We are interested in understanding how environmental variation modulates developmental processes and resulting phenotypic variation. We focus on the C. elegans germline, a molecularly well-tractable system that shows a high degree of environmental sensitivity. The basic germline organization is conserved among Caenorhabditis species, however reproductive schedules and fecundity are very variable between species and isolates. Yet, it remains unclear how evolution of such life history traits is explained by changes in germline properties, e.g. sperm number, oocyte quality or the sperm-oocyte switch. We aim to link environmental and evolutionary variability of the Caenorhabditis germline to better understand genotype-by-environment interactions for developmental traits underlying fitness-related characters. Our first aim was to characterize how germline proliferation and differentiation as well as fecundity are modified in animals exposed to experimental conditions mimicking ecologically relevant environments. Here we present how one specific environment -high temperature exposure (27°C)- affects germline and reproductive properties. In addition to previously reported deleterious effects on sperm function, we found that high temperature significantly impacts germline proliferation and differentiation, apparently through modifications of Distal Tip Cell morphology and signalling through the Delta/Notch pathway. Our second aim was to quantify genotype-by-environment interactions by analysing how isolates of the three hermaphroditic species (C. elegans, C. briggsae and C. sp. 11) differ in germline plasticity across different environments. We uncover significant genotype-by-environment interactions for germline and fecundity in response to high temperature. More specifically, we find that the thermal limits of reproduction are species-specific and may be associated with particular germline defects. We are now using this experimental paradigm to explore how environmental factors impact the Caenorhabditis reproductive system and how germline integrity is maintained in variable environments. Please note: Abstract shown here should NOT be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.