Effects of benign and heat-stress conditions on parent clones and their selfed offspring of the pea aphid

In the face of global climate change, understanding the interaction
between heat stress and inbreeding depression is a critical issue. We
evaluated the magnitude of inbreeding depression under benign and
heat-stress conditions using parent clones and their selfed offspring of
Acyrthosiphon pisum.    The number of nymphs produced by
an adult during the first seven days was counted, and the total area of
all nymphs was measured as fitness components of a clone. Inbreeding
depression was observed during the development of the fundatrix and was
exemplified by the occurrence of sterile fundatrices, which accounted for
28.6% of the adults.    Once clonal lines were
established, no significant overall differences were detected in these
fitness components between a parent clone and its 30 selfed-offspring
clones at a constant 20 °C. However, pairwise comparisons revealed a
significant reduction in the fitness components in a few selfed clones,
whereas one selfed clone significantly outperformed the parent in terms of
the total area of the nymphs. These results demonstrate substantial
variation in the fitness components among sibling clones derived from
selfing.    However, when clones were exposed to either
a single heat stress (35 °C for 6 h) or repetitive heat stresses (35 °C
for 6 h over three consecutive days), inbreeding depression was
exacerbated under the more intense stress conditions. These results
suggest that inbred clones could spread in the population in regions with
mild climates, but are likely to be largely eliminated when exposed to
high summer temperatures.