Abstract
BackgroundConsiderable variation of life cycle duration in given insect species has been frequently recorded. Splitting of populations into cohorts with different life cycle lengths may occur, sometimes even between siblings from the same batch. Larval populations of the stonefly Nemurella pictetii in central Europe regularly split into a very fast developing and a normal univoltine cohort, leading to partial multivoltinism. The causes for such variation remain unknown but presumably act on the larval stage in which most of the life cycle is spent. We therefore studied possible effects of intraspecific competition on growth and development of larvae in the laboratory.ResultsIntraspecific competition had important influence on growth and development of the larvae. High larval densities led to reduced growth and retarded development through interference, not through exploitative competition. All specimens were negatively affected by frequent encounters and the resulting disturbance. There were no dominant individuals able to grow and develop faster than the rest, at the expense of the others.ConclusionDifferences in life cycle length of Nemurella pictetii may result from different larval densities in different microhabitats and resultant different degrees of interference competition. Although competition alone probably does not cause splitting of populations into cohorts with different life cycle duration differences in size and development caused by other factors are certainly enhanced by intraspecific competition.
Highlights
Considerable variation of life cycle duration in given insect species has been frequently recorded
Larvae kept at low density grew faster and already after two weeks attained significantly larger head capsule width across the eyes (HCW) than larvae kept at high density
Differences in development of larvae kept at the two different levels of density are evident from the degree of wing pad development (WPD) (Mann-Whitney U-test, Z = -3.996, P < 0.001; Figure 2) While all larvae kept at low density possessed wing pads at the end of the experiment, the same was true of only 64% of the larvae kept at high density
Summary
Considerable variation of life cycle duration in given insect species has been frequently recorded. Larval populations of the stonefly Nemurella pictetii in central Europe regularly split into a very fast developing and a normal univoltine cohort, leading to partial multivoltinism The causes for such variation remain unknown but presumably act on the larval stage in which most of the life cycle is spent. In the case of extended hatching from eggs, early hatching individuals are often assumed to have an advantage in development resulting from the combined effects of temperature and longer growth period [11,12,13]. Such explanations focus mainly on time as factor.
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