sperm. This phenomenon is known as ＂sperm priming＂ and is interpreted as a strategy to econo- mize the investment in sperm. The cost and benefits of the sperm priming response, however, are expected to depend on a male＇s baseline sperm production （BSP） in the absence of females, because of the different risk of sperm depletion and the nonlinearly increasing costs of sperm pro- duction. We tested this prediction in 2 replicated lines of male guppies Poecilia reticulata that were artificially selected for high and low BSP. BSP has a large genetic variance and a high sire heritabil- ity in guppies, and males respond to the perceived mating opportunities by increasing the number of ＂ready＂ sperm. We investigated whether males with a different BSP differed in their sperm pri- ming response. We found that when the perceived mating opportunities increased, males from low-sperm lines had a stronger sperm priming response than those from high-sperm lines. This result suggests that adaptive plasticity in sperm priming has the potential to evolve in response to different levels of BSP. The comparison between guppy populations with different levels of sperm production would allow to test whether the pattern reported here is also observed at the interpopulation level.展开更多
文摘Using 2009/2010 cropping season survey data from 181 randomly selected smallholder tobacco farmers, this study provides baseline information on tobacco farming in Mara region. Both descriptive and inferential statistics were employed in data analysis. Result indicates that farmers adopted tobacco farming from tobacco farmers in Kenya. Drought and inadequate supply of inputs were identified as the major production constraints. Others were incidence of pests and diseases, shortage of fire woods, poor extension services and hailstones. Low selling price and contradicting grading systems were the major tobacco marketing constraints. The study also revealed that access to extension services was similar across study districts with over 65.7% of the respondents accessing technical expertise mainly from Alliance One Tanzania employees. Given the positive and negative impacts of tobacco farming, majority of the respondents （95.6%） still were willing to proceed with tobacco farming as their main source of income. However, watermelon, maize and sunflower were ranked as first priority alternative cash crops to tobacco in Serengeti, Tarime and Rorya districts, respectively. This study concludes that tobacco farming still is the main household income source; hence, more investment is required to ensure sustainable economic develooment of rural communities in Mara reeion.
文摘Producing sperm is costly and males have been selected to strategically adjust their sperm produc- tion and/or expenditure according to the fitness return associated with a specific mating. For exam- ple, males respond to fluctuations in the mating opportunities by adjusting the number of ＂ready＂ sperm. This phenomenon is known as ＂sperm priming＂ and is interpreted as a strategy to econo- mize the investment in sperm. The cost and benefits of the sperm priming response, however, are expected to depend on a male＇s baseline sperm production （BSP） in the absence of females, because of the different risk of sperm depletion and the nonlinearly increasing costs of sperm pro- duction. We tested this prediction in 2 replicated lines of male guppies Poecilia reticulata that were artificially selected for high and low BSP. BSP has a large genetic variance and a high sire heritabil- ity in guppies, and males respond to the perceived mating opportunities by increasing the number of ＂ready＂ sperm. We investigated whether males with a different BSP differed in their sperm pri- ming response. We found that when the perceived mating opportunities increased, males from low-sperm lines had a stronger sperm priming response than those from high-sperm lines. This result suggests that adaptive plasticity in sperm priming has the potential to evolve in response to different levels of BSP. The comparison between guppy populations with different levels of sperm production would allow to test whether the pattern reported here is also observed at the interpopulation level.
