Figure 12. Strong egg retention may provide a competitive advantage in resource-limited environments.

(A) Age distribution of embryos contained within eggs laid by hermaphrodites (mid-L4 +40 hr) of the 15 focal strains. Embryonic stages were divided into five age groups according to the following characteristics using Nomarski microscopy (Hall and Altun, 2007): 1–2 cell stage, 4–26 cell stage, 44 cell to gastrula stage, bean to two-fold stage, three-fold stage, L1 larva. N=45–72 eggs per strain. (B) Significant negative correlation between hatching time of laid eggs and mean egg retention across the 15 focal strains with divergent egg retention (at mid-L4 +30 hr) (ρ_Spearman=-0.92, p<0.0001). Values are estimates of the time point at which 50% of the eggs had hatched. For each strain, 10–20 adult hermaphrodites (mid-L4 +30 hr) were allowed to lay eggs within an 1-hr window (N=48–177 eggs per strain). The fraction of hatched eggs was scored every hour until all eggs had hatched. (C) Significant negative correlation between egg-to-adult developmental time and mean egg retention across the 15 focal strains with divergent egg retention (at mid-L4 +30 hr) (ρ_Spearman=-0.69, p=0.0041). Values are estimates of the time point at which 50% of individuals had reached reproductive maturity (one or two eggs in utero). For each strain, 10–20 adult hermaphrodites (mid-L4 +30 hr) were allowed to lay eggs within a one-hour window (N=77–318 eggs per strain). After removal of adults, eggs were allowed to hatch and after 45 hr of development, populations were surveyed every two hours to count the fraction of adults that had reached reproductive maturity. (D) Short-term competition of JU1200_WT and JU1200_{KCNL-1 V530L} against a GFP-tester strain (myo-2::gfp) with a genotype starting frequencies of 50:50. The strain JU1200_{KCNL-1 V530L} (strong egg retention, Class III phenotype) outperformed JU1200_WT (regular egg retention, Class II phenotype). For each replicate, 20 laid eggs of either genotype were mixed with 20 laid eggs of the GFP-tester strain on a NGM plate; after 4–5 days (when food became exhausted) the fraction of GFP-positive adult individuals was determined. Relative to the GFP-tester strain, JU1200_{KCNL-1 V530L} showed a significantly higher fraction of adults compared to JU1200_WT (Kruskal-Wallis Test, χ²=11.57, df=1, p=0.0007). N=10 replicates per genotype. (E) Short- term competition of JU751 (Class IIIB, strong egg retention) against each of five wild strains (Class II, canonical egg retention) isolated from the same locality. For each of the five strains, 20 freshly laid eggs were mixed with 20 freshly laid eggs from JU751 and allowed to develop. Adult population size and genotype frequencies were determined after 4–5 days (when food became exhausted). In each of the five competition experiments, JU751 showed a significantly higher number of adults (Wilcoxon signed-rank test for matched pairs, all p<0.05). N=10 replicates per strain.