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Additional file 12. Crosses of novel species (C. dolens, C. astrocarya) with known Caenorhabditis species [3]. Reciprocal crosses between different species and strains were performed as previously described [3], allowing for mating between 5–10 males and 5–10 females on a 55 mm diameter NGM plate. (A) Results of reciprocal crosses between the novel species C. dolens and presumptively close known relatives C. angaria, C. castelli, C. sp. 8, and C. astrocarya (B) Results of crosses between the novel species C. astrocarya and close known relatives, C. guadeloupensis and C. dolens.

International audience; Thermal developmental plasticity represents a key organismal adaptation to maintain reproductive capacity in contrasting and fluctuating temperature niches. Although extensively studied, research on thermal plasticity has mainly focused on phenotypic outcomes, such as adult life history, rather than directly measuring plasticity of underlying developmental processes. How thermal plasticity of developmental phenotypes maps into plasticity of resulting final phenotypes, and how such mapping relationships evolve, thus remain poorly understood. Here we address these questions by quantifying thermal plasticity of Caenorhabditis hermaphrodite germline development. We integrate measurements of germline development and fertility at the upper thermal range in isolates of C. briggsae, C. elegans, and C. tropicalis. First, we compare intra- and interspecific variation in thermal germline plasticity with plasticity in reproductive output. Second, we ask whether the developmental errors leading to fertility break-down at upper thermal limits are evolutionarily conserved. We find that temperature variation modulates spermatogenesis, oogenesis and germ cell progenitor pools, yet the thermal sensitivity of these processes varies among isolates and species, consistent with evolutionary variation in upper thermal limits of hermaphrodite fertility. Although defective sperm function is a major contributor to heat-induced fertility break-down, high temperature also significantly perturbs oogenesis, germline integrity, and mitosis-meiosis progression. Remarkably, the occurrence and frequency of specific errors are strongly species- and genotype-dependent, indicative of evolutionary divergence in thermal sensitivity of distinct processes in germline development. Therefore, the Caenorhabditis reproductive system displays complex genotype-by-temperature interactions at the developmental level, which may remain masked when studying thermal plasticity exclusively at the life history level.

International audience; Sperm competition is a key force driving evolutionary diversification of sperm morphology. In Caenorhabditis nematodes, sperm size is a major factor determining sperm competitiveness: male sperm is larger and consistently outcompetes hermaphrodite sperm, and larger male sperm outcompetes smaller male sperm. To generate an in-depth overview of sperm size variation in Caenorhabditis nematodes, we quantified male sperm size in 100 C. elegans wild isolates from a world-wide collection and in the 26 currently described Caenorhabditis species, including the three androdioecious species. Analysis of C. elegans wild isolates indicates significant levels of heritable variation in mean male sperm size, but Genome-Wide Association Mapping did not allow detection of any significant QTL underlying this variation. The observed sperm size distributions across strains indicate a complex genetic basis involving many loci of small effect. This survey of intraspecific variation also uncovered a strongly reduced mean male sperm size in LSJ1 and LSJ2 strains, recently derived from the reference strain N2. We show through quantitative complementation tests that a nurf-1 deletion in LSJ strains is responsible for reduced male sperm size, suggesting a role of the Nucleosome Remodeling Factor (NURF)-like complex in C. elegans spermatogenesis. Our quantification of sperm size evolution in different Caenorhabditis species confirmed earlier reports that mean sperm size of gonochoristic species is globally larger than in males of androdioecious species, although exceptions occur. While species of the elegans group all display relatively small, and similar, male sperm size, several gonochoristic species outside this group show convergent evolution of distinct, extremely large male sperm. In addition, within-species genetic variation in male sperm size is considerable in all examined gonochoristic and androdioecious species. We present experimental results aimed at understanding how germline and sperm development shape such dramatic variation in sperm size across species, isolate, sex and individual.

International audience; 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.