The effects of ph and food on growth and development in the dipteran Chaoborus americanus from one naturally acid and two naturally alkaline habitats
Hoffman, Eric R.
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Several aquatic insect studies have examined pH tolerance, primarily in terms of individual species survival rather than demonstrating population differences within one species. Additionally, few studies have examined fitness traits other than survival, or the importance of food quantity and quality in assessing tolerance. Therefore, the purpose of the Tender Bog/Redfield Pond and Tender Bog/Dead Dog Pond experiments was to examine whether fitness parameters of an aquatic insect species, Chaoborus americanus. from habitats of different acidity were sensitive to pH stress and if food is an important factor in stress tolerance. Larvae from naturally acidic Tender Bog showed no effect of pH or food alteration on male and female survival, growth, or female fecundity. This response suggests tolerance to native low pH as well as non-native and potentially stressful high pH. Plasticity, however, was observed in survival as well as male and female development time among food and pH treatments between experiments. This response indicates specific tolerance of pH but not general tolerance of all stress (handling in Experiment 1). Conversely, populations from both alkaline Redfield and Dead Dog Ponds showed significant effects of low pH on male and female survivorship and development time, particularly at low food. At high food, both traits were not significantly affected by low pH. This response to low pH suggests that tolerance to pH stress has an energetic cost. Dead Dog female pupal weight and fecundity were also negatively affected by pH stress as expected. Female and male growth, however, showed less plasticity between pH treatments at both food levels than fecundity or development. This suggests a trade-off between development and growth in males as well as growth and fecundity in females when larvae are stressed. Conversely, neither Redfield female fecundity, pupal weight, nor male pupal weight showed any effect of pH stress. This suggests: 1)Redfield larvae show limited tolerance to pH stress, and 2)Tradeoffs occur between female survival and development versus growth and fecundity as well as male survival and development versus growth when larvae are stressed.